Research On The Construction Deformation And Control Technology Of The Shallow-buried Loess Tunnel Under Unsymmetrical Pressure

According to the Liutiaoshan tunnel in newly built connecting line of Datong to Jungar railway and Shuozhou to Huanghua railway which is located in collapsible loess area, deformation characteristics and excavation method have been researched, and numerical simulation of the Liutiaoshan tunnel has been established, then the key technology and construction craft of this tunnel has been summarized, and Construction monitoring and deformation analysis have also been conducted in this paper, which all mainly focus on the construction deformation and control technology of the shallow-buried loess tunnel under unsymmetrical pressure. Depend on the analysis above, the main research results of this paper are as follows:(1) The shallow-buried loess tunnel under unsymmetrical pressure has great Construction deformation and fast deformation release, which can be effected by construction method and supporting measures, apart from physical property of the loess itself, surrounding rock classification and Tunnel depth.(2) According to the numerical simulation of Liutiaoshan tunnel construction, analysis on three construction methods shows performed core-soil sidesteps make the haunch under unsymmetrical pressure, and also raise the arch bottom. Comprehensive method leads to a complex deformation curve, and the deformation of monitoring point will change abruptly to some extent when temporary inverts are removed, and the greatest deformation changes happen in haunch. Center cross-diagram(CRD) method is superior to the other two methods in deformation control of shallow-buried loess tunnel under unsymmetrical pressure.(3) According to the further analysis on comprehensive method, dig overlying soil layer thicker side than dig the thinner side, arch waist position to the thinner side offset2mm and bias effect more obvious; under the condition of large footage vertical settlement value doubles, invert elevation is very obvious. Construction should be mainly from the control level deformation angle to determine the sequence of excavation of soil, from point of view of the control of the vertical deformation to select reasonable footage.(4)According to analysis on field monitoring data of typical section DK95+200, ground surface settlement lasts rising in the whole excavation process, till the supporting construction completes and the chamber becomes a closed stable structure.Vault settlement value early rapid growth, the sinking rate curve in excavation process fluctuation with jump, but with the tunnel face gradually away from monitoring sections then tends to be stable; the clearance convergence value at the beginning of the floating range is bigger and spandrel than arch waist. According to the engineering need to encrypt specific phase and position point or increase the frequency of monitoring.