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Tensile and shear failure are the main damage modes of rocks in geotechnical engineering. To investigate the energy evolution and failure characteristics of coarse-grained sandstone during pure mode I/II loading, loading-unloading tests were performed on cracked straight-through Brazilian discs (CSTBD) with different unloading levels (i), and its acoustic emission (AE) signals and microstructure were monitored. The results show that the AE signals of the CSTBD are negligible before the peak load (Mode I), or appear when the axial load exceeds a stress threshold and then increases significantly before the peak load (Mode II), and the Kaiser effect was observed in the second loading stage. The specimens’ input, elastic and dissipative energies varied quadratically with i. The elastic energy is always greater than the dissipative energy (Mode I), whereas the dissipative energy exceeds the elastic energy at i < 0.5 (Mode II). The crack propagation paths start from the crack tip and extend rapidly and straightly (Mode I) or slowly in the form of wing crack (Mode II) to the loading point. The microstructures of the specimens are mainly intergranular fracture (mode I) and transgranular fracture (mode II). The results provide references for studying energy evolution and failure mechanisms of rocks under mixed modes I+II/I+III loading. [ABSTRACT FROM AUTHOR]

The present study uses the Jiweishan landslide in Wulong District, Chongqing City, China, as an example to design a numerical simulation technique to examine two environmental consequences: corrosion deterioration and underground mining. A shear strength prediction model for the corrosion rate of the structural plane was thus proposed by mimicking the time-dependent weakening characteristics of structural planes by using strength reduction. The discrete element simulation method was applied to reproduce the complete process of dangerous rock body movement and slope instability under the effects of these two factors to clarify the influence of environmental and engineering effects on slope deformation behaviour. This was intended to clarify the overburden movement process, fracture evolution law, and rock formation subsidence characteristics of karst mountains affected by mining from the perspective of geomechanics, and the results showed that the deformation evolution process of the Jiweishan landslide can be divided into two stages: the slow chronic deformation caused by long-term corrosion deterioration and the more severe acute deformation caused by short-term underground mining. The overburden movement and fracture evolution seen under corrosion deterioration and underground mining thus represent a progressive evolutionary process with full spatial and temporal continuity. Corrosion is a long-term synchronous process that creates the transformation of numerous structural planes around a dangerous rock body. Underground mining, in contrast, is typically a short-term trigger factor that can nevertheless easily cause significant differential adjustment of the movement characteristics of different parts of a dangerous rock body that result in distinct spatial differentiations of dangerous rock body movement. Further, the subsidence deformation characteristics of the rock formation plane mainly depend on the spatial position and scale of the goaf created by such mining. Analysing the stress characteristics of the relevant inclined rock strata helps clarify the control mechanism of a mountain's spatial structure's adaptive adjustment. The simulation results in this case were also compared with the results of centrifuge tests and physical model tests to verify the rationality of the simulation scheme, and the conclusions thus remove provide an important reference for the study of landslide development processes and instability mechanisms under multi-factor coupling conditions. [ABSTRACT FROM AUTHOR]

During coal mining operations, the coal will be deformed and damaged due to multiple mining disturbances (MMD), often resulting in disasters, like rock burst. To understand the evolution rules of coal deformation under MMD and its final fracture characteristics after impact dynamic load loading, reduce the adverse effects of mining disturbances, and improve disaster prevention and control capabilities, quasi-static uniaxial cyclic loading-unloading (L-U) and dynamic axial compression tests were conducted on large-sized coal-like samples. During the tests, three-dimensional (3D) laser scanning and acoustic emission (AE) monitoring technology were utilized to accurately capture the full-field deformation and AE response data, facilitating a systematic analysis of deformation and fracture characteristics. The results show that: (1) Under the cyclic L-U effect induced by MMD, each loading cycle causes compression deformation with partial recovery during unloading, presenting an overall "wavy" variation trend. (2) The maximum load is the most critical factor affecting the damaged coal deformation, with smaller load resulting in less overall sample deformation. (3) After the impact dynamic loading, the damaged samples suffered large-scale impact splitting failure, with the compressive-shear layer failure mainly occurred inside the holes. (4) Lower loading during cyclic L-U process correlate with reduced damage degree, and smaller debris particles with a higher fractal dimension when impact failure occurs, indicating a more severe impact failure. (5) With multiple cycles of L-U, the cracks inside the sample gradually extend and expand from around the hole to the outside. The greater the load and the number of cycles, the more serious the crack damage will be. (6) In the practical mining process, it is crucial to reinforce roadway interiors while minimizing low-loading cyclic disturbances induced by MMD. The study has obtained the deformation evolution rules and failure characteristics of coal under MMD, providing a theoretical basis for the prevention and control of corresponding engineering disasters. [ABSTRACT FROM AUTHOR]

Frequent rockburst disasters in deep-buried engineering projects severely impact construction. To explore the influence of axial stress on rockburst in deep-buried tunnels, large-scale true triaxial rockburst experiments were conducted under four different axial stress ratio conditions (ηt, axial loading stress/vertical loading stress) using a self-developed true triaxial loading device under the condition of "pre-loading before excavation". The influence of axial stress on the rockburst process and failure characteristics in deep tunnels was studied using a combination of real-time video monitoring, rockburst debris sieving, and acoustic emission monitoring. The results indicate: (1) all four specimens subjected to different axial stress ratio loading conditions exhibited three stages of macroscopic failure: small particle ejection, flake spalling, and large fragment ejection. Ultimately, "V"-shaped notches appeared on both sides of the tunnel. (2) The failure stress, fragment volume, and fragment size distribution of the rockburst specimens exhibited a clear two-stage failure characteristic with increasing axial stress ratio. In the lower axial stress ratio stage (ηt ≤ 0.7), the increase in the axial stress ratio enhances lateral confinement, thereby increasing the crack initiation strength of the surrounding rock, inhibiting crack formation and propagation, and thus suppressing damage to the surrounding rock of the tunnel. In the higher axial stress ratio stage (ηt > 0.7), the increase in axial stress ratio makes the Poisson effect of the surrounding rock more pronounced, promoting the generation and propagation of cracks along the tunnel axis direction, thereby promoting damage to the surrounding rock. (3) Based on the analysis of acoustic emission parameters (fracture properties), it can be concluded that in the lower axial stress ratio stage (ηt ≤ 0.7), an increase in the axial stress ratio leads to a higher proportion of shear fracture in rockburst damage. Conversely, in the higher axial stress ratio stage (ηt > 0.7), the increase in axial stress ratio gradually reduces the proportion of shear fracture in rockburst damage. [ABSTRACT FROM AUTHOR]

