Erosion at base of retaining wall

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Old 01-05-15, 01:28 PM
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Erosion at base of retaining wall

Some erosion at base of 12 foot concrete retaining wall in backyard. House and retaining wall are 28 years old. Retaining wall is built into the hill into two perpendicular sections.

Erosion isn't across the entire length of the retaining wall. It only occurs at two locations of 4 feet long (one in the middle of one side of wall and the other towards to the end of the other side). No buckling, leaning, or cracks in the retaining wall anywhere else that would indicate a structural issue. Pictures attached.

Previous owners have two trees planted at each location of erosion. Had a few questions.

Is the erosion an immediate structural issue? Are the bushes/trees contributing to the erosion, or were they likely placed to reduce existing erosion? I'd like to limit further erosion, but also want to remove the trees (for aesthetic purposes).

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Old 01-05-15, 02:41 PM
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During rainy or wet periods do you notice water coming out from under the wall at the erosion locations?
 
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Old 01-05-15, 03:01 PM
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Thanks for responding. Been a lot of rain lately to observe, but there hasn't been any puddling or run-off from underneath the wall at all. Just moisture as much as I would from the rain itself.

No areas of severe run-off anywhere on the wall or from the drain pipes either. Just normal dripping down the wall and slow dripping out of the drain pipes. The amount of moisture out of the retaining wall is never much more than what is visible in the drain pipes in the picture.

I will say that the drain pipes closest to the erosion appear to be the most active (i.e. the other drain pipes rarely have any observable moisture dripping out). But it usually isn't enough to even reach all of the way down the base.
 
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Old 01-05-15, 03:52 PM
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Even though yours appear small, trees and their roots are capable of doing significant damage to nearby structures. Roots will travel and grow towards most water sources, and your wall's active weep holes indicate it's hoarding a lot of water behind it. Be grateful you don't have cottonwoods, as I have seen them literally tear concrete walls and foundations apart.

The voided areas under the retaining wall's footings indicate that other factors may be at work as well, such as original ground subsidence and even granular backfill material being moved and displaced. Much of the visible, deteriorated concrete appears to be a previous owner's attempt to fill in void areas under the footings using a low-strength, flowable fill product.

In addition to structural repairs needed, a proactive remedy for your wall's problems would be to make an attempt to remove more water from behind the wall, or try to prevent it from getting there in the first place. I'll never forget the first time I was involved with a retaining wall as a wet-behind-the-ears WisDOT bridge engineer, where our bridge crew was drilling a few weep holes in a wall face--water came shooting out of the first hole as it broke through the back of the wall with such pressure that it almost knocked the drill operator off his feet.
 
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Old 01-06-15, 04:39 AM
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not unusual, bdge, when we drill drain holes into lowest course cells of block foundation walls - have seen it shoot out 3' from the wall imagine the damage it does INSIDE the blocks ?

there likely isn't any proper drainage behind this wall - who knows - ie, crushed stone, piping, soil filter cloth,,, absent those, its likely the base will continue to wash out

looked at 1 job yesterday - house faces an uphill slope to the street - no wonder they've got wtr in the bsmt waterproofing's done when the house is built !
 
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Old 01-06-15, 06:12 AM
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It appears the ground level in your yard is 6-8" lower than the bottom of the walls footer. Drainage aside with no support for the soil under the wall it will just erode out into the yard. Over time it looks like folks have shoved rocks and mortared under the wall to try and support it. The yard should probably be brought up to almost flush with the top of the footer. This would provide freeze protection for the bottom of the footer, provide lateral resistance for the wall/footer being shoved sideways and prevent the soil under the footer from washing away.
 
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Old 01-06-15, 08:18 AM
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Thanks for the input.

There is crushed stone behind the retaining wall, as when we moved in some of the crushed stone had been forced through the drainage pipe on to the footer. So even if there was proper fill material 30 years ago, it may not still be there. So maybe the bush/trees were planted to reduce erosion at those locations, but I wonder if they are making the situation worse?

Sounds part of the best solution would probably be to re-assess/replace the backfill material and possible install additional drain pipes, which isn't something I'm likely to be able to do on my own.

If I would tackle it myself without those steps (knowing it's not a long-term solution) am I looking at replacing/re-filling the current gaps prior to then raising the level of the yard itself?

Should an additional footer be installed at the current footer (i.e. dig down at the base and build up the support to provide additional width at those two locations, would almost look like a step) or just re-fill the current gaps prior to raising the yard?

Rookie DIY here so trying to determine if this is something I'd be able to tackle on my own. If this is something best left to a professional let me know. It's definitely not a small retaining wall.
 
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Old 01-06-15, 09:01 AM
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You mentioned that the wall is not cracking, leaning or buckling. Digging at the base or edge of the old footers is probably an advanced maneuver and should be done by a professional. One DIY action would be to cut down the trees near the wall and bring in dirt. Pack it as tightly as you can in the pockets under the footer. Then put down dirt to about flush with the top of the footer and taper it out into your yard so it's easy to mow.
 
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Old 01-06-15, 02:11 PM
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Pilot, is would there be any issue in re-filling any of the pockets with a concrete product before bringing the soil level up? Any sort of additional drain warranted within the new soil?

I figure if I start to see any cracking/leaning/etc. it'll be time to call in a professional. Anyone have advice on the type of professional I'd be looking for? Searching for retaining wall repair doesn't give a whole lot of options in my area (mostly just companies that build new walls).
 
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Old 01-07-15, 12:58 AM
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there's no way any of the ballast/backfill could enter the drainage pipe IF soil filter cloth had been installed to protect the pipe,,, not only that, BUT using the sock enclosed pipe i ixnay,,, sock's too close to the pipe & won't perform efficiently for any decent amount of time,,, just because they sell it doesn't mean its worth a ****,,, we always install our drainage pipes in a 12' x 8" soil filter cloth lined trench

there may not be a compacted granular base under your wall either as that's a fairly recent development in retaining walls - especially since the arrival of the segmented precast retaining wall
 
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Old 01-07-15, 07:59 AM
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I wouldn't try filling the voids underneath with concrete as a DIY. You might shove some under but it would likely slump down leaving a gap and no support for the wall. You could contact a mud jacking company and have them look at it. They could build forms across the face to block the openings, drill a hole and inject grout under pressure to fill any voids.
 
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Old 01-07-15, 02:22 PM
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Well I'll call around to get a quote on the mud-jacking and see if I can get the current gaps filled once the weather cooperates.

Then I'll get those trees out and get some more soil at the base to at least slow the ongoing erosion (which sounds like there's no real fix unless I shell out for full work behind the wall). Hopefully it helps prolong the time on the wall.

Between this forum and the internet I feel like I know more about retaining walls than I ever planned to know.

Whenever the work gets done (likely when it's warmer), I may re-post to get some feedback on the work that was done.

Thanks ya'll.
 
 

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