Retaining wall fell, need advice

14 years ago

Hi everyone. Long story short, a large retaining wall in my back yard fell over and spilled into the conservation area behind my house. The reason was ruled as "faulty design", so insurance isn't covering it, and the original builder is long gone (it's 13 yrs. old).

My yard is very slowly eroding, making it's way back to the pool area. I do not have the ~$30,000 (we got estimates) to rebuild the wall.

We are the last house on our street, and we have no rear neighbors or neighbors to the left. Funny thing is, our one neighbor and the houses up the street have no wall, their yard kind of "slopes" back into the conservation area.

So I was thinking I could do something similar. I could get a couple loads of fill dirt, and maybe some large rocks, and start to fill in the area and slope it back. Then maybe put some seed down and just let it grow. How does this sound? It would be kind like you see on the interstate (not quite so high, the original was was maybe 6 or 7 feet high). So my question is will this hold. It has already kind of filled in naturally and grass/weeds have started to grow. But it looks like he*l, and it's really weak, I could go back there and jump and take out a big spot of yard. Oh and one of the contractors we got estimates from said "if you have proper fill dirt or clay this wouldn't have happened"...so it makes it sound like we didn't have the right fill???

I just need a quick fix to stop the erosion, and then one day "if" I have the money I could do it right. I have no experience in brick or mortar, so I think if I try to tackle a wall myself I will make things worse. Any advice would be so helpful. Thanks!

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Comments (5)

rfinnegan
14 years ago
I'm here Los Angeles and there are alot of houses in the surrounding neighborhood that are built on slopes. In addition to retaining walls (many built from "recyled" concrete), houses here use ivy as ground cover/erosion control.

Here's a link to the concrete wall approach http://www.sbbg.org/index.cfm?fuseaction=enews.article&article_id=192

Perhaps a combination of the two?

Good luck.
laag
14 years ago
Grading across a property line is illegal unless you own the other land or have an easement. You are also talking about encroaching on a conservation area.

A wall over 4' high requires a structural engineer's design in almost every state. You have a huge surcharge (pool filled with water) and a wall that already failed. This is very serious. If you don't have the money to remedy the situation correctly. you might need to demo the pool and re-grade the back yard so that it does not require a wall.

It was people taking shortcuts that got you into this mess. You can continue down that path if you want, but the results won't get any better in my opinion. Look for advice from qualified people. Right now you are asking a group made up of mostly home gardeners for engineering advice - does that make sense?
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You will need to dig down so that the bottom of the wall (which is the bottom of the footing) is below the frost line. Maybe a regional forum could help you find out what frost depth is. A footing is like a nice thick sidewalk that is created for the wall to sit on. (8" thickness depth would be good. 6" might be OK.) You're building a retaining wall so keep in mind that it needs to be sturdier than a free-standing wall. A footing ought to protrude beyond the footprint of the wall itself, by about 8" all the way around. So that's a total width of 24". If the present excavation only allows for the wall, you would need to excavate farther into the hill, also allowing for the space occupied by the form work. The wall will not look good if the block slopes. Instead, it should be level and to control it's height, step it down with level changes as needed. The footing would step down, too, as needed, in 8" increments (or multiples thereof) to accommodate the block courses. You'll need to use wire mesh in between courses of block. For heft and strength, I would fill the cells of the block solid with concrete as it's built. (Retaining walls that are under built tip over with time. Also, you will need to embed rebar into the footing which turns upward into the wall itself, locking the two together and helping the wall to last. Search Google images for "CMU wall" and you'll be able to see all manner of examples and details. My instructions are general and you must reconcile them with local conditions.
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Not sure which weird directions you're indicating. People might react to anything in pictures or what is said. Mike, I've been supplying landscape advice here for a number of years. I am a landscape architect with a broad background that includes horticulture and fair amount of experience with commercial landscape management/maintenance. So I've seen the common problems from all angles. You would not believe the percentage of times people show up here and say that they're going to do such and such, and they ask for some clarification about how to go about implementing their intentions. The problem is that there is sometimes a fatal mistake in their original ideas, especially when it comes to design of things. Offering assistance to them without any challenge, so that they can go ahead and commit their mistake -- in a delightfully lovely way, of course -- seems counterproductive to actually helping them. It is a trait of human nature to want to help the less experienced avoid pitfalls that they cannot see coming. My hunch, which I mentioned earlier, is that this MAY be one of those times. I can't say for certain because you're not sharing any information about the landscaping that "is well thought out and ready to go." Another reason that makes it hard to give you the short, straight answer that you're looking for is because you've also shared no information about the structure you're building. We have no idea of its layout. If it's a verbatim replacement of the planter (I hope not), I'd run the downspout drainage directly through the planter, using solid 4" pipe, and a long sweep elbow to make the turn to the outfall at the base of the planter. At the in-ground bottom extension of the downspout, the elbow would turn to orient the discharge, as directly as possible, toward the downhill direction ... the reason being to minimize any turns or circuitousness of the water drainage path. Have the tailpiece end up about 3" or 4" above grade at the outfall, projecting outward about 2" from the wall face. Make sure that the underground piping is running continuously downhill with no undulations that would cause water to climb even briefly. You'll probably need to embed a splash block/flat stone/concrete below the outfall, flush with grade. If the new wall is laid out with much difference from the old, then that might necessitate a different approach. I'm generally a fan of keeping drainage at the surface where it works without trouble. Here, the underground portion is direct and short and I wouldn't want to dump a lot of water in a small planter.
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karinl
14 years ago
It seems to me there must be a regulatory environment in the form of your building codes and the terms of the conservation area that will give you some guidelines to determine whether the option you are considering is in fact legal. Can you tell us what the constraints and requirements are?

Do you know anything about the history of how the neighbours came to have slopes and your house came to have a wall? Do any of the others have pools and if so, how's that working out? In our town a couple of years ago, a pool installed at the top of a steep slope apparently generated failure of the slope, causing a mudslide that destroyed houses below and caused loss of life. Even if you only have a conservation area there, you might be required to pay for the cost of clean-up, and if there is something like a fish stream involved, lawsuits can ensue. Do the conservation authorities know about your wall failure yet?

If you do a new wall, it should indeed be done properly if at all. I shudder to think of the liability issues should it fail, for example under a future owner causing injury.

Or of growing ivy - a noxious weed - into a conservation area.

KarinL
(home gardener :-))
cereber0s
Original Author
14 years ago
Thanks for the replies. To be honest I really don't know much about the history of our place and our neighbors' places, looks like I have some research to do. And I honestly didn't know grading across a property line was illegal. Looks like I'll contact SFWMD and see if they can be of assistance. Thanks.
sunnyca_gw
14 years ago
Can you see where your wall went? What was it made of? if cement blocks they could be cleaned up with chisel & hammer, I did mine after Northridge earthquake, much cheaper than hiring someone to come & haul them away & get a new wall. Of course I mixed cement in wheelbarrow & dad set the blocks. used rebar both in the blocks & across to strengthen it. In your case because it is a retaining wall you have to have a cement base. But if you could retrieve all your blocks you could cut the expense greatly. Might have retaining wall put in with chain link fence on top of it or wood as that would cut cost by probably 2/3 but you need to find out why earth is moving. I know of some swimming pools that have poorly built fences or no fences,just hedge & ground isn't moving just because of the pool. If the fill in your backyard is mostly sand that could cause problems. We have some areas out here in Ca. that are extremely unstable- guess you saw the beachside community that buried number of people few years back. People love a hillside house & every couple of yrs some slide down on top of other houses but they just fill it in & rebuild. Good Luck!

Retaining wall fell, need advice

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