| Proposed Xulong hydropower station is an important step of engineering for the management and development of water resources in the upstream of Jinsha River. The dam is concrete hyperbolic arch dam with 213 m, the total installed capacity of up to 2220 MW, and the total storage capacity is 819 million m3. The main engineering geological problem in the design of arch dam research is the stability sutdy. If we do not do thorough research to the dam abutment resisting force body and acquire accurate data of conditions which may cause instability of dam abutment extraction, it may cause serious consequences. Deformation and metamorphism of the left dam abutment rock mass in Xulong dam site area and the late tectonic setting in the contact zone developed cleavage and its discontinuities with dense, formed the shear strength significantly lower than the intact rock mass. Under the action of thrust this strip is likely to become the dam abutment instability of side crack boundary. Due to the structure of the discontinuities which owns features of discontinuity and uncertainty, it caused the resisting force of the left dam abutment is complex and the dam abutment has specific characteristics. Therefore, the analysis of the resistance body boundary conditions of left dam abutment and its stability is extremely necessary.This paper is based on the geological environmental conditions of dam site area. Through the specific investigation on the left resistance body within the scope of the eight exploration drift and the surface resisting force body, it studied on rock built environment and rock mass structure characteristic of the left bank dam site area, and analyzed the side crack boundary. Finally the paper obtains preliminary evaluation results of the potential instability of block stability. The main research results of this paper are listed as follows:(1) Research area has three sets of outcrops bedrock: respectively trias indochinese epoch intrusive granite(γ51), mesoproterozoic xiongsong group of three sections of amphibolites schist(Pt2X3) and mixed rock. Deep acid magmatic activities have great effect on the amphibolite schist mixed metasomatism which formed mixed rock with different degree of metamorphism, intrusion by near the center of syncline hornblend schist, mixed metasomatic decreased gradually, there are mixed gneiss, migmatite and migmatitic amphibolite schist, three kinds of metamorphic banded distribution in space. Mixed rock is developed in the light and dark bands of cleavage structure distribution, along the dark minerals in rock bands which can be split. It will easily appear all sorts of cracks on both sides of mixed rock.(2) Within range of resisting force body on the left of the dam abutment, there are 4 groups dominant direction in structure plane III. The most developed structure plane is near SN, followed by NW, NE and EW. Among them, f57, f69 and f76 have small slope angle. Furthermore, f69 and f76 is low-angle dip structural plane. These 3 structural planes are unfavorable to stability of resisting force body of the dam abutment.(3) Granite flash schist and amphibolites schist contact zone develop three kinds of metamorphic rock. Cleavage structure and mixed rock mass fracture are the densest in this zone, especially in the mixed rock contact zone and mixed gneiss area and high, medium and low degreed adits, and several sites fracture dense with its width greater than 5 m, formed clearly a certain width of weak structure plane.(4) The granite and schist captured body contact metamorphism migmatization is in different degree due to metamorphism of the migmatite zone on both sides. Amphibolite schist prisoners in low elevation range L1 ~ structure developed widely, high elevation relatively weak structural surface development. Amphibolite schist captured L2 has mostly metamorphic migmatite, cleavage structure developed in the mixed rock, medium to high degreed interval mixed rock along the cleavage domain of fissure development. Amphibolite schist captured L3 band high, low elevation ranges of structural plane are more developed.(5) The left dam abutment resisting force body range can constitute 5 side crack boundary, which made up of the lithological contact zone of the 4 side crack boundary, composed of 1 side crack boundary of III structure surface f57. The bottom of sliding surface mainly constitutes structure surface III, IV ~ V grade structure are structural plane and do not reach the III structure surface location. Ultimately this paper confirmed the side crack boundary and the bottom sliding surface can be combined into 5 potential failure blocks.(6) The left dam abutment side crack boundary extraction using conventional weighted method and inverse distance weighting method based on two kinds of methods, through the contrast analysis, the final selection of the inverse distance method of the comprehensive shear strength parameters based on the results of extraction. The bottom sliding surface parameters extraction based primarily on grade IV ~ V grade structure surface and inclined structural surface area proportion weighted made.(7) A preliminary evaluation is made by the application of rigid body limit equilibrium method for the extraction of 5 potential instability body. Finally it obtains the stability coefficient of 5 blocks which has good emergency capacity, and meets the engineering requirements. |
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