National Grid and Skanska/PORR/A Hak JV celebrated the breakthrough on a 5km tunnel to house a replacement gas pipeline 30m beneath the River Humber, when the 3.65m i.d. TBM completed excavation on 10 September 2019. The breakthrough into the specially constructed shaft at Paull on the north bank of the river marks the end of an 18 month drive from Goxhill on the south side, and the start of the next phase, during which the project claims that the longest hydraulically inserted pipeline in the world will be installed.

“Completing the tunnel, which is the first beneath the Humber, is a major milestone for the project team and our partners," said Steve Ellison, Lead Project Manager, Capital Delivery, for National Grid. "Over the next few weeks we will be dismantling the TBM and lifting it out, ready to be transported back to Germany where as much as possible will be refurbished for its next job. The next steps for us here under the Humber involve clearing the pipes, cables and ancillary equipment that has been servicing the TBM and preparing for pipeline installation early next year.”

National Grid in the UK is expecting to complete the almost 5km excavation under the River Humber, as its TBM reaches the last metres of its route 35m below the river bed to house a replacement gas pipeline.

It has taken more than 24,300 concrete segments to construct the 5km tunnel

The 4.4m diameter Herrenknecht TBM, designed for the project, is proceeding slowly for the last section due to varied geological conditions but at the time of publishing was 55m from expected to break through The 5km long x 3.65m diameter tunnel will house a vital new gas pipeline to replace the existing one crossing the River Humber in a trench just below the river bed. Over time, tidal patterns have eroded the river bed, risking its exposure. Due to its importance, National Grid is constructing a new pipeline below the Humber from installations at Goxhill and Paull as a long-term replacement.

National Grid awarded the design-build contract for the new high pressure gas pipeline to the Skanska/PORR/A Hak JV in May 2016, and tunnelling work began in April 2018. The pipeline connects an import location for gas at Easington, on the East Yorkshire coast, to the wider national network, and will carry about 25% of the gas Britain needs, supplying millions of homes and businesses across the east of England and beyond.

It has taken the Herrenknecht TBM 18 months to advance the heading from Goxhill on the south side of the river to Paull on the north bank. The 160m machine has excavated about 160,000t of material – mostly chalk, which has graded and reprocessed at the Goxhill slurry treatment plant for use to restore a former quarry nearby Humberside Airport.

Once the breakthrough is achieved, the TBM will be retrieved at the Paull reception shaft and returned to Herrenknecht in Germany, where components will be renewed and refurbished.

In Spring 2020, work will begin on site to push eight 610m long x 850t sections of pipe on rollers into the new tunnel from the Goxhill side. Two hydraulic thrust machines will push the pipes at about 1m/min into the tunnel, which will be flooded with water to aid installation. When one pipe section has been installed, the next will be moved into position, welded to the one in front, and the push will continue until all 5km of pipeline is installed beneath the river. When complete, it will be claimed as the longest hydraulically inserted pipeline in the world.