SHEAR BEHAVIORS OF ROCK MASS IN THE INTERLAYER FAULT ZONE OF DAGUANGBAO LANDSLIDE

The slide surface of Daguangbao landslide is developed in the interlayer fault zone where the fragmentation degree of rock mass is increased from the upper to the lower with a belt of mud at the bottom. 18 groups of medium-sized direct shear tests were carried out for the samples collected from Daguangbao interlayer fault zone. 42 groups of unconsolidated direct shear tests were carried for the samples collected from mud belt and mylonite belt by controlling the moisture content. The results show that the shear characteristics of the rock mass in interlayer fault zone are related to the degree of fragmentation. Characteristics of strain softening of rock mass with lower degree of fragmentation is more obvious while the shear strength of rock mass with higher degree of fragmentation is worse. The shear strength and the friction angle of mylonite are mostly greater than the soil in the mud belt and the shear characteristics of mylonite is less affected by the ground water than the mud. The shear strength and cohesive strength of the soil in the mud belt are decreased rapidly with the increase of moisture content. The internal friction angle has a negative exponential relation with the moisture content. The shear strength of the soil in mud belt can be greatly reduced with the intrusion of groundwater caused by the rock mass dilatancy during the earthquake. The results of this study are important for understanding the position of the slip surface. It is also important for understanding the influence of the increase of moisture percentage and the further fragmentation on the shear strength of the rock mass in the fault zone.