Experimental research on the strength characteristic of unsaturated structural loess

The loess is structural and unsaturated. Direct shear tests on intact loess and remold loess are firstly carried out by controlling the matric suction of unsaturated soil. Then the effect of the matric suction on the net stress strength index, parameter φ_b in the Fredlund shear strength formula and parameter χ in the Bishop effective stress formula of unsaturated soil is analyzed respectively. The experimental results show that net stress strength index increases with the increasing matric suction, φ_b and χ decreases with the increasing matric suction, and under the same matric suction, the net stress strength index, φ_b and χ of the intact loess are all larger than those of the remold loess. Besides, the unconfined compressive strengths of the intact loess, remold loess and saturated loess are measured by means of the single axial compression instrument. According to the definition of structural indices, the structural index of intact loess and remold loess with different water contents are obtained based on the unconfined compressive strength. Finally, the relationship among the net stress strength index and parameters φ_b, χand structural index is also explored. The values of φ_b and χ unsaturated loess have the monotonic variation with the structural index. Under the same configuration conditions, the values of φ_b andχof the intact loess are greater than those of the remolded loess, which reflects the differences in structural traits of the two types of unsaturated soil.