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increasing sleeper retaining wall life

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  1. #1
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    Default increasing sleeper retaining wall life

    Hi All.

    This is my first post, but spend LOTS of time reading posts on this great forum!!!

    I am building a 40m retaining wall, not very high, between 0.4 to 1m high. Want it to last for a long time, and be cheapish. Planning on using 100 UC 14.8 H-Beams at 2.4m intervals, with treated pine. OK, H-Beams are not that cheap, but last long. The question is how do I get the treated pine to last long? Ideas I have are:

    1) Put plastic sheeting behind sleepers before filling with pebbles and soil. Will have agi pipes coming out under each sleeper of wall at 2.4m intervals. The back of the wall is bush, so not an issue if it doesn't look to great with agi pipes. This way back of sleepers should not get wet, and should have plenty of drainage to get rid of water.

    2) Possibly paint back of sleepers with that thick black waterproofing stuff. Not sure what you call it, but used it for back of besser block retaining wall once to waterproof it. Will this increase life of sleepers?

    3) Another idea is to maybe place sheets of fibre cement behind sleepers before filling with pebbles and soil. Will this be a good idea, increase life of sleepers?

  2. #2
    Soldiers Earned Your Right To Free Speech watson's Avatar
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    G'day,
    Is the black gunk called Pabco Hydroseal??
    The boys will be along soon, so have fun in here ....and again Welcome.

  3. #3
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    Default

    Haven't used them yet, but are planning on using them for a job very soon:

    http://www.modularconcretesleepers.com.au/

  4. #4
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    2400mm is to far to span treated pine sleeper on edge (they will warp and buckle), for the heights you mention would used treated pine posts @ 1200 centers. This way you can stagger the sleepers in the wall giving more strength.
    Paint all cuts (use sealer designed for this purpose)
    Use geo fabric behind wall, (wont make it last any longer, just stop silt comming through wall), using sheeting will shorten life as moisture will be retained in the sheet
    Wall if constructed properly should last 20 years min (buy quality sleepers)

  5. #5
    rrobor
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    Yep that drain is needed. Here in clay your wall would be pushed over if you dont have a drain and some form of buffer between the clay and the wall. In summer clay shrinhs as it dries out , the odd shower fills the cracks with clay dust then in winter the bank gets wet and swells. It can lift huge boulders that way so your wall would not stand a chance. For me I would tar your sleepers on the back, run an aggi pipe along the back then fill with gravel. At a few cm from the top you could add some nice soil if you wanted to plant, to hang over etc.

  6. #6
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    Default Timber sleeper wall

    The jury is out on treated pine in ground (hasn't been around long enough), but if you are going to use it, IMO:
    1. Treat the end grain with an additional treatment, such as black gunk (the techical term). May help, can't hurt;
    2. Create real good drainage (use standard agg pipe covered with liner, lots of fall);
    3. Backfill with large agg (10-20mm or so, not smaller; recycled is fine)

    With any luck, you'll be an old man before the people-who-buy-it-from-the-the-people-you-sold-it-to have to worry.

  7. #7
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    Treated Pine been used in landscaping for over 25 years in OZ and 70 years in the States, As i said buy quality and you be fine

  8. #8
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    Thanks a lot for all the very useful advice! I like the concrete sleepers, but they seem to be very heavy, and getting them all to the back of the house might stuff up my back even more. I think 20 to 30 years for timber sleepers will be fine. With the metal post, even if they rot, the posts will still be there, and should not be too big job replacing sleepers - but hopefully that will be a job for the next generation . I think I will put that black gunk on the back of the sleepers as suggested, with heaps of gravel.

  9. #9
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    Make sure you buy quality sleepers treated correctly, do not cheap out. I tend to look for dark green sleepers , not the light tan green ones as I have found they are not treated as good. ( This method can vary)
    We have removed/repaired many retainer walls over time and found rot in less then 10 year old sleepers. If you want to spend a little more you can order in H5 treated sleepers to be sure . It seems some suppliers claim to be treating to the right rating but it's just not penetrating enough , and these sleepers are often the cheaper ones.

  10. #10
    Old Chippy - 4K Club Member
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    A 3-month old post, but who's counting . . . the job's no doubt done already.

    In any case in-ground should always be at least H4, and H5 is the minimum for structural use in-ground - and that includes a retaining wall.

    The jury is not out on these as one of the posts suggested - the life expectancy is known from more than 70 years of field use and more than 50 in Australia (and yes, with varying preservatives) and various stress testing procedures that place the samples used under simulated and extreme conditions that allows great confidence about the expected life of the different rated treatments.

    For H4 and H5 treated pine the expected in-ground service life is >100 years.

    A few basic rules apply - for example, anywhere you cut into the timber so you disturb the outer preservative layer continuity (ie: if you shorten a piece or notch it out) you need to re-coat with the appropriate preservative to retain the longevity. Plenty of info by searching this forum and googling too.
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.


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