Complex underground conditions make it challenging to conduct extensive coring, and it is difficult for laboratories to carry out a large number of rock mechanics experiments due to the limited number of cores. Rock-like specimens are commonly used in the laboratory to replace coal-rock specimens. In this paper, rock-like specimens with different proportions are produced to study the mechanical properties, failure characteristics, and acoustic emission laws of rock-like specimens under uniaxial compression. The results show that when the rock-like specimen does not contain gypsum, the stress of the specimen decreases rapidly after reaching the peak stress, which is similar to the mechanical properties of hard brittle rock. When the rock-like specimen contains gypsum, the stress of the specimen decreases slowly after reaching the compressive limit, and the failure of the specimen is gentle, which is similar to the mechanical properties of soft rock. When the specimen lacks gypsum, the strength of the rock-like specimen is larger, and the strength of the specimen is positively correlated with the proportion of cement. When the specimen contains gypsum, the strength of the rock-like specimen decreases sharply, and the strength of the rock-like specimen is negatively correlated with the proportion of gypsum. The maximum acoustic emission ringing count increases with higher cement content but decreases with increased gypsum content. The cumulative count change of acoustic emissions approximately underwent four stages, aligning well with the four stages of uniaxial compression failure observed in typical rock. The research results have important reference value for the selection of rock-like materials to replace the original rock materials for laboratory research. [ABSTRACT FROM AUTHOR]

Numerous landslides occur in waste dumps due to unscientific placement. The behavior of waste dumps with different material layouts has yet to be understood when it comes to deformation and failure. In this research, several tests of base friction were carried out on mine waste dumps by considering various material layouts under self-weight loading conditions. The waste dump's displacement was detected by the system composed with image-capture equipment. The findings indicate that the layout of waste materials greatly affected the way a waste dump fails and could be categorized into three types: crest-arced slip, bottom-arced slip, and composite overall slip. Sliding failure caused a gradual development of the slip surface from the dominant fine-gravel material stage to the adjacent waste dump stage. Three phases can be assigned to the waste dump's failure process: the constant deformation phase, strain localization phase, and failed phase. The layout of waste materials exerts a significant influence on the moment that the waste dump's deformation enters the three phases. The waste dump's failure mechanism was explained by describing how maximum shear and volumetric strain developed and transmitted. To determine the most dominant impact during the tests by analyzing the relative degree of volumetric and shear influences on the waste dump, an effect coefficient was proposed. The stability of the waste dump was illustrated and comparatively analyzed based on a simplified approach, in which the moments of initial cracking and local failure were used as a failure index for the model tests. The design and stability analysis of mine waste dumps is strengthened by this study's strong support, thereby minimizing the risk of landslides and promoting the sustainability of the mining industry. [ABSTRACT FROM AUTHOR]

The elevated temperature, high geostress environment, and strong dynamic loading are important factors that induce disasters in deep rock engineering work. The progressive damage and failure behaviors of granite under the coupling of elevated temperature, biaxial stress constraint, and high strain rate were studied by true triaxial split Hopkinson pressure bar (SHPB) tests. The results show that the P-wave velocity attenuation rate kp increases exponentially with temperature, and kp is closely related to the thermal damage of granite grain structures. Under the biaxial stress constraint, the dynamic strength and elastic modulus of granite both increase at first, then decrease with the increase of temperature and a thermal enhancement effect is observed at 150 °C. The threshold temperature for the transition of dynamic failure from brittleness to plasticity is 500 °C. The dynamic strength generated by axial compression and lateral expansion increases exponentially with the strain rate. The lateral stress σ2 enhances the dynamic strength of granite. Under true triaxial stress condition (σ1 > σ2 > σ3 ≠ 0), the enhancement of the dynamic strength is further improved, and the lateral expansion of samples develops along the direction of the minimum principal stress. Under the same stress constraint, the number of impacts that can be borne by granite samples is linearly negatively correlated with heat treatment temperature. The samples are compacted apparently in the early stage of cyclic loading, and the maximum strain experiences three stages: a decrease, slow increase, and sharp increase. When the heat treatment temperature is 700 °C and above, the slow increase stage no longer occurs. Highlights: The progressive damage behaviors of thermally treated granite shows nonlinear growth under biaxial stress constraint and repeated impacts coupling. The dynamic strength of granite under biaxial stress constraint has both the strengthening effect of strain rate and the hardening and weakening effects of temperature. The lateral stress increases the dynamic strength of granite, and the lateral expansion develops along the direction of the minimum principal stress. [ABSTRACT FROM AUTHOR]

An extra-large landslide occurred on June 19, 2021, on the footwall slope of the Nanfen Open-pit Iron Mine in Liaoning Province, China, with a volume of approximately 1.2×107 m3. To elucidate the causative factors, development process, and destructive mechanisms of this catastrophic landslide, comprehensive field tests, investigations, and laboratory experiments were conducted. Initially, the heavily weathered rock mass of the slope was intersected by faults and joint fissures, facilitating rainwater infiltration. Moreover, the landslide contained a substantial clay mineral with highly developed micro-cracks and micro-pores, exhibiting strong water-absorption properties. As moisture content increased, the rock mass underwent softening, resulting in reduced strength. Ultimately, continuous heavy rainfall infiltration amplified the slope's weight, diminishing the weak structural plane's strength, leading to fracture propagation, slip plane penetration, and extensive tensile-shear and uplift failure of the slope. The study highlights poor geological conditions as the decisive factor for this landslide, with continuous heavy rainfall as the triggering factor. Presently, adverse environmental factors persistently affect the landslide, and deformation and failure continue to escalate. Hence, it is imperative to urgently implement integrated measures encompassing slope reinforcement, monitoring, and early-warning to realtime monitor the landslide's deformation and deep mechanical evolution trends. [ABSTRACT FROM AUTHOR]

Abstract During coal mining operations, the coal will be deformed and damaged due to multiple mining disturbances (MMD), often resulting in disasters, like rock burst. To understand the evolution rules of coal deformation under MMD and its final fracture characteristics after impact dynamic load loading, reduce the adverse effects of mining disturbances, and improve disaster prevention and control capabilities, quasi-static uniaxial cyclic loading-unloading (L-U) and dynamic axial compression tests were conducted on large-sized coal-like samples. During the tests, three-dimensional (3D) laser scanning and acoustic emission (AE) monitoring technology were utilized to accurately capture the full-field deformation and AE response data, facilitating a systematic analysis of deformation and fracture characteristics. The results show that: (1) Under the cyclic L-U effect induced by MMD, each loading cycle causes compression deformation with partial recovery during unloading, presenting an overall “wavy” variation trend. (2) The maximum load is the most critical factor affecting the damaged coal deformation, with smaller load resulting in less overall sample deformation. (3) After the impact dynamic loading, the damaged samples suffered large-scale impact splitting failure, with the compressive-shear layer failure mainly occurred inside the holes. (4) Lower loading during cyclic L-U process correlate with reduced damage degree, and smaller debris particles with a higher fractal dimension when impact failure occurs, indicating a more severe impact failure. (5) With multiple cycles of L-U, the cracks inside the sample gradually extend and expand from around the hole to the outside. The greater the load and the number of cycles, the more serious the crack damage will be. (6) In the practical mining process, it is crucial to reinforce roadway interiors while minimizing low-loading cyclic disturbances induced by MMD. The study has obtained the deformation evolution rules and failure characteristics of coal under MMD, providing a theoretical basis for the prevention and control of corresponding engineering disasters.

