| Lianghekou Hydropower Station is a controlling hydroelectric power station of the middle and low reaches of Yalong River. The water inlet slope, the maximum excavation height is 215m, is the maximum excavated volume of the all engineering slope. The geological conditions are complicated of the engineering area slope, the slope stability is mainly controlled by low and middle dip angle-structural surface , and the slope main failure mode is sliding and fracturing. The correct estimation on such a high slope stability has an important significance for the design and support of the engineering slope.Based on the analysis of the basic geological condition, the paper puts emphasis on the study for the rock mass structure, the unloading rock mass partition and the rock quality graded,anslyzes the failure mode of the water inlet engineering slope combined with the slope failure indication, evaluates the engineering stability slope systematically and the support scheme is made accordingly, arrives at such conclusion below:(1)The terrance varies considerably in engineering slope area,in lithology ,the terrance is mainly made of sandy slate and argillaleous siltstone.The terrance accrosses the rock slope at wide angle, and the slope is called cross fall. The stability in the large of the natural slope is well.(2)Through the statistics of joint in the spatial distribution from the tunnel and slope surface,with the use of DIPS software to find out the laws of joint development,and provides the basis for the partition of the type of the rock mass structure and the establishment of the geological model.(3) Make use of a combination of qualitative and quantitative methods to study the partition of unloading rock mass. In the quantitative partition, the methods of wave velocity , RQD,rebound test,radon test are applied. Determine intergraed zontation of unloading rock mass compared with various indicators of value curve.(4)The rock mass graded of the water inlet slope is adopted the method of qualitative judgement and CSMR method ,and get such a conclusion that the structural integrity of rock slope is in general,mainly for III,IV-graded rock mass,is widely distributed in the 2850m elevation after excavation, V-graded rock mass is relatively in small amount, but plays an important part in the stability of the slope deformation.(5) The assessment ot the water inlet slope are adopted the methods of geological qualitative judgement ,rigid block limiting equilibrium method , FLAC3D fast Lagrangian finite-difference procedure and SASW software for block analysis hierarchically and systematically. Analysis for rigid block limiting equilibrium shows that stability of the slope local parts are in danger, the block controlled by middle-angle fault parallel to slope surface, such as f34-3,f32-8 has bad stability. Numerical simulation results show that the sress in the V-grade rock mass distributed in the upper chamber-face slope and the surface of chamber side slope, the fault and rock mass near the fault, and the shearing exit side adjusts largely,tensile stress zone and plastic zone exists corresponding zone.(6) According to model slope instability and slope excavation project status, the support scheme adopts"system cable +anchor wire +link fence-preumatically placed concrete",the result shows that the engineering stability is well after supporting.
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