A methodology is proposed to estimate the dilation parameter, m_dil for intact sedimentary rocks in the plastic region based on the Hoek–Brown yield criterion. Monotonic triaxial compression tests are performed on shaly sandstone and fine-grained sandstone under confining stresses ranging between 4 and 30 MPa. The results show that the peak m_dil is related to σ_3/σ_c , where σ_c represents the uniaxial compressive strength of the rock. A three-parameter non-linear m_dil model describing the development of dilation as a function of cumulative plastic shear strain is developed based on the observed experimental results, and the model parameters are determined by regression analysis. These parameters are found to be closely related to the confining stress. A dilation index is also estimated as a function of stress ratio between deviatoric principal stress and normal stress to highlight the trends of dilation/contraction in the elastic region, yield point, peak stress point, and post-peak region. The proposed model is then implemented in an in-house developed finite element code to compare displacements and plastic volumetric strains around a circular tunnel with those of constant m_dil models. The simulation results show that a constant m_dil ​ does not produce realistic plastic deformation around the tunnel boundary in comparison to a mobilized m_dil . The study concludes that the mobilized m_dil model may be combined with the Hoek–Brown yield criterion for sedimentary rocks to analyze non-associative plastic behavior and displacement distribution in engineering practice.

Finite Element-based Digital Image Correlation (FE-DIC) procedures are developed to determine full-field displacements, specifically for the analysis of discontinuous rock samples. This study evaluates the mechanical behavior of grouted discontinuities in geomaterials, capturing the effects of joint morphology, grouting material, and loading conditions through the FE-DIC approach. Artificial joints were introduced in sandstone, basalt, and concrete specimens with inclinations of 30 ^∘ and 45 ^∘ , and grouted using epoxy resin, cement mortar, and polyvinyl acetate. The specimens were subjected to uniaxial loading to induce Variable Normal Load (VNL) conditions across the joints, and the full-field displacement data were captured using FE-DIC alongside conventional LVDT and UTM measurements. The FE-DIC technique facilitated the quantitative extraction of mechanical parameters such as normal and shear stiffness, enabling its use as a characterization tool rather than solely a deformation measurement method. For rough joints, a Richards’ three-parameter logistic model was fitted to capture the non-linear stress-displacement behaviour, and a new parameter, the specific energy of the joint, was introduced to quantify mechanical energy utilized per unit area for the movement of the joint surface. The spatial distribution of this parameter along the joint length revealed the influence of grouting materials and demonstrated how the proximity of a circular cavity alters the joint’s shearing behaviour. The study also compared Variable Normal Load (VNL) tests with conventional Constant Normal Load (CNL) direct shear tests, showing that shear stiffness under VNL conditions is significantly higher due to load-path dependency. Overall, the work demonstrates the efficacy of FE-DIC as a visualization tool and a rigorous method for the quantitative characterization of jointed geomaterials.

Stope pillars and long-standing drives are left in between two mined-out panels/stope blocks in a room and pillar mine for accessing the dip side panels in order to transport men, materials and machinery. Hence, it is imperative that these drives and mined-out panels remain stable until an alternative transport arrangement is made. Rock quality in the mine changes both in strike and dip directions with GSI ranging from 30 to 60. This study comprises of the stability analysis of two stope designs with 4 m pillar and either 6 m or 8 m room size using numerical modeling technique. The variations of rock mass properties are also incorporated in the analysis with filling and non-filling options. Vertical stresses in stope pillars are also monitored to ascertain the change in ground conditions with mining operations. A total of 16 numerical models are analyzed considering elasto-plastic conditions using Mohr-Coulomb failure criterion. The analysis of equivalent plastic strain (EPS) on the stope pillars suggests that no stope blocks can be mined without filling if GSI of orebody is 40 or below. This study develops two stability charts one for stope pillars inside the panel and the other for pillars along the long-standing drives. These charts help taking judicious decisions for the support system as well as accessing the stope blocks in the dip side panels through the mined-out panels.

Hydrogen is increasingly recognized as a pivotal component in the future of sustainable energy and the transition to a low-carbon economy. Surface-based hydrogen storage methods, such as compressed gas and liquid hydrogen storage, have limitations in terms of capacity, safety, and energy losses during the storage and retrieval processes. The geological formations such as caverns or depleted reservoirs provide a unique and potentially more effective repository for hydrogen with abundant storage capacity. This study investigates the details of subsurface hydrogen storage briefly reviewing the usage of hydrogen as a fuel and its physical and chemical characteristics. It explores the hydrogen production techniques and suitability for securely housing hydrogen. Additionally, it delves into the feasibility for subsurface storage of hydrogen and the potential challenges and risks. In sum, we outline the prospects for LRC-based hydrogen storage in India, and offer an insightful survey for implementation of large-scale storage systems.

