Study on the stability of a large-span subway station constructed by combining with the shaft and arch cover method

Abstract

Based on the actual engineering of Qingniwaqiao Subway Station of Dalian Metro Line No. 5 in China, according to the stratum characteristics of upper soft and lower hard of the station and the complex surrounding construction environment, a method for constructing a large-span underground excavation station by combing the shaft and arch cover method is presented. This method reduces the construction procedure, saves the construction space, and solves the problem of receiving shield machines in the limited construction site. However, the shaft destroys the original arch effect of the arch structure, bringing about the security of the arch cover. The construction process is studied based on numerical simulation and field monitoring data. The development law of ground surface settlement and the shaft and station's structural deformation and mechanical characteristics are investigated. Subsequently, the reinforcement effect of the reinforcement area at the opening of the arch cover and the steel pipes and anchors in the rock mass under the arch foot are analyzed. The most effective surrounding rock reinforcement scheme is determined and the optimal schemes are selected to excavate the middle pilot tunnel and remove the initial support. The results show that the middle pilot tunnel's excavation and the initial support's removal are two key stages to control the surface settlement and the shaft deformation, and the arch cover can effectively restrain the disturbance caused by the excavation of rock mass inside the station to the surface and shaft. Finally, the rationality of the numerical simulation and the applicability of the proposed method are verified by comparing the monitoring results with the simulation results. These results demonstrate the safety and feasibility of constructing a large-span underground excavation station by combing with the shaft and arch cover method, and greatly improve the construction efficiency.