Anhydrite and gypsum minerals in claystones are found in different configurations: isolated nodules, filled veins, continuous layers, massive bodies and combinations of these geometrical structures. Continuous or, better, quasi-continuous records of anhydrite and gypsum content measured in boreholes show frequently a marked spatial variability. This heterogeneity may explain to some extent the variability observed in surface heave measurements and swelling pressures measured against structures such as tunnel linings. An additional cause of observed heave and pressure concerns the presence of discontinuities and open pore space required for the precipitation of gypsum crystals. In all cases water should be present. The paper describes two cases that illustrate the relevance of spatial variability of swelling strains and its identification.The first case analyses the origin of the surface heave recorded in a large power station founded on an Eocene anhydritic marl, fairly homogeneous at a large scale. The marl heave was triggered by two modifications of the initial state of the marl: i) a large excavation and its induced vertical tensile strains capable of opening fissures along stratification planes and ii) the establishment of a table water level that wetted the marl through the open discontinuities. The paper describes long term records of heave strains measured by high precision extensometers, the model developed to quantify the surface heave and its comparison with long term records. In a second case, a highly instrumented concrete rigid circular tunnel lining provided data on recorded swelling pressures at the claystone-invert interface and on the measured strains in reinforcing steel bars. This information was processed to derive the histogram of observed stationary boundary swelling pressures. In addition, the strains records measured on the lining reinforcement provided a benchmark for the 3D model built to relate swelling pressures and internal lining stresses. The procedure led to an approximation of the distribution and intensity of swelling forces against the tunnel lining. This analysis, based on long term real data, helped to define new design criteria, more accurate and substantially cheaper, for tunnels excavated in the same geological formation. The paper concludes by suggesting a set of recommendations to limit the risk of damaging swelling of anhydritic rocks and some comforting actions which may be adopted when the swelling phenomenon has initiated.

When using the calculation of stability (regardless of the methodology that is being used), there are two approaches: deterministic and stochastic. The first prerequisite for any calculations is that there are enough data that can be processed statistically - to satisfy the Student classification. When using the deterministic method, the main value to be taken into account in the calculations is the mean value, whereas when using stochastic calculations, all the results obtained by laboratory or field examinations are equally represented. Thanks to this, non-homogeneity of the massif has been introduced to the calculations. This paper presents the methodology of stochastic calculations, and shows one example of comparative analysis of the results of stochastic and deterministic calculations

The stability analysis of rock slopes holds paramount importance in a multitude of geotech-nical projects, including rock-fill dams, embankments, as well as natural and excavated slopes. Among the various failure modes encountered in rock slopes, planar failure is a significant concern. Numerical analysis employing the Mohr-Coulomb linear criterion is a conventional approach adopted by engineers to evaluate the likelihood of planar failure within rock slopes. Nevertheless, the shear strength behavior of rock masses is universally recognized to exhibit nonlinear characteristics, rendering the Mohr-Coulomb criterion a simplified representation of a more complex reality. To bridge this gap, a range of nonlinear shear strength criteria has been formulated, aiming to more accurately depict the nonlinear behavior of rock masses. The objective of this paper is to provide novel insights into the stability analysis of rock slopes through the application of the Úcar nonlinear criterion. The outcomes demonstrate that the Úcar criterion, when juxtaposed with other nonlinear criteria reported in scholarly literature, provides a more precise estimation of the potential failure wedge.

Carbonate rocks have been widely used as a building material in architectural and civil engineering works due to their great availability and beauty. These geomaterials are frequently exposed to acidic aqueous conditions in outdoor environments that can reduce their durability. This study investigates the impact of immersion in acidic aqueous solutions prepared from hydrochloric acid on the physico-mechanical behaviour of a porous limestone from Alicante (Spain). For this purpose, physical characteristics (colour, density, porosity, P- and S-wave velocities and associated dynamic parameters) and mechanical properties (uniaxial compressive strength and Young's modulus) of limestone samples were determined in its initial intact state and after immersion for one month in acid and neutral solutions with pH values equal to 2, 4 and 7. The results revealed that the exposure of the limestone to the acid solutions increases its porosity and reduces its density, P- and S-wave velocities, uniaxial compressive strength and Young´s modulus, which can be attributed to the hydro-physico-chemical interactions between the minerals of the rock and the pore fluid. The knowledge obtained can serve as a basis for determining the suitability of the use of the studied building rock in acidic aqueous environments such as those generated by acid rain or bio acid attack (e.g., lichens) and for establishing the preventive conservation actions to be conducted in heritage constructions built with this stone.

In many fracture mechanics tests, starter notches are commonly carved in samples to generate a small-size region with high-stress concentration in a precise location of the sample of interest. Contrary to other materials where fatigue pre-cracking is possible, starter notches had to be cut in rocks. A variety of techniques exist, but the most common way is to use sawing or milling techniques. Leaving aside the requirements of precise alignment of the notch with respect the specific geometry of the sample and stress orientation, the intrinsic properties of the notch (e.g., sharp or blunt, thick or thin) likely affect the shape and extent of the fracture process zone (FPZ) ahead the crack tip and the fracture toughness (K_C) itself. In this contribution the effect of cutting a relatively thick (~1 mm using a diamond saw disk) and thin (~0.3 mm using a diamond saw wire) starter notch in 4 distinct rock types with apparent macroscopic homogeneity: Moleanos limestone, Floresta sandstone and Macael and Carrara marbles is analyzed. In the two cases, the shape of the edge of the notch is blunt but with a different radius of curvature. Samples were characterized in advance of testing (V_P & V_S, X-ray micro-FRX) to evaluate the homogeneity of the specimens. Then, fracture toughness tests (12 samples per rock type: 6 with the thick and 6 with the thin notch; 48 samples in total) have been performed using the pseudo-compact tension (pCT) technique, which is intended for the precise assessment of this property in mode I (tension). Some of the tests were also complemented with Digital Image Correlation (DIC) observations focused in the FPZ region. Results show that macroscopic (de visu) homogeneity criterion is not enough to guarantee homogeneous mechanical results. With respect the effect of starter notch thickness, we observe that, within uncertainty, there is no significant difference in K_IC (in MPa m^½) in the case of the Floresta sandstone (thin notch = 0.40±0.01; thick notch = 0.37±0.01) and the Macael marble (thin notch = 1.03±0.04; thick notch =1.07±0.06) while that difference is a little bit more significant in the case of the Moleanos limestone (thin notch = 0.85±0.05; thick notch = 0.93±0.03) and, especially in the case of the Carrara marble (thin notch = 0.75±0.05; thick notch =0.93±0.05).

The historic center of Salobreña (Granada, Spain), is located on the summit of a 100-meter-high promontory of Triassic marbles rock known as “La Peña del Castillo”. In this area, rockfalls of different magnitudes have occurred, some of them at the foot of Salobreña Medieval Castle. Recent events in November 2019 and June 2022 have caused significant social alarm due to their impact on the access roads and assets. Fortunately, there were no reported fatalities. To evaluate the fracturing of rock massif, data from discontinuities families were col-lected using (1) geomechanical in-situ stations, as well as (2) applying remote sensing techniques like LiDAR, and another tools, more cost-effective and accessible than LiDAR instrumentation, that combines drone flights and the application of Structure-from-motion (SfM) technique. After applying each technique individually, the discontinuity families have been evaluated and combined.

Located on the border between Zambia and Zimbabwe, the Kariba Dam was constructed on the Zambezi river between 1956 - 1959, creating the largest man-made lake by reser-voir volume. Heavy spillages have progressively scoured an 80 m deep plunge pool, im-mediately downstream of the dam, threatening its foundations. Given the importance of the dam, the decision to undertake the Kariba Dam Rehabilitation Project (KDRP) to en-sure its longevity, long term efficient operation and its continued contribution to energy security and economic prosperity in the region was made. Under the KDRP, the plunge pool reshaping works seek to reshape the plunge pool, in-creasing the basin energy dissipative capacity to reduce the backward scour towards the dam foundations. The nature of the project, with an open-pit excavation at the foot of an existing dam in full operation is unprecedented and constitutes a real rock engineering challenge. This paper highlights the design activities carried out during the works.

This paper explores the mechanical behavior of phyllite rocks and their relationship with factors that can act as determinants in a slope failure: quartz content, tectonics and rock weathering. The rock failure occurred on the cut-slope of the A-7 highway (SE Spain), impacting metamorphic rocks such as phyllite, slate and quartzite sandstones. The geometric char-acteristics of the slope rupture resemble those of soil, despite the affected materials are rocks. Slope instability affects rocks within the hanging wall block of an E-dipping normal fault, while the footwall block, primarily composed of quartzite rocks, remained stable. This study reveals that in the fault gouge zone, the neoformation of expansive clay minerals takes place. Conse-quently, the pelitic nature of the phyllite rocks, combined with tectonically induced alteration, may have been the main determining factor causing these rocks to behave like soil.

To reduce dilution is the main objective in mining operations. For this case, it is necessary to improve the mine operations and define geotechnical parameters. To reduce dilution, the face drilling and charging standards should be improved as much as possible. Damage zone for the rock mass is another parameter to consider reducing dilution. Improvements began to reduce dilution regarding these issues at Tuprag Efemçukuru Gold Mine where the mining methods are long hole open stope, blind up hole and drift and fill. Initially, string loading was applied on face contour drills and the quality of parallel drillings was improved. In addition to operational applications, geotechnical parameters were correlated with overbreak. The cores for all infill drills have been logged with Barton Q system for geotechnical assessments at Tuprag Efemçukuru Gold Mine. Geotechnical core logging provides useful information to reveal damage zone. According to Q values of drifts, the face contour drillings have been relocated to inside the design for definition of damage zone. The overbreak results have been correlated with Q values section by section to create a legend to locate of the face contour drillings on the design. Q values, overbreak length, relocation distance of the face contour drillings on the design and drill hole diameter parameters were considered to calculate damage zone length for the back and the walls. Due to calculation, spots of each result have been put on damage zone length – Q values graphics for the back and the walls. Distribution of spots created a range on the graphics of the back and the walls. Maximum and minimum limits of the range for the back and the walls were drawn and emerged their formulas on the graphics. Consequently, created legend to relocation inside the design of the face contour drillings was revised with the formulas. A block model, based on the legend, was created as a guide for recommendation to operations. Stopes which have similar rock mass quality were compared as after and before applications to knowledge of benefits. The results showed dilution to reduce for ore drifts between 4% and 15% and for waste drifts between 6% and 11%. Besides, it supplied yield for diesel consumption, consumable consumption, and duration of operation cycle

The weathering process significantly affects the mineralogical and geochemical characteristics of rocks that finally alters the engineering properties of rocks. Three different weathering grades (fresh, slightly, and moderately weathered) of gneiss were collected from Kullu, Himachal Pradesh, India. A comprehensive qualitative and quantitative description is used to point out the weathering grades of gneissic rock. The mineralogical alterations were determined using thin-section analysis. The petrographic analysis revealed that a major alteration was observed in plagioclase feldspar. The sericitization of plagioclase is mainly noticed with progressive weathering. The quartz grains remain intact and unaltered in fresh and slightly weathered stages while minor fracturing was observed in the moderately weathered stage. The partial transformation of biotite was also observed in moderately weathered gneiss. The chemical composition of these three weathering grades of gneiss was determined using X-ray fluorescence (XRF) analysis. The Plagioclase Index of Alteration (PIA) shows a significant increase with increasing weathering grades that supports the higher alteration of plagioclase during the weathering of gneissic rock of Himachal Pradesh, India.

Rock bolting, rock reinforcement is an ongoing work. Its a necessity in all rock excavation related application areas i.e. in civil infrastrcuture projects, underground mining, open pit mining, tunneling etc. The subject of rock reinforcement, rock bolting is contineoulsy evolving and there has been a lot of new developments has happened over the years e.g. new types of rock bolts, development of rock bolting-reinforcement machines, design methdologies, application process etc. This paper will be specifically focusing on open rock slopes above ground. We have observed an application and methodological process error for applying rock reinforcement, rock bolting on an open rock slopes above ground. The problem is our current practice of installing rock bolts or rock reinforcement on rock slopes above ground is either based on random observation or systematic empirical design formula. In author's view, most of the time existing way of installing rock bolts, rock reinformcement miss to consider the impact of structural geology, geometry, gravational slip surface of rock blocks. In this paper we are presenting a new approach called 'cross-bedding-cross-bolting (CBRB)' for open rock slopes above ground. This new approach and application methodology for open rock slopes above ground mainly consider structural geology, geometry and gravational slip surface of rock blocks. We will present the conceptual theroy as well as the applicaiton methodology of the 'cross-bedding-cross-bolting (CBRB)' approach. The paper will also brifely review and present the existing practices for rock bolting, rock reinforcement, standards followed and application methodology. Our expected out come from this paper is to present a safe and cost efective method for securing open rock slopes above ground. Also, to provide a new approach and corrective measures for application of rock bolt, rock reinforcement for open rock slopes above ground.

Mine tunnels are constructed to offer access for various purposes. The tunnel excavation's primary purpose in this specific mine was to provide ventilation and access to the second-ary orebody. The Malmani dolomites, which contain most natural water resources, directly overlie the Black Reef formation, which is composed of extremely fine to silt quartzite in-terbedded with silt carbonaceous shale. Unexpected ground conditions caused significant delays during the tunnel construction (e.g., fault zone, dykes, laminated carbonaceous shales). After the inception of the fault zone, the tunnel construction could only advance for 9 m. The tunnel construction halted due to the porous ground conditions of the carbo-naceous shale that could not be supported. The layered carbonaceous rock mass presented difficulties due to its geochemical degradation. A suitable feasibility geotechnical program would have aided in the viability of excavating this tunnel within the Malmani dolomites and the possible risk of mining into the water compartments

Rock mass classifications have gained great importance for the last decades for tunneling engineering. Apart from some previous attempts along the XX century, the start of the rock mass classifications can be stated during the 70s with the development of the Rock Mass Rating (RMR) and the Q index, which are regarded at present as the references for most of the technicians, engineers and geologists. More recently, other classifications have been proposed, like the Geological Strength Index (GSI) and the Rock Mass Index (RMi), which are attracting more interest. Unlike in other fields, authors of those rock mass classifications suggested employing more than one system with the aim of capturing different aspects of the rock mass as each of them considers different factors for calculating the value. Therefore, some correlations have been proposed between two of the classifications for obtaining the rate in other system when having one of them. This paper aims to advance in this field and observe if it is feasible to correlate these four rock mass classifications: RMR, Q index, GSI, and RMi. With this aim, the data obtained from the Seberetxe tunnel, with approximately 600 m, in the new segment of the Southern Metropolitan By-Pass of Bilbao, in Spain, was employed. This twin tunnel was excavated by drill and blast in siltstone. Results indicate that the four systems can be correlated with acceptable accuracy in a homogeneous rock type with different weathering. This study shows that correlations can be developed between two of the four rock mass classifications as long as the same rock type is analyzed.

The rock mass is composed of homogeneous and heterogeneous rocks, where the stresses are transmitted with their specific values by: condition, depth and properties of the rocks; each stress has three components with their respective direction and their respective magnitude, being the major principal stress σ1, and the minor principal stresses σ3 and σ2. In the rock massif, stresses are recognized by their influence on underground excavations and must be measured. To measure in situ stresses, the Drillhole Detonation Method (DDM) is proposed, which detects stresses in two processes. 1) Detonation of a drillhole obtaining radial cracks of different length and direction, by joining the ends of the cracks elliptical figures are formed called ellipse of stresses whit their major and minor axes. 2) To evaluate the magnitude of the major stress we use the formula σ1 = FC1 · γ · Z, to evaluate the magnitude of the minor stress we use the formula σ3 = FC3 · k · γ · Z. The Correction Factor (CF) = 0.0056 (measured angle) + 1.003 and the coefficient k is obtained by dividing the length of the horizontal axes by the vertical axes of the ellipse. To obtain the direction and magnitude of σ2 a drilhole is detonated in the direction perpendicular to what has been done to obtain σ1 and σ3. The major axis of the stress ellipse represents σ1. The measurement of stresses by the Drillhole Detonation Method (DDM) is: low cost, calculated at the same time, contributes to optimize the support of underground excavations.

The term discontinuity covers a series of geological structures, very different both in origin and mechanical behavior. It includes the formational planes, like bedding planes and foliation planes, moving fractures and the joints. In order to perform more realistic geomechanical classification and modeling, for the geomechanical rock mass classifications, the term discontinuity should allow to differentiate between the formational structural planes, not related to the stress state, and the joints, that actually depend on the regionally and local stresses. Another inconsistency arises when evaluating roughness, since joints cannot present polished planes, which can apply to moving fractures, in general with different mechanical behaviors from each other. The same is true when applying the term persistence to a formational plane, whose extension is infinite when compared to a recent fracture or a joint. According to recent research results of stability analysis in tunnels and rock slopes, related to the new application criteria for joint formation based on changes in confining forces, this paper proposes the need for a new approach in the application of terminology for the rock mass geomechanical classification and for the geotechnical characterization, eliminating the inconsistencies that arise when applying some definitions indiscriminately to any structure and origin of the plane.

The slope stability analysis, the critical height, the estimation of force on retaining walls or the calculation of the anchor force, requires a mathematical formulation that goes through an optimization process to determine the critical sliding surface. The process consists of the solution of a derivative with respect to the critical surface. The analytical solutions that have been found are based on a simple geometry for a triangular shaped sliding body. In this paper a solution procedure is proposed for cases of any geometry, including complex geometries. A simple numerical method called incremental method, is developed, specially designed for the analysis of stability, thrust or anchorage design by means of a spread-sheet. The methodology allows static or pseudo-static analysis. Several analysis cases are shown and their solution is compared with the results using advanced numerical methods, where an excellent correspondence is demonstrated.

