Construction Method Analysis Of The Crushed-gneiss-based Three Lane Highway Ttunnel

With the continuous development of modern traffic cause in our country, the number oflarge section highway tunnel is growing; the problems are more and more to tunnelconstruction; the best construction method whose technical progress is of great significancefor tunnel construction, is key factor to ensure safety, optimization and reduce cost.Jiuzhou Tunnel in Lanzhou is three lane highway tunnel in gneiss area. The maximumexcavation span is15.83m and the maximum excavation height is10.57m. This article is todo the further research on the construction methods of Jiuzhou Tunnel engineering.The contents and methods of the research:(1) Based on the data from monitoring the deformation of surrounding rock andsupporting structure of the tunnel, the variation of stress of supporting structure of tunnel wasget by drawing the time history curve of the stress and displacement using thenonlinear fitting method to analyze the law of the Jiu Zhou tunnel engineering.(2) Relying on the Jiu Zhou tunnel in Guizhou province Lanzhou, the mechanical modelwas established by using Midas GTS numerical simulation. In order to verify the science ofnumerical simulation, the calculation results including the settlement of vault, the horizontaldisplacement of the tunnel clearance and the stress, the internal force and deformation ofsurrounding rock and lining are analyzed and compared with the actual monitoring dataduring the process of the construction, which can provide important technical support andtheoretical guarantee for the construction of the tunnel and reliable technical support tooptimize the design parameters of the tunnel.(3) Combined with the actual cost of the different excavation methods, simulating thedifferent excavation methods such as the two-bench five-step excavation method, Thethree-bench seven-step excavation method and CD method, the deformation and stress ofthe surrounding rock and supporting structure under different excavation methods wereanalysed and the excavation method was selected based on the principle of value engineering.The results of this research:(1) The variation rules with the time of gneiss tunnel excavation through three-benchseven-step excavation method was obtained after actual measurement and analysis: seriousasymmetry appeared in the displacement of the key point and pressure of surrounding rock,stress of steel arch shelf, axial force of anchor and the stress of lining, due to the shallowdepth of this section which was strongly affected by the brush slope construction of the leftline.(2) According to comparative analysis of3D simulation, through the up-beach centerdiaphragm excavation method, it was found that, in broken gneiss tunnel, the deformation and the stress of surrounding rock and of support structures could be reduced, that the maximumsubsidence was1.21cm at the arch crown, that the maximum stress of steel arch is-72.6MPaat the right shoulder, that the maximum compressive stress of lining is-12.0MPa at the waistof arch and that the maximum surrounding rock pressure is319.6KPa at the part of largestspan.(3) The costs of tunnel excavation through two-bench five-step excavation method,three-bench seven-step excavation method and up-beach center diaphragm excavation methodare6407.7yuan/m,7821.7yuan/m and9012yuan/m respectively. Tunnel excavationthrough three-bench seven-step excavation method costs1414yuan/m more than that throughtwo-bench five-step excavation method and2604.3less than that through up-beach centerdiaphragm excavation method. Jiuzhou Tunnel,2768m, through two-bench five-stepexcavation method, costs3.9million yuan less than that through three-bench seven-stepexcavation method, and7.41million than that through up-beach center diaphragm excavationmethod.(4) Based on the analysis comparison, up-beach center diaphragm excavation methodcan effectively control the force and deformation of surrounding rock and of supportstructures, while two-bench five-step excavation method can reduce the engineering cost.