Study On The Interface Scheme Between The Main Body Of Subway Station And Air Duct By Arch-cover Method

Different from the subway underground excavation method often used in general soft soil areas,the underground excavation and arch cover method has been developed for Dalian,Qingdao and Guizhou and other "upper soft and lower hard" soil layers.However,this method has not been used for a long time,and the interface between the main body of the station and the auxiliary structures such as the air duct is complex and difficult to construct.Choosing a reasonable interface scheme can ensure the quality and safety of the construction.At present,the optimal design and method of the interface of the underground excavation station with the dome-cover method have not been studied and verified the best.In this paper,combined with a subway station project of Qingdao,the MIDAS GTS NX finite element analysis software is used to simulate the construction process of the air duct transferring into the main body of the station.By analyzing and summarizing the engineering background and geological overview of the subway station,it is determined that the main project is constructed using the arch-cover method.Combined with the monitoring data at the construction site,the measured data and the numerical simulation results of the air duct depression halfsection interface scheme are compared to prove the effectiveness of the numerical simulation of the other schemes.The key technical indicators such as surface displacement and structural stress of each scheme are analyzed,and the following main conclusions are obtained:(1)Analyze the surface displacement changes of different sections after the construction.The air duct depression scheme is better than the air duct elevation scheme.In the air duct depression scheme,the full-section interface scheme is slightly better than the half-section interface scheme.(2)The construction of the main arch of the station and the construction of the central part of the main body,due to the large excavation span and the large number of sub-excavations,will change the displacement greatly in these two stages.In the actual construction,the displacement monitoring should be strengthened and the support should be done in time.(3)In the excavation stage of the air duct arch,the air duct depression half-section interface scheme has the best stress control effect on the surrounding rock face,while the air duct elevation scheme is poor.The stress control effect of the air duct elevation scheme on the primary support structure is better than that of the air duct depression scheme in the construction stage of the secondary lining of the main arch and the completion stage of the overall construction.(4)Analysis of the stress value of the typical section support structure shows that the overall stress control effect of the support structure of the tunnel-intake scheme of the air duct elevated interface is better than that of the tunnel-intake scheme of the air duct depression interface.In the air duct elevation scheme,the air duct elevation halfsection interface scheme is slightly better than the air duct elevation full-section interface scheme.(5)Combined analysis of simulated data and field monitoring data,there is little difference between the two,and the data both meet or are much smaller than the standard construction requirements,indicating that the arch capping method has better applicability in the "upper soft and lower hard" stratum.The comprehensive analysis shows that for the special stratum of "soft on the top and hard on the bottom",the construction of the station project is suitable for the arch cover method.When ancillary structures such as air ducts are transferred to the main structure of the station,priority can be given to the plan of lowering the full-section interface through the air duct.This has certain guiding value for the subway engineering construction in Qingdao,Dalian and other places.