Abstract: We performed a series of frictional experiments with dry and water-saturated sandstone, marble and granite blocks by using a servo-controlled biaxial loading machine. In the experiments, we compared the stress and acoustic emission characteristics of fault friction for dry and water-saturated samples, and then discussed the effect of water on frictional characteristic. The main results are as follows. Under lower constant average normal stress, sandstone and marble show steady slide while granite shows stick-slip. Mineral components,porosity and sliding surface dominate the frictional characteristic of faults. The frictional strength of water-saturated fault is depended on the comprehensive effect of water to the sliding surface and the surrounding rocks. Water can reduce the strength of sandstone both for sliding surface and surrounding rocks, because it contains some smaller hardness minerals and has a low initial adhesive strength but high porosity. The hardness and frictional properties of calcite controll the frictional characters of marble. Because there are some transcrystalline and intracrystalline micro cracks in sample, the effect of water decreasing the frictional strength is enhanced. Because of hard minerals and closed cementing, the granite had a high initial strength and low porosity, and then the water content plays less impact on granite frictional strength. For both dry and wet sample, frictional characteristics vary with lithology. Moreover, the effect of water content in fault friction is also different for different lithology. Therefore, the lithology of faults is an important topic in the study of reservoir-induced seismicity.

Key words: Frictional strength, Stress, Acoustic emission