Narrow trenches are a common technique for the installation of utility pipelines of small diameter. Theexcavated soil is not always appropriate as landfill and, in those cases, an appropriate soil from some-where else (ex. a borrow pit or another construction site) should be used instead (classical solution, CS).Another common solution is to use a controlled low-strength (cementitious) material (CLSM) as backfillinstead of compacted soil. However, both solutions lead to increased raw material consumption, wastegeneration, need for transportation, and CO2emissions. In an attempt to address these issues, researchersdeveloped an eco-trench (ECO) that reuses the excavated soil of narrow trenches to produce a controlledlow-strength material to be used as landfill. Although technically viable, the sustainability of this solutionversus the traditional solution has not been properly addressed. Hence, this paper aims to develop amethod for the sustainability assessment of trenches. The Sustainability Index of Trenches (SIT), based onthe MIVES decision-making method, enables the assessment and prioritisation of different types oftrenches according to sustainability criteria. Criteria, indicators, weights and value functions were spe-cifically defined based on seminars with experts in thefield of utility services and construction. A casestudy was performed in which four types of trenches (CS, CS with recycling CSþR, CLSM and ECO) wereassessed and prioritised according to SIT. ECO resulted in the most sustainable alternative with a SIT of0.80 out of 1 followed by CSþR, CS and CLSM with SITs of 0.63, 0.40 and 0.38 respectively. The sensitivityanalysis showed consistent results in different scenarios. Thesefindings demonstrate the capability andreliability of SIT as a decision-making tool for the evaluation of the sustainability of different constructionprocesses for trenches and the prioritisation of the most suitable solution for different situations

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