Proctor Compaction Testing of Sub-Grade Material

lakeroadster · Dec 7, 2016

The topic of soil compaction seems to come up here often.

Many contractors want their customers to simply trust the excavator and concrete prep sub-contractors. I'm more of a "Trust but Verify" guy.

I thought I'd take the time to start a thread related to one method of testing compaction.

See attachments below for some visuals of the actual on-site test. I had this test done before my barn slab was poured.

The key is to use fill materials that have known Proctor density data and to be up front with the excavator and site prep sub-contractors. If they buy material from a reputable aggregate provider, they can use previously tested proctor material.

Here's the actual test we had the local testing facility perform. It is a density test on the slab sub grade using a Troxler 3450 calibrated nuclear moisture - density gauge.

6 readings were taken, average was 97.45%, variance of readings were within 3.0%.

This test cost 160 dollars. That's money well spent to know the sub-grade compaction is good, and that it is consistent.

The equipment used to compact the soil, and the maximum lift height before compaction is a highly debated subject. If you have the lifts tested, it takes all the guesswork out of the project.

If there is material that the contractor wants to use that doesn't have Proctor data, that material can be tested for about $100. The kicker is it will have to be consistent. That's why using fill from a reputable aggregate supplier, that screens and processes the material is so important.

Here's a wiki article on Proctor Compaction Test: https://en.wikipedia.org/wiki/Proctor_compaction_test

KDXSR5 · Dec 7, 2016

This is great info to post about. If there is one thing I learned after taking two semesters of soils classes in college, it is that there is so much more going on with dirt than anyone ever cares to think about including contractors and many engineers.

I have been on a few commercial and industrial construction sites that have had proctor tests performed, and have seen first hand contractors try to hide the fact that they did not properly compact their fill/base. It is messed up, but probably more common than just doing the work right in the first place.

mitw44 · Dec 7, 2016

I am an environmental engineer, and have had this test done when placing an impermeable clay cover over a landfill. The clay cover has to be placed so that water can not leach down to the waste beneath it. Two feet of clay cap followed by one foot of soil and vegetative cover is usually prescribed. Usually, maximum lifts of no greater than 6 inches are specified, and a heavy sheeps foot roller has to go over it to compact it.

The proctor test as described above is then required every so many square feet to verify the work is done correctly.

mburrus · Dec 7, 2016

i had a similar test done on my slab... i wasnt here to watch the guy, but it was wither 96, or 98%, i cant remember which.

it is actually required to have those test results on site for the inspector to sign off on OK to pour... they are really strict here with inspections.

pcmeiners · Dec 8, 2016

Tests are cheap, but not around my neck of the woods.

"Many contractors want their customers to simply trust the excavator and concrete prep sub-contractors."
Trust a contractor, thanks for the laugh. In New York, they should have a hunting season for them, no license required.

readhead · Dec 8, 2016

Did you have similar results when you tested the holes for the posts? How much differential between the posts and slab is acceptable?

lakeroadster · Dec 8, 2016

readhead said:
Did you have similar results when you tested the holes for the posts? How much differential between the posts and slab is acceptable?

Acceptable density for the slab sub-grade:

For my project, the structural engineer specified a minimum of 92% of maximum density, as defined by the proctor curve for the given material type. He noted that the density must be uniform across the sub grade area and not vary by more than 4%.

Holes for the building support columns:

For our Lester Pole Barn the holes were not density tested.

The structural engineer specified that as long as the columns are supported, at depth, by undisturbed soil that no density testing was needed.

The holes are excavated to depth (about 4 ft below elevation), loose dirt is removed by hand (shovel) and then either concrete pucks, or poured concrete is placed. This means the bottom of the holes are undisturbed soil. For more information, start at post #29 here: http://www.garagejournal.com/forum/showthread.php?t=289293&highlight=proctor&page=2)

To compensate for excavation depth variances the outer members of multi ply columns are supplied longer than normal, and are cut to length at assembly. Blocking is used in the center members. For a visual of this see post #43 and #48 here: http://www.garagejournal.com/forum/showthread.php?t=289293&highlight=proctor&page=3)

readhead · Dec 8, 2016

So it is assumed that the posts are on 100% soils? So really no different than other types of construction.

Sharpest · Dec 8, 2016

I'm a superintendent on multi-million dollar jobs and due to liability later on down the road, we live and die by soil testing. On my current job, we have dozens if not hundreds of density tests and a ton of proctors from different areas around the site on file. I took one four-hours soil science class when I was in school and HATED it then but the knowledge has paid off in dividends since then.

lakeroadster · Dec 8, 2016

readhead said:
So it is assumed that the posts are on 100% soils? So really no different than other types of construction.

