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.

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.

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.

Detonating cord splitting is a quite common production technique for dimension stone blocks, in granite and gneiss quarries, where the blasts are usually designed based on local experience. The paper relates to a vibrometric test campaign, carried on in a group of gneiss quarries using accelerometric measurements at proximity to the hole’s rows, both in primary splitting and recutting operations. The purpose of the test campaign was to detect (or to exclude) the possibility of impairment of the commercial stone blocks produced by this technique, to check the validity of the blast design criteria adopted, and to obtain experimental data for predicting the friction conditions at the boundaries of the blocks and their expected displacement. The results highlight the limited damage of the commercial blocks obtained, confirming the validity of the detonating cord as a functional technique to split and slightly move the blocks from their original position. The vibrations due to the blast are also very limited even at a short distance, confirming that the technique is precautionary and respects the quality of the exploited blocks.

Anchored mesh systems constitute a widely adopted protective mitigation measure against rockfall, particularly suitable for highly weathered sub-vertical rock face These systems are composed of steel wire mesh panels combined with a regular anchoring pattern. In this work, we investigate by means of discrete element simulations the mechanical behavior of the mesh with the commonly adopted quincunx-like (or diamond) anchoring pattern, comparing with what we have already found for the square pattern. The effects of the loading condition and the mesh system properties on the out-of-plane response of the system are evaluated and ana-lytical relationships for quantifying the mesh punching resistance and maximum deflection are proposed. The results allow quick assessment of the suitability of the design choices and provide an insight on the force transmission paths during the loading of the mesh system.

It is necessary to obtain reliable estimates of the in situ stress state for the design of any underground engineering project in rock, but it is of paramount importance for safety-critical projects such as deep geological repositories for nuclear waste. It is widely considered that in situ stress is a function of depth below ground surface. This often leads to rock masses being partitioned into depth based domains, but there are no universally agreed and statistically robust methods for doing so. In this paper we present a novel method that uses Bayesian linear segmented regression of Cartesian stress components to probabilistically characterize the variability and uncertainty in the depth of non-crisp stress domain boundaries, and the in situ stress state within each domain. We demonstrate the efficacy of the method using synthetically generated stress data, and then apply the method to overcoring stress measurements obtained at the Forsmark site in Sweden.

Analysis of rock slope stability is a key step on the successful design and excavation of open pit mines and quarries. This study shows the rock mass characterization and the different analyses carried out to assess the stability of the final slope of a calcareous quarry. The studied excavation is located on the near-axis flank of a syncline, in such a way that the stratification set varies its dip from some 40º on the nearest zone of the axis to 20º on the farthest zone, creating a slightly complex geometry. This situation requires a set of different approaches to assess the stability of the slopes. For the studied case, a proposed design of the full open pit quarry was received. All the different possible failure mechanisms of the quarry were identified and analysed using limit equilibrium and numerical methods. West slope, which resulted to be parallel in strike to the stratification, featured a planar mechanism stability problem, so it was analysed in detail and a new stable design was proposed. This paper describes the steps carried out to characterize the rock, the discontinuities and the rock mass, as well as the different approaches used to obtain the stable design.

Coastal protection structures are often constructed from locally quarried rock, and are subject to harsh service conditions throughout long service lives. Durability of the rock is essential. By means of a thorough review of engineering standards and similar documents we show that petrological properties are known to be key controls on durability, but seldom feature in design guides. We surmise this is due to the use of subjective petrographic assessments. A review of the wider geological literature shows that quantitative methods are commonplace in petrology, but have not been adopted in rock engineering. We report on recent research work from Iran which shows that durability can be accurately predicted by applying machine learning methods to customary rock mechanics properties, and we suggest that combining these approaches with quantitative petrological data will allow improved design of coastal protection structures.

Open-ended (OE) pile field tests performed in low density chalk have demonstrated a unique installation response not widely observed in other geomaterials. This has encouraged the development of new CPT based design methods (ICP-18). Recently, A campaign of small-scale pile and CPT tests on intact soft rock materials, has been undertaken using a new multi-axis loading frame offering new observations on this unique behaviour. Similarities in model and field scale numerical tests suggest that the effects of stress-state may be less marked in the case of structured materials. Although scaling and stiffness issues certainly exist, the performance of the ICP method is trialled at small-scale enabling a new discussion on the applicability of small-scale pile tests in rock, scaling aspects and the changes intact rock fabric under-goes during subject to pile insertion which are revealed using X-ray tomography.

