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jklingel 03-29-2010 11:31 PM

compaction requirements?
 
Is there any OSHA-type standard for the specs on a compactor used to compact gravel under slabs, around/under footers and foundation walls? I was just wondering if a compactor that pounds out 4000 lbf would pass specs, or if one needs a larger machine, like 5000 lbf or so. I would be compacting gravel at a maximum of 8" lifts, and will have undisturbed glacial silt or undisturbed fractured shist as a base. A 4000 lbf machine, with a minimum of four passes, has been recommended to me by a manufacturer; just double checking. This is for one or two houses, so speed is not critical; I don't get paid either way. Thanks. john

Bondo 03-30-2010 05:16 AM

Ayuh,... If you reduce the lifts to about 1/2 or less than stated,.. You'll make inspection No problem...
You won't get compaction to 8", but 3" or 4" will work...

jlhaslip 03-30-2010 09:27 AM

sprinkle water on each lift will help to tighten the compaction.

jklingel 03-30-2010 01:17 PM

Quote:

Originally Posted by Bondo (Post 421547)
Ayuh,... If you reduce the lifts to about 1/2 or less than stated,.. You'll make inspection No problem...
You won't get compaction to 8", but 3" or 4" will work...

Wow. One of the company web sites lists suggested compaction depths, and they claim their 3250 lbf machine will compact to 14"; the 2475 lbf machine to 12". That sounded generous, and likely perfect conditions, so I thought I'd get a second opinion. Yep; we'll keep the gravel damp. Thanks. j

rustyjames 03-30-2010 02:46 PM

Quote:

Originally Posted by jklingel (Post 421522)
Is there any OSHA-type standard for the specs on a compactor used to compact gravel under slabs, around/under footers and foundation walls? I was just wondering if a compactor that pounds out 4000 lbf would pass specs, or if one needs a larger machine, like 5000 lbf or so. I would be compacting gravel at a maximum of 8" lifts, and will have undisturbed glacial silt or undisturbed fractured shist as a base. A 4000 lbf machine, with a minimum of four passes, has been recommended to me by a manufacturer; just double checking. This is for one or two houses, so speed is not critical; I don't get paid either way. Thanks. john

OSHA is for job safety. If it's gravel, 8" lifts would be fine.

tpolk 03-30-2010 02:57 PM

why such big lifts? are you floating footings? you want something tight order pugmill will come wet and set like concrete. it is basically crush an run gravel wet down which you can do onsite to bypass the extra weight on the haul charge

Daniel Holzman 03-30-2010 04:39 PM

As noted, OSHA is the Occupational Safety and Health Administration, they have nothing to do with specifying standards for compaction of gravel. Compaction of soil is typically specified in terms of Proctor density, which can be measured using a variety of techniques, including nuclear density gage, and sand cone, to mention two common methods. The spec typically refers to a percent of Proctor density, i.e. 90 percent or 95 percent is common.

It is uncommon to see a specification that names a specific model or type of compaction device to be used. Normally, the spec states the required Proctor density, and certain soil parameters (i.e. less than 5% passes the #200 sieve). The contractor is then permitted to use whatever type of machine they choose to achieve the required result. In your case, I doubt anyone is going to certify a specific machine, they may have a specific result in mind.

jklingel 03-30-2010 06:39 PM

answers....
 
Thanks for the input. (1) Why such big lifts? Other than being faster than a 4" lift, I dunno; that is what the engineer said was acceptable, and that is what I hear often. I have only done a few houses, so am just trying to figure out what the hey so I am henceforth doing it for-sure-right, instead of likely-right. This will be a long house. If need be, I'll scale back the lift height. (2) Oh, yeah. OSHA is for safety. Duh. I knew that.... (3) I was hoping there were guidelines like "if you want to meet such-and-such specs, typically a 4000 lbf machine is necessary". I guess I was wishing for too much. Thanks again. john

Daniel Holzman 03-30-2010 08:06 PM

One more detail. You said that the soil would either be undisturbed glacial silt (I think you meant glacial till) or undistrubed fractured schist. In either case, I don't follow why you feel you need 8 inch lifts. Typically with a very strong material like dense glacial till or fractured schist, the engineer would spec a 4 inch thickness of structural fill or crushed stone. Unless there is something truly odd about the soil, you would not need to go even 8 inches thick.

