Experimental Study Of Dynamic Characteristics Of Expansive Soil From Yanzhou-Shijiusuo Railway Under Cyclic Loading

Nowadays,the railway industry in our country is developing rapidly and train speed-up and new high-speed railway are taken as the new developing direction.However,many railway lines need to traverse the expansive soil distribution area.As a expansive soil railway roadbed,it is difficult to guarantee its strength,deformation and stability under the action of long-term cyclic loading and water.So it lays a hidden danger for the healthy operation of the railway.Under this background,expansive soil from yanzhou-shijiusuo railway was selected as the research object.And the effects of water content,loading frequency,consolidation pressure,dynamic stress amplitude on dynamic strength,critical dynamic stress,accumulative plastic strain accumulative pore pressure and other dynamic characteristics of expansive soil under cyclic loading were studied.The main research achievements are as follows:1.The relationship curve between accumulative plastic strain of expansive soil and the number of cycles presents three typical states: stable type,critical type,and disruptive type.We suggest that the maximum dynamic stress under the stable curve should be taken as the critical dynamic stress.2.The dynamic strength and critical dynamic stress of expansive soil are significantly affected by water content and both of them decrease with the increase of water content.When the confining pressure is 50 kPa and the moisture content is from 15% to saturated,the critical dynamic stress of expansive soil changes from 520 kPa to 40 kPa,and the decay rate is as high as 92.3%.Therefore,the car traffic should be restricted during the rainy season.We find there is a critical state line between critical dynamic stress and saturation,which can be used to judge whether the soil is in a stable,critical,or destructive state.3.In the test of unsaturated soil,the critical dynamic stress and dynamic strength increase significantly with the increase of frequency.The relationship between critical dynamic stress and frequency is linear,but the effect of frequency on dynamic strength and critical dynamic stress is not obvious in saturated soil test.4.Based on the Monismith strain model,the empirical fitting model of the failure accumulative plastic strain considering the dynamic stress amplitude,the confining pressure and the number of loads is established.The established empirical model of cumulative pore pressure-accumulative plastic strain can be used to predict the relationship between cumulative plastic strain value and pore pressure value of soil after long-term cyclic loading.