The optimal design of double-row capsule grouting to protect tunnel adjacent to excavation

Deep excavations particularly in deep deposits of soft clay can cause excessive ground movements and potentially damage nearby tunnels. A new grouting technique called double-row capsule grouting (DRCG) has been developed and implemented in practice to mitigate excavation-induced tunnel movement and ensure the serviceability of metro line effectively. Based on the finite element models, the soil displacement field around the tunnel before and after capsule grouting, which is divided into three zones, can be used to illustrate the restoration capacity of DRCG technique. To achieve the optimal control effectiveness of horizontal tunnel deformation, vertical tunnel deformation, horizontal tunnel convergence, and vertical tunnel convergence simultaneously, the optimal design of DRCG technique is conducted. In practical engineering, the engineers are suggested to control the relative depth of capsules within 2 – 4 m, and control grouting volume of near-row capsule less than the volume of far-row capsule. Finally, the mechanism of DRCG to control tunnel deformation is proposed.