Engineering Study On The Engineering Properties Of Changchun Chalky Clay Under The Under The Effect Of Negative Temperature

Seasonal frozen soil is widely distributed in China.In addition to seasonal temperature changes,the soil in this area is generally unsaturated.In this paper,the undisturbed samples of silty clay in Changchun,a typical seasonal frozen soil area,are taken as the research object.Through the GDS triaxial system,considering the three influencing factors of water-heat-force,the mechanical properties of silty clay under negative temperature are studied.The main research results are as follows :(1)Firstly,the basic physical and mechanical indexes of the test soil samples were measured.The moisture content of silty clay in natural state was determined by moisture content test.Through the particle analysis test,it is determined that the particle composition is mainly clay and silt;the soil sample was determined to be plastic silty clay by liquid plastic limit test.It is judged to be medium compressive soil by consolidation compression test.(2)Through the pressure plate instrument test,and on the basis of the soil-water characteristic curve parameter fitting,the relative permeability coefficient of silty clay is fitted.It is found that the silty clay has obvious hysteresis phenomenon in the process of dehumidification and moisture absorption.The relative permeability coefficient of the soil sample has the same change trend,but the relative permeability coefficient in the moisture absorption process has been slightly lower than that in the dehumidification process.This is mainly due to the plastic deformation of the soil sample caused by the upper load during the moisture absorption process.(3)Through the GDS triaxial test of controlling matric suction,temperature and confining pressure,the results show that the total cohesion is negatively correlated with temperature.At the same temperature,when the temperature is greater than-6 °C,due to the increase of matrix suction,the content of pore water decreases gradually,and the ice cementation cohesion decreases gradually.At this time,the apparent cohesion generated by matrix suction is greater than the ice cementation cohesion generated by water-ice phase transition,so the total cohesion increases with the increase of matrix suction.When the temperature is less than-6 °C,the increase of apparent cohesion is lower than the loss of ice cementation cohesion,so the total cohesion decreases with the increase of matrix suction.(4)The elastic modulus of frozen soil is calculated by triaxial test.It is found that there is a strong linear correlation between the elastic modulus of frozen soil and matrix suction,freezing temperature and confining pressure.Through multiple linear regression analysis,a prediction model considering matric suction,freezing temperature and confining pressure of silty clay and elastic modulus of frozen soil is established,and the equation meets the significance requirements.(5)The relevant shear strength parameters obtained from the test and the modified elastic modulus of frozen soil are applied to the numerical simulation analysis of wintering foundation pit engineering.The results show that compared with the normal temperature parameters,the simulation analysis results of silty clay parameters under negative temperature conditions are more consistent with the engineering practice,which further verifies the necessity and practical value of soil parameters under negative temperature conditions.