Advice on working with unstable ground?

[Bote]

My place is in an area classified as “hardwood bottoms” and has sections of unstable clay that will submerge a backhoe. I’ve tried crushed rock of various sizes but they all just sink into the clay. Geotextiles helped a little but not enough to justify the expense. I have projects throughout my property that require me to cross this muck. The most practical method I’ve found is to lay down a pattern of standard concrete blocks and fill them with crushed rock. These will sink under the weight of the backhoe until they finally bottom out and I can then lay rock on top. That's basically how I make creek crossings. A local company sells recycled concrete and I'm told it works well for this purpose. I gave up on trying to get some though, as the state highway department apparently buys everything he makes.

 

[aighead]

What about sheets of plywood or the rubber mats I hear about people using? Maybe a bit pricey but would they work? I could imagine a network of sheets of plywood to drive on to the project where there could be several more so you could move around a bit... Sounds like a drag to deal with.

 

[CM1995]

Bote what is the final product of the areas you need to cross? Are these areas going to be left back to nature or are you building roads and structures?

If the areas are going "back to nature" so to speak brush and small trees make a great road. Basically the brush and trees act like a snowshoe for the hoe. Lay the brush out where you need to go in a thickness that will hold up your backhoe. Sometimes a little dirt, 1' or so across a thick brush mat works good as well.

If these areas are going to become a road, parking or structure you only have a few expensive options.

1 - Undercut the poor soils to a hard bearing and fill back in with stone or structural fill borrowed from elsewhere on your property.

2 - Undercut the poor soils 1-3', lay down geogrid and cover with surge rock (6" minus stone) to grade then choke it off with smaller rock such as DGB or 3/4 crusher run.

3 - Leave the soils in place and bridge with onsite structural fill until it stops moving. That could be a depth of 4' and deeper. It takes around 4' of good structural fill to bridge over normal soft/poor soils in my area.

4 - Hardwood mats like they use for cranes and pipelining. These can be bought new and used. You would need a set of forks for you hoe to move them around efficiently.

Do you have any natural rock on your land? Surface rocks and boulders work very well as the first layer of an undercut of a soft spot. Think largest rocks on bottom and smallest on top.

 

[mowingman]

Buy 12" or larger rip rap and lay a layer of it into the swampy areas. That should hold you up. Then, you can place smaller rock, or even soil on top of it. Back in 72, we built up a creek swamp of almost 3 miles length with boulders. Then placed fill over that for a 4 lane highway.

 

[skyking1]

In Southeast Alaska the common practice in boggy areas is to take out the stumps turn them right over and use them to build your road. Once the stump is completely submerged in soil again it does not rot very quickly and these roads have lasted decades. Pretty much what CM1995 is saying, use what you have to give yourself a base to build on and then come up with 4 in spalls and the like.
If you want to build an actual structure out there, consider piling of some sort. It is pricey but it's the right way to go.

 

[skyking1]

I work for years for a company called Geo Pier. You can Google it or look it up, but essentially the process is drilling the unacceptable loose soils or fill or whatever down to good bearing material. The hole is built back up in lifts with 2x4 rock if needed, then we switched over to inch and a quarter minus. The compacting tool was a very long stem on a hydraulic hammer with a head on it that look like an old flying saucer from the fifties. The hammer was hung double gimbled so that it would swivel. When we got all done you couldn't tell we'd done anything it was still a boggy muddy mess but when they came back to cut the footings there were these bright circles of super hard inch and a quarter. One of the local Costco's was built on 1100 of those Piers that I put in, because at one time someone had hauled up a large layer of bark from the nearby Mill and then covered it with decent material about 9 ft deep. It would have been a huge scraper show to go get that bark. We just bored through it to the native below and built those columns. Sometimes we had to case the top four or five feet of it as we were building but then the casing was just pulled out with another excavator as I topped it out.

 

[Jonas302]

Around here crushed concrete is a premium product and would never be used for a mudhole
we have went right across pumpy clay with geofabric
If you have extra trees a corduroy road will last at least 50 years probably more we still maintain many miles of corduroy swamp crossings

 

[Delmer]

Unstable is almost always a function of wetness, so if you can build up the roadway and lower the ditches, over time the material will be more stable. A layer of brush just thick enough to hold the layers separate and provide a slight drainage plane will help, as would geotextile fabric. I've seen tires used as a grid to fill with stone to hold the whole mess together also, so lots of possibilities.

 

[Bote]

Lot's of good ideas. It's a permanent road but only for my backhoe. No natural rock but plenty of timber. I'd like to try the corduroy option for parts that will get little traffic. 5" minus over geotextile worked OK but kept "rutting"; I had to keep adding more rock. Larger rock will probably work.

Recycled concrete is $8.50/ton picked up. Last year I could have had all I wanted but this year there are several local road projects sucking it up.

I've been trying since the end of May to get to a creek I need to enlarge. My plan is to direct most of the water there. I should make it there this week. Hopefully, keeping the water off the soft areas will help them to firm up a little.

