Abstract

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 Peer Reviewed Document type: Article

Abstract

Installing utility pipelines generates a significant amount of trench arisings, which are usually transported to landfills instead of being reused as backfill material. This practice generates CO2 emissions and wastes raw materials. This paper presents a more sustainable solution, an eco-trench, which is based on re-using trench arisings as backfill and adding a top layer of expansive concrete to improve the eco-trench’s structural performance. The technical feasibility of the eco-trench was evaluated through a finite element model, which identified the degree of expansion in concrete required to avoid failure or subside the stresses caused by traffic. The potential expansion of concrete was measured under confined conditions in the laboratory by means of a novel test developed for this purpose. The results showed that adding calcium oxide generates the required internal stress. The results were then confirmed in a pilot experience. Las zanjas para instalaciones de servicios generan un elevado volumen de materiales de excavación que son transportados a vertederos en lugar de ser reaprovechados como relleno. Esto conlleva un mayor consumo de materias primas y emisiones de CO2 asociadas al transporte. Este estudio presenta una solución más sostenible, denominada ecozanja, basada en la reutilización de los materiales de excavación como relleno de la zanja con una capa superficial de hormigón expansivo. Su aplicabilidad se evalúa mediante un modelo de elementos finitos que permite determinar el grado de expansión necesario en el hormigón para garantizar la resistencia de las tensiones debidas al tráfico de vehículos sobre la zanja. La expansividad del hormigón se evaluó mediante un ensayo desarrollado específicamente para tal objetivo. Los resultados indican que la adición de óxido de calcio genera las tensiones internas necesarias. Asimismo, la propuesta se validó mediante una experiencia piloto en obra. Document type: Article