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.

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.

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.

The stability evaluation of rock masses surrounding large underground caverns under earth-quake effect is an alive and important subject. Under earthquake effect, the mechanical re-sponse characteristics of rock masses surrounding underground caverns are remarkably differ-ent from those under excavation unloading effect. Therefore, it is not appropriate to directly use the methods and criterions that are commonly adopted in static analysis to evaluate the behav-iors of rock masses under dynamic condition. A series of indexes and relevant criterions are included in the system. The indexes of relative displacement, peak stress, depth of damage zone, and rock support stress are proposed as a whole evaluation system. The evaluation sys-tem is then validated in a large underground cavern subjected to earthquake effect. It is con-cluded the system is effective. The presented methods and findings are hoped to provide useful references for other rock caverns with similar stability concerns.

Groundwater flow through fractured rocks was recognized as an important problem connected to several scientific and engineering geological fields, including hydrogeology, rock mechan-ics, geotechnical engineering. Fluid flow in rock masses plays an important role in many geo-logical hazards such as environmental risk. Fractured media are very heterogeneous and the hydraulic and geomechanical properties are strongly dependent on the rock mass spatially varying geometrical parameters. This makes the study of groundwater flow a considerable challenge for modeling purposes in the frame of environmental pollution, especially consider-ing that fractures may act as preferential drainage paths, thus accelerating the transport process. This study aims at shedding light, through a numerical simulation, on the influence played by major fractures on the groundwater circulation in a carbonate aquifer. The numerical model was built in a Q-GIS environment through the FREEWAT plug-in, by considering different scenarios that model the interaction between pumping activity and fracture field.

Rockfall reinforced earth embankments (RPE) are widely adopted defence structures against rockfall, particularly effective for high-energetic or frequent block impacts. Existing design approaches often involve simplifications, as RPE resisting mechanisms during impact has been not yet completely investigated. This study investigates the RPE response at the impact through a series of FEM analyses. Geophysical and plate load tests on an existing RPE are used to calibrate the soil constitutive law of the numerical model. The results of the huge campaign of sensitivity analyses, herein presented, allow to determine the mechanical and geometrical parameters most affecting the structural behaviour.

For underground rock engineering, laboratory testing is performed to obtain objective in-formation about the rock behaviour under compressive or compression-induced tensile fields through biaxial, true triaxial and indirect tensile tests. The ISRM-suggested methods for laboratory testing advocate the implementation of axial loading or strain rates that de-pend on laboratory parameters that are not or only rarely related to in-situ conditions. Near an excavation wall, the tangential strain and therefore strain-rate decreased with increasing distance from the wall. Due to the complexity of physically assembling a multi-platen ser-vo-controlled machine, the influence of uniform and non-uniform tangential strain rate distributions on the mechanical behaviour of brittle materials is rarely tested and is as-sessed here by using the software PFC2D. The mechanical responses for loading with two tangential strain patterns or strain-rate distributions are compared in terms of cracking pat-tern, stress-strain curves, bulking strain and related displacement at the excavation surface.

Material heterogeneity and shear strength variability are the main stability analysis considerations for the interbedded sedimentary rock slope due to interlayer slip potential. In this study, an interbedded sedimentary rock slope located in Terengganu, Malaysia, was examined. The composite stratified geostructure was projected for 2D surface morphology using point cloud photogrammetry, thus plane segmentation for dip measurement. The inter-bedded rock slope was modeled explicitly, where the location of rock beddings and potential weak layer materials are well defined. The limit equilibrium analysis for factors of safety determination was extended with sensitivity and probabilistic analyses for a wider range of failure potential factors. The validation using finite element analysis significantly justified the stability analysis result based on the shear strain behavior.

