The Genetic Mechanism And Stability Study On 2# Toppling Rockmass Of The Yellow River Cihaxia Hydropower Station

CiHaxia Hydropower Station is located at the junction of Xinghai County and Tongde County in Qinghai Province, 2# toppling rockmass is in the downstream dam 1km of left bank. There is intensive toppling of entire slope, and topplled broken phenomenon is found in partial rockmass. There a large number of unloading crack and toppling tensile crack in adits, the development of these geological problems will directly affect the construction safety and the normal operation of engineering, there is important practical significance to analyse the genetic mechanism of 2# rockmass and evaluate the stability of 2# toppling rockmass. On the basis of summarizing the previous studies and site investigation of the 2# toppling rockmass, basic characteristics, structural characteristics, deformation characteristics, genetic mechanism of 2# toppling rockmass were analyzed, using qualitative and quantitative methods to evaluate the stability of the slope, get the following results:(1)Though the table slope investigation, drilling exploration, slope adit exploration and other means, identify the toppling boundary conditions, determine the distribution of 2# toppling rockmass, the area of the body was 1.7×105m2, the average horizontal depth is 151 m, the average vertical depth is 70 m, the volume of toppling rockmass is 1.19×107m3. Combined with depth research of the structural characteristics and deformation characteristics of toppling rockmass, get the development characteristics of toppling rockmass.(2) Based on the analysis of rock deformation and the formation factors of toppling rockmass, its deformation process is divided into the following phases: ① rock initial deformation stage;②rock deformation development Stage; ③rock deformation exacerbate stage; ④ rock tracture surface gradually through stage.(3) The discrete element analysis showed that with the continued development of rock deformation, it is likely to have a conversion of the deformation and failure modes of 2 # toppling rockmass which is from the toppling tension type to creep tension type.(4) Calculation based on rigid limit equilibrium method showed that, in the natural state, storm conditions and seismic conditions, those three stability coefficient is 1.1 above, there is better overall stability of the slope; at the limit(seismic and rainstorm) conditions, the stability coefficient of two less favorable profile ranged from 1.05 to 1.1, the slope is Basically stable. in the natural state, storm conditions and seismic conditions, the maximum displacement magnitude of 2# toppling rockmass is 0.04 m by Finite Element Analysis; at the limit(seismic and rainstorm) conditions,the maximum displacement value is 0.11m; it shows good overall stability of the entire slope, the calculation results are consistent with the rigid limit equilibrium method and on-site evaluation of qualitative results.(5) The stress and displacement fields of toppling slope under different conditions comparative analysis by use of finite element numerical analysis shows that the earthquake and rainfall have more obvious effection to stress and displacement field of the shallow slope; in the earthquake conditions, stress field distribution at shallow slope undergone significant adjustments, there is obvious stress concentration in the lithologic boundaries, weathered zone boundary and the intersection of each other.(6) Acquired by two quantitative assessment method of toppling stability evaluation showed that the earthquake and rainfall are the two main factors which influence the toppling stability.