Abstract: The coupling action of wetting-drying and freeze-thaw is one of the basic forms for the severe climate conditions in high and cold regions, which has significant influences on the normal operation of water supply canals in expansive soils in these regions. Based on the field expansive soils of water supply canals in the northern area of Xinjiang Uygur Autonomous Region, the fissures tests under the unidirectional wetting-drying and the cyclic action of coupling wetting-drying and freeze-thaw are conducted respectively to investigate the influences of freeze-thaw process on evolution rules of fissures in expansive soils. The evolution characteristics of the internal fissures in expansive soils with various cycles can be obtained through the CT scanning and 3D reconstruction. The test results show that the internal fissures in the samples under the two conditions both develop from the surface towards the internal part and the regional distribution of fissures can be obviously captured. A comparison of the evolution characteristics of the internal fissures under different test conditions indicates that the freeze-thaw process in the coupling cycle of wetting-drying and freeze-thaw has significant influences on the focal depth of the fissures, and the induced fracture is macroscopically characterized by the transformation from non-horizontal long fissures into short ones. In addition, it is found that the development of fissures in expansive soil samples under the action of various cycles can be successfully evaluated by using the volume fraction of the fissures.

Key words: expansive soil, wetting-drying cycle, coupling wetting-drying and freeze-thaw, CT scanning, quantitative analysis, fissure, evolution rule