Research on the Prefabricated Design Method for Small and Medium Cross-Section Utility Tunnels Based on Keyway–Bolt Connection

Prefabricated utility tunnels combine factory production with on-site assembly to reduce on-site wet work and improve component quality and construction efficiency. Standardized design workflows and segment layouts coordinated with production, transport, and lifting conditions are essential for the practical application of integral precasting. To address insufficient coordination among cross-sectional dimensions, longitudinal segmentation, and assembly interfaces in utility tunnels with small and medium cross-sections, this study proposes a design method combining integral cross-sectional precasting with longitudinal segmentation. The workflow integrates cross-section definition, route segmentation, interface standardization, and feasibility checks. A keyway–bolt connection and composite joint waterproofing scheme are also proposed. Four drainage box-culvert types at Changsha Airport are used to illustrate the proposed design workflow. For a selected 50 m reach of the single-cell Type A culvert, the estimated cumulative on-site stage duration for the proposed precast scheme was 82.1% lower than the recorded cast-in-place total when curing-related waiting was included. The comparison assumes sequential on-site operations and excludes factory production and transport. The method coordinates component standardization with route adaptation and demonstrates potential to simplify on-site operations, providing a reference for the prefabricated design of utility tunnels with small and medium cross-sections and similar underground box structures.