Method for calculating uplift of shield tunnels subjected to underlying grouting in soft clayey ground

Grouting in the underlying strata is a common remedial measure for the excessive settlement of shield tunnels. In the case of structured soft clays, the grouting process induces dissipation of the 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, a two-stage method for calculating the uplift and settlement of shield tunnels is proposed considering the structural characteristics of the soil. It 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, the parametric study is conducted, considering the parameters of 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 cover-to-depth ratio of the tunnel increases, the final uplift of the tunnel within the grouted range decreases, while the uplift efficiency exhibits negligible change. The proposed method provides support for the design of grouting for uplift of shield tunnel, in soft clayey ground.