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Retaining wall construction advice

Posted by reinharr MN (My Page) on
Tue, Mar 13, 07 at 16:08

I want to build a 24" retaining wall, about 40' long, as cheap as possible. Advice needed please!
The grade at my house is about 30" above the grade at my property line, which is about 8-10 feet away. This means there's quite a bit of slope.
I want to fill this in to have a relatively level platform for parking trailers, RV's, etc. I will have to build a retaining wall near the property line to accomplish this. The height will range from zero to 24". Since this wall will not be visible to anyone (hidden by a fence, to be built just inches away), appearance is not a factor - only cost and longevity.

So my options are:
1) 6x6 timbers (pressure treated?), supported by wood posts sunk 3-4 feet in the ground?
2) railroad ties, supported the same way
3) steel, supported the same way (or perhaps with concrete and galvanized fence poles).
4) Other?

I'm leaning towards the steel plate. I have access to the steel cheap, I just don't know the required dimensions. Obviously it would have to be 30-36" wide (some buried), but what about thickness? Would 3/16" work or would I have to go heavier? Heavier might be a better option, maybe I could space the posts wider apart, or is there some standard distance to use with a wall this height?


Follow-Up Postings:

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RE: Retaining wall construction advice

Will you ever want to drive or park a vehicle on the 10ft strip?


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RE: Retaining wall construction advice

I plan to park a camper trailer there in the future, not a huge one, perhaps 20' at the most.


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RE: Retaining wall construction advice

  • Posted by laag z6CapeCod (My Page) on
    Sun, Mar 18, 07 at 22:47

I agree with PL. A 10' wide parking space with a house on one side and a 2' drop on the other is a recipe for disaster, if you plan on parking an RV (or a car). That having nothing to do with whether the wall is strong enough or not, it just does not have a safe width. A typical parking space in a parking lot is between 9' and 10'depending on local ordinance. Remember that the cars on either side are not on the parking stripe. There is a psychologic response of moving away from walls that makes it more likely that someone will go over the wall. The vehicle would fit, it is just not wise, but that was not your question.

Vertical posts in front of a tie wall is not a strong construction method. You should google "deadmen" (a term for a reinforcement method, not a sarcastic remark - not that I am above those)and "timber retaining wall" to learn better techniques.


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RE: Retaining wall construction advice

Perhaps my estimate ow 10 feet wide was low. I don't have the measurements, perhaps it's more like 12-14 feet. It's definitely wide enough to comfortably park any vehicle.

You're suggesting that a post-supported wall, even 24" high, is not going to be very strong? I will have to look into deadmen (I do know the technique). I was really hoping there would be a way to build this using steel plate - I don't think I can support it without posts on the open side.


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RE: Retaining wall construction advice

I think I would pass on doing the wall of steel. Refer to the drawing below.

You start with steel panels and posts all in a straight line. Then the weight of soil and the added force from vehicle weight causes the panels to bow outward. Even after the vehicle is moved the shifted soil will hold the panels flexed and this will place a constant force on the posts. Now when the vehicle is positioned by a post, that post must bear the lateral force of the retained soil, the force of the flexed steel panel, and the added force of the vehicle weight.

The result can be a post that makes a slight shift. This relieves the bow in the panels and all is back in a straight line, but the wall is no longer vertical. the cycle will then be repeated.

Each cycle will be too small to see or measure but in the end the wall will lay over. If you beef up the posts to carry the loads without shifting, the cost is going to get out of hand.

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RE: Retaining wall construction advice

I've never installed a retaining wall supported with posts like you proposed- but I've removed and replaced several with more traditionally constructed walls.

A good starting point is looking for typical wall details- counties will allow you to get a permit with just a sketch and a note stating you'll follow their wall details because their specs are safe for most circumstances. Here's a set I use frequently:

http://www.fairfaxcounty.gov/dpwes/publications/retainingwall/details.htm

Dave


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RE: Retaining wall construction advice

A 2' landscape wall would not necessarily have alot of weight behind it, but because you plan to park there the wall needs to be able to support a portion of the wieght of the vehicles.

If you use rr ties, I would defintiely use some deadman.

You could also use keystone type interlocking block retaining wall. And I think if you talk a Keystone sales rep, he will probable layout a design including tiebacks for you. (its a pretty small job... but the blocks may be out of your budget)


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RE: Retaining wall construction advice

Have an engineer do the drawing to account for the load of the parking space. You may need geogrid soil reinforcement. Versa-Lok offers free engineering assistance for questions like this about their walls. They've always helped me out in a pinch. 800-770-4525.

Here is a link that might be useful: Versa-Lok


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RE: Retaining wall construction advice

Not sure about this, but I think I recall reading that the weight of traffic on a road radiates out at a 45 degree angle. IF!!!, that's true, the weight of the parked vehicle would only press on the wall if it were parked within 2' of the wall. (Don't know if it's best to include the footer depth with the wall height or not for this - if the vehicle surcharge shouldn't press on the footer, it would need to parked farther from the edge, depending on your fotter depth.) This may all be wrong but it might be worth looking into. I can't find the reference now, so maybe someone told me this. Even if this is true, you still might not factor it in as you'd need to be sure you don't drive too close to the edge - in which case the wall would need to be designed to withstand the vehicle parked right next to the edge. I think I'm rambling; sure sign I don't know what I'm talking about.

Bill


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RE: Retaining wall construction advice

I hate to be flipant but it seems like theres a lot of hipe over a simple 2 foot retaining wall going on here. I have bult many retaining walls up to 8 feet high with everything from rock to timbers and 2 feet just isnt that big. You dont need engeneers or anything. The Keystone type blocks that are designed for such a thing would work great. 6X6 tibers would also be great with "Deadmen" every 6 or 8 feet. A deadman is a timber layed under the actual load bearing surface that ties into the wall. Like a T in the wall. You lay down the first course of wall on well compacted gravel atleast 6 inches or more deep with a good drainage direction. Then you rebar that,or the next course with it, in to the ground with 3 or 4 foot rebar.You lay the deadmen perpandicular to the wall and 6 or 8 feet long. You spike rebar them in at the wall and under the parking pad. Add a course and offset the next set of deadmen. Rinse and repeat. Make sure its all well compacted. IF you want you can set each course of the wall bacl a half inch to create a backward lean into the load area. Make sure it drains and your in buisness. Railroad ties are lame and environmentally unsound. If you want to use 3/16 steel put Upright pipes in concrete every 2 feet and 4 to 5 feet deep. You can also create steel or wood deadmen to weld or bolt to the retaining wall. I would think 6x6 treated timbers would be better but if steel is cheaper for you and yop can weld then just make it bomb proof with 2 or 3" Posts in concrete and deadmen to prevent flex. Good luck, hope all goes well.


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RE: Retaining wall construction advice

I have a retaining wall that was built wrong. It is starting to bow the 2x6" boards that were used to build it with. It's only about a year old so I hate to tear it all out because it is the retaining wall for our parking area, and in about 5' tall. Can't I build another retaining wall right behind the first one? Drill large holes in the old wall and use screw in anchors as dead-men, building the new wall with a lean toward the old wall, start with a good footing install a good drainage system and then fill the center of the two walls with cement?
And help please.
Thanks
Willie
willie@toledoconsultingservices.com


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