HS2: Concern over third pool from tunnelling under rugby club

This brown foam pool appeared in February

Just beyond the pitches at Ruislip Rugby Club, there is a long line of fences and lots of activity from men in yellow high-visibility jackets.

There is lots of monitoring equipment. There are probes in the ground. There is a slight cone-like depression where brown, bubbling water emerged on 20 March.

Beneath these pitches, 15m (50ft) down, there are two tunnel-boring machines drilling a tunnel to Old Oak Common.

Part of the fencing has been cordoned-off and covered in black plastic. You can't see what's behind it.

This is where another tunnelling incident on HS2 happened recently. This is the third time there has been an issue here.

HS2 says a few days ago, a mixture of water cement and sand - grout - was wrongly pumped to the surface through a hole that had been drilled by workers to check ground conditions.

On 20 March, brown water bubbled out of the ground above the tunnel. There was also a white foam that came out in February.

Now there has been an issue with the grout.

The ground here is London clay with sand on top and that is causing the boring machines problems.

The second incident last week was less foamy but "furiously bubbling"

Ruislip Rugby Club is a friendly, community-based club. It has found itself at the centre of a lot of media attention as, just on the edge of its pitches, the biggest engineering project in Europe has hit problems.

Jatin Radia is the chair of the rugby club: "The reality is it does cause further concerns because you've got local residents, local rugby club members. They're naturally concerned about what's going on and asking 'is it safe'?"

Tunnelling under houses nearby

The tunnel-boring machines will eventually go under houses nearby. Speaking to the residents there, most have been reassured by HS2. Surveys have been done on their houses in case there are any problems. But some of them are a bit worried.

Environmental campaigners are concerned about what was in the liquid seen on 20 March. HS2 has said previously it was air and water and it is safe.

Paul Jennings is a local clean water campaigner and says he doesn't believe that.

He has concerns about what is happening to the rocks below, which store water and are known as aquifers, and wants HS2 work suspended by the Environment Agency.

The rugby club pitch is fenced off in many areas with soft and dipping ground

"Ten years go when we started on the consultation with HS2 and the Environment Agency, we were very concerned that the aquifer would be damaged by what goes on within the tunnel. The tunnel has a lot of fluid running around it and it's under pressure and that's going to find its way into cracks and holes," he said.

"And what has happened here is a fantastic demonstration of what our concerns were at the time. We are still worried as there is still a lot of more tunnelling to be done and we're not sure what damage has already been done."

When we were on the pitches filming, we bumped into Mark Kier, who is an anti-HS2 campaigner.

I have filmed with him previously at many protest camps along the line. There are only a handful of them left now. He thinks HS2 should be stopped: "The tunnel is just about to be bored under a whole street of houses that are built on the same strata and the same geology as this, and if there's subsidence here, there's going to be subsidence there."

The problems in Ruislip have meant HS2 have switched tunnelling fluid, which it hopes is better suited to the mixed ground.

The site of a previous bubble pit is still cordoned-off, although the liquid has sunk

An HS2 Ltd spokesperson said: "Our expert tunnelling team are adapting their methods to account for the variable ground conditions in this specific area. Safety is at the forefront of everything we do and they will restart continuous mining once the new approach has been assured."

On the issue with the grout, they added: "A grout leak has taken place during our tunnelling operations. We apologise for the error. After liaison with the Rugby Club, the grout was cleaned up. The area has been temporarily fenced-off and remains safe."

There are still many questions that locals want answered, including if HS2 could have known about the geology in Ruislip and, if so, why it did not mitigate the issue until now. Will similar problems happen again?

Perhaps the problems on the pitches of Ruislip are an engineering one-off and they have been resolved.

Environmentalists say it does not give them confidence that HS2 is a well-investigated and well-planned project.

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