Study On Excavation Method And Construction Parameters Of Super Large Section Highway Tunnel Of Grade ? Surrounding Rock

Due to the rapid development of high-grade highway construction and the dramatic increase in traffic volume,super-large cross-section tunnels have emerged.Compared with the tunnels built in the past,the super-large section tunnels have put forward new requirements in construction methods,mechanical behaviors and support parameters.At present,there are few examples available for reference in this respect at home and abroad.This paper relies on the research project of Liantang super large section tunnel in Shenzhen East,combined with on-site monitoring and numerical simulation,to support the surrounding rock under two construction methods of tunnel.The comparative analysis of the structural deformation and force is carried out,and the better engineering method applicable to the project is obtained.On this basis,the dynamic construction process and construction parameters of the single-side guide pit method are studied.The main research contents and results are as follows:(1)According to the actual situation of the Liantang tunnel,a three-dimensional finite element numerical calculation model is established.The deformation and stress of the surrounding rock support structure under the excavation of the single-wall guide pit method and the double-side guide pit method are compared and analyzed.Based on the stability and construction safety,and taking into account the main factors such as economic cost and construction progress,the single-wall guide pit method is the preferred construction method.(2)The dynamic construction process of the single-wall guide pit method in Liantang tunnel is numerically simulated.The distribution and development law of displacement and stress of surrounding rock and supporting structure of super-large section highway tunnel are studied.The mechanical behavior characteristics of tunnel dynamic construction are summarized..The simulation results show that the tunnel convergence is mostly caused by multiple disturbances of surrounding rock caused by tunnel excavation.To control the convergence of the cave wall,the disturbance of surrounding rock should be minimized,the initial support should be earied out in time,and the loop should be closed as soon as possible.The lower guide is the position where the compressive stress is the most likely to occur,and the reinforcement of the arch portion should be paid attention to during construction.(3)Based on the above numerical model,the effects of construction parameters such as excavation footage,arch spacing and arch type on the stress and deformation of surrounding rock and the bearing structure are further studied.The research results show that the single-side guide pit method for excavation of Class ? surrounding rock super-large section tunnel should be taken at a depth of 2.0m,the arch spacing should be 0.5?0.75m,and the arch type should be I24a?I25a.(4)Comparing the monitoring measurement with the numerical simulation results,the results show that the deformation trend of the surrounding rock and the support structure are basically the same,which can explain the numerical model calculation results can provide some reference for practical engineering.