Mechanical Properties Test And Engineering Application Of Loess Under Freeze-thaw Cycle

Loess is a kind of porous,columnar jointed,yellowish-colored silty soil,which is easy to be affected by freeze-thaw cycle.In particular,all kinds of buildings and public facilities in northwest China are inevitably affected by freeze-thaw cycle.Under the condition of continuous freeze-thaw cycle,the structure of soil will be destroyed and its mechanical properties will be weakened significantly.The freeze-thaw cycle is one of the most important factors affecting the stability and service life of buildings on loess in northwest China.Therefore,the in-depth study of the freeze-thaw cycle of the loess is of great practical value.However,there are few studies on the freeze-thaw cycle of the loess,which are not systematic,lack of comprehensive results and have bright guiding theories.The soil samples used in this study were collapsible loess from taiyuan,Shanxi Province.The following conclusions were obtained by using triaxial test and data simulation after various physical and mechanical properties parameters:1.In this paper,the loess from taiyuan,Shanxi Province was used to obtain the basic physical properties of the natural loess such as density,moisture content and specific gravity through the basic physical properties test.The effects of freeze-thaw cycle on the physical properties of loess were analyzed,and it was found that after freeze-thaw cycle,the pore ratio of loess increased and its density decreased,and then the change of liquid plastic limit of loess after freeze-thaw was tested.2.The static strength index of loess was determined by direct shear test and static triaxial test,and the values of internal friction Angle and cohesive force of loess samples were determined at different freeze-thaw times.The relationship between vertical pressure and shear strength is obtained by direct shear test.At the confining pressures of 50 k Pa,100 k Pa and 200 k Pa,the strength changes of loess at different freeze-thaw times were measured and the Mohr stress envelope of loess was obtained.By comparing the direct shear test with the triaxial test,it is found that the cohesion of the frozen and thawed loess decreases,the internal friction Angle increases and the loess strength decreases.3.A dynamic triaxial test program was developed for remolded loess.The samples with water content of 13% and 18% were put through 0,1,3 and 5 freezing-thawing cycles before the triaxial test,and the dynamic characteristics of the loess under different test conditions after the freezing-thawing cycle were analyzed.The laws between the data obtained from the dynamic triaxial test are analyzed from three aspects: vibration number,dynamic strain,dynamic elastic modulus and damping ratio.It can be found from the analysis of the data that freeze-thaw will degrade the loess structure.Under the same vibration level,with the increase of freeze-thaw times,the dynamic strain increases,the dynamic elastic modulus decreases and the damping ratio increases.The relationship between the maximum dynamic stress and the number of freeze-thaw cycles is analyzed.4.According to the static test and the dynamic test,the soil property parameters obtained were analyzed by numerical modeling with ANSYS numerical simulation software.The results show that under the action of live load and dynamic load when the train passes by,the loess becomes loose after freezing-thawing and the structure weakens,which will lead to the increase of displacement and internal force of the tunnel and make the structure more vulnerable to instability and failure.Numerical simulation results show that the displacement and internal force of the vault are the largest.