Reasonable distance for super-large section neighborhood tunnel of granite residual soil with shallow-buried bias

In order to discuss the relationship between reasonable spacing and degree of bias of granite residual soil shallow-buried bias tunnels with small spacing span, the bias ratio index P was introduced. After the tunnel portal of bias neighborhood tunnel models were built for three kinds of slope gradient, i. e. 1:7, 1:5 and 1:3, the impact of granite residual soil surrounding rock tunnel construction methods optimization and different rates of bias P on the reasonable minimum spacing were discussed based on the software FLAC3D. The results show that the double side heading tunnel construction method is more suitable for bias of 1.13, and that the minimum reasonable distance of tunnel is 24 m, the middle pillar is the weakest part, the settlement of pillar above the group is the largest, the axial forces of the supporting bolt of both sides of the tunnel are the largest, and during the construction process the plastic deformation of both sides near the pillar is also the biggest. The numerical simulation method is feasible and effective; therefore, the rock on the plate of rock pillar must be firstly consolidated during tunnel construction, and rock both in the middle and under the plate must be consolidated to ensure the stability of the middle rock pillars. © 2015, Central South University of Technology. All right reserved.