Analysis On The Penetration Structure Model Of Dam Abutment Rock In The Left Bank Of Dagang Mountain Hydropower Station In Dadu River

Dagang mountain hydropower station is one of the large-sized hydropower projects recent developed in the main Dadu River, whose valley is steep in Nodal region, brae is high and precipitous, and slope excavated is 150~200m. Rock in the dam site produces joints and fractures and planes of disruption with different scale, different genetic types and different mechanical properties in the long geologic process. These joints and fractures and planes of disruption intersect into each other in space, constituting a network fissure system, which control the basic situation of the rock mass structure in the dam areas, and also form the basic geological conditions controlled kinds of engineering geological problems in the dam areas. With the slope excavation and the power construction, the problem of high slope stability is increasingly significant, however, most of the rock slopes'destruction are caused by the seepage of the groundwater in fissures. It should not be neglected that the rock permeability properties impact on slope stability.To fully considerate the effect of permeability properties of fractured rock mass on the stability of the abutment rock mass, this paper taken the 1070~980m dam abutment rock mass in the left bank of Dagang mountain hydropower station as the research object, starting from the structure characteristics of the rock, through studying permeability structure characteristics of the fractured rock mass, deeply discusses and analyses the permeability characteristics of Double fracture in the fractured rock mass respectively to get the permeability coefficient in the different spatial locations of the rock, accurately express the anisotropic features of the permeability characteristics of the fractured rock mass, And supply the corresponding materials and references to the dealing of the stability problem of Rock high slopes. The specific research contents and results are as following: (1)Geological environmental conditions in study area are analyzed from the Regional geological background, stratigraphic lithology, and geological structures. This area is middle-high canyon landscape with steep, complex and varied terrain; it belongs to Yangzi stratigraphic area, whose stratigraphic lithology are major magmatic rocks and a set of dysplasia Algonkian-Mesozoic sedimentary rock; and it is located in the junction of Tethys-Himalayan orogenic system and the west margin of Yangtze platform.(2)The anisotropic feature of the dam abutment rock in the left bank of Dagang mountain hydropower station is concluded, such as rock lithologic feature, characteristics of the fracture structure and weathering unloading features. Through the analysis on and discussing the relationship between various characteristics and permeability structure of the rock mass, the region of the permeability structure of the dam abutment rock in the left bank has been divided.(3)Based on the divided region of the rock permeability structure, the site geological survey and analysis of the measured data as the key point, starting from the statistical analysis on geometric parameters of the jointed rock mass, through the calculation by the bandwidth projection method, the proposal values of the group fissure connecting rate of the rock in the dam abutment different regions of the left bank have been obtained.(4)From the rock structural characteristics , Anisotropy and heterogeneity of the rock have been analyzed and the permeability characteristics of the double fissures have been respectively discussed. Long, big fissures with high conductivity are the leading vadose passageway, whose permeability can be got by conventional analytic calculation. As for small or micro fractures with smaller scale, and weak conductivity, which are affected by the factors such as the attitude, spacing, and gap width of fissures and the composition of fillings in fractures, the fissures'permeability cannot be precisely got just by the materials of water pressure tests, other methods need be used.(5)From the basic theory of seepage flows, through a series of formula deduction and calculation, the equivalent permeability tensor of the single group fissures in the fractured rock mass has been discussed. It is practical and feasible to simulate single drill-hole directional water pressure test by using the finite element method, meanwhile, the nonlinear mapping ability of BP neural network is strong, which can be effectively applied to the inversion of the fractured rock mass permeability coefficient (equivalent permeability tensor). (6)For the single group fissures in the fractured rock mass, based on the single drill-hole directional water pressure test and the BP neural network, only one unknown parameter can be got by the inversion method. According to needs, the connecting correction coefficient can be inversed which is proposed when the conversions relationship between connecting rate of fissures and connecting coefficient is introduced in the paper, and then the equivalent permeability tensor of the fissure rock can be got. Engineering examples prove that the transformational relation and the inversion method are feasible.(7)According to the given calculation methods in the paper, the equivalent permeability tensor of each group of fissures in the penetration structure has been got, then the contribution of each fracture permeability tensor has been summed up by the formula 6-10, finally, the equivalent permeability tensor of the rock mass in the region can be got.