In order to find out the failure mode characteristics of sandstone under the reservoir water pressure

some sandstones are chosen from a certain landslide area of Zigui district in the Three Gorges reservoir area as the experimental material. The self made rock dissolution tester YRK-1 is used. Three different soaking pressures 0

0.4 MPa and 0.8 MPa are set to do the comparative analysis. The soaked sandstones which are affected under different water pressures are uniaxially compressed and triaxially compressed for different soaking periods. The quantitative results concerning different conditions are obtained. The results show that with the growth of soaking time the failure laws of sandstones are as follows: (1) The crack angles of sandstones under three differrent confining pressures decrease gradually and then approrch stable values; moreover

the soaking pressure greater is the tendency of decrease more obvious is. (2) The shear fissures on the surface of sandstones gradually become shorter but the stretch-draw fissures gradually become longer under uniaxial compression test; furthermore

the soaking pressure greater is the tendency of variation more obvious is.