Sustainable utility placement via Multi-Utility Tunnels

Abstract Due to the adoption of short-term planning cycles and the requirement for lowest initial construction costs, the conventional method for utility installation and maintenance in the UK is via open-cut. When taking a long-term sustainability perspective there is a growing body of evidence which indicates that this method is socially disruptive, environmentally damaging and significantly more expensive, i.e. unsustainable. One long-term solution to this problem could be the adoption of Multi-Utility Tunnels (MUTs); a tunnel that co-locates more than one utility underground facilitating their subsequent repair and renewal while eliminating the need for continuous surface excavation. Unfortunately considerably higher short-term direct costs remain a significant barrier to adoption of MUTs. However, there is a lack of research to show where the economic tipping point between the two methods occurs and how it might be influenced by utility type, pipe number (i.e. density), pipe diameter, number of excavation and reinstatement (E&R) procedures avoided, location (i.e. undeveloped, suburban and urban areas), and the choice of MUT being adopted (i.e. flush-fitting, shallow and deep). This paper aims to fulfil this research need by investigating the effect of these influences on the economic viability of various types of MUTs. The results indicate that MUTs can provide a more economically sustainable method of utility placement in all three local contexts, with the tipping points occurring where street works are likely more frequent and/or where utility density is high.