Prop-less Tunnel Openings Design for HS2

Overview

The four tunnel boring machines (TBMs) for the 13.5km long HS2 Northolt Tunnels beneath London completed their drives this year at the Greenpark Way Ventilation Shaft, constructing tunnels with internal diameters of 8.10m (Northolt Tunnels East) and 8.80m (Northolt Tunnels West).

In addition to 34 standard cross-passages between the Upline and Downline tunnels there are twelve adits connecting to the shafts, three of which are large diameter openings, one at Victoria Road Ancillary Shaft (VRAS) and two at the South Ruislip Ventilation Shaft (NSR) and the Mandeville Ventilation Shaft (NMA).

The VRAS connection, approximately 70 m², spanned across six tunnel rings. The NSR and NMA connections spanned across five tunnel rings. Their permanent ventilation openings, each with a minimum area of 27 m², required the removal of segments from three adjacent rings.

To minimise impact on tunnel logistics and reduce overall construction time and to improve safety, all tunnel connections were designed to be constructed without conventional temporary works such as propping, temporary steel framing, or installation of SGI rings around openings. Instead, specially developed opening sets using special concrete segment were employed, incorporating corrosion-protected cast-in steel components that ensure highly rigid and durable connections between ring joints. In accordance with the HS2 project requirements, those special segments underwent pre-installation testing under both fire and sustained loading conditions.

This presentation will discuss the design and construction process which involved significant collaboration between the SCS JV and HS2 teams to ensure a safe and compliant design, manufacturing and testing and successful installation of the special segments and openings formation.

Following the lecture, there will be a networking session in the ICE Kendal's bar with food and drink sponsored by Skanska, Costain and STRABAG.

Skanska

an inclusive and responsible business that is helping to build a better society.

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Costain

improving people’s lives by creating connected, sustainable infrastructure that enables people and the planet to thrive.

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STRABAG

offering a wide range of construction services across the industry and the entire construction value chain.

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