retaining wall construction

taraz579(6)March 21, 2010

Hi, I wasn't sure where to post this, my name is Tara & I'm new here.

My fiancee & I want to plant a rather decent size veggie garden this year (approximately 10'X30') but the catch is it's on a hill. Probably about a 12 foot drop, within about 18' of length, so not too awful steep. That said, we are going to (attempt, rather) level off most of this incline (the majority of our one side yard) and have soil/fertilizer and what-not delivered. However, we need something for support.

Thus, we've been browsing stones for a retaining wall at the bottom. Does anybody have any experience with such a set-up? My father seems to think such a wall will need support inside the single layer of bricks/stones that also form the outer/decorative edge of the wall. Any thoughts on this? (I trust both my fiancee & my father...they are both very smart and constantly exceed my expectations with projects, etc)

My father also made the suggestion of using railroad ties instead. I would like to use these, IF they will hold up & last. I just like the more country/simple look of wood, versus stone, as we will have a stone patio only 15 feet away. Does anybody have any experience with RR tie walls, with such an incline & pressure behind it?

Any other ideas that I haven't considered?

thanks a bunch & have a great day!

tara

happy gardening :)

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terrybull

how high is the wall going to be?

    Bookmark   March 21, 2010 at 10:59AM
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taraz579(6)

we're guestimating 5 feet.

    Bookmark   March 21, 2010 at 11:02AM
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dcarch7

what's your location? weather zone?

post a picture willl help.

dcarch

    Bookmark   March 21, 2010 at 12:38PM
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dan_staley(5b/SS 2b AHS 6-7)

I used to have a landscape design and construction business and usu. did at least one retaining wall/tall raised bed a year, and for our house I chose Allan Block for our raised bed, the Ashlar Blend, as it doesn't look like the cheap ugly cr*p you see everywhere. Our yard is sloped as well and our bed has three height changes, you can see the high part (34"), how you can curve it , height changes . I can upload more if you need them.

For 5' height this product will definitely work and you can do it without hiring a contractor (and your marriage will be strengthed!!!!! from working with heavy objects for a long time ;o) ). I suspect however your jurisdiction requires you to pull a permit for that height, as the pressure behind that wall will be tremendous in that zone and presumed moisture regime. You may need a geogrid behind the wall to alleviate some pressure, and if you do it yourself with no permit I'd definitely recommend it. This product allows for rebar and that's probably needed for that height, esp if your husband will be walking on the wall for garden maintenance. I'd also do a drain behind at the base, so that is a cost as well, but for any block/rock wall you'll have a cost. Poured conc you'll definitely need an engineer's stamp, so block is the way to go IME and Allan Block was the most attractive for us.

I'd avoid railroad ties at all costs. They will not support 5' for long, will deteriorate, will weep creosote, and look bad in 2-4 years. Landscape timbers are little better, save they don't weep creosote. Spend the money and do block. There is no design reason to avoid a stone wall just because there is hardscape nearby.

An alternative is to do boulders or dry-laid stone. I have a buddy who did his large yard in dry-laid that he got free from a quarry, and it looks very fine, but took him a long time and there is a learning curve. But I was there this past Feb. and his yard is very attractive.

Dan

    Bookmark   March 21, 2010 at 12:38PM
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markmahlum

taraz,

I'm doing the same thing that you are- leveling a 35% slope for a greenhouse and 36 foot square raised bed garden. I built a 45' long retaining wall last fall using a poured concrete footing and split face block of a color that matches my rocky-clay hillside. It changes from six feet high at one end to 2 feet at the other. The footing is 4' wide at the 6' high end and becomes narrower as the wall height becomes shorter. The lateral forces against a wall are surprisingly large and an inadequate footing will result in a "tip-over".

But first, talk to your building department. Often, walls of 4' high and less are unregulated. Even a retaining wall of large boulders needs to adhere to a strict design, or a failure is likely.

I still have a good 2' of snow on my leveled garden site so a picture wouldn't show much except that white crap that won't melt this year. Maybe later.

Regards,
Mark

    Bookmark   March 22, 2010 at 10:22AM
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huisjen(z5 ME)

I used to build retaining walls semi-professionally using busted up concrete sidewalks. Here are some rules of thumb:

Make the wall at least twice as wide at the base as it will be high.
Put the starter course below ground.
Lean everything evenly into the hill.
Remember that on the inside of the wall, soil on top of stones holds them down, and that's good.
Wear a weight lifters belt, not one of those silly elastic warehouse workers things.
Get good gloves.

Two 2.5' walls will use much less stone (and labor) than a 5' wall.
Look up "Cornish Hedge" and look at some of the pictures. A cornish hedge is a wall made of two retaining walls with a little dirt in between, and they last for centuries.

Dan

    Bookmark   March 23, 2010 at 7:59AM
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dan_staley(5b/SS 2b AHS 6-7)

Such broken concrete walls as Dan describes are commonly seen in Seattle area.

Dan

    Bookmark   March 23, 2010 at 6:55PM
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