Multi-layer linings have been widely used in deep rheological soft rock tunnels for the excellent performance in preventing large-deformation hazards. Previous studies have focused on the bearing capability of multi-layer lining, however, its failure characteristics and synergistic load-bearing mechanisms under high geo-stress are still unclear. To fill the gap, three-dimensional geomechanical model tests were conducted and synergistic mechanisms were analysed in this study. The model test was divided into normal loading, excavating, and overloading stages. The surrounding rock deformation was monitored by using an improved high-precise extensometer measurement system. Results show that the largest radial deformation appears on the sidewall, followed by the floor and vault during the excavating stage. The relative convergence deformation of sidewalls springing reaches 1.32 mm. The failure characteristics of the multi-layer linings during the overloading stage undergo an evolution of stability, crack initiation, local failure, and collapse, with a safety factor of 1.0–1.6, 1.6–2.0, and 2.0–2.2, respectively. The synergistic load-bearing mechanism analysis results suggest that the early stiffness and late yielding deformation capacity of large deformation support measures play important roles in stability maintenance both in the construction and operation of deep soft rock tunnels. Therefore, the combination of yielding support or a compressible layer with reinforced support is recommended to mitigate the effect of the high geo-stress.

On September 17, 2020, a landslide occurred in Hongzhai Village, Jichang Town, Qinglong County, Guizhou Province, resulting in serious damage to 134 houses and emergency evacuation of 569 people from 127 households. Investigation revealed that the Hongzhai landslide is a deep-seated large-scale landslide with a volume of approximately 6.25×106 m3. Although surface buildings and infrastructure were severely damaged, the overall movement distance of the landslide was extremely short. Through comprehensive analysis including terrain geomorphology, rock and soil structure and material composition analysis, assessment of hydrological changes, and disclosure of multiple slip surfaces through borehole drilling, it was concluded that the Hongzhai landslide is a resurrected ancient landslide along bedding planes. In order to analyze and study the deformation characteristics and resurrection causes of the landslide, methods including UAV aerial survey, engineering geological survey, rock and soil mass investigation, and geophysical exploration were employed to obtain detailed data on disaster development characteristics, influencing factors, and identification features of ancient landslides. The results show that the Hongzhai landslide can be divided into four zones (A, B, C, D) based on deformation and stress transfer direction, with zone B further divided into subzones B1 and B2 based on relative displacement. The deformation and resurrection of the landslide occurred under the joint effects of steep terrain, complex rock mass structures, weak engineering rock masses, and continuous surface infiltration. Various features such as the arm-chair shaped topography at the back edge of the landslide, material differences between the slide body and surrounding rock and soil masses, fault-cutting front edges, and changes in hydrological sedimentation verify the existence of the ancient landslide.

Abstract Red sandstone tests were conducted on the rock mechanics test system to clarify the strength and failure characteristics of red sandstone under triaxial loading and different unloading confining pressure rates. Strength change rules of the red sandstone in various stress spaces were analyzed. Results show that a large initial confining pressure indicates a long yield section and large axial strain. A small unloading confining pressure rate indicates a long yield section and large axial strain at failure under the identical initial confining pressure. The confining pressure reduction increases with the unloading confining pressure rate increasing when the red sandstone fails. The stress path of unloading confining pressure weakens the red sandstone cohesion and strengthens its internal friction angle. The general octahedral shear stress formula for judging whether the red sandstone fails under loading and different unloading rates was acquired on the basis of the octahedral shear stress characteristics of the red sandstone. In addition, a 3D empirical criterion for evaluating the red sandstone strength was constructed through the deviator plane function of Eekelen and the strength envelope curve on the meridian plane. A great initial confining pressure indicates serious internal damage of the red sandstone at failure under the identical unloading rate of confining pressure. A low unloading rate of confining pressure indicates internal serious damage of the red sandstone at failure when the initial confining pressure is the same. The analysis of macroscopic failure characteristics revealed that the stress path significantly influences the failure mechanism of the red sandstone. The results are instructive for determining the stability of underground engineering of the red sandstone.

Red sandstone tests were conducted on the rock mechanics test system to clarify the strength and failure characteristics of red sandstone under triaxial loading and different unloading confining pressure rates. Strength change rules of the red sandstone in various stress spaces were analyzed. Results show that a large initial confining pressure indicates a long yield section and large axial strain. A small unloading confining pressure rate indicates a long yield section and large axial strain at failure under the identical initial confining pressure. The confining pressure reduction increases with the unloading confining pressure rate increasing when the red sandstone fails. The stress path of unloading confining pressure weakens the red sandstone cohesion and strengthens its internal friction angle. The general octahedral shear stress formula for judging whether the red sandstone fails under loading and different unloading rates was acquired on the basis of the octahedral shear stress characteristics of the red sandstone. In addition, a 3D empirical criterion for evaluating the red sandstone strength was constructed through the deviator plane function of Eekelen and the strength envelope curve on the meridian plane. A great initial confining pressure indicates serious internal damage of the red sandstone at failure under the identical unloading rate of confining pressure. A low unloading rate of confining pressure indicates internal serious damage of the red sandstone at failure when the initial confining pressure is the same. The analysis of macroscopic failure characteristics revealed that the stress path significantly influences the failure mechanism of the red sandstone. The results are instructive for determining the stability of underground engineering of the red sandstone. [ABSTRACT FROM AUTHOR]

Excavation in deep weak rock engineering can significantly alter the stress state in the surrounding rock, often leading to varying degrees of floor heave. The excavation stress paths from the immediate floor to the interior floor were determined by simulating tunnel excavation and monitoring stress changes at fixed points on the floor. The characteristic stresses, failure modes, acoustic emission and deformation features of three types of clastic rock under excavation stress paths were experimentally investigated to reveal the floor heave mechanism. The study found that as the distance from the excavation boundary increased, the bearing capacity of the clastic rock gradually enhanced, and the risk of macroscopic failure decreased, transitioning from tensile failure to tensile–shear mixed failure. Simultaneously, the excavation-induced dilational deformation rapidly decreased. A novel method was proposed to evaluate the dilational deformation of surrounding rock induced by excavation based on the strain features of the samples under the different stress paths. The results demonstrated a rapid decrease in dilational deformation from the immediate floor to the interior floor for the three types of surrounding rock, with the maximum total dilation and the greatest risk of floor heave observed in contact cementation surrounding rock. Finally, the floor heave mechanisms of three types of clastic rock were summarized as follows: unloading dilation combined with macroscopic failure; slight rebound of the immediate floor coupled with multiple microcracks; notable rebound of the immediate floor accompanied by few microcracks. This study provides new insights into the mechanics disasters and selection of support measures for deep-buried tunnels. Highlights: Experiments were conducted on three types of clastic rock under excavation stress paths from the immediate floor to the interior floor. The characteristic stress, failure mode, AE characteristics and deformation behavior induced by excavation of three types of clastic rock were studied. A method was proposed to evaluate the dilational deformation of surrounding rock induced by tunneling. The floor heave mechanisms of three types of clastic rock were revealed. [ABSTRACT FROM AUTHOR]

