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Compaction of rock and stone

Compaction of rock and stone

Compaction of rock and stone

Hello all
Mew here a my first time dealing with a compaction test requirement.
First off let me explain that by we are building a metal carport port barn 44x40 on a 4” concrete pad with 12” deep footers.
Also: I am a self contractor property owner with experience in residential building only.
Since the structure was to be built on a slope we hauled in about 40 loads of rock/soil mix and spread it S we went.
Much of it was spread with a tractor loader and some with a large skid steer.
The lower end required about a 16’ depth to near nothing on the upper side.
We had the footers dug and the inspector came and immediately requested a compaction test.
In our area a compaction test is done by an outside Geotechnical company and I pay for it.
Since I have never dealt with this before I was looking for some input about the test and how they could do it in the rock and dirt mix.
From what I have been told they use a rod to press down into the fill then an auger and then some type of cone test where they drop a device onto the fill from a certain height.
Here are my concerns.
The rid and auger is going to be difficult to get through the rock and soil mix.
Is this a good or bad thing so far as the test goes?
If for some reason the test is unfavorable what are my options since I already have the footers dug and everything set up ready to pour?
And as far as compaction what would I use to further compact the fill to possibly get it to the required result.
This has become a sudden nightmare and I just wanted to build a barn to store our truck and farm equipment.
I could have built it without a permit but I was trying to do the right thing.
Any suggestions or thoughts will be welcomed.
Please try and keep it simple and not to technical. I just want to get this all over with and done.


RE: Compaction of rock and stone

This is an issue I run into frequently and I get lots of referrals from the local codes department to deal with this very thing.

You DO need a Geotechnical Engineer. They will come to your site, take pictures, elevations and other measurements and they should take samples of the fill material for laboratory determination of the proper compacted density (called a Proctor Test). Depending upon the sizes and quantity of rock in your fill they should also be able to determine a correction for the in place density measurements.

One way I have approached this in the past is to dig a hole stepping down about 12" at a time and testing the fill with a nuclear gage as I go. I have seen others use an an instrument called a Dynamic Cone Penatrometer which is the rod you spoke of. If the density tests "pass" then you MAY not have an issue.

If the soil does not meet compaction requirements then you still have options, however, none are inexpensive. There are very few readily available machines capable of compacting a 16' thick soil layer so you may have to remove fill and replace and compact in 8" +- loose layers and having the soil tested as you go. Another option may be to have your footings and slab redesigned such that the loads are transferred through the fill down into the natural ground by the use of piles or piers of some type. A Geotechnical Engineer with knowledge of local soils and topography should be able to advise you on this.

One concern I have aside form the compaction is the fact that you have placed 16' of fill on a fairly steep slope. I evaluated one site where a very similar thing was done and water had made its way between the loosely compacted fill and the natural ground causing the fill to slip down the slope. It was a mess. The correction was to remove the fill and create level "benches" in the natural ground and then replace and compact the fill and test for density as the fill progressed. Again, a Geotechnical Engineer with knowledge of local soils and topography should be able to advise you on this as well.

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