Simultaneous construction of subways and utility tunnels: A case project in Shenzhen, China

The increasing urban building density has driven the utilisation of underground space for constructing urban municipal infrastructure and transportation systems, alleviating land scarcity. However, the construction of underground projects within densely populated cities poses challenges such as traffic congestion, secondary excavations, and settlement of adjacent building foundations. Accordingly, the simultaneous construction of subways and utility tunnels (SCSUT) has emerged as a practical solution for developing underground spaces in high-density areas. By integrating the constructions of urban rail transit and municipal infrastructure from a long-term perspective, SCSUT could reduce road occupancy and minimize impacts on existing structures. Despite its advantages, SCSUT implementation remains challenging, with few practical cases available. To gain insight into the SCSUT, this study first examines its necessity and global implementation status. Meanwhile, this research identifies the existing implementation strategies of the SCSUT in terms of construction management, pipeline layout, and typical construction schemes. Furthermore, an in-depth analysis of the largest existing SCSUT project is conducted. Findings indicate that the SCSUT, currently in its early development stage, faces several critical challenges, including the lack of technical standards, complex approval processes and management models, inadequate geological surveys and preliminary planning, and frequent design changes. To realize the significant potential benefits of the SCSUT, future efforts should focus on developing technical standards based on relevant engineering cases, enhancing early-stage planning, and leveraging digital technologies to support construction. This study is anticipated to be a valuable reference for policy improvement and other SCSUT projects similar to the case study.