In this investigation, two different cooling techniques (i.e. water- and air-cooling methods) has been used in order to study the influence of different heating-cooling treatments on the physical properties, microstructural characteristics and point load strength of Himalayan granite collect-ed from Sangla valley, Himachal Pradesh. The temperatures for heat treatment were targeted at 100, 300, 400, 500 and 600°C. As a response to thermal treatments, increase in effective po-rosity and increase in damage coefficient occurs which causes exponential decrease in point load strength. It decreases ~74% and ~81% under air-cooling and water cooling respectively after heating of about 600oC with reference to thermally untreated specimens. The microstruc-tural study reveals that the increase in crack density due to thermal treatments induce intra-, in-ter- and trans-granular cracks, at and beyond 300oC onwards and their coalescence with each other at higher temperatures (i.e. ≥ 500oC) under both the thermal treatments contribute to-wards the variation in point load strength of thermally treated granites.

This study investigates the influence of flaw inclination angles on the mechanical response of rock-like specimens with pre-existing flaws under dynamic loading conditions, employing the Discrete Element Method (DEM) software UDEC. Several Split Hopkinson Pressure Bar (SHPB) compression tests were previously conducted on these specimens, each containing a single non-persistent flaw. The study considered two flaw orientations and a single flaw. Earlier experimental investigations revealed that specimens with unfilled flaws exhibited the highest dependency on flaw inclination angle. Notably, the weakest mechanical response for flawed specimens was observed at a 30° flaw orientation, aligning with the shear failure plane of intact specimens. UDEC numerical simulations were performed to further elucidate the experimental findings. The peak stress response of flaw models obtained were less than intact rock models, which matched well with the experimental results. These simulations provided invaluable insights into the dynamic behaviour of rock-like specimens. .

This study addresses the challenge of accurately estimating support forces to mitigate rock slope failures, employing inverse reliability methods like the Performance Measure Approach (PMA) and the Probabilistic Sufficiency Factor (PSF). A comparison with conventional for-ward reliability approaches, such as the Reliability Index Approach (RIA) and the Forward Monte-Carlo Approach (FMC), highlights the advantages of inverse reliability methods. Focusing on wedge-shaped failure scenarios in the Himalayas, the research emphasizes the applicability and effectiveness of the PMA and the PSF. Results indicate that these inverse methods offer improved accuracy and computational efficiency compared to traditional approaches, making them valuable tools for support force estimation in rock slope engineering. Their reduced computational effort enhances practical applicability, positioning them as promising alternatives in the field.

For coal extraction and removal of overburden, blasting is commonly used in most open-pit coal mines. Blasting generates shock energy that crushes the rock initially and then propagates in the form of waves through the surrounding rock. These ground vibrations are detrimental to the safety of the structures that are located in the vicinity. Though the interaction between blast waves and different structures has been extensively studied to safeguard these structures, the specific behaviour of brick masonry structures under blast-induced ground vibrations (BIGV) remains largely unexplored. The influence of BIGV on structural safety necessitates the incorporation of dynamic structural characteristics into safety guidelines to ensure the safeguarding of these structures. In order to investigate the actual behaviour of structures located near the periphery of a mine, a brick masonry wall was modeled in ABAQUS and analysed under the influence of 10 ground vibration time histories from distinct blast events with varying PPV (Peak Particle Velocity) values. A simplified micro modeling approach utilizing the CDP (Concrete Damage Plasticity) model was employed to accurately predict the wall's response. A comparative analysis was conducted, revealing contrary to popular beliefs, that even at very low PPV values, the structure exhibited significant deformations and stresses. Conversely, in some instances with very high PPV values, the structure remained safe. The primary finding underscores that using PPV alone as the determinant of structural safety possesses several limitations. It is imperative to consider the dynamic characteristics of structures in blast designs for a more comprehensive assessment of safety.

Thermal properties describe how heat and temperature behave in a rock. Sandstone is a very common sedimentary rock found in layers formation in coal mining areas. This rock is used for underground backfilling purposes and other applications in mining. For optimizing the heat load in underground mines, the thermal properties of sedimentary rock are very important. We analyze the results of measurements of the thermal properties, porosity and density of sandstone rocks from the Godavari coal basin, Telangana. The thermal properties were measured by the “FOX50” instrument at room temperature (25⁰C). The thermal conductivity of sandstone rocks ranges from 0.65 to 4.38 W/m. K and it is strongly depending on porosity and density. The average range of density of rock samples is 2.28 to 2.50 g/cm³ and average porosity ranges from 6 to 13 %. The results indicate variations in thermal conductivity and diffusivity across different locations, while specific heat appears consistent throughout all regions. The study also investigated how density and porosity affect the thermal properties of rocks. It was found that thermal conductivity increases with density and decreases with porosity. The assessment of thermal conductivity from porosity and density is made possible by the equations that are provided.

Investigating the possible correlation between various measures of rock strength is a common practice in experimental rock mechanics, as the results of relatively simple and economical tests can yield estimates of mechanical properties that would require more sophisticated experimental procedures. For example, the Schmidt hammer test is one of these experimental setups that have been used to indirectly determine the uniaxial compressive strength and the static modulus of elasticity. Nevertheless, this experimental setup has not been extensively used for the indirect determination of other important mechanical properties, such as the point load strength index and the indirect tensile strength obtained from the Brazilian strength test. For this reason, an experimental program was carried out involving at first the direct determination of the Schmidt hardness, the point load strength index, and the Brazilian tensile strength for rock types of various origins outcropped at the southern part of the Attica Peninsula, Greece. Subsequently, the statistical processing of these results was performed via simple regression techniques, while very good relations were established in the form of exponential equations between the Schmidt hardness and both the point load strength index and the Brazilian tensile strength. Our results can be used for preliminary investigations, at least in the study region, and can enrich our knowledge regarding the correlation between the mechanical properties under consideration.

Traditionally employed laboratory tests allow obtaining strength and deformation properties of rocks, such as the uniaxial compressive strength, tensile strength and Young's modulus. Andesite, a pivotal rock in Ecuador, holds significant relevance to civil engineering and mining, yet its geomechanical properties remain inadequately explored. This study delves into the physical, petrographic, and geomechanical characteristics of andesite from the Tungurahua volcanics geological unit in the Real Cordillera of the Ecuadorian Andes. The findings reveal a massive andesite with porphyritic and hyalopilitic textures, boasting high density (2690±36 kg/m³), low porosity (2.11±1.32%), and minimal water absorption (0.31±0.13%). Mechanically, it proves to be a high-strength rock (204 MPa) with nonlinear elastic behavior up to 40% of the maximum strength and an average secant Young's modulus of 35.06±2.47 GPa. These results contribute to enhance our understanding of Andean andesite properties from the Tungurahua volcanics geological unit.

Limit States Design (LSD), which represents an implementation of Reliability Based Design (RBD), is becoming more widely used in geotechnical engineering. Fundamentally this requires a probabilistic characterization of all uncertainties in a given geotechnical engineering problem. Uncertainty is inherent to rock mechanics and rock engineering, and generally stems from factors such as complex geology, vagueness in instability mechanisms and the highly nonlinear mechanical behaviour of rock masses. Such uncertainties are commonly considered using subjective qualitative assessments, SQAs, using what are known as linguistic variables, e.g. a rock mass may be described as being “slightly weathered”. In this paper we demonstrate why SQAs must be considered as ordinal and not metric (i.e. measured) values. We thus show both why it is not possible to directly consider SQAs in a probabilistic setting, and how doing so may lead to significant errors. To overcome this severe limitation of SQAs we apply techniques recently developed in the broader field of imprecise probabilities in engineering analyses. In particular, we examine how SQAs may advantageously be firstly converted into fuzzy numbers and from those into probabilistic variables. An immediate benefit of this approach is that conditional probability can be used to examine situations where both quantitative measurements (e.g. intact rock strength) and SQAs exist. We demonstrate this by constructing a Bayesian network that combines the two characteristics of intact rock strength and degree of weathering, and show how this leads to an interpretation of rock mass condition that directly supports LSD. Using an example from the literature, we conclude with a brief discussion of how such Bayesian networks can be applied to complex rock engineering projects.

This study assesses the influence of petrophysical properties, petrographic features, and depth on capillary imbibition of basalts and lapillistones from the Upper and Middle Vol-canic Complexes of Madeira Island, Portugal, via multivariate statistical analyses and ma-chine learning methods approach. Results demonstrated that the combined effect of mesofabric, porosity, and pore-type connectedness controls capillary imbibition in lapillis-tones and revealed that there is a strong direct relationship between porosity degree and water absorption coefficient by capillarity, C, in all basalts. The tendency for spontaneous imbibition to decrease with increasing depth is as expected in the studied basalts, except for the sections 23.70 27.20 m and 31.5 34.8 m in two different samples where evidence of fracturing episodes was found which leads to a dual-porosity system that favours water absorption. C is proposed as a complementary coefficient in geotechnical studies of vol-canic rocks.

Pore microstructure in rocks regards shape, volume concentration, distribution and connectivity of pores and cracks and has a substantial influence on many macroscopically observed properties such as rock strength and its deformation and fracture behaviour. Cracks in rocks initiate and propagate in response to the applied stress, with the crack path often driven by local distribution of micro-flaws such as cavities, inclusions, fossils, grain boundaries, mineral cleavage planes, and micro-cracks inside the rock. For sedimentary rocks like sandstone, mineralogical composition of interstitial materials between framework grains is also important factor influencing crack parameters. Although these phenomena are generally known and widely described in the macroscale or mesoscale, the microscopic aspects have not been studied very extensively yet. In order to better understand the process which leads from micro-cracks to macroscopic fracturing and thus extends in scale from millimetres to kilometres, the crack initiation, propagation and growth should be studied just in the microscale. In practical terms, knowledge of the failure behaviour of rock mass due to crack propagation is much needed in some important engineering cases, such as, CO₂ sequestration, high-level radioactive waste disposal or stability of underground workings and slopes. In this contribution, the basic outputs of the study of influence of rock microstructure and composition on the fracture toughness of rocks measured by the chevron notch technique and subsequent analysis of cracks geometry using the X-ray computed tomography are presented. Rock samples selected for experiments are representatives of all three major groups of rocks (igneous, sedimentary and metamorphic), from which sediments, namely sandstones, are the most numerous. Four basic crack parameters were investigated on all rock specimens: (1) crack length, (2) crack width, (3) angle of crack deflection from crack initiation zone, and (4) description of crack course. On the basis of laboratory experiments and analyses, the following fundamental conclusions can be made: (1) the value of crack length generally increases with decreasing rock porosity and this trend is most pronounced within the sandstones, (2) the value of crack length generally increases with increasing value of fracture toughness, (3) the value of the crack length of the sandstones increases with a growing degree of silicification of the matrix, (4) in sandstones, the cracks propagation goes preferably throughout the pore space and may be influenced by limonite pigment and (5) in low-porosity crystalline igneous and metamorphic rocks, the cracks spread along the grain boundaries and often also break grains.

Erosion can cause irreparable damage when it occurs on elaborated elements of the cultural heritage. Even very small erosion rates can result in the loss of valuable sculptural details. Rock erodibility is defined as the lithology-based susceptibility to erosion for a given set of environmental conditions. Wind, rain and hail are examples of the main erosion agents affecting the building rocks used in architectural heritage. Human activity can also be the cause of severe erosion processes in rocks. However, the rock suscebility to erosion determines the efficacy of the erosive process and the effective final material loss from the stone surface. Several research lines address the study of rock erodibility in different contexts (fluvial geomorphology, generation of sediments, tunnel construction, etc.) offering a quantitative approach using indices. However, there are very few works focused on the erodibility of rocks in the heritage context. Erosion, weathering and durability are closely related concepts, usually considered synonymous, but they require an individualized study since the effects and causes associated with each process are very different. In this work, a first approach is proposed to the study of the susceptibility to the erosion of four building rocks widely used in the cultural heritage of Spain. Selected rocks are porous limestones and sandstones with porosity higher than 10%. These rock types are frequent in architectural heritage due to both their availability and their high workability. Erosion Susceptibility of studied rocks has been analysed taking into account both petrographic (texture, structure, mineralogy, heterogeneity and anisotropy) and petrophysical (porosity, pore size distribution and mechanical properties) aspects. The resistance to erosion has been determined by means of the laboratory wide wheel abrasion test. Results show that erosion susceptibility is directly correlated with porosity and inversely with mechanical properties. Grain cohesion, friction angle and tensile strength are key parameters to determine erodibility. Mineralogy probably modify the susceptibility to the material loss, being more resistant the quartz-based rocks than the limestones. Future works, however, should verify the results obtained in this approach including new data and new rock types.

This work presents a multiproxy methodology that combines both in-situ outcrop tests and la-boratory methods, for the petrophysical characterization of a potential sandstone CO2 reservoir. Multiproxy methodology was designed to obtain a complete petrophysical and geomechanical characterization including non-conventional techniques in this type of study. Considered sandstone reservoir corresponds to a detrital Buntsandstein facies of the Iberia Chain (central Spain). Specifically, the involved formations are Aranda-Carcalejos (possible reservoir) and Rané (seal). Four main facies were recognized in the stratigraphic sequence, and the petrophysical analysis of each one was carried out. Main petrophysical differences are found between both channel and sheetflood facies, the former being much more porous and permea-ble and less mechanically resistant than the sheetflood facies. The comparative analysis also highlights the strengths and weaknesses of this multiproxy methodology. This work is part of the in-deep geological characterization of a geological complex for CO2 storage potential evaluation.

In the present paper, statistically significant correlations are obtained between sample di-mensions: height H, width W, and length L, on one side, and compressive strength σp and resistance to cutting KL of the clay sample, on the other side. The geomechanical proper-ties of the coal overburden are determined in laboratory conditions. Coal overburden has a predominantly clayey-silty composition, and samples were taken from the Tamnava East-ern Field (Serbia). Laboratory data are analyzed using multiple linear regression. Results obtained indicate the existence of statistically significant correlations between sample sizes and both σp and KL. These correlations are presented in the form of explicit nonlinear mathematical expressions with corresponding diagrams, which enable further quantitative and qualitative interpretation of the mutual interaction of the analyzed geometrical and ge-omechanical properties. Obtained correlations are with high values of the determinism co-efficient (R > 0.9) and low values of standard deviation. Results are further verified using the ANOVA test. Critical values for certain sample dimensions regarding their effect on σp and KL.

Existing methods for compression tests have enabled the observation of class-II post-peak or snap-back behaviour. However, capturing tensile behaviour in rock testing is still challenging due to stronger snap-back in tension. This work adopts the recently developed Advanced Universal Snap-Back Indirect Tensile test (AUSBIT) to obtain the complete tensile load-displacement behaviour of granite and sandstone Brazilian discs in the post-peak stage through controlled lateral displacement. Digital Image Correlation (DIC) and Acoustic Emission (AE) were employed to analyse the progressive failure mechanisms when compared with the conventional Brazilian tests. Results show that AUSBIT enables controlled failure at extensive lateral displacements by allowing the stable propagation of microcracks. AE data further reveal that cracks formed in AUSBIT release significantly less energy compared to conventional tests. These phenomena were more significant in granite, showing the effectiveness of AUSBIT for controlling the tensile failure of brittle class-II rocks and in attaining the post-peak behaviour.

We have investigated the mode I fracture toughness (K_IC) of granite samples in the presence of various fluids pseudo-compact tension (pCT) test. Prior to the fracture toughness tests, several granite specimens were immersed in deionized water (DIW), hydrochloric acid (2.7M HCl), and sodium hydroxide (0.2M NaOH) solutions for 8 days to evaluate the effects of different reactive environments on K_IC. In addition, a group of specimens of the same rock were submitted to a 24-day immersion cycle using the same fluids (starting with the caustic NaOH solution, then by acidic HCl and finally with DIW), which consecutively soaked the samples every 8 days. The experimental results have been analyzed to assess the corresponding dissipation energies and to identify chemo-mechanical couplings eventually involved in crack initiation and propagation. Results show that, when compared with dry samples, those soaked in any fluid are weakened with a reduction in the threshold energy for crack initiation. However, the different fluids do not result an identical impact over K_IC. We observe that lowest affection is induced by the acidic solution, followed by the caustic one, and finally by DIW (K_IC,dry > K_IC,HCl > K_IC,NaOH > K_IC,DIW). Thus, deionized water exhibits the greatest reduction in fracture toughness (up to 30 %) and the specimens also have a lower average stiffness than the other immersion methods. According to available research (experiments performed with glass materials and molecular dynamics simulations), this may be attributed to micro-scale (molecular scale) processes by which the smaller kinetic diameter of water molecules makes them more accessible to the crack tip, facilitating the hydrolysis of siloxane bonds. Interestingly, despite the fact that the specimens were eventually immersed in DIW in the cyclic test, the K_IC obtained in this case is still higher than that resulting from the individual exposure to the single DIW fluids (K_IC,cycle > K_IC,DIW). That results from the residual hydrolyzing species (Na⁺/H₃O⁺/OH^-, etc.) at the crack tip of the specimens during the cyclic test. The assessments of bulk mechanical energies reveal that, regardless of the chemical environment, approximately 40% of the energy delivered to the samples in each test is consumed by crack initiation, while about 60% is consumed by crack propagation. These results highlight that the chemical environment at the crack tip is the primary factor influencing the subcritical fracture behavior and provide important insights for accurately assessing the fracture toughness of rocks in the presence of fluids.

