Are compaction tests of #610 crushed stone reliable??

[VanMeter123]

I work for a large concrete contractor and although I am not a licensed engineer I do have an engineering degree. I have a project that consists of installing foundations for a large distribution facility. This building has about 4,000 LF of "dock" wall. Which consists of a continuous footing with a 5'-4" tall by 8" foundation wall.

The general contractor is a large design/build firm and their structural engineer has specified that we backfill the wall with #610's which is a gradation of #6's through #10 stone. He also wanted us to install the stone in 6" lifts and use a plate compactor to compact each lift. Which, I agreed to do. After we had backfilled several lineal feet of the wall the GC had their testing firm take a proctor of the #610's and they did a nuclear compaction test on an area we had backfilled. Which of several readings the best being 88% compaction, quite below the 98% they are requesting.

With my several years experience I have always used #57 stone with no compaction to backfill foundation walls and have never had any problems. However, I have never used #610's. I have always heard that you cannot test compaction of #57's understandably so. However, my question is can you accurately test compaction of #610 stone? I thought the only stone that you could test accurately was dense grade aggregate or DGA. Although #610's has some fines in it and is more dense than #57's I am inclined to think that there are still to many voids and compaction tests would not be accurate.

Furthermore, the GC is saying that I need to get "pugged" #610's or wet them as I compact them and that will bring the compaction results up. I just would like some input on whether this will help or are the compaction tests on #610's so unaccurate that no-matter what I do the results are not going to get and better.

Thanks

 

[boffintech]

You asked, “Are compaction tests of #610 crushed stone reliable?” The answer is yes. If a proctor, either D698 or D1557, can be performed on the material then in-place density tests can be performed on it.

My recollection of the gradation for #610 stone is

Percent Passing
1 ½” = 100
1”= 85-100
½” = 40-75
No. 4 = 15-40

so a method C (and possibly method B) of either D698 or D1557 can be performed.

Is the minimum required density 98% of the Standard Proctor D698 or the Modified Proctor D1557?

What were the test results?
Maximum Dry Density (MDD) of Proctor = ?
Optimum Moisture at MDD = ?
In-place wet Density = ?
In-place MC = ?

If your stone has become segregated (is not sweet, has “rock pockets”) then you will get these low in-place density test results. Make sure that your stone is well mixed and that it actually meets the gradation requirements for #610, that an accurate proctor is being used, and that your material is at or near the optimum moisture content.

Also, that plate compactor idea is crap; you need a device that will deliver a lot more energy to your stone like a RAMEX walk behind vibratory roller.

 

[boffintech]

Also, you wrote, “He also wanted us to install the stone in 6" lifts and use a plate compactor to compact each lift.”

I can see a maximum lift thickness requirement, but if the GC is going to direct you as to the means and methods of how you are to perform your work then he should be required to live with the results. If his directions are “use a 6” lift with a plate compactor” and his directions only get the stone to 90% of MDD, well that’s his bad. If on the other hand your contract reads something like “place material in lifts of 6” max. and achieve a minimum of 98% of MDD” and you picked the equipment that got the stone to only 90% of MDD, then it’s your bad.

If you put a heavy vibratory roller on the material and the material is at or near optimum moisture content you can get 98%, but you might also blow out or crack your wall. Was this the reason for him suggesting the plate compactor?

A plate compactor might work great for #57 stone but I seriously doubt it is ever going to get you to 98% of either standard or modified proctor with #610. You need some equipment with more energy like a Whacker Packer (jumping jack) or a RAMEX walk behind vibratory roller.

Also, 6” is the “maximum” allowable lift thickness. You can place the material in thinner lifts so that the energy from whatever equipment you use can better penetrate and compact the material. I understand that this is considered blasphemous talk to contractors, but it is true that you don’t always have to use the max lift thickness when placing fill.

By the way, are dock levelers to be installed? Now? Later? Is this the reason for #610 instead of #57 stone. I’m guessing that the EOR is concerned about long term settlement of the fill material due to forklift and dock leveler vibration.