National Grid's tunnel boring machine has passed the halfway point under the River Humber representing a major milestone in the project to secure 20 per cent of Britain's gas supplies.
The 510 tonne, 160-metre-long machine, named Mary after Mary Fergusson, the first female fellow of the Institution of Civil Engineers, reached the halfway point on her journey from Goxhill to Paull at 2.30am on 8 January. The total length of the journey is 5km.
It has taken 200,000 man hours to get the tunnel to this stage, with a total of 2,023 concrete rings, each consisting of six segments, being put in place behind the machine as she tunnels 35 metres below the bed of the river.
Steve Ellison, project manager, said: "Mary has done a brilliant job to date and we and our contractors are delighted to have reached the halfway point on the tunnel. There is still a lot more work to do but I would like to say a big thank-you to the 40-strong team of engineers who have worked around the clock in very challenging conditions to get us to this important milestone.
"The machine has pretty much been operating 24 hours a day with the odd shut-down for repair or maintenance since the tunnelling work started on 6 April 2018. There are 20 engineers manning her on every shift and they work in very cramped and warm conditions, far below the river bed.
"All the engineers working on Mary have to undergo specialist training. There is only one emergency exit from the machine and that is back along the tunnel, which will be nearly a 5km journey once she gets towards the opposite bank of the river.
Once the tunnel is finished, Mary will be removed from the tunnel via a shaft on the opposite bank of the river at Paull. Work on the next phase of the project will then begin.
A new 42inch diameter gas pipeline will be laid inside the tunnel. This will replace the existing gas pipeline which currently crosses the river and is laid in a trench just below the river bed.