Retaining Wall building in wet conditions

[DiyGuy]

I am 1m below my neighbour. Recently, my neighbour's property constantly pools water where I have already started building a retaining wall below. It never hapened before. We have had dry spells, but this water never goes away. He has said he cannot stop the water, so I need to keep on building in the conditions I have.

 

I can dig and lay the foundations by using a pump to clear the water. I can pump the water out long enough to get the foundation laid. So I should be OK there, but any advice about that would be appreciated.

 

This is the important bit:

 

However, laying the first row of breeze-blocks will be the difficult part. There is a constant flow of water which I am directing to a temporary sump close by. However, there will be an almost permanent 1 to 2 cm flow of water where I want to lay the bottom breeze-block. Once I am up to the second row, I will be fine.

 

Can anyone give me some advice on how to build this with the conditions I have?

 

Other Notes:

 

There is a slight snag. There is less than 1m beteen my neighbour's mud bank and my house. The wall has to go directly against the vertical bank which is my neighbour's land or there is no room. It is replacing an old 50 years old thin wall with a thicker one.

 

The 1 meter deep difference in border height only goes on for about 4 or 5 metres long and is sloping downwards along that stretch.

 

I cannot get drainage behind the wall as that is my neighbour's property. About a 2 meter stretch is already built last summer. There have been no water problems here before, even over the winter when there was a gap between the new and old wall.

 

I can build a lot of drainage holes into the wall and then use some sort of French Drain at the front to divert the water to a sump on my side of the border.

I know I have to put weep holes into the wall, which I will direct to a permanent sump I will be building.

 

 

Edited March 11, 2020 by DiyGuy

[PeterW]

I would be putting a perforated pipe wrapped in geotex and 20mm gravel behind the wall - it will be 150mm wide at most and can sit on top of your founds if needed. 
 

Concrete will art under water - if it is readymix then it will just displace the water, you could always ask for a rapid mix. I would also use shuttering your lift the level of the foundation edges slightly. 
 

Need to see a photo if possible. 

[Jeremy Harris]

You have two problems, really.  The first is getting the wall built in wet conditions, the second is that the combination of hydraulic pressure and lubrication of the slip plane under the wall foundations could cause the wall to fail.

 

The normal solution for both is to install a land drain in a gravel bed at the retained side of the wall, as @PeterW suggests above.  We had to do this behind our big retaining wall, as a requirement stipulated by the SE that designed it.

 

How high is the wall? 

[Declan52]

Dig a hole to act like a sump and guide the water into the hole. Then you can either pump it out to a drain or bucket it depending on the flow.

As above you always put a drain behind a retaining wall otherwise it will push the wall out and over.

[DiyGuy]

Thanks for the replies.

 

PeterW: I would be putting a perforated pipe wrapped in geotex and 20mm gravel behind the wall - it will be 150mm wide at most and can sit on top of your founds if needed. 

 

I already have about 2 metres of wall built last summer before any water flow started. I obviously do not have 150mm pipe behind that.

 

PeterW: Concrete will art under water - if it is readymix then it will just displace the water, you could always ask for a rapid mix. I would also use shuttering your lift the level of the foundation edges slightly. 

 

Not sure what concrete will 'art' means. I will definitely use rapid mix as you suggest.

 

Are you saying the shuttering should be above the foundations, or I raise the foundations. Surely, all this will do is is get the water flowing over the shuttering while building or over the foundation when that is laid?

 

PeterW: Need to see a photo if possible. 

 

I cannot provide a photo as I do not have a modern digital camera. Sorry about that, but I do not really want a smart phone in my life.

 

Jeremy: The normal solution for both is to install a land drain in a gravel bed at the retained side of the wall, as @PeterW suggests above.  We had to do this behind our big retaining wall, as a requirement stipulated by the SE that designed it.

 

I cannot do anything behind the wall on the vertical mud of my neighbour's property. It is not my land. I have very limited space in front up to my house, it is less than a metre.

 

The old, thin, 1 metre tall wall never failed before, but there was never any water before. The water is something new. It has never happened in over ten years, even when there was a gap between the old and new wall when we were building the wall in stages.

 

Jeremy: How high is the wall? 

 

The wall will be up to 6 ft to cover the retained mud and a bit more, also for privacy. However, I can limit it 1 metre and put a fence on top if necessary.

 

Declan: Dig a hole to act like a sump and guide the water into the hole. Then you can either pump it out to a drain or bucket it depending on the flow.

 

I have presently built a temporary sump. I direct the water to the sump which then auto-pumps it away with a pump I have bought.

 

However, you still get this constant 1cm to 2cm deep flow right at the point where I need to put the next breeze block.

 

Me: I can put loads of weep holes in the 2 metre stretch I have already built. And putting weep holes into the new bit I will build will be easy. I can then have a sort of French-Drain to divert the water on my side of the property to a permanent sump I will build.

 

Will that be OK? I have to work with what I have.

 

[Jeremy Harris]

Our retaining wall also has its rear face dead on our neighbours boundary.  Because it was absolutely essential that the rear face of the wall have drainage, I negotiated with the neighbour to excavate a couple of feet of their garden, carefully removing some of their shrubs and plants, and then reinstating and replanting it all afterwards.  Any retaining wall that has water behind it is very likely to fail, if not from the effect of hydraulic pressure, then from lubrication of the slip plane under the wall.  The water is going to find a way out, and what you don't want is water down at the wall foundation level, as that's likely to cause premature failure. 

