Abstract: To study different degrees of initial damage, different drying-wetting cycles and the coupled effects on the development and evolution of pore and fissure of expansive soil, drying-wetting cycle tests and triaxial shear tests (suction is 50 kPa, net confining pressure is 100, 200, 400 kPa, respectively) are conducted on Hefei expansive soil specimens for 3 groups with different initial degrees of damage (the diameter of the cylindrical hole is 0, 2.5 and 5 mm, respectively). If there is no drying-wetting cycle, a certain extent of initial damage can increase soil strength. If drying-wetting cycle is 1-2 times, the initial damage contributes to outcome of crack direction and penetration mode, forming intact block structure that has higher strength than that of the soil without initial damage. If drying-wetting cycle is 3 times, crack is able to expand completely and the strength of the soil with different degrees of initial damage becomes consistent with the soil without initial damage. The evolution mechanism of soil pore-fissure is that: the different strength and shrinkage deformation induced by hydraulic gradient when subjected to drying-wetting process will produce tension and compression stress in micro-crack tips and tear the tips up, which makes the tips combine with the initial hole damage, causing intersection and transfixion of the damage. Furthermore, the fracture is able to develop due to the increased water vapor exchange interface area in the fracture to further balance the compressive stress. The research provides a new insight for the study of expansive soil engineering with initial damage.

Key words: expansive soil, drying-wetting cycle, fissure, damage, mechanical properties