Search

The development of high rockfill dams has imposed greater demands on the compaction quality of rockfill materials. However, because rockfill particles are subjected to crushing under the compaction of a high-powered roller, the rockfill compaction characteristics might be affected. In this paper, a 3D discrete element model of the rockfill compaction process under vibration force was established to investigate the compaction characteristics and the mesoscopic mechanism of rockfill, considering gradation, shape, and particle breakage. The results showed that the geometric accuracy of rockfill particles is well maintained with 30-surface polyhedrons based on SHAPE simplification. The rockfill material with larger aspect ratios showed a larger final cumulative settlement ratio, while those with larger d50 showed a smaller ratio. Due to the combined effects of compaction and particle breakage, the porosity of the surface rockfill particles decreased more rapidly. As the settlement ratio increased and the porosity decreased, the coordination number of the rockfill material increased. In general, the average velocity of particle movement increased with decreasing particle size during compaction. [ABSTRACT FROM AUTHOR]

The excavation-unloading damage effects of western high-geostress slopes on rock were explored by testing the pre-peak confining pressure unloading sandstone reloading mechanical properties. The deformation and failure mechanisms were studied from a mesoscopic perspective using the particle discrete-element method. (1) Approaching the unloading failure, confining pressure increased the specimen bearing capacity attenuation. (2) The confining pressure unloading promoted microdefect propagation and development; the specimens increased rapidly to the damage stress value after reaching the initiation stress value. The penetration fracture zone was more evident and expansive in the model, and the distribution of the dense crack areas was more concentrated in the fracture zone and area. (3) The average interval of the tangential contact force was the largest in the direction of crack expansion and propagation. The strong force chains were shown to primarily bear external loads, whereas the weak force chains played a key auxiliary role in maintaining stability. (4) The number of cracks developing in the confining pressure unloading damage process indicated that the loading process did not cause damage to the specimens. The fracture zones further propagated and formed on the dominant fractures based on the damage caused by the confining pressure unloading disturbance. [ABSTRACT FROM AUTHOR]

Internal erosion is a phenomenon that fine particles migrate through the channels within coarse matrix under seepage flow. Previous studies mainly focused on the internal erosion under steady hydraulic gradient, while the studies on the behavior and mesoscopic mechanism of internal erosion under fluctuating hydraulic condition were rarely reported. In this study, a setup of transparent soil seepage test was developed. Seepage tests on two types of soils with different internal stability were conducted under steady and fluctuating hydraulic conditions respectively to investigate the internal erosion behaviors under fluctuating hydraulic condition. The macroscopic experimental phenomenon showed that when the hydraulic gradient exceeded the critical value, the hydraulic conductivity under fluctuating hydraulic condition increased faster than that under steady hydraulic condition for internally unstable soil, manifesting that hydraulic fluctuation aggravated the migration of fine particles. In order to further reveal the mesoscopic mechanism, a three-dimensional (3D) reconstruction method was employed to rebuild the mesoscopic fabric of soil based on two-dimensional cross-sectional images obtained by the planar laser scanning; and a 3D visualization digital model including coarse matrix, inter-granular pore channels and fine particles was established. By observing the distribution of fine particles in pore channels, it was found that fine particles might clog and accumulate at narrow pore throats under steady seepage. While the perturbation caused by hydraulic fluctuation could break these weak stable structures of clog and accumulation, and then restart the migration process of fine particles.

