Experimental study on grouting uplift after settlement induced by shield tunneling under existing tunnels

To investigate the efficacy of the bag grouting technique in mitigating settlement induced by shield tunneling, a distinct grouting process is formulated subsequent to the completion of a model test simulating the said scenario. Subsequently, an uplift test is conducted to evaluate the technique's impact on the tunnel's flexural deformation, settlement, and changes in additional earth pressure exerted on the superstructure during the grouting-induced settlement test of an existing tunnel beneath a shield tunnel. The experimental findings reveal transverse elliptical deformations occurring within a zone of 120 cm to 250 cm from the northern terminus of the tunnel. Notably, a significant uplift in the superstructure is observed at this location, with the peak uplift reaching approximately 15 mm at the tunnel's midpoint. The greatest increment in additional earth pressure is recorded at the tunnel's midpoint as well. During the grouting operation, the bag grouting method exerts a robust binding effect on the grouting slurry and concentrates the slurry pressure predominantly around the injection point, thereby inducing a soil arching effect in the adjacent soil mass. In practical engineering, it is recommended to employ concurrent multi-point grouting to elevate the tunnel as a integral unit, thereby restoring the tunnel's internal forces and structural configuration to their pre-underpass conditions. Moreover, enhanced monitoring of the tunnel's uplift should be implemented throughout the grouting phase to avert excessive uplift.