Study On Dynamic Response And Settlement Prediction Of Soil-rock Mixed Subgrade Under Traffic Load

With the sustainable growth of Chinese economic development,road traffic building has shown a booming trend.In the process of building roads in mountainous or hilly areas,due to the complex terrain and transportation difficulties,it is inevitable to use the earth rock mixture formed by excavating mountains as the main filling material of the subgrade.At the same time,the subgrade,as the foundation of the road,may occur a series of diseases such as longitudinal cracking and local deformation under long-term vehicle load,which will affect the safety of driving vehicles.Therefore,this thesis takes the soil rock mixture as the research object,studies the static and dynamic characteristics of the soil rock mixture under different conditions through large-scale indoor triaxial tests,and on this foundation,numerical modeling and theoretical calculations are adopted to explore the dynamic response of the soil rock mixture subgrade under different vehicle loads and vehicle speeds,as well as the development law of cumulative settlement of foundation under the action of reciprocating vehicle load.The main work of this thesis is as follows:(1)Through a series of indoor conventional geotechnical tests,the particle gradation and compaction characteristics of the earth rock mixture are analyzed.According to the test results,the physical properties of the filler are obtained,which provides reference for the subsequent large-scale triaxial test.(2)Based on a large static triaxial test,the effects of amount of stone and surrounding pressure on the stress-strain characteristics,adhesion and internal friction angle of the earth rock mixture are studied.The results show that the three different stone content of samples in the confining pressure is 100 k Pa,150 k Pa,200 k Pa,stress-strain curve belong to strain hardening model;When the stone content increases from 30% to 70%,the cohesion is reduced progressively,while the angle of internal friction rises progressively;under the condition of a certain stone content,the surrounding pressure and static strength show a linear growth relationship.Through large-scale dynamic triaxial tests,the influence of different surrounding pressure,dynamic stress levels and times of loading on the accrued plastic strain and dynamic elastic modulus of soil and stone mixes was investigated.The results show that there are salient changes in the variation patterns of the cumulative strain curves of the specimens at different conditions,and the critical dynamic stresses of the specimens in various enclosing pressures are acquired;The dynamic modulus of elasticity initially rises with the growth of the number of vibrations,and then slowly reaches to stability.(3)Using ABAQUS software to create 3D numerical models of road systems,and vehicle loads were simulated using moving uniform loads.Analyze the evolution of dynamic stress and deformation of soil-stone mixed roadbed under different traffic speeds and vehicle loads,and determine the depth of the roadbed area to work.The results show that on the cross section of the road base,the vertical stress at the wheel action position is the largest,and the stress decreases away from the action point;The dynamic stress and deformation attenuate fastest within 1m of subgrade depth;The impact of vehicle load on roadbed is greater than that of vehicle speed;With the increase of vehicle overload rates,the greater the dynamic response of the subgrade,and the depth of the working area of the subgrade is between 2.33 m and 4.15 m.(4)In order to study the long-term settlement of soil-rock mixed roadbed during vehicle passage,an empirical model of cumulative plastic strain for soil-rock mixed roadbed was established according to the results of dynamic triaxial test and its accuracy was verified;Secondly,the influence of vehicle dynamic load on dynamic deflection stress at different depth of subgrade is determined by numerical simulation;Finally,combined with the layered summation method,the long-term settlement calculation method is proposed,and the long-term settlement of typical flexible base asphalt pavement under different vehicle loads is predicted.The results show that with the growth of vehicle load,the dynamic deflection stress also rises little by little;The settlement of roadbed caused by different vehicle load first grows rapidly at the beginning of loading,and then tends to stabilize later;The settlement of subgrade is significantly affected by vehicle overload.When the vehicle overload rate is 100%,the settlement of subgrade is24.65 mm.