Understanding the reinforcement mechanism of the polymeric liner using numerical models is key to measuring its performance for field applications. In this study, numerical models are developed for the coal and the polymer liner, and then, they are validated with the results obtained from the earlier experiments. In the next stage, a field-size coal pillar in an underground mine was simulated to evaluate the liner performance as surface support. In this study, two different scenarios were simulated. In the first case, an unsupported coal pillar was considered, and in the subsequent models, a mine pillar reinforced with polymeric liner was simulated for different thicknesses of liner material, viz. 5 and 10 mm. The results obtained from the numerical simulations are assessed in terms of the major and minor principal stresses and the equivalent plastic strain to evaluate the effectiveness of the liner thickness on the post-yield behaviour of the coal pillar. It was observed that tensile stress was concentrated at the pillar’s corner, which is in the polymeric liner. The extent of damage observed by equivalent plastic strain was nearly 2 m inside the pillar. The magnitude of maximum damage for an unlined pillar is 0.81, and with a 5 mm thickness of liner, the magnitude is reduced by 16

At Hindustan Zinc’s Sindesar Khurd mine an underhand mining methodology has been used to extract the lead-zinc ore from below a depth of 800 m. The rock mass encountered during development and stoping presents challenging mining conditions due to significant strength contrasts, foliation, the presence of faults, and shear zones. For extraction of minerals, the methodology involves back filling of the stopes after they are extracted with cemented paste fill (CPF) which is composed of mill tailings. In this mill tailings, 4

Triaxial compression tests are conducted to determine the dilation behavior of five different rocks, namely, shaly sandstone, fine-grained sandstone (weak), coarse-grained sandstone (weak), fine-grained sandstone (strong), and granite. After yielding, volumetric and shear plastic strains and dilation angles are determined for each sample at every 5-s interval. The dilation angle increases sharply with the initial development of plastic shear strain for strain-softening rocks. On the other hand, for brittle rocks, the dilation angle reaches its peak gradually with plastic shear strain. Based on the experimental data, a three-parameter dilation angle model is developed as a function of plastic shear strain. These parameters depend on the rock types and the ratio of sigma 3/sigma c, where sigma c is the uniaxial compressive strength of rock. In terms of the coefficient of determination (R2), the proposed dilation model fits the experimental data better than the existing dilation model proposed in a previous study . The model also predicts the peak dilation angle more accurately if the angle increases sharply at the initial stages of the plastic shear strain increment. Results show that the prediction error of the proposed model is within 10.27% compared to 15.06% by the existing model. The results also show that the peak dilation angle decreases hyperbolically with the increase of confining stress (sigma 3).

An unstructured Extended Finite Element-based Digital Image Correlation (X-DIC) method is proposed for analysing displacement fields of a rock specimen having a discrete discontinuity. The principle of the X-DIC method is described in the paper and is validated by laboratory experiments. In the experimental setup, a cylindrical hole and an artificial discontinuity plane are embodied into a cuboidal rock specimen and tested under uniaxial compressive load. The surface of the specimen is speckled, and its images taken during the loading process are analysed using the X-DIC algorithm. The results show that the X-DIC can capture non-linear displacement fields and displacement jumps across the discontinuity plane and is effective in estimating the stiffness of joints. The method can also indicate the rock specimen’s onset of cracks and failure before it is visible to the naked eye. It is also demonstrated that X-DIC is a robust method for capturing full-field displacements, in a non-contact manner and can be applied in various rock engineering applications.

The stripping ratio increases as the surface mine gets deeper, causing an increase in the height of waste dump slopes. This threatens stability since dumps are composed of soil-rock mixtures, mostly in an unsaturated state. In this research, field and laboratory studies were carried out on soil-rock mixtures to estimate in situ porosity, a key factor influencing shear strength of these materials, and consequently, the stability of waste dumps at various dump heights. Sand replacement methods in the field and standard Proctor test and consolidated drained triaxial shear tests in the lab were performed to establish the porosity-height relationship curves. It was found that the porosity decreases with height, as described by a negative exponential distribution with an exponent termed the "pseudo-pore mechanical compaction coefficient," which determines the shape of the curve. The proposed relationship was then utilized to evaluate the compaction of soil-rock mixtures at a preresidual state. The parameters of the porosity-height relationship were also assessed for lightly, partially, and fully compacted dump slopes.

