Optimizing Shield Tunneling Parameters for River Dike Safety: Numerical Simulation and Case Study of Soft-over-Hard Strata

This research employs finite element analysis to model the impact of shield tunneling on a river embankment situated near a river channel with overlying soft soil and underlying hard rock. The study is based on the Shenzhen-Shantou Avenue expansion project’s pipe gallery tunnel construction under the Chishi River in China. The primary focus is optimizing shield propulsion pressure and synchronous grouting pressure to minimize embankment settlement and tilting. The simulation results reveal a strong correlation between grouting pressure and vertical embankment settlement. Within the range of grouting pressure 0.01–0.03 MPa, the vertical settlement produced by the grouting pressure of 0.01 MPa is the largest, at 12.8 mm, and an increase of 0.01 MPa in grouting pressure reduces the maximum settlement by 0.65 mm. However, grouting pressure shows minimal effect on lateral embankment displacement and tilting. Furthermore, excessive grouting pressure (above 0.03 MPa) increases the risk of riverbed uplift, highlighting the need for careful pressure control. In contrast, the shield’s propulsion pressure demonstrates a more significant influence on lateral embankment movement. While less effective in controlling vertical settlement, adjusting the propulsion pressure effectively manages lateral displacement and tilting. Increasing propulsion pressure initially shifts embankment displacement away from the river, eventually reaching near-zero lateral displacement at 0.08 MPa. However, further increases in propulsion pressure heighten the risk of embankment overturning toward the river. Therefore, an optimal propulsion pressure range of 0.05–0.08 MPa is recommended to balance minimizing lateral displacement and mitigating overturning risks. This study provides crucial insights for determining appropriate tunneling parameters in similar geotechnical contexts, where soft soil overlies hard rock near a river.