Study On The Stability Of Engineering Slope Of Baihetan Hydroelectric Power Station

The paper mainly study following this order:analyzing the engineering geology condition, realizing the slope deformation, analyzing the deformation mechanism of slope, estimating the analysis quantificationally. Based on ways that combining the spot investigation and analysis inside, engineering geology and rock mechanics,geometrical and mechanical analysis, how the structure of dam area evoluted and the whole evolution of the river valley and also the slope are all generalized and come to a conclusion. According to the process from rock slope to the structure reforming and the epigenetic and superficial reconstruction of rock mass ,it discusses four questions, of which are rock mass structure of the slope, weathering and unloading process and the features of the destruction-deformation and the quality of the rock mass. From a view of how the geology evolved ,the distortion-destruction model of slope are analyzed and the exact period are identified .With all those achievements, the paper generally diagnoses and estimates the slope stability with limit equilibrium theory and puts forward some reasonable proposals at last for excavating slope ratio.Contents list: geological environment of the Dam area: topographic feature, stratum and lithological character, geological structure, stress field, evolvement of the structure and river valley. the structure character of the rock mass on the slope:the distribution and development characteristics of the interlayer shear zone between the interlayers and in the laminates,the distribution characteristics of the faults and fractures, types of the rock mass structure, displacement mechanism of natural slope and the study of instability mode: analyzing distortion mode of natural slope, ascertaining the potential unstable boundary which cause the slope, indicating which period the slope belongs to:analyzing distortion-destruction mechanism of slope,dividing the rock mass into parts,caculating the stability,commenting on engineering slope as a whole and its pasts as well.According the analysis and estimations what have been done, the best excavate the slope ratio are worked out by geological judge and engineering comparison.Achievements: (1)Sloping form north to south, and tilting to the east, the dam area has a landform of Zhongshan gorge. In general, the Jinsha River runs form south to north.. On the left bank of it lies the southeast slope of Daliangshan Mountain which takes a landform similar to the Jinsha River and which is with a height of 2600m.On the right bank of it lies the west slope of Yaoshan Mountain which takes on a landform of gentle slope and steep slope and which is with a height of above 3000m. --------The layers contact with each other by false-integration. The quaternary loose deposition mainly distributes on the bedriver and on the gentle slope.The geological structure of the dam area mainly takes on the form of original construction(original fluid structure, original fracture structure)fracture structure ( including fracture,interlayer shear zone ,fault zone ep.t) and so on. The dam area has a landform of Zhongshan gorge, and the bedriver and both the sides are mainly composed of stiff interlayer shear zone.It is explored that the dam area is a middle stress field area, weak rock burst and rib spallingcan be seen in some place.The magnitude of the bedriver is mainly between 7.0~18.0MPa. The direction of principal stress can be as far as NWW～EW,which intersects with the direction of the bedriver in a large scale.The ground stress of the both sides changes between low and middle, and each the side has a equivalent stress.The stress of the underground workshop of both sides are equivalent too,but the left bank is a litter smaller than the right side.The direction of the first stress is mainly to NEE while those third to NNW. The basic structure format of the dan area is formed in Yanshanian period while the later Himalayan period structure movements include Sichuan Movement, Yanshanian Movement as well as the Newly-structure Movement.All of these further reinforced the format of the dam area,thus forming the present structure. Going throught the Kuangu period and the Gorge period as well as suffering five times rapid insides,the dam area valley has formed its present landform. Its geological time is before the form ofⅡgrade bench ,after the form ofⅢgrade bench,or the early period ofQ3.