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The Chiltern Tunnel South Portal Headwall has been designed to provide a subvertical face for the launch of the TBMs, having an approximate retained height of 20m. The face was designed to have an angle of 70 degrees above the tunnel crown, through 6 m of structureless chalk and drift deposits, and 80 degrees below the tunnel crown a further height of 14m. The subvertical face is essential to enable the beginning of the bore. The South Portal structure is part of the wider South Cutting works, and interfaces with the Chiltern Tunnel at the headwall location. The tunnel portal extends South Ea...

 This video was first broadcast at NCE’s Tunnelling Festival conference 2020. In this session, Atkins principal engineer, ground engineering & tunnelling practice Luke Marriott and Atkins technical director, Ground Engineering & Tunnelling Practice Christopher Chew discuss the challenges on the Humber Feeder 9 Gas Pipeline project. The pair discuss how they overcame tidal affects to successfully replace a strategic pipeline to the National Transmission System. Gain an insight into how the project tunnelled and installed a new pipeline through the bedrock underneath the estuary.