Life cycle assessment, GHG emissions, Subway tunnel, Key sources, Environmental impact, Engineering geology. Rock mechanics. Soil mechanics. Underground construction, TA703-712

This study evaluates the greenhouse gas (GHG) emissions associated with the construction of subway tunnels, aiming to identify the primary sources of emissions and provide insights into emission reduction strategies. Using the civil engineering construction of specific tunnels of a subway line in Guangdong Province, China, as a case study, this research quantitatively analyzes the composition of GHG emissions across three stages: upstream building materials production, building materials transportation, and on-site construction. The results indicate that upstream building materials production and on-site construction collectively account for over 95% of the total GHG emissions during tunnel construction. The analysis further reveals that a small proportion of building materials and construction machinery accounts for the majority of total GHG emissions during tunnel construction, aligning with the Pareto principle. The findings emphasize the importance of accurate evaluation of high-impact building materials and construction machinery, particularly in contexts where basic energy consumption data are limited. Strategies such as utilizing recycled materials and enhancing machinery efficiency can lead to significant emission reductions. For instance, achieving a recycling rate of 10% to 30% for steel and concrete can reduce total GHG emissions from tunnel construction by 5.51% to 9.94%, while improving machinery efficiency by 10% to 30% can reduce emissions by up to 2.29%. These findings provide a scientific basis for low-carbon subway tunnel construction.