Engineering Geological Research On Dam Abutment High Slope Of Ma'erdang Hydropower Station

In the large water conservancy and hydropower project, there are natural slopes with hundreds meter in the deep-cutting valley, the slope stability is attracting more attention in project design and construction. During excavating the spandrel groove in scheme of a high arch dam, there forms artificial slope with the equal height as the natural slopes, which makes the stability problem more outstanding. Therefore, it is signality to study the natural slope and the artificial slope with evaluating the features of stability for project construction and operation.This paper takes the abutment slope of Ma'erdang hydropower project for research object, the distribution characteristics of the structural planes in abutment slope is summarized mainly by means of study on regional geological environment, field survey, statistical analysis and so on. The rock mass structure and the strength characteristic is exposed combined with test in laboratory and outdoor. With the regression analysis method of ground stress field based on numerical calculation, the formation and evolution of the ground stress field is reinstated by simulating the formation and evolution of the valley. On this basis slope structure and deformation and failure mode of the natural slope is studied, slope stability is evaluated. Meanwhile, the global stability of spandrel groove high slope under excavating is evaluated, and the local stability of the slope under excavating is evaluated with the block theory and the limit equilibrium method. The main research contents and conclusion are as follows:(1) By collecting previous research results, regional geotectonic framework is knew. Then according the data treatment and on-site survey many times, engineering geological condition of Ma'erdang hydropower station dam area is studied in detail. It mainly includes formation lithology, geological structure, topography and geomorphology, hydrogeology, physical geological appearance, new tectonic activities and earthquakes, etc.(2) Through analyzing regional ground stress, the present azimuth of regional tectonism intra-region is NEE general, and turned to E-W gradually from northeast margin of Tibetan plateau to south. Combining in-situ stress measurement, ground stress phenomenon in dam area is analyzed. The results show that, the azimuth of the principal compressive stress in study area is nearly E-W, it is anastomose the azimuth of regional ground stress, and the ground stress in dam area is at more than middle level. Basis on the formation and evolution of the valley, the ground stress at the valley area is simulated by the measured value, it is understood at the valley that the principal stress value increased by depth increase, the isoline of principal stress in bank slope has a trend to paralleled with the bank slope, the ground stress has zoning features obviously, etc.(3) According to the structural planes outcropped on ground and in adit, the data is statistically analyzed, and the development characteristic of the structural planes is described from the aspects of structural plane distribution, structural plane grading, structural plane character, structural plane scale, etc. The rock mass quality is evaluated by two method of the rock mass quality classification, rock mechanical strength is exposed by test in laboratory and outdoor according to rock, structural plane, rock mass.(4) Describing slope character from two banks in sam area, the distortion and failure character of the natural slope on the abutment is focused on discussion. On this basis, analysis and summary the slope structure and deformation and failure mode of the nature slope. We come to the conclusion that the slope structure can be divided into layered structure and block structure, which each one can be subdivided. The deformation and failure mode mainly includes relaxed-tension crack, wedge failure, planar failure surface, toppling deformation, potential landslide, etc.(5) Ma'erdang hydropower station is a high arch dam, it's crest elevation is 3273 m, the maximum dam height is 215m, there will be formed shree artificial slopes (upstream slope, spandrel groove high slope, downstream slope). The global stability of the artificial slope is evaluated from perspective of ground stress distribution, we draw the conclusion that the artificial slope has a good stability. Then blocks of arch dam abutment are searched with block theory, local stability is analyzed through computing the stability and predicting the possible failure mode.