| Xiaowan Hydroelectric Power Station of Lancang River, which arc is 295 meters high, is one of the greatest conservancy and hydropower projects in China. Based on the geotectonic rebuild transformation, the rock mass discontinuities of the dam foundation are gradually formed by the geotectonic rebuilding, the process of epigenetic recreation, and the unloaded and relaxed transformation. This paper combines the massive laboratory experiments with plenty of field geological investigations, the survey and the description on the spot. Taken the genesis and engineering geological characteristics of the rock mass discontinuities as the center, it researches on the base of dam rock mass shallow hypergene transformation process and the unloaded and relaxed characteristics in the excavation. The main achievements are as follows:(1)Through a series of laboratory tests, it has established full developed understanding of the physical mechanics characteristics of the dam foundation rock mass: the density, compressive strength and modulus of deformation are larger, Poisson's is relatively small, The dam foundation rock mass belongs to hard to extremely hard rock category, its tensile strength is not high. There are lots of small holes in the Crystal Under the Scanning Electron Microscope. The incidence of the AE (the acoustic emission) changes greatly in different stress level during the process of destruction of rock mass. At the beginning of obvious acoustic emission, the magnitude of stress is at the level of 6～12 Mpa. It reveals that the initial damage of the complete rock near the excavation surface is significant.(2) Starting with microscopic, the dissertation uses the scanning electron microscope (SEM) to analyze fractured surface of the dam foundation rock under various stress states and takes the scanning to the samples of discontinuities. It analyzes the microfailure models of the rock mass, which includes tensile failure and shear failure model. It also studies the microfailure mechanisms and obtains the typical fracture morphology maps of the the dam foundation rock mass. (3) By the comparative analysis of mat slice samples of discontinuities, concludes the existing fracture mechanism including shear failure and tensile failure and the tensile failure is the main rupture, just different in locations. The comparative analysis of the morphology of field discontinuities shows that it emerges as the morphology of river-like patterns, root-like pattern, and so on, and the ease dip discontinuities are tensile failure as the main micro-destruction mechanism.(4) analyzes the phenomena of unloading and relaxation, which includes the development along the fissures,the mat slice phenomenon, the board crack phenomenon, the difference rebound and creep and rock burst. the rock mass of dam foundation is divided into three zones by the degree of unloading and relaxation. The three zones are the Completely unloading and relaxation zone, the strong unloading and relaxation zone and the weak unloading and relaxation zone.(5) Integrates the field investigation with analysis of physical prospecting achievements and the numerical simulation of the dam abutment founfation excavation. Discusses the unloaded and relaxed mechanism of rock mass in the dam foundation of Xiaowan hydroelectric power station. And clarifies the zoning characteristics of unloaded and relaxed rock mass in dam foundation at low height of valley.(6) By precise measurements and statistical analyses, it concludes the characteristics distribution and connectivity parameters of the ease dip discontinuities in the dam abutment founfation and the bed river dam foundation. |
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