Embodied energy evaluation for sections of the UK Channel Tunnel rail link

Using embodied energy as a quantitative measure of environmental impact, this study evaluated the embodied energy of two built sections of the UK Channel Tunnel rail link, now known as High Speed 1, and an alternative design. Results show that contract 220' s 7-15 m diameter twin bored tunnel section of 7-5 km has an embodied energy of 949 TJ, whereas 7-3 km of contract 310' s, consisting mainly of a pile-slab structure, consumed 678 TJ. The alternative design for contract 310, based on a conventional embankment design, would have consumed 640 TJ. By examining the embodied energy content, these geotechnical structures can be categorised into the following two types: (a) structures of which the materials are totally dominant at 90% of the total energy, such as pile-slab; and (b) more direct energy-intensive constructions, where the transportation and installation can collectively account for as much as 40% of the total, such as the tunnel and the embankment. In both types materials are generally the dominating energy consumer: therefore engineers should optimise designs using fewer embodied energy-intensive materials. When compared with the annual UK household energy consumption, the embodied energy values of these structures are equivalent to over 10 000 annual households' consumption. This comparison reveals the large scale of energy involved in geotechnical infrastructure construction, compared to activities in everyday life. This calls for more attention to evaluate the embodied energy of geotechnical constructions as part of design evaluations.