Mechanized tunnelling is the most used construction method for long tunnels due to its high excavation speed and enhanced worker safety. For deep tunnels, the study of the interaction between the ground and the supports is essential for the structural design of both shield and segmental lining which may be subject to heavy loads. For such scenarios, it is crucial also to assess the risk of entrapment of the Tunnel Boring Machine (TBM). Despite the three-dimensional nature of the problem, full axial-symmetric or 3D numerical calculations are rarely employed in the design practice because are time-consuming and demand advanced numerical skills. A recent paper proposed a simple and effective numerical procedure based on full axial-symmetric analyses. The procedure is described and validated by comparing the results of a case study with reliable data reported in the literature, obtained through 3D advanced numerical approaches that explicitly simulate the radial gap closure.

The current paper deals with geotechnical challenges and tunnelling experience gained during the detailed design phase of new tunnels in the frame of the Sotra Link Project (SLP) in West Norway. It consists of several civil works between Bergen and Øygarden, along the existing Riksveg 555: 4 main road tunnels (Kolltveit, Straume, Knarrvika, Drotningsvik), 3 pedestrian and bicycle tunnels, 19 road and pedestrian underpasses, 23 tunnel portals, 22 bridges and viaducts, 14 kilometres of pedestrian and bicycle paths and 24 kilometres of two-lane access. Geotechnical complexities analysed in this work are mainly related to the design of technical solutions for rock support under the following conditions: i) low overburden with loose shallow deposits and interference with existing and new nearby structures, ii) metric fault zone extension with expected swelling potential. Starting from a preliminary solution based on the NGI Q-system, the detailed design overcomes these challenges throughout finite element numerical analyses. This approach leads to a suitable dimensioning of customized linings and specific tunnel face support, together with partial excavation phasing when required. Within this context, two significant case studies are discussed with reference to Drotningsvik main tunnels: the first one concerns the design of the sections close to Kiple Lake (Kiplevatnet), where partial front reinforcement and surface grouting are foreseen. The latter case deals with a fault zone crossing located 500 meters western, by adopting a full front reinforcement and partial excavation phasing. The observational method supported by an extensive monitoring campaign during the construction phase will allow for possible design optimisations based on properly back-analyses. Currently, the delivery tasks for Sotra Link project are in line with the contractual scheduling. The project contract was awarded in September 2021 for a total value of 1.25 billion € and the design phase is expected to finish in 2024, while the infrastructure will be opened to traffic in 2027.

Ornamental rocks are competent rocks that are usually arranged in layers of dozen meters of thickness. These form rock masses, affected by joints and fractures of tectonic origin and very extensive stratification planes. Thus, fractures and faults with extensions around hundred meters often cause important instabilities in mining operations. When blocks with tens of thousands of tons appear, their stability must be evaluated and, if it would be necessary, controlled. There are several known cases of plane failures involving large blocks of rock in limestone and marble quarries. Stability 2D analysis, such as the one developed by the limit equilibrium method of Hoek and Bray (1981), face certain difficulties. It makes sense, that block geometry is variable depending on the sections that we set, besides, this is just one of the differences considered among those chosen sections. In fact, a posteriori study of these instabilities would show, important lateral differences in the resistant conditions of the failure planes that drive to sliding. Moreover, the loading conditions induced, by blasting or by water inflows, are not equal in every single section. Taking advantage of the strength of these large potentially movable blocks, considered as a set of sections, it is possible to transfer the force requirements among them to compensate the lack of resistance of some specific sections with extra of the surrounding ones. So we provide, as an example, the back analysis of a large 40,000 t sliding marble block. Then we have divided a 40 m high and 60 m. wide block into 10 meters slices, to evaluate the whole equilibrium so we can explain the sequence of ruptures that led to its collapse.

