How to find the soft spots in a gravel driveway, best way to fix?

[BT Fabrication]

so, bringing in a new to me machining center that was 9500# on a 18,000# forklift, well right at the edge of the shop door it sank to the frame. the gravel is a mix of crushed asphalt and sand from further up the drive way and washing in from the road on a heavy rain. short of paving it, what is the best approach to prevent it from sinking if anything is moved again?
a good base of 3/4" clear below it and top dressed with Granular A?
the rigger decided to slow down and crawl in the door lip and just spun, didn't help he had the wrong style forklift that was indoor rated and smooth tires on it and low ground clearance.
there will be eventually soon a concrete threshold. I'm just wondering if like some places they put out Portland cement and mix it in the base and roll it out to where it turns solid might do it also.

suggestions?
paving all 300Ft of it is a bit cost prohibitive and not needed as most of it is rock solid ground. only spring melt/rains it all gets soft in places.

 

[Ries]

For my gravel driveways, we excavate down at least 6", a foot is better, lay down 12' wide road cloth, then use 1" or so gravel with fines. Then, it takes about a. year of rain and steady driving over it to get it to really lock up. This lasts ten years or so, then needs redoing. We are about to do round 3, been here 27 years. But I still doubt if an 18,000 lb indoor forklift would be entirely safe. My little mitsubishi with the 4500 payload is ok on it, as long as I dont get too close to the edge. Asphalt or concrete are the only real safe options, and, even then, a big forklift is really really heavy, and concentrates the load. Generally a forklift with 18,000 lb capacity weighs around 26,000lbs.

 

[dalmatiangirl61]

You did not mention soil type, if clay, you can mix in hot lime and it will set pretty well, for more info search soil stabilization. If willing to excavate, or you still have room to fill, I have found crushed concrete works pretty well.

 

[DDoug]

"How to find" is old hat to civil engineers.

"50 ton proof roller"
What Is Proof Rolling?

 

[sfriedberg]

If you have soft spots then paving alone isn't going to really fix your problem. The key to load bearing capacity is subgrade preparation of the road bed. If you don't do that work, then paving is just going to put a thin stiff layer over the soft spots, and you will crater the asphalt or pavement when the road bed shifts out from under the load.

I only put a (reinforced) 4" slab in my shop, but there's a thick bottom layer of 2-4" crushed rock, then another layer of about 1" crushed rock, under the slab. Since they extracted a large willow tree right in the middle of where the shop was going to go, there was no way I was going to get decent load bearing without filling in the deep hole with compacted rock.

I had the shop drive laid with permeable pavers. The ground was saturated when my big mill was delivered by the riggers, who used a 15T forklift (counterweight had 31,000 painted on it). I learned then how bad a job of site prep the pavers had done. They put in rock and sand below the pavers, but there wasn't enough rock or it wasn't compacted properly. The tires on the forklift sunk in about 2", then as the load moved along, sloowwwly raised most of the way back up again, each rigid paver moving down then up like a peg. If I had gone with asphalt or concrete, the whole drive would have been cratered. As it is, I have two very, very shallow troughs (fractional inch deep). They sort of look like road wear, but it's all due to load compression.

 

[neanderthal mach]

Roads need to be excavated and then built to the maximum expected future loads they might see. Simple car or pick up access requirements are a whole lot less stringent than something that might see 5-10 ton or more loads. But fwiw I've built and maintained more than a few miles of road that were fully expected to support 24,7,365 loaded 400+ ton haul trucks or much more rare heavy earth moving equipment moves in excess of 1,000 tons. And do so in all weather conditions from +90F to -50F. I also had pretty much an unlimited supply of blasted hard rock to do so. By the sounds of it your shop access road was never done correctly to begin with if there's any soft spots like that in it. Basic road building 101 is that water drainage and removal of any biological type soil (anything that will support plant growth) is fully removed. And excess water or poor/no drainage will destroy any road no matter how well built it is or what materials are used. The good part is you now know where those soft spots are and roughly how large they are. But your only choice is to completely excavate what's there and down to below what's incorrect to the native hard pan that's below any of the biological soil. If you were to do this yourself? That hard pan starting surface or if your really lucky, high rock content needs to be left completely undisturbed since due to hopefully eons of normal ground vibrations it's already at it's maximum compaction. Frankly I'd highly recommend paying pros to do the work whatever it cost.

