Upright sleeper retaining wall

Discussion in 'Landscaping and Outdoors' started by Charlie Lockhart, Jul 18, 2022.

  1. Charlie Lockhart

    Charlie Lockhart New Member

    Hi all,

    I am a gardener, with some landscaping experience, and I have a client who would like a small terraced area part way up their steep garden so as to give easier access for gardening. I terms of design, I think a curved upright sleeper retaining wall would be best, however I have never built such a retaining wall. From my research I have come up with the attached construction. As I understand it, ideally 1/3 of the height of the sleeper should be in the ground, I expect the maximum height of the sleepers above ground to be 500mm, so I expect the depth of concrete to be 250mm.

    Is this is a good design? Would this give sufficient drainage? Is a depth of 250mm for concrete excessive?

    Any guidance would be much appreciated.

    Attached Files:

  2. Abbadon2001

    Abbadon2001 Screwfix Select

    might be worth looking at the plastic sleeves used for fence posts to give the sleeper maximum life underground, although i'm not sure they make them in sleeper sizes, but they seem to offer up to 200x200 in the square which could prob be manipulated, or go for the sheet product they make for use with sleepers in horizontal and use it a slightly different way... https://www.chilterntimber.co.uk/pr...s heat applied to,the timber cracks or splits.

    I would expect it would be key to make sure the 1/3 is all within the concrete, not just sub-soil.
  3. stevie22

    stevie22 Screwfix Select

    I would go rather deeper if you have a slope as you've drawn. There is very little soil on what we term the passive side of the wall to resist movement.

    Do you mean sleeper sleepers or the sketchily treated lumps of softwood sold as landscape sleepers?
  4. Charlie Lockhart

    Charlie Lockhart New Member

    Thanks I will have a look into protective sleeves.
  5. Charlie Lockhart

    Charlie Lockhart New Member

    The slope is roughly a rise of 1 meter over every 2 meters. Given this incline, how deep do you think I would have to bury a sleeper that I want to be 50cm above ground? I wonder if I could concrete some of the sleepers in particularly deep, as if they are posts, and fix adjoining sleepers to them using heavy duty brackets?

    With regards to the sleepers, do you mean, will they be hardwood or softwood? If so I am not sure yet, I realise that hardwood would last longer than softwood but the cost might be too high for the client.
  6. Truckcab79

    Truckcab79 Screwfix Select

    They’re called Postsaver sleeves. Use them on all my fencing. There isn’t a size to fit sleepers but they sell ‘tack and wrap’. Essentially the same thing on a roll so can be used any size.

    I’d be inclined to dip or paint them in bitumen personally. I’ve got one booked for next Spring. 250 sleepers. Current ones (not by me) have only lasted 6 years and are completely rotten. Very difficult to make them last if any soil at all is against them.
    Abbadon2001 likes this.
  7. Truckcab79

    Truckcab79 Screwfix Select

    Without wishing to sound patronising don’t underestimate the cost of doing this properly. Looks simple. Actually very expensive to do well and so it lasts. If they can’t afford to do the proper version then I’d walk away. Otherwise they’ll be back in a couple of years asking you to replace it all because it’s neither rotten or falling over.
  8. stevie22

    stevie22 Screwfix Select

    I would want at least 1m in the ground if it was mine and I'd want to be using proper sleepers (ie well and truly pickled) to stand a chance of lasting.

    I think Truck has the right of this one: walk away. Or ask them to get an SE to design something which you can price and build with a clear conscience if they are sensible.
    ramseyman likes this.
  9. Truckcab79

    Truckcab79 Screwfix Select

    I know it’s annoying to ask a question and then just be told a load of reasons why you shouldn’t do it so to your original question.

    I would have a minimum of the above ground height below the ground.

    Set into concrete like you would a fence post. Not sat on concrete like your sketch.

    Bitumen rather than sleeves. I love them but they add a bit of width and you’ll have horrible gaps.

    If you want to use galv strap don’t use the rubbishy ribbon stuff that you repair fences with (well, I don’t, but you can). You need 4mm bar minimum. Drilled and securely fixed twice to each sleeper. Overlap at joins.