In this study, to explore the deterioration mechanism of the surrounding rock-ining by the thermal effect of conflagrations, sandstone-concrete bi-materials with various rough interfaces were produced employing three-dimensional scanning and engraving techniques. Uniaxial compression experiments were performed on bi-materials heat-treated from 25°C to 800°C. Combined with acoustic emission (AE) and digital image correlation (DIC) methods, the coupling effects of interface roughness and treatment temperature on mechanical behavior and fracture characteristics were revealed. The findings show that the mechanical parameters present the "U" change of reducing and then growing with the increase of roughness, which is more noticeable at 25°C and 200°C than 400–800°C. The mechanical parameters continuously reduce with increasing temperature. Internal defects in the specimen increase as the temperature nears 400°C. At 800°C, developed microcracks are discovered in sandstone, concrete, and the intermediate interface. Furthermore, failure modes at 25–200°C and 800°C are predominated by tensile and shear failure, respectively. At 400–600°C, the failure mode shifts progressively from tensile to mixed tensile-shear failure as the roughness increases. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Geological Hazard & Control is the property of China Institute of Geological Environmental Monitoring (CIGEM) Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to further promote the application of cementitious sand gravel (CSG), the mechanical properties and variation rules of CSG material under triaxial test were studied. Considering the influence of fly ash content, water-binder ratio, sand rate and lateral confining pressure, 81 cylinder specimens were designed and made for conventional triaxial test, and the influence laws of stress–strain curve, failure pattern, elastic modulus, energy dissipation and damage evolution of specimens were analyzed. The results showed that the peak of stress–strain curve increased with the increase of confining pressure, and the peak stress, peak strain and energy dissipation all increased significantly, but the damage variable D decreased with the increase of confining pressure. Under triaxial compression, the specimen was basically sheared failure from the bonding surface, and the aggregate generally did not break. Sand rate had a significant effect on the peak stress of CSG, and decreased with the increase of sand rate. Under the conditions of the same cement content, fly ash content and confining pressure, the optimal water-binder ratio 1.2 existed when the sand rate was 0.2 and 0.3. After analyzing and processing the stress–strain curve of triaxial test, a Cuckoo Search-eXtreme Gradient Boosting (CS-XGBoost) curve prediction model was established, and the model was evaluated by evaluation indexes R2, RMSE and MAE. The average R2 of the XGBoost model based on initial parameters under 18 different output features was 0.8573, and the average R2 of the CS-XGBoost model was 0.9516, an increase of 10.10%. Moreover, the prediction curve was highly consistent with the test curve, indicating that the CS algorithm had significant advantages. The CS-XGBoost model could accurately predict the triaxial stress–strain curve of CSG. [ABSTRACT FROM AUTHOR]

The mechanical behaviour and failure characteristics of weakly filled granite are important factors affecting the safety and stability of rock masses. This paper presents an experimental study on uniaxial compression of granite containing both planar and circular weak filling of different diameters with the aid of three-dimensional digital image correlation (3D DIC) and acoustic emission (AE) monitoring system. The test results show the following: (1) The contact area between the planar weak filling and the bedrock is in a state of severe local deformation. The annular area of the circular weak filling in contact with the bedrock is in a severe deformation area, with detachment from the bedrock and spalling behaviour occurring. The failure modes of the specimens were summarised, and the spatial morphology of the main fracture surface was quantitatively analysed. (2) The presence of planar and circular weak filling leads to increased AE volatility. The AE hit signal is dominated by the shear signal, but the presence of circular weak filling increases the splitting signal component. (3) In the presence of circular weak filling, the energy interval of the most dominant signal is reduced, and the duration is shortened. The differences in the correlation of AE parameters are concentrated in the low-amplitude signal region. (4) Weakly filled areas will first become areas of spatiotemporal accumulation of microfracture events and will gradually spread. The accumulation and distribution characteristics of microfracture events can be used as indicators to evaluate the propensity, severity and timing of the destabilisation of rock masses containing weak filling. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The instability of double-cavern structure subjected to dynamic disturbances is a key issue for deep rock engineering. To investigate the dynamic responses of deep double U-shaped caverns, comprehensive analyses are conducted by Particle Flow Code (PFC2D), and the influences of incident directions of stress wave, cavern clearances, and cavern height ratios are discussed. The results indicate that the decreasing cavern clearance aggravates the static stress concentration on the intermediate rock pillar. When the stress wave is horizontally incident, the presence of the incident side cavern reduces peak tangential stress and kinetic energy on the non-incident side cavern; the higher the incident side cavern, the less damage on the non-incident side cavern. A vertically incident stress wave causes more severe damage in the intermediate rock pillar compared to a horizontally incident stress wave; the smaller the cavern clearance, the more violent the rockburst in the intermediate rock pillar. Comparatively, the cavern with a lower height exhibits more severe failure at the adjacent sidewall compared to the cavern with a higher height. This work can provide guidelines for disaster prevention of deep double-cavern structures. [ABSTRACT FROM AUTHOR]

In order to address the issue of high development of hard overlying rock water-conducting fracture zones in deep coal mining and achieve water-preserved coal mining by reducing the height of water-conducting fracture zones, a new method is proposed in this study, which combines the techniques of pre-fracturing and weakening of hard main controlling overlying strata. This study comprehensively investigates the modification effect of pre-fracturing and weakening of hard main controlling overlying strata through laboratory experiments, theoretical analysis, and numerical simulation. The control mechanisms of different weakening layers on water-conducting fracture zones are elaborated and validated through field measurements. The results demonstrate that pre-existing fractures can induce the rock mass to shift its failure mode from intact rock fracturing to tension-shear failure controlled by pre-existing fractures, leading to a reduction in the severity of rock mass failure. The weakening effect of pre-existing fractures on the hard rock mass is revealed, and the damage variables coupled with stress and fractures are calculated. The relationship between the degree of weakening and the transformation of rock properties is qualitatively analyzed. It is found that the energy storage capacity of the rock mass is reduced while the dissipation capacity is enhanced after the modification. Numerical simulations are conducted to evaluate the control effect of different weakening layers on water-conducting fracture zones. By comparing the dynamic evolution of overlying rock failure modes, fracture counts, and failure heights, it is observed that the “saddle-shaped” failure mode gradually weakens with the increase of weakening layer height, and the evolution trend of fracture counts follows a pattern of “slow increase-sudden increase”. The dynamic evolution of failure height for unweakened and moderately to highly weakened overlying strata approximately exhibits an “S” shape, while the moderately weakened overlying strata exhibit a “semi-ejection” shape. Based on the analysis of the characteristics of failure in hard rock layers at different positions, the mechanisms of controlling the development of water-conducting fracture zones by different pre-fracturing weakening layers are revealed. Furthermore, using the borehole measurement method, the development height of the “two zones” under the condition of top plate fracturing in Mengcun mine is obtained. It is observed that the fracture extraction ratio is reduced under the condition of pre-fracturing weakening, thus preliminarily validating the inhibitory effect of top plate pre-fracturing weakening on the development of water-conducting fracture zones.It provides theoretical and scientific basis for coupling disaster prevention and control, water resources and ecological protection。

