Shear Slip Failure Research Articles

Experimental study on mechanical properties of S-RM with different rock block proportions in fault zone

The distribution range of soil-rock mixtures (S-RM) in fault zones is wide, with significant differences in mechanical properties, making them the main sites for rock instability and support structure failure in mines. This paper takes the Sanshan Island fault zone as the engineering background, and uses a self-designed small-scale test device to conduct triaxial compression tests to study the strength and deformation failure laws of S-RMs with different rock block proportions (20%, 40%, 60%, and 80%). Combined with numerical simulation test results, the spatial transport laws and microscopic deformation failure characteristics of particles with different particle sizes in the S-RM are revealed. The main conclusions drawn are as follows: (1) For S-RMs with rock block proportions (RBP) of 20%, 40%, and 60%, there is a linear positive correlation between confining pressure and peak strength. When the RBP increases to 80%, there is a non-linear positive correlation between the confining pressure and peak strength of the S-RM sample. Under the same increase in confining pressure, the increase in peak strength of the sample decreases. The influence of confining pressure on the strength and deformation characteristics of S-RMs with high RBP is reduced. (2) During the process of increasing the RBP from 20 to 60%, there is a linear positive correlation between the RBP and peak strength of the S-RM sample. When the RBP increases to 80%, the peak strength of the sample experiences a sudden increase, with an increase of nearly 80 kPa in peak strength. When the RBP is high, the S-RM sample exhibits the mechanical properties of block rocks. (3) The cohesion and internal friction angle of the S-RM sample are positively correlated with the RBP. During the process of increasing the RBP from 20 to 80%, the cohesion increases from 83.12 kPa to 119.38 kPa, and the friction angle increases from 6° to 11°. (4) When the RBP is low (20% and 40%), as the experiment progresses, a significant conjugate shear deformation zone will form within the S-RM sample, and block rock particles will migrate towards this area and undergo shear slip failure between particles. When the RBP is high (60% and 80%), splitting failure mainly occurs at the bonding surface between block rock particles and soil particles inside the sample, and the contact force between particles is relatively large. The relevant research results have important social and economic value for revealing the fracture failure laws of rock masses in fault zones and ensuring the safe development of human engineering activities.

Effect of Lateral Pressure on the Stability of Inclined Layered Rock Tunnel: A 3D-printed Model Investigation by Cement-based Materials

The inclined layered rock tunnel engineering in the alpine canyon area subject to tectonic stress will be influenced by high lateral stress. Currently, there are scarce reports on the impact of the lateral pressure coefficient on the stability of inclined layered rock tunnels. Hence, the mechanical response of the inclined layered tunnel model was investigated based on the 3D-printed model test, supplemented by acoustic emission (AE) and digital image correlation (DIC) monitoring methods under three cases of lateral pressure coefficients of 1.2, 1.5 and 1.8. The results reveal that for the tunnel model with a 60° bedding inclination, the bearing capacity is negatively correlated with the lateral pressure coefficient. The normal deformation of the bedding of the tunnel model is prominent, exhibiting significant asymmetric deformation characteristics. When the lateral pressure coefficient k increases from 1.2 to 1.5, the failure of the tunnel model changes from shear-slip failure along the layer to bedding cracking and buckling failure of the sidewall. The test results have enlightenment significance for the stability evaluation of inclined layered surrounding rock tunnels in the alpine canyon area.

Phase field modelling of tunnel excavation damage in transversely isotropic rocks

Layered rocks, prevalent in geological formations, exhibit complex failure behaviours driven by pronounced anisotropy in their mechanical properties. However, the intricate failure mechanisms remain inadequately understood due to the spatial complexity of these mechanical responses. To address this challenge, this study proposes a novel phase field model tailored for layered rocks. A new strain energy decomposition method is introduced, uniquely formulated based on stress components and designed for transversely isotropic constitutive models. Numerical solutions to the coupled stress-phase field equations are obtained using user-defined element and material subroutines, implemented through a staggered solution scheme. The accuracy and robustness of the numerical approach are validated through simulations of a composite panel with a central hole under tensile loading. Additionally, the model is applied to the excavation of the layered soft rock tunnel, revealing the significant influence of bedding plane angles on displacement and stress field distributions, as well as post-excavation failure modes. Notably, the model captures the predominant shear-slip failure along bedding planes following excavation, effectively reflecting the complex mechanical interactions in layered rocks. This proposed model represents a significant advancement in understanding the failure mechanisms of layered rocks, providing a valuable tool for future geotechnical applications.

