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 for controlling ground deformation during the shield tunneling process in soft soil. The grout filling and spreading mechanism inside the tail-void remains unclear, primarily due to the challenges of observing grout behavior behind the lining in practice and replicating its movement in numerical simulations. This study conducted a scaled model test with a cover–diameter ratio of 1.0, considering varying grouting volume ratios (GVR). A finite element model using the coupled Eulerian–Lagrangian method was established to simulate the grout filling and spreading process. The evolution of ground surface settlement, grouting pressure (GP), vertical displacement, and soil stress around the tunnel were investigated. Results indicated that in soft soil, the grout–mortar initially fills the tail-void before compression. The GPs at the tunnel shoulder and invert were higher than at the crown and waist. Increased GVR caused soil upheaval at the tunnel crown and shoulders and settlement at the invert and spring-line. However, the vertical displacement at the tunnel waist remained unaffected by the variation in GVR. Slight soil stress at the tunnel waist was observed, suggesting a dominant grouting mode of void-filling at the waist.