Weep holes in retaining wall

28 Mar 2011
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United Kingdom
Hi all

I have a block retaining wall about 20 yards long on one side of my property. The wall is about four feet high, and is holding back a section of our lawned garden which is about twelve feet in height, and which slopes down to the level of the top of the wall. Rainwater which falls on this slope drains down through the soil into a perforated pipe which is laid behind the wall, then through a larger aperture which is at the end of the perforated pipe and exits at the base of the wall. The brickie who built the wall added small brick-coloured plastic weep holes which he fitted in the joints of the bottom course of the wall. The water expelled runs into a channel alongside the concrete path and into a drain gully.

This wall was built to replace a similar one which had developed a considerable "lean", and due the amount of rain we've had lately I'm considering retro-adding further weep holes to be on the safe side, as well as in other parts of the garden where heavy rain causes saturation of more level borders which are retained by walls, and where no weep holes are fitted.

I was just wondering what would be the best option? I'm thinking about drilling holes and fitting PVC pipes with geotex membrane over the inner ends to prevent the holes becoming blocked by soil, but I have a feeling there might already be a product on the market which is ready made for this purpose.

Any guidance towards suitable products/ comments about solutions gratefully received.
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Is any water coming out of the existing weep holes? They are at the bottom of the wall? Their effectiveness is determined by the filling behind the wall as 2" of clay is waterproof.
Having dug a few holes in clay, as said 2" of it is waterproof. When I have dug holes, like a 8' deep hole for a septic tank. about 7' below ground there was a little leak, sort of a couple of pints an hour. When I dug a 4' hole to put in a basement staircase, I had the same at about 3' and when I straightened out the internal floor of a barn I had a small puddle appear right in the middle of it. So it would seem that clay has random small "veins" in it, the only fact about them is that the water which is going in must be at a higher level then where the water is coming out. Of course it might not have come out until I cut it!
So if your subsoil is clay, dribble holes will not work unless you have backed your wall with a couple of inches of gravel, so any intercepted veins will eventually leak out via your dribble holes.
If you have some other subsoil then its a bit different, chalk is free draining as is sand. Top soil to that depth is unusual but I guess is half way towards clay else you would not get puddles it in.
If you think its going to help. Are your blocks filled with rebar and concrete (they should be), you cannot drill through the rebar so drill a 20mm hole through a mortar course. It would be useful to drill this hole into the soil as deep as possible. Then loosely wrap your woven polypropolylene from an old builder bag (or geotex if your are rich), held with masking tape if required and poke it into the hole as deep as possible, withdraw the dowel for future use. it would be a good idea to stuff the poly material with a bit of pipe with a million small holes drilled in it, just to stop the tube collapsing, which would reduce its ability to dribble out water.
Waste of time. Water is not siting in the ground behind this wall waiting to burst out.
The subsoil is clay, and as far as I know the builder didn't back the wall with gravel. I don't know if there's concrete, but I do know that he put rebar into the wall at intervals of about six feet, and after about 18 months there is no obvious sign of leaning. I was told by the previous owner of this property that the old wall which was replaced by this one had been leaning for about 15 years, though how true this is I don't know. If true, then without any weep holes at all that wall had withstood a goodly number of wet spells without failing. Its only the severity of the recent wet spell which has made me consider installing further weepholes.

I don't know whether the existing weepholes are doing their job because they're almost always immersed in water within the channel that runs next to the wall, but during wet spells a fair amount comes out of the hole in the wall at the end of the perforated pipe.

I would like to put in a couple of extra weepholes for peace of mind, so I'll follow your advice, and thanks. Are we talking geotex wrapped around a PVC pipe and inserted into the drilled holes?
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Thanks again.
Woody, you're probably right that there isn't a mini-Atlantic behind the wall waiting to burst out, but a couple of extra weepholes can't do any harm, and might even, in the long term, do some good.

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