Earth in drain

[daza]

Hi, wondering if anyone can help...

A couple of weeks ago our drains blocked, (it's a Victorian terraced house in London). When we opened the manhole cover at the bottom of the garden there was earth, (under one cubic foot), blocking the main drain just before it enters the interceptor. All the sewage was backing up behind this obstruction. I cleared it and everything ran okay.

Now, two weeks later, exactly the same thing has happened again. Before I start getting expensive camera surveys done, does anyone have any idea what this can be? Is it a broken pipe letting in earth? If so how comes it has taken so long for it to block again?

Any suggestions gratefully received!!!

Darren

 

[Breesey]

Got any big trees/large bushes/plants nearby?

 

[JohnD]

you have a broken or cracked pipe. You also have a cavity appearing in the ground, where the soil is being washed into the drain. You may not be able to see where this cavity is, until the ground above it caves in, and the surface, or possibly your house, falls into the hole.

there is no practical limit to the size this cavity may be. In London they are measured in units of "DDBs" when they appear in roadways due to failing of old sewers or watermains. One DDB means a hole that is big enough to swallow one Double-Decker Bus.

If the brickwork of the shaft down from your manhole is falling apart, the soil may be coming through there. This often happens if cars have been parked or driven on or beside the manhole cover.

 

[daza]

Thank you for the speedy and informative replies. There is indeed a cherry tree directly above where the pipe (probably) runs so that might be the culprit. Guess I'll have to open my wallet and get a CCTV exam done and find out where the crack is.

thanks again for the information!

Darren

 

[daza]

Just an update so that this might be useful to others...

We had a survey done which could find no problems with the drains!!!

Conclusion
The rats were trying to build a 'nest' on the ledge next to the drain in the inspection chamber. The eaarth fell into the drain and blocked it. I'm still trying to work out how they managed to get that much earth into the chamber.

 

[JohnD]

OOI, was this a survey where they poked a TV camera up the drain?

Might be interesting to have a look down the hole every week or two to see what's happening.