Study On Primary Support Scheme Of Super-long-span Highway Tunnel

The primary support structure is an important guarantee for the safety,and also an important source of the project cost of the highway tunnel.That is the reason why a scientifically and reasonably design of primary support is necessary.Based on the principle of convergence-confinement method,this paper carries on a numerical analysis to Jiangjun mountain tunnel,considering the free deformation before the primary support and the release ratio of stress of tunnel excavation.The main research contents and research results are as follows:(1)To study the problem of release ratio of stress of tunnel excavation,this paper built a numerical model to analyze the influences factors including surrounding rock grade,tunnel shape,excavation size,tunnel burial depth and lateral pressure coefficient.The results show that surrounding rock grade is the main factor influencing release ratio of stress of tunnel excavation when the rest of the five factors have slight influence on it.And corresponding ranges of stress release ratio to different surrounding rock grade is confirmed.(2)The forward analysis numerical model of joint action of the surrounding rock and the primary support structure of the Jiangjun mountain tunnel is established to study tunnel excavation and primary support construction process,and obtain the deformation characteristics of surrounding rock in different construction stages.This paper presents three different approaches to simulate bolts,which respectively are equivalent support force,improve the the rock parametric of bolt reinforcement area and bar element.the results show that the equivalent support force method can best reflect the supporting function of bolts.(3)Based on the principle of convergence-confinement method,considering the free deformation of the surrounding rock before primary support,and combining with the code for design of road tunnel and on-site monitoring results,the safety problem and economic problem of the primary support scheme of Jiangjun mountain tunnel are studied in this paper.The results show that the primary support scheme of Jiangjun mountain tunnel is safe but the economic effect is poor.Therefore,this paper proposed optimized design of primary support.Under the premise of ensuring tunnel safety,by increasing longitude space of anchors,steel arch and grid arch to achieve the purpose of reduce the amount of steel,thereby reducing the cost of the project.