Purposes In the process of in-situ steam-assisted oil shale extraction, the shear strength of oil shale plays a crucial role in the stability of injection and production wells as well as the mining gallery. Additionally, the shear strength of rock formation is influenced by temperature. The variations in the shear characteristics of oil shale under different temperatures and shear angles are investigated. Methods A steam generation apparatus was employed to heat the oil shale. In the experimental setup, steam temperatures were set at 100, 200, 300, 400, and 500 ℃, separately. Subsequently, the steam-treated oil shale was subjected to variable-angle shear experiments at shear angles of 45°, 55°, and 65°. According to the experiment results, the variable-angle shear parameters and peak shear strain of the oil shale were calculated. Furthermore, an analysis of the shear failure characteristics of the oil shale following exposure to different steam conditions was conducted. Findings The research findings can be summarized as follows: 1) At steam temperatures below 300 ℃, oil shale exhibits pronounced brittle failure characteristics, while at temperatures of 400 ℃ and 500 ℃, ductile failure characteristics becomes more evident; 2) The cohesion of oil shale first increases and then decreases with the increase of steam temperature. Similarly, the internal friction angle decreases initially with rising steam temperature, followed by an increase. The shear strength decreases as the shear angle increases; 3) The peak shear strain of the oil shale increases with steam temperature rising, and high shear angle has a significant impact on the peak shear strain of the rock; 4) The shear failure mode of the oil shale transitions from penetrating failure to combined failure with an increase in steam temperature, along with an increase in secondary cracks.

A reasonable heat treatment process for TC4 ELI titanium alloy is crucial to tune microstructures to improve its explosion resistance. However, there is limited investigation on tuning microstructures of TC4 ELI to improve explosion resistance. Moreover, the current challenge is quantifying microstructural changes’ effects on explosion resistance and incorporating microstructural changes into finite element models. This work aims to tune microstructures to improve explosion resistance and elucidate their anti-explosion mechanism, and find a suitable method to incorporate microstructural changes into finite element models. In this work, we systematically study the deformation and failure characteristics of TC4 ELI plates with varying microstructures using an air explosion test and LS-DYNA finite element modeling. The Johnson‒Cook (JC) constitutive parameters are used to quantify the effects of microstructural changes on explosion resistance and incorporate microstructural changes into finite element models. Because of the heat treatment, one plate has equiaxed microstructure and the other has bimodal microstructure. The convex of the plate after the explosion has a quadratic relationship with the charge mass, and the simulation results demonstrate high reliability, with the error less than 17.5%. Therefore, it is feasible to obtain corresponding JC constitutive parameters based on the differences in microstructures and mechanical properties and characterize the effects of microstructural changes on explosion resistance. The bimodal target exhibits excellent deformation resistance. The response of bimodal microstructure to the shock wave may be more intense under explosive loading. The well-coordinated structure of the bimodal target enhances its resistance to deformation.

The failure characteristics of layered rocks are a vital issue for stability evaluations of underground engineering projects. Layered rocks in a restricted true three-dimensional (3D) stress state behave substantially differently from those under uniaxial or conventional triaxial stress. In this study, true triaxial experiments are carried out to investigate the mechanical and volumetric fracturing behaviors of layered composite sandstones (LCSs) with a change in grain size (Cgrain size) between the layers. Under true triaxial stress, the strengths of LCSs increase considerably as the Cgrain size value increases, which is first reported. The strength enhancements of LCSs with increased σ2 (intermediate principal stress) and Cgrain size values are related to the enhanced grain interlocking effect and the interface effect between the layers. As σ2 increases, the volumetric fracturing behaviors of LCSs change from 3D failure toquasi-3D failure characterized by delamination fracture. The effects of σ2 on fracture are revealed by quantifying the cracking morphologies on the layer interface. Aided by the nuclear magnetic resonance (NMR) technique, the correlations of rock porosity with the σ2 and Cgrain size values are established. This paper promotes the understanding of the failure mechanisms of LCSs with a contrast in grain size under true triaxial stress and helps interpret field observations. Highlights: True triaxial compression experiments are performed to investigate the mechanical and volumetric fracturing behaviors of layered composite sandstones (LCSs). The effects of the contrast in grain size (Cgrain size) between the layers and intermediate principal stress (σ2) on the rock behaviors are investigated. The correlations of rock porosity with Cgrain size and σ2 are revealed with the nuclear magnetic resonance (NMR) technique. It is first reported that the strength of LCSs under true triaxial stress increases considerably as the Cgrain size value increases. The volumetric fracturing behaviors of LCSs change from 3D failure to quasi-3D failure characterized by the delamination fracture as σ2 increases. [ABSTRACT FROM AUTHOR]

To quantitatively study the instability and failure characteristics of sandstone with flaws under engineering load, a method for identifying the failure characteristics of rock mass with flaws by date based on Digital image correlation (DIC) technology is proposed. The crack initiation type, corresponding action sequence, and stress level are determined. The uniaxial compression tests of sandstone with a prefabricated flaw at different angles are carried out. And the mechanical properties and deformation field characteristics, and failure characteristics of sandstone with flaws are analyzed. The results show that the peak strength and elastic modulus of sandstone increase and the damage propagation behavior decrease with the increase of flaw angle. Based on DIC technology, the whole process of crack initiation, propagation, and failure is intuitively reflected, the deformation characteristics corresponding to the stress levels of the 4 key points are clarified, and the crack propagation path and key failure areas are mastered. The flaw inclination angle affects the distribution of displacement and strain and determines the new crack initiation position. With the increase of stress value, the horizontal displacement and principal strain increase exponentially at different angles, and the vertical displacement increase linearly. When the inclination angle is 30°, 45°, and 60°, the strain distribution along the crack tip is "Butterfly". The fracture initiation modes of sandstone with a prefabricated flaw at different angles include type I and I–II mixed type. In type I–II, type II acts before type I, and the stress level is lower than type I. [ABSTRACT FROM AUTHOR]

