Study on Directional Micro-Disturbance Grouting for Settlement Control of Shield Tunnel in Sand Layers Based on Numerical Simulation and In-Situ Test

Due to changes in the surrounding environment, the settlement defects of a shield metro tunnel in Wuhan have become increasingly prominent, seriously affecting its safe operation. Directional micro-disturbance grouting can effectively control the settlement of a shield tunnel. However, the grouting parameters S and H directly affect the grouting effect. This study adopts the finite difference method to analyze the influences of parameters S and H on the displacements of the shield tunnel and surrounding soil. The simulation results indicate that as S/D increases from 0.242 to 0.726, the compaction effect of the soil at the tunnel bottom gradually weakens, and the uplift displacements of both the vault and the track bed decrease accordingly, suggesting that parameter S plays a controlling role in the uplift deformation of the vault and track bed. However, as H/D increases from −0.161 to 0.323, the compaction zone of the soil at the tunnel haunch gradually shrinks, while the compaction zone at the tunnel bottom expands. At the same time, the uplift displacement of the track bed increases, and the horizontal convergence of the tunnel decreases. When parameter H varies within the range of −0.161D to 0.726D, it is observed to have a minimal impact on the uplift displacement of the tunnel vault but exerts a significant influence on both the uplift displacement of the track bed and the horizontal convergence of the tunnel. Based on the settlement control requirements for the in-situ grouting test section, the parameters S = 0.403D and H = 0.161D were selected for the in-situ grouting test. The average measured uplift displacements at the tunnel vault and track bed in the in-situ grouting test section were 14.9 mm and 9.1 mm, respectively, being only 2.6% and 4.2% lower than the numerical simulation results (15.3 mm and 9.5 mm). The strong consistency between the field-measured and simulated results validates the rationality of parameters S and H selection.