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I’m a part time builder, but this problem has to do with my own property.
Our house sits approx. three feet above street (alley) level, and along that side of our property that fronts the cement alley there is a 24 foot retaining wall of concrete. It might have been set in there over 80 years ago… don’t know for sure but the house was built in 1912. Anyway — that wall is now deciding to begin a long slow leeeeeeaaan out away from the house. It’s only gained about an inch of lean over the last couple of years .. but it is actually noticeable and is beginning to make me nervous. The wall’s only about 4 inches thick by 4 feet tall … no drainage holes or tie-rods. Is there some kind of old-school RX that might be prescribed to halt the spread of this concrete lollygagging?
Most of what has occured to me amounts to an incredibly labor intensive re-build … but I’m wondering what the ‘pros’ might have to say. Thanks.
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Replies
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Try not to think about it.
*How far is it from the house to the failing wall? That's the key to whether it's an annoyance or a major threat to the structure - or somewhere in between.I have a similar situation, only it's on a neighbor's property. Theirs is higher, and an old retaining wall built right on the lot line is leaning towards me. It's retaining 2-1/2 - 3 feet (sloping), about 34 feet long. Fortunately, it's ten feet from my house, and 30 from their building.Unfortunately, some bozo built a cinder block wall six feet high on top of it - no steel, no grouting. The next earthquake will probably drop all that in my back yard. But it's OK - I don't go back there much.In my case, there's no footing at all under the retaining wall. Amazing as it seems, the bottom of it just sits on grade on my side. Yours also probably has a really inadequate footing. If you want to bring it up to code, there's no sense doing anything but demoing and replacing the wall. On a much smaller one I did do a temporary cosmetic fix by digging a trench on the high side all the way down and then pushing the wall plumb with a bottle jack. But that was only 18" by 5 feet. On something this size, that would be much too dangerous, and enough work that you might as well go all the way and do it right.-- J.S.
*it sounds like the house load is within the zoneof influence.. the retaining wall is failing.. and since it is only a 4 " wall it may not have enough strength that EVEN if it could be tied back with some of the proprietary systems.... the could take the load but the wall would not support the transfer..if you have enough room in front of the wall, you may be able to use it for a one sided pour.. run your tie backs , and incorporate them into the new wall poured in front of the leaning wall....between the house foundation and the 4 ' of upset.. you have a lot of load that has already started to move....get very serious about this... a particularly bad wet season coud destabilize the whole shebang...b hey, but whadda i no ?
*Thanks very much, guys...I'm still mulling and weighing, of course. That's not a bad idea about pouring a retainer on the down side o the lean. The walls around this soggy town (Seattle) that I've seen that look like they are really holding back a LOT of weight and ALSO plumb and solid are ones with periodic 'spines' of upright concrete running every few feet. Difficult to describe but something like upright 'squared columns' that sort of 'counter lean' back into the wall like a chair wedged at an angle against a door. Other than that approach I see a lot of dangerously leaning walls around town. I should have mentioned that I planted some large bamboo in the 'grove' just inside the wall .. I have a dreadful suspicion it may be implicated in the crime. Bummer .. I love the bamboo.The house is only about 5 feet from the wall .. hadn't considered an actual problem with eventual house movement or anything. It's a small house with a cement basement and seems pretty intent on remaining where it was. In our recent earthquake it didn't even wink. Anyway -- thanks again .. I really appreciate the feedback.Aaron
*buttresses... like in a cathedral wall construction...
*Mike >>If you're giving a name to my description .. yeah ... never seen a cathedral wall .. but yeah .. buttresses. They seem pretty foolproof .. like the wall would have to actually 'skid sideways' rather than going over. They should always be built that way -- how foolish is it to just put up a vertical plain against all that enormous pressure over time!? Doing that you gotta then take Rick Louquet's approach as an aftermind.as.
*Aaron,I would bore a short pile, using a 6" post-hole borer, about 3' or 4' from the wall on the inside. Drill a hole in the retaining wall, in line with the pile hole, big enough to take a piece of 3/4" or 1" HT rebar. Weld a 6" x 6" steel plate to the end of the rebar and hammer it through the hole and back-fill and into the pile hole. Put some 1/2" rebar in the pile hole and fill with concrete, well vibrated.While you've got the drill for the hole for the re-bar, drill a few holes through the bottom of the wall for drainage.
*Aaron--How did that little earth shaker affect your wall? For a wall to begin moving after 70 or 80 years means that conditions behind or under the wall have changed. Bamboo might be your problem if you are irrigating it. (Wait this is Seattle.) I would think the first course of action would to relieve hydrostatic pressure by drilling weep holes through the wall at 8' intervals.
*I lived in Seattle for 5 years. Dirt really likes to move in that town. Saw a house pushed into the street by a mudslide on Beacon Hill once. It was a half block from my house. Very disconcerting.Definitely weepholes. I was drilling rebar into a basement on Queen Anne Hill a few years ago for retrofitted footings and when the first hole went through, the water blasted out like a firehose. It took about 6 hours for the water to slow to a point where we could pack in some hydrostatic cement to plug it. The moral of the story is, water has power in your parts.Buttresses are a fine idea if you have room for them. Just make sure you drill rebar into the wall to keep the buttresses from sliding against the wall. Also be sure to dig down to solid soil (not black dirt) for the bottom of your buttresses. Black dirt never quite stops compacting. Ian's idea should work pretty well too. Have fun digging through the bamboo roots.
