| The distribution of Permian system top series Emeishan basalts layer in Chuan and Dian region is rhombus shape that the direction of long diagonal line is north-south approximately. The covering overlay area is about 300,000 square kilometers, the basset area is about 37,538 square kilometers and the mean thickness can reach as thick as 705 meters. The thickness also has the feature of thick in southwest and thin in northeast. It has characteristic of multiple effusive cyclic. Based on the temporal and spatial variation of effusive facies and rock cluster series and so on, dividing the basaltic layer into three regions which are eastern rock region, middle rock region and the western rock region. The Baihetantan hydropower station and the Xiluodu hydropower station of Jinsha river and the Tongjiezi hydropower station of Dadu river located in eastern rock region. The Ertan hydropower station of Yalong river located in middle rock region. The Longkaikou hydropower station and Jin'anqiao hydropower station located in western rock region. This dissertation considered the study of rockmass structure characteristic of the Baihetan hydropower station dam region as research main track. Coupled with the study achievement of other hydropower engineering rockmass structure characteristic, analyzed the rockmass characteristics of Emei mountain basaltic layer of hydropower engineering in southwest of china. The major study achievements showed as following:1. Studied the genesis of rockmass structure in Baihetan hydropower station dam region from three aspects, which are primordial formation, tectonic retrofit and supergene reform. Through the study of the magmatic eruption environment, columnar exterior shape, roughness of jointing and fissure surface of prismatic jointing basalt and the analysis of chemical and mineral components, the conclusion is that prismatic jointing basalt generating from the cooling action of hyperthermia magma. During the evolutionary process period, suffering from the tectonic retrofit of faults, interlaminar and intrastratal disturbed belt, bedding joint and lateral direction joint, and the relief rebound from valley incision, so it can form the current morphosis of prismatic jointing.2. Based on the study of the apparent feature, mineral feature and chemical feature of different degree of weathering of basalt rockmass, the result indicates that the weathering of Emei mountain basaltic layer developed along various structural planes towards the interior of rockmass, which physical weathering is principal and chemical weathering is not obvious. Through the division of belt of rockmass weathering in Baihetan hydropower station dam region, coupled with the division criterion of belt of weathering in Xiluodu hydropower station, Tongjiezi hydropower station and Guandi hydropower station, put forward a comprehensive quantification designation of belt of weathering of basalt rockmass.3. The rockmass structural hierarchy system of Emei mountain basaltic layer concluding interlaminar disturbed belt, intrastratal disturbed belt, controlled fault, general fault, matrix fissure and prismatic jointing. Interlaminar and intrastratal disturbed belt and fault controlled the macro structure of rockmass, and constituted the framework of engineering rockmass. Joint and fissure affect the partial structure and integrity of rockmass. Taken the scope of structural plane as classification law, considered interlaminar disturbed belt and controlled fault as structural plane of gradeâ…¡, intrastratal disturbed belt and general fault as gradeâ…¢, compressed belt and small fault as gradeâ…£, matrix fissure and prismatic jointing as gradeâ…¤.4. Through large quantity data statistic, put forward the partition program of rockmass structure in dam region of Baihetantan hydropower station, considered the space length of fissures and joints as controlled index and the number as reference index. Coupled with the partition program of rockmass structure in Xiluodu hydropower station, Jin'anqiao hydropower station and Ertan hydropower station, established the quantification designation for rockmass structural type in basaltic layer region.5. Based on the study of quantification designation of belt of relief of basalt rockmass in Baihetan hydropower station dam region, coupled with the division criterion of belt of relief in Xiluodu hydropower station, Longkaikou hydropower station and Guandi hydropower station and some research achievement of correlated reference with respect to quantification designation of belt of relief, put forward the quantification designation of belt of relief of Emei mountain basaltic layer rockmass.6. Applied the latest research achievement of rockmass quality classification (modified Q system, 2002), considered comprehensively the tectonic features and some geological factors in Baihetan hydropower station dam region, such as interlaminar disturbed belt, intrastratal disturbed belt, fault, weathering and relief and so on, obtained the results of rockmass quality classification which can coincidence with the reality situation. Through rockmass quality classification for prismatic jointing basalt by RMR system of classification and the code of engineering rockmass classification (GB500218-94) separately, the outcome indicates that the grade of rockmass quality which classified by BQ value(GB500218-94) can higher than the grade which classified by RMR method, so it is diversity for the rockmass quality comprehensive classification to prismatic jointing basalt in dam region compared with the non-prismatic jointing basalt. The rockmass quality comprehensive classification of prismatic jointing basalt should take the mechanical integrity into account, then the rockmass quality comprehensive classification non-prismatic jointing basalt should take not only the mechanical integrity but also the geometric integrity into account.7. The rockmass quality classification of non-prismatic jointing basalt in Baihetan hydropower station dam region is quantized with primary wave velocity, coefficient of integrity and the rockmass quality designation (RDQ). Considering that the prismatic jointing basalt in Baihetan hydropower station dam region is a type of cataclastic and mosaic structure rockmass, and the apparent is also fragmenting, so when it's to specify the rockmass quality classification. The principal quantification designation of rockmass quality classification including three factors which are primary wave velocity, coefficient of integrity and ratio of rockmass permeability (Lu value). Depending on the belt of weathering of dam basement rockmass, the rockmass quality classification and the permeability of rockmass, specified the position of reference surface of high arch dam foundation of Baihetan hydropower station.8. Taken the high arch dam of Baihetan hydropower station as an example, calculated the factor of stability of the representative blocks which selected from varied arch rings. The outcome indicates that the factor of stability of dam shoulder resisting body can satisfy design criteria in any case, whenever is under the case of general load or special load, and it also has some safety stock.
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