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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The selection and the design of rockfall protection works often relies on the evaluation of the energy involved in the possible phenomena. This requires the identification of a characteristic energy value: this is usually done through numerical simulations of block trajectories, both in 2D and 3D, from which the actual reference value of total kinetic energy at a specific location along the slope can be identified. The experience and expertise of the designers play a crucial role in the choice of the input parameters: the process heavily depends on the choices of the reference values themselves, making the approach highly deterministic and often empirical. A possible alternative design approach would rely on the probabilistic description of the phenomenon, through the use of distributions of the most relevant parameters, instead of deterministic values. The method proposed here is based on the identification of the characteristic In situ Block Size Distribution (IBSD) of a rock mass identified as rockfall source area, and 2D numerical simulations of block paths. From a significant number of these simulations, the probability distribution of the design parameters is obtained: in the case of passive protection works, such as flexible barriers or embankments, this corresponds to the definition of the Total Kinetic Energy probability distribution, which can support the identification of the energy level the structure is required to withstand, and to the Bounces Height probability distribution, which can direct the choice of the height of the structure. The significant advantage of this probabilistic approach lies in two key features. The first one is the rigorous statistical treatment of the parameters involved, as required for the definition of the IBSD: this provides in return a significantly reliable method, devoid of empirically based choices, yet simple and quantitative. It is also important to note that the probability distributions of the design parameters can still be used in a traditional design approach to quantitively justify the choice of characteristic values. On the other hand, describing the phenomenon in a probabilistic way also allows for methods based on failure probability to be employed. The second advantage is the possibility to define generalized acceptable levels of residual probability, through which standardize the selection of the design parameters. In this way, the designers, who assume a significant responsibility when dealing with these choices, could be provided with a tool to deal with possible predictable consequences.

This paper presents a methodology to identify key blocks in highly structured rock masses. Calculating the stability of these key blocks is critical to forecasting geotechnical risk in terms of potential failure volume and runout distance. Key blocks are determined using structural mapping data from photogrammetry data acquired by drone flyovers. The Factor of Safety of key blocks is then calculated using limit equilibrium methods. Any key block with a Factor of Safety less than one is then systematically removed from the slope to determine the maximum potential volume of slope unravelling once the key block is removed. This information is then used to determine potential runout distances. Sections of slope predicted susceptible to failure (i.e. Factor of Safety less than one) can be the focus of proactive monitoring or hazard control (e.g. through the forward instalment of barriers, exclusion zones, etc.).

The problems of collapse sinkholes (simas) that have affected the population of Alcalá de Ebro are very old. Since 1980, both the SGOP and the CEDEX, among others, have worked on the investigation of an area located at the entrance of the Population where there have been several subsidences (collapses), affecting a street, the flood defense area of the Ebro River, and some houses. Since then, different recognition techniques have been applied with the intention of assessing the geological-geotechnical model of the affected environment. All the information obtained in previous studies was reviewed and expanded, to improve correlation and the scheme of the internal structure of the subsoil was completed by means of a geophysical profile based on techniques: Cross-hole and MASH. The resulting profile after incorporating all the data obtained in the different research reports carried out/compiled, allows an interpretative model to be reached and the following conclusion to be obtained: The basis of the problem that facilitate the generation of sinkholes-chasms at this point in Alcalá de Ebro is located at a level or stratum, from 4 to 6 meters in relative thickness, located at a depth of between about 14 (from the access street to Alcalá), which is formed by an alternation of highly soluble rocks: massive gypsum ( usually in the form of nodules), glauberite, and possibly thenardites and epsomites. The most relevant thing is that levels or layers of salt (halite) have also been recognized. The apparently affected surface made it possible to evaluate consolidation solutions that were initially based on injections of expansive resins and later on injections of low mobility mortar. The latter were carried out in two phases during the years 2017 and 2018. The aforementioned “mortar columns” descended between 21 and 23 meters until they crossed the affected area and entered firm ground. Once the treatment with mortar was carried out, the embankment was reinforced, on the surface, using flexible geogrids, but with high tensile strength. At present (almost 5 years after carrying out the consolidation works), the results have been monitored, carrying out high-precision level and measurements with terrestrial laser-scanners. Geophysical research work continues to be carried out using Ultra GPR georadar and electrical tomography. The apparent results obtained are positive and allow evaluating a technique of consolidation and improvement of the terrain, in a particularly sensitive point affected by frequent subsidence and collapse processes.

