Study on Bias Characteristics of Multi Arch Tunnel Under Different Side Overburden Thickness

Abstract

The entrance and exit of the Qifengshan tunnel are shallow and the pressure has a certain offset, the overlying soil layer is thin, and the stability is poor. After the excavation disturbance, the upper soil layer tends to slide. The excavation of black holes often causes large deformation, collapse and instability of surrounding rock. In this paper, combined with the geological conditions of the multi arch tunnel and the mechanical characteristics of surrounding rock, the theoretical analysis and numerical simulation are used to study the deformation law of the buried depth, side cover soil thickness and the stress and displacement of the surrounding rock after excavation. The results show that the bias stress of the tunnel under the vertical direction increases with the depth of the buried tunnel. The bias stress of the tunnel in the vertical direction decreases with the increase of the buried depth. The shallower the buried depth is, the more obvious the bias effect is. When the depth of burial exceeds 20m, the increased amount of bias stress is gradually reduced after the bias is applied. The vertical deformation characteristics of the rock mass caused by tunnel excavation with different thickness of the tunnel are analyzed. The vertical displacement is gradually reduced with the increase of the thickness of the side covering layer. When the thickness of the overlying soil is more than 21m, the vertical displacement is less affected by the thickness of the side cladding soil, basically only by the surrounding rock itself.