Filling large hole in a road

[JimMorrissey]

So I eventually removed a massive boulder (size of a car) from the middle of my soon to be driveway. I pulled the broken rock out of the hole and filled it in with the original soil and some extra. The problem is the hole now behaves like a giant jelly donut. If I hit it with my backhoe the dirt in the hole moves like jelly. It's about 6' deep and 10' around. I filled it in lifts and attempted to compact it. Not much compaction took place. The soil is damp (partial clay, say 50%) and maybe on the wetter side than damp. I know it's hard to compact damp soils.....there is an optimum water content for correct compaction.

I'm covering the entire sub-base surface with fabric. I'm just not sure if I should remove the soil and replace it with stone and crushed gravel so I don't have a depression in the road in a year or two. I'm thinking I should, but since I'm using fabric, not sure if I need to. The fabric should bridge the soft spots, that's primarily what it's for. What do you think......

 

[inveresk]

If the fill hasn't been properly compacted, you're likely in time to have problems with deformation of the base. How much will depend on loading. If the driveway is only to be lightly loaded you may get away with it for long enough. If you've heavily loaded vehicles tracking the driveway, problems will arise sooner. However, if you've upfilled to the depth of a car,I can see you'll want to avoid excavating this again (shame you didn't break the rock up and just put it back in the hole). If you still have building works to do, can you leave the road base as is until you finish these, allow construction vehicles to do the compaction for you then top the road off once they're finished and gone? Another option, belt and braces, would be to pour a concrete raft locally over the area of the fill (plus an overlap of, say, 2 feet all round) and include some fairly heavy steel mesh, A193 for example, a couple of inches from the bottom of the slab before topping off. If you've concrete works going on elsewhere, this might be the easiest solution - just order an extra couple of cube.

 

[JimMorrissey]

Inver,

Definite shame but I didn't want a bunch of heaving going on when the ground freezes and thaws pushing massive chunks of rock up into the road surface. It's definitely wet down there at the turn. I know exactly where the hole edges are so I think I'll dig the darn hole out again and fill about 30% of it with broken concrete and stones (up to roughly the frost line). Then I'll fill in lifts for about 25%, then fill the rest with the trucked in 1 1/2" crushed gravel when the road base is being brought in. The fabric will flow into the depression and the base fill will be flush with the rest of the road.

I knew in the back of my mind when I was filling it with dirt I was making a mistake. Oh well, live and learn. This will not likely be my last automobile sized boulder. /forums/images/graemlins/mad.gif

 

[beenthere]

I think you are right to dig it out. At least now is better time than later. If its a pothole that will later be able to collect water, I would consider getting a drain tile in there to drain the area, if that is at all possible.
If clay gets wet and/or stays wet - it's trouble like you say - large jelly roll.

 

[have_blue]

Jim,

I hate jelly holes. I've had several, and they're a real pain until they compact. The problem is caused by covering up mud with light, dry soil that just floats on top of the heavier mud.

Don't know the solution in your parts, but the solution here is rain. When it rains, the jelly holes firm up just fine. I suspect the dirt on top of the mud becomes heavy and settles into the underlying mud, and eventually squeezes out the water. My jelly holes eventually become firmer than the surrounding soil just from a hard rain or 2.

 

[beenthere]

Clay won't firm up that way, unless you get the water out.
But some soils work as you describe, and most often I find when it works that way, it is really the rain driving the underlying frost out of the ground. When water sits on top of frost layer, the area is pretty unstable. But get that frost out, and the area firms up pretty good.
Clay is a different sort of animal, and doesn't always act this way as it holds water pretty well and won't let it 'pass through'. It's why clay is used to line a pond or to line a garbage dump and the like.

 

[Egon]

To check clay for optimum compaction moisture grab a handfull and roll it between your hands. If you can roll it into nice pencil sized thread with no problem its probably about right.

If you dig out the hole transition the edges at a minimum of 45 degrees.

Egon

 

[JimMorrissey]

Bob,

That's some good news. Maybe I'll wait a bit before I dig it up. How deep have you jelly holes been in the past.

 

[JimMorrissey]

This material is not pure clay. It's a mix of clay and "dirt". Actaully if you come from a real "clay area", say Texas, then you'd likely not call this clay. Although it certainly has a bit of clay in it.

I'm hoping with a good hard rain and a nice dry period that it'll settle a bit. Not sure I have the time for to wait for those conditions though.

 

[Soundguy]

Uh.. filling it with a 50% (wet) clay mix.. and you wonder why it is a jelly donut?

Either let it dry thouroughly.. or dig it out and put some clean fill in.

I'm not a fan of using a large wad of clay in my road base.. some clays swell and hold water.. that makes for a huge problem under a road...