Reliable prediction of excavation impacts on surrounding rock mass is one of the crucial sub-ject in rock engineering. In this paper, the impacts of new tunnel construction intersecting an old tunnel is studied using the numerical modeling for case study of the Tehran-Shomal free-way project. The numerical modeling is performed by utilizing FLAC to evaluate the induced displacement and damaged zones surrounding the tunnel as a function of horizontal to vertical stress ratio (k). The results indicate that, both horizontal and vertical displacements induced by excavation and also the plastic zone show asymmetric spatial distribution around the tunnels due to the especial shape of tunnels intersection. The increase of k ration shows direct and re-verse effect on the horizontal and vertical displacement, respectively. In addition, by increasing the k ratio, the total displacement of observation points increases and the mechanism of yield-ing of surrounding rock is converted from shear to tension

This paper focuses on a case study of the use of numerical modelling to assess the influence of in-situ stresses and rock mass mechanical properties on the behaviour of a sill pillar in an underground metal mine. The loading conditions on the pillar are a result of a multiple panel, bottom-up advancing open stoping mining sequence with cemented paste fill. The sill pillar is exposed to increased induced horizontal stresses, which could result in rock mass damage or depending on the rock mass strength and geometry of the pillar. In extreme cases, the pillar may collapse, leading to ore loss or compromised worker safety. The numeri-cal modelling analysis in the case study was used to predict the rock mass deformation as af-fected by the mining sequence, in situ and induced stress conditions, and rock mass and paste fill properties to assess the pillar stability from stress-related damage.

Piezometers are instruments that can produce high-quality information if suitable installation and monitoring procedures are followed. Attention must be paid when prescribing the type of piezometer and the installation procedure in order to minimize errors and optimise the quality of the obtained information. The use of piezometers as geotechnical instruments is a commodity. However, attention needs to be paid to the installation procedure as highlighted in the ISO/EN18674 standards. The aim of the paper is to exemplify how the use of piezometers can be optimized and how the most standard errors can be avoided.

Mining and geomechanical conditions during mining operation in underground mine are changing all the time. The changes depend on many factors, as e.g.: the buried depth, type of rocks, geomechanical parameters of rocks, the size of mining face, the type of exploitation system or the space layout of mining in a field. However, as the result, all these factors influence on the state of stress. They determine the value of abundant stress and the direction of principal stresses. What is interesting, there is not only change in the primary stress next to the exploitation panel, but the rotation of the principal stresses as well. This fact is very often omit, because it’s impossible to solve this problem analytically. One can only assess it using numerical methods or carrying out expensive and time consuming rock mass monitoring underground in a mine. Employing numerical calculations the state of stress around the roadway is often determined in 2D models, which cannot show the stress rotation. This information can be found only using 3D models. However, the most valuable results can be received with the help of in situ measurements, which can be carried out with some biaxial or triaxial stress meters. The paper presents the results of underground monitoring and numerical analyses of state of stress in the rock mass during longwall panel advance in a coal underground mine. The in situ stress measurements were conducted with the help of biaxial stressmeters with vibrating wire installed in the coal ribs of a maingate, approx. 10 m deep in a non-fractured rock. The measurement data were registered automatically every 6 hours. This data allow to calculate not only the value of major and minor stresses but also changes of the angle of a major stress. The results of stress monitoring, together with the results of geomechanical parametrs of rocks done in the laboratory, were the base for 3D numerical modelling. Thanks to modelling the rule of principal stress rotation were shown. Conclusions are of a crucial importance for planning mining operations. The knowledge about the stress regime and its possible change can help in support system design for gates and improve the staff safety.

Ryukyu Islands constitute the south-west part of the Japanese archipelago. The age of the basement is pre-Cenozoic and the basement rocks are chert and schists. Cenozoic sandstone, shale and limestone overlay the basement rocks. These rock units are followed by Tertiary Shimajiri formation and all formations are covered by Quaternary Ryukyu limestone and Holocene deposits. The geo-engineering issues are mainly associated with the Shimajiri formation and Ryukyu Limestone. Particularly, landslides and stability issues of open or underground excavations in Shimajiri formation are major geo-engineering problems. It is well known that mudstone of the Shimajiri formation are subjected to degradation due to cyclic wetting and drying in relation to the water content variation. They also have time-dependent characteristics. The intact mudstone has uniaxial compressive strength (UCS) ranging between 0.6-3.6 MPa under natural water content conditions. Particularly, younger mudstone belonging to Shinzato Formation has lower UCS while older mudstone belonging to Yonabaru Formation has higher UCS. When mudstone layers are exposed to atmospheric conditions they absorb or desorb water and they exhibit volumetric swelling or shrinkage. This interaction with water causes their degradation and the physico-mechanical properties become a function of water content. The authors have been involved with a project where the mudstone layers belonging to Shinzato Formation and having some small normal faults caused some instability problems during a construction of a deep open-cut waste storage facility as a result of groundwater level changes during a heavy rainy period. New horizontal borings were done and cores from these borings utilized for tests on uniaxial compressive strength and Brazilian tests under different water content. The experimental studies involved the evaluation of physico-mechanical properties as a function of water content. Furthermore, groundwater diffusion characteristics of mudstone and related volumetric changes are experimentally investigated. During experiments, it is observed that some samples failed along some existing structural weakness planes. A multi-parameter monitoring system was installed and measurements were carried out for almost one-year. On the basis of these studies, some limit equilibrium analyses on the stability of the open-cut excavation and discrete finite element analyses (DFEM) on its measured deformation response were carried out. The outcomes of this integrated study involving various experiments, monitoring and numerical analyses are presented and their implications in practice are discussed.

