Pioneering Precast Arch Tunnels for High-Speed Rail
The Channel Tunnel Rail Link (CTRL), a 67-mile high-speed rail line connecting London to the Channel Tunnel near Folkestone, has revolutionised travel between London and Paris. Trains now achieve speeds of up to 300 km/h between St. Pancras and Gare du Nord, significantly reducing travel time.
As part of this £5.2 billion project, two cut-and-cover tunnels near Hollingbourne and Sandway were required. Initially designed as in-situ reinforced concrete box structures, a value engineering exercise involving RLE and Geoquest, resulted in an alternative solution using precast concrete arch segments.
This innovative design marked the first use of a Geoquest precast arch over a high-speed rail line. The Hollingbourne tunnel, measuring 360m in length, and the 170m Sandway tunnel feature backfill cover ranging from 0.5m to 5.5m. The slender 325mm-thick arch sections were developed using finite element analysis to ensure material efficiency. Both tunnel portals were constructed using precast concrete headwalls and wingwalls.
Construction was phased to accommodate temporary road diversions, with the first 170m of the Hollingbourne tunnel erected on schedule in just four weeks. This rapid construction process and the efficient use of materials provided a cost-effective and innovative solution for these critical infrastructure elements.
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