Study on Construction Sequence and Key Working Procedures of Cross-Tunnel Groups in Large-Section Subway Stations Using Underground Excavation Methods
To investigate the mechanical behavior of cross-tunnel groups in large-section shallow-buried subway stations during excavation and propose the optimal construction scheme for intersecting air ducts,this paper relies on the Yudaishan Station Tunnel Project of Chongqing Metro Line 4.A three-dimensional numerical simulation model of the cross-tunnel groups in the station is established.The study examines the influence of excavation sequences of two intersecting air ducts with the main tunnel,and the impact of full pilot tunnel excavation versus hanging a 2-meter portal for each section of the air ducts on the structural stability of the tunnel groups.The results show that the tunnel crown settlement increases towards the end of the station.Temporary support structures effectively control tunnel deformation and stress during construction.When the hanging portal method is adopted for each section of Air Duct No.3 compared to full pilot tunnel excavation,the maximum crown settlement can be reduced by approximately 1.3 cm,and the structural safety factor at the haunch increases by up to 22%.Constructing Air Duct No.3 first results in more stable surrounding rock around Air Duct No.6 compared to constructing Air Duct No.6 first,and the plastic zone extension around Air Duct No.3 is also smaller.The two key procedures that cause the largest incremental crown settlement at measuring points and significantly reduce the structural safety factor are the excavation of the two-step benches at the bottom of the station tunnel and the removal of the final temporary support.These are the critical steps in the construction process.
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