<p>Fault gouge is rock texture within fault zones that may include rock fragments (RF) and foliated structures. Previous studies have primarily focused on remould soils, the natural structure and rock fragments of fault gouge are not considered. Their mechanical properties have been the subject of debate. Therefore, we conducted indoor triaxial tests and improved direct shear tests to analyze the failure characteristics and mechanical resistance curves of undisturbed fault gouges. The peak strength decreased with increasing water content, whereas the failure characteristics transitioned from brittle to transitional to ductile behavior. In addition, we observed various phenomena on the shear plane of fault gouge, such as bypassing RF, scratches, peeling, clay powders (CP) and rolls, which led to fluctuations in residual strength. The formation processes of these phenomena were observed by scanning electron microscopy (SEM). The combination of the phyllosilicate crystal structures demonstrated the variation in the shear-fracture surfaces. At the macroscopic scale, on the basis of the similarity principle combined with the mechanical parameters of tunnel boring machine (TBM) excavation, the penetration depth was shown to be directly related to the shear strength of the fault gouge. On the basis of scratch tests and theories, a scratch and cutter model was established, thereby revealing the physical causal reasons for rate-and-state friction (RSF) laws. This study elucidates the kinematic mechanisms of creep landslides with gravel slip zones accompanied by changes in velocity.</p>