Stability Analysis of Neighborhood Tunnels with Large Section Constructed in Steeply Jointed Rock Mass

To investigate the instability of two neighborhood tunnels with large crossing section during the construction, the Tushan subway station was taken as study background, which was built in steeply jointed rock mass. Based on the excavation method called traditional double side drift, numerical simulations of four different face excavation sequences in the two neighborhood tunnels were conducted to optimize construction sequence to improve the stability during tunneling. The results show that first excavation of the right tunnel produced less deformation of the tunnels due to joints dip. The effects of rock mass discontinuities on the stability of the tunnels were studied through comparison between the real condition with joints and the assumed condition without joints. Furthermore, six initial supporting systems with different parameters were compared, and the field observations of deformations along tunnel profile show good agreement with the numerical results. Based on the numerical simulation, the length of rock anchors could be designed asymmetrically, which is more economical than the symmetrical design. The optimized thickness of shot concrete and spacing of steel sets was 35 cm and 60 cm, respectively.