Direct tensile testing is generally accepted as the most accurate method of determining tensile strength, but indirect methods are commonly employed due to the difficulty and precision re-quired to obtain viable results with the direct method. Accurate values of tensile strength are important, especially regarding design. Thus, values obtained from the direct tensile test are beneficial to be able to utilize and compare them to other experimental values and different methods. This paper presents the development and implementation of the direct tensile test at the Geotechnical Engineering Laboratory of the University of Cantabria, following the ASTM standards. The lessons learned are highlighted. The results of direct tensile tests on Moleanos limestone are here compared with the results of previous indirect tensile tests, namely the Brazilian (splitting tensile) test. The fracture pattern of the direct tensile tests is also presented and analyzed.

The ring test, which is one adaptation of the Brazilian test, was proposed in the 1940s. The laboratory test consists of the application of a diametric load on a ring specimen, in order to estimate the tensile strength indirectly. Its great advantage over the traditional test (disk samples) is that by having a point of weakness (the hole), it is guaranteed that the failure begins in the center of the specimen, a necessary condition for the Brazilian test to be valid. However, the ring test could not be used until the new empirical solution is proposed, because the result of the analytical solution is quite distant from the expected. The analytical equation is based on the theory of elasticity and does not consider the non-linearity of the rocks. According to this analytical solution, in the case of a specimen with a tiny hole, its tensile strength would be six times greater than that obtained with the Brazilian test. The empirical solution is independent of the rock type and correlates the load necessary to break a disc with the load that should be applied in a ring, is based on more than a hundred tests carried out on different materials and laboratories. In the present paper, the empirical solution is analyzed and the advantages/disadvantages of the different internal hole sizes are commented on. Also, how to prepare the ring sample is explained. Being highlighted that the sample preparation is very simple and does not need any special device. In the laboratory, sandstone blocks (lithic arkose) from Burgos (Spain) have been tested with different sizes of rings. The proposed empirical solution takes into account a change in the failure mechanism observed at certain hole sizes.

This review is focused on an innovative and non-destructive laboratory approach, referred to as IRTest, to estimate the rock porosity by Infrared Thermography. Based on the positive out-comes achieved through the use of Infrared Thermography for rock mass characterization, the study of the cooling behavior of rocks has suggested that the porosity grade is linked to the cooling speed of a previously heated rock specimen. The technique has been applied to different rock types, in terms of both porosity grade and lithology. Achieved results demon-strate that there is a positive linear relationship between rock porosity and CRI10 (Cooling Rate Index), corresponding to the infrared thermal monitoring of the rock cooling within a 10 minutes time window. IRTest was applied to differently shaped and sized rock samples, prov-ing the suitability of this technique on a variable statistical population, and suggesting the in-novative potential of Infrared Thermography for the rock laboratory characterization.

Rock mass shows bi-modularity behavior, consisting that elastic modulus having different ratios in compression and tension. Being the compressive elastic modulus always greater than the tensile modulus. In practice, the most common is to estimate the elastic modulus in compression, given that the uniaxial compression test is widely carried out. The direct tensile test requires a specific device, so the tensile strength usually is estimated by the indirect tensile test (Brazilian test). Ye et al. (2009) proposed an equation to estimate the tensile elastic modulus with the Brazilian test, using strain gauges attached in the horizontal direction on both sides of the specimen. However, they did not have how to perform the direct tensile test to compare the results. In the present paper, the elastic modulus is obtained in three different ways: in the compression test, in the direct tensile test, and in the Brazilian test (diametric load). A series of laboratory tests has been done in anisotropic sandstone (lithic arkose), from Burgos, Spain. Being remarkable that the mechanical behavior of the anisotropic rock mass is dependent on the inclination of the foliation planes, the tests were carried out with inclinations of 0°(horizontal) and 90° (vertical). These two configuration are the extremes of tensile strength.

A large-scale two-dimensional test rig was constructed to test block models that were loaded upward in the middle by a concentrated load which simulates the uplift load of a rock anchor. The objective of the tests was to quantitatively demonstrate the arching effect formed in the blocks of the model under the load of a rock anchor. Block models with different patterns of joints were constructed in the rig frame. Horizontal stresses are applied to the blocks by hydraulic cylinders. An upward load is applied in the bottom of the blocks along the middle line. During the test, the full-field displacements of the blocks were monitored with digital image correlation (DIC). The arching effect in the block model was clearly displayed by the DIC images. It also demonstrated that the load-bearing capacity of a block model was higher than the weight force of the overlying blocks within the failure cone that is the calculation rule of the current design method. The load capacity increased with the applied horizontal stress. The shape of the failure cone in a block model was structurally dependent on the joint patten of the model. The test results of five block models with different joint pattern will be presented in the paper.

Despite the new technologies available to assess the stability of rocky slopes, empirical methods continue to be a fundamental part of the initial evaluation process, verification of computational models, and monitoring of construction processes on site. The objective of this article is to propose improvements to the empirical method Q-slope by presenting five graphs based on the original method proposed by the authors in 2015. The graphs will al-low for reducing the time of data collection in the field, optimizing the evaluation of in-trinsic parameters of the method, and enhancing the technical transfer of the procedure.

Numerous Underground Rock Engineering (URE) projects like subsurface road/railway tunnels and hydroelectric power projects are constructed in the Lesser and Sub Himalayas, India. From the geological point of view, the Lesser Himalayan and Siwalik sandstones have been found in these regions. The design of the nationally eminent URE structures in the Himalayan region requires data on the physicomechanical properties of the rock. Hence, a comprehensive study has been conducted to determine the physicomechanical behaviour of the Lesser Himalayan and Siwalik sandstones. This study includes physical characteristics such as dry density (ρd), bulk density (ρb), saturated density (ρsat), effective/apparent porosity (neff), and water content (w); mechanical characteristic, i.e., Unconfined Compressive Strength (UCS) with acoustic signatures. The correlation between the Lesser Himalayan and Siwalik sandstone's physicomechanical properties is established. The AE characterization of the Lesser Himalayan and Siwalik sandstones under uniaxial compression loading is linked to their mechanical characteristics.

A considerable amount of slope stability analysis has been observed in jointed rock masses in which the GSI (Geological Strength Index) estimated at the outcropping level is considered input data to define the rock mass strength. However, this procedure is unsuitable when the rock outcrop scale and the slope scale are significantly different (e.g. open-pit slopes), resulting in an overestimated rock mass strength. For this reason, and in the absence of criteria to modify the GSI based on the scale effects, in this research, a new GSI version is proposed, called GSI_e or “equivalent GSI”. To define an expression for obtaining the GSI_e in terms of the rock mass properties, comparative stability analyses were conducted in a series of hypothetical slopes using two approaches: the first considers the rock mass as a discontinuous medium of rock blocks separated by discontinuities; the second considers the rock mass as an equivalent continuous medium characterized by an equivalent GSI. For the adequate equivalent GSI value, evaluated in each analyzed slope, the safety factor and the failure surface are similar in both approaches. In conformity with the results, a GSI_e formulation in terms of the slope height, the spacing, the intact rock strength, the persistence, and the joint conditions has been proposed. Finally, the formulation was validated by applying it in some cases of mining slopes where the failure occurred.

Rock tunnels are used extensively to convey water for the purpose of generating power, and such tunnels represent the main cost elements in typical Norwegian hydropower developments. Under Norwegian hydropower tradition, the key cost-reducing measure is to keep most of the tunnel length unlined, limiting the length of steel liners. Essential to this concept is to ensure that the stress in the surrounding rock mass exceeds the water pressure inside the tunnel, to avoid hydraulic failure. Reliable estimates of rock stress are required for the safe design of unlined pressure tunnels, and a new rock stress testing method, the Rapid Step-Rate Test, has therefore been developed to enable efficient estimates of rock stress. Since its introduction in 2021 the test method has been adopted by several contractors and plant owners, and some insights from the first few years of RSRT-testing are given, together with recommendations on proper test execution.

The excavation of underground infrastructures in geological sequences containing sulphates may cause swelling, water weakening, creep and karst. All these phenomena have been observed in tunnels for decades, but related technical problems still remain. This is especially true for geologically complex domains as Alpine environments, where the mechanical behviour of sulphates needs to be evaluated in relation to the structural complexity of the fracture network and of the 3D geometries of the orogenic context. This study, that is developed in the framework of the SALT project, a multiscale and interdisciplinary investigation of sulphate salts in the Alpine region, proposes a description of the main features of outcropping sulphates in Western Alps, providing useful preliminary information to afford technical issues related to sulphates during the realization of infrastructures in the Alps.

A method to determine the five elastic constants of a transversely isotropic rock from a single-orientation core using strip load test was proposed. When the strip load test is used, the five elastic constants can be determined either by strain inversion method or artificial neural networks. However, it was found that elastic constants resulted from strip load test show sensitive reaction to rock heterogeneity. One of the ways to solve this problem is to measure larger number of strain values. It is known that the digital image correlation (DIC) method can measure large amount of strain values of rock specimen, replacing the strain gauge attachment method. Comparing with the strain gauge attachment method through numerical simulation, this study investigated how stably elastic constants can be determined when the DIC method measures strain values. The results show that determined elastic constants using the DIC method are more stable than those from the strain gauge attachment method

Representative elementary volume (REV) is defined as the rock mass volume with respect to the size of geotechnical structures, above which the rock mass is considered homogeneous and isotropic. The REV of a jointed rock mass can be determined using finite numerical analysis, but the effect of using different finite element (FE) model settings has not been widely studied. This paper aims to compare various finite element codes and their settings for determining the REV size of an excavated jointed rock mass. We used the scriptable, free program ADONIS and Rocscience's RS2 and RS3 to numerically analyse circular excavation in a rock mass intersected by orthogonal joint sets with specified joint spacing. We examined the effect of implementing the extended finite element (XFEM) method, shear strength reduction, and 3-dimensional analysis. The determined REV sizes in terms of the opening diameter to joint spacing ratio are generally comparable for all analyses and programs, except when XFEM is enabled in RS2 such that the explicit joint interface does not conform with the FE mesh, the REV size becomes relatively larger. XFEM, SSR, and 3-dimensional analyses required significantly higher computational time. The lattermost could exceed the computation capacity when analysing a densely jointed rock mass. Considering computation efficiency, a 2-dimensional, efficient and representative FE model for a complete range analysis to obtain a reliable REV size of a jointed rock mass is preferred over a 3-dimensional analysis.

Knowledge of three-dimensional (3D) in-situ stress distribution plays a crucial role in the safety and productivity assessment of numerous rock engineering projects. The stress distribution analysis in coal seams in particular poses considerable challenges because they can present a complex variation in stress direction and magnitude despite the lack of major structural features such as large fractures/faults or intrusions. The uncertainties with coal stress simulations is partly linked to i) the lack of borehole stress constraints in the coal seam, ii) the lack of a proper optimisation technique to meet available constraints in over-underlying strata of coal seam and iii) the scarcity of open-source numerical simulators capable of handling complex structural models and optimisation techniques. Here, the stress state of a coal mine is simulated through developing an efficient in-house Finite Element (FE) numerical simulator (3DiStress) capable of importing complex geological models (structural and property). The 3DiStress is equipped with an automatic optimisation algorithm to meet the local stress constraints during the 3D Finite Element stress simulation. Two geological models of different sizes are simulated to eliminate any potential boundary effects on simulated stresses. The obtained numerical results confirm the considerable variations, particularly in the orientation of the horizontal in-situ stresses well-aligned with the local stress map of the region and are found to be linked to non-uniformity in the structural geometry and heterogeneity in elastic properties of the coal seam and its surrounding formations.

Understanding the flow dynamics in rock masses presents a significant scientific and practical challenge. These rock masses are characterized by several discontinuity features such as bedding, joints, fractures, and faults, serving as important reservoirs for various geo-resources like water, oil, steam, CO₂, and methane. However, comprehending the complex interaction of fluid and gas flows within the networks of rock mass discontinuities remains a challenge. The study of flow dynamics within these discontinuities holds broad applications in fields such as geothermal energy, tunnelling, oil and gas extraction, nuclear waste disposal, and CO₂ storage. This research focuses on investigating fracture permeability through direct field surveys and remote techniques such as laser scanning, ground, and drone photogrammetry. Field work in compulsory nor understanding the discontinuity network, in order to collect the essential data enabling the construction of representative 3D discontinuity networks. The development of these networks aids in understanding the flow behaviour within specific geological contexts. Notably, our approach incorporates advanced image analysis techniques to extract the trace of discontinuities from photogrammetric images, contributing to the refinement of the geological model. The findings of this research have practical implications, particularly in identifying potential hazards associated with water and methane inflow during tunnelling, geothermal energy and oil and gas operations, nuclear waste disposal, and CO₂ storage. Furthermore, this approach supports environmental protection efforts by providing a better understanding of flow dynamics, thereby contributing to the safeguarding of natural resources. Compliance with regulations such as the EU Water Framework Directive and the DNSH rule is essential in promoting environmental compatibility. This research offers a valuable methodology for understanding the flow dynamics within rock masses, focusing on discontinuity networks. By employing advanced data collection techniques and integrating advanced image analysis processes, this approach serves as a valuable tool for various applications. It represents the intersection of theoretical understanding and practical application, with implications for managing natural hazards, resource exploitation, and environmental safeguarding.

Coastal communities are increasingly exposed to the impending hazards of climate change and global warming. More intense and frequent extreme weather events, sea level rise and tidal inundations are making not only sandy coasts but also rocky coasts highly vulnerable to both erosion processes and instability phenomena. Rockfalls and cliff collapses are increasingly induced by the higher frequency-magnitude of atmospheric and marine processes, such as storm water events, nearshore current actions, hydrodynamic impacts of wind‐induced waves and sea spray, which are responsible for rock weathering, basal erosion (undermining and notching), loss of defensive beaches and removal of protective fallen debris from the lower cliff face. The occurrence of such instability phenomena require a deeper understanding of the failure mechanisms of coastal cliffs in order to develop appropriate management plans and coastal zone governance, so as to be able to increase public safety and reduce land loss and damage to structures, infrastructures and economic activities (tourism, industries, fishing, aquaculture, etc.). In this paper, a parametric study is performed on soft rock cliffs with basal notches, in order to investigate the effects of the undermining on the stability of the rock masses. To this aim, 2D FEM numerical analyses are carried out with the RS2 code from Rocscience. The cliffs are assumed to have different heights and joints with variable depth and persistence.

Discontinuities such as joints, bedding planes and faults govern the mechanical strength and deformation of rock masses. Thorough knowledge and proper simulation of discontinuity mechanical behaviour are of paramount importance in all rock engineering projects. Nowadays, many computational codes allow to explicitly model discontinuities rather than considering their role within the context of an equivalent continuum representation of the rock mass. Over the past decades, several theoretical and empirical constitutive models have been proposed and implemented in numerical codes. The accuracy of reproducing the discontinuity mechanical response and, in turn, the complexity of these models have increased conjointly with advances in computational methods. Even if the usage of advanced constitutive models to realistically reproduce the discontinuity behaviour is more attractive, the strong nonlinearity of these models may provide difficulty for their implementation, with consequent numerical convergence and stability problems and, in addition, the definition and calibrations of the required parameters might be toilsome. A compromise between the complexity (realism) of a constitutive model, the challenge of its numerical implementation and the definition of the parameters characterizing the model response is thus needed. Therefore, simplified models are still more commonly adopted in practical rock engineering due to their user-friendliness and easy-to-determine parameters, but their adoption might result in non-fully optimized design solutions because they might not thoroughly capture the discontinuity behaviour as experimentally observed. This paper discusses the results of a numerical study that examines the influence of adopting different constitutive models for simulating the behaviour of a fractured rock mass. The paper initially provides an overview of the main constitutive models proposed in the literature by focusing on their theoretical consistency (suitability) and practical values (complexities and limitations). It then introduces the features of a proposed constitutive approach aimed at guaranteeing the theoretical rigorousness and overcoming potential implementation issues of the empirically derived formulation of the Barton-Bandis criterion. The proposed model has been implemented in the finite element code PLAXIS and its performance is inspected through numerical analyses. The results are compared with those obtained with an elasto-plastic constitutive relationship with strain-softening based on the Coulomb yield criterion, providing insights to better constrain the implications and suitability of adopting different constitutive models for assessing the stability of engineering works in fractured rock masses.

During tunnel excavation, the accumulated wall displacement and the tunnel support load result from both the tunnel advance and the time-dependent behavior of the surrounding rock mass. One approach to analyze the interactions between tunnel wall displacement and support load is the Convergence-Confinement Method (CCM) using analytical closed-form solutions or empirical Longitudinal Displacement Profiles (LDP). This approach neglects the influence of the time-dependency of ground response resulting in delayed deformation increasing significantly within time after the excavation stage. This time-dependency is particularly crucial in tunnels in squeezing ground, which remains one of the most difficult problems in tunneling. Predicting large tunnel convergence and the influence of time on tunnel deformation in tunnel squeezing, which leads to very high loads on tunnel support, remains a major challenge in tunneling. Failure to consider the added delayed displacements in the preliminary design can result in a false selection of the installation time and the support system type, causing safety issues, cost overruns, and project delays. This paper discusses a revised CCM to estimate the tunnel's support system loads in squeezing ground conditions considering the time-dependent ground response. The proposed approach combines laboratory-scale physical model test results and observations from squeezing tunnels worldwide. The paper explains the new time-dependent CCM and the improvement offered to extend the methodology in the analysis and design of squeezing tunnels. The proposed methodology is validated against Venezuela's Yacambu´-Quibor water conveyance tunnel, which has experienced extreme ground squeezing.

