The law of surrounding rock deformation and surface settlement of shield tunnel passing through upper soft and lower hard rock

Abstract With the rapid increase in the number of urban subway construction in China, the geological distribution encountered in the tunnel construction process is gradually diversified, especially when the excavation is carried out in the upper soft and lower hard formations, there are certain differences in the physical and mechanical properties of the tunnel palm surface, the surrounding rock and the distribution position of the soft and hard rock junction surface, which can easily lead to the occurrence of large deformation or even collapse of the surrounding rock of the tunnel. In order to study the deformation of surrounding rock and the change of surface settlement when the shield tunnel crosses the upper soft and lower hard strata, relying on the actual project of the shield tunnel crossing the upper soft and lower hard strata of Shenzhen metro line 13. Firstly, based on the molar stress circle theory and the theory of elastic mechanics, the influence of internal friction angle and cohesion on the surrounding rock stress is analyzed, and the first yield location and distribution characteristics of the surrounding rock stress of the upper soft and lower hard strata are divided based on the calculation formula of the surrounding rock stress; Secondly, the inclination angle of the soft and hard rock junction surface of the above soft and hard formations is α variable, and the MIDAS GTS NX numerical simulation software is used to set seven working conditions of 0°, 15°, 30°, 45°, 60°, 75°, 90°, and analyze the influence of inclination on the surrounding rock stress of the tunnel, the plastic yield position of the surrounding rock, and the deformation of the surrounding rock. Finally, the surrounding rock deformation and surface settlement monitoring data after the completion of the construction of the soft and lower hard strata in the Liu ~ Bai section of Shenzhen Metro Line 13 are summarized, and the numerical simulation is compared and analyzed to verify the accuracy of the numerical simulation results, and the final research results can provide a certain reference for similar projects in the later stage.