Properties of Drained Shear Strength of Expansive Soil Considering Low Stresses and Its Influencing Factors

y The shallow failure of most expansive soil slopes undergoing wet-dry cycles occurs during or after long-term rainfall. According to the actual failure state of an expansive soil slope, the conventional direct shear equipment with low normal stresses was used to evaluate the effects of initial dry density, initial moisture content, and number of wet-dry cycle with or without loading on drained shear strength for the compacted expansive soil from Nanning, China. The saturated drained direct shear tests were also performed on the natural expansive soil specimens from Nanning by considering the influence of wet-dry cycles with loading and low normal stresses. Furthermore, consolidated drained triaxial compression tests on compacted specimens were conducted. The test results show that the drained shear strength of expansive soil was primarily affected by the magnitude of normal stresses, and also influenced by the initial moisture content, initial dry density, and number and type of wet-dry cycles. It is more realistic to consider the effect of loading during wet-dry cycles than that without loading. The effective drained shear strength envelopes with low normal stresses were plotted and well fitted by the generalized power function. At low normal stress levels, the drained shear strength still decreased with the increasing number of wet-dry cycles, and the effective cohesion intersects tended to be zero after being subjected to eight wet-dry cycles. This provided a theoretical basis for properly interpreting the shallow failure of expansive soil slopes.