| There are plenty of hydroenergy in west China to be exploited. It is an important strategy to accelerate economic development of west China by exploiting hydroenergy in mountain area. However, hydropower station in west China, especially south west China, are mainly located in high mountain and canyon with complex geological condition and worse character of rock and soil mass. As a result, the suitability of the geological environment for the hydro-junction becomes one of the key engineering geological problems. There are some characters including complex geological condition, thick deposits under the bed river, high artificial slopes, and plenty of caverns at the planed Qizong hydropower station. The dam of this hydropower station is designed to be high core rockfill dam. The main engineering geological problems includes instability of phyllite rock slopes and wall rock of caverns, and the engineering character of deep and thick deposits under bed river. In this paper, the engineering characters of phyllite rock mass and deep-thick deposits are studied to discuss the treatment of the main engineering geological problems. The suitability for construction of high rockfill dam is evaluated by engineering geological method, and some cognition is obtained in the study on theory and application of phyllite and deep-thick deposit.(1)In this paper, microstructure of phyllite, micro-fracture mechanism and rock mass structure are studied synthesized to acquire the regularity of engineering character of phyllite by analysis on aeolotropy character. Then, the stabilities of engineering slopes and gaverns in phyllite are studied by several methods, and the suitability for construction of engineering slopes and huge caverns in phyllite is discussed. In addition, the engineering character of deep-thick deposits lied under bed river in west China is generalized and analyzed systemically which add new origin types for deep-thick deposits, and the technique of suitability evaluation for construction of dam on deep-thick deposits lied under bed river is proposed.(2)According to the investigation of geological conditions of the dam area, the spacial distribution and variation of phyllite are discovered, and the composition and microstructure characteristics of rock is studied, and the types of rock mass structure and the development of discontinuities are summarized. The composition and micro-defects of the phyllite are discovered. The achievements have a guiding role in the research of engineering-mechanics characteristics of phyllite and analysis of the stability of cavern and rock slope.(3) The anisotropy of sericite phyllite and siliceous phyllite are analyzed by series of physical and mechanical tests, which indicates that the anisotropy of phyllite is mainly reflected in the velocity of sound wave, uniaxial compression strength, triaxial compression strength, and shear strength. Qualitative evaluation of anisotropy of the rock is based on the shape of response curve of rock anisotropy, that is how the rock strength varies by the orientation angle. The anisotropy ratio is advanced to evaluate the anisotropy of phyllite, and the most influence of anisotropy on the rock strength was to uniaxial compression strength. Then, the engineering geological character of phyllite is summarized and the proposed value of physical and mechanical parameters of rock mass is put forward, according to test data and engineering geological analogy. These parameters are the basis of stability evaluation of engineering slope and underground cavern.(4)According to the layout of the hydraulic architecture of Qizong hydropower station, some typical phyllite slopes and phyllite caverns are selected to analyze their stabilities by numerical simulation method. The distribution of stress and deformation of the slopes and caverns are studied under excavation. This study indicates that: 1)the rock mass strength of phyllite at Qizong hydropower station is high, and the whole engineering slope is stable, 2) the instabilities of caverns are influenced by the anisotropy of the phyllite, and the designed axial of the caverns put the stability of wall rock at a disadvantage. As a result, some suggestions such as reasonable arrangement and strengthening supporting can make the right bank meet the requirements of the layout of hydraulic architecture.(5)In this paper, the relationship between spacial distribution and structure of the deposits at the dam area is studied. And conclusion is obtained as follow: 1) The origin of deposits of the riverbed at the dam area is complex. The deposits include boulder and glaciofluvial accumulation of block stone and reduced stone of Late Pleistocene epoch, deposit formed by mudflow, diluvium and circulation flow, and accumulation of sand, boulder, reduced stone with silty clay interbedded and silt. 2) The deposits are with high thickness, better stratum, better water permeability, low compressibility, high mechanics strength and high bearing capacity. 3)The most important layer to dam is the lenticle sand seam in the boulder and gravel stratum, which is with little thickness, discontinuity, middle water permeability, middle compressibility, low mechanics strength, and low bearing capacity. According to the existed dam engineering experience in the deep and thick deposits, the physical and mechanical parameters of the deposits at Qizong hydropower station is similar to other engineering in west China, and there are some advantages that the dry density of the coarse-grained soil is larger, and the bearing capacity is greater. As a result, the engineering characteristics of the deposits at Qizong hydropower station meet the geological conditions of high rockfill dam construction.(6)The result of stability analysis of the deposit at the dam site indicated that, 1) sliding of the dam foundation is in low possibility because deep and thick deposits are mainly composed of boulder and gravel stratum with compact structure and high strength; 2) the stratum ofâ‘¢-1 andâ‘ might generate failure by piping because of their coarse grain and high permeability coefficient; 3) the dam foundation could generate seepage deformation because of quicksand in theâ‘¢-2 stratum andâ‘¡-2 stratum with sand soil and silty soil, and theâ‘¡-1 stratum with fine sand; 4) there are some engineering geological problems, such as non-uniform settlement of the dam foundation, low bearing capacity of dam foundation, and liquification of the dam base, in theâ‘¢-2 stratum and theâ‘¡-2 stratum with plenty of lenticle sand seam with variation of thickness and depth of burial.(7)The topographic feature at the dam site is suitable for rockfill dam. Large open style spillway, seepage tunnel, rapid flood passage tunnel, training tunnel and ground factory could be arranged on the cross ridge on the right bank after strengthened supporting. The whole stability of the dam foundation is stable, however, there are some engineering geological problems such as seepage deformation, non-uniform settlement, and liquidation of sand seam in the upper part. Propose was advanced that the lenticle sand seam be excavated in the upper part, the soil of dam base be treated by consolidation grouting and tamping. The deposits'engineering characteristics after treatment can meet the engineering condition of core rockfill dam with 350m height. And as a result, it is suitable for the studied area to construct high core rockfill dam.The research has achieved aims of suitability study for high dam of Qizong hydropower station. And some theoretical and regular achievement are obtained in anisotropy mechanical character of phyllite, origin and engineering character of deep and thick deposits lied under bed river. These achievements can direct excavation of artificial slopes and caverns in the phyllite area, and construction of high dam in the deep and thick deposit.
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