| The terminal area of the first Jinping Hydropower station lies in typical V-type canyon, the relative height of both slopes is among 1500 and 1700m. Trend of the rock is consistent with river flow. The left bank of the dam area is reverse slope, EL.1800m above is sandstone and slate and EL.1800m below is marble. There are f5, f8, f38-2, f38-6 faults, with a corrosion layer extrusion mud cracks and other undesirable geological structure; the right bank is dip slope of marble, there are f13, f14 faults and weak structural planes such as greenschist. The double curvature arch dam of Jinping 1st is the world's highest arch dam, whose height is 305m and crest elevation is 1885m. Right and left bank of the arch built in the rock foundation at EL.1600 ~ 1730m. Left bank of the arch built in concrete pedestal at EL.1730 ~ 1885m.The compression fault zone, faults and joints crack are developed. Steep fissures are more developed of partial sites at the left bank. The surface cracks are more developed at right bank. Joint fissure of dam site could be grouped into primary and structural. Primary surface is mainly layer of sandstone, and slate and thin to medium thick layer of marble, and the schistosity plane of greenschist. Structural surface is mainly steep dip; the development is related to lithology, thickness and structural positions. Generally fissures are developed in a hard marble and metamorphic sandstone joint slate than the relatively soft and greenschist; and fissures are developed in thin marble joints than the thick massive marble; and fissures are developed at left bank than the right bank.In order to better evaluate the quality of dam foundation and find out the type and grade of structural planes and their geological characteristics of rock mass structure, this paper based on a large number of field surveys and statistical precision measurement analysis, and combined with three-dimensional laser scanning and other means to identify RQD, fragmentation, Jv and other structural parameters of different rocks, and structure of surface orientation, shape, position, weathering and other geological characteristics. Therefore, the correct description of the rock mass structure of project areas is of important guiding significance to Jinping 1st hydropower project.A comprehensive understanding of the dam system, topography, lithology, geological structure, weathering and unloading, groundwater and geological conditions such as stress state is set up in this paper. Evaluate the structural characteristics of rock is based on the specific geological environment. Contents and results are as follows:(1) Find out the structure of surface rock mass, and physical and mechanical properties and parameters, and the type of rock mass structure of the standard.(2) The main weakness in the dam is fault and extruded, corrosion mud cracks, weathered greenschist. According to the field investigation, geological features and the impact of the structure are summarized and recommendations are made accordingly(3) According to the geological conditions of slope excavation, joint position, undulating rough, the degree of opening, filling, trace length, volume, number of joint Jv, rock mass quality index RQD, rock block index RBI and other quantitative indicators are obtained. According to base surface survey, RQD has a good correlation with RBI. Based on their correspondence and integration of the various Rock class RBI's statistics, RBI evaluation standard is presented.(4) Study has been done on fissures of different geological units and different parts of distribution. The distribution of various rock types is clarified.(5) Due to fully exposed fissures of Jinping 1st hydropower station, fracture trace length is well studied. A large number of field test data have been carried out and validated the existing track length estimation model. |
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