| Baihetan Hydropower Station is featured by multiple stratums and complex lithology, whose construction of foundation rock directly applies stratums containing 9 sub-layers and 50 small layers of lithology. The main lithology include nearly 11 species, such as porphyritic basalt, aphanitic basalt, micro-crystalline basalt, columnar joints basalt, amygdaloidal basalt, amygdaloid-contained basalt, breccia lava, tuff, etc. made up of complex media type systems. Such lithology of rock has presented very distinct differences in respect to the apparent lumpiness, longitudinal wave velocity, mechanical property and other aspects. The most obvious presentations have been involved in columnar-jointed basalt and breccia lava, whose apparent structure and mechanical property have presented huge contrast. According to existing norms or general methods for the classification of rock structure and rock mass, the columnar-jointed basalt with the best mechanical property has been judged to be the worst rock mass for the dam foundation while the breccia lava with the worst mechanical property has become the best rock mass of the dam foundation. Therefore, the classification results haven't reflected the true geological nature of the engineering. Meanwhile, distinct differences in relation to various aspects, such as multiple stratums, complex lithology, different lithology of different rock mass have created problems and challenges faced by the classification of rock structure of dam foundation, the quality classification of rock mass, the evaluation of mechanical parameters, etc. The present research would provide great significance in both theory and engineering practice for the engineering geological evaluation of this kind of complex dam foundation of multi-stratum and multi-lithology and the accurate characterization of the true engineering geological conditions having great contrast between the apparent structure and mechanical property. Taking the Baihetan Hydropower Station's dam foundation rock mass featured by multi-stratum and multi-lithology as the objective of study and focusing on the classification of the complex structure and the evaluation of of the dam foundation rock mass, the major results have been achieved as follows:(1) By analyzing the basic characteristics of the rock mass featured by multi-stratum, complex lithology, the distinct differences between the textinite characteristics and structural surface developmental extent, based on a large number of onsite structural surface investigations, acoustic measurements as well as field and laboratory tests, related issues on the current classification of rock structure using single lumpiness indicators as well as the textinite nature and structural surface effect impacting the rockmass structure have been discoursed and analyzed. In addition, the factors and key indicators participating in the evaluation of rockmass structure classification have been put forward. Besides, considering the typical characteristics, including the diversity of the rock lithology of dam site, distinct varied structures, different velocity of the background, the integrated extent indicators for classification- identical quality integrality coefficient and the unified indicators for different structural types- normal structure coefficient has been established. and rock mass structure classification schemes based on the consideration of textinite characteristics and structural surface effect have been established, by which the classification result can accurately reflect the true engineering geological conditions of rock featured by huge contrast between the related apparent structure and mechanical property.(2) The weathering and unloading features of dam foundation rock have been studied using velocity ratio, the total number of cracks per element area, on-site judging and other qualitative and quantitative indicators to hold weathering zoning of the dam foundation rock mass in horizontal and vertical directions and to analyze the weathering characteristics of different rock lithology. Besides, the volume of open structural surfaces and the Drilling Lu-Rong Value have been used for the unloading classification of the dam foundation rock.(3) A large number of onsite rock mass deformation tests have been carried out, focusing on the deformation characteristics of columnar joints basalt. Besides, tests of situ velocity synchronization and homonymous stress deformation on rock mass of different lithology have been integrated to obtain the relationship between the longitudinal wave velocity and the modulus by satisfactory correlation.(4) Statistical analysis of textinite characteristics, longitudinal wave velocity , spacing of structural surface, number of structural sruface per element area and other indicators of rock mass characteristics has been conducted, by which those rock mass whose characteristic indicators is identical or similar have been judged as effective similar rockmass. According to the said status, 11 kinds of rockmass of the dam foundation have been comprehensively treated into four similar lithologic layers of amygdaloidal basalt, aphanitic basalt, columnar joints basalt and breccia lava.(5) According to the typical characteristics of dam foundation rock mass, it has determined that the main factors participating and quantitative indicators in the rock quality classification should be include rock mass structure, weathering, unloading, structural strength, stiffness and longitudinal wave velocity, longitudinal wave velocity of seismic wave, deformation and strength parameters. The rock quality classification schemes have been established as well.(6) Methods of sharing and jointly using of information about similar lithologic layers have been applied, according to rock quality classification schemes, the quality of 50 small layers (lithologic layers) of the dam foundation have been classified based on which small layers of rock mass have received a layer-joining treatment. Using the theoretical formula to obtain the comprehensive modulus and integrated velocity of the large layer (sub-layers of rock) after the layer-joining treatment, the large layer of rock has been finally treated with a rock-level classification.(7) The present thesis has established related relationships to take the values of mechanical parameters of rock mass in respect to various small layers of each level and theoretical formula has been used to study the value-taking of mechanical parameters of large layers in different levels after the layer-joining treatment.(8) Evaluation of rock mass of dam foundation in relation to structure, weathering, unloading, rock quality and other aspects of engineering geological conditions has been carried out and rock quality classification has been held for the identification of the basic construction surface location according to the classification results of rock mass.
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