Evolution rules of fissures in expansive soils under cyclic action of coupling wetting-drying and freeze-thaw

The occurrence and evolution of fissures are the significant characteristics of expansive soils under the action of various external factors. With regard to the deterioration of slopes of the canals of expansive soils in high and cold regions in the northern area of Xinjiang Uygur Autonomous Region, the tests on the fissures in expansive soils are performed under the unidirectional cyclic action of coupling wetting-drying and freeze-thaw considering the processes of the foundation soils of the canals witnessing water supply, water cut-off, freezing and thawing. By means of the CT scanning and 3D reconstruction techniques, the evolution characteristics of the internal fissures in expansive soils are quantitatively described under the cyclic action of coupling wetting-drying and freeze-thaw, and the influences of various coupling wetting-drying and freeze-thaw cycles on evolution rules of 3D fissures in expansive soils are investigated. The test results show that the internal fissures in the samples exhibit the development characteristics of obvious regional distribution. The growth depth of the fissures gradually tends to be stable after five cycles, corresponding to 40% of the initial total height of the samples. A comparison of development morphologies of the internal fissures in the samples under various cycles indicates that the development mode transforms from the shallow scattering distribution at the initial stage to the deep gathering one at the final stage. By using the four indices of porosity, bending, branching number and dead endpoints of slices, the evolution rules of the spatial distribution and connectivity of the fissures with the cycles can be quantitatively depicted more satisfactorily. The achievements of this study have certain reference values for further revealing the deterioration process and failure mechanism of canals of expansive soils under the coupling action of wetting-drying and freeze-thaw.