Study on mechanical behavior of inclined cemented tailings composite backfill (CTCB) under uniaxial compression

The goaf volume in the vacancy method of hard rock mines is significantly larger than the filling capacity, forming layered and inclined planes during the large-scale filling process. This results in unclear mechanical impact mechanisms on the backfill. To investigate the effect of interface inclination angle on the mechanical behavior of backfill, a set of cemented tailings composite backfill (CTCB) samples with interface inclination angles of 15°, 30°, and 45° are prepared. Uniaxial compression tests and digital image correlation techniques are used to investigate the influence of various interface inclination angles on the strength, deformation behavior, and failure mode of the CTCB. The results show that: (1) The uniaxial compressive strength (UCS) of the CTCB weakens with increasing interface inclination angle but consistently shows exponential growth with curing age (CA) regardless of the interface inclination angle. (2) The interface inclination angle controls the behavior and classification characteristics of the stress-strain curve of CTCB samples, and the increase of interface inclination angle weakens the elastic modulus. (3) The interface inclination angle significantly influences the failure mode and classification characteristics of the samples compared to CA and tailing-to-cement ratio (TCR), with shear slip failure induced by the former and axial splitting failure induced by the latter. The research provides a theoretical basis for understanding the mechanical behavior and stability control of inclined CTCB in underground mining.

Experimental research on creep characteristics and failure mechanism of mining roadway in nearly vertical coal seams

Introduction: Nearly vertical coal seams present a significant challenge for the coal mining industry due to their difficult accessibility. However, these seams account for a substantial proportion of the world’s coal reserves. Therefore, it is vital to conduct research on disaster control techniques for safe mining of these seams.Method: The research team used experimental research, theoretical analysis, and numerical calculation methods to investigate the creep characteristics and failure mechanisms of layered sandstone roadway in nearly vertical coal seam.Results and discussion: These findings revealed that the maximum moment and concentrated stress of the sandstone located on the side of the roadway roof was positioned in the middle of the nearly vertical structure, making it more susceptible to transverse shear failure. On the other hand, the nearly vertical structure on the floor side was prone to shear slip failure initiated from the bottom of the structure. This led to the asymmetric instability of the roadway. The practical implications of this research are significant for the safe mining of nearly vertical coal seams. The results could help inform the development of disaster control techniques.

Propagation and complex morphology of hydraulic fractures in lamellar shales based on finite-discrete element modeling

We explore the controls of stress magnitude and orientation relative to bedding on the resulting morphology/topology of hydraulic fractures using a combined finite-discrete element method (FDEM). Behavior is shown conditioned by the ratio of principal stresses λ=σ3/σ1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda ={\\sigma }_{3}/{\\sigma }_{1}$$\\end{document} and relative inclination of the bedding. When the lateral pressure coefficient (λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda$$\\end{document}) is less than 0.67, hydraulic fractures predominantly initiate as tensile fractures along the wellbore, aligning with the maximum principal stress direction. Conversely, for λ≥0.67\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda \\ge 0.67$$\\end{document}, shear cracks are favored to initiate for the minor stress difference, leading to a less predictable initiation and extension direction. Simultaneously, diminished stress differences correspond to elevated reservoir breakdown pressures, displaying a linear correlation with lateral pressure coefficients and little influenced by equivalent bedding orientation. Bedding plane orientation significantly impacts the mode and morphology of hydraulic fracture propagation. Bedding parallel to the direction of the minimum principal stress (σ3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\sigma }_{3}$$\\end{document}) favors layer-penetrating and bifurcated fractures, whereas inclined bedding facilitates the emergence of numerous steering-type and capture-type fractures. Especially at steeper inclinations (β=60∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta =60^\\circ$$\\end{document}), hydraulic fractures readily extend along the bedding surface, inducing macroscopic shear slip failure. Under high-stress disparities, the breakdown pressure exhibits greater sensitivity to bedding inclination, and its influence pattern aligns with the variations in tensile strength, typically reaching maximum and minimum values at bedding inclination angles of 0° and 60°, respectively.

