Calculation method for the overlying shield tunnel uplift subjected to underlying grouting in soft clayey ground

Grouting in the underlying strata is a common remedial measure for excessive shield tunnel settlement. In the case of structured soft clays, the grouting process induces dissipation of excess pore pressure in the surrounding strata, which leads to settlement of the tunnel after the grouting process and subsequently reduces the uplift efficiency. In order to predict the longitudinal deformation of shield tunnels caused by grouting in the underlying strata, this study proposes a two-stage calculation method for the uplift and the settlement of shield tunnels considering the structural characteristics of the soil. The method is applied to a grouting uplift case in Ningbo Metro Line 2, and the calculated uplift efficiency of the tunnel is approximately 51%, which is close to the measured uplift efficiency of an interval of Shanghai Metro Line 2 in soft clayey ground. Furthermore, parametric study is conducted, considering parameters regarding grouting, strata, and tunnel. The results indicate that the final uplift settlement and uplift efficiency of the tunnel are positively correlated with the coefficient of subgrade reaction and grouting volume, while negatively correlated with the yield stress of the strata. As the tunnel cover-to-depth ratio increases, the final uplift of the tunnel within the grouted range decreases, while the uplift efficiency exhibits negligible change. The calculation method proposed in this study provides support for the design of grouting for shield tunnel uplift in soft clayey ground.