STUDY ON MECHANICAL RESPONSE AND FAILURE MECHANISM OF EXCAVATION UNLOADING IN LOESS SLOPE

Loess landslides induced by excavation occur frequently.The loess area of the construction project had a great threat by such landslides.They seriously hindered the construction of various infrastructures.To promote and understand the mechanical response, the mechanism and deformation and failure process of loess slope during excavation unloading process is a prerequisite and important basis to this type of landslide prevention.On this basis, this paper carries out the conventional triaxial test and the triaxial shear test of saturated loess under unloading path to emphatically analyze the mechanical response and deformation characteristics of saturated loess under two kinds of stress paths, and studies the formation mechanism of Shangwazi landslide in Lanzhou.The results show the following.(1)Compared to the general conditions, under lateral unloading, pore pressure increase is low.But unloading caused lateral pressure is greatly reduced.So pore pressure then rapidly grows and effective stress decreases, which is more unfavourable to slope stability.(2)Under the conditions of lateral unloading, the strain required to reach the peak intensity is smaller(1% ~2%), which indicates that the slope is more destructible under unloading conditions.(3)Two saturated soils under different stress paths on shear strength parameters are significantly different, compared with standard triaxial shear test, vacuum under triaxial shear, c' decreased 62.32% ~76.92%and close to zero, effective friction angle φ' value 26.92% ~29.77%.(4)Using FLAC-3D to simulate the upper embankment landslide, the results of lateral unloading triaxial shear test are more in line with the real stress path of soil, which proves that the failure mode of Shangwazi landslide is a type of "backward progressive".