Application of Mindlin Solution in Calculation of Ground Settlement in Composite Stratum Shield Tunnel Construction

In the coastal areas of South China, Southeast China and North China, it is common that the upper part of the tunnel body is a soft soil layer, and the lower part is a hard rock stratum with high strength. The problem of land subsidence caused by shield tunneling has not been studied at present. To address this situation, the idea of using Mindlin solution to solve for surface subsidence was continued. In order to overcome the limitations of extended Mindlin solution for non-uniform strata, the layer state vector was introduced, and the integral transformation and matrix derivation were used to solve the relationship between displacement and stress at different layers. An extended Mindlin solution for composite formations was established. Finally, the adaptability of the Mindlin solution and the extended Mindlin solution to the surface subsidence of shield tunnels in composite strata were compared and compared with the actual engineering monitoring data. The derivation process shows that using the Mindlin solution or the extended Mindlin solution to solve the surface subsidence faces difficulties and needs to be simplified to a certain extent, while the engineering monitoring data show that the calculation results of the Mindlin solution are large, which can be used as a reference for engineering design. The method of extended Mindlin solution for calculating surface subsidence has certain accuracy.