Normally, two in situ methods are used to assess the rock at-rest earth pressure coefficient (k0): one is the Hydraulic fracturing method that obtains in-situ stress average over a sample of a few square meters, and the other one is the Overcoring techniques that measures in-situ stress average over grain size areas. This paper analyses a total of 17 hydraulic and 51 overcoring successful tests into the Sandstone rock. The parameter k0 has a big influence on the structures constructed into the rock. In this analysis is presented a secant pile wall with piles of diameter 0.75 m separated 1.8 m embedded into the Shale and Sandstone rock. At the beginning the movements predicted by 2D numerical model were ten times greater than the movements observed in the inclinometers during the excavation. Thus, in this study was found out that this large difference of the movement is due to the larger k0 coefficient. Next, the k0 coefficients were corrected so that the movements predicted by the numerical model match with those measured. The calibration of the k0 coefficient was up two times the empirical Jaky’s k0 coefficient. This calibration had influence reducing the resulting forces of the wall during the excavation phases. Finally, the k0 results from the in situ tests and the calibration values were compared, showing that both results concur for the k0 lower bound of the test results.

In the Montserrat Massif (in Catalonia, NE of Spain) a common mechanism of rockfall generation is the differential erosion of thin weak layers, composed by fine-grained rocks commonly described as lutites or mudstones, interleaved within the conglomeratic rock mass which shows a long-term durability. Both materials are terrigenous and detrital clastic rocks, formed in an alluvial fan delta during the Eocene epoch, and exhibit very different behavior against weathering. This difference is explored in the laboratory through durability tests, before and after being subjected to freeze-thaw and wetting and drying ageing tests, and then correlated with theirs textural and mineralogical properties. The findings allow to explain the morphologies and detaching mechanisms observed in the field. The laboratory tests performed are X-ray mineralogical analysis, petrographic analysis of thin sheet samples, simple compression with strain gauges, Brasilian indirect tensile strength, Slake durability, and ageing by freeze-thaw and wet-dry cycles. Five different detrital textures from conglomerate to fine sandstone with muddy matrix (wackestones) have been identified and grouped into two main geotechnical units related to rockfall dynamics. On the one hand, the rock blocks of conglomerate and coarse sandstone susceptible to fall; on the other hand, the weak levels producing under digging of the previous ones formed by fine-sandy wackes and muddy wackes. Despite geomechanical similarities in intact conditions, they differ clearly once weathering cycles are applied by humidity and temperature. Thermal weathering is found as very relevant when explaining the rockfall preparation mechanism leading to toppling. A synoptic model of this mechanism is drawn accordingly. Different influencing factors on the rock block stability are analyzed. Thanks to the monitoring of the rock mass carried out in Montserrat, representative examples of the flexure-toppling mechanism on rock blocks and needles are found. The annual thermal cyclic behavior is shown as composed by elastic and plastic components that evidence the weakening of the base.

In recent years, the historic centre of Florence, enlisted as a UNESCO World Heritage site, has experienced several incidents where fragments have detached from the structural or decorative elements of its historical buildings. Notable examples include the detachment at the Basilica di Santa Croce in 2017 (which led to the death of a Spanish tourist) and the ones at Palazzo Corsini in 2018, at Palazzo Ginori Conti in 2019, and at Palazzo Pucci Sansedoni in 2020. The detachment phenomenon is a common issue in urban areas where stone materials are used in historical constructions; Florence`s stone-built heritage, however, presents unique characteristics that amplify the risk of significant detachments. Specifically, the types of sandstone used in Florentine historical constructions, known as "Pietraforte" and "Pietra Serena," contribute to the increased risk of sudden collapses due to specific attributes that make them susceptible to detachment and structural instability over time. For example, convolute laminations and calcite veins, typical macroscopic characteristics of Pietraforte, often represent critical discontinuities in an otherwise compact matrix. Currently, the detachments issue has been managed through continuous monitoring and periodic removal of loose and instable material. However, this approach is not cost nor time effective and fails to provide a sustainable long-term solution for both the preservation of UNESCO World Heritage List monuments and the safety of visitors. The existing safety regulations and protocols do not offer specific guidelines for interpreting and addressing these detachment phenomena, so the personnel in charge of emergency safety interventions must rely on empirical assessments, lacking comprehensive recommendations for dealing with the complexities of these natural and variable materials. To better understand and address this problem, a new approach is therefore needed and its foundations are presented in this study. To address the lack of specific risk assessment methods for these unique facades within existing protocols, we propose the adoption of a rock mechanics perspective to adequately account for the diverse lithologies and their variable mechanical behaviour. By utilizing tools from slope stability and rock mass analysis, such as intact rock characterization via NDT (Non-Destructive Testing) surveys and discontinuity characterization trough geomechanical survey and Point Clouds analysis, we aim to define risk parameters that are more suitable for these particular structures, establishing the operational framework for a diagnostic protocol that aids decision makers to better direct and assess the need for conservative and safety interventions.

