Probabilistic carbon assessment of slurry shield tunneling: A hybrid life cycle analysis (H-LCA) integrating uncertainty quantification

Accurately quantifying the carbon footprint of slurry shield tunnels requires overcoming system boundary truncation and data uncertainty. This study adapts and integrates a hybrid life cycle analysis (H-LCA) model with probabilistic uncertainty analysis, utilizing a modularized accounting unit to address system boundary truncation and data uncertainty. The approach expands system boundaries by Process-Based (P-LCA) and Input-Output Analysis (I–O LCA), while quantifying uncertainties via Data Quality Indicators (DQI), triangular distributions, and Monte Carlo simulation. Applying the H-LCA framework to a slurry shield tunnel case shows that material production is the dominant emission source (approximately 94%), characterized by high stability (Coefficient of Variation, CV = 5.8%) compared to construction-phase volatility. Furthermore, scenario analysis demonstrates a significant, probabilistically quantified emission reduction potential through the use of recycled materials. The framework provides a robust foundation for carbon accounting and risk-informed decision-making in sustainable transport infrastructure development.