| The proposed hydropower station is located in the territory of Tibet Autonomous Region,Mangkang County of middle reaches of Lancang River Gorge,located in the high and cold mountain area.Under the special geological background and climate condition,the valley on both sides of the shoulder slope and ridge area formed many broken loose rock mass.Broken loose rock mass mostly is cataclastic texture,mosaic structure,part of a granular structure,and in the state of limit equilibrium,if it got the action of exogenetic force,it is possible to instability and endanger the safety of the engineering.Therefore,it is necessary for the project to study the genetic mechanism and stability of the broken loose rock mass.Based on a large number of geological survey,this paper used geological analysis method to analyze the structure surface features of the broken loose rock slope.At the same time,according to the sketch of the adit rock structure,this paper carved out the rock structure.Also,according to the rebound and velocity value of the rock,this paper quantitatively delineated the depth of the broken loose rock mass.Combined with the slope deformation and failure characteristics,this paper analyzed and summarized the deformation and failure mode of the rock mass.From the valley stress evolution and the rock mechanics parameters and deformation and failure characteristics which analyzed from the unloading test of rock,this paper analyzed the causes of the broken loose rock mass.Finally,this paper selected a typical broken loose rock slope of the left bank of the middle dam to analyze the stability.Achieved the following main results:(1)Through investigation of the broken loose rock mass,this paper found them in the vertical distribution mainly concentrated in the elevation 2750m~3330m,and slope mainly were 30 to 50 degrees;in the horizontal direction mainly closed to the slope surface,and mostly located outside of strong unloading zone.(2)According to the investigation of structural surface of the adit and slope,it is concluded that the valley slope mainly developed 4 groups IV of structural plane,which group 1 was outer slope gently dipping structural surface(sandwich),three groups of steep dip structural plane.In addition,developed 7 groups V level structure.At the same time,based on the sketch of the adit rock structure,this paper divided into cloddy pulverescent structure ~ cataclastic texture,cataclastic ~ block like structure and embedded crack ~ block structure from the outside to the inside of the slope.(3)According to the deformation and fracture characteristics of the slope rock mass,this paper summed up five kinds of deformation and failure mode:(1)Different rebound along low-angle structures;(2)Slip crack;(3)Slippage-cut-crack;(4)flexural toppling;(5)Relief cracking along steep structure.(4)From the internal factors(formation lithology,rock structure of the slope,crustal stress)and external factors(plateau freezing and thawing action and topography),this paper briefly describes the formation of the broken loose rock mass.Mainly,from the valley stress evolution and the rock mechanics parameters and deformation and failure characteristics which analyzed from the unloading test of rock,this paper analyzed the causes of the broken loose rock mass.It is precisely because of the stress release of the unloading valley,the hidden steeply dipping fractures of the slope were expended and showed,then the original sparsely distributed steeply dipping fracture became dense.During the steep fractured generating intensive,hard and brittle dacites with steeply dipping structural were cut into chunky.And in the unloading process of the valley,the rock would along the steep structural surface in the slope produce relief cracking occurring strong expansion phenomenon.Also would along low-angle structures produce different rebound to the direction of the valley airport,making the original valley slope rock mass produce a more severe form of relaxation.In this low stress environment condition,made the valley slope rock mass in fragmentation loose state.(5)This paper selected SL19 slope of broken loose rock mass where the axis of the middle dam located to analyse qualitatively and quantitatively the stability.According to the rigid limit equilibrium method,in the natural state,stability coefficient of the A slope was about 1.16,overall in the basic steady state;under the seismic condition,the stability coefficient around 1.02,overall in unstable state.In the natural state,stability coefficient of the B slope was about 1.17,overall in the basic steady state;under the seismic condition,the stability coefficient around 1.02,overall in unstable state.According to numerical methods,in the natural state,stability coefficient of the A slope was about 1.10,overall in the steady state,but the shallow table stability is significantly lower;under the seismic condition,the stability coefficient around 1.04,overall in unstable state,the shallow surface stability is also significantly lower. |
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