HS2’s giant tunnelling machine Mary Ann broke through on Friday 9 May, marking the end of her mission to excavate the first bore of what will soon become the longest railway tunnel in the West Midlands.
The 125-metre-long machine began constructing the 3.5-mile (5.8km) Bromford Tunnel, which starts at the Warwickshire village of Water Orton and extends to the northeast Birmingham suburb of Washwood Heath, in July 2023. The TBM was named Mary Ann, by the local community, in a nod to the Warwickshire-born writer better known by her pen name George Eliot.
The tunnel breakthrough – HS2’s first in Birmingham – is a significant milestone for the project, which will almost halve journey times between Britain’s two largest cities, whilst freeing up valuable track space on the heavily congested West Coast Main Line for more local, regional and freight services.
During the 22-month-long mission, the team on board the 1,600-tonne machine worked at depths of up to 40 metres. They skilfully navigated Mary Ann under the Park Hall Nature Reserve, the M6 motorway, and the meandering River Tame – which they crossed four times, with a headspace as low as five metres. A 450-strong team supported the civil engineering feat.
“Today’s breakthrough is a significant milestone for the project and I’m immensely proud of the men and women who have worked day and night to bring Mary Ann and her crew home safely,” said Mark Wild, HS2 Ltd’s chief executive.
“Washwood Heath is set to become one of the most important sites on the entire HS2 network – the point at which the railway will be operated, controlled and maintained using the very latest digital technology.
“HS2’s construction is transforming the West Midlands, and the £10bn investment boost it is already driving across the region will multiply in the years ahead.”
Mary Ann excavated around one million tonnes of spoil during the tunnel drive. In line with HS2’s sustainability policy, the excavated earth is being reused to support construction of the nearby Delta Junction, a complex network of 13 viaducts that will enable high speed trains to travel between London, Interchange Station in Solihull and Birmingham Curzon Street Station.
At peak production, the TBM advanced at around 30 metres per day. The crew worked in tandem to navigate the giant boring machine, ensuring the cutterhead sliced through the earth, while simultaneously reinforcing the excavated tunnel with concrete segments – each weighing up to seven tonnes.
The precision-designed segments were manufactured at Balfour Beatty VINCI’s pre-cast factory at Avonmouth near Bristol. The TBM lined the tunnel walls with 20,797 individual segments, making 2,971 concrete rings to form the tunnel.
Jules Arlaud, Balfour Beatty VINCI’s tunnelling director said: “This achievement follows years of design, planning and preparation from BBV, in close collaboration with HS2 and our partners. The team will now move onto the next phase of work inside and outside of the tunnel, while our second TBM, Elizabeth, continues to make great progress on the second drive.”
Image credit: HS2
