I've been trying to establish a decent gravel road across some spotty "pumping soil" areas with mixed results. Some spots will stabilize with a load or two of bull rock, but in others, the rock just squishes out. We almost turned a dump truck over when he got in one of the soft spots and dug about 4' deep before we hit stable sand. My dirt contractor is recommending some geogrid material to hold the sub grade rock in place. The stuff I can see on the web looks like it might be effective. Has anyone had any experience with this approach?

In my experience you have to have a solid foundation to build on. If the soil/rock below the geogrid isn't able to hold the geogrid is liable to fail after some time. You'll be right back to starting over.

If it's a small area I would dig it out until you can build it up. Large fist rock will help to build up. We've thrown in it silty wet areas to build up until we can place some gravel on top.

It'd be beneficial to see what is causing the issue (poor drainage, broken utility line, etc). Make sure to address any of those to avoid continuing soft locations.

I'd consider either lime or cement stabilization

Depending on clay type, line can be very effective. Cement will work with anything, but is more expensive. Depending on the size of the soft spots, you can get surprisingly good results just hand spreading a couple bags I the hardware store lime. Better if you can till it in some. If the areas are larger, highway construction types can spray on a lime slurry.

It will be one of three things that will cure it.

1.) dig out small area and refill with bank sand
2.) lime
3.) lay down geotextile material and build our gravel road on top of it.

What I have notice is the soft spots seem to hold ponding water longer then the surrounding stable soil. So when I on a big tire piece of equipment I avoid those area because you almost instantly sink

I do know this. I have never fixed these issue by going on the cheap. Dig them up and put down a min of 4 in gravel and have some one drive a roller over it to pack it down.

If that doesn't work. Peel back the gravel and put down the geotextile fabric and recover.
Hopefully all you have is some small localized soft spots.

The bad spots are about 10-30' long. I think when we dig it up for the geo stuff, we might throw some lime down first. The road is in pretty good shape for normal vehicle traffic, but we are trying to get the barndominium started and will need about 700 yards of select fill, then concrete. Once you bust through the crust with a load in one of these spots it's all over. If we can get things firmed up to get past that point, I think we'll be home free.

To answer the earlier question, there is no water line leak, just flat coastal prairie. We hit clay at about 18-24" and it's at least 24" thick so the water just stays trapped in there. After 70" of rain last year, we're still finding bad spots from time to time. I found a youtube video that looks similar entitled "Extreme Soil Liquifaction". Ours is not quite that bad, but if you were to go a bucket deep on ours, you'd pull up soup rather than dry dirt.

May need to kay down mat like they do in oil filed construction. Basicslly a wooden bridge laid on the ground

I've got a truck application that had to support bulked trucks during the thaw in ND using geotextile cloth and approx 14-16" of rock on top. Also know of an application where they used a substantial amount of geotextile in the port of Corpus Christi to support stockpiles of barite ore. In either case, you have to plan on some deflection but the geotextile +substantial amounts of material on top would likely work.

Most localized soft spots could likely be improved by drainage. Contact your local friendly civil engineer and offer to pay him in deer hunting.

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Depending on clay type, line can be very effective. Cement will work with anything, but is more expensive. Depending on the size of the soft spots, you can get surprisingly good results just hand spreading a couple bags I the hardware store lime. Better if you can till it in some. If the areas are larger, highway construction types can spray on a lime slurry.

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Clay will not break down enough for cement to do its thing and is a waste. Lime is very effective but has to be mixed in well and then remixed after 48 hours. Requires lots of water. Slurry is simply hydrated lime and again, must be mixed in and should be remixed after 48.

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The bad spots are about 10-30' long. I think when we dig it up for the geo stuff, we might throw some lime down first. The road is in pretty good shape for normal vehicle traffic, but we are trying to get the barndominium started and will need about 700 yards of select fill, then concrete. Once you bust through the crust with a load in one of these spots it's all over. If we can get things firmed up to get past that point, I think we'll be home free.

To answer the earlier question, there is no water line leak, just flat coastal prairie. We hit clay at about 18-24" and it's at least 24" thick so the water just stays trapped in there. After 70" of rain last year, we're still finding bad spots from time to time. I found a youtube video that looks similar entitled "Extreme Soil Liquifaction". Ours is not quite that bad, but if you were to go a bucket deep on ours, you'd pull up soup rather than dry dirt.

