Research On Key Construction Technology Of Large Span Suubway Station With Arch-Cover Method Under Complex Condition

With the continuous development of urbanization,the intensive flow of people and increasingly congested traffic have become a prominent problem that restricts the urban development.Subway is widely built in more and more cities for its safety,rapidity,punctuality and strong carrying capacity,which greatly relieves the pressure on the urban transportation system.As an important part of subway engineering,the design and construction of subway stations are limited by many factors such as geological conditions and surrounding environment.Dalian is located in the coastal area with developed groundwater,and at the same time the geological conditions show obvious characteristics of upper soft and lower hard,Dalian subway introduced mature construction methods in soft soil areas in the early construction of underground excavation station,which caused many problems in the practical construction process.Complicated transforms in working sequences and a lot of blast measures resulted in prolonged construction period,and the self-stability of rock mass was not fully utilized,thus there was a large safety margin of surrounding rock.Engineering technicians put forward a new construction method-arch cover method on the basis of traditional construction method and the special geological conditions.As a new construction technology,arch cover method is still in the stage of continuous development.Based on the Shikuilu station under construction in Dalian Metro Line 5,this thesis studies the settlement and stress deformation law,supporting opportunity of pilot tunnel,and stability under the condition of blasting and fluid-solid coupling according to the characteristics of large span,hard rock and rich water.The main research work are as follows:(1)According to the three-dimensional finite difference numerical calculation model of Shikui Road Station,the settlement deformation and stress change during the whole construction process are analyzed,and the corresponding preventive and control measures are proposed.At the same time,the main construction parameters are optimized and analyzed,which can provide a reference for the construction decision.(2)Based on the convergence confinement principle and zone state index,a method for determining supporting opportunity is built.Taking the construction of small pilot tunnel as an example,supporting opportunity is analyzed,and the influence of overlay strata thickness on supporting opportunity is compared.Finally,the distance between tunnel face and the support is determined.This method can be used to guide the timing of initial support and the construction footage during the construction of the main pilot tunnel of arch cover method.(3)According to the actual blasting parameters,equivalent load of blasting is calculated and the load is applied through the triangular impact load time-history function.The function is loading in FLAC3D by using FISH function.Combined with numerical calculation results and blasting monitoring data,the influence of,blasting on existing tunnels,underground pipelines and surrounding rock during the main pilot tunnel construction stage,and the influence of blasting on secondary lining structure are analyzed too.At the same time,the safe blasting footage is determined according to the calculation results and the specification requirements.(4)The distribution of pore pressure and seepage field under the condition of fluid-solid coupling is analyzed in the construction process of arch cover method,and the areas where seepage is concentrated are pointed out.The deformation of the supporting structure is compared under the conditions of fluid-solid coupling,static calculation and measured deformation.The deformation of the supporting structure with and without seepage and the measured maximum value are compared.At the same time,the internal force of supporting structure is analyzed.In addition,the influence of blasting on the permeability of surrounding rock is also an alyzed.The results provide a basis for the applicability of arch cover method under water-rich conditions.This thesis reveals the general rules of deformation,stress,seepage characteristics and blasting response in the construction process of arch cover method under complex conditions,puts forward targeted advice and control measures,enriches the theoretical basis for the design and construction of arch cover method,and can provide reference for the.construction of underground excavation stations in water-rich and hard rock strata.