New £8.2million gas pipe for Sheppey

You can’t miss the ‘road closed’ signs springing up across Sheppey as gas distributor SGN upgrades its ageing network with new plastic pipes.

But less than three miles away an even bigger operation has been going on, hidden from most people’s eyes.

The same company has been tunnelling under the Swale as part of an £8.2 million operation to lay a new 12-inch (400mm) high pressure main to feed the Island.

The green line shows the route of the new gas main under the Swale

Contractors Phoenix Civils moved onto the site near Ridham Dock last August to prepare for one of SGN’s most challenging projects.

A specialist team from LMR Drilling UK arrived on January 6 and after two weeks of setting up machinery completed the drilling in two-and-a-half weeks – 10 days ahead of schedule.

Workers are now busy dismantling the rig and preparing to connect the new pipe to the network.

The drilling rig used to tunnel a new gas main under the Swale to the Isle of Sheppey. Picture: SGN

Once the pipe has been tested and connected, drivers and train passengers will begin to see scaffolding going up around the Kingsferry Bridge as work switches to removing the existing 60-year-old steel pipe from inside the towers.

Although relatively quick, drilling the borehole was not without its challenges.

SGN engineers Nathan Clarke, left, and Simon Thurlow on the bank of the Swale. PIcture: John Nurden

SGN’s project manager Simon Thurlow, 50, explained: “Not only are the Sheppey marshes a site of special scientific interest and are covered by the Ramsar International Convention on wetlands but we also had to negotiate with eight or nine different landowners plus working in line with our consents set out by Natural England.”

He added: “This has been a very complex project. It has been planned since 2017 and I became involved in 2019.

“It took a long time to get everything in place. But once we were ready, the actual drilling was completed ahead of schedule.”

Tricone bit breaks through after tunnelling under the Swale. Picture: SGN

At the heart, or probably the head, of the horizontal directional drill (HDD) was a state-of-the-art device clamped to the front which used gyroscopes, and similar technology to that in top secret Cruise missiles, to guide it under the Swale.

After drilling down 23.5 metres and then along 573 metres it emerged on the Sheppey side bang on target.

“It was incredible to see,” said Simon. “We had red guideposts in place and it popped up right next to them.”

New gas pipe being pulled back to the mainland under the Swale from Sheppey. Picture: SGN

At the same time, a dedicated mud engineer had been shipped over from Poland to take soil samples, sometimes as many as 15 a day, to ensure the lubricant mix of slurry fed back into the drill hole remained at exactly the right consistency to allow the manoeuvre to be completed in one continual process.

The samples were all tested onsite.

The polyethylene pipe normally comes in 12-metre lengths but for the Sheppey project they were specially shipped as 18-metre lengths by pipe manufacturer Aliaxis to reduce the number of joints.

The new gas pipe stretched out along the Sheppey marshes ready to be pulled under the Swale. Picture: SGN

The pipes were laid out in a single line on the Island side before being fused together in one long strip by heat welding. The whole pipe was then gently pulled back under the Swale to the mainland.

The project has been so high profile that a stream of “top brass” from SGN regularly visited the site to watch the operation at first-hand. At one stage, a temporary viewing platform was installed so visitors could see the drill in action.

Removing the drilling equipment from site

The Ridham Dock site is now being stripped of equipment. And waste mud stored in a giant manmade lagoon is being taken away in a fleet of tankers to be environmentally disposed of.

The drilling site will then be returned to its original condition as 4,000 tonnes of aggregate used to support the rig are removed and the topsoil replaced.

The new pipe will be connected to the rest of the Sheppey main and to the gas feed on the mainland side near a buttress leading to the Kingsferry Bridge.

New pipe will be connected to the gas feed here. Picture: John Nurden

The team is waiting for permission to close the Ridham Dock Road to complete the task. Then it will be out with the old pipes.

Site project manager Nathan Clarke, 53, from Rochester, will be in charge of that. He joined British Gas as an 18-year-old school-leaver.

Old gas pipe, left, under the Kingsferry Bridge to be removed. Picture: SGN

He explained: “The old pipe runs underneath the carriageway, down one tower, along the inspection tunnel under the Swale, up the other tower and under the roadway to the Island.

“We will be hanging scaffolding from the road to access the pipe but because the Swale is tidal we will also need rescue boats on the water while we are working.

Because the access doors to the Kingsferry Bridge are this small the old gas pipe must be cut into one-metre lengths. Picture: John Nurden

Because the access doors to the bridge’s inner workings are so small, the pipe will have to be painstakingly removed in short lengths.

Nathan said: “There will be scaffolding inside the bridge to take the weight of the pipe as we cut it into one-metre-long sections. These will be rolled to the towers where electric hoists will lift them up.”

Kingsferry Bridge linking the Isle of Sheppey to the mainland. Picture: John Nurden

Remote “cold cutters” will slice into the steel. Each cut is likely to take 45 minutes.

Nathan added: “Because it is in a confined space, we can’t use oxyacetylene torches. And every time the bridge lifts for a boat we will have to stop work. Few people realise just how much work goes into project like this behind the scenes.”

It might almost make the gas bill for Sheppey’s 15,000 customers seem worth it!

Note:

Southern Water began its £7.5 million project to install two new water supply pipes to Sheppey in October 2022, three months after its old main across the Kingsferry Bridge burst and left 40,000 Islanders without water for three days during one of the hottest summers on record.

The work was finally completed almost a year later in September 2023.

Project team leader Peter Simmons blamed the delays on “major challenges”.

He said: “There were all sorts of changes in the soil, clay and shells which made life pretty tough. But we had a brilliant team and overcame every hurdle.”