No assumption... The columns are supported by undisturbed soil. Your term "100% soils" doesn't address compaction or density: http://www.about-home-design.com/basement-construction.html

Foundation, or footings, must be placed on solid ground, or what’s called undisturbed soil. Undisturbed soil is soil that has been in place for thousands of years.

No one has dug it up and filled it back in. It was compacted by Mother Nature with gravity. The soil particles have become tightly packed. Undisturbed soil will not compact under the weight of the house. That’s what you want...

Angelfire · Dec 8, 2016

Damn, I wish I could have gotten that price! I had mine tested as well, and it was two locations as I had my shop building and a home addition going at the same time but my charge was significantly higher. Most testing agencies in my area are not familiar with doing residential so when you call they tend to up the price to make it worth their time. That all being said, I still consider it money well spent and I'm glad I did it. My dirt guy and concrete guy thought I was crazy but oh well....

readhead · Dec 8, 2016

In your previous description you indicated that the posts were on undisturbed soil and I called that 100%. I think we are talking about the same thing.

lakeroadster · Dec 10, 2016

readhead said:
In your previous description you indicated that the posts were on undisturbed soil and I called that 100%. I think we are talking about the same thing.

1jjpop · Dec 11, 2016

I like to see a 8'' lift of dirt , then use a sheepfoots roller & make 8 passes with the roller. or keep rolling till you get a 3'' walk out . [meaning a roller is suppored on its feet] & not going in the ground 3'' . If it is good enough to build the interstates .Its Good enough for me. You can't beat A sheepfoots roller for compaction . Running over it with rubber tires don't cut it. Unless you have 2 or 3''lift.

lakeroadster · Dec 11, 2016

1jjpop said:
I like to see a 8'' lift of dirt , then use a sheepfoots roller & make 8 passes with the roller. or keep rolling till you get a 3'' walk out . [meaning a roller is suppored on its feet] & not going in the ground 3'' . If it is good enough to build the interstates .Its Good enough for me. You can't beat A sheepfoots roller for compaction . Running over it with rubber tires don't cut it. Unless you have 2 or 3''lift.

Opinions vary on the means to the end. That the beauty of the compaction test, it doesn't care how you arrive at the destination, only that there is verification that the job is right at the end. :thumbup:

allenb12 · Dec 11, 2016

Last project I managed we took over 4,500 density tests. Around 400 proctors. There are two types of proctors. Standard and modified. Modified and standard. Because we had a laboratory technician on site every day all day we paid the laboratory a hourly rate, not by the test. Much cheaper that way.

Trochu · Dec 11, 2016

lakeroadster said:
6 readings were taken, average was 97.45%, variance of readings were within 3.0%.

This test cost 160 dollars. That's money well spent to know the sub-grade compaction is good, and that it is consistent.

Just so you know, generally, a test of 94%, regardless of what your structural engineer said, isn't "good". Typical specifications in my part of the country are as follows:
-Narrow trenches for utilities: 95%;
-Top 1' of subgrade: 98%;
-Sub-base: 98%
-Base, for concrete surface: 98%; and,
-Base, for asphalt surface: 100%.

I've never seen a specification less than 95% (landscaped areas and trenches) let alone 92%. Your first clue should have been a structural engineer providing geotechnical specifications. Nobody would go to a geotechnical engineer for structural recommendations, it goes both ways.

Anglefire said:
Most testing agencies in my area are not familiar with doing residential so when you call they tend to up the price to make it worth their time.

Familiarity? Thats just an excuse, the test is exactly the same whether its for commercial, residential, industrial, or a municipal project.

Trochu · Dec 11, 2016

allenb12 said:
Last project I managed we took over 4,500 density tests. Around 400 proctors. There are two types of proctors. Standard and modified. Modified and standard. Because we had a laboratory technician on site every day all day we paid the laboratory a hourly rate, not by the test. Much cheaper that way.

A proctor every 12 tests?!? :yikes:

david71984 · Dec 12, 2016

If you paid your structural engineer to do any analysis on geotechnical data than you should get a refund. Just because you have undiaturbed soil does not mean it is suitable for structural integrity or a certain load applied. There is a reason we do pile load tests and other analysis based on soil properties. I am an expert in this field so trust me when I say that engineer is incorrect and I hope he is not a PE. He can lose his license for that.

david71984 · Dec 12, 2016

Trochu said:
A proctor every 12 tests?!?

