Can a waste pipe blockage cause the pipe to burst?

[mstampfer]

The kitchen sink waste pipe under the house is broken causing subsidence of the concrete floor in the kitchen. The insurance company claims the pipe leading to the gully has burst due to a fat blockage and won't pay up as they don't cover blockages. Is it possible for this to happen? Unless the leak is enormous surely there would be water overflowing in the sink. My guess is that the floor has shifted causing the clay pipe to break up. Is this just the insurance trying to dodge?

 

[Burnerman]

Faulty salt glazed drains, when leaking badly, can wash away some of the subsoil beneath the house, causing subsidence and cracking in extreme cases.
Drains don't burst due to fat blockages - but clumsy attempts at unblocking them can.
John

 

[ScottishGasMan]

Sounds like it, you'd need a lot of pressure to burst the pipe so unless your sink is 20 floors up off the ground I'd be getting some 3rd party advice and looking at the insurance ombudsman or whoever deals with that, as you say it would back up not burst

 

[bernardgreen]

It would take a lot of pressure to burst a pipe. The fat blockage would have been blown down the pipe by the pressure long before the pressure was enough to burst the pipe. The pressure needed to burst the pipe would be several bar ( 1 bar supports a column of 32 feet of water ) If the pressure to burst the pipe was say 5 bar then the height between pipe and the sink would have to be 160 feet, anything less and the water would overflow out of the sink and the pipe wouldn't burst.

So yes it looks like the insurance company are ignorant about hydraulics and trying to avoid paying out your claim. The only way it might have burst the pipe is if the fat block held water in the pipe and then the water froze, expanding as it froze and that burst the pipe. Very un-likely the pipe could freeze.

 

[Hugh Jaleak]

Has someone had a go at cleaning it out before using high pressure water jetting? This could be enough to break an old salt glazed pipe in already poor condition, with the results you have now....

 

[mstampfer]

Thanks for your responses. They're all very useful and informative. @Hugh The loss adjusters looked down the pipe with a CCTV camera. By the looks of it the pipe hasn't been cleaned in the past 100 years. I suspect that won't be a way out for the insurance. Ditto for the ground under the house freezing over as that would be covered by the insurance. @ScottishGasMan I've responded mentioning that I'll to seek 3rd party advice from FOS or CILA. It's going to get interesting...