Study on the Characteristics of Safety Distribution Changing with Buried Depth for Metro Station in Upper-Soft and Lower-Hard Stratum

The reasonable buried depth of metro station should be investigated for Qingdao with the upper-soft and lower-hard stratum. Strength reduction method has been utilized to study FOS of metro station under different buried depths. As the buried depth increases, the curve of FOS can be divided into three parts as the slowly changed part, the rapidly-increased part, and the gradually-decreased part. Taking FOS = 1 as limitation, the formula of least rock cover thickness has been derived. Based upon the formula, the characteristics of safety distribution changing with buried depth for metro station which behaves as three zones (DI, E, DII) have been discovered. Two typical metro stations have been used to verify the research results.