Friable chromite ore was extracted from an open-pit mine surrounded by limonitic host rocks which are friable and weathered. The mine has reached its pit limit and it is decided to further extract the ore body by underground methods. However, the conventional mining techniques are not suitable for the desired level extraction from the underground since the surface benches and crown pillar cannot be made stable under the prevailing ground conditions. The GSI value of the ore and host rock is about 25–35 with stand-up time less than one hour. The high monetary value associated with the ore prompts the proposition of an innovative mining approach for extracting the ore from underground. The paper delineates the novel mining methodology, emphasising key aspects of mining and backfilling sequence, providing stope and pillar dimensions with safety factors and support mechanisms for decline and other developments. For this purpose, numerical models of 36 mining and backfilling sequences are developed, incorporating variations in stope and pillar dimensions. The stope width is maintained at 20 m, with variable heights 30 m, 40 m and 50 m, while the pillar width is varied as 20 m, 40 m and 60 m. The models are characterised in terms of strength and stability by introducing a novel sequence factor (SF) and average cumulative plastic strain (ξa), respectively. Their inter-relation helps recommend the safe mining operations.

A novel underground mining method is proposed to extract friable chromite ore bodies in weak and weathered limonitic host rock below an open-pit mine. The conventional underground methods do not instill confidence since GSI (Geological Strength Index) of ore bodies and host rock lies below 35. Series of dimensions of transverse stopes along the strike are suggested based on a detailed analysis of multiple mining and backfilling operations by simulating 36 three-dimensional numerical models. For each operation or sequence, a strength-based "Mining Sequence Factor (MSF)" is devised that helps quantifying its equivalent strength compared to in-situ conditions. This factor along with the Average Equivalent Plastic Strain (AEPS) developed on the pillars as obtained from numerical models is used to determine the safe operations with desired yearly production target. The paper provides an in-depth analysis of this method and suggests minimum pillar dimensions of 40 m, whether insitu or backfilled. The paper, in addition, lays the design of underground drives and their support system as per NGI (Norwegian Geotechnical Institute) guidelines and 3D numerical studies, the performance of which is analysed considering distribution of stress and equivalent plastic strain.

Soil-rock mixtures (SRM) from mine overburden form heterogeneous dump slopes, whose stability relies on their shear strength properties. This study investigates the shear strength properties and deformation characteristics of SRM in both in-situ and laboratory conditions. Total twelve in-situ tests were conducted on SRM samples with a newly developed large scale direct shear apparatus (60 cm x 60 cm x 30 cm). The in-situ moist density and moisture content of SRM are determined. Particle size distribution is performed to characterize the SRM in laboratory. The bottom bench has the highest cohesion (64 kPa) due to high compaction over time while the other benches have consistent cohesion values (25 kPa to33 kPa). The laboratory estimated cohesion values are high compared to in-situ condition. It is further observed that for in-situ samples, the moist density notably affects the cohesion of SRM, with cohesion decreasing by 3 to 5 % for every 1 % increase in moist density. At in-situ condition, internal friction angles are found to be 1.5 to 1.7 times compared to laboratory values which is due to the presence of the bigger sized particles in the SRM. The outcomes of the research are very informative and useful for geotechnical engineers for slope designing and numerical modeling purpose.

A numerical procedure of finite element (FE) method for nonlocal displacement measurement from digital images is proposed. The method is a two-scale model of displacement measurement, which constitutes the classical FE displacement, and a nonlocal displacement measured from the attenuated relative displacement of the neighboring pixels. The traditional finite element-based digital image correlation (FE-DIC) method suffers from noisy and overestimated displacement fields near singularities, analogous to the Gibbs phenomenon. Due to its selective displacement adjustment, the proposed Nonlocal DIC (NL-DIC), detects the displacement jump with reasonable accuracy and smoothen the noise in the vicinity of discontinuity. The algorithm does not require input regarding the affected region from the discontinuity and works as an automated system. The method's de-noising property helps to decrease the displacement uncertainty for finer meshes. A robust, three-parameter Discontinuity Resolution Index (DRI) is introduced to assess the metrological performance of DIC algorithms for discontinuous displacement measurement. The proposed framework is validated on three numerical experiments exhibiting discontinuities. Practical guidelines are provided, underscoring its applicability in capturing sharp kinematic features with improved robustness.

Polymeric liners provide resistance to the shearing of exposed rock layers/ blocks of an excavation. Understanding the reinforcement mechanism of liner through laboratory experiments and numerical models is the key to measure its performance for field applications. A lined beam exhibited strain hardening behaviour under flexural load with an increased capacity as compared to an unlined beam showing tensile-brittle failure. The substrate material and the interface was then modelled numerically to understand the damage behaviour of the samples. The results showed that micro-cracks developed at the interface due to shearing and the growth of micro-cracks was restricted in lined sample. Plastic shear strain distribution in numerical models showed that the material started failing in shear from the supporting rollers. A distinct diagonal shear crack started to form between the loading and the support roller points, causing the ultimate failure. Cracks also propagated laterally along the interface as found during experiments.