The pre-peak microstructure evolution of the material is crucial in determining the strength and failure scheme of the material, but is not captured by the existing shear strength parameters models which focus on post-peak stage information. Novel concepts of pseudo-cohesion and pseudo-internal friction angle that account for both the pre-peak and post-peak stage information were proposed in this study, based on the experimentally observed response of the rock mechanics parameters to an external load (the maximum principal stress). These two parameters were analytically derived as functions of maximum principal strain, with coefficients to be determined (i.e., by applying the Mohr–Coulomb criterion with these parameters to experimental data). The dependence of pseudo-cohesion and pseudo-internal friction angle on the axial strain and confining pressure was investigated. The evolution of the strength parameters was found to relate to the propagation of micro-crack developed in the loading process, as revealed by PFC2D simulations reproducing experiments. The results show that (1) analytical model characterizing the pseudo-cohesion and internal friction angle as the quadratic function of axial strain accurately reflects the mechanical response characteristics of the specimen; (2) before the residual stage, the pseudo-cohesion first increases and then decreases with increasing strain, while the pseudo-internal friction angle increases continuously; (3) for the sandstone specimens studied, the pseudo-cohesion at the peak stress increases by a gradually decreasing rate with increasing confining pressure, while the pseudo-internal friction angle at the peak stress decreases by a decreasing rate with the increasing confining pressure; (4) CPM well characterized the mechanical properties of rock under multiple confining pressures, as the total stress–strain curves and failure modes of numerical specimens reproduced the experimental results. The evolution of rock pseudo-shear strength parameters is closely related to the external load and the generation, propagation, and penetration process of rock cracks. The rock pseudo-shear strength parameters are gradually mobilized with the increasing load, and the propagating of cracks owing to the decrease of mobilizable maximum cohesion and the increase of mobilizable maximum internal friction angle. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of fiber orientation on the resistance of seepage-induced erosion in fiber-reinforced sand. To clarify the discrepancy and mechanism of different-oriented fibers improving the resistance of the sand matrix, a series of DEM-Darcy coupling simulations were conducted. The microscopic parameters of fiber-reinforced sand were confirmed by the rigorous calibration procedure. The fibers perpendicular to the seepage direction were found to increase the difficulty of moving fluid through the specimen and significantly reduce the erosion rate of the specimen. These macroscopic behaviors acquired corresponding explanations at the mesoscopic scale, including the evolution of fiber-sand contact orientation, coordination number, average normal contact force, tensile force, and energy dissipation. According to the simulation results, it is found that the highest proportion of tensile force in perpendicular fibers can reach 80%, while the parallel fibers are only 40%, which indicates that the perpendicular fibers have a significant netting effect. The mesoscopic behaviors reasonably revealed the role of the fibers with different orientations on the sand matrix during the seepage. This study is beneficial for further understanding the mechanical behaviors of fiber-reinforced sand under seepage-induced erosion in safety engineering. [ABSTRACT FROM AUTHOR]

The excavation-unloading damage effects of western high-geostress slopes on rock were explored by testing the pre-peak confining pressure unloading sandstone reloading mechanical properties. The deformation and failure mechanisms were studied from a mesoscopic perspective using the particle discrete-element method. (1) Approaching the unloading failure, confining pressure increased the specimen bearing capacity attenuation. (2) The confining pressure unloading promoted microdefect propagation and development; the specimens increased rapidly to the damage stress value after reaching the initiation stress value. The penetration fracture zone was more evident and expansive in the model, and the distribution of the dense crack areas was more concentrated in the fracture zone and area. (3) The average interval of the tangential contact force was the largest in the direction of crack expansion and propagation. The strong force chains were shown to primarily bear external loads, whereas the weak force chains played a key auxiliary role in maintaining stability. (4) The number of cracks developing in the confining pressure unloading damage process indicated that the loading process did not cause damage to the specimens. The fracture zones further propagated and formed on the dominant fractures based on the damage caused by the confining pressure unloading disturbance.

In order to study the influence of stress path on the true triaxial macroscopic and mesoscopic deformation characteristics of rocks, a calibrated granular flow numerical specimen was established using the discrete element method, and the loading planes were selected as meridian plane, n-plane and the fixed-axis plane. Numerical experiments with different stress paths were conducted on the numerical specimen to analyze the true triaxial deformation evolution of rocks from the macroscopic and mesoscopic viewpoints, and the numerical simulation results were compared with the D-P yield criterion to verify the correctness of the results. The research results showed that: for the same stress increment, the anisotropy of strain increment was the lowest when loading along the meridian plane, and the stress reached the yield plane fastest when loading along the n-plane, resulting in the largest strain increment and the two-way unloading in fixed-axis plane produced the largest strain increment in all stress path loading processes. The elastic-plastic deformation characteristics were analyzed using the relative imaging of stress space and yield surface, defining deformation anisotropy parameters; the correlation between stress and strain increment paths was quantitatively analyzed at the mesoscopic view level, and it was concluded that the number of contact force chain transformations and strain increment deflection angle were negatively correlated, and the numerical model produced the largest number of microcracks with the most obvious internal damage when loaded along the n-plane, and the smallest number of microcracks with the least internal damage when loaded along the fixed-axis plane. [ABSTRACT FROM AUTHOR]

