Effect of pre-grouting on the ground deformation and its mechanism in the construction of tunnels with small-spacing and large-section

The ground deformation is difficult to control in the construction of tunnels with small-spacing and large-section. Taking a crossover track tunnel in Beijing Metro line 12 as a case, a refined numerical model for tunnels with small-spacing and large-section is established to research the effect of pre-grouting on the ground deformation. Rationality of the numerical model is validated by the good consistence between the field measured simulated results, including the ground and pipelines settlement. Further, by comparing the results of numerical models with and without pre-grouting measures, the effect of pre-grouting measures on the ground deformation, involving in the settlement, horizontal displacement, and the plastic region, are analyzed quantitatively. The implementation of the pre-grouting measures reduces both the maximum settlement at surface and horizontal displacement by approximately 67.5 %, and the PEEQ distribution region is limited to the region outside the pregrouting, and the moderate and severe disturbance areas are respectively reduced by 65 % and 80 %. Finally, the control mechanism of the pre-grouting on the ground deformation is revealed based on the strength-stiffness theory.