Soil-rock mixture (S/RM) is a very complex discontinuous medium material, which is a multiphase system consisting of high strength rock blocks (Rocks), relatively soft filling components (Soils) and ...corresponding pores. Because the mechanical properties of various components of soil-rock mixtures under external loads are very different, and there are extremely complex interactions between them. Therefore, the mechanical properties of this geotechnical material (such as stress transfer, failure mode, crack propagation, bearing capacity, etc.) are quite different from those of homogeneous geotechnical materials, and largely depend on the internal structure characteristics of soil-rock mixtures (such as particle size composition, particle shape, particle distribution and arrangement). Due to the complexity of the model, the simulation of its meso-mechanical properties is mostly confined to the random simulation of regular blocks. In this paper, an automatic generation method of PFC∼2D numerical model of soil-rock mixture microstructure based on digital image processing is proposed, and the experimental simulation is carried out with matlab. Thus, the rapid, real and automatic modeling of heterogeneous material microstructure by PFC∼2D software is realized. The PFC∼2D numerical calculation model of soil-rock mixtures is established. The results show that when the stone content is 80%, the analysis should be caused by the large amount of rock, which leads to the large internal voids, and the sudden unloading between the rock and the rock during compaction and then the structural reorganization.
•Propose the experimental and particle flow numerical models for tunnel leakage.•Predict the settlement of sand layer and laws of water and sand loss.•Explore the distribution of seepage fields by ...the design of a seepage tracer device.•Discuss the migration and soil arching effect of sand particles from the fine scale.•Conduct the parametric analyses for different influencing factors of tunnel leakage.
Most of urban ground collapses and tunnel failures are caused by joint leakage of shield tunnel lining. This paper conducts a series of model tests and particle flow simulations aiming to investigate the geo-hazards and explore the associated failure mechanism due to tunnel leaking. Based on critical width of leaky joint, taking leaky joint location, overburden depth and height of overlying water level as influencing factors, the settlement of the sand layer and the law of the water and sand loss is effectively predicted. Then, the focus is on designing a seepage tracer device to explore the distribution of the seepage field and its flow line variation. Finally, the particle flow numerical model of tunnel-sand is employed for the soil arching effect and flow line changes during seepage erosion to discover the fine scale influences of sand particle migration and loss around the shield tunnel on the surrounding environment.
Coal burst tendency is the natural property of whether coal rock mass can have coal burst, and the distribution of fissures has an important influence on it. In order to study the influence mechanism ...of the original coal fissures on the energy dissipation characteristics and coal burst tendency, the PFC2D numerical simulation method was used to conduct uniaxial compression tests on coal specimens with different fracture types. The results show that: ①With the increase of the inclination angle of the fissure, the compressive strength and elastic modulus of the macroscopic mechanical parameters show a trend of decreasing first and then increasing; when the inclination angle of the fissure is 30, both of them reach the minimum value. The relationship between the macro-mechanical parameters of different fracture types is: non-coplanar parallel double-fissure specimen < single-fissure specimen < co-planar discontinuous double-fissure specimen.②The variation law of elastic strain energy and total strain energy is s
Fracture initiation and propagation in fluid-saturated rocks are controlled by interaction between fluid flow and rock deformation. The description of hydromechanical coupling is essential for ...modeling the fracture process. In this paper, an improved hydromechanical model is proposed in the framework of the particle flow simulation method. This model provides a better description of hydraulic properties before and after breakage of bonds and can efficiently describe fluid flow through porous rock matrix and along fractures. The efficiency of the proposed model is first assessed by comparisons with analytical solutions and typical experimental evidences. A series of numerical simulations are then realized to investigate effects of some key parameters such as confining stress, fluid injection rate and viscosity on the initiation and propagation of fractures.
Grouting method is one of the commonly used methods for soft roadway reinforcement. Through the discrete element simulation method, the grouting process of coal seam was studied, and the grouting ...effect under different coal strength and grouting pressure was explored, and the diffusion form of the slurry in the coal seam was obtained. The results show that: the coal seam grouting goes through the stage of “permeation-rapid splitting-slow splitting-stability”. The crack expansion in the grouting process is mainly caused by the tensile stress at the crack tip. Under the action of slurry pressure, the tensile stress concentration is formed at the crack tip, and the slurry splits the coal seam when the starting pressure is reached. Grouting pressure and coal strength have great influence on grouting effect, and the influence of grouting pressure on slurry diffusion radius decreases gradually. The smaller the compressive strength of coal is, the larger the grouting diffusion radius is, and the more fully developed
Based on the conventional triaxial compression test of marble, the microscopic parameters corresponding to the macroscopic mechanical properties of marble were obtained by PFC2D, and on this basis, ...discrete element method models were established to conduct numerical tests of triaxial compression of marble under different confining pressures and loading rates to study the effect of loading rates on the rock specimens. Under the same confining pressure, brittle damage occurs in marble when the loading rate is low, and the damage type transforms from brittle to ductile as the loading rate increases. The peak strength, cracking stress, damage stress, cohesion, and internal friction angle of marble appear to increase with the increase in the loading rate under the same confining pressure. The characteristic stresses and strength parameters are linearly related to the loading rate. The influence of the loading rate on the peak strength is the most significant. With the increase in the confining pressure, the fitting coefficient of the linear relationship between initiation stress and loading rate decreases from 18.9 to 15.4 for different confining pressures, indicating that the growth rate of initiation stress decreases with the increase in the confining pressure when the loading rate is increased, and the increase in confining pressure suppresses the growth rate of initiation stress with loading rate.