In this study, the authors compare analytical voussoir-analogue based solutions with numerical ones, implemented through 2D distinct-element-method based simulations, in the context of the application of these analyses to the design of underground rooms in bedded rock masses, based on the conditions found in a particular underground room and pillar carbonate mine. Some guidelines are given on how to derive key parameters required for both approaches based on laboratory rock testing, rock mass characterization, and in-situ observations. Particular attention is devoted to quantifying the influence of the roof span, bedding dip, and the occurrence of an overload (associated with highly-fractured beds over the already-detached roof). The performance of the analytical solution in calculating the maximum deflection and compressive stresses within a beam is verified through several 2D numerical models, which, in turn, are capable of capturing the instability mechanisms occurring in the mine.

Modulus is an essential input parameter for the design of excavations and can be referred to as the loading modulus due to its determination under loading conditions. The loading modulus is usually calculated from results of uniaxial compressive strength tests, without considering confining pressure. In this study, a series of uniaxial and triaxial compressive tests on synthetic isotropic specimens has investigated the impact of confining pressure on the resulting loading modulus. The results demonstrate that confining pressure significantly influences the determined loading modulus, highlighting its importance as a key parameter. A Tangent technique calculated at 50% peak strength with a 10% range is concluded as the most reliable method for determining the loading modulus. In addition, contrary to deviatoric stress, total axial stress is identified as the most competent parameter for evaluating deformation and strength, due to its inclusion of confining pressure in the axial direction.

Rockburst, a phenomenon occurring in highly stressed grounds, poses a significant risk due to the safety of underground mines due to a sudden and violent rock failure. Integrated ground support systems are generally utilised to enhance stability and minimise rockburst hazards. This study employs ABAQUS software to assess the performance of integrated support system in potential burst-prone areas. The effects of bolt spacing, and fibre-reinforced shotcrete were examined based on deformation in burst-prone areas (PBPA) and energy absorption of the support system. The results indicate that rockbolt spacing of 1 m to 1.3 m and 2 m leads to a decreased volume of PBPA by 47%, 41% and 34%, respectively. Stress and displacement are highest in the bolts within these areas, as indicated by the energy absorption results. The result shows that energy absorption is 6.90 kJ/m^2 when applying the integrated support system, which comprises rockbolts with 1 m spacing and 75 mm thick fibre-reinforced shotcrete.

Blasting is widely used in tunneling when mechanical excavation methods cannot be applied due to rock conditions or cost constraints. The blast design of the contour holes defines the damage to the remaining rock, which might change the rock support requirements. This study investigates the crack behavior in sequential boreholes through small-scale experiments on rock-like specimens. Cylindrical samples, prepared with speckles for Digital Image Correlation (DIC), varied in decoupling ratio, and the detonation cord was detonated simultaneously in the blast holes. The data was collected with an ultra-high-speed camera (UHSC) for DIC. The results indicated the development of the cracks between the boreholes and their behavior towards the boundary of the samples. The results showed that in this experimental configuration, there is no significant difference between the different decoupling ratios. This study shows the importance of an optimum blast design to minimize the damage to the remaining rock.

In the early stages of a deep tunnel design, it is essential to identify and assess the potential hazards that could occur during construction. One of these hazards is the development of significant deformations around the tunnel after excavation, which is often referred to as "squeezing” phenomenon. The most widely used tool for estimating the squeezing potential is an abacus introduced by Hoek and Marinos (H&M) in 2000. It allows to simply estimate the percentage of tunnel convergence by knowing only the uniaxial compressive strength of the rock mass (σcm) and the in-situ stress. The chart has several important advantages, such as ease of use and the relevance of the information obtained, making it a very useful tool. However, there are also some limitations, which are poorly known in the engineering community. Consequently, this abacus may be used outside of its scope. Firstly, the chart is based on analytical models that aims to catch the behavior of a tunnel excavation in a perfectly plastic rock mass characterized by a Mohr-Coulomb behavior (Duncan Fama 1993) and Hoek&Brown behaviour (Carranza-Torres and Fairhurst 1999) which is not always realistic in the area near the excavation. The other problem lies in estimating the uniaxial compressive strength of the rock mass. While easy to comprehend, it is very hard to estimate in practice. Several formulations can be found in the literature that lead to very different values of σcm. Consequently, important discrepancies exist in the estimated convergence values. This paper aims to clarify the underlying hypothesis and to update the H&M chart by replacing σcm with the uniaxial compressive strength of the intact rock (σci) and by introducing curves of GSI (Geological Strength Index) isovalues. To achieve this, a Monte Carlo simulation is conducted on the input parameters (in-situ stress, GSI, σci, the Hoek&Brown parameter mi, dilation angle), like the original approach. However, unlike Hoek and Marinos, who relied on analytical expressions, the new chart is based on numerical modelling, allowing the rock mass to be characterized using a generalized Hoek and Brown failure criterion. The variation intervals of the input parameters for the Monte Carlo simulation and the expressions linking these parameters to those used in the numerical modelling have been updated. Finally, results give an improved assessment of the expected convergence and allow to consider uncertainties about the in-situ stress, σci and mi to get a confidence interval of the estimation.

The measurement of mode I fracture toughness (K_IC) , which represents the resistance to the propagation of pre-existing defects under tensile stress, is crucial for various engineering applications involving rocks, such as tunnel boring, rock drilling, hydraulic fracturing, and oil exploration. Recently, the pseudo-compact tension (pCT) test has been proposed as a reliable method to measure K_IC in rocks under pure tension conditions, yielding consistent results for both fragile and ductile rocks. Although the pCT method offers several advantages, such as simple sample preparation, small sample requirement, and controlled fracture propagation beyond the peak load, its original approach requirements the use of a specially designed, large-size testing device. This limitation may restrict the broader adoption of this testing methodology. To overcome this drawback, we present in this work a simplified pCT test apparatus that can be easily installed in any conventional compression frame. The proposed device, thanks to its mechanical configuration, allows for application of true tension to the notch of the sample while the axial actuator of the frame operates in compression over the loading piston. The mechanical behavior of the prototype was assessed numerically with a finite element method model in ABAQUS, and experimentally using aluminum specimens. Additionally, to further evaluate its stiffness and performance, digital image correlation (DIC) was employed to obtain full-field strain characteristics of the critical, most stressed parts of the apparatus. To validate the new configuration, polymethyl methacrylate (PMMA) specimens with different notch lengths were tested. The results demonstrate that the new simplified pCT test system exhibits sufficient stiffness and provides comparable K_IC values with those previously obtained with the reference pCT testing device.

Shear stiffness is an important parameter governing deformation behavior and stress dis-tribution. However, its current use is inadequate for detailed models, particularly in sedi-mentary rocks. Most published shear stiffness data for sedimentary rocks are for joints at low normal stresses, with limited available at normal stresses above 1 MPa. This paper ad-dresses this deficiency by presenting results from direct shear testing for bedding parallel fractures under high normal stress and implementing a recently proposed method to isolate fracture deformations, this method is then validated using several measurement methods. The shear stiffness of 18 samples from the Bowen Basin (QLD, Australia) was obtained for different values of applied normal stresses (1 to 8 MPa). The results show a strong positive correlation between applied normal stress and shear stiffness. The findings high-light opportunities for improvement in current guidelines and emphasize the need for them to better reflect results and data processing protocols.

Solving engineering tasks and assessing the suitability of rocks as building raw materials requires determining the physical properties. Ultrasonic testing as nondestructive testing is useful for the initial assessment of elastic properties. Adapting seismic tomography technique for application at the laboratory scale using ultrasonic frequency waves allowed the characterisation of variations in ultrasonic propagation velocity inside the study granite specimen. The P- and S-wave velocities were measured using 54kHz and 250kHz transducers. The dynamic modules and anisotropy ratio were calculated based on obtained seismic wave velocities. The ultrasonic tomography method allowed for an initial assessment of the homogeneity of the rock medium, which allows an optimal selection of its lithological variety for a given engineering purpose.

Although the determination of joint shear strength of layered heterogeneous rock masses constitutes a challenge in engineering, since they are widely present in natural rock masses, the available scientific-technical publications are relatively scarce. Studies have mainly been focused on homogeneous rocks. Thus, the objective of this research is to evaluate the effect of heterogeneity on the shear behaviour of different types of rock joints and provide the basis for evaluating the stability of the heterogeneous rock masses, as well as to know the differences and similarities with respect to the behaviour of homogeneous rock joints. In this research, various direct shear tests have been conducted on artificial joints of heterogeneous rocks with different joint roughness coefficients, as well as tests on artificial joints of homogeneous rock in order to allow comparisons between them. The experiment consisted of performing 18 direct shear tests on rock joints of homogeneous and heterogeneous materials with three different roughness profiles. These rock joints were shaped in the laboratory with artificial stone materials, manufactured using different dosages of lime, cement and sand, obtaining samples of low, medium and high strength. The test results show that in heterogeneous materials there is a great influence of the block of rock with lower strength. In this sense, it was shown that the strength of the weak rock is dominant in the joint shear strength when there are wide strength differences between the joint faces. On the other hand, if the rock of the lower face of discontinuity is of low or medium strength and the upper face is of medium or high strength, the joint shear strength is lower than the case in which both faces are of low or medium resistance. This situation occurs for all roughness profiles, although especially in the profiles with the highest JCR. In other words, if the results were transposed to a natural slope, a homogeneous shale-type slope would be more stable than a heterogeneous one with alternating shale and limestone. The shear behaviour is also heterogeneous in the damage suffered by both faces of the joint. That is, when the heterogeneous rock blocks that, assemble the joint, exhibit a great difference in the strength, the degradation of the asperities only occurs on the side of the rock with lower strength, while the one with greater resistance remains intact.

Field-scale rock masses are discontinuous and heterogeneous in that they are composed of different sections of intact rock intersected by discontinuities. Joints are common discontinuities in rock masses that have formed previously in the rock mass's geological history. Joints can be grouped based on their orientations and other properties. When subjected to stresses, deformations occur in these rock masses. These strains either accumulate in the intact rock blocks or generate movements along discontinuities. Reproducing the stress-strain behaviour of rock masses at laboratory scale or by means of physical models is a complex task. To attempt to replicate rock mass behaviour at the laboratory scale, jointed laboratory-scale cylindrical granite samples were prepared with two different configurations of jointing. The specimens contain two smooth joint sets, forming intact rock blocks of similar sizes. Compressive laboratory tests were conducted at various confinement levels on jointed granite samples, where global deformations were measured using LVDTs (Linear Variable Differential Transformer) and corrected using energy approaches to estimate the total deformation produced in the entire jointed specimen. Furthermore, some strain gauges were fixed on the intact rock blocks to compute the localized strains in these blocks. The results of the deformations on these laboratory tests can be compared to previously conducted tests on intact rock. Based on the strain measurements of both the intact and jointed samples, it is possible to compute a preliminary estimate of the stiffness of the joints, particularly that of the sub-horizontal contacts. Moreover, the indirectly obtained local deformation values are compared to those obtained using strain gauges in order to understand the heterogeneous nature of strain in these rock mass analogue samples, which can help to better understand deformation processes of field-scale rock masses. In conclusion, this study presents the results and a first interpretation with preliminary conclusions of a set of triaxial tests conducted on jointed samples, where an estimate of the stiffness parameters was obtained based on the observed deformations on the different constituent blocks of the samples.

Rocks are natural materials and their microstructure is usually complex, involving for example voids, cracks, planes of weakness, different sizes of grains or different minerals. The micro-structural properties of the rocks influence fracture propagation, for instance, under opening fracture modes (Mode I). This paper presents fracture propagation analysis of notched rock prismatic samples tested under four-point bending conditions using a petrographic microscope of transmitted and polarized light. The two analyzed rocks are a Floresta sandstone and a Mol-eanos limestone. After testing, the sample is reconstituted and thin sections of the area sur-rounding the main fracture are obtained. The initial type of fracture (i.e. transgranular or in-tergranular), the initial deviation of the main crack and its overall sinuosity are studied to try to gain a deeper understanding of fracture processes in rocks.

Rock fractures play a significant role in the mechanical behavior of fractured rock masses. Understanding the shear strength characteristics of rock fractures is crucial for a wide range of rock engineering applications. In the literature, many experimental studies have been presented to analyze the shear strength of rock fractures. The strength of rock fractures is significantly dependent on fracture geometry that can be altered during the historical shearing process. This study presents a brief analysis of repeated direct shear of mated rock fractured. We conducted five repeated shear test simulations under constant normal load conditions using a predictive shear model presented in our previous work. The fracture surface used in the first round of shear simulation is scanned from a natural granite fracture surface. After shearing, the fracture surfaces are repeatedly used for the next rounds of shear simulations. The results generally show that the repeated shear induces irreversible surface degradation, which reduces the shear strength and normal displacement. The findings of this study provide valuable insights into the shear strength behavior of rock fractures, which can be utilized to enhance the accuracy of numerical models for analyzing the mechanical behavior of fractured rock masses and to provide practical implications for the design and stability assessment of rock structures in various rock engineering projects.

Characterizing rock mass discontinuities is a crucial aspect of rock engineering. Current automatic methods for discontinuity identification from 3D point clouds generally do not provide mathematical descriptions of individual 'joints'. To overcome this limitation, this article proposes a three-stage approach with the following steps: (i) identification of 'dis-continuity sets' or 'families'; (ii) identification of 'clusters', defined as continuous sets of nearby points that belong to a given discontinuity; and (iii) identification of 'individual joints,' defined as one or more 'clusters' whose spatial position suggests that they conform to a single discontinuity, even without fulfilling a continuity condition. The process con-cludes with a mathematical representation of joints using convex hulls, which can be em-ployed to characterize the rock mass. The proposed approach is validated using synthetic and real cases. Results illustrate that the developed tools can efficiently identify convex hulls that represent individual rock discontinuities from 3D point clouds.

An excavation wall is commonly constructed as a support structure to give support vulnerable slopes of soil and rock ground, particularly in hilly regions. Many studies are available on excavation walls in soil, but a few investigations have been done on excavation walls in rock. Also, those studies often overlook cohesion between rock joints. This study addresses this gap by developing a two-dimensional physical model of a flexible excavation wall supporting a footing on an artificial rock mass with orthogonal joints and with slight staggering. The ap-parent cohesion value resulting from the staggered rock joints was analytically calculated using force equilibrium analysis. Afterward, a distinct element model (DEM) was created using the universal distinct element code (UDEC) to compare experimental observations. The out-come of the analysis shows the experimental values align more closely with numerical values when apparent cohesion is considered in the numerical model.

The Gordon Underground Power Station in Tasmania is part of the Gordon-Pedder Hydro-Electric Scheme owned and managed by Hydro Tasmania. Completed in 1978, the station's 96m length, 22m width, and 31m height cavern reaches a depth of 183m below ground beneath Lake Gordon. The Gordon cavern was designed with a traditional arched roof profile. At the time of construction, Lack, Bowling, and Knoop (1975) published detailed studies that documented the in-situ rock strength, stress regime, and deformation modulus that provides a record for us today. The cavern support consists of grouted rock bolts, steel mesh, and approximately 150mm sprayed shotcrete. The rock bolts used are slot and wedge type with copper grouting tubes. These bolts were adopted by the Hydro-Electric Commission of Tasmania and the Snowy Mountains Hydro-Electric Authority for many of their projects at the time. Recent inspections across Hydro Tasmania's portfolio (Sainsbury et al, 2002) revealed that many of these slot and wedge bolts are ungrouted and have some level of corrosion. The cavern roof is covered with an average thickness of approximately 150mm shotcrete. While still functional, the shotcrete has deteriorated over time and requires ongoing inspection. To assess the current stability of the Gordon Power Station a detailed three-dimensional discrete element model (3DEC) has been developed. The model accurately matches the as-built excavation sequence and monitoring data from the time of construction until the present time. The model provides a basis to consider the potential long-term ground support degradation on the overall cavern stability.

The Well-being of Future Generations (Wales) Act 2015, based on the United Nations Sustainable Development Goals, is key to decision-making at the Welsh Government, and particularly in relation to transportation. One of the key outcomes of this act has been the Wales Road Review, stating that building new highways must end, with a shift to investing in public transport and active travel networks. Management and maintenance of existing strategic transportation links therefore becomes more critical. With this in mind, existing highways will still receive funding to ensure their continued operation, and will need to, in many cases, continue to operate past the ‘normal operation’ phase of their service life. This paper presents a case study of an engineering scheme developed to provide major maintenance and renewal for six rock cuttings forming the A477 trunk road, a critical transport link between Ireland (via the Pembroke Dock) and the United Kingdom through west Wales. The aim of the project was to assess the condition of the rock mass and the rock slope stabilisation systems that have been in place for nearly forty years. The stabilisation measures (tensioned rock anchors, rock dowels, shotcrete and rock netting systems) were considered by the asset owner to be entering their ‘end of life’ phase. During the ‘end of life’ phase, the risk posed by rock fall hazards can increase significantly, and failure rates of the systems begin to show a marked increase. The cuttings were assessed by combining remote sensing methods with detailed inspections undertaken by rope access trained Engineering Geologists. Close liaison between all stakeholders throughout the project was key to successful delivery and was especially important during the early phases. The design was developed using the latest industry guidance on inspecting and maintaining grouted anchors. An observational approach to the testing and renewal of the tensioned anchors, and renewal of the other aspects of the rock slopes and stabilisation systems was integral to the design. Working safely above the A477 was an important consideration throughout, as the highway had to remain open to traffic and not be subjected to any significant disruption. An inspection and maintenance strategy was developed for the cuttings with the aim of providing a best practice example to be used for other highway rock cuttings throughout Wales. This paper highlights the need for a collaborative and observational approach to extending the ‘normal operation’ phase of aging highways rock slopes.

