1.5-2m Drystone retaining wall on a slope—surface prep

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1.5-2m Drystone retaining wall on a slope—surface prep

Postby lstwhl » Thu Jun 11, 2015 7:43 pm

I have an opportunity to plateau the ground such that the existing ~7°slope begins up to 3-4m away from the foot of the wall. What would be the best practice and how would this inform on depth of foundations?

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Re: 1.5-2m Drystone retaining wall on a slope—surface prep

Postby jerryg » Thu Jun 11, 2015 10:34 pm

Eh? are we in legoland?
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Re: 1.5-2m Drystone retaining wall on a slope—surface prep

Postby lstwhl » Fri Jun 12, 2015 1:25 pm

jerryg wrote:Eh? are we in legoland?


Eh?
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Re: 1.5-2m Drystone retaining wall on a slope—surface prep

Postby jerryg » Fri Jun 12, 2015 7:36 pm

er sorry mate..... can you rephrase your question in such a way that it could be understood by someone (like me) who are always here to help if we can, and let's face it there are very few others on this site that ever reply with anything helpful.

Actual pictures of the site would better inform rather than pretty little lego blocks, even a few words on the legoblocks would help.

or even a few line drawings
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Re: 1.5-2m Drystone retaining wall on a slope—surface prep

Postby lstwhl » Sat Jun 13, 2015 12:53 am

jerryg wrote:er sorry mate..... can you rephrase your question


I'm building or rather preparing the ground for a retaining wall 1.5-2m high and some 20m in length to basically support the grey and yellow "lego block". (Final design might be two disconnected L-shapes to deal with N-S and E-W gradient changes whilst working in some sort of ramp/steps for access.) From the base of the existing (but failed concreted) wall there is an immediate perpendicular 7° slope. I've presumed that for greater integrity I should flatten the slope to create a horizontal plain to build the wall up from. My question is how far should the slope be offset away from the base of the wall and is there a point of diminishing returns? (I could go to 4 metres but that's more than double the work than to create a 2m plain.)

Side profile:

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(Legoland got upgraded with a lego oak tree and lego pond.)

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I suppose another question: when creating a dry stone wall where the top is level but base is through undulating or stepped ground, is there a recommended maximum change in height when building the foundation layer? Say across a 1.5m disparity, would it require 2 stepped foundation layers of 0.75m or 3 at 0.5m, perhaps just one?

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Re: 1.5-2m Drystone retaining wall on a slope—surface prep

Postby bloop » Sat Jun 13, 2015 9:57 am

Hello,

Your requests for information regarding a drystone retaining wall are somewhat over complicated. All you or whoever builds your wall needs to remember is a simple rule of thumb. Including the hearting, the depth of the wall from external face to earth bank should be approximately half the envisaged finished height. This means that given your undulating terrain, from left to right the linear form of the prepared bed would vary in depth according to the chosen height line - where the wall will be higher the depth will be greater.

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Don't despair Jerry, you are not alone.
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Re: 1.5-2m Drystone retaining wall on a slope—surface prep

Postby jerryg » Sun Jun 14, 2015 11:46 am

As Bloop I think you are overcomplicating matters.

There is no need to worry that the ground falls away at the base of the wall.

A least 1 third of the walling I do is of walls that go across slopes, sometimes across 60 degree slopes. I have just finished a wall that falls away steeply below the wall for about 3m into the river Duddon.

Here is a wall that crosses a 60 degree slope, it is at Brantwood house near Coniston Lake if you want to check it out.
brantwood a.jpg
brantwood a.jpg (44.29 KiB) Viewed 4488 times

This wall is 3.6m high with a 1m base width decreasing to .7m at ground level, with a 1.5m high wall on top of it. If I had followed the standard width at the bottom is half height, would make this a 1.8m wide base. There is a height at which this rule becomes obsolete. I would say width = half height on works for walls between 1.2 and 2m high. Below 1.2m the wall becomes too narrow, and above 2m the wall is too wide.

I would also suggest that the profile of the wall is not like your drawing. If you prepare the earth bank at the same batter as what is required for the retaining wall, I would suggest that the base of a 2m wall is .7m reducing to .5m at the top.
revetment walla.jpg
revetment walla.jpg (13.25 KiB) Viewed 4488 times


Make sure you have enough throughs that go all the way from the face of the wall and dug into the earth bank. Also make sure that all the face stones are placed length into the wall, and also that no soil is shovelled back in behind the face stones, this will get washed out.

The most important issue you have is to make sure that whoever builds the wall knows what they are doing and will not cut corners.
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