Soundguy

 

[JimMorrissey]

Yeah, I'll dig it out. I've got some fill material for a good portion of it. Not worth a sag in the road and a massive puddle two years down the road.

I didn't have clay on my last two properties and don't have a whole lot of experience with it....aside from art class in 4th grade.

 

[have_blue]

</font><font color="blue" class="small">( Bob, How deep have you jelly holes been in the past. )</font>

Mostly 2-4 feet. I had 1 so bad I couldn't hardly cross it with my tractor. It's like I was driving across a huge Tempra mattress. It stayed there for weeks, then we had a hard rain. I was thinking "Oh boy, I'll really sink now!" Imagine my surprise 3 or 4 days aftrer the rain it was solid as could be!

I know it sounds counter-intuitive, but dry dirt is the culprit, not wet dirt. Even topsoil on top of wet clay settles and compacts when it gets a good soaking and becomes heavy enough to squeeze the water out.

 

[Corm]

Hello Jim. I also live in Vt, and live in an area with that nasty clay soil. Based on my experience in maintaining a 1/4 mile drive for nearly 20 years now, and doing lot's of digging around my home, I would do as HaveBlue suggests, and leave it for a while. Once it dries, it'll be just like cement. One other thing I've learned - if you dig a big hole like what you did, unless you provide adequate drainage, be sure and backfill it with native soil. Filling the hole with gravel, sand, or topsoil, will only create a hole that never dries out. The surrounding clay will act like a big bowl. This has been my hard earned experience, take it for what it's worth.

Good luck with whatever you decide to do!

Corm

 

[dmccarty]

Jim,

Is your driveway going to be gravel with not concrete or asphalt?

If its just gravel I don't think you will have a problem. I dug some massive holes when I removed the stumps in the way of my driveway. Some of the $%^&*( where twin trees 30+ inches in diameter. EACH. What A Mess. I had one stump with a tap root that was over 6 feet long. It took two work days, about eight hours total to get that thing out....

I can remember three big holes I dug that where at least 10-12 feet across. I think one only had to be a couple feet deep. The other two where 5 to 6 feet deep. I filled in the holes with whatever soil I had, clay. It set for maybe a year or so until I built the driveway.

The soil was bouncy for a while but eventually compacted.

I put down geotextile fabric and put on 3-4 inches of ABC. Not had a problem since. IF you just put in gravel and the hole does shrink add more gravel.

Later,
Dan

 

[JimMorrissey]

Thanks guys....appreciate the input.

What I've done is remove all the soil I put in which was making it jelly-like.......Then I filled the hole with some broken slabs of concrete and a bunch of large and small rocks mixed with the native soils. It is extremely firm now. My only concern is that the rocks might return to the surface during the freeze/thaw cycle each spring. Hopefully this won't happen as the main rock base is below the frost line and rocks transfer heat. I believe it was the right thing to do in the long run. We'll see /forums/images/graemlins/tongue.gif The reason I didn't leave it with the original soil is that I don't have six months or a year to wait for natural compaction to take place.

BTW, I forgot to mention that the road will be 1 1/2" crushed gravel over geotextile with about 6" of "surepak" crushed stone on top. I'm thinking 8" of the big crushed gravel base will do the trick, however the engineers plans call for 12". I will probably end up with 12" in the end.

 

[earthface]

I know the exact problem. I had those jelly holes on simular soil on a place i had that had a poorly constructed road. I learned how to fix and here is what I did to those spots and was after wards able to run a forklift on them year round after wards.
First you will have to remove 2 to 3 ft of soil dirt. Then put in layer of broken rock up to 6 in, cover with dirt pack, Put in next layer 6 t0 8 in of railroad balast cover with dirt compact well. Then about 6 to 8 in of 1 1/2 in minus cocer with dirt compact. When hole dry out cover with what you use as top layer. This will form a cap and short of backhoe or cat will stay, You dont want to have a large cement cap unless you plan to pave it later. Because if you leave it gravel road you will need to grade sometimes.

 

[LarryRB]

Jim,
I don't want to come across here as a smart --s. However, there is a reason "spoils" are re-piled somewhere and fresh fill brought in... Running the highway dept, if we moved large boulders from the any town dirt roads, which is done several times in any given year,, that spoil was brought back to the garage and fresh fill takes it's place. Replacing virgin dug dirt with the same, for some reason will never settle again.. Have some other gravel dropped next to this hole, dig out the original spoils and push the fresh stuff in. Put in a foot or so, and compact by rollng the hoe bucket, another foot, same thing, and keep going till your 6" above grade, Roll it with the tires several times and you should be 3" or so above grade. Within two weeks, it will be back to grade... I've tried several times over the years to replace fresh dug spoils and replace the same., EVERY SINGLE instance, I ended up returning, dig it out, and replace with fresh. Not good when several homes depend on a road and a "jelly hole" is permanent,