Coal mining in the eastern part of Saar district (Germany) caused numerous seismic events. After a ML = 4.0 event (93.7 mm/s PPV) in 2008 mining was stopped for good. Coal has been extracted by the longwall mining method at depth below surface of 1600 m. During extraction the mine water was kept below the deepest seam by pumping at central shaft. In 2013, the pumps were shut down and the water level in the shaft rose. Seismic events occurred immediately and the water level in the shaft was kept from 2015 on constant at 300 m higher compared to the level during mining. Two cluster of mine-water induced seismic events were observed. One cluster is located around the panels in the area where seismic events occurred during mining, which is no surprise. Another cluster is in the undisturbed rock mass away from longwall operations, i.e., in an area of approximately 6 km² surrounded by separate fields of panels. The only conduits for water in that otherwise undisturbed area/ volume are several 6 m x 5 m gateways directly connected to a shaft outside that area. Major faults are present there and the mining authorities wanted to know whether seismic events may occur with further rise of mine water in the shaft. This paper describes the methodology for arriving at estimates of future seismic events caused by elevated pressure from mine flooding. Substantial numerical modelling was necessary for estimating the spatial water pressure distribution over time. Fault planes from focal analyses were compared with known discontinuity orientations at different scales. Finally, based on the concept of the mobilized friction angle of discontinuities, it was concluded that the major faults will not contribute to the seismic events during further rise of mine water.

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, 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 a RDB approach, the paper will focus on the description of the rockfall phenomenon, namely the action on the hybrid barrier/attenuator. To describe the process of a moving block impacting it, two main parameters are identified: the Total Kinetic Energy (E_k) and the position of the impact location with regard to the structure. Assuming a 2D simplification of the problem, the second parameter corresponds to the height of bounces (H) in a given position along a slope. This works shows how, by employing a robust statistical approach and a suitably large set of numerical simulations, it is possible to define the Cumulative Distribution Functions (CDFs) of these parameters. From these two curves, it is possible to identify, through the use of proper statistical tests, the best-fitting PDFs and, therefore, use them as input for a probabilistic design approach such as RBD.

El Caminito del Rey, a renowned hiking trail located in the province of Malaga, Spain, is not only celebrated for its breathtaking beauty, but also for its notable susceptibility to rockfalls. The trail traverses a rugged terrain characterized by towering cliffs comprised of various rock formations, including limestone and conglomerate. The structural integrity of these rocks is gradually compromised over time due to weathering processes such as freeze-thaw cycles and erosion. When coupled with the influences of gravity, vibrations arising from human and wildlife activity, as well as natural seismic events, the stability of the cliffs becomes compromised, resulting in frequent occurrences of rockfalls along the trail. Despite persistent efforts to mitigate these risks, such as regular inspections and the installation of protective barriers, the inherent geological nature of the gorge renders the complete prevention of rockfalls an intricate challenge. In light of these circumstances, this study aims to take the initial steps towards implementing an advanced safety system on El Caminito del Rey with regards to rockfall hazards. The primary component of this undertaking involves the development of a susceptibility model based on rockfall simulations. The process unfolds in three key stages. Firstly, a comprehensive virtual 3D model of El Caminito is generated. Secondly, ancillary data and meticulous characteristics of the rocks constituting the gorges are compiled and incorporated. Lastly, utilizing the aforementioned information, rockfall events are simulated. This abstract will expound upon the challenges surmounted during the course of the project, as well as provide an overview of the principal findings. Furthermore, the forthcoming research agenda for the area will be outlined, seeking invaluable feedback from the interested audience. This feedback will play a crucial role in guiding future research efforts in El Caminito, with the ultimate objective of enhancing the safety of the trail. While the allure of El Caminito del Rey's awe-inspiring scenery remains undeniable, the trail managers are diligently prioritizing visitor safety by proactively preparing for potential rockfall hazards. Through the implementation of an advanced safety system informed by the findings of this study, the aim is to strike a balance between preserving the enchanting experience offered by El Caminito and ensuring the well-being of its visitors.

