Abstract:

Experimental studies were undertaken on an expansive soil from Nanning area in order to establish relationship between shear strength indices and cyclic drying and wetting parameters. It is shown that the shear strength of expansive soil decreases with increasing number of cycles and finally reaches to a constant state. The value and cyclic number of the constant state reduce with increase of amplitude of variation of water content. Furthermore, the mercury intrusion porosimetry (MIP) test was applied to determine the pore size distribution curve of expansive soil during wetting-drying cycle. The MIP test results show that the bond of soil is irreversibly damaged by cyclic drying and wetting, which leads to increase the volume of pore. In high water content, volume of outer-aggregate pores increase with number of cycles; while in low water content, volume of intra-aggregate pores will increase. As a result of degradation of microstructure, the shear strength of expansive soil quickly decreases.

Key words: expansive soil, shear strength, wetting-drying cycle, MIP test