Centrifuge shaking table tests were conducted to reveal the intrinsic mechanisms of the effects caused by complicated seismic histories on the liquefaction resistance of a saturated sand deposit. The centrifuge model was shaken by a well-designed seismic sequence including 16 shakings in a certain order. Macroscopic and mesoscopic dynamic responses of the sand deposit were measured and analyzed. Experimental results demonstrated that seismic histories had positive or negative effects on sand liquefaction resistance though sand was densified after previous shakings; these effects were well indicated by the changes in anisotropy characteristics of sand fabric caused by the previous shakings. [ABSTRACT FROM AUTHOR]

A series of COMSOL numerical models were established to study the chemical compatibility of GCLs (geosynthetic clay liner). The effect of chemistry on the mesoscopic structure and the hydraulic conductivity of GCLs was investigated. The factors, including the initial mobile porosity, the swelling ratio, the pore size, and the ionic strength, were discussed as well. The mesoscopic mechanism of the physical and chemical processes of GCLs was explored by the COMSOL models. The hypothesis that the final mobile porosity and the final pore size are the key factors of the hydraulic conductivity of GCLs was proven by the simulation. Meanwhile, when the ionic strength increased from low to medium, the changes in pore size, mobile porosity, and hydraulic conductivity were obvious. However, when the ionic strength increased from medium to high, the changes of these parameters tended to be gentle, and the changes in hydraulic conductivity were not obvious. Moreover, a theoretical model considering the effect of the initial particle size, the initial mobile porosity, and the ionic strength was developed to predict the hydraulic conductivity of GCLs in a chemical solution. This theoretical model was verified by experimental data. A good agreement was obtained. [ABSTRACT FROM AUTHOR]

The local scour around offshore pile foundations often seriously affects the normal operation of offshore wind power. The most widely used numerical simulation method in the study of local scour is the Euler two-fluid model (TFM). However, the contact effect between sediment particles is neglected in this model. Thus, the momentum and energy transfer between sediment particles and the fluid is not realistically reflected, which limits its significance in revealing the mesoscopic mechanism of local scour. Therefore, the computational fluid dynamics-discrete element method (CFD-DEM) numerical model was applied in this study, which fully considers the contact between solid particles and momentum transfer between two phases. The model was first verified by experimental data of a local scour test under clear water scour. Then, the mechanism of local scour was further discussed from macro and micro perspectives. The results showed that CFD-DEM could be effectively used to study the local scour around a pile foundation. The local scour was comprehensively affected by flow velocity, gravity, fluid force, drag force, and interaction between particles, etc. Although the maximum average drag force happened in the area about 90° from the direction of incoming flow, the maximum scour depth always occurred at about 45°. Corresponding findings and conclusions can be used for future reference when designing and protecting the offshore wind power pile.

In order to explore the influence laws of EPS (Expanded Polystyrene) particle sizes on the dynamic deformation characteristics of light weight soil, under the conditions of 15% cement content and 50% EPS particles volume ratio, indoor dynamic triaxial tests of light weight soil with EPS particle sizes of 1 ~ 3 mm, 3 ~ 5 mm, and 5 ~ 6 mm are carried out. Light weight soil numerical models are established by using the PFC3D discrete element software, and the micro mechanical properties of light weight soil with different EPS particle sizes are discussed from two aspects of contact force and displacement field. The results show that as EPS particle sizes increases, the weak contact surface between EPS particles and solidified soil particles increases, and stress concentration is easy to occur. The dynamic strength of light weight soil decreased by 5.75% ~ 20.04% and 7.06% ~ 34.96% with the increasing of EPS particle sizes from 1 ~ 3 mm to 3 ~ 5 mm and 5 ~ 6 mm, respectively. The contact force between EPS particles and soil particles is smaller than that between soil particles in the numerical models. With the increasing of the loads, the contact force of particles increases, and the particles move from the two ends to the middle. With the increasing of EPS particle sizes, the distributions of contact force are more uneven, the specimens are easier to be destroyed, and the displacement field is asymmetrical. However, the displacement interface gradually moves to the middle position with the increasing of loads. It is consistent with the laws that the macroscopic dynamic strength of light weight soil decreases with the increasing of EPS particle sizes. [ABSTRACT FROM AUTHOR]

