Characteristics of deep-seated crack in dam site of Yebatan Hydropower Station

There is a series of symmetric deep-seated cracks (DSC) in the abutment slope of Yebatan Hydropower Station. The special geological phenomenon is analyzed to provide a scientific basis for a comprehensive analysis on rock mass quality and availability evaluation. Through particular field survey, seismic tomography (CT) and sonic wave testing (V_p), the spatial distribution characteristics and macroscopic geological features of DSC are summarized. Additionally, DSC is divided into different types. According to these analyses, the controlling factors of DSC are studied completely by using the engineering geologic analogy method. The spatial distribution range of DSC ranges between 80 m and 140 m in horizontal direction from the surface of rock slope. The horizontal depth of DSC is positively correlated with the elevation of abutment slope, but there are not any connected cracks at two sides. The majority of DSC inherits early tectonic joint formation with tensile characteristics, and the weathering of rock is strengthened because of underground water. The slackness extent of DSC can be divided into three types: slightness, medium and severity. The formation and distribution of DSC are controlled by the regional factors and other factors such as the slope shape, the material foundation of the slope and the micro topography. The crust upward, incised valley and magnitude of the tectonic stress are the prerequisite for DSC. Furthermore, the rock property and complex slope structure provide material foundation for DSC. These are reasons for the symmetric distribution of DSC.