The depletion of mineral reserves has led to deeper underground mining which comes with challenges such as rockbursts, large deformations, and inaccurate dilution estimations. Therefore, stope stability remains a significant safety factor in underground deep mining. In fact, assessing the stability of stopes is essential to better predict instabilities and sloughing around the excavations. This study compares the stability analysis of open stopes using stability graphs and numerical modelling, to evaluate the effect of different variables on the stability of excavations. The study concludes that using stability graphs alone does not suffice to determine stope stability; numerical modeling is also essential to complement the findings. Additionally, the stability analysis of a stope in a 1000 m deep mine will differ from a stope in a 2000 m deep mine, with similar geometry and geological conditions. In conclusion, using the stability graphs in deeper mines may underestimate the stability of the stope.

Stable slope performance is a crucial aspect in the early stage of pit commencement to achieve the plan of ore extraction during the operational phase immediately after complet-ing the feasibility study. Understanding of geotechnical conditions increases with the ex-posure of the excavated slope during pit development. A reliable slope parameter shall be proven once the proposed geometry is correctly applied, resulting in a stable slope. How-ever, on some occasions, unforeseen risks may arise due to limited geotechnical infor-mation during the feasibility study. This paper discusses the efforts performed at the Bozshakol copper mine in the early stages of pit development, including the establishment of geotechnical programs, implementation of control measures for early instability concerns, addressing groundwater issues, interacting with the mine plan for design adjustment processes, and eventually optimizing pit design throughout the development stages.

ABSTRACT: Hydraulic erosion occurring at dam spillways can be critical for the dam struc-ture. Current assessment methods rely on empirical correlations between water erosive force and rock mass resistance, yet they stem from limited data, affecting their accuracy. This problem is addressed by using a laboratory-scale physical model simulating spillway condition. This model assesses various rock mass parameters, including water pressure, joint characteristics, and block size. By modifying concrete block arrangements, different geomechanical conditions are repre-sented, allowing pressure evaluation. Key parameters like joint opening and orientation, and block shear strength are studied in various conditions. The model's test section, equipped with pressure sensors, facilitates an analysis of hydraulic erosion processes, enhancing our understanding of spillway rock mass erosion dynamics. This innovative model promises a better evaluation of hy-draulic erosion's complexities, a crucial aspect of effective spillway design and maintenance.

Hoek-Brown failure criterion is one of the most widely used failure criterion for rocks in the world. For its use, the mi empirical parameter for a specific rock type is needed. To determine the mi constant, a triaxial test is recommended, which gives a linear relationship s1-s3. How-ever, the full stress path for every rock starts with uniaxial tension and this gives a nonlinear envelope. 55 series of tests are carried out for 4 rock types: sandstone, claystone, limestone and conglomerate - to show what is the difference between the results of the mi determina-tion, using two different approaches. The analysis of the results shows that the consistency with the regression models developed by researchers is higher if using the second set of re-sults – with average tensile strength. So this approach allows to determine the mi parameter more precisely for every tested type of rock.

Locality Devils Town in Serbia hosts a rock formation constituting of weathered andesitic tephra deposits shaped by erosion into many bizarre landforms.Tephra layer comprises of homogeneous but poorly graded andesitic fragments ranging from pebble to boulder size, which are submerged into weathered volcaniclastic matrix. Through the years, erosion carved into loose material leaving more resilient parts to stand out. They appear as numerous closely spaced pillars, up to 15 m in height and a few meters across, commonly capped with a large andesitic boulder. The site is labeled as natural heritage and has been recently subjected to holistic monitoring projects, including non-invasive techniques such as terrestrial LiDAR, Structure from Motion and Photogrammetry. These have provided several sequences of point clouds, allowing change analysis to take place. Herein, a preliminary sequence, dating from 2017-2018 is used to reconstruct instabilities that have been recorded on the walls of one of these distinct pillars. The analysis was first targeted at locating source areas of minor rockfall events. Three such features were identified on the pillar north face, by recognizing negative change in point cloud surface, i.e., deficient rock mass. Underneath them, in the base of the pillar, less distinctive mass accumulations are noticed in the post event point cloud, which likely represent the runout zones. All source features depict irregular andesitic fragments of about 1–2 dm³ in volume, positioned in the upper third of the pillar. Trajectories of these detachments were simulated using 2D and 3D geotechnical tools. Rock fragment and ground properties required for running the simulations were assumed from field observations and index properties determined using the portable tools (SH70 needle penetrometer, Schmidt’s hammer, etc.). Reconstructed trajectories show good correlation with the post-event (2018) point cloud, where accumulated material, i.e., suffice of rock mass coincides with runout locations. Due to relatively ductile ground, fragments did not bounce significantly, and their kinetic energy is quickly dissipated, making them to stop within a close range around the pillar perimeter. In perspective, further systematic monitoring could help determine the rockfall rate, and related loss of mass on an annual basis. Such findings could help understanding the erosion and weathering process better and undertake strategies towards the site’s sustainability and resilience to climate change and extreme weather conditions.