Solid waste created by the ferrous mining industry has a major number of notable differences. The deficiency of recognition of solid waste features is the key factor limiting its discarding and reuse. In this paper, cemented tailings backfill (F-CTB) was prepared by combining the defluorinated solid waste made in the process of mine's water treatment and tailings. The impact of content of defluorinated solid waste on macroscopic strength and microstructure of filling was investigated experimentally. Lab findings reveal that with the growth of content of defluorinated solid waste in backfill, fill's strength decreases and then increases. Fill's damage mode changes to tensile damage-shear damage-tensile damage, which leads to the following conclusions: in the case of the sufficient amount of defluorinated solid waste, F-CTB will not be delaminated and its strength will be increased. Through the analysis of energy, one can accomplish that, in the case of content of defluorinated solid waste in 60 %, the dissipated energy is smaller, and F-CTB will be stronger and stronger. Energy dissipation is reasonably small while F-CTB's inner cracks is less. The microstructure of F-CTB was observed by SEM and analyzed by energy spectrum. As the content of defluorinated solid waste increases, the hydration products and Ca(OH) 2 crystals in F-CTB will hinder cracks' generation/development ensuring F-CTB's strength. This research sheds new light on clarification of efficient use of defluorinated solid waste in backfill form and offers some practical ways on its efficient treatment and disposal technique. [Display omitted] • The defluorinated solid waste on macroscopic strength and microstructural evolution was investigated. • Lab findings reveal that with the growth of content of defluorinated solid waste in backfill, fill's strength decreases and then increases. • In the case of content of defluorinated solid waste in 60 %, the dissipated energy is smaller. [ABSTRACT FROM AUTHOR]

Geological hazard surveys demonstrate that the history of prior seismic events could affect soil liquefaction resistance under the subsequent earthquakes. The liquefaction of soil with prior seismic history seems not sensitive to the densification after prior reconsolidation. Many attempts of the previous studies have concentrated on the mechanism, impacts, and evaluation of prior destructive seismic history, including large cyclic shear strain and liquefaction history. However, less attention has been paid to the mesoscopic mechanism of the non-liquefying histories commonly caused by weak earthquakes from an experimental view. In this study, centrifuge shaking table tests combined with an inflight mesoscopic image acquisition system were utilized to investigate the macroscopic and mesoscopic behaviors of clean sand deposits under complex seismic sequences. The sequence consisted of three types of seismic motion with different intensities that were equivalent to weak, medium, and strong earthquakes, respectively. Experimental results show multiple weak earthquakes can improve sand liquefaction resistance obviously, which was demonstrated by different evolution patterns of reliquefaction resistance during the tests with and without prior weak earthquakes. The beneficial effects of non-liquefying history were also seen in the cases of models with extensive liquefaction history. Mesoscopic images analysis revealed that multiple weak earthquakes eliminated slender voids, made the particles that constituted loose mesostructures rotate to equalize the voids distribution, and caused quick downward movement of small particles to strengthen interlocking effects among particles. • Concurrent multiscale reliquefaction behaviors of sand deposits are measured using centrifuge shaking table tests. • Sand liquefaction resistance affected by non-liquefaction history is revealed with considering strong earthquake history. • Weak earthquakes equalize void distribution and bolster interparticle interlocking by shifting small particles downward. [ABSTRACT FROM AUTHOR]

