A hybrid construction method for shallow buried urban tunnel with ultra-small clear distance

During the construction process, it is difficult to ensure the structural safety of shallow buried tunnel with the ultra-small clear distance since the tunnel is prone to instability and the surrounding rock and soil are in an adverse stress condition. To address this issue, a hybrid construction method is proposed to enhance tunnel stability and reinforce the surrounding rocks and soil. First, aiming at an actual tunnel, numerical analysis are provided to compare the effectiveness of different construction methods such as the bench method, advanced reinforcement method, and grouting reinforcement method. Second, the performance of the combination of advanced reinforcement and grouting reinforcement are discussed, and, on the basis of this discussion, the hybrid construction method, combining the advanced small pipes reinforcement, middle rock wall reinforcement, and grouting reinforcement, is proposed. And the characteristics of proposed method is compared with the traditional CRD construction method. The results reflect that using the hybrid construction method can enhance the stability of the tunnel and its effect is similar to that of the CRD method. Finally, the effectiveness of proposed hybrid construction method is verified by using the measured data obtained during the construction of an actual tunnel with the ultra-small clear distance. The results shown that the proposed method can enhance the stability of the tunnel and improve the bearing capacity of the surrounding rock and soil.