Shield tunneling in soft soil is prone to losing control of posture and seriously deviating from the designed tunnel axis, which can cause significant ground settlement and tunnel misalignment. This paper develops a large-scale indoor shield tunneling model test platform and conducts shield posture adjustment model tests to examine the interaction between the shield and soft soil. Based on these tests, the distribution and evolution of earth pressure and pore water pressure around the shield, as well as the surface displacement under in-situ posture adjustment and tunneling posture adjustment modes are investigated. The results indicate that the earth pressure around the shield and ground displacement are significantly related to the shield tunneling posture mode. When the shield is in the constant posture angle tunneling mode, the sudden changes in earth pressure and ground displacement are mainly due to the in-situ posture adjustment at a large angle before excavation. However, under the subsequent dynamic tunneling effects of the shield shell approaching and leaving the soil in the excavation, the mutation amount gradually dissipates. When the small-range dynamic posture adjustment mode is adopted, the earth pressure around the shield and surface displacement will change synchronously with the shield posture mode and reach their peak value when the posture angle of the shield is maximum. Moreover, there is a plastic limit in the earth pressure around the shield during the posture adjustment, and under the plastic deformation and flow of the soil, the formation will cause soil loss and ground settlement. These findings offer important information on how the shield interacts with the surrounding soil as well as recommendations for constructing shield tunnels in soft soil.

A pipeline with long-term hidden leakage will greatly reduce the stability of the ground between the pipeline and tunnel in the process of tunneling through existing pipelines in unsaturated soil. Excessive settlement of the surrounding strata and pipelines can occur when the shield excavation face approaches below a pipeline, which can lead to engineering accidents. This study is based on a self-developed model experimental system for tunneling through an existing pipeline with a double-line tunnel shield. The ground settlement and pipeline deformation caused by shield construction with small-scale and no leakages are investigated. An experimental study is conducted and the accuracy of the results is verified through a comparison with theoretical solutions. The results demonstrate that there is a significant increase in ground settlement and pipeline deformation under the influence of leakage water. It is also determined that the displacement field generated by the excavation of a double-line tunnel is not simply a superposition of the displacement field generated by the excavation of a single-line tunnel. The repeated disturbances caused by the excavation of a double-line tunnel significantly influences the redistribution of the displacement field. Additionally, a three-dimensional (3D) model of shield construction considering the influence of pipeline leakage is established. This study discusses the ground settlement and pipeline deformation patterns caused by changes in the vertical and horizontal leakage diffusion ranges. The computational results indicate that the diffusion depth of a leakage is the primary factor controlling the extent of settlement.

With the continuous expansion of urban underground space development, stratum disturbance induced by shield construction has an important impact on the safety of existing underground structures and surrounding environment. Through the independent research and development of the shield tunneling test device, the load of different stratum stress levels was realized, and the change law and influence range of the stratum disturbance in shield construction under different burial depth conditions were analyzed. The results show that the change rate of earth pressure in the strata around the tunnel decreases with the increase of the horizontal distance from the tunnel. The ratio of soil pressure after shield tunneling to initial soil pressure is about 60%-80%. The change of buried depth ratio has little influence on the soil stress path at the vault and bottom. The stratum disturbance degree based on the change of stress is defined, and the stratum disturbance degree gradually decreases with the increase of the burial depth ratio, indicating that the deep burial condition will reduce the disturbance effect of shield excavation on the stratum. After the completion of the shield tunneling, the height of the vertical influence range of the disturbance is between 0.5D and 0.8D above and below the tunnel (D is the diameter of tunnel), the width of the horizontal disturbance range is about 0.5D when the shield reaches the monitoring section, and approximately 1.2D to 1.5D when the shield passes far away.