Horizontal Deformation of a Tunnel Controlled by Capsuled Expansion Technique in Soft Clay: Field Trial and Numerical Analysis

Controlling tunnel response induced by lateral excavation in soft clay has become a significant focus of modern research. Capsuled expansion is an innovative active control technique used to control the deformation of existing shield tunnels. In this study, a prefield trial was performed to explore the response of an existing metro tunnel horizontal deformation in soft clay to capsuled expansion. The fully coupled hydromechanical analysis was adopted to further investigate the long-term mechanisms of horizontal tunnel deformation controlled by capsuled expansion. The horizontal deformation of the tunnel exhibited a positive linear correlation with the expansion diameter. With an increase in the expansion diameter, the control efficiency gradually increased and approached a limit value, and the relative control effect on convergence also improved. The tunnel deformation induced by the capsuled expansion is attributed to the synergistic effects of compression, shielding, and deformation compatibility. The interplay among these factors determines the development of stress in the soil around the tunnel, ultimately governing the deformation response of the tunnel structure. Finally, the mechanisms of the different control strategies were explored to obtain the optimal control effect.