First Midlands tunnelling machine launched
TBM’s journey marks ‘another major milestone’ for HS2 construction work.
TUNNEL boring machine Dorothy began its mile-long journey under Long Itchington Wood in Warwickshire at the beginning of December, making it the first TBM to be launched on the Midlands section of HS2.
As reported in The RM’s
December issue, the 2000 tonne machine, which is 125 metres long, is named after Dorothy Hodgkin, the first British woman to win the Nobel Prize in Chemistry. It was set in motion by HS2 chief executive Mark Thurston.
The construction and assembly of the TBM involved around 170 engineers and it will be staffed around the clock by members of the tunnelling team for around five months until it completes the excavation of the first bore. After breaking through, expected in spring, Dorothy
will be disassembled and taken back to the north end of the tunnel to begin the process of creating the second bore, due for completion in early 2023.
It will be the first tunnel on the project to be finished, requiring the extraction of 250,000 cubic metres of mudstone and soil. Once removed and separated at the on-site slurry treatment plant, it is destined for reuse in embankments and landscaping along the route.
Green tunnels
Tunnelling under Long Itchington Wood – a site of special scientific interest with ecosystems that have developed over hundreds of years – is intended to preserve the area and manage the environmental impact upon it.
The final section of the southern end will be what’s known as a ‘green’ or ‘cut and cover’ tunnel, where a cutting is excavated and an earth roof created, to minimise its visual impact on the natural landscape.
Three prefabricated green tunnels are also being produced for other parts of the HS2 route by Stanton Precast Ltd at its new plant in Ilkeston, Derbyshire. Stretching a total of four miles, they will be made up of thousands of sections that will be assembled on-site by engineering company Matière. Work on piecing the first 1.5 mile structure together at Chipping Warden in Northamptonshire will begin early this year. Once completed, it will be covered with earth and landscaped to help it blend into its surroundings.
The Chipping Warden green tunnel will require more than 5000 individual segments and is expected to be fully complete in 2024. Five different concrete precast segments (one central pier, two side walls and two roof slabs) will be slotted together to make each section of the double arch, comprising separate halves for north and southbound traffic.
Similar structures at Wendover in Buckinghamshire and Greatworth in Northamptonshire will follow. To reduce the noise of trains as they leave them, the design will include porous portals that have openings along their length to slow the build-up of the pressure waves caused by the movement of the trains inside.
Stanton Precast is expected to create up to 100 jobs as a result of winning the contract.