The evolution of grouting pressure and ground deformation induced by synchronous grouting during shield tunneling in soft soil: An investigation based on scaled model test and CEL simulation

Synchronous grouting is critical in shield tunnel construction, especially in soft soil. A scaled model test platform was developed to investigate this process, with tests conducted at a cover-diameter ratio of 1.0 and varying grouting volume ratios (GVR). A finite element (FE) model using the Coupled Eulerian-Lagrangian (CEL) method was established to simulate grout filling and spreading in the tail-void. The FE model analyzed ground surface settlement (GSS), grouting pressure (GP), and vertical displacement and stress distribution around the tunnel. Results indicated that in soft ground, grout initially fills the shield tail-void before transitioning to compression. GP at the tunnel shoulder and invert is higher than at the crown and waist. High GVR significantly reduces GSS and soil disturbance. Increased GVR causes soil upheaval at the tunnel crown and shoulders and settlement at the invert and spring-line, while vertical displacement at the tunnel waist remains unaffected. Soil stress at the tunnel waist is lower, suggesting grout primarily fills the tail-void near the waist, with compression playing a secondary role. Soil stress at the waist does not vary with cover-diameter ratio, indicating stability and confirming grout-filling dominance in this area.