(2) Accroding to the research of the dam area rocky structure,the dam area has three kinds of structures,including:interlayer and layer gentle shear zone,small and middle scale fault as well as basic fracture.There are 11 interlayer shear zones called C2-C1 in the dam area ,they are formed in the upper of the rocky layer and are easily breaked up when the tuff is formed. Because that the tuff is sensitive to water, local muddy interlayer is easily to be formed with the effort of underground water. This will decrease the stiffness of the structure, and will form gentle slopes as well as penetrating layers which distribute among the rocks. They are also the mainly controlling layers.Developing from the inner rocky layers of shear zones, the inner shear zones mainly exist in the one side of the basalts of the rocky layers. Except a few ones whose steep dip is >25°,most of them are extending in waves. Compared with the interlayer shear zones, its distribution is more complex and causal, and it is not so widely extended.Fault zone: its fault strike is mainly NNE~NE, NNW and NW~NWW,with its width within 1m, length within several hundred meters.The substance of this layer is mainly breccias and cuttings, also the fault layer exists in somewhere. There are many slopes in this layer,forming slope Angle of Cut face as well as bulk sideslip surfaces.Matrix crack: Mostly filling in the 0.2~0.5cm calcite vein and quartz vein ,the inside silky weathered rock is closely intertwined while the slightly weathered rock mass is mostly teny tension,and the unloading inner crack takes on tension.The priority direction of it is N35°~45°W , SW∠80°~85°,extending a little longer.Because of the fracture restriction of NW priority,the NE direction crack (the secondary priority) and the SN direction crack(the third priority) only developed in the patial place,and is much shorter and smaller.With a steep slope,the matrix crack is straight ,rough,damp ,close and non-filling.Based on the above statistic features and the exploring lines,the rocky structure of the dam area can be divided into districtions:4 districtions on the left bank,3 districtions on the right bank.(3) Cohere with the structure feature of the rock mass in Dam area, some conclusion are drawn. The main instability mode of the left bank is bloke gliding which caused made by the interlayer shear zone of low-angle dip and structural surface of steep-angle dip. And the anaclinal slope in the right bank determines its instability mode which called samall scale rock mass.Base on the analysis on the deformation-destruction mechanism of natural slope and with a consideration of its topographic feature, stratum lithology, rock mass structure, deformation and failure of the rock mass and the deposit of collapse,the displacement are divided into 3 main parts,12 in detail.All of those parts are in stable after the stability estimations of every past.In the line of the check and estimation of the bulks boundary,slope on the left bank has12 unfavorable bulks.With the estimation of the stability,all the bulks are in safe except LB6.The excavation of the spandrel trough slope on both banks may arise ari proximal surface for the latent bulks.The spandrel trougj slope on both banks make up 9 unfavorable bulks,including 6 on the left bank and 3 on the right.By woking out of the stability,it is ensured that bulks are all in stable and the right bank may be more steady than the left bank.(4)According to the calculation results on stability of spandrel trough slope on both banks,the worst disturbing condition is earthquake.The excavation of the spandrel trough slope on the left bank is safer to both upper and lower reaches than the right bank.The edge spandrel trough slope on the upper reach is more susceptible to rainstorm while the lower one is susceptible to earthquake.Most od all,the lower reach edge slope on right bank is worst for earthquake resistant.The strong and weak unloading interfaces are latent slip planes as the structural planes of both gentle and steep on the right bank have a tendency to the inside slope.The data worked out by limit equilibrium shows that the slope is in stable and the worst disturbing condition is earthquake when is raining heavily.(5) it is suggested that the best slope ratio for engineering slope are as following. The spandrel trough slope on the left bank : new and slightly lower weathered rock mass :1:0.3,Slightly upper weathered rock mass :1:0.45~1:0.5,the spandrel trough slope on the right bank :new and slightly lower weathered rock mass :1:0.25,slightly upper weathered rock mass :1:0.35~1:0.5,the covering layer :1:1.25 When the new and slightly lower weathered rock mass is excavated, a service road of 3m wide have to be fixed every 50m. while the slightly upper weathered rock mass is excavated, a service road of 3m wide have to be fixed every 30m.High side slope at intake on the right bank :new rock mass :1:0.2, slightly lower weathered rock mass:1:0.25, slightly upper weathered rock mass :1:0.35-0.4,covering layer:1:0.25。And a service road of 3m wide have to be fixed every 50m when the slope is excavated.The slope on the cable-crane plateform : new and slightly lower weathered rock mass :1:0.3,slightly upper weathered rock mass :1:0.5,covering layer :1:1.2.A service road of 3m wide have to be fixed every 50-60m.