Washout through retaining wall

Discussion in 'Hardscaping' started by PaproskiLandscaping, Jan 31, 2008.

  1. PaproskiLandscaping

    PaproskiLandscaping LawnSite Member
    Posts: 39

    So here is the problem:
    About five years ago (on an account I have had for the last year), the previous LCO built 3 tiers of large stone retaining walls. He then back filled them with fill. They look pretty good and have not moved, but because he only used very large rocks there are sizable holes in between. During a heavy rainstorm the water runs behind the wall and washes fill through the wall and onto the turf.
    The customer is definitely interested in mitigating this in some way, but short of tearing down the walls and rebuilding them with smaller rocks, drainage and landscape fabric, I cannot come up with a quick fix. So my question is has anyone else ever run into a situation like this, and what have you tried to fix it?
  2. ChampionLS

    ChampionLS LawnSite Bronze Member
    Posts: 1,066

    Whether you build a retaining wall from Segmental Block, or natural boulders, there needs to be a drain field behind the wall to capture water and drain it away. The only way to fix your problem would be to excavate behind the wall down to grade (equal to, but NOT below grade) and install a drain pipe. You can use perforated ADS pipe, or regular perforated PVC pipe. PVC pipe has hole only on one side so those holes MUST face down. Since your using boulders, you'll need to cover the backside with geotextile fabric and back fill with clean stone. You do not need geotextile between the stone and your retained earth, but should cap off the drain field with geotextile just before reaching your final grade. This prevents organic soil from washing down through the top and clogging your drain field. The drain pipe must pitch away from either side of the wall and exit to daylight.

    When building a wall using SRW blocks, never use clean stone for the base. This must be solid non-impervious stone right up until exposed grade at the base level. You install your drainpipe at this level, and continue with clean stone from that point up. You do not want to allow water to saturate below grade (below the drain pipe too) and wash out under your wall.
  3. BrandonV

    BrandonV LawnSite Platinum Member
    Posts: 4,228

    maybe put a birm with a french drain a little further up the hill (before the walls) to catch the runoff before hand? pics would help.
  4. LB1234

    LB1234 LawnSite Gold Member
    Posts: 3,210

    Thinking outside the box a little...not that it really 100% solves the problem. But..it is a quick fix to the washout problem.

    Get a bunch of plants that grow well between rocks and are drought/heat tolerant. Some chicks n' hens, rock jasmine, stonecrop, creeping juniper, etc. This should help a lot with the washout and help stabilize the soil. Water will still get through but the washout won't be nearly as bad. You'll basically be fixing the problem by softening the walls and adding some interest and color.

    good luck:waving:
  5. ChampionLS

    ChampionLS LawnSite Bronze Member
    Posts: 1,066

    Here's your hens & chics... going down the river!...:dizzy:

  6. LB1234

    LB1234 LawnSite Gold Member
    Posts: 3,210

    I read it as stone being natural stone boulders.

    He claimed they haven't moved and he wanted a 'quick fix'. Adding vegetation will help with the erosion quickly. Fix it permenantly...no.
  7. leaflandscape

    leaflandscape LawnSite Member
    Posts: 241

    But the waterfall of soil effect is kind of nice too!
  8. simsstonesalesman

    simsstonesalesman LawnSite Member
    Posts: 3

    If the option exists, add steps to the wall and channel the runoff to that area. You still need to deal with drainage on the other two sides.Consider a swell on each side to divert the water away from your wall.
  9. mrusk

    mrusk LawnSite Gold Member
    Posts: 3,260

    There is nothing wrong with using 3/4 clean stone as retaining wall base.
  10. ChampionLS

    ChampionLS LawnSite Bronze Member
    Posts: 1,066

    The only time this would be permitted would be in a shoreline retention project, and a job like that is totally different than any inland design. When building a wall, your base, back fill behind, and inside any hollow units must be soild 2A Modified. You want non-pervious material there right up until the grade of the property in front. At the same time, this is at the point you place your drain pipe and clean stone for drainage.

    IF you were to use clean stone for the base layer of any wall project, water will fill up BELOW the drainpipe and wash out under the base course of block.

    Here's a PERFECT example of water undermining this retaining wall, because the contractor used clean stone instead of non-pervious base material. :cry:

    It won't be long before this wall settles and becomes unstable. For those of you who have stood at the beach when a wave washes over your feet..same thing...the sand washes out and you sink.


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