Numerical Simulation On Dynamic Deformation Characteristics Of EPS Particles Light Weight Soil By Discrete Element Method

As a new type of synthetic geotechnical material,light weight soil mixed with EPS particles is widely used in highway,railway,bridge head and abutment back backfill engineering because of its advantages of light weight,high strength,good self-reliance,simple construction technology,excellent vibration isolation and heat insulation.In this paper,loess is used as raw material,EPS particles as light material and cement as curing agent to prepare light weight soil mixed with EPS particles.The influence of EPS particles size and EPS particles volume ratio on the dynamic deformation characteristics of light weight soil was studied by dynamic triaxial test in laboratory.The PFC^3D discrete element software is used to establish the dynamic triaxial test numerical model of light weight soil.The feasibility of the numerical model of light weight soil is demonstrated by comparing the hysteretic curves of indoor test and numerical simulation.The micro mechanism of dynamic deformation of light weight soil is discussed from three aspects:indirect contact force,displacement field and velocity field.The results show that:?1?The hysteresis curve of EPS light weight soil reflects the nonlinearity,strain accumulation and the hysteresis of dynamic strain to dynamic stress.With the development of dynamic loading,the axial strain?_d increases,the dynamic stress?_d increases in the form of hyperbola,and the backbone curve is strain hardening.The dynamic strength of lightweight soil decreases with the increase of EPS particles size and EPS particles volume ratio,and increases with the increase of confining pressure.?2?With the increase of the friction coefficient of particles,the failure strength of the backbone curve of numerical simulation of lightweight soil is increasing.Compared with EPS particles,increasing the friction coefficient of soil particles makes the failure strength increase more significantly.With the increase of particle stiffness ratio,the failure strength of the backbone curve increases,but the axial strain corresponding to the failure strength decreases,and the initial elastic modulus of the sample increases slightly.With the increase of contact bond strength,the failure strength of light weight soil backbone curve increases gradually.Under high confining pressure,the contribution of bond strength to shear strength of the specimen is basically unchanged,while the contribution of friction strength to bond strength increases,making the specimen more mal eable.?3?Under different test conditions,compared with the hysteresis curves of numerical simulation and the dynamic triaxial tests in the laboratory,the peak values of dynamic stress and corresponding dynamic strain of light weight soil mixed with EPS particles are similar.At the same vibratio n level,the peak value of dynamic stress increases with the increase of confining pressure,and decreases with the increase of EPS particles size and EPS particles volume ratio.However,because the particles in the numerical simulation are rigid bodies,and the shape characteristics and stress state deviate from the actual soil sample,the method of applying reverse velocity to the wall is used to simulate the change of stress direction,resulting in the slightly large fluctuation of the hysteretic curve and the rapid reduction of dynamic stress during unloading.As a whole,the hysteretic curves of indoor dynamic triaxial test are basically consistent with the simulation results,and the three-dimensional discrete element model can simulate indoor dynamic triaxial test of light weight soil wel.?4?In the light weight soil numerical samples,according to the value of contact force of particles:soil particles-soil particles>soil particles-EPS particles>EPS particles-EPS particles The particles at both ends of the sample move towards the middle in the vertical direction,and the particles in the middle move towards the periphery in the horizontal direction.The displacement of the middle particles is always smaller than that of the two ends,which shows a certain"lag".In the loading stage,the indirect contact force and displacement of particles increase as a whole,which is consistent with the development law of dynamic stress and axial strain in the hysteretic curve,which shows that the sample is compressed in the macroscopic.In the unloading stage,the indirect contact force of particles decreases gradually,and the displacement of particles in reverse motion decreases,which is reflected in the rebound deformation of samples.?5?With the increase of EPS particles size from 1-3mm to 3-5mm and 5-6mm,its normal and tangential stiffness decreases,the contact force between EPS particles and soil particles is smaller,and the contact force distribution in the numerical sample is more uneven,resulting in stress concentration.The displacement distribution of particles is asymmetric,the increment of displacement at both ends is increasing,and the displacement interface moves to the middle position gradually,which makes the extrusion belt of the sample move from both ends to the middle.This is consistent with the law that the dynamic strength of light weight soil decreases with the increase of EPS particles size.?6?With the increase of EPS particles volume ratio from 40%to 50%and 60%,the number of EPS particles in the sample increases,the backbone structure of soil particles decreases,and the particles movement speed in some areas is too large,which makes the bearing capacity of the sample weakened and more vulnerable to damage.This is consistent with the law that the dynamic strength of light weight soil decreases with the increase of EPS particles size and volume ratio.