GHG emission efficiency of prefabricated composite subway stations: A novel case study of Shenzhen, China

Rapid urbanization has spurred large-scale subway construction and led to the emergence of the prefabricated composite subway station (PCSSs), a novel station paradigm that integrates cast-in-situ (CIS) and prefabrication techniques, with significantly different greenhouse gas (GHG) emission boundaries than traditional stations. However, GHG emissions from PCSSs remain unclear. Under the current concept of sustainable construction, understanding the main GHG emission characteristics is essential to optimize the design and construction mode of PCSSs and facilitate their initial development. In this regard, this study innovatively takes the PCSS in Shenzhen Urban Rail Transit Phase 5 as a case study to analyze the PCSS's GHG emission efficiency from cradle-to-end of construction, and explore the key factors affecting GHG emissions. The results indicate that PCSSs reduce GHG emissions by 2.98 %–4.91% compared to traditional CIS stations, and interestingly, the PCSS's GHG emissions increase with the increase of prefabrication rate, which is primarily due to the nature of prefabricated composite technology. The GHG emissions in the production stage, transportation stage and construction stage accounted for 67.38%, 3.16% and 29.46%, respectively, among which the GHG emissions in the PCSS transportation stage are 3.04% higher than those in CIS stations. From a sub-project perspective, the enclosure structure (54.67%) and main structure (43.67%) are the main contributors to GHG emissions. Using formworks more than 40 times is effective for low-emission prefabricated composite construction. This study provides a systematic method for calculating GHG emissions of the novel PCSS model and offers industry practitioners scientific numerical analyses to enhance the PCSS's environmental benefits.