During the coal mining process in soft rock mines with abundant water, the rock mass undergoes cyclic loading and unloading at low frequencies due to factors such as excavation. To investigate the mechanical characteristics and energy evolution laws of different water-containing rock masses under cyclic disturbance loading, a creep dynamic disturbance impact loading system was employed to conduct cyclic disturbance experiments on various water-containing soft rocks (0.00%, 1.74%, 3.48%, 5.21%, 6.95%, and 8.69%). A comparative analysis was conducted on the patterns of input energy density, elastic energy density, dissipated energy density, and damage variables of different water-containing soft rocks during the disturbance process. The results indicate that under the influence of disturbance loading, the peak strength of specimens, except for fully saturated samples, is generally increased to varying degrees. Weakness effects on the elastic modulus were observed in samples with 6.95% water content and saturated samples, while strengthening effects were observed in others. The input energy density of samples is mostly stored in the form of elastic strain energy within the samples, and different water-containing samples adapt to external loads within the first 100 cycles, with almost identical trends in energy indicators. Damage variables during the disturbance process were calculated using the maximum strain method, revealing the evolution of damage in the samples. From an energy evolution perspective, these experimental results elucidate the fatigue damage characteristics of water-containing rock masses under the influence of disturbance loading. [ABSTRACT FROM AUTHOR]

In order to clarify the relationship between the mechanical properties of coal-rock composite and the loading rate and rock–coal strength ratio, uniaxial compression tests were carried out on coal-rock combinations with three different rock–coal strength ratios at four different loading rates. The rock–coal strength ratio is a ratio of the compression strength of rock to the compression strength of coal. The test results indicate that the relationship between the mechanical properties of coal-rock composite and loading rate is influenced by both the strong and weak components in the composite. The peak stress and elastic modulus mainly depend on the weak component, while the peak strain is determined by both the strong and weak components. For peak stress and elastic modulus, when the weak body is the same, the relationship with loading rate is the same, otherwise it is different. The relationship between the mechanical properties of coal-rock combination and is not affected by the loading rate. The weak body in the coal-rock combination is the main body of damage, and the greater the value of , the more severe the damage. At the same time, the failure mode shows a gradual transition from weak body failure inducing strong body failure to only weak body failure. [ABSTRACT FROM AUTHOR]

In order to study the interconnection between macroscopic and microscopic failure characteristics of different textured sandstones, three types of sandstones from Xianghualing mining area were analyzed using petrographic analysis, sedimentary phase discrimination, and uniaxial compression and shear tests to observe the microscopic structural characteristics . The results show that compressive strength of terrestrial sedimentary quartz sandstone is the largest, followed by feldspathic sandstone, and marine sedimentary glauconitic sandstone is the smallest. In uniaxial compression, quartz sandstone and feldspathic sandstone exhibit brittle failure on a macroscopic scale, while glauconitic sandstone shows ductile failure with softening characteristics. On the microscopic scale, quartz sandstone undergoes intergranular failure with a smooth surface, while feldspathic sandstone experiences intergranular and transgranular failure with a small scallop‑shaped surface and minimal adhering debris, and glauconitic sandstone displays a flat‑granular composite fracture surface with obvious grain crushing and pronounced scratches. The failure characteristics are jointly controlled by the grains, cemented material and structural weak planes. The shear test microscopically shows that the quartz sandstone occurs has transgranular failure first and then intergranular failure, with uneven surface, scrapes and debris, while the feldspathic sandstone occurs transgranular failure mainly and intergranular failure, with partially flat surface, scrapes and debris. The glauconitic sandstone simultaneously exhibits intergranular and transgranular failure, resulting in a smooth surface with almost no abrasion or debris. The microscopic failure characteristics are influenced by the grain strength and cementing materials. [ABSTRACT FROM AUTHOR]

This work discussed the results from tests conducted to study the desorption and outburst characteristics of soft and hard coal under different gas conditions. The research found that gas type has a greater influence on the outburst and desorption characteristics of soft coal. Triaxial compression failure can improve the desorption rate of coal specimens, and the gas desorption rate of hard coal is more affected by triaxial compression failure. In the outburst experiments, the greater the test gas pressure, the greater the crush degree of the coal specimen, and the proportion of small-sized coal powder (<0.1 mm) increases but gradually stabilizes. Moreover, the acoustic emission (AE) signals during the outburst process were recorded, and the evolution law of gas pressure in the outburst carven was also analyzed. Finally, the changes in AE signals and gas pressure could be used to predict the damage and destruction characteristics of coal specimens well. [ABSTRACT FROM AUTHOR]

To characterize the failure of rock mass surrounding underground tunnels, biaxial compression tests were conducted on a real sandstone model with a straight-walled arched hole. The acoustic emission (AE) system and digital image correlation (DIC) optical inspection equipment were used to investigate the crack evolution process and failure precursors of the tunnel. A two-dimensional particle flow code (PFC2D) was used to conduct numerical simulations on the sample, so as to investigate the mesoscopic failure mechanism of rock mass. The results show that the failure of the single tunnel constructed in sandstone occurs mainly in the walls on both sides (between the spandrels and arch feet), showing slabbing failure characteristics and a certain abruptness. The crack initiation in sandstone in early stage is not obvious, and the crack propagation in rock mass is rapid when acoustic emissions are enhanced. The small increments in the AE count and amplitude and the continuous reduction in the b-value can be used as precursors for the failure of rock mass. When the height–span ratio is 0.8 and 1.0, the stress distribution around the chamber is more uniform, and when the height–span ratio is greater than 1.0, the stress is mainly concentrated in the vault and arch bottom. In the PFC simulations, tensile fractures firstly initiate in the middle of walls and at the arch feet, arcuate fracture concentration zones are then formed, in which shear fractures appear and a few particles spall from the surfaces. When approaching the ultimate bearing capacity, rock masses on both sides of the tunnel are fractured over large areas, and the slender coalesced fractured zone develops to the deep part of rock mass, causing failure of the sample. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The mechanical behaviors of shales with transversely isotropic characteristics under dynamic loading have great significance for structural instability in geotechnical engineering. To understand the effect of transverse isotropy on the deformability and tensile strength of shales subjected to dynamic loading, a group of impact Brazilian tests were carried out on shale specimens via a split Hopkinson pressure bar (SHPB) testing system. High-speed digital image correlation technology was applied to monitor the fracture process. The experimental results demonstrate that the failure strength has considerable anisotropy as the bedding angle of the embedded layers changes. Moreover, the tensile strength of shales with vertical bedding is usually higher than that of shales with parallel bedding. The observed failure mode is mainly the interaction between tensile and/or shear fractures, and with increasing loading rate, layer-activated fractures tend to occur. Furthermore, five typical failure patterns of transversely isotropic shales characterized by different mechanisms under dynamic Brazilian testing were found. The shales were sensitive to the strain rate when the deformation and fracture response under dynamic loading were assessed. In addition, the modified Nova‒Zaninetti criterion that considers the strain rate effect was proposed according to the Brazilian splitting data and dynamic coordinate system. The established criterion not only properly represents the law of dynamic strength but also provides a new understanding of the effect of strain rate on strength. It has proven to be effective for predicting the dynamic strength characteristics of shales. Highlights: With increasing loading rate, the layer-activated fractures tend to occur. Under high strain rates, cracks generally develop along diversified directions inclined to the bedding planes. Five typical failure patterns of transversely isotropic shales under dynamic Brazilian splitting were concluded. The modified Nova‒Zaninetti criterion considering strain rate effect was proposed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Southeast University / Dongnan Daxue Xuebao is the property of Journal of Southeast University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The dynamic disasters of deep mining coal and rock mass are frequent and easy to be instable. Aiming at the deformation of coal-rock roadway under the coupled static and dynamic load, a new equipment which can simulate the actual situation dynamic environment is used to carry out the coupled static-dynamic loading test of coal-rock combination. The failure law and mechanical behavior of combination are studied. Test results show that weak structure significantly affects mechanical response of coal-rock combination. The coal part with lower strength firstly reaches the crack initiation stress. The strength of the combination is dominated by the coal part. The post-peak stage of the stress–strain curve under the coupled static and dynamic load presents a stepped reduction, which shows yield process. The dynamic load level has a significant effect on the mechanical behaviors of the combination. The elastic modulus decreases under dynamic loading. The peak stress of the combination is positively correlated with the dynamic load level in a certain range, and the peak strain was negatively correlated. The energy accumulation and dissipation are closely related to the failure of the samples. The strain energy is more concentrated in the area where the failure occurs first. The AE energy under dynamic load is developed from the traditional “four-stages” characteristic under static load to three stages. The interval release stage appears because of the appearance of intermittent disturbance load makes the AE energy of the sample change intermittently. The dynamic instability of samples accompanies a sudden increase in AE energy rate, hysteresis loop area and strain. Compared with the shear failure of single lithology sample, the failure mode of the combinations is mainly tensile, and it turns into tensile-shear failure under dynamic load. The fragmentation of samples is different under different failure modes. The fragmentation index can characterize the failure mode and crack propagation characteristics of coal-rock combination. The research provides reference for large deformation dynamic disasters of surrounding rock.

