Numerical Simulation Of Thermal-Dynamic Responses Of Crushed Rock Embankment In Permafrost Regions

Permafrost is a general term of dispersed materials such as soil,rock,soil and so on,which is in zero or below zero temperature and contain part of freezing water.The ice content and the proportion of water in different phases in permafrost will change obviously with the change of external temperature,which determines that the mechanical and thermal properties of permafrost are dynamic and unstable.Therefore,in the construction of railway,highway and other road engineering in permafrost area,the embankment of crushed rock structure is widely used to strengthen cooling and cooling of permafrost,prevent the permafrost from heating up or even thawing settlement,and protect the thermal stability of permafrost embankment.However,the displacement and deformation of crushed rock embankment have the characteristics of discontinuity and non-uniformity,which is more prominent under the action of dynamic load.So the numerical analysis method of block discrete element(DEM)can be adopted.This method takes a full account of the interaction between blocks and can simulate the deformation of discontinuous media with multiple contact surfaces effectively.The dynamic response of crushed rock embankment can be simulated and studied effectively.This paper is based on crushed rock embankment in the Qinghai-Tibet Railway,and based on the indoor triaxial test of the crushed rock aggregate,the feasibility of using DEM to analyze the mechanical problem of the crushed rock aggregate is verified.On the basis of this,establishing the thermal-dynamic response model of crushed rock embankment,based on the typical temperature field of four seasons,the dynamic responses of crushed rock embankment is analyzed by DEM under seismic load and train load.It can provide reference for safe operation of Qinghai-Tibet Railway and engineering technology.Mainly carried out the work for following aspects:(1)Based on the calculation principle of DEM,the triaxial shear test of crushed rock aggregate is simulated.It is verified the reliability of DEM for analyzing the mechanical problems of crushed rock material.It is found that the deformation and failure of crushed rock aggregate is mainly due to the sliding and separation of blocks to form shear band under shear action.With the increase of axial strain,the shear band also extends continuously.According to the Mohr strength envelope,based on the results of the numerical analysis,it is found that the cohesive force of crushed rock aggregate is almost zero,which is in accordance with the condition that there is no cohesive force between crushed rock blocks.(2)Establishing the thermal-dynamic response analysis model of crushed rock embankment in permafrost.Based on the temperature field environment of four typical seasons,the seismic dynamic response of crushed rock embankment under seismic load is analyzed by DEM.The results show that the response values of acceleration,velocity and displacement of the upper embankment are stronger than those of the lower foundation.After the seismic load is loaded,the horizontal residual displacement at the foot of the right slope is the largest,and which at the foot of the left slope is relatively the smallest.Compared with the initial value,the maximum principal stress is basically the same,while the minimum principal stress response value is smaller than the initial value but the sign does not change.The response of physical quantities in different seasons is basically the same,the horizontal residual displacement at the right foot of the slope on 15 October was the largest,at about 1.302 mm.(3)Establishing the thermal-dynamic response analysis model of crushed rock embankment in permafrost.Based on the temperature field environment of four typical seasons,the seismic dynamic response of crushed rock embankment under train load is analyzed by DEM.The results show that the response values of acceleration,velocity and displacement in the upper part of embankment are stronger than those in the embankment.After the train load is loaded,the residual displacement at the top of the embankment is the largest,the residual displacement decreases from the top of the embankment to the bottom of the embankment,and from the center of the embankment to the two slopes of the embankment.The principal stress value after loading is basically the same as the initial value.The response of physical quantities in different seasons is basically the same,the residual displacement is the largest on October 15,which is about 0.0045 mm.