THE MINIMUM BURIED DEPTH OF SHIELD TUNNEL CONSIDERING THE EROSION OF YELLOW RIVER
DAI Zhiren1，ZHANG Shasha2
(1. China Railway First Survey and Design Institute Group Co.，Ltd.，Xi?an，Shaanxi 710043，China；
2. School of Highway，Chang?an University，Xi?an，Shaanxi 710064，China)
Abstract：The minimum buried depth of shield tunnel below the riverbed of Yellow River for Metro Line 1 in Lanzhou was studied considering the weak cemented gravel layer with rich water and under high pressure. Two methods for calculating the minimum buried depth were put forward according to the stability of cutting face and the stability of counter-floating of the segments at the rear of shield tail respectively. The upward buoyancy acted on segments was divided into two parts，namely the static buoyancy depending on surrounding liquid grout，and the dynamic buoyancy due to the vertical unbalanced force generated by formation stresses. The decisive role of upward buoyancy on the minimum buried depth was made clear，and the corresponding minimum depth was obviously larger than 1.0 D. The minimum buried depth 1.0 D in the code for design of metro(GB50517—2003) has to be improved. The safety and feasibility of the tunnel alignment design was proved with considering influence of bridge piers near the project site. The influences of local erosion of existed structures on new structures was made clear.
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2015, Vol. 34 
