DEVELOPMENT MODE AND FORMATION MECHANISM OF MIDDLE-LOWER DIP JOINTS AT LARGE HYDROPOWER STATION DAM SITE IN SOUTHWESTERN CHINA

The presence of middle-lower dip joints is one of the important geological defects in dam foundation. Analysis of development mode and formation mechanism provides an important foundation for the stability of slopes. This paper is based on detailed analysis of the spatial distribution, combined with geological analysis, SEM and numerical simulation. It interprets the formation mechanism of middle-lower dip joints at a large hydropower station dam site. The results are as follows:(1)Intermittent rapid down-cutting of the river is the main reason for the alternative distribution of middle-lower dip joints; (2)Main fracture mechanism is coexist of tension and shear, a small number of samples show the shear fracture; (3)If faults and dykes exist in slopes and their widths are large, relaxation effect along the whole weak belt is obvious and the distribution of shear strain increment belt is not obvious.(4)If the width of weak belt and distance to the slope surface are both small, on the one hand, shear strain increment is concentrated along the dip direction of weak belt, on the other hand, concentrated degree and number of middle-lower dip joints increased. In addition, density of middle-lower dip joints also increased.