Comprehensive life cycle assessment of pipeline trenches beneath trafficable roadways backfilled with recycled aggregates

With rapid urban development, an increasing proportion of underground infrastructure continues to be installed beneath pavements of trafficable areas, requiring materials with sufficient bearing capacity for backfilling deep excavated trenches. To address the growing scarcity of natural aggregates and the overuse of landfills, this study explores the potential of recycled aggregates for sustainable trench backfilling through a comparative life cycle assessment (LCA) against conventional methods, based on data obtained from real-life full-scale trench constructions. The study assesses three trench types: the control trench (CT) with natural crushed rock, the recycled unbound trench (RUT) with a blended mix of recycled materials in unbound form, and the recycled cemented trench (RCT) with similar recycled materials bound with cement. The LCA revealed that the RUT achieved a 71 % reduction in greenhouse gas emissions compared to the CT, while also reducing acidification, particulate matter formation, and marine ecotoxicity by around 50 %. Scenario analyses show that adopting green cement (e.g., fly ash) and electrifying construction processes further reduce emissions by up to 36 % and 32 %, respectively. Emission volatility for CT was high, with a standard deviation of 80.43 kg CO 2 -eq in transport emissions, emphasising the stability benefits of recycled alternatives. RUT also aligned strongly with sustainable development goals (SDGs), notably contributing to climate action (SDG 13.2) and air pollution reduction (SDG 3.9). These findings reinforce the combined impact of material circularity, energy decarbonisation and sustainable construction practices in enhancing the environmental performance of deep sewer trench backfilling in trafficable areas. • Backfilling of deep pipeline trenches in trafficable areas using recycled aggregates. • Recycled unbound trench (RUT) reduced GHG emissions by 71 % compared to control trench (CT). • Green cement and electrification reduced emissions by up to 36 % and 32 %, respectively. • Transport emissions for CT showed higher volatility than the stable RUT values. • RUT strongly supports key SDGs, and green electricity further enhances performance.