Ries mention of using that road cloth is a good one, it's designed to allow water to only go one way (drainage) and continuously drain it out of your roads sub base. But that water needs a place to drain to or it's useless. You also CAN'T just dump loose material into any deeper hole that's been excavated. Depending on just how deep you might have to go, that sub base can be an un-crushed rock, gravel and sand mix, but it also needs to be put in and then vibratory compacted, or a bit less effective, heavy track or wheel packed in no more than 6"-8" deep layers. Then your final 6" or so of road surface is at least crushed gravel because it will bind together and compact harder than anything else. Most people tend to think roads are flat across there width, when correctly done there not, on something like multi lane interstates there either sloped a degree or two towards the best drainage, or when narrower with a center crown to each side to promote surface water drainage. And a good all weather road surface does require at least half decent maintenance. Any potholes or areas with standing water need to be kept filled or drained. And for best compaction you should have approximately 8% to absolutely no more than 9%-10% moisture content. All of the above are just general points and your exact situation for your road area could come with tougher to solve side issues of course. There are for various reasons areas that could be called almost bottomless as far as excavating to that natural hard pan or native rock. One trick for that is to excavate deep enough to maybe 4'+ and then add what they did in the old logging days that's still used sometimes even today. Simple 12"+++ diameter logs placed side by side cross ways to the direction of road travel and then back filled on top of those. I'm not sure about everywhere, but up here it's generally called a corduroy road for the obvious reason. Basically it spreads the loads out over a far larger area allowing it to support much heavier weight than without it. I've seen that type of road built through really soft areas that were then supporting 100+ ton off road logging trucks when it's done right. Much better but almost out of the question due to costs, but closely spaced vertical steel or wood piles driven into the ground will do this even better since the support then comes from the frictional drag on each pile. As long as that's above what the psi loads applied to the road surface is it will remain stable. But just like good concrete foundation work, good solid road building isn't cheap. Start cutting corners and your only throwing your money away. It's a whole lot cheaper to do it right once than to have to tear out what you've already done and then do what you should have the first time. Even more so if your planning on any future hard surfacing of that road and expect any longevity out of it.

I've worked around and had to further compact areas going by there test results, but have never personally used these, Nuclear densitometry - Wikipedia Quite specialized and you'd need to hire a contractor with one if there's still any areas your unsure of. But tbh, with that previous delivery already showing up the problem areas it's probably not necessary. I also think but don't know for sure that these density checking machines are a bit limited in just how deep they can check and still be 100% sure of there results.

 

[john.k]

Next time you see some scrap 3/8 plate on ebay ,get some ....its a lot cheaper to lay down some plate where you want to go...........soft spots in drives are either poorly filled excavations,or caused by water soakage......the very best construction will go soft with rising water from the subsoil.

 

[DDoug]

I had the shop drive laid with permeable pavers. The ground was saturated when my big mill was delivered by the riggers, who used a 15T forklift (counterweight had 31,000 painted on it). I learned then how bad a job of site prep the pavers had done. They put in rock and sand below the pavers, but there wasn't enough rock or it wasn't compacted properly. The tires on the forklift sunk in about 2", then as the load moved along, sloowwwly raised most of the way back up again, each rigid paver moving down then up like a peg.

Like Dis' ?....
James Gets Stuck - The Grand Tour Floating Bridge Scene #Lochdown - YouTube

 

[BT Fabrication]

Next time you see some scrap 3/8 plate on ebay ,get some ....its a lot cheaper to lay down some plate where you want to go...........soft spots in drives are either poorly filled excavations,or caused by water soakage......the very best construction will go soft with rising water from the subsoil.

ya i believe that was my problem, the soil all around has tons of rock in it, but the water table comes up(right near a river) when it rains or snows, probably didnt help that it rained a couple inches the night before. so up by the road was soft where the shoulder meets the driveway and goes all down hill into my yard.
then within 2-3 ft of the shop door was soft and one other spot by what used to be a pool.

digging down you get 2-6" river rock in the sub grade that is a pain to move with even the bigger skid steers and tooth buckets or excavators.

also doesn't help that it never seems to stop raining around here in the great lakes basin.

my approach I am figuring out is to dig out my bad spots where it sunk 1-2" into the gravel, and bring in some large 1-2" rock where the good sub grade is, not surprised the previous owner was cheap when the drive was built, same as cheeping out on steel doors on the shop and just cut the bottom off it and a wood 2x4 frame covered in aluminum flashing... that list goes on and on.

