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Western China bears abundant hydropower development potential, but the riverbed the ubiquitous deep overburden layer (thickness greater than 30m). Evaluation of the engineering geological properties has become one of the problems often encountered in the western hydropower development process. Is a canyon area Jinsha Jiang Qizong hydropower construction of the High Dam, a large library, the most dam up to 356m. Hub area riverbed and terraces distributed thickness of 60 to 127m deep overburden its complex causes, including alluvial, alluvial debris flow deposits and colluvium and other causes. All excavation due to the thickness of the cover layer, both technically and from an economic point of view difficult to accept or implement Therefore, the main engineering geological problems facing the Monolith deep overburden layer construction of high dams suitability. Exploration data - situ testing and laboratory test data based on analysis of the cases power station dam site deep overburden layers soil spatial distribution, causes and engineering properties, anti overlay foundation slip stability, deformation, seepage stability, the sand liquefaction comprehensive evaluation and analysis. Analyzes the cases of power station dam site deep overburden their causes can be divided into three layers, five sub-layers, respectively: (1) eggs (block) gravel (crushed) stone layer is sandwiched in fine sand or silty clay layer ( al fgl Q 3 ), better their physical and mechanical properties, the natural density of 2.2 to 2.3 g / cm 3 , void ratio 0.25 to 0.3, the foundation allows the bearing capacity of 0.6 to 0.9 MPa, compressive modulus of 50 to 70MPa, permeability coefficient of 1.0 × 10-1 to 1.0 × 10 -3 cm / s; (2) -1 egg (block) gravel (crushed) stone layer is sandwiched between fine sand and silty clay layer ( al the pl sef the Q 3 ), the natural density of 2.15 ~ 2.25 g / cm 3 , void ratio of 0.25 to 0.3, the foundation allows the bearing capacity of 0.4 ~ 0.6 MPa, compressive modulus of 25 to 40 MPa, the permeability coefficient of 1.0 × 10 -5 to 3.0 × 10 -4 cm / s; (2) -2 fine sand layer ( al the Q 3 ), its physical and mechanical properties of poor natural density of 1.8 ~ 2.1g / cm 3 , void ratio of 0.7 to 0.8, the foundation allows the bearing capacity of 0.2 ~ 0.25MPa, compression modulus of 10 to 15 MPa, the permeability coefficient of 2.0 × 10 -5 to 1.0 × 10 -3 cm / s; ③ -1 of drift (block) eggs (broken) gravel layer (alQ4) of the natural density of 2.1 to 2.2 g / the cm 3 void ratio of 0.3 to 0.45, the foundation allows the bearing capacity of 0.4 to 0.7 MPa, compressive modulus of 30 ~ 50MPa, the permeability coefficient of 2.0 × 10-1 to 3.0 × 100 cm / s; ③ -2 sand and silt layer ( al Q 4 ), the layer of physical and mechanical properties is poor, the the natural density 1.8 to 2.0 g / cm 3 void ratio of 0.45 to 0.7, the foundation allows bearing capacity of 0.15 to 0.2 MPa, compression modulus of 8 ~ 12 MPa, the permeability coefficient of 7.0 × 10 -4 1.0 × 10 -3 cm / s. Overall forced? Zeng Ju Abduction pan-yo murmured removal stunned mud the fluorene the Xiao-mortem lip shrimp? Skid stability to meet the requirements, there are also gravel infiltration, covering layer deposition of large deformation, there can be liquefied sand some problems, but these problems can be engineered measures to be addressed, overburden dam foundation after by the project with the construction of high core rockfill dam conditions.
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