The characterization of the thermal properties of crushed rock samples is not experimentally straightforward. In the case of thermal conductivity, some authors estimate this property based on solid rock plugs (e.g. optical thermal scanning, split bar, line heat source) what is not a convenient approach for granular materials with variable grain sizes. On the other hand, the determination of the specific heat of rock samples is typically based on enthalpy balances (e.g. differential scanning calorimetry, DSC) by achieving thermal equilibrium between the hot sample immersed in a reference fluid at a constant temperature. However, such techniques require small-volume comminuted samples if the grain size of the rock forming minerals is significant. All of the previous methods require, in addition, precise information on the physical (grain density, porosity, etc.) and mineralogical properties of the materials tested. To cope with these problems, the preferred approach of some researchers when dealing with granular materials is to assess thermal conductivity by estimating its heat capacity based on cylindrically-packed volumes and then applying to the bulk a radial heat source and simultaneously measuring temperature in selected locations along the diameter of the cylinder. Then, the measured thermal conductivity is an average conductivity of the packed porous sample (i.e. a combination air-filled porosity and the solid grain skeleton). This contribution presents the experimental methodology applied to assess thermal properties in aggregate rock packs as well as the analysis of the results of several tests carried out with basaltic aggregates intended for thermal energy storage.

Understanding the structure of the porous network in chalk is essential for many fields such as unconventional reservoirs, geothermal energy, CO₂ storage, or engineering. First, the study described qualitatively and quantitatively the properties of the porous network of chalk, a major component of the upper crust of Champagne-Ardenne. The chalk studied comes from the Grand Mont quarries (Saint-Germain-la-Ville, France). The study utilized various techniques including water porosity, mercury injection porosity, capillary water uptake tests, P- and S-waves propagation velocities, and scanning electron microscopy. Non-destructive and high-resolution 3D imaging methods such as X-ray microtomography and nuclear magnetic resonance were employed to determine pore geometry. Secondly, chalk was studied to understand its behavior during fluid circulation experiments at contrasting temperatures (cold rock - hot water // hot rock - cold water). A set of 130 samples was tested in 4 devices in order to produce a circulation of fluids: i) 150 cycles of water uptake by capillarity were carried out on chalks heated to 80 °C or at room temperature, with water at 8 °C or at 80 °C; ii) 150 thermal shock damage tests were obtained by quenching the samples at 80 °C in water at 0 °C; iii) a continuous transfer of water (10 L) at 80 °C or at room temperature was carried out by means of a device using the call of air exerted by desiccators placed under vacuum; iv) 10 L in chemical equilibrium with chalk circulated in control samples (without thermal stress) thanks to the design of a constant charge permeameter. The results showed that the water weakening phenomena in the chalk are not irreversible and that the temperature variations did not significantly affect the porous network or cause internal damage. However, the circulation of cold water in chalk preheated to 80 °C led to a reduction in water connectivity, due to the recrystallization of calcium and carbonate ions saturating the fluid and to the thermal expansion of calcite grains during cyclic heating phases. On the other hand, this recrystallization did not necessarily lead to a reduction in the volume of the pores. For experiments involving continuous circulation, the water connectivity has been further reduced. The uninterrupted flow of fluids increased the chances of a grain detaching from its position and entering a pore, thereby rearranging the pore space.

