Study On Construction Methods In Large-Span Loess Tunnel

With the rapid development of transportation demands as well as the long and largetunnels constructed both at home and abroad，bell-mouthed road tunnels with large–spanappear one after another in the urban transportation.As the relatively low strength of loess，large soan loess tunnel with large deformation after the excavation. Together with large spanloess tunnel’soeciaty of span large and flat shape, construction of the difficulty is self-evident.In this paper, combined the Dunliang tunnel, Seven-step three-stage methods and bothdiagram methods of the large span loess tunnel are studied by theories analysis，andnumericalsimulation.The main researh is as follows:1.Five kinds of large span loess of seven-step three-stage method、ring cut method、bothdiagram method、cross diagram method and center diagram method commonly used in tunnelconstruction method for analysis and comparison, the respective advantages anddisadvantages and the applicable conditions.2.Seven-step three-stage method have obvious advantages, can be used in theconstruction of DunLiang highway tunnels, construction efficiency, high speed, low cost, bothdiagram method can effectively control the settlement, but its large construction difficulty,long period, high cost.3.Through andnumerical simulation shows: The arch dome subsidence should be paidattention mostly in course of tunneling portal constructing; the use of both diagram method tocontrol the arch dome subsidence well under the same conditions, while the three-stepseven-step method is larger.This study gives an effective guidance of the construction of DunLiang highway tunnels,and can provide a reference for future similar projects.