In the UK, National Grid’s 510 tonne Herrenknecht TBM ‘Mary’ is now halfway through its 5km journey under the River Humber, a major milestone in the project to secure 20% of Britain’s gas supplies via the 3.65m diameter tunnel.
The 160m long machine reached the halfway point on the journey from Goxhill to Paull at 2.30am on Tuesday 8 January, giving National Grid and their joint venture contractors Skanska, PORR Bau GmbH and A. Hak cause for celebration.
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 35m 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.
“As you would expect, safety is our prime concern. All plant has a fire suppressant system, conditions in the tunnel are monitored along its entire length and we have regular emergency exercises and employ an on-site emergency team.”
And, once the tunnel is finished, and Mary is removed from the tunnel via a shaft on the opposite bank of the river at Paull, the work on the next phase of the project will 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.
This pipe at risk of being exposed by shifting tides. Work has been carried out to keep it buried but the Humber Pipeline Replacement project offers a long-term solution.
Already, the eight ‘strings’ or sections of gas pipe which will be pushed into the tunnel have been laid out and welded on a vast pipe ‘field’ on the Goxhill site. Work to install them in the tunnel will take around a year to complete