Study on the Safety Degree Index and Stability Control of Joint Surrounding Rock of Large-Span Metro Station Constructed by Arch Cover Method

The arch cover method constitutes a novel construction technique recently employed in subway station development. Nevertheless, the specific geological compatibility of this approach within environments characterized by jointed rock formations remains an ambiguous and understudied area. In response to this issue, taking into account the impact of joint, a local zone safety index (ZSIsu) evaluation method based on the ubiquitous joint model was established to reflect the safety state of the local rock mass around the station after excavation. Combined with the actual project, the construction techniques and support schemes were expounded. Based on various indicators of safe construction, the potential failure mechanism were analyzed. To broaden the application scope of the method, corresponding measures were developed and validated through practical engineering applications. The arch adopts double-layer superimposed primary support and pilot tunnels adopt advanced small pipe grouting, which effectively controls the deformation of the rock mass and provides reliable initial support. The combination structure of crown beam + bolt + steel pipe pile at the arch foot significantly enhances the bearing capacity of the surrounding rock. The side wall using anchor + steel pipe pile effectively prevents the sliding failure of the rock mass of the side wall. This study broadens the application scope of the method, demonstrating its suitability even for local geological conditions with poor rock mass.