The Joint Roughness Coefficient (JRC) is an important parameter used to quantify the roughness of rock joints which significantly influences their shear behavior. Traditionally, two methods are used for estimating JRC. The first method relies on optical observation utilizing the Barton-Choubey suggested table. After obtaining the rock-joint profile using a profilometer, a comparison with the ten standard joint profiles in the Barton-Choubey table follows. This method exhibits a high degree of subjectivity. The second method involves a series of demanding laboratory tests, which are time-consuming and costly. In recent years, a third approach has been introduced, based on empirical equations that are functions of one statistical parameter. Whereas the scientific community has suggested a wide range of parameters, this paper uses Myers’ statistical parameter Z₂, which is the root mean square of the first derivative of the rock-joint profile and is considered highly reliable. After digitizing the rock-joint profiles obtained from different directions on a rock-joint surface, the estimation of Z₂ for each profile succeeds. Next, the parameter Z₂ applies to the empirical equations, and the JRC value is derived. Then the results are compared to those of the two usual methods. The JRC_s index value of the entire discontinuity surface is also studied instead of the JRC value in different directions. This concept is more realistic for the shear strength of rock joints study because the shear behavior of discontinuities in the field develops on rough surfaces of irregular morphology. This work concludes that a) the alternative JRC index calculation method simplifies the quantification process by requiring only digitized rock discontinuity profiles and, at the same time, limits subjectivity, and b) the JRC_s index of the rock-joint surface is an extension to the two dimensions of the JRC index of the rock-joint profile.

Cored samples are used at different design stages of underground excavations to determine the laboratory properties of intact rocks, including the Unconfined Compressive Strength (UCS) and Young’s modulus (E). Previous research has revealed that when cores are retrieved from deep and high-stress environments, they may experience damage in the form of microcracks, which can affect their laboratory properties. In this research, the influence of coring stress path on damage formation and associated strength degradation is investigated using an advanced numerical program based on the hybrid Finite-Discrete Element Method (FDEM). For this purpose, two-dimensional (2D) FDEM models of laboratory specimens were generated with triangular elements representing grains. Models were then calibrated to the laboratory properties of undamaged Lac de Bonnet (LdB) granite, the typical host rock at the Underground Research Laboratory (URL) in Manitoba, Canada. The laboratory properties used for model calibration include the unconfined and confined compressive strengths, as well as the direct and indirect tensile strengths. In the next step, the coring stress path obtained from a 3D elastic continuum model for a vertical borehole at the 420 Level of the URL was applied to the calibrated 2D model. This resulted in the formation of microcracks, oriented parallel to the major principal stress direction. The damaged numerical specimen was then subjected to uniaxial loading until failure. The results of the unconfined compression test simulation indicate that the damaged specimen exhibits lower peak strength and deformation modulus compared to the undamaged specimen. It is concluded that the hybrid FDEM employed in this research can replicate the unloading-induced brittle damage mechanisms, including crack initiation and crack opening during core drilling, as well as crack closure during uniaxial loading. Furthermore, the FDEM can simulate associated changes in the laboratory properties of hard, brittle rocks. This research addresses the need for more reliable design parameters for underground excavations in the mining, civil, nuclear waste, and petroleum industries. Future work involves investigating the influence of grain-scale geometric and stiffness heterogeneities on drilling-induced core damage. This will be achieved by generating homogeneous (consisting of one mineral type) and heterogeneous (consisting of four mineral types) grain-based FDEM models of LdB granite laboratory specimens utilizing Voronoi blocks.

The Callovo-Oxfordian (COx) claystone is a quasi-brittle anisotropic sedimentary rock considered in France as a potential host rock suitable for deep geological repository of nuclear wastes. Firstly, the objective is to reproduce localised failure and cracking mechanisms in shearing and opening modes to characterise the material deformation and fracturing observed at macroscale. Secondly, this work investigates the effects of the inherent anisotropic nature of the COx claystone on the macroscopic shear strength. A 3D numerical model based on the distinct element method has been developed to reproduce the main features of its mechanical behaviour under triaxial loading conditions, considering its inherent anisotropic nature through morphological aspects. A series of triaxial loading tests was simulated using 3DEC to reproduce the experimental data obtained on the COx claystone. The proposed distinct element model is able to well reproduce rock anisotropic behaviour and the influence of confining pressure on the rock failure mode.

Simplified analytical evaluations of chemical explosives such as TNT, ANFO, PETN, and emulsion reveal notable distinctions when compared to cylinder expansion experiments and equation of state (EOS) data. The reliability of simplified analytical methodologies in determining the reaction zone of these explosives is questionable. In contrast, employing computational methods has become commonplace to achieve a more precise description of detonation products. This paper aims to delve into the behavior of chemical explosives through the application of combined Eulerian-Lagrangian smoothed particle hydrodynamics (ELSPH). The objective is to derive parameter sets for these explosives aligned with the JWL (Jones-Wilkins-Lee) equation of state (EOS). This approach not only provides a pathway to characterize explosives used in rock blasting but also proves valuable in compensating for the inherent limitations in experimental measurements. It accommodates variations in explosive properties across different industrial batches of detonation products, acknowledging the challenges posed by restricted accuracy in experimental measurements.

This work is an attempt to improve the fundamental understanding of the role of the fracture network in rock mass failure and in estimating rock mass effective strength. In most rock masses, the ubiquitous presence of natural fractures reduces the deformation modulus and strength compared to the properties of intact rock. The relationships of rock classification systems, such as the Geological Strength Index (GSI), take this effect into account only qualitatively. Their predictive capacity is very limited especially when extrapolation to scale and anisotropy aspects are important. A description of the fracture network relevant to strength includes the fracture density, the preferential orientation sets but also the multiscale organization of fracture sizes, generally described by power-law models and scaling exponents. All these parameters are keys to quantify rock mass properties, as well as their scaling behaviour, in terms of connectivity, flow and transport capacity and mechanical modulus properties. Previous work has shown how the rock mass modulus can be related to geometrical indicators suitable for multi-scale fracture networks. We pursue this work and further use the Discrete Fracture Network (DFN) based approach for modelling the rock mass. It is combined with numerical models developed in the software 3DEC® to generate numerous synthetic rock mass samples on which UCS and tensile mechanical tests are performed. In these numerical simulations, cracks appear in the rock surrounding the fractures as the deformation increases until peak stress is reached. Building on the established relationship between DFN percolation parameter and rock mass elastic modulus and considering the correlation between the latter and the effective strength, we develop indicators to quantify the evolution of damage and DFN properties, between the initial and the peak stress state, and to relate the ratio between the strength of the intact rock and the strength of the effective rock to the geometric and mechanical variables characteristic of fracture networks.

Factor of safety (FoS) procedures while using finite element methods (FEM) require stable calculation models. When FoS < 1 this condition is not verified, and the safety analysis cannot be completed. An alternative approach is presented to determine the factor of safety for unstable rock slopes, considering the Hoek-Brown (HB) failure criterion and using Plaxis 2D software for the calculations. The proposed methodology defines a modified HB material with better properties than the original, by applying an upgrade factor in its yield function. Then, FoS ≥ 1 is now obtained by calculating with the improved material, and FoS of the original material would be the result of dividing the FoS of the improved material by the corresponding upgrade factor. Various materials are required to calculate the same FoS to improve the accuracy of the results. The proposed methodology has been tested with a rock slope example for different material conditions.

Rock-Socketed Piles (RSPs) are a common type of deep foundation used to support heavy concentrated loads from the superstructure, and to transfer them to deeper hard rocks. Due to its worldwide applications, several works have been focused on the study of the load and shaft resistance – settlement response when the RPS is axially loaded, using field load tests, exper-imental small-scale physical tests and numerical models. However, despite previous efforts, an in-depth analysis of the stresses mobilized at the pile-rock interface (PRI) is still needed. This work aims to provide a contribution in that direction, using a 3D numerical model of axially loaded rough RSPs developed with the Distinct Element Method (DEM). Then, the stress path and the behavior at the pile-rock interface (PRI) of RSP are analyzed. Finally, DEM results are compared with results obtained with the cavity expansion theory proposed by others.

Due to the complex and poor rock conditions in Japan, the auxiliary methods are often used during the excavation by mountain tunneling method. Vertical pre-reinforcement bolt method, in which rebars are cast vertically to reinforce the ground above the tunnel before the excavation stage, is suitable for stabilizing the ground with small overburden, constraining subsidence of the ground surface and the behavior of unstable slope. However, a quantitative design method for this method has not yet been established due to the variety of design concepts such as its placing density and length, the variety of expected performance of the method itself, and the lack of clarity of highly effective rock conditions and so on. In this report, a model test and numerical analyses are carried out to examine the effect of the method, and a fundamental design approach was shown. In the model test, aluminum bar laminates were used as the ground material, and metal ball chains were set to simulate the vertical pre-reinforcement bolt. Internal displacement which simulated the excavation action was reproduced by pulling the PTFE sheets set around the tunnel model. Numerical analysis using the finite difference method was carried out for parametric study after the replication of the model test and to confirm the effect on the behavior of the ground and support structure of full-scale tunnel with vertical pre-reinforcement bolt around the tunnel. From the results of the model tests, the effect of integration of ground above tunnel in the reinforced area was confirmed, and the necessity of the reinforcement in the side area of tunnel was also shown if more stability of tunnel was demanded. From the result of numerical analysis, it indicated that its application might decrease the shear strain of ground and the change of apparent stiffness of ground might be brought by the integration of ground. Based on these results, an approach of a quantitative design was shown. It clarified that placing vertical pre-reinforcement affects the scale of support structure, and also a note to design the most suitable support structure and the relationship between the reinforcement conditions and the effect of this method were clarified.

In many occasions, especially when dealing with poor-quality rock masses, the importance of fast support placement is essential. If placement of the support is delayed, high convergences will develop due to the loss of confinement when creating the hole. As a result, the conditions of the geotechnical quality of the rock mass worsen and lead to excessively high pressures that require the rehabilitation of the support. The role of the support and reinforcement of underground roadways and infrastructures, is to control the convergences of the cavity and eliminate possible rockfalls. The support elements form a system composed of internal and external elements. The elements that work internally reinforcing the rock can be bolts and cables. The other part of the system is the external support that works on the exposed rock, as shotcrete, mesh or a combination of both. The aim of this work is to analyse the technical considerations to be taken into account to correctly design the support of roadways and infrastructures in underground mines and to propose a set of practical recommendations to enhance the support design. To explain the behavior of the different support elements, the role they play in each case is defined. The most common situations are considered according to the type of rock mass and stress conditions. When stability is conditioned by the structure of the rock mass, it is necessary to secure isolated blocks that are formed around the excavation. In this case, the bolts and cables must be able to anchor the blocks to the firm rock mass to transfer the load to the stable rock area, considering the calculations of the forces to withstand the static action of gravity in order to reach the safety factor prescribed in the ITC 04.6.05 currently in effect in Spain. The second role that the supporting elements can play is to reinforce the rock around the roadway or underground accesses so that an arch is formed and can withstand the tensile loads of the ground or to form a beam in the case of solid flat roofs on stratified rocks making them stable. The ultimate goal is to improve the safety of roadways by applying ground support that will maintain the excavations stable and reduce the need for future rehabilitation.

Ground support systems must be engineered to provide a solution for underground mines in static, quasi-static and dynamic geotechnical ground conditions. To prevent large deformations caused by rockbursts or squeezing ground conditions, rockbolts are widely used efficient counter measures. Self-drilling hollow rockbolts are gaining popularity as a means for ground support in rapid underground mine development. This paper describes a recent development in self-drilling rock bolt technology and introduces the Falcon Bolt. The Falcon bolt is a self-drilling R32 hollow bolt with a specially designed mechanical anchor that enables point anchoring and torque-tensioning prior to injection of a pumpable bonding agent. In rockburst-prone or squeezing ground conditions, a decoupled version of the bolt with a high elongation steel grade allows sufficient deformation to occur to dissipate kinetic energy from mobilised rock in a rockburst event or displace with squeezing ground movement. To determine the dynamic performance of the decoupled Falcon bolt, a campaign of mass impact tests were completed at the CANMET MMSL drop test facility in Canada. The results showed that the decoupled Falcon bolt is capable of withstanding 50kJ impacts, i.e. a 2.9 tonnes mass moving at a velocity of 5.9 m/s, without fracture. To further enrich our understanding, the authors performed a numerical study of the dynamic response of the Falcon bolt under dynamic loads using the finite element analysis (via ABAQUS). Replicating dynamic bolt response using numerical modelling techniques at the laboratory scale is a key stepping-stone towards more accurately simulating the complex bolt-rock interactions in a full-scale rockburst event.

When deep tunnels are excavated in poor ground, squeezing conditions occur and the design of supports must follow the yielding principle. To this aim, special elastic-plastic elements embedded in the preliminary support can be employed. The presence of the elastic-plastic elements radically modifies the ground-lining interaction mechanisms making necessary the use of numerical analyses. Particularly relevant is the case of the anisotropic geostatic state of stress. The paper reports and discusses some results obtained by 2D numerical ground-lining interaction analyses of yielding preliminary support with initial non-isotropic stress field. Results of classic rigid support and isotropic state of stress are also reported and compared. Specific attention will be given to the effect that the stress anisotropy has on the lining bending moment.

Skin support provides resistance to the shearing and spalling of exposed rock layers/blocks, as well as protects the surface from open atmospheric contact. Polymeric liners are one such skin support that can be applied to the roof of excavation to enhance load-deformability behaviour. Understanding the reinforcement mechanism of the polymeric liner to the rock in laboratory experiments and numerical models is key to measuring its performance for field applications. The failure behaviour of hydrostone plaster beams when coated with a thin layer of polymeric liner was studied experimentally and numerically. The flexural bending experimental results for load-deformation behaviour of polymeric liner-coated samples showed remarkable difference from the specimens without polymeric liners. The lined beams exhibited Strain hardening behaviour, whereas unlined beams showed tensile-brittle failure. The average load-carrying capability increased nearly 2.5 times for un-notched samples. The substrate material and the interface between the polymer and the substrate was modelled numerically using a cohesive-zone based interface model, to understand the damage behaviour of the samples with deformation as observed during experiments. The results showed that once plaster had yielded, cracks started to generate in the beam. However, the polymeric liner restricted the growth of micro-cracks and their propagation. From the plastic shear strain development it was also evident that plaster started to fail in shear from supporting rollers. As a result, a distinct diagonal shear crack started to form between the loading and the support roller points, causing the ultimate failure. Also, at the interface of liner and plaster, cracks propagated laterally from the roller support points as observed during experiments.

A unified quantitative index and criterion for the stability evaluation and control of tunnel surrounding rock support system composite structures based on plastic complementary energy and over force have been established. It will provide scientific basis and guidance for the selection and quantitative regulation of dynamic support schemes under different conditions. When the rock mass is good or the ground stress is low, the damage evolution is less than the self equilibrium evolution, and the plastic complementary energy eventually tends to stabilize. Support is not required or simple support can be provided as needed. When the rock mass is medium or poor, or the ground stress is medium or high, the damage evolution is greater than the self equilibrium evolution, and there is a minimum value of plastic complementary energy. It is necessary to provide appropriate or strengthened system support in a timely manner. When the rock mass is extremely poor or the ground stress is extremely high, the damage evolution is far greater than the self equilibrium evolution, and the plastic complementary energy increases sharply. It is necessary to immediately strengthen the system support or even advanced support is required. A method has been established to determine the optimal support timing and reinforcement force. The timing of support has a significant impact on the effectiveness of support. The earlier the support time, the better the surrounding rock support effect, but the greater the stress on the support structure, which may damage the support structure. The later the support time, the worse the support effect of the surrounding rock. Even the support cannot suppress the evolution of damage to the surrounding rock, ultimately leading to instability and failure. The optimal support timing is when the plastic complementary energy reaches its minimum value, and the required reinforcement force is optimal, ensuring the support effect without damaging the support structure.

When using the calculation of stability (regardless of the methodology that is being used), there are two approaches: deterministic and stochastic. The first prerequisite for any calculations is that there are enough data that can be processed statistically - to satisfy the Student classification. When using the deterministic method, the main value to be taken into account in the calculations is the mean value, whereas when using stochastic calculations, all the results obtained by laboratory or field examinations are equally represented. Thanks to this, non-homogeneity of the massif has been introduced to the calculations. This paper presents the methodology of stochastic calculations, and shows one example of comparative analysis of the results of stochastic and deterministic calculations

The stability analysis of rock slopes holds paramount importance in a multitude of geotech-nical projects, including rock-fill dams, embankments, as well as natural and excavated slopes. Among the various failure modes encountered in rock slopes, planar failure is a significant concern. Numerical analysis employing the Mohr-Coulomb linear criterion is a conventional approach adopted by engineers to evaluate the likelihood of planar failure within rock slopes. Nevertheless, the shear strength behavior of rock masses is universally recognized to exhibit nonlinear characteristics, rendering the Mohr-Coulomb criterion a simplified representation of a more complex reality. To bridge this gap, a range of nonlinear shear strength criteria has been formulated, aiming to more accurately depict the nonlinear behavior of rock masses. The objective of this paper is to provide novel insights into the stability analysis of rock slopes through the application of the Úcar nonlinear criterion. The outcomes demonstrate that the Úcar criterion, when juxtaposed with other nonlinear criteria reported in scholarly literature, provides a more precise estimation of the potential failure wedge.

