Overview
- HS2 and contractor Align confirmed completion of civil works on the twin-bore Chiltern tunnel and its five ventilation and access shafts, marking the project’s largest tunnelling milestone.
- Two 2,000-tonne tunnel boring machines launched from Maple Cross in 2021 broke through in early 2024 after advancing about 16 metres per day, followed by internal walkways and 40 cross passages.
- Porous 220-metre portal extensions and shafts up to roughly 78 metres deep were installed to manage air pressure and prevent sonic booms at planned operating speeds of 200 mph.
- Excavated spoil has been reused to create around 120 hectares of chalk grassland on the Hertfordshire–Buckinghamshire border, which HS2 says boosts Hertfordshire’s remaining biodiverse grassland by nearly a fifth.
- Despite the milestone, the wider programme still lacks a firm completion date, with CEO Mark Wild leading a reset and a new cost and timetable due this year as ministers review options at Euston.