| The Dagangshan hydropower station of the Dadu River being planed to build is an important step station in the trunk stream of the Dadu River. It is the important energy production base in support in diversion of electricity from the western to the eastern regions. But The Dagangshan area lies in a composite location of the different structural units, marked by intense neotectonic movement and frequent seismic activity, has relatively strong active tectonic system accompanied with various endogenic geologic hazards. Especially, the horizontal distance is four to five kilometer from the Moxi fault that is the southeast segment of the Xianshuihe fault to the dam of the Dagangshan hydropower station. In this case it seems necessary to conduct a quantitative assessment and zone of the regional crustal stability for planning and construction of hydropower projects along the Dadu river valley in the Dagangshan area, the estimate result possesses academic and practical significance.On the base of investigation and anysis of the geological background(regional stratum and rock, tectonic framework, regional gravitational field, earth crust and mantle construction and deep-seated structure), neotectonics character(seismo-geology, the crust shape change, neotectonic geomorphic features) , regional fault and its activity, the author conduct a quantitative assessment and zone of the regional crustal stability for the far-field region, near field region and the dam area of the Dagangshan hydropower station by means of the geological anysis(qualitative method) , comprehensive fuzzy mathematic method(quantitative method) and finite element technique.On the basis of the quantitative system of classifying crustalstability and the quantitative assessment, the area is divided into four zones for the first time, as well as seism orogical and geophysical parameters are studied and the crustal stability is classified as stable, sub-stable, sub-unstable and unstable. The result of qualitative and quantitative method: the Hangcaoshang region' s stability class is "sub-stable" , the Moxi region' sis "unstable" ,and the Luding region' sis "sub-unstable" .The dam of the Dagangshan hydropower station is located on the sub-stable Huangcaoshan block, the structure is simple, the fault' s scale is small, the level is shallow, neotectonics is feeble, have not the induced earthquake structure, its seismic intensity is 8 degree because of the influence of surrounding structure. By finite element technique analysis the distribution of the stress and strain, the result shows that the Moxi fault is the discontinuity zone of strain, the intersection leg is also stress concentration point, it is the area of high pressure and high shearing strength, the area is in the unstable state, and that the Dagangshan region lies in the central section, its stress doesn' t ooncentrate, the strain and shape change isn' t obvious, is in the state of low pressure and low shearing strength, is stabler than the west region, accordingly the dam area of Dagangshan hydropower station is in "substable" . |
