Environmental and economic impacts of combining backfill materials for novel circular narrow trenches

Over the last few years, several policies and new technological solutions have targeted the construction sector with the aim of reducing the sector's impacts on the environment. Among the different technological advances proposed, the reuse of materials in construction has been reported as a promising solution for an increase in sustainability and circularity. In particular, a type of cities' undergrounds assets for which materials' reuse is being explored are trenches for protecting services (i.e., water and gas transport pipelines, and optic fibre and other telecommunications services). Nonetheless, the economic and environmental benefits and impact of this type of system is still insufficiently quantified. In this research study, the economic and environmental impacts of four scenarios of trenches were assessed by using Life Cycle Costing (LCC) and Life Cycle Assessment (LCA). The four alternatives analysed consisted of: (1) the classical solution; (2) the classical solution with the reuse of soil; (3) the control low-strength material, and (4) the eco-trench. The results allowed concluding that in the eco-trench system, for which all material is reused, the environmental and economic impacts could be reduced by more than 80% and 50%, respectively. A parametric study for which the dimensions of the trenches were varied, permitted to reinforce these results and to quantify the impact's change along with the width and depth of the trench. Overall, this study provides a comprehensive view of the high-impact potential of reusing material for the construction of trenches in cities. The outcomes allow also remarking that the eco-trench system could be an attractive and advantageous solution for urban infrastructure stakeholders, both from an economic and environmental perspective.