Engineering Geological Feasibility Study Of High Arch Dam Construction At Baihetan Hydropower Station, Jinsha River

Engineering geological feasibility evaluation of high arch dam construction isa complicated systematic engineering. Taking Baihetan hydropower station as acase, this paper examines the genesis of rock mass structural plane in the dam area,including petrographic formation, structural deformation and epigeneticdeformation, based on abundant in situ measured data, indoor testing, statisticsand analysis. On this basis, it systematically studies the developing feature of rockmass structural plane and demonstrates rock mass quality classification related withfeasibility evaluation of high-dam construction. It also simulates the geostress fieldvariation in the dam area by 3D model. The destroying mechanism in slopes isanalyzed and simulated by UDEC discrete element model. With analysis ofabutments anti-slip stability on condition that slipping surface was formed byinterbed intrastratal dislocation, lateral structural planes was formed by fault andbasal joints, the controlling effect of rock mass structural plane to the abutmentsanti-slip stability is further discussed. Finally the stability of high slope is analyzedand evaluated. The following conclusions were made based on the above research.1. By the method of engineering geological classification and with theengineering geological conditions and significance of structural plane, this papercarries out systematic classification for the structural plane exposed by explorationin the study area, and constructs geological condition description system. Thisaccomplished the classification of rock mass structural plane in the study area andprovided support for deep study of the engineering geological conditions in thestructural plane.2. Four rock mass quality classification plans were adopted in this paper forthe study of rock mass quality in the study area, including Engineering Rock MassClassification Criterion(GB50218-94), Engineering Geological Classification ofWater Conservancy and Hydropower Surrounding Rock (GB50267—99), Rockmass RMR classification (Bieniawski, 1973), Rock Mass Quality Index hydraulic ZClassification (Xiaowan,1995). The conclusion shows that the fitting degree is the best for BQ-T, better for BQ-Z and T-Z. All the values reached 74%, with therelation of logarithmic fitting. It can also be discovered that the fitting related withRMR classification system are mainly linear fitting, but the fitting degree is low,commonly below 57%. Generally, in the four classification assessments, three ofrock mass quality classification is well related. On the quantitative basis, the rockmass classification in study area was accomplished by combining fieldclassification with water conservancy and hydropower engineering geologicalsurvey standard and by correlation. Rock mass in dam site area of Baihetanhydropower station has experienced multi-stage structural geological action andlater epigenetic deformation in geological history, so the structure is complicated.The application of rock mass quality classification solved the problem of rock massquality classification in the study area, which is very important for furtherassessment of engineering rock mass stability and for the decision of suitableengineering measure.3. In the study of slope destroying mechanism at dam area, it is found thatslope deformation destroying phenomenon in the dam area of Baihetan hydropowerstation can be divided into two kinds according to the genesis mechanism. One isthe unloading dynam-relaxing rock mass formed by epigenetic deformation, theother is the aged deformation body controlled by low-angled structural plane,which is dominated by creeping slip and tensile cracking. According to the analysisand numerical simulation, the slope deformation destroying in the dam area ofBaihetan hydropower station will be dominated by block sliding, decompositionand avalanche that controlled by low-angle structural plane andsteep-dip structural plane, while the probability of whole sliding isrelatively less.4. With understanding of anti-slipping boundary condition of the abutmentsand by vector method in rigid limit equilibrium analysis, this paper evaluates thestability of large blocks with different loading at the abutment anti-slipping ofBaihetan. The result shows that the stability can meet the requirement of arch dam.The stability coefficient of little block at the left abutment can not satisfy therequirement, so it is better to avoid the block in engineering design. The stability ofblocks at the right side can satisfy the requirement, but under earthquake loadingthe safety reservation of block 1 and block 3 is little, reinforcement measures suchas replacement or anchorage can be carried out on lateral plane or slipping surface. 5. From stability condition of bank slope and present survey for rock massdeformation destroying at bank slope, the stability of dam area in Baihetanhydropower station is that low level is better than high level; generally the stabilityof natural slope at the right bank is much favorable than that of the left bank, andthe slope deformation destroying degree of the right bank is much less than that ofthe left bank.According to numerical simulation, the slope at the left bank is stable innatural condition with saturated groundwater, but it may be unstable in earthquake(Ⅷ) condition or groundwater plus earthquake condition, with 0.749 for thesmallest stability coefficient. Certain engeering method has to be adopted for thepurpose of safe...