The Aurunci and Riviera di Ulisse Regional Parks are known for their cultural landscape and related trails that, every year, are hiked by thousands of visitors. The “San Michele Arcangelo” historic trail is the most important trail of the Aurunci Regional Park (central Italy) and forms the cultural asset of the park. The trail is located along the southern slope of Mt. Altino, prone to rockfalls, and is hiked every year by thousands of faithfuls on pilgrimage who are exposed to such kind of instabilities. The trail of Punta Cetarola in the Riviera di Ulisse Regional Park is a significant example of coastal trail, corresponding to a segment of the ancient “Flacca” road and, similar to the “San Michele Arcangelo” historic trail, is developed along a slope prone to rockfalls. To contribute to a better understanding of the condition of development and evolution of rockfalls in these two areas, providing a susceptibility scenario able to support the adoption of mitigation measures, a specific analysis was completed on the basis of field and literature data. Photogrammetric reconstruction of accessible slope sectors and scan-line-based field outcropping analyses were completed to derive geomechanical features of rocks and estimate potential detaching block volume. Possible mechanisms of detachment were analyzed using the reduced complexity Markland test method. Susceptibility to rock block detachment, rockfall propagation and block deposition was analyzed using GIS processing and deterministic/probabilistic propagation analyses. In particular, adopting the Rockyfor3D software, results of slope analyses and simulations indicated: i) the potential for rock blocks detachment by wedge and planar sliding or toppling, ii) the localization at higher elevations over the whole study area of slope sectors susceptible to block detachment, iii) the moderate susceptibility to both propagation and deposition of rock blocks along the trail, iv) the control exerted by the hydrographic network on rockfall propagation, v) the control exerted by screes and slope angle on rockfall deposition.

Coastal communities face recurring erosion problems and flooding. It is complex to carry out a technical-economic balance, which allows for finding an effective solution. With increasing risks and associated management costs a congruent solution designed, which consists of the conformation of modules, composed of an exoskeleton of rhomboidal meshes of high yield strength (>1650MPa) stainless steel duplex, rock block fill, which can be executed in place or precast. This solution designed by gravity, in which the structure's weight plays an essential role, is efficient when faced with certain significant wave height and slope inclination conditions. For its design, in addition to the demands in energy and uplift terms, the abrasion generated in the components, the sediment dragging process that causes both the entry and exit of the water from its bracing, only the use of stainless steel as the only material, guarantees the effectiveness.

Coal Pillars are important structural elements in underground mining. Unstable pillars can result in collapse of roof and walls and even coal burst; hence its reliability analysis is of great importance. This paper presents a novel probabilistic framework to assess system reliability of section pillar. The variation of coal mass parameters, such as UCS, friction angle, cohesion and Young’s modulus, are considered. Two different failure modes, with respect to pillar stress and strain, are investigated to obtain reliability indices using FLAC3D, Stochastic response surface (SRSM) and First-order reliability method (FORM), then Bimodal bound and Linearization methods are adopted to compute system failure probability. Finally, coal mass parameters from a typical coal mine are employed and results suggest that both stress and strain limit states could have significant influence on the system reliability. The approach proposed in this paper could be a useful tool on the risk management of underground pillar.

Secured drapery systems with meshes have been used for years to stabilize the surface material in slopes and ensure the safety in different infrastructures. Historically, one of the first materials used as a mesh was double-twisted mesh. Over time, the need for materials with higher performanc-es arose, leading to the installation of steel cables or rope panels over the mesh, which was a slow and labor-intensive process. Furthermore, it is necessary to verify the use of meshes in the design, as geomechanical models are often complex and unrealistic. Key mechanical characteristics for de-sign are the tensile strength, punch resistance, and punch deformation. However, the transverse ten-sile strength is often overlooked, despite evidence showing its relevance. This article presents a re-liable numerical model calibrated using laboratory tests. It demonstrates the influence of transverse tensile strength on deformation and punch resistance, enabling the optimization of bolt design with-in secured drapery systems.

