Achieving sustainability in tunnelling through innovation

Abstract

“Insanity is doing the same thing over and over again but expecting different results” so the saying goes. With the challenges of delivering ever more infrastructure while reducing the impact of this activity to a sustainable level, it is clear that we need new solutions. Taking the case study of sprayed concrete linings, this paper will examine possible innovations to reduce the environmental impact as well as discussing some of the obstacles. Sprayed concrete linings consist of two of the largest contributors to the embodied carbon of a tunnel - concrete and steel reinforcement. Apart from equipment, improvements come in two forms - either replacement of materials or changes in the design. The substitution of components - for example, by cement replacements, fibres or GFRP rock bolts - only offer limited gains. Adopting new design concepts such as permanent sprayed concrete linings or Composite Shell Linings, incorporating spray applied waterproofing membranes, offers the greatest advances. Like all innovations, these face opposition due to their lack of a proven track-record, the limited data on their performance and an absence of established design codes or production standards. This paper will start by reviewing the state-of-the-art in terms of carbon costing for tunnel projects before going on to illustrate the potential benefits of these innovations as well as highlighting successful projects using them. Both hard rock and soft ground are considered.