Ha, yes our specifications call for a check proctor (1 or 2 point curve) every 5 field densities and a sand cone density check every 10. Actual full proctor testing is performed every 1200-1500 cubic yards or visual material change.

By the way you should never trust an aggregate source for their density information. It is NEVER the same. The correct way would be to run test on the actual stockpile prior to being delivered. Plus it is not calibrated by the technician with the density data either. FYI

MagKarl · Dec 12, 2016

Nice to see some real life experts contributing to this thread.

brownbagg · Dec 12, 2016

I been doing testing and inspection for the last 32 years, started in the soil, concrete and now into welding and structural steel. Yes the info presented here is correct. I have even had some of the check points and sandcone jobs. but my daily activity is usually 60-90 densitys per day. I keep a sand cone in my truck

lakeroadster · Dec 12, 2016

david71984 said:
If you paid your structural engineer to do any analysis on geotechnical data than you should get a refund. Just because you have undiaturbed soil does not mean it is suitable for structural integrity or a certain load applied. There is a reason we do pile load tests and other analysis based on soil properties. I am an expert in this field so trust me when I say that engineer is incorrect and I hope he is not a PE. He can lose his license for that.

So just to be clear, you are saying that in your opinion every undisturbed soil footer requires density testing? Is that something in your experience that is being done on home projects, garage projects or any pole barn project you have been involved with?

Isn't that something that should be specified by the jurisdiction when permits are pulled... like engineered truss drawings?

74grabber · Dec 17, 2016

1jjpop said:
I like to see a 8'' lift of dirt , then use a sheepfoots roller & make 8 passes with the roller. or keep rolling till you get a 3'' walk out . [meaning a roller is suppored on its feet] & not going in the ground 3'' . If it is good enough to build the interstates .Its Good enough for me. You can't beat A sheepfoots roller for compaction . Running over it with rubber tires don't cut it. Unless you have 2 or 3''lift.

Sorry bud I have to pick on you here.

I'm a quality control area manager (multi states) for a multi billion dollar road and highway construction company. Been here a little over 15 years. If you have ever been West of the Mississippi you have more than likely drove on a road we built, been in a commercial or private plane that landed on a runway we built, or used water from a canal we built.

Not once have we ever done a "8 inch lift of dirt", not once have we ever judged compaction based off of the amount of roller passes, and most certainly have we never judged it on the the walkout!

Very good right up OP, nice to see homeowners going through the extra steps.

raffaelli · Dec 17, 2016

On our project sites, we require compaction proctors under all concrete, including sidewalks. We do not accept anything under 95%.

Cant have a stable structure without stable soil.

brownbagg · Dec 17, 2016

the undisturbed soil has always been a myth on the principal that the soil would sur charge over million of years, and it possible to build a house on undisturbed soils if the footers are design right, we are talking small house, single story.

but like the guy said, nothing gets pour till compaction is done, even on undisturbed soil

ms fowler · Dec 18, 2016

Lots of good info, but some that needs correction, slightly.
A Proctor test. aka Moisture-Density curve is a LAB test. It establishes both the optimum moisture content and the maximum density for a particular soil, compacted using a specific amount of energy. In the lab, the soil is prepared at different moisture contents and allowed to cure so that the moisture is thoroughly mixed in with the soil. The mixture is then compacted in a steel mold using 3 or 5 lifts and a drop hammer. The Standard test uses 3 lifts and a 5.5lb hammer dropping 12". The Modified test uses 5 lifts and a 10 lb hammer dropping 18". You can see the difference in energy used ( 12,400 ft lbs versus 56,250 ft lbs). Modified Proctors give higher max density and lower optimum moisture content than Standard Proctors. As the series of points are plotted a pattern emerges. From a dry state, density increases as moisture increases ( The air voids in the dry samples are increasingly filled with water in the wetter samples--water weighs more than air, so the density increases. UNTIL--until you have nearly all the air voids filled with water--then, as you add more water, the water displaces some of the soil. Water weighs less than soil....so the density decreases.

