Study On Mechanical Effects And Applicability Of Subway Station Excavation Using Primary Support Arch Cover Method In Rock Formation

With the development of economy and society,the scale of cities and population number continue to increase,and the increasing private cars bring traffic congestion,frequent traffic accidents and other issues.The development of the rapid rail transit system with large transport capacity(mainly subway and light rail system)is a fundamental way to solve the problem of urban passenger transport.Station is an important part of the subway,with the construction of subway city increased year by year,the construction of the subway station is facing complex and varied layer.Qingdao is located in the "soft-upper and hard-lower" strata,and the Quaternary surface soil thickness is small,many stations are located in the granite,in view of that soft soil excavation method is too conservative,the builder put forward the primary support arch cover method,but its rock stability,safety margin and so on in the excavation process remain to be studied.For the different surrounding rock grade and thickness of rock formation,according to the methods of numerical simulation,model test and field test,this paper study the mechanical behavior and applicability of the primary support arch cover method,by taking surrounding rock deformation,surrounding rock stress and the supporting internal force as the main research indicators.In this paper,the innovation and results are as follows:(1)The finite element numerical model of the subway station excavated by the primary support arch cover method is established by using COMSOL Multiphysics.According to the different types of surrounding rock(???)and the thickness of overburden(2m,4m,6m,8m),12 kinds of working conditions are divided and calculated,The thickness of ?,?,? grade rock formation is respectively about 2m,slightly less than 4m,slightly less than 6m.(2)The thickness of the overburden under the condition of ?,? and ? grade rock is 3m,5m and 7m.The finite element strength reduction method is used to calculate.The calculation shows that the safety factor under the ?,?,?surrounding rock is 1.6,1.7 and 1.6 respectively.The main damage form is the collapse of the vault.(3)The large-scale geomechanical model test is carried out to simulate the whole process of excavation and support of the primary support arch cover method.The deformation law of the surrounding rock,the internal stress of the surrounding rock and the initial supporting stress evolution are analyzed.The results show that the surrounding rock and the stability of the excavation process can be ensured when the thickness of ? grade rock formation is more than 4m.(4)Haichuan Road Station is excavated with the primary support arch cover method,monitoring surface displacement,cave convergence,reinforcement stress in excavation process.The results show that the surface subsidence,the safety of the initial support,the stability of the surrounding rock meet the national standard and the construction requirements.The primary support arch cover method is applicable in such strata.