Time-dependent effects play a significant role, accounting for up to 70% of total deformations in tunnels (Sulem et al. 1987) [Int J Rock Mech Min Sci Geomech Abstr 24(3): 145–154]. The focus of this study is to determine whether the information from convergence measurements in a tunnel section can be used to identify specific constitutive law parameters describing both the short-term and long-term behaviour of the ground. Due to scale effect, actual in-situ mechanical parameters may differ from laboratory test results. Thus, the main objective is to directly calibrate constitutive law parameters, such as elasto-plastic or elasto-visco-plastic, from in-situ convergence measurements. A fractional constitutive law, for which an analytical solution is available for the stress and displacement field around the tunnel, has been chosen to model the behaviour of the ground. The use of fractional models is motivated by their ability to capture the time-dependent response of the ground with a good accuracy. Compared to classical constitutive laws, fractional laws enable to better describe the creep behaviour of the rock mass with a number of parameters that is significantly reduced (e.g., Caputo and Mainardi, 1971 [Pure Appl. Geophys. 91: 134–147]; Bagley and Torvik, 1983 [AIAA J, 21: 741–748]). This problem is framed as an optimization search, aiming at minimizing the squared error between convergence data points and the constitutive model predictions. Two approaches are combined to assess tunnel wall deformation: one empirical and one constitutive. The empirical convergence law (Sulem et al. (1987) [Int J Rock Mech Min Sci Geomech Abstr 24(3): 145–154] enables the extrapolation of convergences to long-term scenarios, serving as the basis for the optimization process subsequently applied to a specific constitutive law. The proposed method permits to characterize both the short-and long-term ground behaviour which can ultimately improve tunnel design. The method provides a means of calibrating constitutive parameters for implementation in numerical models and of assessing the long-term ground-lining interaction.

Solar energy installations are a prominent renewable energy source, requiring robust foundation systems to ensure their structural stability, cost-effectiveness, and long-term performance. This study presents a comprehensive assessment of the lateral load resistance of short socket piles for solar plant foundations in Bosnia and Herzegovina through experimental testing and numerical analysis. The experimental investigation was conducted to obtain data on the lateral load performance of the reinforced concrete bored piles. A total of 3 piles with a diameter of 40 cm and a length of 120 and 150 cm were installed for testing purposes. The pile socket depth, reached by the percussion drilling technique in dolomitic limestones, ranged from 20 to 50 cm, with the remaining upper portion of the piles being within clayey debris soil or highly fractured rock mass. Horizontal loading was incrementally applied at a point 20 cm above the ground surface, according to the procedure of the Quick load test outlined in ASTM D3966 – 07. The piles were tested until relatively large displacements were observed, ranging from 2.5% to 10% of the pile diameter, and unloaded to record the irreversible displacements. The test results indicate a notable increase in lateral pile displacement after reaching pile cap displacements ranging from 1% to 2.5% of the pile diameter, providing valuable empirical data for validation and calibration. To complement the experimental findings and gain deeper insights into pile behavior, a 3D numerical back-analysis approach was applied. The analysis included the nonlinear behavior of solid pile and rock mass elements supported by a discrete reinforcement embedded beam model. Good agreement between the model and measured data was obtained, indicating that the pile-rock mass system failed primarily due to reduced pile stiffness related to concrete cracking. Back-analysis results generally helped refine the understanding of pile-soil interaction mechanism, load distribution, and deformation patterns, enhancing the accuracy of predictions and design recommendations.

Coal mining presents several geotechnical challenges around the world. Limitations including data uncertainty and geological anomalies, coupled with risk acceptance in the form of “controlled” bench and inter-ramp scale slope failures in industry guidelines make slope collapsing an unavoidable and foreseeable aspect of economic rock slope designs in the mining industry. Technological advancements, such as three-dimensional slope stability modeling and ground-based interferometric synthetic aperture radar monitoring, in conjunction with traditional site investigation techniques such as drill core logging and face mapping, and remote sensing including photogrammetry and laser scanning, have proven to be successful in improving slope failure risk management. Improvements have included reducing personnel exposure to slope failure risks and earlier detection of emerging hazards which enable better remediation planning. This paper presents two case studies from coal mines in Colombia and Australia involving multi-bench, semi-ductile failures that were successfully managed using slope monitoring and response protocols. The data collected was utilized to improve geotechnical understanding enabling a more reliable forecast of future slope design risks and control measures to mitigate them.