*These are some great ideas and I really wanna thank you guys. Ian, you paint a perfect step by step of how to proceed, thanks!Mike .. I was -- most unfortunately -- in Asia when the biggest quake in 50 years hit Seattle. When I heard about it I was crestfallen ... you can plan on attending a total eclipse or the aurora borealis .. but a quake is unforseeable ... I missed a stunning wonder of nature. But you're right, something doesn't begin moving after 75 years without a change of circumstance. The quake's not to blame cuz I noticed the changes before I departed and they grew no worse in my one month absence. I really am now thinking that I have to admit that my much cherished bamboo is the culprit .. I just refuse to go after it with a crowbar and shears so I'm going to have to find some sort of compromise. But if you ask what's changed since the movement began ... it's gotta be the beautiful, big, bold stand of giant bamboo. I'm so sorry to admit that. Weep holes sound good ... except that the opportunistic bamboo would force it's way through!Thanks again for all of the sound feedback! (Maybe I'll just sell the house.)AS
*Aaron --I thought of something else to worry about. It sounds like you have two parallel (or at least formerly parallel) walls: the retaining wall, and the wall of your basement, with the dirt and bamboo roots between them. If you strengthen the retaining wall enough, perhaps the basement wall will become the weakest link. Maybe the way to go is something like Ian's tieback idea, only with the horizontal holes drilled all the way through both walls so they're tied to each other. Or perhaps I'm not understanding the geometry here correctly.-- J.S.
*regarding your bamboo I had to use a chainsaw to cut up the huge mass of tightly interwoven roots to solve a similar problem. inadditon to drain holes I would fill a 6'' wide trench of gravel behind the wall to promote the drainage... Dennis
*I was going to mention keeping an eye on the foundation also, but that being built as a unit will probably be able to take on any little bamboo.Retaining walls just stand on their own merit, and should be leaned into the hill to resist, as long as possible, soil creep. A 4" x 4' x 24' retaining wall has a lifespan, and it looks like yours is right there. The bamboo may have pushed it over the edge, but it sounds like you guys have some very plastic soil over there, and even the small load on the wall did it in. I like the ideas above, but keep in mind that the wall could be gone in a morning. You could then construct something stable and appealing for not a whole lot more than the fixes, tie it back into the soil, backfill with a drainable material, and maybe have an excuse to buy new tools. You need to decide if the house is worth it.
*Thanks again, guys.Please send money.as
*The check is in the mail, Aaron...
*Aaron--If you replace your wall there are two types of concrete walls to consider. The cantilever and the gravity retaining walls. A cantilever wall consits of a spread footing with the retaining wall on top. This requires re-bar placement and engineered drawings by a licensed engineer. The gravity wall is built with the bottom of the wall thicker than the top. (The back tapers in thickness from the base to the top.) My building bureau has a presribed plan for gravity walls that (if the steps are followed) eliminates the engineering requirement. Basically the thickness of the base resists the overturning moment of the top of the wall and eliminates the need for a footing. Each type of wall requires drainage holes to eliminate the hydrostatic pressure of ground water.Was that a total eclipse? I was amazed how pitch black it was during the one we had twenty years ago. I thought it would just get dark like at dusk. But it was dark!
*MIke >> I was just remarking that one can plan well in advance to see an eclipse ... but that a quake is unpredictable. I was sad that I missed such a stunning event. Once in a lifetime sort of thing.However ... I DID see that total eclipse some 20 years ago that you refer to. But I was at a fairly cloudy location so it was a great disappointment. When we looked up we just saw planes with adverts on them since the local advertizers knew that everyone would be looking up just then so they 'took advantage' of it. Vulger commercialism.There was a site fairly nearby where we were where thousands of people gathered in hopes of a clear morning. It was totally cloudy there as well UNTIL THE MOMENT OF THE ECLIPSE! ... then the clouds totally parted for the duration of the event ... then re-covered the sun again when the eclipse had passed. This was a mindblower .. but true as can be.as.
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I'm a part time builder, but this problem has to do with my own property.
Our house sits approx. three feet above street (alley) level, and along that side of our property that fronts the cement alley there is a 24 foot retaining wall of concrete. It might have been set in there over 80 years ago... don't know for sure but the house was built in 1912. Anyway -- that wall is now deciding to begin a long slow leeeeeeaaan out away from the house. It's only gained about an inch of lean over the last couple of years .. but it is actually noticeable and is beginning to make me nervous. The wall's only about 4 inches thick by 4 feet tall ... no drainage holes or tie-rods. Is there some kind of old-school RX that might be prescribed to halt the spread of this concrete lollygagging?
Most of what has occured to me amounts to an incredibly labor intensive re-build ... but I'm wondering what the 'pros' might have to say. Thanks.