Research On Mechanical Properties Of Construction By The Large Span Interval Tunnel In The Rear Wiring Section Of Lanzhou Subway

Rail transit construction in our country has developed rapidly in recent years,the city subway tunnel as a kind of underground shallow buried tunnel,on the premise of without affecting the road traffic,often uses the method of subsurface excavation.For now days,subway tunnel subsurface excavation methods are generally divided into NATM and Shield Method in the domestic and overseas.In the process of subway tunnel excavation with NATM,the surrounding rock stress redistribution,the forms of supporting structure is complicated,the control requirement of the surrounding rock deformation and surface settlement strictly,in consideration of the safety?economy and applicability during the process of the tunnel construction,according to the different formation lithology,it is especially important to choose the correct construction methods and reasonable supporting forms.In this paper,based on the Rear Wiring section tunnel of DongGang station,part of the subway Line One in Lanzhou,using the method of laboratory test,field monitoring and numerical simulation,comparative analysis the application of the double side drift method and CRD method in the shallow buried large span tunnel in loess strata of Lanzhou subway,and get the following main research results:1.Through indoor soil test results of the Rear Wiring section tunnel of DongGang station,part of the subway Line One in Lanzhou,we get the result that the moisture content of the loess is about 27%,the degree of saturation is high,the values of C and ? in vertical and horizontal direction is different,the strength of the loess and the permeability in different directions show the anisotropic characteristics.2.Based on the field monitoring test section of the primary support's surrounding rock pressure and reinforcement stress by the double side drift method,primary support's surrounding rock pressure ranges from 10.6 to 232.6 kPa,the distribution regularity is poor,stress larger parts mainly concentrated in the arch waist,spandrel;the inner and outer steel parts of Grid steel frame are mainly in compression,the maximum stress value is 108.27 MPa,which is located in the outer edge of the steel YGKO+64 section left arch waist,under pressure,meet the design value of compressive strength of steel.3.By using the three-dimensional finite element software,simulate the double side drift method with six excavation and CRD method with four excavation,the surrounding rock arch to arch shoulder waist position deformation are large,method of double side vault settlement is larger,CRD method spandrel settlement is larger,the two kinds of method points caused by tunnel excavation section maximum settlement is 29.6 mm and 42.8 mm respectively,summarizes the double side drift six excavation method to control the surrounding rock deformation and the surface subsidence effect is better than CRD four excavation method.4.In the monitoring section of numerical simulation,the double side drift six excavation method and CRD four excavation method's maximum level of surrounding rock pressure stress were 0.33 MPa,0.31 MPa,the biggest vertical compressive stress were 0.48 MPa,0.52 MPa;both models' primary support is given priority to with compression,tensile area mainly appears in hance and the position of inverted arch to the arch foot,the maximum tensile stress were 0.78 MPa,0.93 MPa,the maximum compressive stress is respectively 9.54 MPa,9.43 MPa,meet the tensile strength and compressive strength of concrete design requirements.5.The Peck formula gauss curve can be better to conform to the actual working condition of fitting analysis of lateral surface subsidence effectively,the maximum surface subsidence range is 36.65 ~ 41.29 mm;Lateral settlement trough width coefficient range is 0.71 ~ 0.81.Using the Boltzmann function can relatively good fitting the surface measuring point's longitudinal settlement of this tunnel.