Carbonate rocks have been widely used as a building material in architectural and civil engineering works due to their great availability and beauty. These geomaterials are frequently exposed to acidic aqueous conditions in outdoor environments that can reduce their durability. This study investigates the impact of immersion in acidic aqueous solutions prepared from hydrochloric acid on the physico-mechanical behaviour of a porous limestone from Alicante (Spain). For this purpose, physical characteristics (colour, density, porosity, P- and S-wave velocities and associated dynamic parameters) and mechanical properties (uniaxial compressive strength and Young's modulus) of limestone samples were determined in its initial intact state and after immersion for one month in acid and neutral solutions with pH values equal to 2, 4 and 7. The results revealed that the exposure of the limestone to the acid solutions increases its porosity and reduces its density, P- and S-wave velocities, uniaxial compressive strength and Young´s modulus, which can be attributed to the hydro-physico-chemical interactions between the minerals of the rock and the pore fluid. The knowledge obtained can serve as a basis for determining the suitability of the use of the studied building rock in acidic aqueous environments such as those generated by acid rain or bio acid attack (e.g., lichens) and for establishing the preventive conservation actions to be conducted in heritage constructions built with this stone.

In many fracture mechanics tests, starter notches are commonly carved in samples to generate a small-size region with high-stress concentration in a precise location of the sample of interest. Contrary to other materials where fatigue pre-cracking is possible, starter notches had to be cut in rocks. A variety of techniques exist, but the most common way is to use sawing or milling techniques. Leaving aside the requirements of precise alignment of the notch with respect the specific geometry of the sample and stress orientation, the intrinsic properties of the notch (e.g., sharp or blunt, thick or thin) likely affect the shape and extent of the fracture process zone (FPZ) ahead the crack tip and the fracture toughness (K_C) itself. In this contribution the effect of cutting a relatively thick (~1 mm using a diamond saw disk) and thin (~0.3 mm using a diamond saw wire) starter notch in 4 distinct rock types with apparent macroscopic homogeneity: Moleanos limestone, Floresta sandstone and Macael and Carrara marbles is analyzed. In the two cases, the shape of the edge of the notch is blunt but with a different radius of curvature. Samples were characterized in advance of testing (V_P & V_S, X-ray micro-FRX) to evaluate the homogeneity of the specimens. Then, fracture toughness tests (12 samples per rock type: 6 with the thick and 6 with the thin notch; 48 samples in total) have been performed using the pseudo-compact tension (pCT) technique, which is intended for the precise assessment of this property in mode I (tension). Some of the tests were also complemented with Digital Image Correlation (DIC) observations focused in the FPZ region. Results show that macroscopic (de visu) homogeneity criterion is not enough to guarantee homogeneous mechanical results. With respect the effect of starter notch thickness, we observe that, within uncertainty, there is no significant difference in K_IC (in MPa m^½) in the case of the Floresta sandstone (thin notch = 0.40±0.01; thick notch = 0.37±0.01) and the Macael marble (thin notch = 1.03±0.04; thick notch =1.07±0.06) while that difference is a little bit more significant in the case of the Moleanos limestone (thin notch = 0.85±0.05; thick notch = 0.93±0.03) and, especially in the case of the Carrara marble (thin notch = 0.75±0.05; thick notch =0.93±0.05).

The historic center of Salobreña (Granada, Spain), is located on the summit of a 100-meter-high promontory of Triassic marbles rock known as “La Peña del Castillo”. In this area, rockfalls of different magnitudes have occurred, some of them at the foot of Salobreña Medieval Castle. Recent events in November 2019 and June 2022 have caused significant social alarm due to their impact on the access roads and assets. Fortunately, there were no reported fatalities. To evaluate the fracturing of rock massif, data from discontinuities families were col-lected using (1) geomechanical in-situ stations, as well as (2) applying remote sensing techniques like LiDAR, and another tools, more cost-effective and accessible than LiDAR instrumentation, that combines drone flights and the application of Structure-from-motion (SfM) technique. After applying each technique individually, the discontinuity families have been evaluated and combined.

Located on the border between Zambia and Zimbabwe, the Kariba Dam was constructed on the Zambezi river between 1956 - 1959, creating the largest man-made lake by reser-voir volume. Heavy spillages have progressively scoured an 80 m deep plunge pool, im-mediately downstream of the dam, threatening its foundations. Given the importance of the dam, the decision to undertake the Kariba Dam Rehabilitation Project (KDRP) to en-sure its longevity, long term efficient operation and its continued contribution to energy security and economic prosperity in the region was made. Under the KDRP, the plunge pool reshaping works seek to reshape the plunge pool, in-creasing the basin energy dissipative capacity to reduce the backward scour towards the dam foundations. The nature of the project, with an open-pit excavation at the foot of an existing dam in full operation is unprecedented and constitutes a real rock engineering challenge. This paper highlights the design activities carried out during the works.

This paper explores the mechanical behavior of phyllite rocks and their relationship with factors that can act as determinants in a slope failure: quartz content, tectonics and rock weathering. The rock failure occurred on the cut-slope of the A-7 highway (SE Spain), impacting metamorphic rocks such as phyllite, slate and quartzite sandstones. The geometric char-acteristics of the slope rupture resemble those of soil, despite the affected materials are rocks. Slope instability affects rocks within the hanging wall block of an E-dipping normal fault, while the footwall block, primarily composed of quartzite rocks, remained stable. This study reveals that in the fault gouge zone, the neoformation of expansive clay minerals takes place. Conse-quently, the pelitic nature of the phyllite rocks, combined with tectonically induced alteration, may have been the main determining factor causing these rocks to behave like soil.

To reduce dilution is the main objective in mining operations. For this case, it is necessary to improve the mine operations and define geotechnical parameters. To reduce dilution, the face drilling and charging standards should be improved as much as possible. Damage zone for the rock mass is another parameter to consider reducing dilution. Improvements began to reduce dilution regarding these issues at Tuprag Efemçukuru Gold Mine where the mining methods are long hole open stope, blind up hole and drift and fill. Initially, string loading was applied on face contour drills and the quality of parallel drillings was improved. In addition to operational applications, geotechnical parameters were correlated with overbreak. The cores for all infill drills have been logged with Barton Q system for geotechnical assessments at Tuprag Efemçukuru Gold Mine. Geotechnical core logging provides useful information to reveal damage zone. According to Q values of drifts, the face contour drillings have been relocated to inside the design for definition of damage zone. The overbreak results have been correlated with Q values section by section to create a legend to locate of the face contour drillings on the design. Q values, overbreak length, relocation distance of the face contour drillings on the design and drill hole diameter parameters were considered to calculate damage zone length for the back and the walls. Due to calculation, spots of each result have been put on damage zone length – Q values graphics for the back and the walls. Distribution of spots created a range on the graphics of the back and the walls. Maximum and minimum limits of the range for the back and the walls were drawn and emerged their formulas on the graphics. Consequently, created legend to relocation inside the design of the face contour drillings was revised with the formulas. A block model, based on the legend, was created as a guide for recommendation to operations. Stopes which have similar rock mass quality were compared as after and before applications to knowledge of benefits. The results showed dilution to reduce for ore drifts between 4% and 15% and for waste drifts between 6% and 11%. Besides, it supplied yield for diesel consumption, consumable consumption, and duration of operation cycle

The weathering process significantly affects the mineralogical and geochemical characteristics of rocks that finally alters the engineering properties of rocks. Three different weathering grades (fresh, slightly, and moderately weathered) of gneiss were collected from Kullu, Himachal Pradesh, India. A comprehensive qualitative and quantitative description is used to point out the weathering grades of gneissic rock. The mineralogical alterations were determined using thin-section analysis. The petrographic analysis revealed that a major alteration was observed in plagioclase feldspar. The sericitization of plagioclase is mainly noticed with progressive weathering. The quartz grains remain intact and unaltered in fresh and slightly weathered stages while minor fracturing was observed in the moderately weathered stage. The partial transformation of biotite was also observed in moderately weathered gneiss. The chemical composition of these three weathering grades of gneiss was determined using X-ray fluorescence (XRF) analysis. The Plagioclase Index of Alteration (PIA) shows a significant increase with increasing weathering grades that supports the higher alteration of plagioclase during the weathering of gneissic rock of Himachal Pradesh, India.

Rock bolting, rock reinforcement is an ongoing work. Its a necessity in all rock excavation related application areas i.e. in civil infrastrcuture projects, underground mining, open pit mining, tunneling etc. The subject of rock reinforcement, rock bolting is contineoulsy evolving and there has been a lot of new developments has happened over the years e.g. new types of rock bolts, development of rock bolting-reinforcement machines, design methdologies, application process etc. This paper will be specifically focusing on open rock slopes above ground. We have observed an application and methodological process error for applying rock reinforcement, rock bolting on an open rock slopes above ground. The problem is our current practice of installing rock bolts or rock reinforcement on rock slopes above ground is either based on random observation or systematic empirical design formula. In author's view, most of the time existing way of installing rock bolts, rock reinformcement miss to consider the impact of structural geology, geometry, gravational slip surface of rock blocks. In this paper we are presenting a new approach called 'cross-bedding-cross-bolting (CBRB)' for open rock slopes above ground. This new approach and application methodology for open rock slopes above ground mainly consider structural geology, geometry and gravational slip surface of rock blocks. We will present the conceptual theroy as well as the applicaiton methodology of the 'cross-bedding-cross-bolting (CBRB)' approach. The paper will also brifely review and present the existing practices for rock bolting, rock reinforcement, standards followed and application methodology. Our expected out come from this paper is to present a safe and cost efective method for securing open rock slopes above ground. Also, to provide a new approach and corrective measures for application of rock bolt, rock reinforcement for open rock slopes above ground.

Mine tunnels are constructed to offer access for various purposes. The tunnel excavation's primary purpose in this specific mine was to provide ventilation and access to the second-ary orebody. The Malmani dolomites, which contain most natural water resources, directly overlie the Black Reef formation, which is composed of extremely fine to silt quartzite in-terbedded with silt carbonaceous shale. Unexpected ground conditions caused significant delays during the tunnel construction (e.g., fault zone, dykes, laminated carbonaceous shales). After the inception of the fault zone, the tunnel construction could only advance for 9 m. The tunnel construction halted due to the porous ground conditions of the carbo-naceous shale that could not be supported. The layered carbonaceous rock mass presented difficulties due to its geochemical degradation. A suitable feasibility geotechnical program would have aided in the viability of excavating this tunnel within the Malmani dolomites and the possible risk of mining into the water compartments

Rock mass classifications have gained great importance for the last decades for tunneling engineering. Apart from some previous attempts along the XX century, the start of the rock mass classifications can be stated during the 70s with the development of the Rock Mass Rating (RMR) and the Q index, which are regarded at present as the references for most of the technicians, engineers and geologists. More recently, other classifications have been proposed, like the Geological Strength Index (GSI) and the Rock Mass Index (RMi), which are attracting more interest. Unlike in other fields, authors of those rock mass classifications suggested employing more than one system with the aim of capturing different aspects of the rock mass as each of them considers different factors for calculating the value. Therefore, some correlations have been proposed between two of the classifications for obtaining the rate in other system when having one of them. This paper aims to advance in this field and observe if it is feasible to correlate these four rock mass classifications: RMR, Q index, GSI, and RMi. With this aim, the data obtained from the Seberetxe tunnel, with approximately 600 m, in the new segment of the Southern Metropolitan By-Pass of Bilbao, in Spain, was employed. This twin tunnel was excavated by drill and blast in siltstone. Results indicate that the four systems can be correlated with acceptable accuracy in a homogeneous rock type with different weathering. This study shows that correlations can be developed between two of the four rock mass classifications as long as the same rock type is analyzed.

The rock mass is composed of homogeneous and heterogeneous rocks, where the stresses are transmitted with their specific values by: condition, depth and properties of the rocks; each stress has three components with their respective direction and their respective magnitude, being the major principal stress σ1, and the minor principal stresses σ3 and σ2. In the rock massif, stresses are recognized by their influence on underground excavations and must be measured. To measure in situ stresses, the Drillhole Detonation Method (DDM) is proposed, which detects stresses in two processes. 1) Detonation of a drillhole obtaining radial cracks of different length and direction, by joining the ends of the cracks elliptical figures are formed called ellipse of stresses whit their major and minor axes. 2) To evaluate the magnitude of the major stress we use the formula σ1 = FC1 · γ · Z, to evaluate the magnitude of the minor stress we use the formula σ3 = FC3 · k · γ · Z. The Correction Factor (CF) = 0.0056 (measured angle) + 1.003 and the coefficient k is obtained by dividing the length of the horizontal axes by the vertical axes of the ellipse. To obtain the direction and magnitude of σ2 a drilhole is detonated in the direction perpendicular to what has been done to obtain σ1 and σ3. The major axis of the stress ellipse represents σ1. The measurement of stresses by the Drillhole Detonation Method (DDM) is: low cost, calculated at the same time, contributes to optimize the support of underground excavations.

The term discontinuity covers a series of geological structures, very different both in origin and mechanical behavior. It includes the formational planes, like bedding planes and foliation planes, moving fractures and the joints. In order to perform more realistic geomechanical classification and modeling, for the geomechanical rock mass classifications, the term discontinuity should allow to differentiate between the formational structural planes, not related to the stress state, and the joints, that actually depend on the regionally and local stresses. Another inconsistency arises when evaluating roughness, since joints cannot present polished planes, which can apply to moving fractures, in general with different mechanical behaviors from each other. The same is true when applying the term persistence to a formational plane, whose extension is infinite when compared to a recent fracture or a joint. According to recent research results of stability analysis in tunnels and rock slopes, related to the new application criteria for joint formation based on changes in confining forces, this paper proposes the need for a new approach in the application of terminology for the rock mass geomechanical classification and for the geotechnical characterization, eliminating the inconsistencies that arise when applying some definitions indiscriminately to any structure and origin of the plane.

The slope stability analysis, the critical height, the estimation of force on retaining walls or the calculation of the anchor force, requires a mathematical formulation that goes through an optimization process to determine the critical sliding surface. The process consists of the solution of a derivative with respect to the critical surface. The analytical solutions that have been found are based on a simple geometry for a triangular shaped sliding body. In this paper a solution procedure is proposed for cases of any geometry, including complex geometries. A simple numerical method called incremental method, is developed, specially designed for the analysis of stability, thrust or anchorage design by means of a spread-sheet. The methodology allows static or pseudo-static analysis. Several analysis cases are shown and their solution is compared with the results using advanced numerical methods, where an excellent correspondence is demonstrated.

In this investigation, two different cooling techniques (i.e. water- and air-cooling methods) has been used in order to study the influence of different heating-cooling treatments on the physical properties, microstructural characteristics and point load strength of Himalayan granite collect-ed from Sangla valley, Himachal Pradesh. The temperatures for heat treatment were targeted at 100, 300, 400, 500 and 600°C. As a response to thermal treatments, increase in effective po-rosity and increase in damage coefficient occurs which causes exponential decrease in point load strength. It decreases ~74% and ~81% under air-cooling and water cooling respectively after heating of about 600oC with reference to thermally untreated specimens. The microstruc-tural study reveals that the increase in crack density due to thermal treatments induce intra-, in-ter- and trans-granular cracks, at and beyond 300oC onwards and their coalescence with each other at higher temperatures (i.e. ≥ 500oC) under both the thermal treatments contribute to-wards the variation in point load strength of thermally treated granites.

This study investigates the influence of flaw inclination angles on the mechanical response of rock-like specimens with pre-existing flaws under dynamic loading conditions, employing the Discrete Element Method (DEM) software UDEC. Several Split Hopkinson Pressure Bar (SHPB) compression tests were previously conducted on these specimens, each containing a single non-persistent flaw. The study considered two flaw orientations and a single flaw. Earlier experimental investigations revealed that specimens with unfilled flaws exhibited the highest dependency on flaw inclination angle. Notably, the weakest mechanical response for flawed specimens was observed at a 30° flaw orientation, aligning with the shear failure plane of intact specimens. UDEC numerical simulations were performed to further elucidate the experimental findings. The peak stress response of flaw models obtained were less than intact rock models, which matched well with the experimental results. These simulations provided invaluable insights into the dynamic behaviour of rock-like specimens. .

This study addresses the challenge of accurately estimating support forces to mitigate rock slope failures, employing inverse reliability methods like the Performance Measure Approach (PMA) and the Probabilistic Sufficiency Factor (PSF). A comparison with conventional for-ward reliability approaches, such as the Reliability Index Approach (RIA) and the Forward Monte-Carlo Approach (FMC), highlights the advantages of inverse reliability methods. Focusing on wedge-shaped failure scenarios in the Himalayas, the research emphasizes the applicability and effectiveness of the PMA and the PSF. Results indicate that these inverse methods offer improved accuracy and computational efficiency compared to traditional approaches, making them valuable tools for support force estimation in rock slope engineering. Their reduced computational effort enhances practical applicability, positioning them as promising alternatives in the field.

For coal extraction and removal of overburden, blasting is commonly used in most open-pit coal mines. Blasting generates shock energy that crushes the rock initially and then propagates in the form of waves through the surrounding rock. These ground vibrations are detrimental to the safety of the structures that are located in the vicinity. Though the interaction between blast waves and different structures has been extensively studied to safeguard these structures, the specific behaviour of brick masonry structures under blast-induced ground vibrations (BIGV) remains largely unexplored. The influence of BIGV on structural safety necessitates the incorporation of dynamic structural characteristics into safety guidelines to ensure the safeguarding of these structures. In order to investigate the actual behaviour of structures located near the periphery of a mine, a brick masonry wall was modeled in ABAQUS and analysed under the influence of 10 ground vibration time histories from distinct blast events with varying PPV (Peak Particle Velocity) values. A simplified micro modeling approach utilizing the CDP (Concrete Damage Plasticity) model was employed to accurately predict the wall's response. A comparative analysis was conducted, revealing contrary to popular beliefs, that even at very low PPV values, the structure exhibited significant deformations and stresses. Conversely, in some instances with very high PPV values, the structure remained safe. The primary finding underscores that using PPV alone as the determinant of structural safety possesses several limitations. It is imperative to consider the dynamic characteristics of structures in blast designs for a more comprehensive assessment of safety.

