Accounting Method and Indicators of Multilevel CO2 Emissions Based on Cost During Construction of Shield Tunnels

With the rapid expansion of shield tunnel projects in China, precise accounting of CO2 emissions throughout the entire process is essential for advancing green and low-carbon construction practices. This paper introduces an innovative CO2 accounting methodology utilizing a cost-based carbon emission coding system. It adopts a multilevel approach to carbon emission accounting, aligned with this coding system, which facilitates a detailed examination of carbon emission ratios and characteristics across various construction techniques. The analysis includes six typical shield tunnel projects varying in diameter, focusing on sub-projects to scrutinize CO2 emissions and establish specific indicators. The findings indicate that CO2 emissions per 10,000 yuan of investment, approximately 30.25% (or 3025 kgCO2e/10,000 yuan), are more consistent than those per unit of length. Moreover, the study highlights differing CO2 emission trends among sub-projects compared to whole tunnel projects, assessing emission indicators and distribution patterns in four sub-projects: shield excavation, segmental lining, internal structure, and tunnel reinforcement. From these findings, the paper suggests more precise and tailored strategies for CO2 reduction. This research provides a theoretical basis for future construction planning and carbon management strategies.