Abstract: To research the influence of wet-dry cycles on the shear strength of expansive soil modified by weathered sand, indoor direct shear tests were carried out by quad direct shear apparatus. Before the shear tests, the expansive soils were first mixed with weathered sand in a ratio of 10%, 20%, 30%, 40%, and 50% respectively, and then treated by wet-dry cycles for 0-5 times. Results showed that: 1) after the first wet-dry cycle, internal friction angle increased slightly. As the number of wet-dry cycle increased, the internal friction angle gradually decreased and finally became stable. With the increase of wet-dry cycles, cohesion decreased in a quadratic function. 2) Shear strength declined with the increase of wet-dry cycles. The decline reached the maximum in the second and third cycles, and then gradually mitigated and finally stabilized. When the mix rate of weathered sand was 30%, the shear strength of expansive soil reached the maximum, and the attenuation of shear strength induced by wet-dry cycles could be effectively alleviated. Moreover, the sensibility of modified expansive soil to seasonal climate change could be reduced, and the project safety is ensured.

Key words: wet-dry cycles, expansive soil, weathered sand, shear strength