In-situ stress knowledge involves the entire process of enhanced geothermal system (EGS) development, such as borehole stability, hydraulic fracturing propagation patterns, and mitigation of induced seismic risk. To eliminate the influence of high temperature, we employ the Anelastic Strain Recovery (ASR) technique for in-situ stress measurements in geothermal boreholes. ASR is a rock-core-based three-dimensional stress measurement method. Using the ASR method, we successfully measured the magnitude of in-situ stress at depths of 1500-4000m in China's first large-scale EGS site. To evaluate induced seismicity and fracture stimulation during EGS development, we simulated the variations in fracture slip tendency (Ts) near the injection well using the in-situ stress data. The results show that T_s is initially small, but as injection pressure increases to 46 MPa, the fractures reach a critical state (Tsmax=0.6), and further pressurization leads to gradual slipping of the fractures (Ts>0.6).

The integration of Rock Engineering in European Geotechnical Standards is one of the great achievements of the future Eurocode 7: 202x (EC7). The design of a geotechnical structure, according to prEN1997:202x [1], comprises five major tasks:1. Reliability management: a series of classifications that combine to place the geotechnical structure into a single Geotechnical Category. 2. Ground investigation: whose main outputs are a representation of the ground and groundwater at the site, known as the “Ground Model”, and the results of field and laboratory tests relative to different ground properties and test parameters. 3. Design verification: covering all the procedures to verify that no limit states are exceeded in any design situations that the structure encounters during its service life. 4. Design implementation: in which the structure is constructed while meeting the design assumptions and other detailed plans developed during the design phase. 5. Reporting: all work carried out during the design and execution of the geotechnical structure must be documented by carrying out the following reports: Geotechnical Investigation Report (GIR), Geotechnical Design Report (GDR) and Geotechnical Construction Record (GCR). The paper shows the different tasks that the designers must perform to verify the stability of a rock excavation: reliability management, ground investigation and design verification. During this process, the various new concepts that appear in the future EC7 (Geotechnical Category, Ground Model, Representative values, Design Situations and Design Cases) were applied. The results obtained show that the problem of a rock slope stability can be successfully solved in the frame of the Partial Factor Method, developed in the future EC7. The case under study is a rock slope produced by an excavation of an open pit next to an existing building. The excavation depth is 15 m (5 m in soil material and 10 m in rock material) with an angle of slope of 90º, as can be seen in Figure 2-left. This case was proposed by Guido Nuijten as part of the works performed by the final project team of the future Eurocode (CEN TC250-SC7-PT6).

The conventional design approach of any type of passive protection work aiming at reducing the risk associated with rockfall is energy-based: the total kinetic energy of the falling block in a given position of its trajectory (action, in Limit State Design (LSD) terminology) must be compared to the maximum energy absorption capacity of the protection work (resistance, in LSD terminology). The LSD approach, implemented in Eurocode 7 (EC7), shows some limitations in the case of unconventional geotechnical problems such as rockfall phenomena, since the main parameters of these systems are not considered. To overcome these limitations, one proposed solution is the application of Reliability Based Design (RBD) approaches through the definition of a reliability index, a useful and complementary tool to provide geotechnical structures with a uniform probability of failure. The RBD approach deals with the relationship between the loads that a system must support and the system's ability to support those loads. The RBD therefore shifts the analysis towards a fully probabilistic one, in which each parameter is considered a variable expressed by a known Probability Density Function (PDF). In this work, particular attention has been given to innovative rockfall protection structures such as hybrid barriers and/or attenuators: they do not stop the block by capturing and retaining it in a deformable net, but by dissipating its kinetic energy (up to 0 for hybrid barrier) and forcing it along a trajectory close to the ground or guiding it towards a collecting area. Therefore, in ideal conditions, the block does not stop within the net itself. Considering the applicability of RDB approach, the paper focuses on the response of these structures to the impact of the block and their absorption capacity at different stress levels. The rockfall barriers are made up of a series of structural elements (cables, interception panels, pots, anchoring system, …) which contribute together with the absorption of the impact energy. In this context, numerical modelling represents a powerful solution to reproduce the behaviour of these structures subjected to dynamic impacts at different Kinetic Energy levels. With this purpose 3D numerical simulations by FEM software ABAQUS were carried out, starting with simplified models to identify which parameters most affect the system response. In addition, different structural element components were analysed to reproduce their behaviour both in static and dynamic conditions to test their absorption capacity useful for the RBD approach.