In France, abrupt collapse raises more problems of risk management than progressive subsidence. Thus, these two types of phenomenon need to be distinguished. Bases on Tincelin & Sinou (1962) principle, we have attempted to develop an easy-to-use methodology through the retro-analysis of the subsidence of part of the Vins-sur-Caramy mine in 1959. Works is based on a geotechnical analysis of a core drilling and mechanical laboratory tests. Method consist on the examination of two criteria a stability criterion (geometric criterion) and an overburden massiveness criterion (geological criterion). The geological criterion, more complex to understand, was examined using the deformation modulus (Em) of the overburden. This method provides an initial response to the case of the Vins sur Caramy mine. Further research will involve comparing this and other cases.

The present paper summarises the activities related to 3D rockfall hazard assessment in the zone of the heritage dam Matka near Skopje. The concrete arch dam is 29 meters high and it was constructed in the mid 30^ties of the 20^th century. It is the first ever built dam in Macedonia, is survived the infamous Skopje earthquake of 1963, and still working today at full capacity, after almost 90 years of operation. The wider zone around the dam and its lake are situated in the steep gorge of river Treska, characterized by pronounced rockfall hazard in general terms. The entire area is also known as a natural rarities site and attracts many tourists and rock climbers. In order to assess the rockfall hazard for the dam and its appurtenant structure (spillway) a 3D rockfall simulation was performed. In the first stage, the main challenge was to prepare a high-quality 3D model of the terrain and the dam. Several contemporary and innovative surveying techniques were combined in order to achieve this, explained briefly in the paper. Based on findings from engineering-geological mapping, old geological datasets, stereographic analysis, and defining seismic forces, local slope stability analyses were performed. Kinematic analyses confirmed the possibility for detachment of rockfalls, which is observed in reality, and not only in the exact zone of the dam profile. Next were defined the properties of the rockfall seeder zones. The shape, size, and weight of the possible rockfall blocks endangering the dam and the spillway structure were modeled. Due to uncertainties, both point and line types of seeders were applied. The software RocFall3D of the company Rocscience was used to perform the simulations. After running of the program, the paths of possible rockfalls were obtained and then analyzed. Results show that for the given position of the familiar rockfall zones, there is no direct hazard for the dam. The opposite was concluded for the spillway structure. Therefore, for this zone were performed additional analyses of the expected kinetic energy and the other dynamic components of the possible rockfalls. Possible protection types for the spillway were then discussed. The application of protection measures is obvious and subject to further design, however, many limitations can be expected due to the natural protected status of the entire area.

The doublet disastrous earthquakes occurred on February 6, 2023 in the south-east part of Türkiye. The first earthquake is named as The Pazarcık earthquake and occurred at 4:17 on February 6, 2023 and the second earthquake is named as Ekinözü (Elbistan) earthquake and occurred at 13:24 on the same day after about 9 hours. The first earthquake ruptured the segments of East Anadolu Fault (EAF) and Dead-Sea Fault. The Pazarcık earthquake was initiated at Narlı fault belonging the Deas Sea Fault System and involved the Pazarcık segment and Amanos segment belonging to East Anadolu Fault System, subsequently. The estimated total rupture length was about 250-270 km. The Ekinözü earthquake involved E-W trending Çardak fault with a total rupture length of 120-130 km. The magnitude of the Pazarcık earthquake has been estimated by different institutes and it ranged between 7.7 and 8.0 while the magnitude of the Ekinözü earthquake estimated by different institutes and they range between 7.6 and 7.7 (Aydan and Ulusay, 2023).

Several roadways and railway and underpass tunnels were damaged by the Pazarcık earthquake. In addition many rockfalls occurred at the portals of railway and roadway tunnels. The damage by faulting was quite severe at the railway tunnel near Ozan village and the offset was more than 200 cm. Another faulting induced damage occurred at an railway underpass tunnel at Kozdere and the relative slip was more than 30cm. The damage to concrete lining of the new Erkenek tunnels occurred at several places. Despite linings were reinforced, severe spalling and collapse were observed. DLI of the Erkenek tunnels ay be designated as 5 while it may be designated as 7 for the Ozan tunnel. These tunnels were excavated in weak rocks such as phyllite, serpantinized ophiolite and some slope mass movements were observed during excavation. The damage in the new Erkenek tunnels may be related to mass movements caused by heavy ground shaking. The old Erkenek tunnel was excavated in hard limestone and the damage was light although the tunnel was unsupported.

