Subsidence above path of London Water Ring Main

[Vet Tech]

Hi,

I am looking into damage to residential property located above the line of the large underground Water Ring Main that runs around London.

This was a massive tunneling project that started around 1976 and carried on for several years thereafter. The tunnel runs for 80Km around London at a depth of between 30M and 50M. The diameter is 3.2M. New extensions are currently being added to it.

With any large underground tunnel there is some settlement at ground level. This gives rise to subsidence which in turn results in cracks and other damage to property.

As fellow DIYers, I reckon some of you will have encountered such damage.

I'm trying to get a feel for the scale of the problem in terms of how many properties were affected and how much the ground settlement was on average. Also to find out if compensation was paid out by Thames Water for damage arising.

Thanks in advance.

[Adrian C]

Are you an ambulance chaser?

Finished suing councils over dodgy pavements and causing decreases in vital council services while overpaid gangs do totally unnecessary work replacing pavements down whole streets?

Is my home buildings insurance going to rise due to your fishing expedition? Same for my water bill?

London needs investment in the water system for the benefit of all Londoners. Don't divert it elsewhere :-(

[Andrew Mawson]

Thames

Well it went past the corner of an industrial unit I leased some years back in Bermondsey, and there was no perceptable damage as they did it, nor was there any apparent by about 2000 when I left it.

AWEM

[stuart noble]

That's what buildings insurance is for. No doubt they would claim against TW if they thought it was appropriate.

[Vet Tech]

Heaven forbid.

No, it's just that they are going to build an extension to the tunnel and this will go directly under my house!

So I'm trying to assess the potential risk as regards possible damage to the house. If I do suffer subsidence then it would make a nonsense of my insurance premiums in the years ahead.

So, no ulterior motive -just a bit worried about it all. If no one has had a problem then we are all happy. :-)

[Invisible Man]

Any idea how they are doing it? I have heard of 2 types of tunnel boring machines being used but I may be out of date

Some tunnel boring machines (TBMs) are self propelled. Others are pushed forward by a type of ram placed in a vertical shaft. The ram pushes the machine forward and the ram is pulled back every so often to allow tunnel lining segments to be added and then the ram pushes again via the segments. A slow drying lubricant is used to assist the passage. In either case there should be minimal disturbance to the ground above but unforeseen ground conditions are sometimes encountered and complications can arise. I believe there is the odd TBM abandoned under London where it hit soft ground and nose dived.

[Adrian C]

In that case I owe you an apology.

Ultimately, as has already been stated, your insurance company is probably more interested in this than you - and should cover should the worse ever happen. I'm feeling good that it won't, these are works which are waaaaay deeper than anything else dug in London - and chances are that if you were to suffer property subsidence; the finger would be first pointing elsewhere to other more local influences of ground shift.

But, I'm not a lawyer/civil engineer or seismologist.

If you have been contacted about the works on the extension, it would be interesting to know what statements have been issued by the contractors to allay householders concerns about the works and any risks.

Is there a PR Website?

[John Rumm]

I would have thought that if it is deep enough and cut cleanly enough (i.e. with a boring machine) then there would little if any subsidence.

[Roger]

The message from John Rumm contains these words:

Didn't they have a monster cave-in when constructing the original ring?

I may have been mistaken. A quick google didn't produce a likely candidate.

[stuart noble]

I read an interesting book about what goes on below ground in London. Can't remember the title but ISTR the guys working on this ring main are extremely well paid but don't (or can't) do the job for long

[A.Lee]

Heathrow Terminal 4? An extension to the rail line below ground caused an office block to collapse. Alan.

[Adam Aglionby]

Think you have to be lot nearer the surface to cause problems generally, some of the city centre tubes cross over each other in a corkscrew because when originally built couldn`t get wayleaves from landowners above.

Try asking on news:uk.rec.subterranea

Adam

[Adam Aglionby]

New Austrian Tunneling Method if remember, pin the tunnel lining to its surrounding earth , but sprayed rather than cast sections, dunno if its still popular,along with Gerards Cross Tesco Value Tunnel very possible to spend lots of money and have lots of letters after your name and still get it very wrong.

Adam

[John Rumm]

There was one with a tube extension that almost swallowed a supermarket car park IIRC.

[Roger R]

The tunnels were cut in the clay band using a boring machine that cuts a precise circular hole. The concrete ring segments are installed within minutes as the clay slowly closes in and squeezes the segments together. I would have thought there would be no perceptable subsidence due to such small displacement at such a depth.

Of course if a tunnel is in loose gravels then there can be major problems.

Roger R