ABSTRACT: The assessment of fracture properties such as crack tip opening displacement (CTOD), plastic zone size, and crack development is essential for understanding the behavior of cracks and fractures in geological materials. Crack displacement requires full-field strain measurement as the strain field develops in front of the propagating crack. The point-based strain measurement devices, such as strain gauge and extensometers, fails to capture crack growth. This study proposes a Finite Element based Digital Image Correlation (FE-DIC) method for measuring fracturing process especially, crack tip displacement and associated strain localization. The paper outlines the FE-DIC algorithm and its validation with numerical images and laboratory testing. The numerical images are created using Irwin's near-crack tip displacement approximation function around a center crack in an infinite plate under equibixial tension (Irwin, 1957). In the laboratory, the Mode I three-point bending fracture test is performed on a cuboidal slab of sandstone and basalt rock with a center notch. The results show that the FE-DIC method can capture the non-linear displacement field as the crack propagates and also estimate plastic zone around the crack. The findings of this study provide evidence supporting the efficacy of the global FE-DIC method in visualizing strains and fracture propagation. 1 INTRODUCTION The study of the rock fracturing process is crucial for designing various geotechnical projects such as mines, dams, reservoir, underground nuclear waste disposal, and tunnels (Guo et al., 2023; Xing et al., 2022). Most rocks exhibit strain-softening to brittle behavior and fail without any prior indication. To understand the failure mechanism of rocks due to fracture propagation, the insight of full field deformation under various loading conditions is a necessity. Critical challenges in characterizing the crack-induced rock failure includes locating the crack, estimating its propagation path and identifying the strain localization zone in the crack tip where the stress-strain relationship is non-linear, which acts as the precursor of the macroscopic crack extension known as Fracture Process Zone (FPZ) (Qiao et al., 2023). These challenges are more prominent while dealing with brittle materials like rock, which fails at low strain and thus demands a robust fullfield deformation measurement method.

The role of crown pillar between two main levels in any underground metalliferrous mine plays a pivotal role in maintaining the stability of extracted open stopes in each level.Thus, the dimension of the crown pillar left intact between the main levels in the underground should be competent enough to withstand the induced stresses developed as a result of extraction as well as blasting, especially in large scale production methods such as large-diameter blasthole stoping method.In addition to the crown pillars in adjacent levels, a barrier crown pillar of sufficient thickness is also left intact between the ultimate pit bottom and the first level of extraction.These horizontal pillars are of utmost importance as it is one of the deciding factors in determining the stability of the existing underground structures throughout the life of mine.The present study focuses on the stability of a crown pillar left intact between two main levels existing below an open pit mine operating simultaneously with the underground mine.The targeted proposed production of the underground mine is around 5 million tonne per annum.In this paper, a total of 135 finite element models of the underground mine have been analyzed considering elasto-plastic material model.The simulation models are assessed in terms of plastic damage index with variation in material properties, crown pillar thickness, stope-extraction sequence and depth of mining.Based on the results obtained, some useful conclusions have been drawn considering both multi-variate regression and k-cross validation models.

Hydrogen as an energy source has gained a considerable interest because of its potential to minimize carbon emissions. The storage of hydrogen is the key for establishing a hydrogen value chain and large volume storage in underground can be a promising option. However, selecting an appropriate underground storage facility is a complex task, subject to the thermomechanical behavior of the host rock, as well as of the stored gas under high pressure and temperature. This study aims to provide an overview of the key components related to subsurface hydrogen storage, as well as recent advancements and challenges in commercializing the technology. Lined Rock Cavern (LRC) as a storage facility of hydrogen shows great promise and is the focus of this study. An overview and insight of the prevalent mechanisms of hydrogen embrittlement causing degradation to liner are discussed in the paper. The experimental procedures and modeling techniques of the degradation process at various scales in assessing the safety and stability of large-scale subsurface hydrogen storage facilities, such as LRCs are outlined.

A coupled numerical framework based on smoothed particle hydrodynamics (SPH) and finite difference method (FDM) has been developed to analyze the coupled process of fluid flow in a deformable poro-elastic medium. The salient feature of the developed coupled model is that the porous media has been simulated by two separate layers to describe solid and fluid phase with their respective governing equations and solved simultaneously with mutual transfer of variables from one phase to another. SPH being meshfree method has advantage over grid based methods to simulate large deformations and fracture propagation and hence used for simulating the solid phase while the pore pressure variation in the fluid phase has been analyzed by FDM. Detailed mathematical framework and procedure explaining the mutual exchange of information between SPH and FDM has been discussed in this paper. The change of porosity due to solid deformation and its impact on variation of fluid pressure has also been included in the proposed model. The developed coupled model has been finally validated with three standard benchmark problems by comparing numerical results of the proposed model with those of analytical solutions, to establish its accuracy and versatility in modeling fluid flow through deformable porous rock media.