The Shaimdrone Project developed by Geoconsult, with the collaboration of the Polytechnical University of Madrid (UPM, Civil Engineering & Telecommunications Engineering), and financed by the Center for Technological Development and Innovation (CDTI), proposes a methodology for semi-automatic analysis, evaluation and management of massive geometrical data (3D point-cloud models, or 3DPC models) collected from rock slopes using drones. These technological advances increase the working safety of the technician who performs inspections on slopes at the roadside and reduces the impact on the road user due to temporary occupations. Both benefits optimize the duration of field work and increase the capacity and objectivity of risk analyses of the road slopes using and therefore of a better risk assessment.

From the R-SHRS (Rock and Soil Hazard Rating System) risk indexes for rock slopes (Geoconsult 2019, 2021) and the parameters that conform them, advances associated to Shaimdron allow the semi-automatic gathering of data, to compute geometrical parameters from the analysis of the 3DPC models, which are integrated in the R-SHRS_infra category. Similarly, the measurable aspects of the rock and soil masses that form the slopes are grouped in the category R-SHRS_geo, while the parameters that require historical records and frequency phenomena –hence being not measurable from point clouds– are groupted into R-SHRS_freq.

For the Shaimdrone Project, a methodology is developed to obtain data through drone flights, in which their flight operating parameters –distances, heights and flight speeds– are optimized for adequate data collection. Algorithms are also developed to obtain cross sections of the 3DPC models, and to identify lithoclases and joints. The identification of joints defining the rock mass structure of the study area has been carried out with advanced image processing techniques that reduce the noise associated to the irregularity of rock masses. The advanced data processing allows the user to compute aspects such as spacing, persistence, fracture rates (RQD), roughness, block volume, etc. Results obtained from the analysis of the 3DPC models, as well as from other complementary analyses, are integrated into a “risk reports application” that develops risk measures for a given road section, to be also stored in databases and integrated into GIS/BIM environments, for an adequate management of the information and to facilitate subsequent mitigation and investment plans to be conducted by the infrastructure manager.

Rockburst can be referred to the damage that occurs in rock excavations as a result of a seismic event that generates sufficient energy to cause violent failure of the rock mass. Rockburst events are known for their unpredictable and violent nature, representing a significant threat to workers’ safety, mining productivity, and operational costs. Therefore, a quantitative assessment of rockburst damage is significant for geotechnical risk management in seismically active underground mines. Over the past few decades, numerous studies have been conducted on predicting rockburst damage potential. Despite the scientific achievements and technological advances in ground control, rockburst damage still threating underground mine operations because of the elusive character of the rockburst phenomenon. This paper introduces a dimensionless index to quantify the rockburst damage hazard. Well-documented rockburst damage data compiled from an underground mine located in Canada and Australia were used to establish the index. The input data parameters include the capacity of the ground support system, stress conditions, presence of geological structure, excavation span, and peak particle velocity. The overall results showed that the predicted hazard level using the proposed index had good correlations with the actual rockburst damage scale. In addition, it was found that the most important parameters were the stress and support conditions. It was concluded that the results of this research could be used as a prediction tool to help engineers to adequately assess rockburst damage in seismically active mines.