Rockfalls are threatening natural hazards because of their rapidity and the few precursory phenomena associated, that, in highly frequented areas, result in a high geological risk. Stability analyses for risk mitigation strategies depend on the knowledge of discontinuities constituting the rock mass. However, the manual characterisation of rock joints can be hindered in case of large and/or inaccessible areas. This is the case of the Vallepietra shrine (Central Italy), site of historical and religious importance (whose origin dates back to the 11th century), destination of thousands of pilgrims, and located beneath a 200-m-high and 700-m-wide sub-vertical calcareous rock wall. Within a preliminary site characterization, a comparison between manual and semi-automated procedures of rock mass discontinuities recognition was performed on a test area close to the shrine, where in addition to a geomechanical station, a laser scanner survey was performed to obtain a point cloud of the rock mass. The latter was analysed through Discontinuity Set Extractor (DSE) software to obtain the main discontinuity sets in terms of dip and dip direction and then compare them to the outcomes of the manual survey. The results obtained from the two techniques were in good accordance and led to the recognition of four main discontinuity sets. Rock blocks were also retrieved from the rock wall for laboratory tests. Cylindrical samples of rock material were trimmed out of the blocks to perform unconfined compression (UCS) and splitting tensile strength (STS) tests. The use of radial and axial strain gauges allowed to evaluate the elastic moduli of the rock material. The results in terms of strength and stiffness were in good agreement with literature on similar rocks in Central Italy. The joint friction angle was determined by performing tilt tests both on jointed blocks and on specimens with planar-sawed joints, obtaining values typical of moderately weathered rock. The orientation of slope and discontinuities, together with experimental laboratory and field data (UCS, STS and Schmidt Hammer) on rock material and joints were used to determine the rock and slope mass ratings (RMR and SMR) as well as to perform kinematic analyses to check planar/wedge sliding and toppling failure compatibility. As a future perspective, by extending laser scanner surveys to other sectors of the rock wall and by further refining the point cloud analysis, the geomechanical characterisation of the entire rock wall could be achieved overtaking the manifest limitations of manual surveying in such distinctive areas.

Natural stone has been used for façade applications for centuries. Initially, stone elements were rather thick, when used as construction elements, and the durability was appropriate. Scientific research on properties of marble began in the late 19th century. In the years following, the thickness of natural facade stones decreased from over 1000 mm (as in construction elements) to typically 20-50 mm (in cladding applications) because of new cutting technologies and equipment being developed by the industry. Even though most marble claddings perform satisfactory, durability problems have begun to appear at an increasing rate after some 50 years of using thin cladding Well-known buildings such as the Amoco Building in Chicago, SCOR tower in Paris, and the Finlandia Hall in Helsinki have had their marble cladding replaced after less than 30 years at the cost of many millions of Euros. The deterioration gives a very considerable change in the appearance of the panels. They bow, warp or break. Most cases of bowing involve Italian marble from the Carrara area, simply because it is the most widespread and used marble type. It is, however, vital to emphasize that many building facades with Carrara marble perform well, and furthermore other marbles and limestones from other areas also exhibits durability problems. This study is dedicated to the physical and mechanical characterization of two marbles and two limestones: Carrara (IT) and Ruivina (PT), Pedra de Ançã (PT) and Estremadura (PT). It combines the analysis of experimental results (physical, mechanical, and aging properties) to allow the study of potential mechanical strength decay over time. The selected natural stone materials are often used as cladding materials and are different in mineralogy, texture, preferential orientation of grain shape and grain size distribution. The reduction in mechanical resistance was evaluated by initial bending strength and after thermal shock and freeze-thaw aging tests under standard test conditions according to the current standard in force. Other properties such as compressive strength, anchorage breaking load, elastic modulus, ultrasound velocity, volume mass, water absorption at atmospheric pressure and by capillarity and other physical indices were accessed. Result show that marble and limestone decay is linked to temperature variations and moisture. These factors are seen key features in the degradation processes. An updated and comprehensive review of the selected stones structural decay was made to consolidate the understanding of façades structural degradation.