Rock engineering projects that implement the observational method often use a ‘traffic light’ scheme to indicate the system’s status. Such schemes are convenient in practice, but subjective and ambiguous definitions of performance associated with each colour in the scheme and lack of clarity of risks are drawbacks. We tackle these deficiencies by proposing a probabilistic traffic light system with an extended colour range. Simulations using the convergence-confinement model (CCM) for a circular tunnel are presented to demonstrate the system. The geometry and colours of the bivariate cumulative probability distribution provide essential information regarding the system’s behaviour. We conclude that a probabilistic traffic light system can help assess the performance of rock engineering projects being designed and constructed using the OM in accordance with Eurocode 7.

For improving the quality and reliability of geotechnical investigations process, the concept of 'influence region' has been recently proposed. The concept of influence region is an attempt to move from 'experience-based' geotechnical investigations to a 'mathematical equation-based estimation and understanding' of ground investigations. It’s an attempt to improve quality of existing geotechnical process and to make it more reliable. Although the newly proposed concept of influence region is based on author's field experience and conceptualized while working in real life projects, its theory still needs to be tested and validated. Considering need of testing and validation of this new concept of 'influence region', and proving it's theory, in this paper we are proposing different methodologies for field and laboratory tests. The paper will cover geotechnical investigations in different ground conditions i.e., soft-medium-hard conditions for both soil as well as for rock and will propose testing methodologies for both laboratory and field testing. The proposed methodologies will consider geo-mechanics, hydraulics, deformation parameters for soil and rock for testing the concept of influence region. To explain practical application of the concept we will be estimating influence region of RQD* (*Rock Quality Designation) parameter. RQD is most commonly used parameter for accessing the quality of rock. RQD is one such parameter which is applied in almost all empirical formula for accessing quality of rocks. The expected outcome of this paper is to have testing and validation methods for both lab as well as for field testing for proving the concept of 'influence region' of geotechnical investigation points, sampling zone. Also, to show the practical application of the concept, an example of RQD influence region estimation and its equation is presented. Author's view is as influence region concept is an equation-based understanding of geotechnical ground investigations, it has potential to be included in Eurocode/ ISO standards. By providing testing, validation methodologies and showing practical application of the influence region concept, this paper will serve as a scientific tool to geotechnical engineers.

Flysch materials are a common source of slope instabilities and other geotechnical problems. Some attempts of characterizing such materials have been done, probing to be a challenging aspect. One European region where flysch materials are abundant is the Spanish Basque Arc Alpine region. A broad geological-geotechnical investigation was conducted on 33 locations spread in an area of approximately 100 km² in the Spanish Basque Arc Alpine region to geomechanically characterized the “Upper Cretaceous Flysch” materials found in the area. Such characterization was done following a GSI vs. uniaxial compressive strength of the intact rock chart given by other authors. Even though that procedure showed to be appropriate, values of Hoek-Brown parameters proposed based on such chart, showed not to match very well with the ones obtained in the laboratory for the 33 points analyzed. This caused the estimation of shear strength parameters of flysch materials to be poor. To improve it, Artificial Neural Networks were used. These artificial intelligence algorithms are of common use in engineering and enable to find no-linear correlations which may be difficult to find otherwise. Results show a very good performance when using Artificial Neural Networks, achieving determination coefficients R² between laboratory values and numerical ones close to 1.

