Research on Measurement Analysis and Protection Scheme of Crossing Shield on Tunnel Foundation Pit

Based on the Huiyi middle section of Pengzu Avenue tunnel engineering in Xuzhou city, the protection scheme of the shield tunnel near the foundation pit in silt area is studied, and the protection method of combining MJS and pipe-roof is proposed. Study of field measuring data shows that, MJS reinforced body is uniform in silt area within a certain depth range, and the reinforce strength is adequate. Besides, the feasibility of the pipe-roof jacking in the MJS is studied, and adding the alloy wedge tooth block on the bit can increase excavating efficiency. According to the monitoring data of metro shield tunnel in the process of excavation and the transverse chart of main construction steps, the relevant influencing factors of shield tunnel deformation are studied in detail. The study indicates that: (1) the protection scheme of MJS and pipe-roof can control the shield deformation induced by the excavation of the upper foundation pit within the limited range. (2) MJS can effectively control the injection pressure, which has little effect on the shield tunnel with reinforcement period; (3) Heavy construction machines should be concerned when driving over the shield, which can cause large settlement deformation of the shield tunnel. In addition, the finite element model is established according to the actual protection method, and the rationality of the model parameters is verified by comparing with the measured data. By establishing a variety of protection models, the necessity of MJS with pipe curtain protection method is verified.