Eiffage Kier Ferrovial BAM (EKFB) with Arcadis Setec COWI (ASC) for HS2

1. Background EKFB JV is to design and build the 'Green Tunnels' (GTs) as part of the HS2 Contract C2/C3. The design of the GTs is being carried out by COWI UK Ltd on behalf of ASC JV (Arcadis - Setec - COWI). The GTs are: • Wendover, 1.4km • Greatworth, 2.7km • Chipping Warden, 2.5km The GTs are Precast Concrete (PC) Cut and Cover Structures (including the 'porous' portal structures) that offer significant construction benefits and efficiencies. 2. Innovative form The PC arched structure for the tunnels (and porous portals) consists of five elements – the central wall, side walls and roof elements, as well as wing walls at the end of the porous portals. The cast in-situ invert slab, the structural backfill and the waterproofing complete the structure. The arched roof segments will articulate on bespoke tongue and groove joints ('pin-joints') at the top of the side and central walls. Once the structural cross section has been assembled, structural fill will be placed around the structure, following a carefully-designed sequence of backfilling to avoid out-of-balance loading. The outside double layer of bespoke waterproof membrane will be protected by a geotextile layer. The portals are designed to ensure compliance with HS2 spatial requirements and aerodynamic performance. Emergency doors through the central wall are provided at 350m centres for means of egress into the adjacent bore. The design life of the structure is 120 years. This type of construction is structurally efficient and innovative, and it is the first time that this has been adopted in the UK for high speed rail in relatively high overburden (up to 16m). The invert slab is connected to the sidewall arch and the central wall using reinforcement loops (a 'loop to loop' connection). Full scale physical tests of these connections were carried out to validate the design. The pin joints formed between the pre-cast concrete side wall and pre-cast concrete central wall require full scale fire testing, designed by COWI and carried out for the first time for this type of joint. The structural arrangement has been optimised based on the maximum forces as well as fire considerations (Eureka170). Both sets of the large-scale (Fire and ‘loop to loop’) tests were carried out by CERIB and validated the concept design. 3. Other Considerations Another prime driver for new concept was the need to mitigate the environmental impact, primarily noise and visual impact of the railway and construction traffic. Other environmental considerations are related to construction activities (i.e. reduced material use, off-site manufacturing, storage and assembly areas) and include appropriate mitigation and restoration measures associated with vegetation, trees, natural habitats according to all relevant environmental laws and UK regulations. Specification and procurement of construction materials is streamlined to reduce the impacts on natural resource depletion, energy use and greenhouse gas emissions, by concrete replacement and local sourcing of materials. A key objective throughout the design life of the structure is durability and minimising maintenance requirements. To that end, prefabrication of structural elements and concrete offer improved durability through stringent factory-controlled quality procedures.

This award seeks to showcase a tunnelling concept or proposal that would see underground space used in a creative way to address a specific challenge. The challenge being addressed could be urban densification, energy production and storage, inter or intra-city transport, water supply and distribution or any other infrastructure challenge. The concept or proposal does not need to have secured financial or political support but it should be possible to offer evidence of how the opinion and support of key stakeholders has been sought. The concept or proposal could be entirely unique, a bespoke version of an existing concept or the first use of an previously used concept in a new territory.

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