A damage constitutive model of layered slate under the action of triaxial compression and water environment erosion

Based on the macroscopic structure control theory, The slate with a significant bedding plane is a composite rock mass composed of rock blocks containing microscopic defects, joint surface closure elements, and shear deformation elements. Considering the coupling damage effect of water erosion and triaxial compressive load on bedding structure plane, the transversely isotropic damage constitutive model of slate under triaxial compressive load is derived with the dip angle of bedding and confining pressure as the variable. Firstly, based on the statistical theory of continuous damage mechanics and the maximum tensile strain criterion, the transversely isotropic deformation constitutive model of rock block with micro-defects is given; Secondly, based on the phenomenological theory of closed deformation and shear-slip deformation mechanism of layered structural plane under the coupling action of water erosion and triaxial compression load, the calculation formula of axial deformation of layered structural plane under the coupling action is given; Finally, to verify the accuracy of the established constitutive model, triaxial compression tests are carried out to study the influence of dip angle and confining pressure on the macroscopic mechanical properties and mechanism of slate. The results show that: the established triaxial compression damage constitutive model of bedding slate can accurately describe the stress–strain relationship of bedding slate after water environment erosion. With the increase of bedding dip angle, the strength and deformation capacity of the bedding slate first decreases and then increases, showing a U-shaped distribution as a whole. There are three main types of failure: tension shear composite failure, shear slip failure, and splitting tension failure.

Brittle rock mass failure in deep tunnels: The role of infilled structural plane with varying dip angles

Filled rock discontinuities are commonly encountered in underground engineering excavations, and their mechanical behavior has a significant impact on the stability of surrounding rocks. However, their performance under three-dimensional stress conditions has rarely been explored in the past. In this study, we summarized the typical failure characteristics of filled structural planes in deep-buried tunnels and conducted laboratory true triaxial tests on granite specimens to investigate the effect of dip angle and infill thickness on the failure characteristics of high-stress brittle surrounding rocks. The study monitored the characteristics of vertical stress-displacement, acoustic emission, acceleration, and failure process of granite specimens during the loading process and revealed the failure mechanism of brittle rock masses under the influence of infill thickness and structural plane dip angle. The results showed that the dip angle of structural planes has a significant influence on the failure mode of rock masses in deep tunnels. There exists a critical range of dip angles, within which the rock mass undergoes shear slip failure along the pre-existing structural plane, manifested by rock spalling near the structural plane. Beyond this critical range, the rock mass experiences strain-type brittle failure, characterized by violent rock ejection. Furthermore, the filling of structural planes can change the failure mode of rock masses and lead to more severe damage when the friction coefficient of the structural plane falls below a specific threshold. Additionally, it was revealed that a perpendicular ejection force exists on the free surface of the rock mass under loading, which is approximately vertical to the normal direction and is the primary factor responsible for the formation of vertical parallel cracks within the rock mass. The findings of this work are of paramount importance for comprehending the failure characteristics of deep-buried tunnels containing infilling joints.

Shear Mechanical Properties of Bolt-Grout Interface under Different Bolt Surface Profiles

The shear behavior of the Bolt-Grout interface has a significant effect on the stability of a bolting system. In this paper, a series of shear tests were conducted on Bolt-Grout interfaces, and the effects of rib spacing, rib angles, and normal stress on the shear characteristics and failure modes of the Bolt-Grout interface were investigated. The results showed that the shear strength varied nonlinearly with an increase in rib spacing and angle, and also that it increased linearly with an increase in normal stress. With smaller rib spacings, the effect of rib spacing on peak shear strength was more apparent. The failure modes of the interface can be categorized as shear-slip failure, shear-break failure, and composite failure. The proportion of shear-slip failure and shear-break failure mainly depends on the rib spacing, rib face angle and normal stress.