 

[gbent]

If the situation is an occasional move, it will be cheaper to get a rigger with road plates than to fix your driveway properly.

 

[sfriedberg]

Like Dis' ?....
James Gets Stuck - The Grand Tour Floating Bridge Scene #Lochdown - YouTube

Not quite that dramatic, but sort of, yes, at much lower speeds and a much higher load. The forklift was in no danger of bottoming out on the pavers, of course.

 

[michiganbuck]

If the situation is an occasional move, it will be cheaper to get a rigger with road plates than to fix your driveway properly.

Or rent a track loader...build a sled.

Re: only spring melt/rains it all gets soft in places.

 

[john.k]

Whats needed is a "swampie" a D5 dozer with 48" track plates ,and a winch on the back .....they will work in tidal mud like thick soup (very stinky soup) pushing mangroves and spreading pumped sand for real estate development.......or a big dragline with "swamp mats",even with the mats you can get stuck.

 

[neanderthal mach]

A swamp cat or big dragline is needed? By BT Fabs description it's a couple of soft spots in most likely a less than two lane graveled access road to his shop. Even those toy but common as dirt Hitachi 215 sized hoes would easily do the whole job from start to finish in less than a shift.

If the area is already full of river rock then at most digging it out deep enough and then hauling the garbage material away and replacing it with a few loads of uncrushed pit run would fix the problems. Add a load of crush for surfacing and the jobs done.

 

[john.k]

yes,Ive been told a million times not to exaggerate.

 

[michiganbuck]

300" x 4" will be about 52 tons and still not likely enough at spring thaw swell where topsoil and the like can be like a sponge.

From frozen solid to near solid again in about 1 month... A 3 axial car hauler trailer may be enough to bring in a 10K lb something.

 

[Garwood]

My soil is like concrete in the summer and soup in the winter/spring. My driveway is road fabric topped with a foot or two of 3" minus topped with 3/4 minus. I've had lots of loaded 30K forklift traffic on it and it's solid.

Parts of my driveway have been here since 1926. A lot of the old stuff was slag from the nearby steel mill. Slag sets up just like concrete, but fractures under heavy loads. I ripped the slag up, laid down fabric and mixed the slag in with the big rock and it's done good.

 

[mjr6550]

I did not have time to read through all of the posts, so forgive me if I am repeating something. If you need to have stone delivered maybe you can pay the driver to run up and down the driveway a few times. A heavy dump truck is good way to find soft spots. Of course, if its too soft you may have to pay for towing.

If you need to excavate soft areas I would backfill with 3 to 6 inch stone first, depending on the depth, and then modified stone (with fines).

If you have a foundation or frost wall at the garage door area the area adjacent to the foundation would have been excavated, and backfill was often not compacted. That may have been your problem.

 

[matt_isserstedt]

Been there twice at my current place. Most recently last summer.



I had ideas of pouring a ~6" thick pad with rebar in front of the door...basically just enough to offload a trailer, make the 1/4 turn move and go into the shop. But this is expensive work. John had the best idea with some rusty steel plates, then you can even use machine skates if needed.

I repaired the holes filling with 5ksi bagged concrete bought from the box store, works good enough.

It also works better to do this in the dead of February when everything is frozen solid, but this was in July when the grade is dried out but the asphalt is buttery.

 

[BT Fabrication]

had found my issue, dug out the soft spots that only had about 2" of gravel on top and nothing but top soil underneath for 12-18" , and fine sand in spots backfilled with 3/4" gravel and crusher run on top( granular A) here.