A 4 inch thick layer of structural fill is simply a pad to support the concrete, and it allows for drainage. It can likely be adequately compacted using almost any small machine, typically a plate whacker is used, or a hand held vibratory roller. Especially since this is residential, not commercial. You should check with the designer, you may be overkilling this project.

jklingel 03-30-2010 10:26 PM

more answers
 
Thanks for the questions/info. I did not go into great detail before, so here is a bit more info. (1) GLACIER SILT [1]
The pulverulent material, produced by glacial erosion, that is washed out beneath a glacier and deposited at lower levels by glacial streams. We've got the stuff all over the place here. Maybe "till" is another name for it??? (2) Under the slab, I think we'll be packing approx 6". That, I am not too concerned w/. (3) Around the foundation walls, which will be 50" to the top of the 8" high footer, is where one concern for compacting will be. The trenches around the foundation wall will be big enough to work in comfortably, and may be a tad over-sized because I may be digging them w/ my skid steer instead of renting a hoe. I'll have to get info on rental price, etc. Either way, there is going to be some serious back-filling and compacting to do. The house will be 96' long x 44' wide, with an additional "foundation wall" down the center in both directions, if that makes sense. (4) The engineer has spec'd a 12" deep by 20"-24" wide compacted fill under the footers, too, to give more bearing area under the footer. The short of the long is, I will be compacting for a long butt time, and therefore want the lifts as high as possible. I hope that clarifies things a bit. If anyone has any other suggestions, now's the time. Thanks. john

tpolk 03-31-2010 05:53 AM

make sure you trenchs are safe to work in, step back your removed material

Clutchcargo 03-31-2010 07:55 AM

I don’t have anything useful to contribute to this thread but for those of use that have no idea what you’re talking about, what does this mean?
“compacting gravel at a maximum of 8" lifts”

jklingel 03-31-2010 01:59 PM

Quote:

Originally Posted by Clutchcargo (Post 422100)
I don’t have anything useful to contribute to this thread but for those of use that have no idea what you’re talking about, what does this mean?
“compacting gravel at a maximum of 8" lifts”

That just means putting down 8" of gravel, compacting it, then 8" more, compacting, etc.

Daniel Holzman 03-31-2010 05:28 PM

You are not going to save any time by compacting in large lifts, i.e. lifts over 4 inches thick. The reason is that as the lifts get thicker, the total number of passes required to achieve the required density is going to increase rapidly. At some point, depending on the energy delivery of your compacter, you will not be able to deliver enough energy to compact the bottom of the lift to required Proctor density, and you will theoretically need to hammer away at the lift for essentially an unlimited time to achieve the required density.

In the commercial world I practiced in for years, the typical maximum lift I ever saw compacted was 4 inches of structural fill, and that was with a large vibratory roller. The experienced contractor knew that with a 4 inch lift, they could get the required compaction with a minimum number of passes, typically two each direction. If they kicked the lifts to say 6 or 8 inches, they would need say 4 passes in each direction, but there was a real risk they would not meet the compaction requirement, and they would then have to recompact. Time is money, so I never saw anyone take the chance. If you are needing more than two passes each direction, you are either using improper technique, your lifts are too thick, the soil is at the wrong moisture content, or you need a larger machine.

In the case of residential work, there may not be any test performed of the compaction, in which case the engineer may simply specify a maximum lift thickness (typically 4 inches), a minimum energy for the machine, and a minimum number of passes each direction. In the commercial world, the density is almost always measured, so it is up to the contractor to select means and methods to achieve the needed result.

jklingel 03-31-2010 07:47 PM

Great points!
 
Dan: I see the logic to what you are saying. The one manufacturer I contacted said 4 passes would be necessary w/ an 8" lift, (w/ his 4000 lbf machine) but it now makes more sense to keep the lifts to 4" and go over them 2, or maybe 3, times. I did not think about the graph of lift height vs pound-feet of the vibrator being non-linear. The light bulb just turned on. Thanks. BTW: On the glacial silt vs till, we/I may be using the wrong term, or I may not hear the right word when people speak it. I have significant hearing loss in certain frequencies and it screws up some words big-time. QUESTION: Have you ever heard of over-compaction? I heard my dad talking about that at a house we were working on years ago, but I never asked if he was just horsing around; he is an engineer, but he horses around a lot, too.


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