The continuous convergence monitoring during and after excavation is an important tool in the application of the observational method for tunnels design (Schubert 2008. Geomech. Tunn. 1(5):352–357). Previous works have shown that, the direct analysis of convergence measurements with empirical models allows reliable long-term predictions of ground deformations. It is shown that, by monitoring convergence for a few tens of days, these models can provide valuable insights for the design of support systems and the evaluation of their performance in time (e.g. Sulem et al. 1987. Int J Rock Mech Min Sci Geomech Abstr, 24(3):145–154; Guayacán-Carrillo et al. 2016. Rock Mech. Rock Eng. 49(1):97-114; Liu, et al. WTC 2019). During the last decade, machine learning techniques have experienced vast growth in geotechnical engineering. These techniques present advantages concerning their computational performance and their applicability to high-dimensional non-linear problems. With the emerging use of these techniques, some questions arise as: (1) how these ones will contribute to the design of underground structures? and (2) what is its efficiency and accuracy using small datasets, as it is the case in rock engineering projects? The present work aims to propose a simplified Symbolic Regression (SR) approach in order to evaluate its applicability on the convergence evolution prediction. SR is a machine learning technique that aims to identify an underlying mathematical expression that best describes a relationship between input and output parameters (Stephens 2019. gplearn.readthedocs.io; Koza, J. (1992). MIT Press). In this work, special attention is given to anisotropic closure evolution, which depends on the anisotropy of the initial stress state and the intrinsic anisotropy of the rock mass formation. Moreover, the time needed on convergence monitoring is also studied, by taking into account different time intervals (corresponding to the duration of convergence monitoring). The results show that SR present a good predictive accuracy in comparison with the semi-empirical law proposed by Sulem et al. (1987) [Int J Rock Mech Min Sci Geomech Abstr 24(3): 145–154]. It is observed that this approach performs well with the small dataset used in this study and can be considered a useful alternative.

The rock mass properties are crucial for any structural design and the estimation of these properties is done using the Geological Strength Index (GSI). This study introduces a methodology to predict the GSI values using advanced image processing and Artificial Neural Network (ANN) techniques. The pictures and the face mapping data from an Iron ore mine are taken and using image processing techniques, including black-and-white conversion, joint highlighting, and noise reduction, the fractal dimensions of the rock faces are evaluated. An ANN model is developed which utilizes the fractal dimensions and the surface condition index as inputs and predicts the GSI values. This methodology aims to overcome the subjectivity of qualitative assessments, providing a more accurate representation of rock mass strength. The R2 value of the developed ANN model is 0.67 which indicates a positive correlation between predicted and qualitative GSI values from the standard chart.

The expansion of the underground infrastructure and the necessity to maintain the functionality of existing tunnels highlights the role of structural health monitoring to track the behavior of the structure. In the study performed, the focus is on segmental tunnel linings for deep and long tunnels. The aim is to reconstruct in real-time the stress field in the tunnel structure starting from a few monitoring data. The framework is based on the combination of finite element (FE) models of the lining in the hosting rock mass and machine learning algorithms, which are deployed for real-time estimation of the stress distribution in the lining. An approach based on synthetic data generated with FE simulations permits to reconstruct a thorough picture of the structural stress state based on a few monitored points. The method is applied to a full-scale test, in which three piled lining rings were tested under geostatic-like loads.

In NATM tunnel excavation sites, rock mass evaluation at tunnel face heavily influences the determination of support patterns of tunnel construction. Currently, this evaluation is performed by skilled engineers who score the rock mass according to several predetermined evaluation criteria. This method heavily relies on the subjective standards of the engineers. Thus, a uniformed and standardized evaluation method has not been established. In this study, the applicability of machine learning to rock mass evaluation is verified to achieve a qualitative evaluation method. A support vector machine (SVM) model was developed to predict the support pattern of one tunnel face to test applicability at tunnel construction sites.

We propose a new approach leveraging 3D Hough transform to detect discontinuity planes from traces in digital rock models, where clear planar surfaces are not apparent. Our method assumes that that the discontinuity plane behind a trace on the rock surface aligns roughly parallel to the trace's local direction, like a door rotating around a hinge. We begin by estimating local trace directions using multi-scale principal component analysis. These directions then inform the weighted voting of trace points within the Hough space. Peak-searching identifies initial planes, which undergo refinement to eliminate spurious or duplicate results. Applied to synthetic data and two natural outcrops, our method performed discontinuity extraction from traces with varying degree of success. This approach shows promise as an analytical tool in geology with potential for further optimization.