Assessing the suitability of geological formations as safe locations for seasonal hydrogen storage requires in-depth geological knowledge and good engineering practice. Establishing the safety and viability conditions of such projects requires solid multidisciplinary experimental evidence. In this context, the role of seal formations is crucial, in particular when considering H₂-tightness and their related transport properties. While there is a wide number of works addressing the performance of low-permeability seal rocks (salt formations, shales, etc.) when exposed to a variety of gasses (CO₂, N₂, CH₄, etc.) there is a significant lack of information on the behavior and interaction of H₂ with natural rocks under realistic geological storage conditions. In this work we will present results of experimental works developed on seal rock materials of potential interest for H₂ storage (Late Miocene marls) under representative field conditions (60 ºC; 17.5 MPa vertical stress; 8 MPa pore pressure; dry density ~1.7 g/cm³). Due to the poor machinability of the rock, a sample reconstitution methodology was required to perform the tests. These included a stepwise sequence of liquid (in situ sampled formation fluid; 4.26 mS/cm) and gas (H₂; 99.9992 purity) steady-state injections aimed at assessing its intrinsic permeability and breakthrough pressure either in single and multiple drainage/re-imbibition stages.

The creep behavior of rocks significantly affects the long-term stability of underground spaces. This phenomenon becomes more remarkable in the case of soft rocks, deep underground construction, and rocks subjected to high stresses. A better understanding of the creep behavior of rocks is crucial for the analysis of the time-dependent behavior of rocks. In this study, a new creep constitutive model is proposed by replacing a Newtonian dashpot in the Burger model with the fractional derivative dashpot and introducing a viscoplastic element to model the accelerated phase of rock creep. The proposed model is validated by the creep test results of soft rocks, which shows that this model can comprehensively describe rock creep characteristics.

The ideal circumstance for accumulation and passage for CBM gas is well developed pores and cracks in gas reservoirs. To explore the multi-scale characteristics of pores, two coal samples have been collected from Raniganj Basin, which has been of interest to scientists and policy-makers due to its abundance of CBM resources and favorable conditions for CBM enrichment in eastern India. Quantitative pore features as evaluated by fluid based method (low-pressure N₂ and Co₂ adsorption) and image based method (Field Emission Scanning Electron Microscope) in this investigation. By utilizing these methods, Characteristics of nano pore including pore size distribution, pore volume, specific surface area and pore shape has been understood. To study the effect of pores on methane adsorption, a full scale pore estimation model has been introduced with the combination of BJH, BET, Langmuir and NLDFT model to establish the micropore (0.4-1.6 nm) and mesopore (1.6-20nm) attributes. According to the case study’s analysis, Raniganj coal samples have a certain specific surface area and mesopore and micropore volume, varying from 8.2913 to 11.8303m²/g and 0.0165 to 0.0188cm³/g for mesopores and 32.042 to 39.416m²/g and 0.014 to 0.017cm³/g for micropore. Mesopore size distributions are multimodal and micropore size distributions are unimodal. The surface fractal dimension of both coal samples is determined using the area-perimeter approach based on microphotographs. The value of the fractal dimension ranges from 1.17 to 1.30. These findings of the study demonstrate that the coal surface has a clear fractal aspect and that fractal theory is a useful tool for understanding the complicacy of pore morphology.

It is not uncommon that seismically active zones are generated away from the region where anthropogenic activities, such as mining excavation and fluid injection, caused a severe change in the in-situ stress. It is still quite challenging to predict the occurrence of such dynamic instability in the remote regions because the stress change in such regions is relatively small and the rock mass is presumed to be stable from a theoretical point of view. It can be deduced from previous field measurements that one of the factors contributing to the occurrence of the rock mass instability is pre-existing stress heterogeneity resulting from the macroscopic stiffness variation of the rock mass. The present study addresses this problem by performing the numerical simulation of the in-situ stress state in a sedimentary basin with a boundary traction method whilst considering the difference in stiffness among geological layers as well as the geometry of the boundary. First, a model parametric study is conducted whilst changing the stiffness of each geological layer. The result indicates that the difference in stiffness between the basement and sedimentary rock significantly disturbs the in-situ stress state, leading to a remarkable increase in deviatoric stress from the hydrostatic stresses applied to the model boundaries. The degree of the stress discrepancy is more pronounced with the decrease in the stiffness of the sedimentary rock situated above the basement. Then, the geometric effect of the geological boundary between the basement and the sedimentary basin is investigated. Interestingly, the result shows that the deviatoric stress of the rock mass increases above a convex geological boundary, indicating a large potential for instability. In contract, when the boundary is concave, the maximum stress decreases above the boundary, but the stress increases in the basement beneath the boundary. This implies that the risk for rock mass instability decreases above the boundary and vice versa. These results clearly shed light on the mechanism of the dynamic instability taking place away from the region where the in-situ stress was severely disturbed due to anthropogenic activities. Importantly, the presented method needs to be combined with the heterogeneity of rock mass strength in the future in order to develop a more reliable prediction method for the dynamic instability of rock mass.

