When mechanically excavating deep-buried large-section metro stations, stringent deformation control requirements for the surrounding rock must be adhered to. Calculations indicate that horizontal convergence in certain areas of the station exceeds acceptable limits, necessitating adjustments to construction parameters to comply with these requirements. This study, based on a project for the Chongqing Metro Line 18, establishes a three-dimensional numerical analysis model for an underground excavation station by utilizing the characteristics of the stratum-structure model. A comprehensive 3D numerical simulation was conducted to evaluate the deformation characteristics of the stratum and surrounding rock resulting from excavation, and to determine optimal excavation parameters based on deformation control. The key findings are as follows: (1) Under the original excavation design parameters, the horizontal convergence displacement at the arch foot met specification requirements and was smaller than that at the sidewall. However, the horizontal convergence displacement at the sidewall exceeded the 20 mm limit specified by the relevant codes, failing to satisfy deformation control standards. (2) The deformation of the surrounding rock increased with factors such as the distance between the excavation face and the initial support, as well as the length of the excavation step. While the spacing between adjacent pilot tunnels had a relatively minor impact on overall station deformation, the number of pilot tunnels, in conjunction with other parameters, proved beneficial for controlling surrounding rock deformation. (3) Among the parameters examined, the distance between the excavation face and the initial support, along with the excavation step length, exerted the greatest influence on deformation. Based on deformation control criteria, the optimal excavation parameters were determined as follows: the distance between the excavation face and the initial support should not exceed 6 m; the excavation step length is set to 1.5 m; the number of pilot tunnels is established at 11; and the spacing between adjacent pilot tunnels is set at 10.5 m. (4) Field monitoring data closely corresponded with the effects observed from implementing the optimized parameters, thus validating the reliability of the optimization scheme. The results of this study provide a valuable reference for the excavation of metro stations under similar conditions in the future.

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.