The freeze-thaw action is an important decay process that frequently affects building rocks in cold regions. This phenomenon can lead to a degradation of their physico-mechanical properties, affecting the service life and compromising the aesthetic and structural functionality of stone construction elements. The aim of this research is to establish the physical and mechanical damage induced by the recurrent frost action on a porous limestone from the province of Alicante (south-eastern Spain) marketed worldwide as building material. For this purpose, specimens of the limestone were firstly fully saturated in water, then subjected to 20 and 40 freeze-thaw cycles and finally oven-dried at 70 ⁰ C until constant mass was reached. Each cycle lasted 24 h, consisting of 8 h of freezing at -20 ⁰C and 16 h of thawing in water at 20 ⁰C. Once the abovementioned conditioning treatment was performed, physical and mechanical parameters of the limestone, such as absorption, effective porosity, P- and S-wave velocities and uniaxial compressive strength, were determined in laboratory and compared with the corresponding parameter values of the intact (untreated) rock. The results showed that the freeze-thaw action increases the absorption and effective porosity and reduces the density, P- and S-wave velocities and uniaxial compressive strength of the porous limestone. In addition, the most-used coefficients to describe its weathering against the cyclic freeze-thaw action were calculated, which served to clarify its potential utilisation in cold climatic zones.

Reverse k-ratio and geological complexities have significantly contributed to design challenges and instability within the rockmass. The rock engineering design process within this shaft had to consider that mining had to occur in a rockmass that included large blocks of ground truncated by major geological weaknesses, reef planes with different strike, dip orientations, and a rockmass impaled with joint and fracture planes. The off-reef tunnels in the weaker shale rock type tend to squeeze and are supported with ring sets when the deformation occurs within these tunnels. Designing tunnels near this rock mass considered the presence of a weak, highly altered Westonaria Formation Lava, which directly over-lays the high-grade Ventersdorp Contact Reef conglomerate within the shaft. Westonaria Formation Lava has significantly contributed to instability, posing an immediate risk to shaft barrel stability and a medium- to long-term risk to continued ore extraction within the excavating environment.

The stability graph method is a widely used empirical method for dimensioning open rooms/stopes and support design based on stope geometry and stability number. Despite numerous developments, such as expanding databases and introducing new concepts and factors, a comprehensive understanding of its underlying mechanisms and universal applicability necessitates thorough numerical and theoretic analyses across various scenarios. This paper presents a rigorous investigation employing numerical models featuring multiple joint sets to replicate the structurally controlled failure of open stopes, a predominant failure type encountered in the stability graph databases. Detached blocks within these models are treated as overbreak and identified by defining thresholds for normal and shear displacements on joint planes. The concept of equivalent linear overbreak/slough (ELOS) is referred to in the numerical models to quantify the failure, similar to the ELOS stability graph method. The results obtained from numerical models and empirical method for the cases with different stope dips and sizes, and different critical joint set orientations have been compared to evaluate the performance of stability graph under different scenarios. It is found that the agreements between the numerical and empirical results on different surfaces of the open stopes are different. Notably, the adaptation of a modified stress factor A significantly enhances agreement, particularly for the hanging wall, characterized by a lower confinement stress state. Furthermore, larger ELOS values on the back surface of stopes with a critical joint set angle of 45 degrees are identified compared to those with a critical joint set angle of 30 degrees. It has opposite trend to the stability graph results. To address this inconsistency, modified factor B values are proposed for different surfaces based on normalized analyses of numerical models with varying critical joint set angles. In conclusion, the numerical simulation results align well with stability graph outcomes when using modified factors, A and B. This research has improved our understanding of the empirical stability graph method and promotes its reliability in predicting the stability state and unplanned dilution in open stopes. These insights are significant for mining engineers and practitioners seeking more accurate and robust stope stability assessments in their operations.

