Prediction of surface displacement caused by shield construction in soil-rock composite strata

When the shield tunnel passes through the soil-rock composite strata, it is easy to cause surface subsidence. In order to explore its law, the convergence mode of shield excavation face in a composite stratum is analyzed. The influences of layered strata on the surface displacement are considered. The traditional stochastic medium theory is simplified. The formula for calculating the surface displacement caused by shield construction in the composite stratum is deduced. Relying on the shield tunnel project of Huancheng North Road-Tianmushan Road in Hangzhou, the calculation and reliability verification of the surface subsidence are carried out. A total of 26 groups of measured data of surface settlement in China are collected and analyzed. The corresponding soil loss ratios are obtained through the inverse analysis, and the distribution and value laws of the soil loss ratios are further analyzed. The results show that the values by the simplified method is similar to those of the traditional stochastic medium theory, and the calculated curves are consistent with the measured data. The soil loss ratios in the composite stratum are distributed between 0.09% and 2.2%, which is similar to that in the cohesive soil. In the same project (section), the soil loss ratios decrease with the increase of the hard rock ratio and are roughly linearly correlated.