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You have to get rid of the water. Cut ditches on both sides and allow the water to percolate out. It's the only feasible option for uncompacted sandy loam over impervious clay.

Had to cut ditches along my road in North Carolina. Probably not analogous, but it was a pain in the ass. Roads through forest eat up a lot of my time.

Lots of good input to chew on here. The drainage idea makes perfect sense, but I'm afraid the ditches are likely to consist of the same soupy stuff once we get down a couple of feet. I'll bounce some of these ideas off my contractor.

The deer hunting is not very interesting, but there are plenty of hogs and there's 3 weeks left in turkey season!

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The drainage idea makes perfect sense, but I'm afraid the ditches are likely to consist of the same soupy stuff once we get down a couple of feet.

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I think that's the point. Cutting down to that level will allow the trapped water to drain, which seems to be the root cause of the instability.

May not be practical, but I saw some kind of ladder liking devices for putting into golf courses, etc so that fire trucks could cut across.

Sounds like you are trying to do something for large equipment though

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Clay will not break down enough for cement to do its thing and is a waste. Lime is very effective but has to be mixed in well and then remixed after 48 hours. Requires lots of water. Slurry is simply hydrated lime and again, must be mixed in and should be remixed after 48.

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I just finished a subdivision project where we stabilized clay with cement and it worked great. The geotech called for 6% lime when we bid it, but after the lime series tests came back they determined it needed more like 12-14% (a ridiculous amount). We ended up using cement instead and, as I said, it worked great. This was just south of Manor. So, while I'm not an engineer, I disagree that cement won't work in clay.

Lime stabilization plus geogrid is your best bet, along with using aggregate base on top.

As stated above, you need to follow protocol with lime - first you need to determine how much lime is required. Too little and you are wasting money, too much and you end up both wasting money and not getting the results you are looking for. You need to know how many pounds per yard, then you apply and mix, let it cook for 24 to 48 hours, then remix and compact. It's a nasty process, but it works well.

Use a good geogrid, apply the lime stabilized material on top then the aggregate base on top of that and you should, generally speaking (and not knowing the specifics of where you are at and what is causing the failures) have a decent road for a while, traffic dependent.

The most important piece of any road is the sub-grade - if it is not solid the top paving will fail no matter what you put in.

In an area like you have described the first thing you have to do is pump out the water and then muck out every bit of saturated soil. Over excavate a little to make sure you get any wet material out - there may be a wet layer just above the clay that extends out further than the existing hole (just hasn't failed yet). That soil will never dry out on its own. If you have to re-use it spread it out thin and turn it a couple times to get it completely dry before you put it back in.

The least expensive option would be 1) dry out the existing material like I described, 2) put it back down in 12" to 18" layers hitting each lift with a compactor 3) put down geotextile fabric 4) top with some kind of base material (Crushed concrete, crushed limestone etc.) 5) be sure and "crown" it a little - the area will probably subside a little and you dont want a birdbath that will hold water again. 6) cut some drainage ditches along the sides to give any runoff somewhere to go other than standing on the road.

A step up would to bring in new dry Clay/sand backfill (usually called "select fill") to fill in the hole. Lime can get real expensive real quick unless it is a tiny area, and it has to be mixed in real good or it will be a waste of $$.

On the geotextile fabric there are a couple options. The normal fabric (looks like the same material silt fence is made out of) is cheap and does fine. If you are going to use bigger rock (bull rock) there is stuff called Geo Grid designed to support the bigger rock. The goal of the fabric and grid is to keep your top paving material intact ( not squishing down and mixing with sub grade) - the fabric keeps the fines from migrating down and the grid does the same for the bigger aggregate.

Hope that helps.... I have the same issue at my lease in Roans Prairie area which is part of the Piney Woods. Thick layer of fine sand before you get to clay. Only options are to compact the heck of what is there and then crown it with good ditches on the side, or dig it all out and replace with good select fill and base. If you leave the existing sand it will always be a little soft and slick right after a rain, but if you crown it good and keep rainwater from standing or running across it, it will dry out faster. As long as you dont rut it up too bad it will be livable.