Review of carbon footprint in materialization stage of tunneling projects

The transportation industry is China's third-largest source of carbon emissions, with tunnel engineering representing one of its primary contributors. Consequently, achieving carbon reduction in this sector faces serve challenges. In recent years, extensive research has been conducted worldwide on the carbon footprint of tunnel engineering. This study focuses on the materialization stage of tunnel projects—including material production, material transportation, and on-site construction. The paper reviews carbon emission calculation methods and data sources across these stages, summarizes representative inventory analysis results, and explores the application of machine learning techniques in carbon emission prediction. The results indicate that carbon emissions from tunnel engineering are mainly concentrated in the material production stage, followed by on-site construction, while the material transportation stage contributes the least. Under similar construction conditions, the carbon emission intensity of drill-and-blast tunnels is approximately twice that of shield tunnels. Finally, the study identifies key challenges in current research on the embodied carbon footprint of tunnel engineering and proposes directions for future work.