The rapid movement and extensive displacement of gravel-silty clay landslides result in significant property damage and loss. Following the destabilization of the Shaziba landslide in Enshi City, it transformed into a...
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The rapid movement and extensive displacement of gravel-silty clay landslides result in significant property damage and loss. Following the destabilization of the Shaziba landslide in Enshi City, it transformed into a debris flow, ultimately obstructing the Qingjiang River and creating a barrier dam. This study delves into the failure mechanism, leap dynamics, and motion processes of this specific landslide by employing a blend of ring shear testing and the discrete element method. Initially, the residual shear strength of the sliding soil was assessed through ring shear tests conducted under various coaxial stresses and shear rates within the sliding region, using field surveys and aerial imagery. Building upon this foundation, the entire progression of the landslide-from sliding to settlement-was replicated using PFC3D, allowing for an examination of the landslide's movement characteristics such as speed, displacement, and trajectory. The findings indicate that the shear displacement and residual friction coefficients are higher at elevated shear rates compared to lower rates. The landslide commences with an initial acceleration phase, with the silty clay material's movement lasting approximately 757 s, reaching a maximum velocity of 32.5 m/s and a displacement exceeding 1000 m. The simulated settlement volume of the landslide (9.31 x 105m3) closely aligns with the results obtained from field investigations (1.5 x 106m3). This research offers comprehensive insights into recent Shaziba landslides, serving as a valuable resource for enhancing our understanding of the dynamics involved and mitigating the potential risks associated with such events.
Activating closed natural fractures (NFs) in hot dry rock (HDR) reservoirs is a critical way to improve fluid conductivity and stimulate production. However, the current hydraulic fracturing simulation technology is l...
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Activating closed natural fractures (NFs) in hot dry rock (HDR) reservoirs is a critical way to improve fluid conductivity and stimulate production. However, the current hydraulic fracturing simulation technology is limited in its ability to investigate the interaction mechanism between hydraulic fractures (HFs) and NFs under the interference of mineral heterogeneity in HDR. In this study, we combine a modified hydro-grain-based model (hydro-GBM) and the smooth joint model (SJM) to establish a discrete element model of granite with closed NFs, investigating the effects of in-situ stress, approach angle, and physico-mechanical properties of NFs on interaction modes. Our results show that mineral heterogeneity induces HFs on both sides of the borehole to propagate asymmetrically along low-strength minerals and mineral boundaries, enhancing the complexity of HFs. As the approach angle, NF interface friction coefficient, or NF bond strengths decrease and differential in-situ stress or NF permeability increases, the offset of HFs propagating along NFs increases, thus promoting the activation degree of NFs and resulting in a decline in the average activity level of acoustic emission (AE) events and the proportion of large events in NFs. Furthermore, numerical simulations reveal the evolution laws of fracturing results, such as breakdown pressure, fracture propagation pressure, spatial distribution of microcracks, fluid pressure field, and normal stresses on NFs, which provide valuable insights for constructing complex and efficient fracture networks in HDR reservoirs. A smooth joint coupling hydro-grain-based model is proposed to describe the crystalline rock with closed natural fractures from the mineral grain *** model reproduces the interaction modes between hydraulic fractures and natural fractures similar to the experimental *** of in-situ stress, approach angle, and physico-mechanical properties of natural fractures on interaction processes are dee
Damage and fracture during rock creep have long been a focal point in rock mechanics research. To investigate the cross-scale damage and fracture behavior of pore-deficient sandstones, this study quantitatively assess...
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Damage and fracture during rock creep have long been a focal point in rock mechanics research. To investigate the cross-scale damage and fracture behavior of pore-deficient sandstones, this study quantitatively assesses the creep fracture characteristics of various pore-deficient sandstones using fracture mechanics and the Digital Image Correlation (DIC) method. The creep damage characteristics are analyzed through the first law of thermodynamics and the Discrete Element Method (DEM). In addition, the microscopic mechanisms of creep damage in rocks are explored using crystal mechanics, Scanning Electron Microscope (SEM) tests, and machine learning techniques. This study also establishes the relationship between microscopic damage and macroscopic damage and fracture. The results reveal that the contribution of Mode I fracture to rock composite fracture decreases with increasing porosity. Creep damage predominantly occurs during the stable creep stage, with a higher porosity corresponding to a faster creep damage rate. Furthermore, the larger the exponent between the fractal dimension and the damage variable, the more pronounced the mineral dislocation fracture during rock damage. These findings provide valuable insights into the understanding of creep damage and fracture in rocks.
