Research Into The Deformation Control Of Shallow Loess Tunnel Undercrossing Railway Station Area

In order to ensure the safe construction of the tunnel and the safe operation of the railway station during the tunnel construction period,the settlement and differential settlement of railway track will strictly be controlled in the project of Xi’an Metro Line Four passing through the National Station Area.However,the geological condition of this field is poor,the underground water level is high,and the buried depth of the tunnel is shallow,so the experience design and construction scheme can not ensure that the track settlement control within the safe range.Therefore,this paper relies on this project,to study the deformation control of shallow-buried loess tunnel undercrossing the railway track or railway turnout area.By combining loess laboratory test technology,automatic monitoring technology and finite difference numerical simulation methods,this paper study the deformation mechanical from the test section first,then discuss surrounding rock reinforcement and tunnel construction optimization technology for the undercrossing section,the main research contents and results are as follows:(1)The relationship between physical and mechanical properties,and water moisture content of saturated soft loess were obtained by laboratory test,then the finite difference numerical model were established by combing the laboratory result and geological survey.The deformation mechanism in shallow buried tunnel was analyzed from three aspects,including which were the depth of tunnel,the stress release rate and the water content of saturated loess,then analyzes the deformation mechanism of tunnel surrounding rock and its influence area,At last,some corresponding technical measures were put forward for this project.(2)Statistics related shallow-buried tunnel construction case to of long pipe-shed,which reinforced tunnel vault,and hole section grouting method,which reinforce the tunnel face and surrounding rock.Numerical model is calculate the deformation control effect of different diameter pipe shed,and the result show that the most suitable is radius 159 mm,the thick 8mm,the best suitable range of pipe roof is 150° above tunnel vault.The variation regularity of surrounding rock reinforcement is obtained through the physical and mechanical performance experimental of soil sample from the full face grouting test section.Then the experimental parameters were introduced into the numerical model,the most reasonable grouting range is calculated as 2m,not the larger the better.(3)After determining the reinforcement scheme of surrounding rock,the three steps and seven construction method,CD method,CRD method and the two side-wall pilot tunnel method were simulated,the results showed that the CRD method were determined the most reasonable method for the tunnel crossing zone.Then study on optimization of CRD method,it is concluded that the smaller step size and larger step distance are favorable to the deformation control.It is suggested that the construction step of 0.5m the construction step 3m should be taken as the construction parameters;50% of the reserved core soil area is reasonable.Then study on the influence of temporary support removal on tunnel deformation,the result show that the method of ‘remove one by every two’ can reduce the deformation and speed up the construction efficiency.(4)Study on the stability and deformation of temporary invert when application of Brukk Robot in tunnel construction.The result showed that the Brokk Robot can be well applied to the tunnel excavation process through the 2d and 3d force calculation.At the same time,the security of the scheme for the opening of the middle wall is demonstrated,which can provide reference for other similar projects.The research methods and results can be applied to deformation control of largesection shallow tunnel in loess area.