Experimental study of uniaxial compressive mechanical properties of rough jointed rock masses based on 3D printing

Abstract Roughness and inclination are important factors affecting the strength and deformation properties of jointed rock masses. Serrated joint specimens with varying joint roughness coefficient (JRC) and inclination angle were manufactured by 3D printing technique and cement mortar material. Then, uniaxial compression tests were performed for serrated joint specimens. The results show that when inclination angle equals 0° or 90°, the stress–strain curves of serrated joint specimens with various JRC values are basically the same and display a similar variation trend as that of the complete specimen, hence JRC presents a very little impact. When inclination angle varies from 30° to 60°, the stress–strain curves display a significant difference for various JRC values. Both the compressive strength and peak strain increase with the JRC value. With the increase in JRC value, the stress–strain curve exhibits a stress drop point, and with the further increase in JRC value, the stress drop point obviously delays or disappears directly. Variation in uniaxial compressive strength and deformation modulus with inclination angle is approximately U-shape for serrated joint specimens and displays typical anisotropic characteristics. Due to the variation in inclination angles and JRC values, failure modes of serrated joint specimens under uniaxial compression varies from splitting tensile or shear slip failure to compound tensile and shear failure. Rough serrated joint has a strengthening effect on the resistance ability to vertical load, and large roughness can effectively slow down the shear slip failure of jointed rock masses.

Numerical Analysis of Interbedded Anti-Dip Rock Slopes Based on Discrete Element Modeling: A Case Study

Varying geological conditions and different rock types lead to complex failure modes and instability of interbedded anti-dip rock slopes. To study the characteristics of failure evolution of interbedded anti-dip slopes, a two-dimensional particle flow code (PFC2D) based on the discrete element method (DEM) was utilized to establish an interbedded anti-dip rock slope numerical model for the Fushun West Open-pit Mine based on the true geological conditions and field investigations. The slope model with an irregular surface consists of interbedded mudstone and brown shale as two different rock layers, and a number of small-scale rock joints are randomly distributed in the rock layers. The influence of different inclination angles (20° and 70°) of the rock layer and slope angles (60° and 80°) on the stability of interbedded anti-dip rock slopes was considered. The evolution of the failure progress was monitored by the displacement field and force field. The simulation results showed that the rock joints in the rock stratum promoted crack initiation and increased the crack density but did not change its shear-slip failure mode. A large inclination angle of the rock layers and slope angle can lead to topping slip failure along the slip zone. However, shear-slip instability generally occurs in interbedded anti-dip rock slopes with small inclination angles of the rock layer and small slope angles. These results can contribute to a better understanding of the failure mechanism of interbedded anti-dip rock slopes under different geological conditions and provide a reference for disaster prevention.

Failure Behavior and Surrounding Soil Stress Responses of Suction Anchor in Low-Strength Muddy Clay

Anchorage failure of a suction anchor is more likely to occur in low-strength muddy clay. This paper focuses on the failure behaviors of suction anchors and muddy clay stress responses. The centrifugal model test was used to study the loading processes of suction anchors with various pulling angles. Firstly, the multi-stage developing process of anchoring force was analyzed according to the test results. Numerical modeling was used to validate the test results. The displacement of the suction anchor and muddy clay soil were analyzed using the numerical results. Then, the numerical and testing results were compared to analyze the horizontal soil pressure responses around the suction anchors. It was found that the change in loading direction affected the distribution and development of soil stress. The horizontal soil resistance played a crucial role in improving the bearing capacity. The soil stress variation and anchor displacement revealed that the suction anchors exhibited multi-attitude coupling movement during the inclined pulling. The vertical pulling suction anchor showed shear–slip failure behaviors, while the inclined pulling suction anchors showed compression–shear–slip coupling failure behaviors. The results of this study provide insight into the interaction mechanism between suction anchors and muddy clay, serving as a reference for the design and application of suction anchors.