The occurrence of coal mine accidents is mostly caused by the instability and failure of the coal pillar and its overlying roof rock layer. To study the influence of different coal-rock height ratios on the deformation failure and energy evolution mechanism of the coal pillar-roof system, uniaxial loading and cyclic loading and unloading tests are conducted on coal-rock structural body with coal-rock height ratios of 1∶3, 1∶2, 1∶1, 2∶1, and 3∶1, respectively. The relationship between deformation and energy evolution of coal-rock structural body are analyzed, and the stability of coal-rock structural body are quantitatively evaluated through the load-unload response ratio. The test results show that the peak strength of coal-rock structural body under uniaxial loading and cyclic loading gradually decreases with the increase of coal-rock height ratio. The peak strength of coal-rock structural body under cyclic loading test is lower than that in uniaxial loading test. The higher the coal-rock height ratio, the smaller the reduction rate of the peak strength of the structural body under cyclic loading; the input energy, elastic energy and dissipative energy of the composite increase nonlinearly with the increase of stress. The coal-rock height ratio is positively proportional to the average elastic strain, average elastic energy, average residual strain, average dissipative energy, total residual strain and loading and unloading response, and inversely proportional to the total elastic strain, total elastic energy and total dissipative energy of the composite during cyclic loading.

Abstract In a variety of fields such as exploitation of geothermal energy and the reconstruction of nuclear waste storage, both of high-temperature and cooling process change the physical and mechanical properties of granite. Uniaxial compression tests were performed on five groups of granite samples at 25 °C, 200 °C, 400 °C, 600 °C and 800 °C after water cooling, and CT scanning, acoustic emission(AE) monitoring and X-ray diffraction(XRD) scanning were used to investigate the structure properties and failure characteristics of granite. It is found that the proportions of pore volume greater than 106 μm3 and less than 105 μm3 with are positively and negatively correlated with the thermal treatment temperature respectively. The mechanical properties of granite are significantly deteriorated by temperature gradient shock, and crack development scale during failure process overall increases as implied by AE response. The failure intensity index η is proposed to characterize the failure severity of granite, and the value of η descends with the increase of thermal treatment temperature, indicating the failure severity of granite is alleviated. Three types of loading failure mode are classified for water-cooled high-temperature granite. The failure mode of granite at 200 °C and 600 °C is tensile failure and tensile-shear failure respectively, while the granite samples are dominated by shear failure at 25 °C, 400 °C and 800 °C.

In order to master the mechanical strength characteristics of the colluvial deposit and the influence of water content on it，a typical loose colluvial deposit of landslide in southwest China was taken as a research object. A series of large-scale direct shear tests were carried out under different water content conditions and normal stress, the macro mechanical characteristics such as stress-strain, particle breakage, volumetric strain, shear plane failure and so on in the shear process of the colluvial deposit were analyzed, and the determination method suitable for its shear strength was proposed. The research indicates that the colluvial deposit shows obvious strain hardening characteristics under different water contents, and the shear stress displacement curve has no significant peak value, but there is a certain degree of stress "jump" phenomenon. Besides, the shear process produces a relatively obvious particle crushing phenomenon, and the relative particle crushing rate increases with the decrease of water content or the increase of normal stress. Meanwhile, the tests show that the shape of shear failure surface is not an ideal plane. With the increase of water content, the shear surface gradually changes from an irregular shape of "convex up and concave down" to a flat failure surface with a certain angle with the shear joint in space. Combined with the analysis of the characteristics of the normal stress, shear stress and stress ratio on the shear plane during the shear process, a method for determining the shear strength of the accumulation based on the stress ratio is proposed, and the effectiveness of this method is verified. This method is not only simple to operate, with little human interference, but also can better reflect the essence of the shear failure of the soil rock mixture. Finally, the tests reveal that water has an obvious softening effect on the colluvial deposit. The apparent cohesion c and internal friction angle φ linearly decrease approximately with the increase of water content, and the deterioration effect of apparent cohesion is greater than that of internal friction angle. The research results can provide a reference for the determination of shear mechanical properties and strength values of deposits in the southwest mountain area.

On October 6, 2021, a high-position landslide disaster occurred in Yanwo Village，Rongshan Town, Lizhou District, Guangyuan City,Sichuan Province, around 13: 00. The landslide resulted in the destruction of 4 houses, 3 power lines, the burial of a 170-meter-long rural road, and the blockage of a 350-meter-long river channel. By utilizing a variety of remote sensing information sources, including multi-period satellite data before and after landslide, high-precision UAV aerial images, and airborne LiDAR data, the characteristics of high landslide and its sliding mode are studied by using a four-dimensional analysis approach combining three-dimensional space with time. Starting from the development background of high landslide, the deformation and failure characteristics and sliding mode of high landslide are summarized by analyzing the deformation characteristics before sliding and the dynamic procession of the high landslide. Based on the deduced landslide progression and the stability evaluation of the residual landslide at the rear, three sliding modes for future high-position landslide events are predicted and analyzed: Firstly, the back edge of landslide continues to be disjointed and move, causing a direct shear failure of the front part of the landslide by squeezing. Secondly, the trailing edge of the landslide continues to be disjointed and move, resulting in the sliding landslide occurs along the existing landslide channel. Thirdly, the initiation of the front part of the landslide trigger a tractional landslide in the middle and rear parts of the landslide. High-position landslides are common in the southwest mountainous areas, and during early geological hazard investigations, they should be effectively identified, and disaster prevention and mitigation measures should be strengthened.