In consideration of the actual environment of the cold region, a test scheme of freeze–thaw (FT) cycles was adopted to explore the mechanical characteristics of sandstone with mode-I cracks under the three-point bending, tensile, and compressive compression tests. And to explore the chemical and freeze–thaw (FT) damage mechanisms, variations in the ion concentration of solutions and the microstructures of sandstone are observed and analyzed under the FT cycle. Experimental results show that the sandstone has a marked tendency to weaken after repeated FT cycles. The pH and chemical composition of chemical solutions had different effects on the deterioration degree from FT in sandstone. From the combined effects of the chemical corrosion and the FT cycles, the ion concentration that was dissoluted from a chemical solution had a clear, cumulative time periodicity. The surface of the sandstone sample was found to exhibit variable degrees of degradation after the combined effects of chemical solutions and FT cycles, and with an increasing number of FT cycles, the degradation degree in the surface microstructure of the sandstone gradually increased. Meanwhile, the interior of sandstone samples was clearly degraded. Specifically, the size of mineral particles was reduced, their edges and corners gradually disappeared or became smooth, the surface roughness of the mineral was found to decrease, and its structure became loose. [ABSTRACT FROM AUTHOR]

Tumor treatment fields (TTFields) can effectively inhibit the proliferation of tumor cells, but its mechanism remains exclusive. The destruction of cellular microtubule structure caused by TTFields through electric field force is considered to be the main reason for inhibiting tumor cell proliferation. However, the validity of this hypothesis still lacks exploration at the mesoscopic level. Therefore, in this study, we built force models for tubulins subjected to TTFields, based on the physical and electrical properties of tubulin molecules. We theoretically analyzed and simulated the dynamic effects of electric field force and torque on tubulin monomer polymerization, as well as the alignment and orientation of α/β tubulin heterodimer, respectively. Research results indicate that the interference of electric field force induced by TTFields on tubulin monomer is notably weaker than the inherent electrostatic binding force among tubulin monomers. Additionally, the electric field torque generated by the TTFileds on α/β tubulin dimers is also difficult to affect their random alignment. Therefore, at the mesoscale, our study affirms that TTFields are improbable to destabilize cellular microtubule structures via electric field dynamics effects. These results challenge the traditional view that TTFields destroy the microtubule structure of cells through TTFields electric field force, and proposes a new approach that should pay more attention to the "non-mechanical" effects of TTFields in the study of TTFields mechanism. This study can provide reliable theoretical basis and inspire new research directions for revealing the mesoscopic bioelectrical mechanism of TTFields.

A series of COMSOL numerical models were established to study the chemical compatibility of GCLs (geosynthetic clay liner). The effect of chemistry on the mesoscopic structure and the hydraulic conductivity of GCLs was investigated. The factors, including the initial mobile porosity, the swelling ratio, the pore size, and the ionic strength, were discussed as well. The mesoscopic mechanism of the physical and chemical processes of GCLs was explored by the COMSOL models. The hypothesis that the final mobile porosity and the final pore size are the key factors of the hydraulic conductivity of GCLs was proven by the simulation. Meanwhile, when the ionic strength increased from low to medium, the changes in pore size, mobile porosity, and hydraulic conductivity were obvious. However, when the ionic strength increased from medium to high, the changes of these parameters tended to be gentle, and the changes in hydraulic conductivity were not obvious. Moreover, a theoretical model considering the effect of the initial particle size, the initial mobile porosity, and the ionic strength was developed to predict the hydraulic conductivity of GCLs in a chemical solution. This theoretical model was verified by experimental data. A good agreement was obtained.

The cemented mercury slag is widely distributed in Guizhou province, China. It has the characteristics of loose structure, big difference in particle size and so on. It is of great significance to study its mechanical properties and failure mechanism. The representative cemented mercury slag was selected for uniaxial compression- CT scanning test. Based on the particle discrete element PFC3D program, the numerical experiments corresponding to the laboratory test were carried out. The microscopic failure law and mechanism under uniaxial compression were studied. The results show that the stress-strain curve o£ the sample has the characteristics o£ strain softening. Before the peak strength, the structure o£ the specimen tends to be tight, the cracks begin to appear near the peak strength. In the strain softening stage，the structure is rapidly destroyed； the crack number grows slowly before the peak intensity. After the peak intensity，there is a sharp increase，and the overall variation is step-like. As the axial stress increases，the displacement increases continuously，and the angle between the displacement contour and the horizontal plane gradually becomes larger，eventually reaching 45°，The force on the parallel bond key gradually increased and is reduced until the final damage. The particle displacement vector near the upper part appears chaotic after the peak intensity. The contact number of particles increases at the initial stage, but with the increase of axial stress, the number of particle contacts gradually decreases and decreases sharply after the peak intensity. [ABSTRACT FROM AUTHOR]