 

[CM1995]

Skyking we worked on one little job at a school for autistic children that had 42 geopiers that Geo Pier installed. It was slick installation. They had a 316 and 318 Cat one with an auger and one with the probe hammer. Couple of loads of #57's and #8910 IIRC and they were in and out in a couple of days. For what they charged I'd like to be in that business.

Lot's of good ideas. It's a permanent road but only for my backhoe. No natural rock but plenty of timber. I'd like to try the corduroy option for parts that will get little traffic. 5" minus over geotextile worked OK but kept "rutting"; I had to keep adding more rock. Larger rock will probably work.

Recycled concrete is $8.50/ton picked up. Last year I could have had all I wanted but this year there are several local road projects sucking it up.

I've been trying since the end of May to get to a creek I need to enlarge. My plan is to direct most of the water there. I should make it there this week. Hopefully, keeping the water off the soft areas will help them to firm up a little.

How much 5" minus did you put over the fabric - what depth? What I've found is it takes at least 18" of stone over fabric to start to bridge over very soft soils.

Crushed concrete here is $8.50 TN plus delivery. First time we used it was on a job a week or so ago and it's great for trench backfill in a parking lot. The guys pushed it in the trench, ran over it with the mini and after several inches of rainfall the 4' deep trench settled 3/4 -1" and that's with no mechanical compaction. The material we received looked to be plant/truck washout as it had no wire or other debris just a nice graded sand/gravel mix.

If you have enough trees and brush to sacrifice that looks to be your best option.

 

[skyking1]

Yes the patent on those GeoPiers was a good one.
OP are you doing this with a backhoe only?

 

[Bote]

CM1995 I only laid down 12" and that's probably where I went wrong. I have little experience in this area. The quarry where I get larger rock has a civil engineer who advised me to go with the 5" minus. I'm going to try a few tons of larger rock before I spend $400/truckload.
I did clear a rock storage area where trucks can unload without getting stuck.
I'm going to try the corduroy option for an area that only requires temporary access.
Skyking, I'm using a backhoe only. It would be nice to have something with tracks sometimes. I'm tempted when I see smaller dozers for sale that are within my price range. Locally, they seem to offer more bang for the buck than skid steers.

 

[Bote]

Skyking, in addition to the backhoe I'm also using ballast forks haha. Years ago I managed three railroad yards. The ballast forks are one of the useful tools I discovered. Last year, someone stole my ballast forks, railroad adz and timber jack. I had to order the ballast forks from a railroad supply place. I lucked up and found the railroad adz in a ditch a month later. It was my grandfathers and is nearly a hundred years old.

 

[skyking1]

I'm confused, bote. I looked up ballast forks but did not see where you put the diesel or where the seat is.
I would suggest that if you do have an area of stumps on hand and a decent road to put in, that you go ahead and rent an excavator and get wood in down low with it. I know it's kind of a budget buster but stumps that are a liability seem to be a better solution than $400 a load Rock.

 

[Scout_1969]

Similar to what’s already been said, ditch, elevate, slope to drain. Most of the times native materials will work especially for a backhoe path. If small springs pop up, might be a different story

 

[AzIron]

I work for years for a company called Geo Pier. You can Google it or look it up, but essentially the process is drilling the unacceptable loose soils or fill or whatever down to good bearing material. The hole is built back up in lifts with 2x4 rock if needed, then we switched over to inch and a quarter minus. The compacting tool was a very long stem on a hydraulic hammer with a head on it that look like an old flying saucer from the fifties. The hammer was hung double gimbled so that it would swivel. When we got all done you couldn't tell we'd done anything it was still a boggy muddy mess but when they came back to cut the footings there were these bright circles of super hard inch and a quarter. One of the local Costco's was built on 1100 of those Piers that I put in, because at one time someone had hauled up a large layer of bark from the nearby Mill and then covered it with decent material about 9 ft deep. It would have been a huge scraper show to go get that bark. We just bored through it to the native below and built those columns. Sometimes we had to case the top four or five feet of it as we were building but then the casing was just pulled out with another excavator as I topped it out.

That is one of the most repetitive jobs I have ever seen and I have never seen a crew destroy a sub grade faster than the crew that did about 6 jobs in front of us last year

It's a neat product and works good but engineeres here were trying to sell it as a way to get away from cassions but it didn't turn out to be much cheaper and the schedule was slower might have just been the guys doing it

 

[skyking1]

Much cheaper? any cheaper is what counts to the bean counters.

 

[CM1995]

I have never seen a crew destroy a sub grade faster than the crew that did about 6 jobs in front of us last year

I'll put $100 on the plumbers and electricians we work around over that geo pier crew.

 

[AzIron]

Much cheaper? any cheaper is what counts to the bean counters.

Till the almighty schedule gets involved cheaper no longer means as much if your cheaper product takes 10 days longer than casions it becomes a mute point on cheaper

 

[CM1995]

Till the almighty schedule gets involved cheaper no longer means as much if your cheaper product takes 10 days longer than casions it becomes a mute point on cheaper

Try telling that to the shiny white hard hats sitting in the A/C trailers who stare at computers all day..