In-Situ Test and Numerical Simulation of Anchoring Performance of Embedded Rock GFRP Anchor

Compared to traditional steel reinforcement, GFRP anchors demonstrate outstanding mechanical performance and corrosion resistance, and so they are an ideal substitute for steel reinforcement in anti-floating projects. Based on finite element software, a 3D axisymmetric calculation model of GFRP anti-floating anchors in medium-weathered granite was established in this paper. Combined with the in-situ ultimate pull-out tests, the bonding anchoring performance and bearing characteristics between the anchor body, anchoring mortar, and rock–soil mass were analyzed. The research findings indicated that the cohesive bonding elements exhibited a high degree of conformity in defining the interface contact relationship of the GFRP anti-floating anchor anchoring system. The axial force of the GFRP anti-floating anchor body is “attenuated” along the depth direction, and there was a critical value of anchoring length; under the same conditions, the reasonable anchoring length should be 3.5~5.0 m. All the anchors in the in-situ tests exhibited interfacial shear slip failure between the anchor body and the anchor mortar, with an average maximum load of 450 kN, which is consistent with the maximum failure load of the simulated anchors. Compared to a load of 50 kN, the maximum stress of the anchor mortar increased by 50% under a load of 450 kN. The displacement variation of the surrounding rock–soil mass showed a decreasing trend from the inside to the outside and from the top to the bottom. The research results provided valuable references for the optimization design of GFRP anti-floating anchors.

Dynamic Mechanical Behavior of Rock Specimens with Varying Joint Roughness and Inclination under Impact Load

The influence of joint roughness and inclination on the dynamic mechanical properties of rocks is a prominent research area. In order to investigate the effects of joint roughness and inclination on the dynamic mechanical properties of jointed rocks, impact tests were conducted using a spilt Hopkinson pressure bar (SHPB) apparatus for prefabricated serrated joint cement mortar specimens with varying joint roughness and inclination. The failure mode, stress wave propagation characteristics, peak stress, and stress wave energy transfer law under impact load were analyzed. The results indicate that both joint inclinations and joint roughness coefficients (JRC) have a strong influence on the failure mode, peak stress, and stress wave energy transfer of jointed specimens. The jointed specimens exhibit three distinct failure modes under impact load, namely splitting tensile failure, shear slip failure, and compound failure of splitting tensile and shear. The peak stress initially decreases then increases with the increase in joint inclination angle, namely a V-shape variation, while it gradually increases with JRC increasing from 0 to 20. Jointed specimens exhibit the lowest peak stress at an inclination angle of 45° and JRC of 0. The variation of transmitted energy coefficient is similar to the peak stress, while the variation of reflected energy coefficient is opposite to the peak stress. At joint inclination angles of 0° or 90°, the reflected energy coefficient increases with the increase of JRC from 0 to 20, while the transmitted energy decreases. However, when the joint inclination angle is in the range of 30° to 60°, the reflected energy coefficient gradually decreases with JRC increasing, while the transmitted energy coefficient gradually increases.

Combined effects of freeze–thaw cycles and chemical corrosion on triaxial mechanical properties of sandstone

To study the combined effects of freeze–thaw cycles and chemical corrosion on deterioration mechanism of triaxial mechanical properties of sandstone in cold regions, triaxial compression tests were carried out on homologous sandstone specimens after corrosion action of acidic, alkaline or neutral solution and cyclic freeze–thaw action, by taking the pH value of the hydrochemical solution and the number of freeze–thaw cycles as control parameters. The failure mode of triaxial compression is shear-slip failure, and the deviatoric stress–strain curves can be divided into four stages of compaction, linear elastic, yield, and failure. The stress–strain curves and deterioration law of triaxial mechanical properties were analyzed. With the increase of freeze–thaw cycles, the peak stress, peak strain and modulus all decrease, the deterioration degree of the rock specimens increases, and the yield plateau and plastic characteristics in the yield stage become weaker. The strong acid solution shows the largest degree of damage, and the peak stress, peak strain and modulus decreased significantly. The precipitates produced by the reaction between the strong alkaline solution and the specimens adhere to the specimen surface, pores, and fissures, thereby inhibiting further damage and deterioration. Confining pressure is an essential factor affecting the rock mechanical properties. As confining pressure increases, the strength and deformation-resistant ability of specimens increase, and the yield stage on the stress–strain curve is more obvious. The sensitivity of acidic solution to the deterioration of mechanical properties of sandstone is obviously greater than that of alkaline solution. These results provide a theoretical basis for the construction of geotechnical engineering structures in cold regions.