• Effect of polymer shapes on damage and fracture evolution of 3D-PPL based fills were studied. • Three shapes of polymer (e.g., cross, quarter, and EEP) were used to prepare filling specimens. • 3D-PPL demonstrated a certain interface bonding and supporting effect on filling specimens. • Incorporating 3D-PPL into CTB materials effectively decrease the penetrated pores' number. • The 3D fractal dimension of cracks in 3D-PPL based fills is greater than that of ordinary fills. The strength property and damage mode of cementitious tailings backfill (CTB) are governed by its structural characteristics in the presence of the microstructure/internal defect effects. However, this correlation is still unclear for 3D-printed polymer (3D-PPL) based CTB materials. Hence, the mechanical properties of microscopic damage and fracture evolution of 3D-PPL reinforced CTB were studied in this study. The fracture of CTBs with three shapes of polymer (cross, quarter, and EEP) were visualized and digitally characterized by the Brazilian splitting test, scanning electron microscopy (SEM) and industrial computed tomography. Experimental results indicate that CTB's failure mode mainly starts from the low-density pore area, gradually evolves to a crack, and finally expands to the main crack by the center of the specimen. 3D-PPL has a certain interface bonding and supporting effect on CTB specimens, and the 3D-PPL specimen's porosity is significantly below that of ordinary backfill. Incorporating 3D-PPL into CTBs effectively decrease the penetrated pore number, while enhancing the density of CTB's microstructure, which dominates the strength and integrity of specimens. 3D-PPL-based backfill specimens also indicate a complex and diverse damage pattern, with a negative link between crack volume and tensile strength. The 3D fractal dimension of cracks in 3D-PPL-based fills is greater than that of ordinary fills. Combined with SEM-EDS tests, CTB's hydration materials were mostly CSH gels, which interleaved as nucleating agents to inhibit crack growth. The findings of the present work will be beneficial for manufacturing and operational usage of 3P-PPL-based backfills. [ABSTRACT FROM AUTHOR]

In order to better understand the mechanical properties of graded crushed rocks (GCRs) and to optimize the relevant design, a numerical test method based on the particle flow modeling technique PFC2D is developed for the California bearing ratio (CBR) test on GCRs. The effects of different testing conditions and micro-mechanical parameters used in the model on the CBR numerical results have been systematically studied. The reliability of the numerical technique is verified. The numerical results suggest that the influences of the loading rate and Poisson's ratio on the CBR numerical test results are not significant. As such, a loading rate of 1.0–3.0 mm/min, a piston diameter of 5 cm, a specimen height of 15 cm and a specimen diameter of 15 cm are adopted for the CBR numerical test. The numerical results reveal that the CBR values increase with the friction coefficient at the contact and shear modulus of the rocks, while the influence of Poisson's ratio on the CBR values is insignificant. The close agreement between the CBR numerical results and experimental results suggests that the numerical simulation of the CBR values is promising to help assess the mechanical properties of GCRs and to optimize the grading design. Besides, the numerical study can provide useful insights on the mesoscopic mechanism.

Instances of historical earthquakes demonstrated that sandy grounds can liquefy more than once (reliquefaction) when earthquakes occur in succession (e.g., the main shock and aftershocks). Previous laboratory experiments proved that the resistance of sand to reliquefaction might be lower after its first liquefaction despite an increase in density after the first liquefaction. To clarify the reliquefaction behavior of sand and its mesoscopic mechanism, a series of small-scale shaking table tests were performed for different shaking durations on a sand specimen to simulate multiple liquefactions. Mesoscopic images of the sand particles were taken with a stereomicroscope and an industrial camera both before and after each liquefaction. Then, a digital image processing technique was used to obtain the mesoscopic parameters of the sand particles, namely, the apparent void ratio, long-axis direction, and average coordination number. The test results demonstrated that the sand specimen could reliquefy up to three times according to various shaking durations, suggesting that the density of the sand specimen plays a significant role in the reliquefaction behavior of sand. The analysis of the mesoscopic parameters indicated that the long-axis directions of sand particles are prone to be horizontal in the initial state (before the first liquefaction), whereas after liquefaction and redeposition, the long-axis directions tend to be vertical, suggesting that the decrease in reliquefaction resistance results from the change in the mesoscopic structure of the sand. [ABSTRACT FROM AUTHOR]

