Based On The Nonlinear Failure Criterion Of Shield Tunnel Excavation Surface Stability Analysis

Shield construction technology is widely used in urban underground engineering construction due to its small effects on the environment, during shield tunneling, by applying certain pressure on the ahead soil of excavation surface to guarantee the stability of the tunnel itself and shield tunnels smoothly. Therefore, it is the key problem how to determine the excavation surface limit support pressure, which ensures the stability of excavation surface. The existing research of the shield tunnel excavation surface stability mostly adopts linear failure criteria, but many practical engineering problems and geotechnical test data show that geotechnical media obeys the nonlinear failure criterion, and the linear failure criterion is just one special case. In this paper, the nonlinear Mohr-Coulomb failure criterion is applied to researching the stability of shield tunnel excavation surface based on the nonlinear characteristics of geotechnical material, the main study works focus on the following several aspects:(1) Using FLAC secondary development platform of VC++ to embed the nonlinear Mohr-coulomb failure criterion in the source program of the FLAC own constitutive model, realizes the secondary development of numerical simulation software FLAC, comparing the existing data with the results of numerical calculation, verifies the validity of the research and development of the process, at the same time, analyses the nonlinear parameter on the influence of excavation surface limit support pressure.(2) Based on the nonlinear Mohr-coulomb failure criterion of deterioration, according to the limit equilibrium theory, using the shallow tunnel excavation face wedge failure model, theoretical formula of the excavation surface support pressure is obtained. Citing a specific example, comparing the limit equilibrium theory solution with the numerical simulation solution is to verify the correctness of numerical simulation results under the action of nonlinear failure criterion.(3) Applying the linear and nonlinear failure criteria, explores that the support pressure impact on the stability of the excavation surface by designated six different overload areas and the custom of overload mainly affected zone, finally, with an instance of shield tunnel excavation surface instability, the numerical method and wedge body model are applied to solving the excavation surface limit support pressure, and the numerical and theoretical solution of limit support pressure were contrasted with the measured soil pressure, further examines the reliability of numerical calculation under the nonlinear Mohr-coulomb failure criterion.