Thermal properties describe how heat and temperature behave in a rock. Sandstone is a very common sedimentary rock found in layers formation in coal mining areas. This rock is used for underground backfilling purposes and other applications in mining. For optimizing the heat load in underground mines, the thermal properties of sedimentary rock are very important. We analyze the results of measurements of the thermal properties, porosity and density of sandstone rocks from the Godavari coal basin, Telangana. The thermal properties were measured by the “FOX50” instrument at room temperature (25⁰C). The thermal conductivity of sandstone rocks ranges from 0.65 to 4.38 W/m. K and it is strongly depending on porosity and density. The average range of density of rock samples is 2.28 to 2.50 g/cm³ and average porosity ranges from 6 to 13 %. The results indicate variations in thermal conductivity and diffusivity across different locations, while specific heat appears consistent throughout all regions. The study also investigated how density and porosity affect the thermal properties of rocks. It was found that thermal conductivity increases with density and decreases with porosity. The assessment of thermal conductivity from porosity and density is made possible by the equations that are provided.

Investigating the possible correlation between various measures of rock strength is a common practice in experimental rock mechanics, as the results of relatively simple and economical tests can yield estimates of mechanical properties that would require more sophisticated experimental procedures. For example, the Schmidt hammer test is one of these experimental setups that have been used to indirectly determine the uniaxial compressive strength and the static modulus of elasticity. Nevertheless, this experimental setup has not been extensively used for the indirect determination of other important mechanical properties, such as the point load strength index and the indirect tensile strength obtained from the Brazilian strength test. For this reason, an experimental program was carried out involving at first the direct determination of the Schmidt hardness, the point load strength index, and the Brazilian tensile strength for rock types of various origins outcropped at the southern part of the Attica Peninsula, Greece. Subsequently, the statistical processing of these results was performed via simple regression techniques, while very good relations were established in the form of exponential equations between the Schmidt hardness and both the point load strength index and the Brazilian tensile strength. Our results can be used for preliminary investigations, at least in the study region, and can enrich our knowledge regarding the correlation between the mechanical properties under consideration.

Traditionally employed laboratory tests allow obtaining strength and deformation properties of rocks, such as the uniaxial compressive strength, tensile strength and Young's modulus. Andesite, a pivotal rock in Ecuador, holds significant relevance to civil engineering and mining, yet its geomechanical properties remain inadequately explored. This study delves into the physical, petrographic, and geomechanical characteristics of andesite from the Tungurahua volcanics geological unit in the Real Cordillera of the Ecuadorian Andes. The findings reveal a massive andesite with porphyritic and hyalopilitic textures, boasting high density (2690±36 kg/m³), low porosity (2.11±1.32%), and minimal water absorption (0.31±0.13%). Mechanically, it proves to be a high-strength rock (204 MPa) with nonlinear elastic behavior up to 40% of the maximum strength and an average secant Young's modulus of 35.06±2.47 GPa. These results contribute to enhance our understanding of Andean andesite properties from the Tungurahua volcanics geological unit.

Limit States Design (LSD), which represents an implementation of Reliability Based Design (RBD), is becoming more widely used in geotechnical engineering. Fundamentally this requires a probabilistic characterization of all uncertainties in a given geotechnical engineering problem. Uncertainty is inherent to rock mechanics and rock engineering, and generally stems from factors such as complex geology, vagueness in instability mechanisms and the highly nonlinear mechanical behaviour of rock masses. Such uncertainties are commonly considered using subjective qualitative assessments, SQAs, using what are known as linguistic variables, e.g. a rock mass may be described as being “slightly weathered”. In this paper we demonstrate why SQAs must be considered as ordinal and not metric (i.e. measured) values. We thus show both why it is not possible to directly consider SQAs in a probabilistic setting, and how doing so may lead to significant errors. To overcome this severe limitation of SQAs we apply techniques recently developed in the broader field of imprecise probabilities in engineering analyses. In particular, we examine how SQAs may advantageously be firstly converted into fuzzy numbers and from those into probabilistic variables. An immediate benefit of this approach is that conditional probability can be used to examine situations where both quantitative measurements (e.g. intact rock strength) and SQAs exist. We demonstrate this by constructing a Bayesian network that combines the two characteristics of intact rock strength and degree of weathering, and show how this leads to an interpretation of rock mass condition that directly supports LSD. Using an example from the literature, we conclude with a brief discussion of how such Bayesian networks can be applied to complex rock engineering projects.

This study assesses the influence of petrophysical properties, petrographic features, and depth on capillary imbibition of basalts and lapillistones from the Upper and Middle Vol-canic Complexes of Madeira Island, Portugal, via multivariate statistical analyses and ma-chine learning methods approach. Results demonstrated that the combined effect of mesofabric, porosity, and pore-type connectedness controls capillary imbibition in lapillis-tones and revealed that there is a strong direct relationship between porosity degree and water absorption coefficient by capillarity, C, in all basalts. The tendency for spontaneous imbibition to decrease with increasing depth is as expected in the studied basalts, except for the sections 23.70 27.20 m and 31.5 34.8 m in two different samples where evidence of fracturing episodes was found which leads to a dual-porosity system that favours water absorption. C is proposed as a complementary coefficient in geotechnical studies of vol-canic rocks.

Pore microstructure in rocks regards shape, volume concentration, distribution and connectivity of pores and cracks and has a substantial influence on many macroscopically observed properties such as rock strength and its deformation and fracture behaviour. Cracks in rocks initiate and propagate in response to the applied stress, with the crack path often driven by local distribution of micro-flaws such as cavities, inclusions, fossils, grain boundaries, mineral cleavage planes, and micro-cracks inside the rock. For sedimentary rocks like sandstone, mineralogical composition of interstitial materials between framework grains is also important factor influencing crack parameters. Although these phenomena are generally known and widely described in the macroscale or mesoscale, the microscopic aspects have not been studied very extensively yet. In order to better understand the process which leads from micro-cracks to macroscopic fracturing and thus extends in scale from millimetres to kilometres, the crack initiation, propagation and growth should be studied just in the microscale. In practical terms, knowledge of the failure behaviour of rock mass due to crack propagation is much needed in some important engineering cases, such as, CO₂ sequestration, high-level radioactive waste disposal or stability of underground workings and slopes. In this contribution, the basic outputs of the study of influence of rock microstructure and composition on the fracture toughness of rocks measured by the chevron notch technique and subsequent analysis of cracks geometry using the X-ray computed tomography are presented. Rock samples selected for experiments are representatives of all three major groups of rocks (igneous, sedimentary and metamorphic), from which sediments, namely sandstones, are the most numerous. Four basic crack parameters were investigated on all rock specimens: (1) crack length, (2) crack width, (3) angle of crack deflection from crack initiation zone, and (4) description of crack course. On the basis of laboratory experiments and analyses, the following fundamental conclusions can be made: (1) the value of crack length generally increases with decreasing rock porosity and this trend is most pronounced within the sandstones, (2) the value of crack length generally increases with increasing value of fracture toughness, (3) the value of the crack length of the sandstones increases with a growing degree of silicification of the matrix, (4) in sandstones, the cracks propagation goes preferably throughout the pore space and may be influenced by limonite pigment and (5) in low-porosity crystalline igneous and metamorphic rocks, the cracks spread along the grain boundaries and often also break grains.

Erosion can cause irreparable damage when it occurs on elaborated elements of the cultural heritage. Even very small erosion rates can result in the loss of valuable sculptural details. Rock erodibility is defined as the lithology-based susceptibility to erosion for a given set of environmental conditions. Wind, rain and hail are examples of the main erosion agents affecting the building rocks used in architectural heritage. Human activity can also be the cause of severe erosion processes in rocks. However, the rock suscebility to erosion determines the efficacy of the erosive process and the effective final material loss from the stone surface. Several research lines address the study of rock erodibility in different contexts (fluvial geomorphology, generation of sediments, tunnel construction, etc.) offering a quantitative approach using indices. However, there are very few works focused on the erodibility of rocks in the heritage context. Erosion, weathering and durability are closely related concepts, usually considered synonymous, but they require an individualized study since the effects and causes associated with each process are very different. In this work, a first approach is proposed to the study of the susceptibility to the erosion of four building rocks widely used in the cultural heritage of Spain. Selected rocks are porous limestones and sandstones with porosity higher than 10%. These rock types are frequent in architectural heritage due to both their availability and their high workability. Erosion Susceptibility of studied rocks has been analysed taking into account both petrographic (texture, structure, mineralogy, heterogeneity and anisotropy) and petrophysical (porosity, pore size distribution and mechanical properties) aspects. The resistance to erosion has been determined by means of the laboratory wide wheel abrasion test. Results show that erosion susceptibility is directly correlated with porosity and inversely with mechanical properties. Grain cohesion, friction angle and tensile strength are key parameters to determine erodibility. Mineralogy probably modify the susceptibility to the material loss, being more resistant the quartz-based rocks than the limestones. Future works, however, should verify the results obtained in this approach including new data and new rock types.

This work presents a multiproxy methodology that combines both in-situ outcrop tests and la-boratory methods, for the petrophysical characterization of a potential sandstone CO2 reservoir. Multiproxy methodology was designed to obtain a complete petrophysical and geomechanical characterization including non-conventional techniques in this type of study. Considered sandstone reservoir corresponds to a detrital Buntsandstein facies of the Iberia Chain (central Spain). Specifically, the involved formations are Aranda-Carcalejos (possible reservoir) and Rané (seal). Four main facies were recognized in the stratigraphic sequence, and the petrophysical analysis of each one was carried out. Main petrophysical differences are found between both channel and sheetflood facies, the former being much more porous and permea-ble and less mechanically resistant than the sheetflood facies. The comparative analysis also highlights the strengths and weaknesses of this multiproxy methodology. This work is part of the in-deep geological characterization of a geological complex for CO2 storage potential evaluation.

In the present paper, statistically significant correlations are obtained between sample di-mensions: height H, width W, and length L, on one side, and compressive strength σp and resistance to cutting KL of the clay sample, on the other side. The geomechanical proper-ties of the coal overburden are determined in laboratory conditions. Coal overburden has a predominantly clayey-silty composition, and samples were taken from the Tamnava East-ern Field (Serbia). Laboratory data are analyzed using multiple linear regression. Results obtained indicate the existence of statistically significant correlations between sample sizes and both σp and KL. These correlations are presented in the form of explicit nonlinear mathematical expressions with corresponding diagrams, which enable further quantitative and qualitative interpretation of the mutual interaction of the analyzed geometrical and ge-omechanical properties. Obtained correlations are with high values of the determinism co-efficient (R > 0.9) and low values of standard deviation. Results are further verified using the ANOVA test. Critical values for certain sample dimensions regarding their effect on σp and KL.

Argillaceous and anhydritic rocks, along with rocks containing pyrite, are prone to swelling by adsorbing water, leading to an increase in volume or external pressure due to deformation constriction. This swelling behavior can have adverse effects on underground openings, potentially compromising their serviceability, and it can also pose a risk to structural safety. The swelling behavior of pure claystones (rocks without anhydrite) is well understood in the context of tunneling, with the swelling-strain relationship typically determined through oedometer tests conducted in laboratories. However, when dealing with rocks containing anhydrite, the processes associated with the anhydrite-gypsum transformation have only been partially explored. To gain comprehensive insights into these processes and address various related questions, additional types of tests beyond the one-dimensional oedometer tests are necessary. In this paper, we describe the setup of experiments and the corresponding testing procedure used to study the swelling behavior of rocks containing anhydrite. The results from a systematic test series serve as the data foundation for understanding the coupled mechanical and chemical processes responsible for swelling behavior. By better comprehending these mechanisms, we can enhance our understanding of the rock's behavior under various conditions and potentially improve the safety and stability of underground structures.

Crystalline rocks such as granite and gneiss, sedimentary rocks such as mudstone and clay rocks, tuff belonging to volcanic rocks, and rock salt are considered as host rocks for deep geological repository for high-level radioactive waste worldwide. In Korea, all of the above rock types are distributed except rock salt. Considering the distribution of rock types by area, granite took up 30%, metamorphic rock 30%, sedimentary rock 25%, and volcanic rock 6%. In order to evaluate the suitability of the rock types distributed on the Korean Peninsula as the host rocks for deep geological disposal of high-level radioactive waste, the Korean peninsula was divided into four tectonic structures, and then various multidisciplinary analyzes were performed with deep drilling on the four rock types of granite, gneiss, sedimentary rock, and volcanic rock. Based on the literature and information obtained from deep drilling, considering the geological and rock mechanical characteristics, granite among crystalline rocks and Jinju formation and Jindong formation among various sedimentary rocks were derived as proposed candidate rock types. For the derived rock types, multidisciplinary geological information will be obtained through additional multidisciplinary data review, analysis and further detailed investigation. This information is intended to provide basic data that can be used by high-level radioactive waste project agencies when deciding on candidate sites and rock types.

The Rhenodanubian Flysch Zone of Austria comprises cretaceous claystones, siltstones, sandstones and marly limestones. Such rock types are often referred to as weak or soft rocks due to their behaviour when exposed to water or subject to mechanical load. Even though the rock types appear quite uniform on a macroscopic level, they can exhibit a broad variety of geomechanical properties. In this study, the flysch rocks were investigated with respect to their slaking durability, uniaxial compressive strength, abrasivity and mineralogical composition. The influencing factors affecting material behaviour and correlations of different mineralogical-petrographical and rock mechanical parameters are elaborated. It is shown that granulometric and mineralogic properties correlate well, and that the presence of carbonate minerals can favour the slaking resistance. Sheet silicates seem to affect slaking only after many testing cycles. While the rocks exhibit a wide range of slaking durability and low to moderate strength, abrasivity is limited to low values. Unlike in crystalline rocks, quartz imposes less influence on durability, abrasivity and strength. The correlations of engineering rock properties of these soft rocks are weaker compared to those of grain bound crystalline rocks making their characterization and classification challenging.

Stress polygons defined by the Coulomb failure criterion play an integral role in earth sciences and geology for the classification of crustal stress regimes. While the minimum principal stress (σ3), pore pressure, and friction angle of the rock considerably influence rock strength, the intermediate principal stress (σ2) also plays a crucial role. In conventional stress polygons, the boundaries of rock strength are represented by straight lines based on the Coulomb failure criterion. However, when considering σ2, these boundaries should ideally be drawn as curved lines. In our study, we redefined the stress diagram by involving σ2, using true triaxial test results and the Mogi–Coulomb failure criterion. This approach revealed notable visual discrepancies in rock strength boundaries compared to those defined by traditional Coulomb failure criterion. Our findings underscore the importance of incorporating σ2 in failure criteria to accurately draw rock strength in stress diagrams.

A series of laboratory tests have been performed to assess the effects of progressive de-formation on the elasticity and compressive strength of the VQ rock sequence. Specimens of basalts and pyroclastic rocks were obtained from twelve boreholes drilled with depths between 40 and 160 m. UCS tests were performed on a highly stiff and fatigue-rated load frame model MTS 815. Specimens were subjected to increasing-amplitude cyclic loading experiments. Changes in the elastic properties were observed in both sedimentary and vol-canic rock types as the rock approached the rupture. A significant difference in strength was obtained, with UCS values ranging between 13.5 and 23.97 GPa for the basalt, and be-tween 0.96 and 1.27 GPa for the pyroclastic sequence. Our results suggest that the differ-ences in stress failure may explain the debilitating nature of the contacts between basalts and pyroclastic rocks that might explain ground ruptures.

Mode I fracture toughness (K_IC) is one of the most important parameters for predicting and preventing catastrophic failure of cracked structures in brittle material. Several laboratory methods have been suggested to determine the mode I fracture toughness. However, many of them require lengthy sample preparation procedures, premature failure of samples, and difficulties in obtaining the precise value of the fracture toughness property. In this paper, the recently proposed pseudo-compact tension (pCT) method is used to evaluate the crack length effect on mode I fracture toughness in an isotropic homogeneous material, benefiting the advantages of this method including; simplicity of the test, high level of test control and high accuracy of the K_IC value. For this purpose, several disc shaped PPMA samples were loaded in pure tension by performing pCT tests. Digital image correlation (DIC) method was utilized to assess and monitor the distribution of the deformation field during the tests. DIC results were also used to compare the effect of crack length on the deformation field variation in samples. Very good agreement was found between the K_IC values estimated in this study and those reported in the past for the similar material; indicating that the pCT method is convenient for the assessment of K_IC. The experimental results also show that the initial crack length has a net impact on K_IC, although the magnitude of its influence is closely related to material structure and type. According to the obtained results, an increase in the initial crack length leads to increase the ultimate displacement at failure point, decrease the maximum load, and finally decrease the mode I fracture toughness of the material.

The Karavanke tunnel connects the highway A2 in the Republic of Slovenia with the highway A11 in the Republic of Austria on European corridor 10. It is a twin-tube, two lane tunnel, with total length 7864 m of which the Slovenian side is 3450 m long. The construction of the first tube was finished in 1990s while the construction of the second tube started in 2020 and is still ongoing. The construction of the tunnel was characterized by demanding and diverse geological conditions, high overburden of up to 900m, and occurrence of methane and high-pressure water ingresses. The subject of the research is the section of the tunnel in the Lower Triassic (Werfen) formation, which consists predominantly of grey limestone and dolomite with lenses and nests of gypsum and anhydrite and red and grey clastic sediments (sandstone and claystone). The formation is tectonically lightly to moderately disturbed, except for a more prominent fault zone, where high water inflow was recorded during the excavation of the first tube and in a smaller amount occurred also during the excavation of the second tube. The rockmass stability was expected to be mainly discontinuity governed, with possible deeper failures along fault zones. Due to the occurrence of gypsum and anhydrite, the occurrence of swelling and squeezing was also expected. The sets of geological parameters for characterization of rock mass (GSI, RMR and BT), which were determined based on geological mapping during the excavation of the first tube, and from geological investigations, were compared with the parameters determined during the tunnel excavation. The latter were obtained based on the observation of the deformation field around tunnel and numerical back calculations, which were carried out to fit the measured deformations. The difference between rock mass parameters determined up-front and those back calculated is studied to derive variation between the two, with an aim to mitigate subjectiveness in the up-front definition of the parameters. Conclusions are developed to present a more objective methodology in determination of realistic parameters to characterize rock mass conditions applicable for tunneling in carbonate rocks.

