Determination of Supporting Time of Tunnels in the Xigeda Stratum Based on the Convergence-Confinement Method

Abstract

The mechanical properties of the surrounding rock of the Xigeda stratum are easily affected by water content. In order to obtain the support characteristics of Xigeda strata, the finite difference method was used to obtain the longitudinal deformation of the surrounding rock at a certain distance from the tunnel excavation face under different water contents. Then, the longitudinal deformation profiles of a Xigeda stratum tunnel were obtained under different water content conditions. The accuracy and applicability of the results were verified through error analysis and comparison with existing research results. Based on the convergence-confinement principle, it is proposed that the best time to apply support is when the displacement increment of the surrounding rock has a sharp increase point. The support construction time under different water content conditions was obtained with the distance from the tunnel excavation face as the control index. The results show that with the increase in water content, the longitudinal deformation profile’s growth trend is steeper near the excavation surface and it is gentler when the distance from the excavation face becomes large. At a water content of 20%, the support should be applied 2.67 m behind the excavation face; at a water content of 25%, the support should be applied 1.46 m behind the excavation face. The result has a certain guiding significance for the safety of tunnel construction in the Xigeda stratum.