Study Of The Expansion Type And Stability Of Highway Tunnel Change

Because of sustained growth of economic and increase of income in China,car ownership is becoming higher and higher,resulting in highway capacity constraints.To meet this demand,it is necessary to reconstruct and extent current highway,which includes reconstruction and extension of highway tunnel.One of the common way is to build a new four lane based on original bi directional and four lane to make small-distance tunnel.This paper reaches schemes for tunnel reconstruction and extension,excavation,rock stress and strain during construction and characteristics under force in initial stage by taking combination of theory research,indoor model experiment,finite element analysis and relying on extension of certain part of Fuzhou-Xiamen-Zhangzhou highway,providing reference to related projects.The contents include:(1)By comparison of separated tunnel and small-distance tunnel,this paper comes to the conclusion that the best way to extension is to build a four-lane between two original tunnels and extent the right one.(2)The paper summarizes characteristics of ground subsidence and rock stress-strain during reconstruction at original position and proves that is it reasonable to extent tunnel on one side using indoor model experiment.(3)In this paper,we use finite element analysis to analyze tunnel of V level rock.The double side drift method can prevent surrounding rock subsidence and deformation effectively.Thus during excavation of V level rock,we recommand to use double side drift method.(4)We usew dynamic construction mechanics to analyze the result of selected excavation scheme on V level rock.It turns out that rock subsidence,stress and strain are controllable.The arch and spandrel of tunnel,part of sprayed concrete may have tension failure and shear failure,but the failure is limited and won’t affect stability.Though most of the anchors are in tension,the maximum tension is far less thant tensile value of anchors and the secondary lining only under small tensile and shear stress,making it play the role of security assurance.(5)This paper also summarizes construction process of extension of original tunnel and precausions when dismantling lining,providing reference for similar projects.