In recent years, tunnel-boring machines (TBMs) have been widely applied in deep coal mining. Turning is an inevitable challenge in TBM tunneling, and a TBM turning roadway exhibits greater instability than a straight roadway, as engineering experience has indicated. This study aimed to explore the failure mechanism and evaluate the support performance of a deep-turning roadway. Several numerical models were established to investigate the deformation of the roadway, the stress distribution, and the failure zone of the surrounding rocks under different tunneling conditions. The results show that the tunneling depth influences the failure pattern of the turning roadway: deep tunneling with high in situ stress can cause asymmetric failure of the turning roadway, while shallow tunneling with low in situ stress does not. Moreover, the change in turning radius, namely the change in roadway geometry, does not influence the stability of the turning roadway. In addition, the support actions for both the straight and turning roadways do not differ significantly, and the amount of controlled deformation of the surrounding rocks is proportional to their natural deformation.

Rockmass in deep mining is highly susceptible to large-scale collapses under high stress and blast-induced disturbances, leading to casualties and economic losses. To investigate the evolution characteristics of goaf instability and the types of seismic sources that induce instability, an experiment on goaf instability was designed under uniaxial compression conditions based on actual mining operations. The entire experimental process was monitored using digital image correlation analysis and acoustic emission monitoring. By calculating the digital speckle field on the surface of the rock specimen during the experiment, the evolution characteristics of the deformation and strain fields from the beginning of loading to complete failure were analyzed. The study explored the dynamic behavior of cracks from initiation to propagation and eventually inducing large-scale collapse. The results show that the instability process of the goaf begins with the formation of tensile cracks. As stress increases, shear cracks occur in the specimen, leading to macroscopic failure. Furthermore, based on the differences in overall microfracture types measured by RA-AF characteristic parameters during specimen failure, large amplitude acoustic emission events corresponding to the formation of dominant macroscopic cracks were selected, and the focal mechanisms of these events were inverted. The results indicate that shear failure sources are significantly more prevalent than tensile failure sources in acoustic emission events leading to goaf instability. These findings can provide useful guidance for the support design and the prevention and control of rockmass instability disasters.

Complex underground conditions make it challenging to conduct extensive coring, and it is difficult for laboratories to carry out a large number of rock mechanics experiments due to the limited number of cores. Rock-like specimens are commonly used in the laboratory to replace coal-rock specimens. In this paper, rock-like specimens with different proportions are produced to study the mechanical properties, failure characteristics, and acoustic emission laws of rock-like specimens under uniaxial compression. The results show that when the rock-like specimen does not contain gypsum, the stress of the specimen decreases rapidly after reaching the peak stress, which is similar to the mechanical properties of hard brittle rock. When the rock-like specimen contains gypsum, the stress of the specimen decreases slowly after reaching the compressive limit, and the failure of the specimen is gentle, which is similar to the mechanical properties of soft rock. When the specimen lacks gypsum, the strength of the rock-like specimen is larger, and the strength of the specimen is positively correlated with the proportion of cement. When the specimen contains gypsum, the strength of the rock-like specimen decreases sharply, and the strength of the rock-like specimen is negatively correlated with the proportion of gypsum. The maximum acoustic emission ringing count increases with higher cement content but decreases with increased gypsum content. The cumulative count change of acoustic emissions approximately underwent four stages, aligning well with the four stages of uniaxial compression failure observed in typical rock. The research results have important reference value for the selection of rock-like materials to replace the original rock materials for laboratory research.

Joined fractures are an important factor affecting natural rock masses' mechanical and deformation properties. In this paper, indoor uniaxial compression experiments reproduce prefabricated cracks' generation, extension, and coalescence in rock-like specimens. For the fractured specimens, a single crack with an inclination of α = 45° was placed on the left and right sides, and a third crack with an angle of β = 30°, 45°, 60°, and 90° to the single crack on the right side was placed in groups III–VI, respectively. All cracks extended in the thickness direction. Vertical pressure was applied at a constant loading rate of v = 0.1 mm/min until the stress dropped dramatically. In addition, numerical calculations were performed on the rock specimens using PFC2D, a sub-module of the Discrete Element Method (DEM). The experimental results agree with the numerical simulations in that the strength of the specimens containing a conjugate crack is significantly reduced, and the mechanical and deformation properties of the specimens are related to the internal angle of the conjugate crack, with the lowest peak strength and lowest percentage energy dissipation at β = 45°. [ABSTRACT FROM AUTHOR]

Many landslide events occur during or immediately after rainfall, which is one of the main factors that induce slope instability. In this study, a physical model test was conducted to investigate the hydrological response and failure mechanism of fractured rock slopes with anti-dip and strong weathering characteristics under rainfall conditions. Considering the connectivity and development of fractures, a model slope was constructed using prefabricated rock blocks and joint fillers based on a permeability coefficient of the joint fillers that is much larger than that of the prefabricated rock blocks to embody the preferential flow phenomenon of fractures. Gradient cyclic incremental rainfall events were used in the experiment to reflect the effect of previous rainfall on the slope behavior. The results indicate that during rainfall events, the rock blocks become severely softened, and tension cracks that gradually expand are generated on the slope surface. These cracks then penetrate into the joints and fractures developed in the rock mass, forming preferential paths for rainwater infiltration. The failure of the slope started at the toe and gradually developed into the middle and upper parts. This study may provide a feasible method for the model testing of fractured rock slopes under rainfall conditions. [ABSTRACT FROM AUTHOR]

Dynamic compressive parameters of coal specimens were driven not only by impact velocities, but also by preloaded confining pressure, and impact loading methods. This paper investigates the influences of dynamic parameters based on the split Hopkinson pressure bar (SHPB) experimental data obtained from the dynamic compressive impact tests on 12 coal specimens under four different impact velocity. The analysis of the experimental results confirmed that with an increase of dynamic velocity, and then the dynamic compressive strength is constantly increases. When the dynamic velocity is 8.10 m/s, and then reacheed the maximum dynamic strength of 25.11 MPa of the coal specimen. Furthermore, the dynamic velocity of 8.10 m/s was defined as the threshold value of the dynamic strength increased. The greater of dynamic velocity, the higher degree of fragmentation of the coal specimens. The transmitted energy, reflected energy, and absorbed energy of coal specimens shows a directly proportional relationship with the incident energy. The results highlight the first and second dynamic deformation moduli can clearly explained the deformation laws of elastic and plastic stages of the coal specimens. It is also found that the maximum of strain rate is 177.28 s−1 and the maximum ultimate strain is 2.47 × 10−2of the coal specimens. The research results were beneficial to supplement the coal-rock dynamics theory, thus also providing a direction for safety and effective mining and crushing in coal mines. [ABSTRACT FROM AUTHOR]