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JinpingⅠHydropower Station dam is located in the west of Yalong River bend,which is the first stage of Yalong River Hydropower Development category，whosegeological structure is complicated. There is a huge deformation and crack rock,referred to as "large body ", in the abutment between elevation of1825~1930m inthe sand slate, whose bottom sliding surface is f42-9, upstream side fracture surface isSL44-1and rear cut face is lamprophyre veins. The position of large body is unique,which impact the stability of the slope seriously. In this paper, review the boundarycondition of "large body" in left bank abutment based on the engineering geologicalconditions and the excavation data; build block geometric model according to reviewresults; review the stability and strengthening force using block limit equilibriumtheory, then, evaluate the block safety using reliability analysis methods. The mainresults are as follows:(1) According to the engineering geological environmental conditions of leftabutment in the head of the dam, combined with previous geological survey andrevealed information by excavating, review the various structural surface of "largebody " in detail, including: the boundary development of "large body ", structural planoccurrence, extension length, width of fracture zones, filling material of fracturezones and affect band. In addition, statistic and analysis the test data in constructionand the lining cracks in shear-resistance cavity at back-slope of left bank dam,as wellas fault f42-9.Finally, boundary conditions of the "large body " is given.(2) Build "large body" geometric model using space block limit equilibriumanalysis, obtain the geometric parameters, the various forces condition in detail. Calculate the sliding block method, net force, slip vector and stability coefficient ofvarious conditions in the construction and operation. The results show that: the mainslip way of large body is double sliding surface sliding with f42-9faults and deepcracks SL44-1sliding surface; the stability coefficient in operation is above thedesign safety factor,which meets to the design requirements, it is a stable block. Insupporting effect, the shear-resistance cavity is better, its mechanism contains twocases: the replacement effect of shear-resistance cavity increases the shear strength offault f42-9, at the same time, it brings a passive sliding shear to fault f42-9. Anchor boltsupport force effect exists in the group made was not able to play a supporting rolefully, Anchor supporting force is not able to play a completely supporting role due toexist of anchor cable group effect. Through the fault shear strength index sensitivityanalysis of calculation parameters of f42-9, found cohesion c is more sensitive than theinternal friction angle φ, otherwise the water pressure on the slider influence thestability greatly,the full water strength each increase of10percentage points, stablecoefficient reduces0.05.(3) Analysis the reliability using reliability analysis method by choosing severalinfluential factors (Anchorage force, Anchor direction and f42-9fault of the strengthparameters), which influencing the block stability factor obviously. The results showthat the stable coefficient is1.247in running period of extreme conditions underrainstorm and seismic condition,4.79%the failure probability.
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