looking for some information on the effectiveness and practicality of water compaction (ie root soakers) on over digs and utility trenches under slabs particularly in clay soils.
My background was in heavy commercial construction mainly concrete placement for years so it came as a huge surprise to me to see the “acceptable” practices in residential new builds that my new employer uses. Clay backfill, zero compaction methods, no sand, no use of mesh or rebar among other things. So it didn’t come as a surprise the resulting problems of 11 month walk through of unlevel ac units, washed out sidewalks, sunken driveways, cracked garage slabs etc…
They are now looking into using the practice of water compaction with root soaking rods.
My question is how effective this method can even be in; one clay soils, the period necessary (We’ll turn turn houses around in as little as 3months. They have done the actual Extreme Home Make Over with Tye Pennington before), and other potential problems like the always convent muddy building site.
Other logistical problems I see are often we do not even have water meters set until 2 weeks before closing, while site concrete is already placed. The Basements are typically still damp as it is right up to the closing date. A constant mucky site when we deal with mud tracked around the subdivisions as it is with only Mother Nature to contend with and the resulting erosion control measures and drain commissioner issues.
From the companies stand point we want to solve the issues with concrete and settling with as little of expenditure as possible. So what does this cost curve look like when you spend x dollars on say mechanical compaction or sand backfill, versus the cost of just repairing after the fact. Do we continue to gamble on replacing say 20 driveways a year out of the 80 homes built or could that number be reduced by just enough with water compaction to offset the cost of using a combination of control methods like sand, reinforced concrete, compaction, etc… on all 80 homes instead.
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no one has encountered this problem?
bump
Unfortunately, this seems to be the way many/most project builders think and do business. If they can make it past what ever warrantee period they are obligated too, they win and are home free. At least most of the time.
On the other hand I understand the necessity of reducing cost. By reducing cost, more folks may be able to afford a home even if it does start to fall apart before it should..
I'm not a soil expert, but I have never heard of compacting clay soils by deep watering. You might do some good on sandy or granular material that way. Still you are not going to get anywhere near the 90* compaction generally recommended. I don't think you will find an engineer that would sign off on that method. Why don't you check with an engineer if you really want some sound and professional advice. Let us know what he says.
I doubt any one around here is prepared to back up any advise that they may give you.
Good luck and hope you find an economical solution to your problem.
If the clay has signficant shrink/swell potential, wetting it is
likely to just cause additional problems. Thatt is, wet it thoroughly and it expands; allow it to dry and and it shrinks. It looks like you're in NC; shrink-swell soils are a signficant problem in parts of the Piedmont region in VA and NC. There are ways to overcome the problem, but it sounds like you would benefit from consulting a soil scientist and/or engineer.
To ease drainage concerns and soil movement........
Here in NW Oh., backfilling with stone is the way to go.
Water will probably work, but not on the short time schedule you guys work with. You'd need to basically flood the site and then let it drain/dry for a month or so. And maybe repeat 2-3 times.
Hydraulic compaction can work under very limited circumstances.
I have been the Construction Engineer for about a hundred miles of large diameter water main, that utilized vibro-jetted, and jetted compaction. Which is about as much experience as anyone out there. I also did a bit of research on it when I was in college.
The material to be compacted must be well graded, granular, free draining, and have a low plasticity index. Typically no more than 1 or 2% of the material can pass through a number 200 seive. This means that it will not work with a clayey soil. Regardless of whether the clays involved are expansive.
The soils around the excavation must be porous enough to accept the water and let it drain away. You can, in rare instances, get around the free draining surrounding soil requirement, by installing pumping points, or dewatering wells and pumping the water out of the soil.
Personally, I think that in your situation, I would look at a controlled low strength materila or CLSM. These are lean portland cement grouts that have a compressive strength of only 200 to 400-psi, which allows them to be hand excavated if necessary. Another option I have seen used a few times, was pea gravel for backfill, which if you hit it once with a vibrator is as compacted as it will ever be, and then pouring a CLSM slurry into the pea gravel to bond it into place. This has an advantage over the CLSM, in a lower cost due to the decreased amount of cement required. I have used both for pipe backfill, where they worked extermely well.