Experimental Investigation on Active Control of Tunnel Structure Deformation Using Capsule Grouting Technique

Abstract Tunnel failure caused by excessive deformation has become a significant threat to the operational safety of urban subway systems. To address this issue, a novel method, the capsule grouting technique (CGT), has been proposed as an effective solution for controlling tunnel deformation and reducing failure risks. The CGT offers the advantage of controlling tunnel deformation both efficiently and precisely. However, the mechanisms behind deformation control of CGT remain unclear because of its limited practical applications and reliance on numerical simulations for most research. Consequently, this study designed and implemented a systematic model test of CGT. The deformation control mechanisms of CGT were explored, and factors affecting its performance were analyzed. In addition, the shielding effect between capsules was observed for the first time in this study via model testing, and its impact on CGT performance was analyzed. The results indicated that CGT can effectively control horizontal and vertical tunnel deformation, with the horizontal deformation being greater than the vertical. Increasing relative soil density and reducing the horizontal and vertical distances between the capsule and the tunnel both led to greater tunnel deformation caused by capsule expansion. Moreover, the capsule expanded vertically from top to bottom within the soil during the grouting process. The shielding effect confines additional stress caused by capsule expansion within a specific region, enabling precise control of tunnel deformation. These findings offer insights into the optimal use of CGT for controlling tunnel deformation and preventing structural failure.