3D Static And Dynamic Analysis On Macro And Meso Characteristic Of Soil-rock Mixture With Irregular Rock Particles Using PFC^3D

Soil-rock mixture is an extremely complex geotechnical medium,in which the particle size and strength of "soil" and "stone" are quite different,which makes the microstructure characteristics of soil-rock mixture have a great influence on its macro mechanical properties.The randomness and complexity of its microstructure determine that its mechanical behavior is very complex,and this kind of material is widely distributed in nature.In order to fully reveal the influence of stone content and stone particle shape on the macro and micro mechanical behavior of soil-rock mixture,it is necessary to establish the relationship between macro mechanical behavior and micro mechanism of soil-rock mixture,and explore the bearing capacity and deformation and failure characteristics of soil-rock mixture from the mechanism,so as to strengthen the understanding of this kind of special geological body,This is of great significance for disaster prevention and construction of practical projects.Based on discrete element software and FISH programming language,the static triaxial numerical test model of flexible boundary and the dynamic triaxial numerical test model of rigid boundary for soil-rock mixture are established,the monitoring program and post-processing program of real-time output average coordination number and contact force chain are developed.Through a large number of static and dynamic triaxial numerical tests,the effects of stone content and stone particle shape on the macro and micro mechanical behavior of soil-rock mixture are studied.The main contents and innovations of this paper are as follows.(1)On the basis of scanning and numerical restoration of the true shape of stone particles,the shape of stone particles can be divided into three categories: slender,flat and spherical.In order to simulate the effect of rubber membrane in laboratory test,a flexible boundary composed of particles was developed.The static triaxial numerical test model of soil-rock mixture with flexible boundary was successfully developed,and the simulation of flexible confining pressure loading was realized.The undrained effect under dynamic condition is simulated,and the dynamic triaxial numerical test model with rigid boundary is developed.The monitoring program and post-processing program of real-time output average coordination number and contact force chain are developed.(2)The method of controlling preloading friction coefficient and boundary contraction method are proposed to control the density and randomness of soil-rock mixture.By setting the upper and lower limits of the loading speed,the overflow problem of the loading speed of the servo control in the traditional calculation method is effectively solved,and the accuracy of the servo control is significantly improved.(3)Compared with the actual laboratory test data,through the sensitivity analysis of soil meso parameters,test boundary conditions and soil-rock mixture meso parameters under different rock content,the influence of each parameter on the numerical test is quantitatively evaluated,and the rapid calibration of soil-rock mixture parameters is realized.(4)Based on 9 groups of orthogonal static triaxial tests of soil-rock mixture,the relationship between meso parameters(soil soil,soil stone,stone stone contact parameters)and macro parameters(elastic modulus,compressive strength)of soil-rock mixture is analyzed,and the four parameters nonlinear relationship formula of macro parameters and micro parameters of soil-rock mixture with stone content from 0% to 40% is obtained by regression.(5)Based on the reconstruction model of soil-rock mixture,the static triaxial discrete element numerical simulation is carried out,and the numerical experiments are carried out for soil-rock mixture with different stone content(20%,40%,60%,80%)and stone particle shape(slender,flat,quasi spherical).The macro and micro mechanical parameters of the soil-rock mixture in the numerical experiment are quantitatively analyzed,such as the particle contact and the strength of the contact force,the strength of the contact force,the strength of the contact force and the strength of the contact force the evolution process of particle movement and coordination number changes with the loading process explains the influence of stone particle shape and stone content on the shear strength and deformation characteristics of soil-rock mixture.The results show that the mechanical properties of soil-rock mixture are significantly affected by the shape of stone particles and the stone content,and the variation law is complex.When the stone content is 40%,the local force transfer skeleton can be formed,and when the stone content is 60%,the integral skeleton can be formed.The angular(slender,flat)stone particles can effectively improve the shear strength through occlusion.During the shear failure process,the movement and rotation of the stone particles cause the internal structure adjustment,which affects the macro shear strength and deformation characteristics of the soil-rock mixture.(6)The effects of stone particle shape,stone content and confining pressure on dynamic shear modulus and damping ratio of soil-rock mixture are studied,and the mechanism of dynamic characteristics difference is expounded.The results show that the dynamic shear modulus decreases,and the dynamic damping ratio increases with the increase of dynamic strain.The results show that the angular stone particles can improve the dynamic shear modulus and dynamic damping ratio of soil-rock mixture.At the same time,the increase of stone content also leads to the increase of dynamic shear modulus,and the dynamic damping ratio decreases with the increase of stone content.