Triaxial Shear Tests Study Of Unsaturated Reshaped Loess

The Ili River Valley is located in the northwest of Xinjiang in China. The special geological and topographical features make the Ili Loess are different from the loess in Loess Plateau, which has pure characteristic of Aeolian Loess. The land area is extremely wide but rainfall is less. Irrigation is relying on the snow which is on the mountain. Therefore, the construction of the channel engineering in Xinjiang is particularly imperative. In many cases, the slope soil which due to dug canal foundation and channel are in the unsaturated state, but the classical theory of soil mechanics are treat soil as two-phase material. On the contrary, the loess under the unsaturated present different properties due to soil particles not only contain pore water, but also pore air, and matric suction, thus the unsaturated loess showing different strength properties from saturated loess. Therefore, It is the base of the high fill channel and the analysis of slope to study the strength characteristics under the unsaturated condition, and obtain strength parameters as well as the relationship between stress and strain of unsaturated soil.This paper used indoor experiment studied the soil water characteristic curve of reshaped loess, and obtained the corresponding matric suction values of samples with different volumetric water content. Triaxial shear test with constant matric suction of unsaturated soils was carried out by FSY30 stress and strain controlled unsaturated soil triaxial apparatus. The characteristics of the stress-strain curves under different matric suction and confining pressures, the change of shear strength parameters are studied. The results are as follows:(1)The volumetric water content of soil sample decreases with the increasing matric suction. The soil water characteristic curve is divided into three stages, which are slow change stage, steep change stage, and residual stage. The results shows that the air saturation value(AVE) is equal to 2.20 k Pa, the residual volumetric water content is 0.21, moisture residual, the middle tangent slope is equal to-246.3,and the Saturated volumetric water content is 0.54.(2)In triaxial shear test with constant matric suction of unsaturated soils, the relationship curve between stress and strain of the samples with different confining pressure, saturation and density are all hardening curve, and there were no peak in the curves. The failure modes of soil samples with the raising confining pressure form uniform failure to bulging damage.(3)The friction angle of soil samples are decreased with the increase of the saturation under the same matric suction. However, the values of soil cohesion are increased gradually with the increasing saturation. Increasing the matric suction can improve the cohesion of soil, but the impact on soil friction angle is not obvious.(4)The relationship curve of soil cohesion and moisture content showed a quadratic parabola relationship under the same matric suction and density. The trend of the change of cohesion decreased first and then increased with the increasing moisture content under the large density, but under the small density, the trend is opposite. The different matric suction influenced the value of cohesion.(5)The relationship curve of friction angle and moisture content showed a quadratic parabola relationship under the same matric suction and density. With the increasing moisture content, the change of friction angle of specimens with same density is not obvious, and there was no significantly change. With the increase of matric suction, the sensitivity of friction angle to the change of moisture content was decreased.(6)The variation range of unsaturated loess strength parameter value bf by the unsaturated soil triaxial shear test with the saturation was from 8.81 degree to 11.59 degree, and the average value was 10.04 degree.These results will provide references for the construction of channel engineering in Ili, and offer basic data and parameters for the improvement of the theory of strength, and supply data reference for stability evaluation of high fill slope.