Simulation Of Particle Flow In Soil-arching Effect Of Pile-net Structure Subgrade

In recent years,the pile-net structure subgrade has been widely used in high-speed railway subgrade engineering,and has achieved good application results.In the course of its work,the soil arching effect is the main load transfer mechanism,but the theoretical research on the formation,evolution mechanism and engineering design of the soil arching effect still lags behind the practical application.Based on the discontinuous characteristics of soil,this paper establishes the discrete element analysis model of soil arch formation and evolution,and analyzes the formation and variation of soil arch under static and dynamic loading conditions from a microscopic point of view,and then studies the different embankment height and pile cap width.The soil arching pattern and load transfer mechanism of the pile-net structure under the design conditions,such as the net spacing of the pile,the strength of the geogrid and the internal friction angle of the embankment,the soil settlement law under the soil arching effect is obtained.The conclusions and results are as followsAccording to the indoor soil arching model test,a two-dimensional particle flow analysis model was established and verified.The variation of contact force chain,vertical stress and vertical displacement of the pile foundation in the subgrade was analyzed from a mesoscopic perspective..The results show that the contact force chain between the particles shows obvious stress concentration on the top surface of the pile.With the occurrence of differential settlement of piles and soils,it is inclined to the upper part of the pile and gradually evolves into an elliptical arch with an arch height of about 1.15 times.Clear spacing.With the increase of relative displacement of piles and soils,the"soil arch structure" experienced the evolution process of production-development stability".According to the size and distribution of the vertical stress of the soil inside the embankment,the embankment structure is divided into three areas:stable zone,soil arching zone and recovery zone.The vertical stress above the pile top and the soil between the piles in the stable zone increases linearly with the increase of the embankment depth,and the slope is about the weight of the embankment filling.The vertical stress above the pile top in the soil arching zone increases faster,while the stress above the pile is smaller.The lowermost recovery zone is located inside the soil arch structure,and the vertical stress between the piles increases linearly.The vertical displacement of the upper part of the embankment appears as a stratification phenomenon,and there is a distinct equal surface.In order to study the bearing characteristics of pile-net structure subgrade under static load and its influence on soil arching effect,a static element discrete model of static load is established,and an effective simulation of soft soil between piles is proposed.Particle flow method.Furthermore,the discrete element analysis model under different conditions of different embankment height,pile cap width,pile spacing,geogrid strength and internal friction angle of embankment is established,and the influence law of the above engineering design parameters on soil arching effect is obtained.The results show that the embankment filling height has a significant influence on the formation of soil arches.When the ratio of the embankment height to the net spacing of the piles(h/s)is greater than or equal to 1.5,the pile-soil stress ratio has a peak value,and the soil arch fully functions at this time;When the ratio of the embankment height to the net pile spacing is less than 1.5,the pile-soil stress ratio does not reach the peak value,and the soil arching effect is incomplete.In addition,the greater the ratio of the width of the pile cap to the clean spacing of the pile,the higher the strength of the geogrid,the greater the internal friction angle of the embankment filler,the greater the pile-soil stress ratio,and the more obvious the soil arching effect.Establish a three-dimensional particle flow analysis model of pile-net structure,and analyze the variation of vertical displacement and vertical stress of the pile-space structure.The results show that the soil arch occurs in the upper part of the adjacent pile,and the force chains are connected to each other to form a dome-like structure.The height of the vault is about 1.15 times the diagonal spacing of the diagonal piles.When the soil arch structure reaches a steady state,the relative displacement of the piles and soils is 3mm,which is larger than that in the two-dimensional state.The pile-soil stress ratio between the pile top and the four pile cores is 6.19.It is smaller than the two-dimensional state;thus,the numerical results obtained by the two-dimensional model calculation result for the soil arching effect are large.Establish the particle flow analysis model of pile net structure under dynamic load,and study the dynamic characteristics of soil arch structure under long-term cyclic loading.When the dynamic load amplitude of the embankment surface is the same as the static load,the contact force chain shape between the embankment particles is constant,but the arch height is lower than that of the static load.Under the dynamic load,the surface of the embankment is large,the soil between the piles is obviously settled,and the vertical stress on the top surface of the pile is less than the static force under the same conditions.With the increase of the vibration period,the vertical stress above the soil between the piles increases remarkably,the pile-soil stress ratio decreases,and the soil arching effect is weakened.In addition,the frequency of the dynamic load is also an important factor affecting the soil arching effect.The higher the frequency,the more obvious the weakening effect of the soil arching effect.The above research results have laid a foundation for further deepening research on the mechanism of soil arching effect of pile-net structure.