Experimental Study of the Mechanical Properties of a Flexible Grid Filling Body

The fill mining method has become more widely used due to its advantages of a high resource recovery rate, reliability and safety, and reduced surface tailings storage. However, the mechanical properties of the cemented fillings in fill mining are similar to those of ultra-low strength plain concrete, and there are problems such as high brittleness, low bending and tensile strength, and sudden failure. Using a flexible grid as reinforcement material, uniaxial compression, tensile, and shear tests of a flexible grid filling body were carried out, and the results were compared with the mechanical properties of the filling body without the flexible grid. We drew the following main conclusions: the uniaxial compressive strength of the flexible grid filling body gradually increased with the decrease in the grid spacing (the increase in the grid density); the grid dimension had little effect on the uniaxial compressive strength of the flexible grid filling body. The uniaxial tensile strength and shear strength of the flexible grid filling body increased with the increase in the grid dimension; and they first increased and then decreased with the increase in the grid spacing, and there was an optimal grid spacing. From the perspective of the macroscopic failure mode, the flexible grid filling body specimen after the uniaxial compression test had a conjugate shear failure, forming a “dumbbell shape” with two large ends and a small middle. After the uniaxial tensile test, the macroscopic failure mode of the specimen was tensile failure. After the shear test, the macroscopic failure mode of the specimen was shear slip failure. It is proposed that the tensile strength, shear strength, cohesion, and internal friction angle strengthening coefficients of the flexible grid filling body with different dimensions and spacing are higher than the elastic modulus strengthening coefficients. The experimental results can provide a certain reference and guidance for mine filling.

Damage characteristics of weak rocks with different dip angles during creep

To investigate the influence of the weak layer dip angle on the creep rupture of the composite rock mass, this paper conducts a graded loading creep experiment on the composite rock mass with different dip angles using the acoustic emission method to examine the fracture evolution process. With increasing load grade, the cumulative total ring count of the rock mass shows a “U”-shaped trend, and the acoustic emission spatial positioning results show that acoustic emission events in the rock mass fracture process are primarily concentrated in the vicinity of the weak layer, while events in other areas are few and dispersed. For rock masses with weak layer dip angles of 0° and 15°, cracks occur in both soft and hard rocks, where shear cracks are dominant in soft rocks, tensile cracks are dominant in hard rocks, and finally, the rock mass mainly exhibits tensile splitting failure. For rock masses with weak layer dip angles of 30° and 45°, most of the cracks exist in the interior of the soft rock, which is dominated by shear cracks. With increasing graded loads, the shear cracks continue to develop along the direction of the weak layer, the upper rock mass keeps slipping and dislocating, and the final failure mode is mainly shear-slip failure. The damage evolution varies with the inclination angle of the weak layer, which can be divided into three stages: initial damage accumulation, damage acceleration, and damage destruction. This demonstrates the ability to predict, prevent, and control the occurrence of creep disasters in rock masses with weak layers.

