Some fault rupture propagation tests were conducted in which wet soil were used to model a cohesion soil in real condition. Results of these tests show that by increase of water content, the shear band of fault rupture propagate in a narrower zone so the distorted area above the ground was decreased. Ductile soil has the ability to deform more before a developed shear band reaches to the surface. This behavior can be interpreted by strength parameters of the wet soil. For this purpose, some series of direct shear tests were conducted, studying the effect of water content on some strength parameter of granular soil. All of these tests were carried out in both low and high vertical stress. The results indicated that increase of water content to a certain value lead to increase in internal friction angle and beyond this limit it decreases. The response of cohesion was vice versa. Also the internal friction angle was increased as the vertical stress decreased. The results were discussed in both high and low vertical stress.
