Problems with french drain

[Fizzer]

Hi All,
We had a really productive day yesterday, the living room has a lot less cement in it now (and is 2" wider than it was) , the horrible 60's chimney is being dismantled and Rob has done some excavation at the back of the house in preparation for the digger on monday to make the french drain.

This is where our problem lies. Rob has dug 3 test holes and it seems that although the wall is about 19" thick above ground, below ground it's a mix of stone, rubble, earth and very very sodden lime. The wall looks undercut by 6"-8". The external ground levels are 4' high and we were planning to dig down, install a french drain then backfill with gravel.

Rob is very concerned about undermining the wall during this process and causing subsidance or collapse. This pic should give an idea of our predicament:

We have also noticed that there has been some 'activity' here before, there are remains of an old waste pipe and also below the window has a wide slab of concrete (previous repair?)

the new plan is to dig a 1' deep trench along the base of the wall on monday then dig some more inspection holes to see if it gets any worse further down.

If anyone has any ideas as to what we can do I'd be v grateful. Even if we do dig down 4' we're going to have problems attaching our dpm to the outside of the wall

 

[Lime]

A digger?!
I wouldn't allow a digger anywhere near this trench!
It has to be dug by hand and with care.

From your description of the wall great care needs to be taken to avoid damage and maybe some repairs carried out in the process of digging out.

 

[Tom]

I agree with Lime...NO digger! It looks like the wall needs underpinning in small and slow stages. You may have a better idea of what you could do now you've seen our property

Jaqy

 

[Penners]

From the look of your sketch and photo, I tend to agree with the previous posters. Underpinning may be necessary, and in the meantime you need to go very carefully with your excavations.

I would only excavate (by hand) short sections at a time, and take whatever remedial action seems necessary, before moving on to the next section.

 

[Nemesis]

Consider doing something different - an internal membrane arrangement may be less disruptive and safer.

 

[Penners]

I agree.

 

[Fizzer]

Hi Folks, finally got home. Just done a 320 mile round trip to lincolnshire to see Jaqy's place. Thanks very much for the guided tour and the advice guys. It really was enlightening

I've had a chat with Rob, I think he's a bit relieved that we're not going to go any further with the digger near the wall. However it's too late to cancel it so he's going to remove the steps, the concrete path and a couple of shrubs. He'll also dig the soakaway and connecting trench.

At the moment we're thinking that underpinning would be a good option, we really would prefer to control the water outside of the wall instead of tanking. I think in the long run, if the wall is shored up well and made dry it will last another few hundred years.

This does however put back our plans a bit while we sort out how to get it underpinned properly.

 

[joe1978]

Hi fizzer,

let me know how you get on with the back wall. I have a very similar arrangement in my new home and although the survey didn't say damp on that wall It'll be handy to know for the future...just in case!!!

joe

 

[Mark]

How about rather than putting the drain right against the wall you put it 5 or 6 feet away (keeping the 45 deg from the external base of the wall). That might improve the drainage in the short term while you can do the wall renovations more slowly as and when.

 

[Fizzer]

eek!
quote for underpinning, lining the wall, installing a french drain, refilling, rebuilding the end 2M of our leaning wall with a pier and resetting 3 square M of roof tiles...

Guess...

 

[MdB]

£5k? - I'm having a similar but much larger job done shortly so would be interested in what you are being quoted if you don't mind letting us know.

 

[Fizzer]

it's pretty much double that.

I suppose we have to take into account the fact that they need to dig 4' before they get even to floor level and there is additional work for drainage etc.

We'll get some other quotes though...