COMPARATIVE TEST STUDY BETWEEN FULLY SOFTENED AND RESIDUAL STRENGTHS OF LOESS

This paper carries out comparative test study between fully softened strength and residual strength. It is to solve the selection problem of the strength parameters of the resurgent and creeping loess landslides. It takes the typical soils of Shanxi province as the research objects and uses the preloading consolidation method to prepare the saturated remolded samples for repeated direct shear test in order to get the parameters of fully softened strength and residual strength. The test results show that the fully softened strength of loess has such special characteristics that its cohesive force is almost equal to zero and its particles have no directional arrangement. The fully softened strength is closely related to the secondary consolidation stress and the clay particle content of the sample. The stress-strain curve of the sample under secondary consolidation stress less than 300kPa is strain softening model which means fully softened strength is greater than residual strength. The samples with higher clay particle contents have more obvious strain softening appearance than the lower ones. The stress-strain curve of the sample under secondary consolidation stress greater than or equal to 300kPa is the ideal plastic model which means fully softened strength is approximately equal to residual strength. The difference between the fully softened friction angle and the residual friction angle has close relationships with the secondary consolidation stress, the preloading consolidation stress and the clay particle content of the sample. The difference between the fully softened friction angle and the residual friction angle decreases with the increasing of the secondary consolidation stress, eventually, tends to be equal to 0.When the preloading consolidation stress is less than 300kPa, the difference between the two friction angles and the effect of the clay particle contents on them appear power law increasing with the decreasing of preloading consolidation stress. When the preloading consolidation stress is greater than or equal to 300kPa, the fully softened strength is approximately equal to residual strength and its parameters can approximately replace the parameters of residual strength. The research results supply a reference to the selection of the strength parameters used in the stability analysis for the resurgent and creeping loess landslides.