The most economical, environmental, and friendly method for recycling gangue is filling mining with cemented waste rock backfill (CWRB), which solves the environmental problems caused by gangue ...discharge and reduces the mining damages. Evaluating the mesoscopic structure of CWRB is of great significance for maximizing the utilization of gangue recycling and improving the economic benefits of filling mining. This paper constructed the particle flow model of cemented waste rock backfill (CWRB) considering particle size distribution (PSD) of aggregates and hydration of cementing material to investigate the effect of the PSD of aggregates on its mesoscopic structural evolution. The strain energy, crack, force chain, and particle fragment of CWRB during the whole loading were discussed. The binary processing and calculation on the crack image were performed to analyze the fractal dimension of crack distribution by compiling program. The influencing mechanism of the PSD of aggregates on the strength of CWRB is revealed from the mesoscopic levels of crack evolution, force chain structure, and particle fragment. The results show that the strain energy increases firstly and then decreases with the PSD fractal dimension, while the crack number decreases firstly and then increases with that. The cracks with less number and more uniform distribution present the smaller fractal dimension, CWRB with a low fractal dimension of crack distribution has higher strength, the fractal dimension of crack distribution exhibits a correlation with the PSD of aggregates. CWRBs with the PSD fractal dimensions of 2.4–2.6 have the largest strain energy and the smallest crack number, performing the superior structural evolution during loading. This study presents the huge potential of optimizing PSD in CWRB application from a new perspective, it is of great significance for strengthening the internal structure of CWRB and reducing engineering cost.
Shear tests on sandstone containing non-connected joints under the unloading normal stress but fixed shear stress conditions were conducted with various initial normal stress and unloading rate. ...During the unloading process, continuous shear dilation could be observed. For initial normal stress = 5–20 MPa, the sliding initiation normal displacement decreased by 17.14–66.32 % but the sliding initiation shear displacement increased by 21.91–98.19 %. The sliding initiation normal stress declined by 7.18–15.57 % for unloading rate = 0.002–0.01 MPa/s but increased by a factor of 3.18–3.53 with the initial normal stress. Shear sliding of the jointed samples was more prone to occur at a smaller initial normal stress with a larger unloading rate. From the numerical simulation results via PFC2D, during the unloading process, cracking was first initiated from central part of the rock bridge and propagated gradually to coalesce with cracks developed from the joint tips. The penetrating fracture surfaces led to shear sliding of the jointed samples, and shear wear occurred on the fractures as shear displacement continued increasing. For unloading rate = 0.002–20 MPa/s, quantity of cracks corresponding to shear displacement of 1.2 mm decreased by 12.18–36.34 %. Cracking degree was more serious for the samples at a low unloading rate due to progressively developed cracks near the main failure planes before shear sliding and more accumulated cracks in the shearing wear stage for fractures under a larger normal stress.
•Unloading normal stress induced shear sliding of jointed fine-grained sandstone was studied.•Rate effects on unloading normal stress induced shearing properties was analyzed.•Stress evolution and cracking characteristics of rock bridge was simulated by particle flow code.
Abstract
To study the reinforcement mechanism of expansive slurry from a mesoscopic perspective, shear simulation tests were conducted on a slurry–fractured rock mass composite using PFC2D (version ...5.00.35). The tests analyzed the distribution of cracks, the process of damage evolution, the distribution characteristics of intergranular contact forces, and the displacement of particles. The results indicate that (1) the volume expansion of the expansive slurry compressed the rock mass, causing the slurry particles to penetrate the pores of the rock particles. This process increased the contact area between the slurry and the rock mass, improved the friction, and intensified the degree of interlocking between the slurry and the rock mass, thus improving the bonding between them. (2) Both composite rock masses exhibited similar macroscopic damage patterns consistent with the laboratory tests. During shear tests, both composites experienced four stages of crack development: crack initiation, slow crack development, rapid crack development, and stable crack number. (3) The expansion stress, along with its reaction force and friction force, increased the integrity of the composite rock mass, reducing the differences in particle displacement direction and velocity. This led to improved internal deformation coordination within the composite rock mass, resulting in fewer cracks during shear tests.
