Study On The Macroscopic Mechanical Properties And The Mesoscopic Mechanisms Of Cohesionless Coarse-grained Soil Considering Particle Breakage

Cohesionless coarse-grained soil is a commonly used filling material in road,railway and other engineering fields.Particle breakage of coarse-grained soil will significantly change its mechanical properties and affect the safety and durability of the engineering.The existing researches either ignore particle breakage,or consider particle breakage,but the particle breakage model needs to be optimized,and the mesoscopic mechanism explanation is insufficient.Load mode and particle property are the main factors affecting particle breakage.In this dissertation,particle models that can accurately characterize particle breakage was established.Through laboratory tests and discrete element simulation,the influences of confining pressure,cyclic load and particle shape on particle breakage were analyzed,and the influence mechanism of particle breakage on macroscopic mechanical indexes was revealed from the mesoscopic perspective.The main research contents and conclusions of this dissertation are as follows:(1)The breakable particle model with real shape was constructed by Voronoi division method.Based on single particle crushing simulation,the influence of particle size,cell number,loading speed and micro strength parameters on single particle crushing strength was studied.A calibration method of micro-bonding parameters was proposed to precisely control the distribution characteristics of spherical particle crushing strength.A particle aggregate model that conforms to Weibull distribution of real particle crushing strength was constructed.It laid a foundation for the discrete element method to study the breakage characteristics and mechanical properties of coarse-grained soil.(2)The effects of confining pressure and intermediate principal stress coefficient on the mechanical properties of coarse-grained soil considering particle breakage were investigated by numerical simulation of triaxial compression tests.The influences of confining pressure and intermediate principal stress coefficient on breakage degree and pattern were analyzed.The evolution laws of coordination number,sliding contact proportion and contact force of coarse-grained soil with confining pressure and intermediate principal stress coefficient under breakable condition were clarified,and the mesoscopic mechanism of shear strength and volume change was explained.The applicability of the relationship between shear strength and fabric anisotropy parameters under breakable case was verified,and the reason for the change of shear strength was revealed based on the fabric anisotropy.The influence of particle breakage on macroscopic and mesoscopic characteristics of coarse-grained soil was clarified.(3)The effects of loading times and dynamic load amplitude on the macroscopic and mesoscopic mechanical properties of coarse-grained soil considering particle breakage were investigated by the confined cyclic loading test and discrete element simulation.The evolution laws of macroscopic deformation characteristics,particle breakage characteristics and mesoscopic variables of coarse-grained soil with loading times under different amplitudes were analyzed,and the relationship between input energy and relative breakage was established.By comparing the plastic strain considering particle breakage or not,it was clarified that particle breakage is an important reason for permanent deformation of coarse-grained soil.Based on the coordination number,sliding contact proportion,contact direction,contact force magnitude and distribution at steady state,the mesoscopic mechanism of the influence of amplitude and particle breakage on plastic strain of coarse-grained soil was revealed.(4)The influence of particle shape on mechanical properties of coarse-grained soil considering particle breakage was investigated by numerical simulation of triaxial compression test.Particle models with different elongation index,flatness index and angularity were constructed,and the influence of particle shape on the breakage degree and pattern was explored.The correlation between relative breakage and input energy under different shape parameters was clarified.The effects of particle shape and particle breakage on macroscopic and mesoscopic properties such as shear strength,volume change,coordination number and contact force were obtained.Based on the fabric anisotropy,the mesoscopic mechanism of the shear strength variation with the particle shape was revealed.