Comparative Assessment of Embodied Carbon in Cantilever Concrete Retaining Walls and Sheet Pile Walls

Retaining walls store significant amounts of embodied carbon, yet this aspect is often overlooked due to high material requirements. Although awareness regarding carbon assessment in the built environment sector is growing, comparative studies across different retaining wall systems remain scarce. This study presents a comparative analysis of embodied carbon—within the cradle-to-site scope (Modules A1-A5, BS EN 15978:2011)-for Cantilever Concrete Retaining Walls (CCRW) and Concrete Sheet Piles (CSP), ranging from 1 to 4 m in height. Unlike previous studies that focused on a single system or specific life-cycle stage, this research quantifies emissions arising from material production, transportation, and on-site construction activities. The results indicate that total embodied carbon increases with wall height for both systems. However, CSP consistently generates higher emissions-ranging from 20%-30% higher at lower heights to nearly 90% higher at a height of 4 meters—primarily due to production emissions and a heavier transportation burden. A proportional analysis reveals that material production (A1–A3) accounts for over 85% of total emissions in both systems, whereas transportation (A4) represents a significant additional burden for CSP. This study also identifies emission hotspots and opportunities for carbon reduction for each system. The findings highlight the importance of incorporating embodied carbon considerations into the early design stages and emphasise the need for material optimisation for CCRW and supply chain optimisation for CSP to achieve retaining wall solutions with lower carbon footprints.