A specification of ___% compaction is a faulty spec. A proper spec ALWAYS references the method used to get the maximum density. A test of 95% of a Std is not the same as 95% of a modified. Modified tests came about because compaction equipment got better, and some people cannot understand a test result of 108%. They think of Proctor values as absolute instead of relative--based on the energy used to compact the sample.
The results of the lab-Proctor test are taken into the field where a tech tests the soil after it has been compacted. The age-old method involved digging a small hole and filling it with sand ( Sand Cone). The sand was used to calculate the volume of the hole, and the soil taken from the hole was weighed--so you had a weight and a volume-and that gives you a density. The more modern method uses radioactive particles to estimate the density and moisture of the soil to be tested--much faster, and generally accurate. The density and moisture from this test is compared to the Proctor value, and you get a % compaction.
Practices have varied over the years. 95% of a Std was the normal specification for low-rise building. Interstate Highways usually require 95% to 97% of a modified proctor.

here is an image of a Proctor curve:
http://www.ipm.iastate.edu/ipm/icm/2005/5-9-2005/soilmoist.html

ms fowler · Dec 18, 2016

brownbagg said:
the undisturbed soil has always been a myth on the principal that the soil would sur charge over million of years, and it possible to build a house on undisturbed soils if the footers are design right, we are talking small house, single story.

but like the guy said, nothing gets pour till compaction is done, even on undisturbed soil

Sorry, but I must respectfully disagree.
Surcharge is part of the mechanism, but so is "structure" and chemical bonds. Undisturbed earth has greater strength than disturbed earth compacted back to the original density.
It is a misunderstanding ( at some very high levels) that undisturbed earth can be compacted. It cannot. It may be toothed up--thus disturbing it, and destroying the original bonds--and then it may be compacted.
Many times, the crews digging footings disturb the earth far more than they need to. If they use a backhoe with long teeth and rake it across the footing, they do tear up soil several inches deeper than the bottom of the footing. This loosened soil should be compacted. However, if they use a flat blade and scrape no deeper than the planned bottom of the footing, then they do not disturb that soil, and could place the concrete directly on the undisturbed soil.

bowtiguy · Dec 18, 2016

As fellow Coloradan, how does Bentonite work into this mix? We live north of Denver ( hwy 7 & I25) and Ive seen dozens of $500,000 homes having basements redone. Am I correct in assuming that proper compaction of the soils was not completed before foundations were poured? ( they turn EVERYTHING over here & compact before they build)

Before we build on our UNDISTURBED property in the foothills west of Loveland/FoCo, will drilling holes/soil samples give us all the information we need prior to construction?

KDXSR5 · Dec 18, 2016

bowtiguy said:
As fellow Coloradan, how does Bentonite work into this mix? We live north of Denver ( hwy 7 & I25) and Ive seen dozens of $500,000 homes having basements redone. Am I correct in assuming that proper compaction of the soils was not completed before foundations were poured? ( they turn EVERYTHING over here & compact before they build)

Before we build on our UNDISTURBED property in the foothills west of Loveland/FoCo, will drilling holes/soil samples give us all the information we need prior to construction?

Living in Wyoming, we have a lot of the city I live in built on bentonite. The only proper and long lasting solution, IMO, is get past the bentonite and support your structure on/in a stable soil type deeper in the ground. Bentonite is an expansive clay, and relying on it to support a structure is a very poor choice. Expansive soils don't care about compaction. I see houses, some old and some brand new, being raised and having their foundations replaced every year.

Piles, both friction and bedrock bearing, with pier foundations are becoming more common here for construction in bentonite areas, and even that is not always 100% safe. I finished up working on a large high school project earlier this year that was built on piers in a bentonite area, and the foundation is already having issues.

If possible build where their is no bentonite. My house was built in the sand. My neighborhood is a nice one, but not the most desirable in the city. All of the "desirable" areas are built on bentonite. No thank you, I will gladly live here and never have to deal with the hell that is expansive soils.

Google "building on bentonite" or "building on expansive soils" and you will quickly realize that the experts reccomend doing what I did and finding another place to build.

And yes, drilling and pulling core/soil samples and having them examined by the proper labs will tell your engineer what they need to know for properly designing a foundation for your house. Good luck!

ms fowler · Dec 18, 2016

Bentonite is a wonderful material----in certain applications. It makes great drilling mud. But, as a foundation material, I would rather not.

I heard a story about when they were first building the interstate highways through a mountainous area known for bentonite. The drill logs showed nothing, but after they blasted out the road way, they noticed the remaining rock face was moving. They used an instrument to locate the exact zone of movement, then re-drilled and sampled continuously in the zone of movement and found a tiny layer of bentonite. Not much, but just enough to allow the mountain side to slide. Slippery stuff, and very expansive.

bowtiguy · Dec 19, 2016

Thanks for the information gents. I don't think bentonite will be an issue up there. More like, how much dirt will be covering the rock!?

Next step is to get a LARGE precast culvert into the 50' w X 20' deep ditch that separates the cul de sac from the property to get a drill on site.

Thanks for all the info Lakeroadster, it will come in handy poring both the garage and house slabs!

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