Experimental study on fully softened shear strength of expansive soil

The fully softened strength tests are carried out on the expansive soil samples from the Yangtze-Huaihe River Water Transfer Project. The fully softened strength indexes under different moisture contents and shear rates are discussed and analyzed. On this basis, they are compared with the shear strength indexes from the wetting-drying cycle direct shear tests on expansive soil. The results show that in the fully softened state, the cohesive force of expansive soil is close to zero, and the fully softened strength is mainly determined by the inernal friction angle. The inernal friction angle is little affected by the moisture content and shear rate. The strength indexes obtained from wetting-dring cycle tests and fully softened tests are applied to the safety analysis of simple expansive soil slope respectively. Compared with the wetting-drying cycle direct shear tests, the fully softened strenght tests need less lab work and shorter test peroid. The fully softened strength indexes can also reflect the failure mechanism of the shallow failure of expansive soil slopes after wetting-drying cycles in practice. It is recommended to apply the fully softened strength indexes in the analysis of the shallow stability of expansive soil slopes after wetting-drying cycles.