Comparison of construction methods for shallow burial tunnel with soft rock and large span

Abstract

Engineering accidents often occurred in new tunnel construction because of the shallow burial tunnel with soft surrounding rock and large span. In this paper, the Three-step excavation method, ring excavation reservation method, CD method and double pilot tunnel method were compared by the numerical simulation method. The results show that: the settlement of the surface caused by the double pilot tunnel method is the smallest in the four excavation methods and the settlement of the surface can be effectively controlled by this method. The vault crown settlement and convergence deformation values by the double pilot tunnel method are the smallest in the four excavation methods. The stable condition of the surrounding rock by the double pilot tunnel method can be reached earlier than the other three methods. There are little differences in the stress of surrounding rock among the four excavation methods. However, the stress level of the support structure is different. The stress of the support structure by the double pilot tunnel is the smallest and it is less than the allowable tensile stress of shotcrete. Through the comparative analysis of various parameters, the double pilot tunnel method in the construction of shallow tunnel with soft rock and large span is recommended.