Assessing the carbon cost of utility installation via multi-utility tunnels (MUTs)

Progressive urbanization and the concomitant requirement to develop new cities fuels the need for more sub-surface utility infrastructure. Conventional methods of utility placement, i.e. open-cut trenching techniques, are expensive in terms of their many social, environmental, and indirect economic costs. This necessitates consideration of alternative construction methods such as Multi-Utility Tunnels (MUTs). However, a lack of quantification of their short-term and long-term costs and impacts (i.e. a comprehensive understanding of all the consequences of moving to MUTs) inhibits uptake. Carbon accounting, a globally important consideration, is increasingly adopted within the construction industry and could be used as a convincing argument for why alternatives such as MUTs might be a preferred method of utility placement in cities that are advancing global sustainability agendas. This paper compares carbon cost estimations of open-cut excavations with flush-fitting MUTs. The results show that although flush-fitting MUTs have much greater carbon footprints in the short-term compared to open-cut installation methods, they would save a considerable amount of carbon in the long-term (over their lifetime) by eliminating the need for numerous excavation and reinstatement (E&R) procedures, which are inevitable for repair and maintenance of buried utility services. The research reveals the tipping points in favour of flush-fitting MUTs, in terms of carbon saved, when repetitive E&R works are eradicated, to support their adoption.