    Avoid Wickes or any DIY place for ‘sleepers’. Lawsons are good. Their Oak ones are even better. Or any decent landscaping supplier. Reclaimed will have been soaked in creosote for years but won’t look crops. Adobe hardwood even better if you can find them.
  10. Resmond

    Resmond Active Member

    If going a metre underground might work out cheaper to build a concrete block retaining wall then front it with sleepers
    Abbadon2001 likes this.
  11. Charlie Lockhart

    Charlie Lockhart New Member

    I'm not sure where to start with building a concrete retaining wall. What type of block would you suggest, bearing in mind I want to achieve a curved wall.
  12. Charlie Lockhart

    Charlie Lockhart New Member

    Ok, thanks for your guidance. I feel like a small deck faced with sleepers might be more feasible.
  13. Charlie Lockhart

    Charlie Lockhart New Member

    This is all very useful, thank you. One thing I am concerned about, is the potential for the trench to collapse, especially such a deep trench and at such a steep incline (1 meter rise over every 2 meters).

    I also feel like an easier option may be to construct a small curved deck on the side of the sloop and face it with sleepers.
  14. Truckcab79

    Truckcab79 Screwfix Select

    Totally different look of course but certainly easier to construct and probably cheaper for client too.
  15. robertpstubbs

    robertpstubbs Screwfix Select

    You could concrete steel posts (maybe RSJ) into the ground. Then fix horizontal bars between the posts. Then bolt vertical sleepers to the horizontal bars.

    It would be possible to build curves or angles into the horizontal bars.

    If the steel is suitably protected it should last well. Rotting of the sleepers wouldn’t have too much impact on strength and in any case they would be fairly easy to replace.

  16. Resmond

    Resmond Active Member

    tbh not really my area, id imagine 7n solid concrete blocks 9” so 2 blocks deep, curved can be done and will add to the strength but adds to labour time..
    I think your rethinking of a raised deck is a sensible compromise if they go for it but might require PP depending on the height of the deck
  17. stevie22

    stevie22 Screwfix Select

    1 in 2 is a steep slope so any kind of a structure is going to need to be keyed into the ground to stop it sliding away.

    Your deck would be only 600 wide before it gets to 300 high and into planning territory.

    Robert's idea is good or you could go a step backwards and use a "Berlin" wall. All this needs is a set of UBs or UCs set in the ground and sleepers dropped into the web. Would give a bit of an industrial look.

    Whatever you do do not take on liability for design (some sketchy geezer on t'interweb suggested...).

    What you are looking at with your initial sleeper on end of the above is a cantilever retaining wall which can fail in several ways: it can break, it can rotate or it can move sideways wholesale.

    A simple model is to picture the wall and draw a line30 deg off vertical on the high side, This wedge will try to slide downwards pulled by gravity and to do this the wall has to move. This is called the active wedge. For the wall to move it has to displace soil on the low or passive side. We normally take a line at 60 deg to vertical here. There is friction on both wedges both of which help to hold them in place and gravity helps the passive wedge. It the becomes a matter of balancing forces and moments (turning effects) to keep the wall stable. The angle varies according to soil strengths but 30 is a fair average. Now put your slope on and see how much bigger the active wedge is and how the passive has diminished. Hence you have to go much deeper to find stability.

    Gabions could be a way forward fo you: easy and quick and inherently flexible,
    robertpstubbs and Abbadon2001 like this.
  18. Charlie Lockhart

    Charlie Lockhart New Member

    Thanks for the suggestion. Do you have any guidance on how deep the RSJs would have to be concreted into the ground?
  19. robertpstubbs

    robertpstubbs Screwfix Select

    I can’t give precise guidance, but it would depend on factors including the distance between the RSJs along each terrace, the number and spacing of terraces, and the type of soil and whether it has been disturbed.

    Stevie referred to the active wedge and the passive wedge. With spaced RSJs the passive wedge is concentrated round the RSJs rather continuing across the whole terrace.

    My gut feel is that there should be twice as much concreted into the ground as the height of the terrace, but I’m only a “sketchy geezer”.
  20. Truckcab79

    Truckcab79 Screwfix Select

    That’s essentially my method, 2/3 in 1/3 out. In my non-engineer head it makes sense if the half way point isn’t above ground so that the pivot point is always below. Probably has no validity to back it up whatsoever but it seems to work.

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