Research On The Key Technology Of Multi Layer Tunnel Construction Under Deep Excavation

With the rapid development of urbanization process,urban pivotal project due to conditions,many sections are not suitable for open cut or total open-cut,to avoid deep foundation pit,forming underground three-dimensional structure.With the improvement of the road network,a large number of grade separation section tunnel becomes inevitable.At present,there is not much experience in the construction of this kind of multilayer grade separation section tunnel.Therefore,it is of great significance to study the key technology of multilayer tunnel construction under the deep foundation pit,in this paper,Chongqing Shapingba transport hub reconstruction project as the basis,launched the following research:1.Based on the displacement criterion,getting the partition of impact of two kinds of proximity relations,considering the overlapping effect of multilayer tunnel,this paper puts forward the calculation method of multilayer tunnel overlap effect,and verifies the applicability of the calculation method.2.Based on strength reduction method,the failure mode of surrounding rock in the tunnel under the foundation pit is obtained.A method for calculating the load of shallow buried tunnel is proposed.According to the characteristics of deep buried tunnel at the bottom,the calculation method of the load of bottom crossing tunnel is presented.3.In this paper,the construction sequence,construction method,excavation step distance of the single layer tunnel and the double-layer tunnel are compared.The effects of surface subsidence,stress on the rock and the stress and displacement of the supporting structure are comprehensively compared,the reasonable construction timing,construction method and excavation step are given.4.The distribution law of the surrounding rock loose circle in the mechanical excavation and blasting excavation is studied.The influence of blasting on the rock plate in the horizontal parallel and overlapped tunnel is studied.The safety control standards and reinforcement measures of the rock column in the blasting excavation are given.