Life cycle assessment of carbon emissions for cross-sea tunnel: A case study of Shenzhen-Zhongshan Bridge and Tunnel in China

Due to significant population concentration and capital influx in Guangdong-Hong Kong-Macao Greater Bay Area, the construction of cross-sea tunnels with significant consumption of various resources and materials, has been frequently witnessed. However, there is a lack of knowledge regarding how carbon emissions of cross-sea transportation infrastructure are generated across its life-cycle stages. This study proposes a life cycle assessment (LCA) approach for quantifying the carbon emissions and exploring the carbon reduction potentials with a case study of a world-renowned cross-sea tunnel project in Guangdong-Hong Kong-Macao Greater Bay Area. The results find that this project contributes approximately 849 kilotons CO2eq of carbon emissions with an emission intensity of 1.1 kilotons CO2eq per meter. The materialization stage is the largest contributor of carbon emissions (474.9 kilotons CO2eq), followed by service stage (248.3 kilotons CO2eq, accounting for 29.2 %). Some carbon emissions of raw materials can be offset by using recycled materials. The discarded concrete, block, stone, and sand, occupying over 90 % of the total recycled waste in weight could achieve a 93.5 % of carbon reduction potentially. It provides the opportunity to reveal the engineering details and carbon emission for a world-class super complex cross-sea transportation infrastructure. This study makes one of the first attempts to quantify life-cycle carbon emissions of cross-sea transportation infrastructure, which enriches foundational dataset for environmental impact assessment in this emerging field. The findings of this study can provide scientific references for formulating targeted low-carbon strategies for cross-sea transportation infrastructure across its different life-cycle stages.