[DiyGuy]

Thanks for the reply again Jeremy.

 

Unfortunately, the neighbour is very strange. He will not allow anything done on his property. Any normal person would have just diverted the water or stopped it. He has enough room in his garden.

 

His present position is he intends to do nothing about the water and is claiming it is nothing to do with him as it is natural flow. He has no money to do anything.

 

The old retaining wall never had this drainage and that was there when we came. It never failed, but there was no water then. There were not even any weep holes in the old wall. We are going to put those in on the new wall.

 

I know everyone says it is essential the rear face has drainage, but the weird conditions I have means that is almost impossible.

 

Is there anything I can do, such as buttresses, posts, or anything my side to compensate for the weird conditions I face?

 

 

[Jeremy Harris]

The only solutions I can think of that may work would be to forget about making a brick, block or concrete retaining wall, and look at a porous option, like gabions or perhaps timber crib.  The problem with these options is that both tend to take up a fair bit of space.

 

There's no solution that can avoid the problem of a retaining wall slip plane being lubricated by water, other than drainage to remove the water before it gets down to that level.

 

Our neighbour wasn't easy to deal with, but we managed to negotiate with him, on the basis that we covered all the costs, including the full reinstatement of the strip of his land we'd disturbed and building the side of the boundary wall above the retaining wall that faced his house to his (expensive. . . ) spec (it's rendered on our side, but stone faced on his side).

[PeterW]

It it is this wet then I would look at a timber crib that is stepped at 30 degrees and gravel filled. It will become self draining and as long as it’s not above about 4 ft tall will be pretty stable 

[Roundtuit]

Where is the water coming from? Sounds like it might not be just percolating through the soil due to the wet season?

[Temp]

 

3 hours ago, DiyGuy said:

However, laying the first row of breeze-blocks will be the difficult part. There is a constant flow of water which I am directing to a temporary sump close by. However, there will be an almost permanent 1 to 2 cm flow of water where I want to lay the bottom breeze-block. Once I am up to the second row, I will be fine.

 

Google found underwater mortar but no idea how readily available it is...

 

https://rotafix.co.uk/products/masonry-repairs/rotafix-underwater-applied-mortar/

 

Rotafix Under Water Mortar powder is a blend of special cement powders, high quality graded sand, and a unique combination of polymers and admixtures. The powder, when mixed with water, produces a mortar which is wash-out resistant and waterproof. The ready to use mortar powders are packaged in 25kg moisture proof durable bags and have a shelf life of 2 years.

 

https://www.epoxyproducts.co.uk/Epoxy%20Mortar%20Underwater%20482015.pdf

 

EPOXY MORTAR—UNDERWATER Is for use in exceptionally wet conditions and for underwater applications. For fixing slip bricks and reinstating structures exposed to heavy battering from sea, such as sea walls and jetties. For repairing submerged concrete.

 

I'd do my best to eliminate the water and leave gaps in that first course so any can drain to your side rather than build up.

 

 

 

Edited March 11, 2020 by Temp

[Temp]

 

3 hours ago, PeterW said:

I would be putting a perforated pipe wrapped in geotex and 20mm gravel behind the wall - it will be 150mm wide at most and can sit on top of your founds if needed. 

 

+1

 

Even a 60mm diameter pipe would be better than nothing.  When you have the second course built and its set up good, wait till he's gone to work, drop in the pipe and cover it up with gravel and soil.

[DiyGuy]

@Jeremy Harris and @PeterW those are nice ideas. The bit of wall I have already built has some space in front. I could do something like that in front of that wall to give it stability, and then do that in place of the wall for the rest of the stretch. That could still look nice.

 

@Roundtuit from what I can see from a distance it is coming from either his well or from a portable pond he has. The portable pond has moved recently. He always had a hose draping into it when he had it close to the pavement, so he may have a hose in it now. The new position of the pond and the well could both drain to the soggy area in his garden which now affects me.

 

@Temp thanks for those links. They look useful. I will look into that a bit more.

 

@Temp Work :). You, me and the rest of us work. He has been 'depressed' and not worked for 8 years on maximum benefits having his rent paid in a big house. Coincidently, he suddenly caught 'mental health' when it was advantageous for sentencing and was convicted of a violent crime against someone else.

 

Edited March 11, 2020 by DiyGuy

[Roundtuit]

1 hour ago, DiyGuy said:

 

@Roundtuit from what I can see from a distance it is coming from either his well or from a portable pond he has. The portable pond has moved recently. He always had a hose draping into it when he had it close to the pavement, so he may have a hose in it now. The new position of the pond and the well could both drain to the soggy area in his garden which now affects me.

 

 

Legally, if you're downhill, I think you have to accept 'natural' drainage going in your direction, but if it's due to some sort of activity on your neighbours land, like downpipes or water storage, then I believe he has some responsibility.  Not sure that helps you much if a) he's not co-operating, and b) got no money, but depending on how you think it would go, I'd consider researching the legal situation a bit further (Google, not solicitors!) and perhaps suggesting that you can help him out with his legal obligation by putting in a perforated pipe FOC!