In this study, geotechnical, geological, and seismic refraction investigations were carried out along NH 310A in Sikkim, India, to assess slope instability. Namok Khola is one of the most unstable slopes identified al...
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In this study, geotechnical, geological, and seismic refraction investigations were carried out along NH 310A in Sikkim, India, to assess slope instability. Namok Khola is one of the most unstable slopes identified along the Gangtok–Chungthang road. The area contains highly deformed mica schist with a thick layer of weathered material comprising sandy silt. Field tests using the Standard Penetration Test (SPT-N) revealed the presence of soil and weathered material up to a depth of 5.5 m. Seismic refraction testing was performed to identify slip surfaces of the landslides, confirming the existence of bedrock at depths ranging from 6 to 9 m below the surface. The seismic velocity within the upper weathered zone ranged from 650 to 700 m/s. Two distinct velocity zones were observed within the bedrock, representing disintegrated and intact bedrocks with velocities ranging from 2000–2100 m/s and 3900–4000 m/s, respectively. Laboratory analysis of samples obtained through borehole drilling validated the results of the seismic refraction tests. particle flow code (PFC) is used in this study to model the landslide and examine its dynamic properties. The simulation demonstrated that failure happened for about 39 s, with the major sliding event lasting 14 s. The maximum average displacement was 125 m, while the most significant measured displacement was 170 m. Results from the simulation have demonstrated good agreement with the actual landslide characteristics of Namok Khola sliding.
In this study, three-dimensional laser scanning technology is applied to obtain real geometric data of aggregate particles in cemented materials, and a characterization method of surface roughness of aggregate is prop...
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In this study, three-dimensional laser scanning technology is applied to obtain real geometric data of aggregate particles in cemented materials, and a characterization method of surface roughness of aggregate is proposed to quantify the surface roughness of aggregate. A series of three-dimensional direct shear tests are conducted using particle flow code. The shear mechanical properties of cemented materials with different cementation degrees and different surface roughness levels of aggregate particles are investigated through the direct shear tests. The results show that the roughness level of aggregates and the cementation degree both affect the mechanical properties of cemented materials. As the degree of cementation increases, both of the internal friction angle and cohesion increase. As the degree of roughness increases, the internal friction angle increases while the cohesion decreases. The surface roughness of aggregate is in linear relationship with the internal friction angle and in nonlinear decreasing relationship with the cohesion.
This paper presents a rapid and effective calibration method of mesoscopic parameters of a threedimensional particle flow code(PFC3D)model for sandy cobble *** method is based on a series of numerical tests and takes ...
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This paper presents a rapid and effective calibration method of mesoscopic parameters of a threedimensional particle flow code(PFC3D)model for sandy cobble *** method is based on a series of numerical tests and takes into account the significant influence of mesoscopic parameters on macroscopic ***,numerical simulations are conducted,with five implementation ***,the multi-factor analysis of variance method is used to analyze the experimental results,the mesoscopic parameters with significant influence on the macroscopic response are singled out,and their linear relations to macroscopic responses are estimated by multiple linear ***,the parameter calibration problem is transformed into a multi-objective function optimization *** simulation results are in good agreement with laboratory results both qualitatively and *** results of this study can provide a basis for the calibration of microscopic parameters for the investigation of sandy cobble soil mechanical behavior.
Rock bursts pose a significant risk to coal mine operation safety. Thus, accurately discriminating coal bursting liabilities is crucial for predicting and preventing rock burst events. To better understand the effects...
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Rock bursts pose a significant risk to coal mine operation safety. Thus, accurately discriminating coal bursting liabilities is crucial for predicting and preventing rock burst events. To better understand the effects of a varying bedding angle on the crack propagation rule, failure mode and bursting liability level of coal and coal-rock combinations, we propose an optimized machine learning-based model. Additionally, uniaxial compressive tests are conducted using PFC3D software on samples with different bedding angles. The results indicate that, among the nine light gradient boosting machine discriminant models constructed using three data preprocessing methods and three parameter optimization algorithms, the optimal model is identified as the particle swarm optimization-light gradient boosting machine discriminant model based on Z-score standardization method, which exhibits the best stability and has a F1-score of 93.6%. Bedding has a significant impact on the failure modes of two kinds of samples, resulting in an evident bedding effect on their bursting liability. The uniaxial compression strength and bursting energy index of both samples show a reduction-rising trend with an increasing bedding dip angle. However, the bursting liability level of these samples is not affected by 0 degrees or 90 degrees bedding dip angle. Therefore, when assessing the bursting liability of samples, the influence of coal seam bedding and its dip angles should be thoroughly considered.
