Abstract: In general, the bank-tower-type water intake is built in the steep slope near the deep water zone, and the thickness of rock ridge used for the water retaining cofferdam is thin during excavation procedure of the foundation pit due to the construction. In addition, the upstream surface of the bank slope form a cavern subjected to water erosion, and the thin-walled rock ridge presents overhanging state; further the left bank slope is unstable induced by hydro-mechanical coupling and excavation action. Based on research about permeability theory and hydraulic aperture expanded model of fractured rock mass, the numerical method is adopted to simulate the excavation procedure of the foundation pit; further, compared the calculated deformation values with monitoring data. The results indicate that the permeability of thin-walled rock ridge become weakened after grouting, and the foundation pit excavation scheme that gradually install internal support is reasonable. The deformation of overhang rock ridge is in a reasonable range. Differently, the self-weight of rock ridge and water pressure of upstream face lead to inclined deformation of the thin-walled rock ridge towards river in initial excavation stage while towards the bank slope in later excavation stage. For the design and construction of foundation pit of water intake located on steep bank slope; the research results have important reference values and theoretical significance.

Key words: steep overhang, water intake tower, foundation excavation, rock cofferdam, permeability stability