Knowledge of the in situ stress which affects a rock mass is of great importance for underground excavations and tunnel design. The main method for measuring in situ stress in the laboratory is the determination of the Kaiser effect of a rock, which is a spectrum of acoustic emissions (AE) that can be interpreted as a stress memory effect based on the hypothesis that samples remember the stresses to which they were previously subjected. The present communication describes in situ stress characterization through the determination of the Kaiser effect for the San Marcos tunnel project, which is part of the high-speed railway line in Gipuzkoa, in the Astigarraga-Irún section. For the study of in situ stresses, data from 5 groups of representative samples of the studied materials were compared. For each sample, 4 sub-samples were obtained, 1 vertical and 3 horizontal, arranged at 45º to each other to determine the Kaiser effect for different orientations. Kaiser points were determined when subjected to uniaxial compression with a criterion based on the energy of the AE emitted per unit of time. This criterion allows for a clear separation of noise from the real physical effects that produce AE. In addition, a comprehensive laboratory characterization of the samples was carried out through determination of uniaxial compressive strength for each sample with measurements of the elastic moduli, tensile strength through the Brazilian test, ultrasonic wave transmission velocities, and triaxial test strength, as well as mineralogical, petrographic, and textural characterizations using thin sections. The results show that minimum and maximum stresses are approximately arranged across the horizontal plane, while intermediate stresses are arranged across the vertical plane. The results are reasonably consistent despite some uncertainties, the main one being the orientation of the stress ellipsoid. There are also limitations associated with the homogeneity, lithology, and preparation and testing process of the samples themselves. Based on the results obtained, we conclude that the analysis of the Kaiser effect in laboratory samples is a technique that can provide useful information to determine the stress state of a rock mass.

Understanding the in-situ stress state as a function of depth, is a fundamental concern for optimal underground structures design, minimize geotechnical risks, and foster mining activities, especially in a geologically diverse region like the Canadian Shield. The assessment of stress-depth relationships in the Canadian Shield, predominantly built on statistical methods, revealed that solely relying on these tools might produce misleading interpretations. This research emphasizes the limitations of only depending on statistical tools, highlighting the need for an integrated approach that combines strong geological insights for comprehensive interpretation. Indeed, past relationships divided the in-situ stress data into depth domains were largely driven by statistical techniques, but such domains often overlooked the complex geology of the Canadian Shield. For instance, classifying zones deeper than 500-600m as undisturbed zones might not be universally applicable across the Canadian Shield. Our methodology deliberately disregarded geological influences to only assess the effectiveness of statistical tools in establishing stress-depth relationships in an expanded dataset of 330 stress measurements. The results highlighted the inadequacy of general depth domains. Also, clustering analysis methods such as K-nearest neighbor (KNN), Hierarchical, and the Normal mixture method were utilized to group the stress-depth dataset. While these techniques offered a structured method to identify the optimal number of depth-related clusters, the geological rationale behind these clusters remained unclear. Yet, the developed models for these clusters showed weak predictive accuracy. Moreover, the study assessed the efficacy of multivariable outlier detection methods such as Mahalanobis, Jackknife, T2, and KNN on the determination of in-situ stress-depth relationship. After initially removing identified outliers to refine the dataset, the regression outcomes remained unsatisfactory. This highlighted that some outliers might indeed have geological or tectonic significance. Rather than discarding them, their geological significance needs to be deeply analyzed. In fact, these extreme stress values might be attributed to unique geological or tectonic scenarios. In conclusion, while statistical tools offer valuable insights, a balanced integration of these tools with robust geological insights is essential to capture the complexities of in-situ stress-depth relationships in the Canadian Shield.

In the context of expansion phenomena rock structure refers to the availability of voids or fissures to allow the growth of gypsum crystals. Two case histories illustrate the significance of this concept. In a first case, a building founded on massive anhydrite of Triassic origin, experienced a sustained heave rate of its pillars. Swelling strains concentrate in the damaged upper 3-4 m of the rock. Pillar footings were underpinned by micropiles designed to avoid the upward friction induced by the active layer. The second case describes the heave of deep piled foundations of the pillars of a railway bridge. Continuous extensometers identified a 12m thick active layer below the pile tips. Hydraulic cross-hole test identified a fractured anhydritic claystone, initially unsaturated, that received water inflow from a shallow aquifer because of the construction of piles and reconnaissance borings.

The suitability of a sandstone from Central Italy as armourstone source, was investigated at the specimen and block scale. Once the physical properties were determined, the rock material was subjected to ultrasonic pulse, mechanical and wear/durability tests. The re-sults were linked to the petrographic features observed at the optical and scanning electron microscope. Possible defects in blocks were investigated through drop tests and by com-paring wave velocities measured on specimens and blocks. The rock has good physical, mechanical and durability index properties, whilst its wear resistance addresses the use of blocks in moderately stressing conditions (e.g. internal harbour areas). Blocks can be downgraded if affected by diffuse oxidation, as it is associated to a reduction of physical and mechanical properties.

It is known that some organisms can bore holes in rock formations consisting of such as limestone, sandstone and tuff. The authors investigated some sites in the Ryukyus Islands, Japan and found many examples of rocks bored by organisms. This study is concerned on the role of several organisms on the toe erosion along sea cliffs and their subsequent collapse. The authors carried out some observations on bio-erosion state and causes of rocks along sea-shores with cliffs in several major islands of Ryukyu Archipelago. Rocks are various depending upon the geology of each island surveyed. The erosion state and porous structure of rocks and their effect on their mechanical strength are assessed. Some available mechanical stability assessment methods are utilized to assess the stable and collapsed cliffs surveyed. It is understood that the most likely mechanism would be the dissolution of constituents of rocks by the mechanical excavation or enzym/salvia produced by these organisms and their subsequent discharge of debris from the holes as the UCS of rocks are generally greater than 25MPa. The length of bored holes is generally 5-15 cm with a diameter of 1-25 mm. The bored rock sites are found to be within the tidal and splash zones. Besides, the action of sea waves resulting from high waves caused by hurricanes and typhoons imposing some impact type forces, porous structures resulting from bored holes by organisms cause the strength reduction and cyclic degradation, which can be evaluated from the method utilized in this study. Therefore, the cliff stability can be asssed with the incorporation of the role of bio-erosion. It is anticipated that this study would be quite unique by bringing different disciplines of science and engineering together to this special kind problems and provide some scientific answers to the problems encountered in nature.

It is better to align the tunnels along good rock mass having homogenous rock mass with relatively less discontinuity sets, fault, shear, and fracture zones. However, it is not possible to completely avoid but it is possible to align the tunnel in such a way that these geological structures impact less in the stability. It is important that the engineering geological character of faults, shear, and weakness zones should be mapped and assessed so that their behavior is well understood. This article aims to assess a serious tectonic fracture zone that the planned 13 km long Hemja-Patichaur road tunnel crosses. For such assessment, data achieved by extensive field mapping and rock mass quality assessment using both Q and RMR systems of rock mass classification will be used. The characterization of the tectonic fraction zone will be made and engineering geological, and rock mechanical properties will be estimated using both field measurement data. Finally, a comprehensive stability assessment of the road tunnel will be carried out for the rock mass of the tectonic fracture zone using analytical and numerical methods.

In this work, computational techniques are applied via discrete element modelling to describe, understand and analyse the mechanical response of a rock medium under the impact of a rock block, inducing an impact fracture of the system. The system consists of a set of monosized rock layers (impacted system) and a singular rock block (impacting system). An attractive feature of the study is that it involves irregular rock geometries, in order to create more realistic modelling. The numerical modelling focuses on the influence of parameters such as the size ratio and irregular shape of the rocks (both the impacting rock and the impacted one) and the fall height (impact velocity) from an energy perspective, to determine the fracture patterns, the altered area of ​​influence, the post-impact degree of fragmentation and the breakage probability of the system based on the energy it receives. The results show a high influence of the shape and size of the rock that impacts on the impacted granular system, inducing a network of forces within the rock system that alters and weakens the surrounding rocks, leaving them prone to fragmentation even at low energy. The application of these findings allows the optimization of underground design in mining systems (mainly applied to hard rock caving mining), both to obtain the optimal degree of fragmentation and to control geomechanical risks in underground environments, mainly controlled by the continuous dynamism of the rock mass under fragmentation.

The present study aims to investigate the dynamic properties of fine-grained sandstone rock collected from the coal mining region of India under indirect tensile dynamic loading conditions. A three-dimensional numerical model similar to the split Hopkinson pressure bar (SHPB) setup is developed to validate the experimental results employing the strain rate-dependent Drucker-Prager constitutive model in finite element software, ABAQUS. The validated parameters are then used to simulate the specimen response of fine-grained sandstone rock with pre-flaw of varying orientations, i.e., 0°, 30°, 60°, and 90°. The analysis results demonstrate the reduced dynamic tensile strength of fine-grained sandstone rock with pre-flaws and varying crack orientation. The stress-strain responses at the flaw center and flaw tip highlight significant variations in their values showcasing the sensitivity of orientation to loading rates. This research contributes insights into the crack propagation behavior of sandstone rock under indirect tensile dynamic loading conditions. Additionally, this study also offers a valuable understanding of the directional influences of loading rate on the strength behavior of rock specimens.

In underground development and production blasting, the investigation into blast-induced rock mass damage has garnered extensive attention over the past several years. We have seen a log-ical evolution of blast induced damage modelling techniques. Practitioners have pursued prag-matic approaches. Notable among these models are those employing near-field peak particle velocity (PPV) contouring, complemented by site-specific damage thresholds. However, the application of these techniques encounters limitations, particularly in more intricate mining en-vironments. This paper briefly discusses the evolution of blast damage predictive techniques, whilst also introducing and demonstrating the concept of maximum velocity mapping, an approach that bridges the gap between practical, peak particle velocity-based methods and advanced computational modelling. Through a destress blasting application, the concept captures the three-dimensional shape of blast damage envelopes, considering key factors contributing to blast-induced damage such as point of initiation, velocity of detonation, potential interaction between multiple charges and the impact of boundary conditions.

Knowledge of in-situ rock stress is important for underground projects like mining, nuclear repository, hydropower and other utility tunnels and caverns for the assessment of stability condition. Specifically, it is very important to know the minor principal in-situ rock stress for the design of unlined pressure tunnels and shafts. If a rock stress map is available, it provides an approximate knowledge about the magnitude and orientation of in-situ rock stress and helps to plan and design the underground structures. This manuscript presents the methodology for developing in-situ rock stress map for south-western part of Norway where many un-lined pressure tunnels and shafts of hydropower projects are located. The development of such map is believed to be useful for both early-stage planning of underground waterway system of hydropower projects as well as for mining and civil engineering underground projects where in-situ rock stresses information is needed.

Copper mining in Poland is currently carried out entirely in the Lower Silesian Copper Basin. Over the 60 years of mining, mining activities covered an area of almost 600 square kilometres. Taking into account the scale of excavation and the depth of the deposit location already exceeding 1,200 meters below ground level, the mining operator must face a visible intensification of geomechanical threats such as seismic activity, rock bursts and rockfalls. In order to minimize the risk of serious accidents and maximize operational efficiency, geomechanical risk assessment using numerical modelling has been implemented in selected mining panels in recent years. This study presents a comparison of the results obtained using geomechanical hazard monitoring systems with the results obtained on the basis of FEM-based numerical modelling. The methodology for preparing a numerical model and the method of determining the strength parameters of rocks were described. For comparison purposes, the distribution of various parameters obtained as a result of numerical modelling, such as stress, displacements and the Safety Factor are combined with in-situ collected parameters such as convergence, stress distribution and areas of instability occurrence. The comparison results prove the reliability of the obtained simulation outcomes, which can be the basis for further use of numerical modelling, after appropriate validation, for the prediction of geomechanical hazards.

Outliers in a dataset are unavoidable and pose a two-pronged problem: first, how do you define and detect an outlier, and secondly, how do you handle outliers? Rock engineering’s ap-proaches to answering these questions include relying on engineering judgement to determine what data points are outliers and removing these outliers to get a better fit. The “engineering judgement” portion of outlier definition and detection in rock engineering makes reproducibil-ity difficult, as engineering judgement is inherently subjective and often not made transpar-ent. Through the results of a survey, this paper aims to demonstrate that extreme caution should be used when i) employing engineering judgment for outlier detection and removal in rock engineering and ii) interpreting the results of a statistical analysis of data where engineer-ing judgment was used to remove outliers. This paper finds that more transparency is needed when engineering judgement is employed for outlier detection and/or removal.

The aim of this paper is to introduce the concept of fracture index for performance pre-diction of Tunnel Boring Machines (TBM) in excavation of rock tunnels, and to examine the influence of rock fracture intensity and its frequency on machine performance. For this purpose, field data from six tunneling projects excavated by TBM were examined. The database included more than six hundred data points. The fracture index, which rep-resents the fracture count over an arbitrary length of scanline or borehole core with similar intensity of fracturing, provides an insight into the fracturing and joint frequency and state of rock masses. The analysis shows that fracture index can offer a critical quantification of rock mass cuttability, and can heavily impact mechanized rock excavation process, and significantly affect TBM performance.

ICL Súria & Sallent (ICL IBERIA) operates two salt and potash mines, Vilafruns, at the southern block of the Tordell fault and at a moderate depth, and Cabanasses, where depths of 1,000 m are reached, at the north of the aforementioned fault, in the province of Barcelona, Spain. The Cabanasas mine is currently accessed through Shaft 2; a 680-meter-deep shaft refurbished in 2004. In order to expand the mine and to increase its extraction capacity, the company decided to build a 5,023 m transportation ramp (19% inclination) in which a depth of 915 is reached. The section of the ramp allows the installation of the belt and the crossing of transport equipment during its excavation, being 9.4 x 5.5 m, with widths every 1,000 m and six By-passes. The construction of this mine ramp took place between 2012 to 2020. The ramp crosses the characteristic materials of the Catalan Potassic Basin. During the excavation of the ramp, several problems have appeared, derived, first, from the intersection of a calcareous aquifer (PK 0+640), from the Tordell fault (PK 1+150) and at a greater depth, above 600 m overburden, squeezing conditions were encountered. The squeezing conditions turned to be severe developing a creep behaviour. The deformation associated to this behaviour has ranged from 4 (0,5%) to 80 cm (8,5%) with creep velocities reaching 0,5 mm/day. The paper describes the support design methodology used, including creep stress-strain calculation with FLAC3D, developing a sequential application of the support elements in order to generate a yield response of the support was adopted, involving also a final structural shotcrete lining (SCL) usually 48 m behind the excavation face, including a strut slab/invert. A risk heat assessment of the ramp was done, and in the Suprasaline unit it was decided to adopt a temporary support that will have to be repaired periodically. Cabanasas ramp is operating successfully since April 2021.

Sea stacks like the E.T. formation at Hopewell Rocks Provincial Park, New Brunswick, Canada, are one of the world’s most popular geotourism landmarks. Failure of sea stacks poses a risk to public safety; this study uses 3D Finite Element geomechanics numerical models with input from UAV-based photographs, 3D Structure-from-Motion photogrammetry models, and erosion records to predict time of failure of the E.T. formation. A novel aspect of this study is the comparison between simplified symmetric and more realistic asymmetric erosion patterns, and impacts on simulated stability. Using symmetrical erosion, the predicted time of failure is within the years 2071 and 2123, but asymmetric erosion models show significantly earlier failure that may occur between the years 2056 and 2078. Ongoing work aims to address sensitivities of input properties, and possible future accelerated erosion rates due to climate change.

In this paper, a Discrete Fracture Network (DFN) model was created by numer-ical simulations which can be used to quickly and precisely estimate several input parameters necessary for rock mass classification. The paper shows how a large amount of useful information from the DFN model can be incorporated into the process of calculating the RMR value. The concept was tested by using the point clouds of real rock slope, acquired with LiDAR laser scan-ning technology. The fitting, calibrating, and generating of DFN model was performed in special-ized ADFNE MATLAB package. In this work, a rock slope on which conventional RMR classi-fication protocol was performed, is used to compare conventional versus DFN-based RMR classification. The results show how and to what extent the RMR values differed depending on procedure. The calibrated DFN approach was more reliable for scoring specific RMR parameters.

Rockbolt is an integral support element in reinforcements and stability of Tunnels. It is observed that sometimes in tunnels contractual specifications, Factor of Safety (FoS) of rockbolts is defined in terms of loads with a value ranging from 1.5 to 3, and pullout tests are carried out to ascertain the contractual requirements. The author wishes to point out it is inappropriate to define FoS of rockbolts in terms of a load carrying capacity alone. The above FoS values are applicable in cases of wedge failures or low in-situ stresses (Li, 2017). The bolt installed in the tunnel periphery experiences different strain along its length, and axial forces coming on rock-bolt are unequally distributed. It is suggested that FoS should also consider the strain capacity of rockbolt system. This paper gives a review of interaction and decoupling behavior of rock-bolt-grout-rockmass, and highlights aspects related to rockbolt FoS for tunneling applications.