Earth Pressure Balance Shield Tunneling Surface Subsidence Caused By Numerical Simulation

The shield driving method, as one of the main construction methods of metro tunneling, has been used widely in China. The soil displacement and ground surface settlement induced by construction is the main issue during shield tunnel design and construction. In this thesis, the soil displacement and ground surface settlement induced by shield tunnel construction were analyzed completely by using 3D FDM and some significant results were obtained. The main research contents are as follows:(1) It is analyzed that the key steps during the construction with shield driving method; the main reasons for soil displacement; and the advantages and disadvantages of the existed FEM simulation methods for shield construction. The shortages of the existed method modeling the load of shield construction were covered and the 3D FDM model was established so as to simulate the shield construction process more reasonably and completely.(2) It is studied that the factors influencing ground surface settlement during shield construction by using 3D FDM, including soil pressure in pressure cabin, grouting pressure, and strata loss percentage. It is obtained that the most important factors affecting the ground surface settlement of the shield tunnel are strata loss percentage and grouting pressure. The role of increasing soil pressure in pressure cabin is limited to decrease the ground surface settlement of tunnel.(3) According to the research results in the thesis, the three dimensional simulation of ground surface settlement of one certain shield tunneling section in No.3 subway in Guangzhou was conducted. The results indicate that the strata deformation induced by the shield construction has obvious three dimensional characteristics, where the vertical and horizontal displacements of the strata located at different places along the runnel axis line are large; the surface settlement of the soil at the front of shield face, the peripheral layer of the shield and the back of the shield has different properties.(4) The effects of the different distance of excavation face of two adjacent tunnels and the grouting pressure of the second tunnel to the ground surface settlement were simulated during the construction process of shield tunneling.