DEVELOPMENT AND DISTRIBUTION CHARACTERISTICS OF COMPRESSIONAL FRACTURE ZONE IN DAM SITE AREA OF YEBATAN HYDROPOWER STATION

The exploration shows that the grained cutting band with certain thickness and extension length is widely developed in the quartz diorite on both sides of the dam site of Ye Batan Hydropower Station. This kind of cutting band not only reduces the integrity of rock mass, but also deteriorates the quality of foundation rock mass. According to its manifestation and developmental characteristics, it is called "compressional fracture zone". Based on the field investigation, this paper describes in detail the typical compression fracture zone newly revealed during the construction period. The development and distribution characteristics of the compression fracture zone are revealed. The study shows that the compression fracture zone develops in both strong and weak unloading zones and deeper areas. It is mainly distributed in the medium elevation of the left bank. The compressional fracture zone in the dam site of Ye Batan Hydropower Station is formed by tectonics. It appears as a clastic debris strip with a clear boundary and a certain thickness and extension, which is developed in fresh, complete and hard rock mass with obvious boundary. It may be formed by tectonic forces and generally attached to faults or structural planes of larger length. Its extent is limited and its occurrence is unstable. Most of the cleavage lithification in the zone, and part of the grains can be observed in directional arrangement, with zonal characteristics, no obvious dislocation distance. All these belong to the characteristics of rock mass extrusion deformation under the condition of high ground stress. At the same time, the compressional fracture zone is easily affected by the later transformation, and weathering, rust dyeing and muddy bands can be observed in some extrusion fracture zones. They are mainly distributed in the clamping or confining area of faults(long structural planes), the end of the fault(long structural planes), or the side of the long structural planes.