Unstable Shear Slip Failure and Seismic Potential Investigation Using DEM in Underground Mining

Perturbations arising from mining operations significantly affect the stability of rock masses, and the influences aggerates with the rapid increase of mining-operation depths during recent years. The subsurface structures with major discontinuities subject to seismic hazards resulted from the shear-slip behaviors of rock masses. In order to identify the shear-slip regime of discontinuities and calculate seismic moment and seismic energy involved with shear-slip behaviors, we use discrete element modeling to study the shear slip failure along discontinuities in an underground mine. The recorded characteristic and properties of sub-contacts in DEM provide a basis for computing and visualizing the temporal and spatial distribution of seismic moment and seismic energy with mining operations. We computed the seismic energy and seismic moment using the numerical modeling method and the analytic method. We compared the result of summing seismic energy and seismic moment from the subcontacts of numerical models and the result of the analytic method. We confirmed that this tool can be used in comparative analyses. We also found that seismic moment and seismic energy, associated with shear stress drop and shear displacement increase, accumulate in the vicinity of major discontinuities. Mining operations at a greater depth cause greater changes of seismic moment and seismic energy, leading to a higher risk of inducing seismic hazards. Quantifying seismic potential using discrete element modeling can greatly facilitate the investigation of instability of geological discontinuities and thereby can help estimate the potential of seismic hazards.

Study on the Solid Production Mechanism of the Fractured Granite Reservoirs-Example of YL Area in Qiongdongnan Basin

The granite buried hill gas reservoir in YL area of Qiongdongnan basin faces a serious problem of solid production, which seriously affects gas well production and reduces economic benefits; however, the solid production mechanism of fractured granite reservoirs is still unclear. In this study, the reasons for solid production were revealed and the mechanism was clarified based on the analysis of geological and mechanical characteristics of the granite buried hill reservoir. The solid production of fractured granite reservoirs can be divided into three modes, those being shedding of fracture filling and solid particles on the fracture wall, shear slip failure along the fracture, and shear failure of granite matrix. Take the YL area in the Qiongdongnan Basin as an example, the solid production of fractured granite reservoirs is mainly based on shedding of fracture filling and solid particles on the fracture wall and shear slip failure along the fracture, the possibility of shear failure of granite matrix is less. In addition, the closer the wellbore, the greater the risk of shedding of fracture filling and solid particles on the fracture wall. The high-angle fractures have a greater risk of shear slip failure. In addition, the direction of the minimum horizontal principal stress is higher risk of solid production. The research provides the basis and foundation for safe and efficient development of fractured granite reservoirs and for later measure selection and optimization.

Study on Mechanical Properties and Crack Propagation of Raw Coal with Different Bedding Angles based on CT Scanning.

The deformation and damage characteristics of coal are the important foundation that affects the fracturing potential of coal reservoirs and the development plan of coalbed methane (CBM). To reveal the influence regulation of primary fractures and the bedding angle of coal on its failure and provide theoretical basis for CBM development, raw coal samples of no 16 coal seam in Wenjiaba Coal Mine, Zhijin County, Bijie City with different bedding angles were selected as the research object, and uniaxial compression tests were carried out on them, and CT scanning and crack reconstruction before and after sample failure were carried out. The results show that (1) the compressive strength, elastic modulus, and Poisson’s ratio of coal show a strong bedding angle effect, and the changing trend of each index is basically the same. The coal samples with bedding angles of 0 and 90° are the highest, while the coal samples with bedding angles of 30° are the lowest, and the overall distribution is an approximate “U” with the increase in bedding angle. With the increase in bedding angle of 0–90°, the failure modes of coal samples are tension-shear combined failure, shear-slip failure, and splitting tension failure in turn. (2) The observation of raw coal and CT scanning show that the primary cracks in coal samples are well developed, especially in the lower part of 0° samples, the cracks in 30° samples, 60° samples, and 90° samples are evenly distributed and develop at a certain angle with the weak bedding surface, and microcracks parallel to and nearly perpendicular to the weak bedding surface are developed in 45° samples. At the same time, banded minerals in coal and rock samples are also well developed. (3) The characteristics of crack propagation and evolution in coal samples with different bedding dip angles are significantly different. The bedding dip angles and primary cracks of coal seam have a great influence on crack propagation. With different bedding angles, the propagation modes are different. The crack propagation mainly includes two ways: forming a certain angle with bedding and extending along the bedding plane. (4) The fracture characteristic parameters of coal in the primary state and after failure have the same law with the bedding dip angle, showing a trend of high at both ends and low in the middle, which is an irregular “U”-shaped distribution and has a similar law with mechanical characteristic parameters.