A significant rise in the world’s mean temperature (1.1ºC in 100 years) is produced mainly due to the emission of greenhouse effect gases (GHG), particularly carbon dioxide (CO₂) emission (IPCC, 2022). Carbon capture, storage, and utilization (CCSU) is being developed as an alternative to curbing the direct emission of CO₂ into the atmosphere. This process involves capturing CO₂ directly from emitting industries and injecting it underground in supercritical state (31.48ºC and 7.38 MPa). The primary goal is to identify a suitable geological reservoir capable of storing CO₂ for extended periods without the risks of migration. Among the various reservoir alternatives, a depleted oil and gas reservoirs stand out as a viable option. These rocks formations own high porosities, offering great void space for CO₂ storage, and their high permeability facilitates the injection of CO₂.

This paper explores the potential of using glauconitic sandstone extracted from a depleted oil and gas reservoir as a viable CO₂ storage option. The experimental investigation focused on observing the effects of subjecting samples to supercritical CO₂ (scCO₂) at 10.5 MPa and 60ºC for a duration of 30 days within the pressure cell at the UNPSJB's geomechanics laboratory (Argentina). Subsequently, a detailed analysis was conducted to evaluate the changes in petrophysical properties and mechanical behavior of the samples before and after the CO₂ ageing process. To achieve this, various mechanical tests, including direct tensile, uniaxial compressive, and triaxial compressive tests, were carried out at the geotechnical laboratory of CEDEX (Spain).

Based on the mechanical results obtained, it became evident that the mechanical strength of the sandstone decreased after undergoing the carbonation process, as assessed using the Hoek-Brown failure criterion. Regarding porosity, two primary modifications were observed. Firstly, there was a slight reduction in the sandstone's porosity after its exposure to carbon dioxide. Secondly, the pore size distribution exhibited variations, with an increased percentage of pores having smaller diameters. These findings suggest a preliminary hypothesis that chemical precipitation may have taken place within the larger diameter pores during the scCO₂-aging of the samples. To validate this hypothesis, additional analysis of the SEM, XRD, and XRF results will be conducted.

The study of salt structures has important guiding significance for oil and gas exploration and production in salt-bearing sedimentary basins. Previous studies have mainly focused on exploring the influencing factors such as syntectonic sedimentation, preexisting faults and preexisting salt diapirs of salt tectonic deformation. However, there is still a lack of systematic research on the effect of geometric properties of preexisting salt diapirs on the later stage shortening deformation. In this paper, particle flow method is used to investigate the geometric properties of preexisting salt diapirs such as its geometry, depth, width and the combination styles of preexisting salt diapirs on the geomechanics of salt-related structures during shortening. Model results show that the preexisting salt diapirs play an important role in geomechanics of salt-related structures. During shortening, salt bearing structures are prone to plastic flow, local accumulation and thickening, which affect the structural style of the overlying layers. The structural styles mainly include reverse faults and fault-related folds, box-folds, salt nappe structures and salt welding structures. The depth of preexisting salt diapirs is important for controlling the growth of diapirs. The width affects significantly the amount of shortening, which can be accommodated by extruded diapirs. The combination style of preexisting salt diapirs has a certain impact on the deformation of overlying salt tectonics. In addition, the reliability of the simulation is further verified by comparing the model results with the typical seismic profiles of salt tectonics in the Tarim Basin in China.