In opencast mines, overburden removal is the first step for mineral extraction, which is disposed of as dump slopes made of several benches. Shear strength is the most significant factor for establishing the slope stability of the dump. The laboratory techniques to determine the shear parameters, such as cohesion (C) and internal friction angle (Φ), don’t represent the actual behavior of the samples. In the present work, a large-scale in-situ direct shear apparatus is fabricated for determining the shear parameters of a dump in constant normal load (CNL) condition. The apparatus was tested over dumps of iron-ore mines in Odisha, India. The peak shear stresses corresponding to various vertical stresses, viz. 25, 50, 75, and 150 kPa, were found to determine a Mohr-Coulomb failure envelope. The in-situ C and Φ were measured to be 31.41 kPa and 48.99⁰, respectively. These in-situ tests give realistic data, which is very helpful for the optimistic design of overburden dumps.

The limit equilibrium model in boundary element codes has become a popular method to simulate the behaviour and failure of pillars in underground workings. Albeit good results have been obtained through this model, the calibration of this model is cumbersome due to the multitude of parameters that require calibration. An alternative solution was presented to verify and calibrate the model through the use of physical modelling in a laboratory. For the experiments, an artificial pillar material was used and cubes were poured using the standard 100x100mm civil engineering moulds. The friction angle between the artificial “pillar” and the platens of the testing machine was varied by using soap and sandpaper. Different modes of failure were observed depending on the friction angle. The results of the preliminary numerical modelling indicated that the model is able to simulate the stress-strain behaviour of the laboratory models, thereby verifying that the limit equilibrium model appears to be a useful approximation of the pillar failure. This paper further investigates the numerical modelling of the laboratory experiments conducted.

The complex geometric morphology of single rough-walled rock fractures, coupled with the occurrence of nonlinear flow, adds complexity to the fracture flow process. Despite decades of research on nonlinear flow behavior in single rock fractures, existing models still fall short of adequately capturing such behavior during shearing. In this study, a series of coupled shear-flow tests are conducted on single rock fractures under constant normal loads. The results show that the Forchheimer equation effectively describes nonlinear flow, with its nonlinear coefficients associated with fracture geometries. The evolution of fracture geometries induced by shearing is quantified and its impact on nonlinear flow is considered. An empirical equation is then proposed, incorporating the peak asperity height and hydraulic aperture, to evaluate the Forchheimer nonlinear coefficient. The proposed equation is validated through experimental results, demonstrating its effectiveness in characterizing nonlinear flow behavior in rock fractures during shearing.

Rock mass is the host media in a wide range of geotechnical applications. The failure behaviour of rock mass is complex and strongly influenced by various geological structures, from micro to macro scale. To have a proper structural design and safe construction, a thorough understanding of failure mechanism around an underground excavation is essential. That includes an investigation of the cracking processes of rock mass and, in particular, how micro-cracking around the excavation progresses to macro-cracking of rock mass. In order to reveal the rock mass cracking process of an underground excavation, laboratory investigations on real rocks containing an opening, can provide a proper understanding of its complex behavior. In this regard, different advanced techniques can be implemented to monitor the cracking process around the excavation in real time and to explore the rock mass behavior more deeply. This paper aims to experimentally investigate the fracture evolution and damage behavior of rock specimens containing an opening under the uniaxial compression, incorporating digital image correlation (DIC) method and acoustic emission (AE) technique. For this purpose, uniaxial compression tests were conducted on granitic rock blocks containing a circular opening. In addition, four strain gauges were installed in as many directions around the opening to record the local strains. The synchronized AE output parameters and DIC plots with the stress and displacement data extracted from the servo-controlled loading frame, together with strain gauge data have been compared and analyzed in detail to reveal the mechanisms of crack coalescence. Finally, different criteria have been implemented to estimate damage stress threshold values. Combined analysis of AE parameters, DIC and stress-strain data allows to identify and discriminate different cracking stages including crack initiation, growth, coalescence and damage in tested specimens and their results are mutually consistent. AE results provide with reliable information to characterize the fracture evolution stages and different stress thresholds. Likewise, the local strain levels recorded by strain gauges are in a fair good agreement with the strain field measured with DIC. The type of crack initiation and failure around circular opening are also well characterized and in accordance to the theoretical crack distribution around excavations. The results of this study provide significant insights of the cracking processes in rock mass around an opening.