Study On Optimization Of Excavation And Support Of Double-Arch Tunnel With Three-Layer Lining And Asymmetry

The shallow buried bias double-arch tunnel has problems such as thin cover layer,relatively broken surrounding rock and low hardness,which leads to the self-stabilization ability of the surrounding rock during construction is difficult to be automatically arched,so it is easy to cause surface settlement.Safety poses a major safety hazard and increases the difficulty of construction.Therefore,it is of great significance to optimize the construction scheme of double-arch tunnel under shal ow buried bias.Based on the engineering background of Rongwu Expressway Loess Hill Tunnel,the construction method and process of double-arch tunnel are understood through geological data,site investigation and design data consulting,and the problems in the construct ion process are found out by feedback from the actual construction situation.Through Midas GTS NX geotechnical finite element analysis software,the numerical simulation of shallow-buried and biased Loess Ling tunnel is carried out,and the existing construction scheme is optimized.The main contents and results are as follows:(1)As a shallow-buried double-arch tunnel,the biased mountain has a large influence on the surrounding rock pressure distributio n and horizontal displacement of the Huangtuling tunnel.At the same time,the tunnel middle wall appears locally on the shal ow side of the excavation process stress.(2)Aiming at the problems of complex construction steps,high construction technology requirements and small working space of the construction face in the original scheme of double-sided pilot pit method for left tunnel,the single-sided pilot pit method is adopted to replace the double-sided pilot pit method in the optimization scheme.The numerical simulation proves that the single-sided pilot pit method can effectively reduce the tunnel while solving the above problems.Settlement of surrounding rock and stability of supporting structure are guaranteed.(3)In the construction of unbalanced tunnel,two construction sequence of excavating shallow-buried side caverns and deep-buried side caverns are discussed.This paper simulates two construction sequence,compares and analyses the influence of two construction sequence of surrounding rock pressure and deformation of tunnel.It can be concluded that excavating deep-buried side caverns in advance can prevent the instability of mountain body caused by disturbance of unbalanced pressure mountain body caused by construction of shallow-buried side caverns.The construction of one side of the ca vern has an effect on the middle partition wall,and at the same time,the stress of the middle partition wall can be symmetrically distributed to avoid the influence of eccentric load on the middle partition wal.(4)The spacing of double-arch tunnel is small,and the stress superposition caused by parallel excavation in the same direction results in the displacement and deformation of tunnel sidewall,which affects the stability of tunnel surrounding rock.In the optimization scheme,the reverse construction method of left and right holes is adopted to avoid the stress overlap caused by the parallel excavation of adjacent chambers in the same direction,reduce the deformation of the top area of the middle partition wall,ensure that the compressive stress state of the middle partition wall remains unchanged,and prevent the cracking caused by the eccentric pressure state.