Study On The Effect Of Freeze-thaw Cycle On Properties Andslope Stability Of Loess Subgrade

Loess is widely distributed in North and Northwest area of China.These areas are seasonal frozen soil areas.With temperature changes,loess in these regions will experience several freeze-thaw cycles every year.Because of the action of freeze-thaw,the physical and mechanical properties of loess have changed,which directly affect the stability and durability of project.Through the preliminary investigation and study on the prevention of loess landform geological disasters in Shanxi Province,it was found that freeze-thaw action is one of the important reasons to induce the loess geological disasters.However,the study of seasonal frozen soil is not much.And it is limited in the Gansu,Qinghai Province.Therefore,it is very important to study the effect of freeze-thaw cycles on loess.This paper mainly in the Dongzhonghuan Project in Taiyuan as background,analyzing the influence of different cycles of freezing temperature and cycles times of two soil samples(original soil and loess subgrade filler)on the shear strength after indoor freeze-thaw cycle test.Andthe results of laboratory test was used for analyzing slope stability in loess subgrade.This test used 30 groups soil sample.1,3,5,and 9 cycles of freeze-thaw cycles were carried out under freezing temperature of-20 ?,-10? and-5?.The shear strength was measured by direct shear test.And after direct shear tests,moisture content of soil sample was measured.The stability analysis of the slope was carried out by using finite element analysis software ABAQUS.The main results and conclusions are as follows:1.In mechanical Properties of loess: After freeze-thaw cycles,the shear strength of the soil sample is reduced.The cohesion is reduced obviously,and the variation of the internal friction angle is very small.So internal friction angle was considered not change in projects.The shear strength decreased with the number of freeze-thaw cycles and freezing temperature.Specific performance: The lower freezing temperature,the lower shear strength.After the first freeze-thaw cycle,the shear strength reduced most,and then the shear strength decreased with the increasing number of cycles.The change of cohesion is almost the same as shear strength.And the shear strength of collapsible loess is lower than that of non collapsible loess.2.In physical properties of Loess: The moisture content of the soil samples did not change in the closed system after freezing and thawing cycles.That is,in closed system,freeze-thaw cycles had no effect on the moisture content of the loess.After the freeze-thaw cycles in the closed system,the moisture content of the soil samples did not change basically.3.Subgrade slope stability: Analysis of stability of subgrade slope in engineering by strength reduction method.The results show that the safety factor of subgrade slope stability decreases after freeze-thaw cycles.Compared with before freeze-thaw cycles,the plastic strain zone in the slope is faster and the plastic deformation zone is larger after freeze-thaw cycles.