Soil Erosion Near Blukhead Repair

sledgeNLMay 6, 2014

New home owner here and short story is, there is a concrete pad by the retaining wall of our lake house. The soil began eroding from under it due to run off from rain coming down some steps from the house. I've just now started the process of breaking up the concrete to get an idea of the damage. The problem is, what do I do now? I'm thinking of digging it out some to make the hole more uniform and laying down Polyethylene Woven Geotextile Fabric, tossing some concrete rocks on it, then filling it with dirt, then adding some sod to hold the soil. That doesn't solve the problem of the water flowing onto the area. Perhaps a French Drain? Thanks for the help, we are new to owning a lake house!

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sledgeNL

Pic

    Bookmark   May 6, 2014 at 4:48PM
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yardvaark

That is some VERY THIN looking concrete. Do not understand your idea of patching concrete with sod! It needs concrete repair. But I don't think anyone can help you with such an incomplete knowledge of the existing conditions. French drain? What would be the point of that be if there is a lake 2' away that can accept any amount of water? Looks like you need thicker concrete everywhere ... 4", not 2". Maybe you could tamp in a solid base (at the excavation) and then go over the top of the entire slab with a decent thickness.

    Bookmark   May 6, 2014 at 6:33PM
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sledgeNL

So you are saying that the concrete slab is structural? It does not continue the length of the bulkhead, there is grass on the sides. I've outlined the concrete are in the pic.

    Bookmark   May 7, 2014 at 8:22AM
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marcinde(7)

When I do a seawall, I say "have your engineer send me the specs of what I'm to do." I recommend you do the same.

    Bookmark   May 7, 2014 at 8:44AM
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sledgeNL

I'm a bit confused, I don't want to do any work to the bulkhead/reaining wall, I want to replace the missing soil, and help to ensure it doesn't erode away. I don't believe the concrete pad is structural, it's not thick, and only overlaps the top of the training wall. Am I missing something?

    Bookmark   May 7, 2014 at 11:36AM
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yardvaark

I am saying that the entire slab is too thin. It can't help but crack in multiple places because of that. Water that enters a crack at the surface and penetrates below the slab is bound to find a way out (through the lake wall) eventually. Over time, it carries sediment (which is holding up the thin slab) away. Eventually, it forms a cavity or subsides. As the support for the slab evacuates, the slab cracks further.

Fill the hole with solid material packed in hard. Pour a whole new slab -- that has reinforcing and is 4" (nom.) thick. How you prepare for a new slab depends on if it will be over the top of the wall, or flush with the wall. If it is flush, there will be removal of some (or all) of the existing concrete. If the top of the lake wall is in decent shape, I would pour the slab flush with it. If there is any chance that this area could be used as a secondary gathering place, I would enlarge the slab by taking its full width all the way back to the stone retaining wall that borders your yard. Meet the step there flush so that one step can be eliminated.

If you just patch the hole, figure that in a while, you'll be patching another part of it and that that this process will be, more or less, ongoing.

    Bookmark   May 7, 2014 at 11:55AM
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sledgeNL

Thanks. I didn't want to replace the concrete as I didn't see it's purpose, but if it's serving as some sort of protection barrier against water then I'll need to reconsider that. That's also why I mentioned a french drain earlier. I thought that putting one at the base of those steps and sending the water directly into the lake would minimize erosion.

    Bookmark   May 7, 2014 at 1:52PM
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pls8xx

I suggest you make a thorough inspection of the sea wall and its foundation. Some minor repairs now may save you big money down the road.

    Bookmark   May 7, 2014 at 2:03PM
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yardvaark

"Thanks. I didn't want to replace the concrete as I didn't see it's purpose..."

OK, now I get it. The obvious purpose -- a paved surface by which to get to the dock and a place for people to stand while they're waiting for access to it (or whyever) ... which everyone thinks is something you're trying to preserve -- is not desired by you and you're willing to do away with it. In that case, packing the hole well with earth and planting sod over it will work IF you baby the sod sufficiently that it grows well. If it doesn't, and it begins eroding (there must be an underground path down there) you stand a chance that moving water will find it again. If the sod roots and grows well, it will protect the soil. Doing it this way, I'd remove the thin concrete and be done with it. If necessary, pour a new walk that is better.

    Bookmark   May 7, 2014 at 2:35PM
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sledgeNL

Thanks Yardvaark!!! I plan on examining the bulkhead while I'm in there digging around. I also found some instructions on a construction website that I plan on following:

Dig all the dirt from the washout all the way to the bottom
Estimate enough bulkhead cloth (I'm using Polyethylene Woven Geotextile Fabric) to create a sack large enough to fill the resulting hole.

Weight the sack down to the bottom of the hole with a brick or equivalent.

Fill the sack with ScottâÂÂs Lawn Turf Builder. This soil is shedded and mulchy so does not seep through the cloth when water from the lake washes into it.

Pack the soil as best you can

As the repaired area settles, fill the area with more Turf Builder until the settling stops. Hopefully you left enough of the bulkhead cloth to reach the top of the bulkhead. When the settling has become minimal, the excess cloth can be trimmed.

    Bookmark   May 7, 2014 at 3:24PM
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yardvaark

That sounds like product-selling instructions, to me. I would just fill with everyday dirt, pack well and sod. Again, babying the sod a little early on will pay off later. But do as you please. Good that you have water nearby!

    Bookmark   May 7, 2014 at 6:18PM
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nandina(8b)

How come this new property owner did not include repair of bulkhead walkway as a condition of purchase? After viewing the pictures presented carefully numerous problems compounding one upon another are noted. End of discussion. Professional advice is needed both to correct construction mistakes and to repair a liability.

    Bookmark   May 8, 2014 at 12:50PM
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