Abstract：Slip-weakening is one of the characteristics of faulted rock material under a certain loading condition. Non-uniform rock structure may exist in the vicinity of the slip surface in a rock slope. Some portions of the slip surface may be mutually penetrated but the others may not. For the latter case，the cracks or the fault surfaces will undergo shear deformation before a successive surface forms under certain loadings. As the slipped portion advances，slip-weakening occurs over a distance behind the crack tip. In the weakening zone，the shear strength will decrease from its peak value to residual friction level. The stress will redistribute along the crack surface. Therefore the changed local stress concentration will cause the crack to extend and the ratio of penetration of the slip surface will increase. From the large-scale view of the whole slip surface，the shear strength will decrease due to the damage of the interior rock structure，and the faulted rock behaves as a softening material. Such a kind of mechanism happens in many practical landslides subjected to strong earthquakes. It should be noted that this mechanism is different from that of the breakage of structural clay，in which the geological material is regarded as a medium containing structural lumps and structural bands. The strain-softening property exhibited in the structural clay is the result of structure damage (i.e. the disintegration of the soil structure). The softening behavior of faulted rock should be regarded as a comprehensive result of the whole complicated process including slip-weakening，stress redistribution，crack tip extension and the penetration of slip surfaces. This process is accompanied by progressive failure and abrupt structural damage. The size of slip-weakening zone is related to the undergoing strain. Therefore，once a landslide is initiated (local or integrated)，the effect of slip-weakening will exist in a certain length behind the crack tips until the formation of the whole slip surface even without dynamic loading.
