Particle Flow Based Modeling On Soil Feature And Research Of Soil Arching Mechanism

Based on DEM software PFC 3D,by which can analyz soil mechanics through particle flow,this thesis builds the mapping relation between macroscopic and microcosmic representive factors of soils including sand and clay.Further,this thesis gives a feasible method on simulating soil with typical properties.And finally,a numerical model is built to reveal the soil arching mechanism including the stages like arc formation,development,settlement and failure,and to investigate how frictional angle and cohesion influnces the soil arching.The mapping relation shows: To discrete element sand model,as the friction coefficient among the discerete element(balls)increases,the friction angle of sand model increases;other factors like stress history,normal stiffness,stiffness ratio(of nomal over shear derection)make little difference on sand strength;while Poisson's ratio is mainly affected by stiffness ratio,Young's modulus is mainly affected by normal stiffness and stiffness ratio;hence,the suggested simulation priority assignment of sand should be friction angle,Poisson's ratio,and Young's moduls.To clay,as the friction among the discerete element(balls)increases,the friction angle of clay model increases;as the bond strength among the discerete element(balls)increases,the cohesion of clay model increases;while Poisson's ratio is mainly affected by stiffness ratio,Young's modulus is mainly affected by normal stiffness and stiffness ratio;hence,the suggested simulation priority assignment of caly should be friction angle,cohesion,Poisson's ratio,and Young's moduls.The numerical model shows: Sand without cohiesion cannot form stable arch and will collapse similarly inspite of the variation of its friction angle.With cohesion,clay preforms three typical feature: little cohesion can not resist the shear force between balls and the soil will collapse same like sand;Huge cohesion between balls can resisit all internal force without bond broken,so that the soil performs as concrete;With cohesion varies in a proper range,the internal force occurred in soil will be relaxed as the bond brekes and soil structure reforms,which accompanied by the formation of stable soil arch.In summary,cohesion among soil is the key factor of stable soil arch while the friction angle of the soil can only influce the performance of soil arch instead of being a key factor that determines the existence of soil arch.