The storage of CO₂ in reservoir rocks is a crucial method for mitigating greenhouse gas emissions, but its application in Argentina, especially in the San Jorge Gulf basin, remains unexplored. Our study focuses on understanding how CO₂ affects the mechanical, petro-physical, and chemical properties of the Castillo and Pozo D-129 formations, which con-tain varying amounts of pyroclastic material. Rock samples were collected, core-drilled, and subjected to supercritical CO₂ conditions. Tests included uniaxial compression, air permeability, mercury porosimeter, XRF and XRD. Findings revealed that rocks after supercritical CO₂ aged treatment reduce the mechanical strength between 14 to 28%. Chemical analyses find variations in the mineral composition between carbonated and non-carbonated samples. Additionally, a reduction in porosity was observed in the treated specimens.

Robust geomechanical models are critical for forecasting and monitoring geomechanical issues associated with hydrocarbon production. Geomechanical responses to carbon utilisation and storage(CUS) have received little attention in the literature. This research proposes to investigate the poromechanical response of faulted depleted gas fields to CUS. The study area is located in the Bredasdorp Basin in South Africa. A one-way coupled geomechanical model is developed to gain insights into the geomechanical challenges related to CUS in faulted depleted gas fields. This model combines a dynamic model derived from earlier studies on the EM gas field with a 3D geomechanical model created using Petrel software. Particular attention is given to modelling the 3D petrophysical Young modulus in the underburden to obtain a more accurate mechanical response. Three geomechanical deformation case scenarios were formulated to assess the behaviour of the E-M gas field. The first scenario, known as the Depletion case, involved simulating natural gas production for nine years. In the second scenario, EGR_CO₂, EGR was simulated in the depleted gas field for 17 years, followed by CO₂ storage for 40 years. The final scenario, STORE_CO2, focused on injecting CO₂ into the depleted gas field over 40 years. The research outcomes unveiled notable observations regarding the geomechanical aspects. One signification revelation was the substantial contrast in the change in stress between the central and peripheral regions of the reservoir. Moreover, during the depletion phase, the reservoir experienced a subsidence of 30 cm, while an uplift of 18 cm was observed during the injection phase. Additionally, it was found that the uplift of the underburden compensated for the loss of fluid support, enabling the reservoir to uphold the overlying overburden despite the liquid phase depletion. However, after 40 years of CO₂ injection, the caprock exhibited failure, whereas the reservoir rocks remained stable. Furthermore, depletion heightened the probability of fault slippage, whereas CO₂ injection significantly reduced deviatoric and shear stresses, indirectly minimising the tendency of fault activation. Finally, the geomechanical issues associated with fluid injection in the reservoir during EGR depend on whether the production of natural gas balanced CO₂ injection. The reservoir is expected to remain stable if injection and production are balanced.

Naturally fractured/cleated coals are likely to develop viscoelastic strain rate-dependency during geological engineering activities such as coal mining, coal seam gas production and gas injection into coal seams. A full investigation of strain rate-dependency of naturally fractured coals is thus crucial to have safe and optimised coal seam operations. The micro-scale mechanisms causing the core-scale rate dependent observations, however, are not yet fully understood. In this study, we conduct a series of systematic multi-scale experiments to shed light on the mechanisms controlling the strain rate dependency of coal. The multi-scale experiments consist of core-scale triaxial testing of coal specimens with different strain rates under isotropic and deviatoric loading on different coal specimens. Every loading is followed with an unloading to analyse the energy dissipation during the tests and ensure that any bulk damage is avoided. A series of micro-scale tests on jointed coal specimen coupled with microscopy and digital image correlation (DIC) analysis is additionally conducted to further study the micro-scale processes controlling the macro-scale strain rate-dependent behaviour of the specimens. The results of triaxial tests on dry specimens show a clear strain rate-dependency under isotropic loading where a higher strain rate causes a stiffening effect on coal specimens. No strain rate-dependency is, however, observed for specimens under isotropic loading when fractures are closed by carbon dioxide (CO₂) saturation at different pressures nor under deviatoric loading for any specimens. Unloading of specimens, on the other hand, shows a considerable strain rate dependent energy dissipation in isotropic loading tests. The results of the micro-scale tests on coal’s fracture interestingly indicates that the asperities damage under normal stress controls the energy dissipation and strain rate-dependency of the bulk of specimens. The combined results reveal that, for the first time, the strain rate-dependency in naturally fractured coal within its elastic limit is attributed to damage of the asperities of pre-existing fractures under fracture closure process.