In order to reveal the macroscopic mechanical properties and mesoscopic failure mechanism of cemented soil-rock mixture (CSRM, for short) that widely exists in nature, a series of large-scale triaxial tests are carried out. Firstly, specimens of soil-rock mixture without cement and specimens mixed with small amounts of cement are compared to demonstrate that it is necessary to further divide soil-rock mixture into CSRM and uncemented soil-rock mixture. Then, laboratory large-scale triaxial tests on CSRM specimens with different rock block proportion (RBP, for short) are conducted to explore the effect of RBP on the macroscopic mechanical responses of CSRM. Finally, based on the developed three-dimensional discrete element modeling technology for irregularly shaped rock blocks and soil-rock mixture, a numerical simulation of laboratory tests is performed to analyze the mesoscopic failure mechanism of CSRM. The results indicate that CSRM specimen with 3 % cement exhibits strain softening and localization, whose strength and modulus increase dramatically compared with those of specimen without cement. Peak strength and brittleness index of CSRM specimen both are decreased with increasing RBP under the confining pressures of 0.1, 0.2 and 0.3 MPa. In CSRM specimens, microcracks initiate at the soil-rock interfaces, and then propagate in soil matrix bypassing the rock blocks with multiple tortuous failure bands coming into being throughout the specimen eventually. The effect of RBP on strength of CSRM depends on the combination of skeleton-effect of rock blocks and cementation-effect of the specimen. [ABSTRACT FROM AUTHOR]

Particle flow code was used to reconstruct the brittle-ductile-plastic transition behavior of Jinping marble，and obtained micro-parameters were used to construct the discrete element model of rock fragmentation with disc cutter. The process of a single TBM disc cutter intruding into rock with a single fissure was simulated，the effect law of fissure angle and confining pressure on rock fragmentation was analyzed，and finally the microscopic mechanism of rock fragmentation was discussed. The results show that:Under the action of a single disc cutter，the rock mass with a single fissure shows four phases consisting of compression failure，regular cracks initiation and propagation，crushed zone formation and main cracks coalescence；Wing crack appears at the central section when the fissure is horizontal，and it appears at the section near the fissure tip while the fissure angle is small，with the increase of fissure angle，wing crack appears at the fissure tip. The crushed zone increases with the confining pressure，and the lateral crack propagates towards free surface under high confining pressure；Fissured rock mass is easier to be damaged compared to intact rock，and the difficulty degree of rock mass failure varies with fissure angle，which is 15°<45°<60°<0°<30°< 90°<75°. It is more difficult to be damaged under the confining pressure than that without the confining pressure，and the difficulty degree increases with the confining pressure. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of fiber orientation on the resistance of seepage-induced erosion in fiber-reinforced sand. To clarify the discrepancy and mechanism of different-oriented fibers improving the resistance of the sand matrix, a series of DEM-Darcy coupling simulations were conducted. The microscopic parameters of fiber-reinforced sand were confirmed by the rigorous calibration procedure. The fibers perpendicular to the seepage direction were found to increase the difficulty of moving fluid through the specimen and significantly reduce the erosion rate of the specimen. These macroscopic behaviors acquired corresponding explanations at the mesoscopic scale, including the evolution of fiber-sand contact orientation, coordination number, average normal contact force, tensile force, and energy dissipation. According to the simulation results, it is found that the highest proportion of tensile force in perpendicular fibers can reach 80%, while the parallel fibers are only 40%, which indicates that the perpendicular fibers have a significant netting effect. The mesoscopic behaviors reasonably revealed the role of the fibers with different orientations on the sand matrix during the seepage. This study is beneficial for further understanding the mechanical behaviors of fiber-reinforced sand under seepage-induced erosion in safety engineering.