The mechanical properties of rocks weaken under dry-wet *** weakening may significantly modify the safety reserve of underground caverns or reservoir bank ***,meso-damage has not been carefully studied based on microm...
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The mechanical properties of rocks weaken under dry-wet *** weakening may significantly modify the safety reserve of underground caverns or reservoir bank ***,meso-damage has not been carefully studied based on micromechanical observations and ***,in this study,meso-damage of a yellow sandstone is investigated and a meso-damage-based constitutive model for dry-wet cycles is ***,computed tomography scanning and uniaxial compression tests were conducted on yellow sandstones under different dry-wet ***,the evolution of rock mesostructures and the damage mechanism subjected to dry-wet cycles were simulated using the discrete element method with particle flow code in 2 Dimensions(PFC2D)***,a constitutive model was proposed based on the meso-statistical theory and damage ***,this constitutive model was verified with the experimental results to check its prediction *** is found that the radius and number of pore throats in the sandstone increase gradually with the number of dry-wet cycles,and the pore structure connectivity is also *** contact force of sandstone interparticle cementation decreases approximately linearly and the continuity of the particle contact network is continuously *** meso-deformation and strength parameters show similar declining patterns to the modulus of elasticity and peak strength of the rock sample,*** meso-damage-based constitutive model can describe well the rock deforma-tion in the initial pressure density stage and the damage stage under the coupling effect of dry-wet cycles and loads.
Stepped failure is a typical mode in alpine valleys and usually manifests as brittle fractures determined by joints. Tension-shear extension criteria were proposed to reflect the intrinsic mechanism of this failure mo...
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Stepped failure is a typical mode in alpine valleys and usually manifests as brittle fractures determined by joints. Tension-shear extension criteria were proposed to reflect the intrinsic mechanism of this failure mode. These criteria combined the theory of linear elastic fracture mechanics and the Mohr-Coulomb (M-C) strength criterion, including propagation trends and fracture conditions, and reflected the fracture behavior of rock bridges determined by joints. The proposed extension criteria were numerically applied in the 2D particle flow code (PFC2D). The mesoscopic strength parameters were calibrated according to a mathematical relationship, which could satisfy the relationship between stress and strength with the proposed criteria. For massive rock slopes dominated by stepped joints, it is determined through theoretical and experimental analysis that rock bridges undergo tensile failure under low normal stress levels, which gives a reasonable explanation of why rock bridges observed in situ generally undergo tensile fracture. The internal mechanism of rock bridge failure is revealed through mechanical analysis of fracture behavior, which is considered in the numerical method. Taking the Xiaowan Hydropower Station as an example, it is confirmed that the simulation results truly reproduce the mesoscopic mechanism of the stepped failure of the slope.
Cracks are a ubiquitous phenomenon in rock masses, and their presence can significantly impact the dynamic mechanical behavior and evolution process of rocks. In this study, we utilized a two-dimensional particleflow...
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Cracks are a ubiquitous phenomenon in rock masses, and their presence can significantly impact the dynamic mechanical behavior and evolution process of rocks. In this study, we utilized a two-dimensional particle flow code (PFC2D) to investigate the dynamic compressive strength, peak strain, and dynamic elastic modulus of randomly distributed cracked sandstone samples. We analyzed the effect of varying the number of pre-existing cracks on rock deformation and energy absorption under impact loading. Our findings demonstrate that the dynamic compressive strength, peak strain, and dynamic elastic modulus of cracked sandstone follow a two-parameter negative exponential relationship, with crack density being the most influential factor on dynamic compressive strength. The duration of each stage of cracked rock deformation is dependent on the number of pre-existing cracks, with an increase in the number of cracks resulting in a shorter elastic deformation stage. The presence of cracks also affects the energy absorption rate and elastic energy storage capacity of a sample, with a higher number of prefabricated cracks resulting in greater elastic energy conversion and crushing energy dissipation capacity. The interaction of cracks weakens the dynamic elastic response of rock specimens, and this effect becomes more pronounced with increasing crack density and loading rate. Our study provides valuable insights into the influence of cracks on rock dynamic mechanical behavior and has practical implications for rock engineering design and risk assessment.
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