Study On Construction Dynamic And Secondary Lining Optimization Of Twin Tunnel With Small Spacing In Loess Region

The paper took metro line four 'four road station to Datang Furong Garden Station interval parking line of large section and small spacing tunnel as the research object,and the numerical simulation and field monitoring method were used to study the Construction process,construction parameters and deformation regularity by considering the construction processes of shallow-buried twin tunnels with small spacing in loess area,On the basis of this,the thickness of the secondary lining is optimized.The research results of this paper provide scientific basis and technical guidance for the construction of small clear distance tunnel of Xi'an Metro Line four.The main work and achievements of this paper were as follows:(1)The excavation of the tunnel : Paper was based on the actual engineering background,select the appropriate calculation parameters,through the finite element software to analyze the three kinds of large section tunnel excavation method,By comparing the displacement of the soil and the stress analysis of the supporting structure,the optimum construction method is obtained.(2)The optimization of construction parameters: According to the theoretical research and experience selecting the reasonable spacing between large and small section tunnel face.Three dimensional numerical simulation analysis of tunnel construction process with different spacing is carried out.Compared the surface subsidence,supporting structure deformation and stress and distribution of plastic zone,get the face spacing between the 3 times of the diameter of the tunnel when appropriate.It is the displacement tendency of the maximum surface settlement and supporting structure(3)Stress and deformation law of tunnel: According to the optimization results of the paper,the stress and deformation law of the soil and support structure in the whole process of tunnel excavation are summarized and analyzed by numerical simulation,The deformation and force characteristics of the loess tunnel were obtained in the excavation process.In this paper,the reliability of numerical simulation results are verified by comparing with the monitoring data,and the theoretical guidance is provided for the construction of the next tunnel.(4)Secondary lining optimization :Based on the related content of tunnel design,the force of two lining structures with different thickness is solved by the finite element software.The internal force distribution and deformation of the lining structure of large section tunnel are obtained.The variation law of the stress of the large section lining structure with the thickness is studied,and the most unfavorable position of the stress in the lining structure is obtained at the arch of the arch.Based on the stress situation of different thickness lining structures,the safety coefficient and reinforcement quantity of different thickness lining structures were calculated by reference.According to the calculation results,a mathematical model is established to target the cost of the project.The cost of lining structure with different thickness is calculated by means of solving the objective function with the strength and reinforcement ratio as the constraint conditions,and when the concrete thickness of the constraint is 60 cm,the construction cost is lowest.