The Experimental Study On Matric Suction Of Expansive Soil By Filter Paper Method And Numerical Simulation

Expansive soil is mainly exists in the form of unsaturated soil,matric suction is one of the important parameters affecting in unsaturated soil,therefore,study the influence of matric suction on unsaturated soil is very necessary.In this paper,the expansive soil in Yichun is taken as the research object,the filter paper method is applied to measure the total suction and matric suction of unsaturated expansive soil in conditions of different dry density and wetting-drying cycles,based on the experimental results,and make analysis on the seepage and stability of foundation pit in conditions of wetting-drying cycles.The main results are as follows:(1)The experimental study on total suction and matric suction of soil under different initial conditions was carried out by the filter paper method.It is shown that under the same initial conditions,the dispersion of the total suction is small while the distance between the filter paper and soil surface is 3cm,which can be considered as the standard test distance when the total suction is measured by the filter paper method;the concept of pseudo matric suction is introduced,the pseudo matric suction values of soil in different initial conditions can be obtained through the fitting formula of total suction-distance,and compared with the true matric suction which was measured,it is shown that there is a good linear relationship between the pseudo matric suction and the true matric suction,and a prediction method of matric suction is proposed.(2)Using the model of Fredlund and Xing to fitted the soil water characteristic curve of expansive soil under the conditions of drying and wetting cycles,the law of the variation between the fitted parameters and the number of cycles “n” is obtained,an empirical model which is related to the number of cycles “n” is established,and the rationality of the model is verified.(3)Based on the empirical model of soil water characteristic curve of expansion soil under the conditions of drying and wetting cycles,the finite element analysis software Geo-Studio is applied to simulate the seepage and stability of foundation pit under the conditions of drying and wetting cycles.It is shown that under the same water content conditions,with the increase of the cycles number,the matric suction of soil decreases gradually,the safety factor of the foundation pit decreases gradually,and the amplitude of the reduction is becoming smaller.Therefore,the influence of wettingand drying cycles suitable be considered in the seepage and stability analysis of foundation pit.