Abstract: Direct shear test was conducted on weak expansive soil specimens of two different dry densities under dry-wet cycles. The test soils were collected from the bank slope of Xuhe River in Nanjing. The shear stress, cohesion and internal friction angle of soil after dry-wet cycles were analyzed, and the variation rules of direct shear strength were investigated. Test results indicated that cracks of expansive soil expanded and widened irreversibility with the increase of dry-wet cycles; cohesion of soil of different densities decreased with the increasing of dry-wet cycles, and tended to be uniform; internal friction angle showed no obvious change. Moreover, overburden pressure during the direct shear had an apparent influence on shear stress decay. Larger overburden pressure resulted in smaller decay. In conclusion, shear strength parameters under low stress is recommended for stability analysis of expansive soil slope.

Key words: weak expansive soil, dry-wet cycles, direct shear strength, strength decay, overburden pressure