Study on Support Effect of Large-Section Metro Station Excavated Using Expanded Arch Foot and Bench Method

Aiming at the difficulty in surrounding rock deformation control during the construction of deeply buried mined large-section metro stations, taking a large-section mined metro station on Chongqing Rail Transit Line 18 as the engineering background, this study adopts the expanded arch foot and bench method for station excavation and investigates the surrounding rock support effect during the construction process. A three-dimensional numerical model is established by using Midas GTS NX, and combined working conditions of support structures, including anchor bar, sprayed concrete, temporary support, steel arch and secondary lining, are set up. The control effects of different support schemes on surrounding rock are compared and analyzed from three aspects: displacement field, stress field and plastic zone distribution. Combined with field monitoring data, the rationality of the selected support scheme is verified. The research results show the following: (1) After the expanded arch foot and bench method is determined as the optimal excavation method for the station, the horizontal displacement of the side wall under the original support scheme exceeds the limit and fails to meet the specification requirements. (2) The surrounding rock control effect is positively correlated with the perfection degree of the support system. A single support form presents the weakest capacity in controlling surrounding rock deformation and stress. The addition of anchor bars and temporary supports can gradually improve the support performance. The composite support system of “anchor bar + sprayed concrete + temporary support + steel arch” achieves the optimal control effect, which can constrain arch crown settlement, ground surface settlement and horizontal clearance convergence within the specification limits, significantly reducing stress concentration and the scope of the plastic zone. (3) The deviation between field monitoring and numerical simulation results is less than 15.2%, which verifies the applicability and safety of the composite support system for station construction, adopting the expanded arch foot and bench method. The research findings can provide technical references for the support design and construction of deeply buried mined large-section metro stations under similar geological conditions.