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Abstract Mechanical property of fault gouge is the weakest in the geological materials composing the fault. In order to understand the influences of physico-mechanical properties of fault gouge on the characteristics of ground motion near fault and the damaged styles of structures，the direct shear tests on undisturbed samples of fault materials containing fault gouge from Longmenshan fault are conducted using conventional soil test method in laboratory；and investigations into natural fault material structures and mineral distributions are carried out. The slice identification results show that，mineral composition of black fault gouge is similar to that of gray breccia and the color of black is caused by limonite. The basic physical property test results show that the grain size of black gouge is smaller than that of gray gouge，distribution of grain size is very inhomogeneous，and the specific gravity of black gouge is less than that of gray gouge. Direct shear test results show that shear strength of fault materials with low void ratio is higher than that with high void ratio；and the peak shear stresses are larger for these specimens with high water content compared to those of specimens with low water content but the same void ratio. The maximum shear stresses do not appear until the shear tests stop，instead，the entire shear displacement is characterized by strain hardening or perfectly plastic behavior. The shear strength reaches the lowest for those specimens with shear zone in the interface between different layers.
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Received: 31 August 2009
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2011, Vol. 30 
