Collapsed Drain Sink-Hole?

[McAhuna]

Discovered a worrying hole just below the ground outside our 1928 house, just a small entrance but about 1foot deep by 1foot wide underneath.

The house is built on clay, but the 'groundsure' report from 2 years ago when we purchased said the risk of subsidence in the area was very low.

This is the second hole I have discovered. The first one I filled in. Both holes were/are in the vicinity of drains. Which now makes me think broken drains could be the problem? But how likely is this and how do I tell for sure? How serious a problem is this?

I am a bit lost as to my next steps and any advice would be much appreciated. Thanks

 

[JohnD]

It's very common when salt-glaze clay cracks and breaks.

In clay soils, the house sinks or moves and the drain doesn't, so it commonly snaps the gullies at their bend, and the bend where horizontal drains turn up to meet iron soilpipes. The flow of leaking water washes the ground away leaving a cavity. Commonly it is covered over or filled in with concrete to hide it, but the soil continues being washed away out of sight. You might find lots of red worms, which live on sewage, and if the house was built with lime mortar, it may have been washed away and need refilling once you have excavated and washed the mud out of the joints. In some cases the base of the wall may be undermined.

Dig them up and replace the broken parts.

 

[big-all]

are you on a shared drain ??
as in a terrace or other situation where you and a neigbour share the same drain
if so any maintainance is the responcibility off your council or water company

 

[McAhuna]

are you on a shared drain ??
as in a terrace or other situation where you and a neigbour share the same drain
if so any maintainance is the responcibility off your council or water company

Thanks for the advice.
We are a semi-detached house. I don't believe we are on a shared drain, the drain goes off our property directly onto the highway. How do we tell for sure though?

 

[McAhuna]

It's very common when salt-glaze clay cracks and breaks.

In clay soils, the house sinks or moves and the drain doesn't, so it commonly snaps the gullies at their bend, and the bend where horizontal drains turn up to meet iron soilpipes. The flow of leaking water washes the ground away leaving a cavity. Commonly it is covered over or filled in with concrete to hide it, but the soil continues being washed away out of sight. You might find lots of red worms, which live on sewage, and if the house was built with lime mortar, it may have been washed away and need refilling once you have excavated and washed the mud out of the joints. In some cases the base of the wall may be undermined.

Dig them up and replace the broken parts.

Thanks for the advice.
That sounds way beyond my very basic DIY abilities. Who should I approach for help?

 

[JohnD]

digging a hole is uncomplicated work for a DIYer with a spade and some energy.

Ask around for recommendations of a small local builder.

 

[big-all]

Thanks for the advice.
We are a semi-detached house. I don't believe we are on a shared drain, the drain goes off our property directly onto the highway. How do we tell for sure though?

lift the lid and get your neigbour to run a tap or flush the toilet

 

[vinn]

What are we looking at?
Why the raised concrete platform aspect - what is the black material - what is the white shiny thing?
Have rats been an issue?
Can you step back and take a more general photo showing the context of the above two photo's?

 

[McAhuna]

What are we looking at?
Why the raised concrete platform aspect - what is the black material - what is the white shiny thing?
Have rats been an issue?
Can you step back and take a more general photo showing the context of the above two photo's?

Sure, here you are. The problem area is located by the photo date stamp in this picture. Thanks for looking at it.

Q: Why the raised concrete platform aspect? A: Not sure what you mean here. The vertical bricks at the rear surround the drain. The 1.5foot area of horizontal concrete is actually at ground level surrounding the drain - The main hole can be found underneath here, but the small entrance to this hole is at the front of the horizontal concrete area.
In the foreground of the picture, the shingle flower bed is slightly lower in comparison to the concrete area, but only because I have recently dug it out (I cleared the flower bed of soil and replaced it with a shingle garden) Incidentally, it was this work that revealed the presence of a the much deeper hole by the drain.

Q: what is the black material? The lining to the new shingle garden. So nothing to do with the drain or the problem.

Q - what is the white shiny thing? There is white feather that strayed into the picture beside the small entrance hole. If thats what you mean?

Q - Have rats been an issue? A: There are a lot of rats around this area since we back onto an overgrown railway sidings. I have seen rats in the back garden, but I haven't seen them at the front or in this specific hole. I did notice recently that some of the black lining we mentioned had been nibbled at a couple of metres away, so it is a possibility.

Thanks for your advice.

 

[McAhuna]

are you on a shared drain ??
as in a terrace or other situation where you and a neigbour share the same drain
if so any maintainance is the responcibility off your council or water company

big-all, Looking again (see attached pic), the down pipe from the roof gutter serves both properties and flows into our drain as well as our neighbours drain. Would this count as a shared drain do you think?

 

[vinn]

The shared rainwater pipe is very common & nothing to do with your ground difficulties.

OP, I think that you must, as advised by others, dig out the gulley(?) and trench the drain across to the shingle garden at least.
You must chip out the bit of concrete being careful not to cause further damage to the drain pipe below.
You must also locate the man hole that the drain connects to, and watch a test bucket of water poured down the gulley appear from the m/h inlet.

Take photos and come back on this thread.

 

[foxhole]

The holes could be drainage off the garden put in to stop that recess where the drain pie is from flooding.?

 

[McAhuna]

The shared rainwater pipe is very common & nothing to do with your ground difficulties.

OP, I think that you must, as advised by others, dig out the gulley(?) and trench the drain across to the shingle garden at least.
You must chip out the bit of concrete being careful not to cause further damage to the drain pipe below.
You must also locate the man hole that the drain connects to, and watch a test bucket of water poured down the gulley appear from the m/h inlet.

Take photos and come back on this thread.

Firstly, thank you for your advice Vinn, it is much appreciated. I hear what you are saying.

However, the issue that is holding me back is that this is the second hole I discovered. The first one I already filled in, but as the pic shows is was in a much less accessible position underneath the kitchen wall. I would be very wary of digging here without causing much worse problems. Which leads me to the question would it be worth getting CCTV drainage surveys of the whole drainage system done? I have seen these advertised for about £150. Has anyone any experience of these and is it an option?
Alternatively you can buy your own inspection cameras in Aldi for about £40

If both of these are red herrings, the spade is coming out.

 

[Hugh Jaleak]

If spending the money will give you peace of mind then I would get a CCTV survey done. Old salt glazed drains have very little give in them, cracked and broken pipes are not uncommon, and I'd still hazard a guess there is some rat activity in the drains. If there is no apparent dampness around these holes, then my thoughts are its rats digging an exit rather than a leaky drain washing the subsoil away.

If you identify what is going on, and the level of damage apparent in the drainage system, it gives you a better idea of a way forward. Any breaches in the drains need locating and repairing, to block off all possible exits for rodents. Should the system require major works, then it would be worth checking if your house insurance would cover it.

 

[vinn]

OP,
Your today's photo doesn't show anything of interest - or I'm missing something.
Is that the rear gulley?
There's a cable or pipe running along the ground - if thats a live cable or a gas pipe then its in a vulnerable position.
Maybe another photo showing the rear gulley and the rear elevation?


Are you referring to a hole at the front of the house by the porch, and a second hole at the rear of the house?

I would dig out at the front as I advised you above - whatever, it will have to cracked out sometime.
FWIW: you can use a phone as a drain camera, there's vids on u-tube about how to do it. But I would leave it out for now.

From whats on the photos is it that the only manhole is at the back of the house and the front "gulley" is draining to ...?