Meso-numerical Study Of Triaxial Tests On The Particle Breakage Properties Of Coarse-grained Soil Under Shearing And Its Influence On Strength

The phenomenon of particle breakage is a mesoscopic phenomenon in the process of loading.Particle breakage has a significant impact on the strength and deformation of coarse-grained soil.It can reduce the shear strength of the soil,reduce the bearing capacity of the foundation,and then affect the security and stability of the structure.In view of the fact that the discrete element method can be used to simulate and observe the changes in the meso-level of soil particles,this paper focuses on the coarse-grained soils with breakable particles.Based on the PFC method,the numerical simulation of the triaxial test is carried out to explore the development of particle breakage during the shearing process,as well as the law and its influence on the mechanical properties of soil and its internal mechanism.The main work done in this paper and the conclusions obtained are as follows:(1)Compile the PFC program for the numerical simulation of the triaxial test of different drainage paths.Combining the basic principles and methods of discrete elements,the simulation of different drainage paths is realized through servo control.Sensitivity analysis of density,confining pressure,and bonding strength is carried out in numerical experiments under different drainage paths.Through comparison with existing research results,the correctness of the procedure and the rationality of the meso-parameters are validified.(2)Numerical simulations of triaxial tests under different densities,different confining pressures,different particle crushing conditions and different drainage paths were carried out.Furthermore,the effects of compactness,consolidation confining pressure,bonding strength and drainage conditions on the shear strength of soil samples after crushing are studied.The results show that:(1)The higher the confining pressure,the greater the number of broken particles.Compared with the unbroken sample,the greater the number of broken particles,the greater the decrease in strength.(2)The higher the bonding strength,the smaller the number of broken particles and the smaller the strength drop.(3)The degree of particle breakage is related to multiple factors such as consolidation confining pressure,bonding strength,and drainage conditions.(3)Comparing the results of different levels of particle crushing under different drainage paths,it is found that:(1)Under drainage conditions,particle crushing has a significant impact on volumetic strain,and the impact on strength is smaller than that of undrained paths;and under undrained conditions,particle crushing can cause the increase in pore water pressure of the sample,which is in good agreement with the volume change under drainage conditions;(2)The increase in effective stress is the main cause of particle breakage,especially under undrained conditions,when the sample has the higher dilatancy,the effective force is even greater than the total stress.(3)The impact of particle breakage on the macroscopic properties of soil has a change process from quantitative change to qualitative change.When the number of broken particles in the early stage is small,the strength of the soil will fluctuate;when the number of broken particles is large enough,the soil begins to soften sharply.Therefore,the phenomenon of particle breakage has a significant effect on the relationship of the stress-strain curve.