Density Tests 1

[belzer]

I want to verify dry density and wet density numbers on a Troxler 3440.

I know how to verify dry density---proctor x % of compaction=
dry density number.

How do I verify the wet density number?

Thanks

 

[darthsoilsguy2]

if you are double-checking someone elses tests, the biggest problem you'll have is location. field techs hardly ever give exact locations and hardly ever are exactly correct with regards to elevation or location if given. depending on the site, reference points may be few and far between. this is industry standard or at least standard for the industry.

wet density goes up and down as in-situ moisture content varies over time. the wet density can change during construction too. example: 1.contractor compacts fill at -4' below subgrade 2.tech performs density test and passes it 3. no fill is placed for 1 week in this area and you get no rain and temps in the 90s. the dry density will not have changed but moisture will have left the soil.

 

[oldestguy]

All nuclear density and moisture testing should be verified by some other method, such as the well proven sand cone method. Most techs don't do any calibration like this, and that is why some conflicting job problems can come up.

So if you wish to have some proof of what they give you, ask for a test technique by a proven method at that same location and at same time.

With testing costs something that do not result in a better end product visually, the tendency is to use the lazy way, such as the nuke meters. Results may not be even worth what they cost, depending on technique and other things.

You may think you have great accuracy, when it more likely is good precision, but lousy accuracy, like 125.36 pounds per cubic foot indicated, when the actual number may be 118.0 pcf.

 

[DirtDelight]

Can I ask why you are trying to verify the wet density ?

 

[casimmons]

wet density = dry density x (1+moisture content)
with moisture content as a decimal

 

[civilperson]

belzer,
How do you know the % of compaction to use in your check of dry density?

 

[belzer]

Sometimes I need to "adjust" numbers to correct for proctor changes.

Nothing "critical" but necessary to facilitate movement on job.

cassimons response is familiar, I will verify tomorrow.

Thanks for responses!!!!!

 

[BigH]

Be careful. A Professional Engineer in Ontario, a coiuple of years ago, lost his license for 2 years for "adjusting" numbers to facilitate movement on the job.

 

[BigH]

In addition - you might want to check the troxler moisture content with a laboratory moisture content. Years ago, we did this for crushed stone granular fill in Toronto and the laboratory moisture content was 70% of the troxler moisture. So we corrected for the laboratory moisture content - but we had justification. You should calibrate your troxler moisture with the lab and the density with, say, the sand cone.

 

[Mickney]

"adjust" numbers to correct for proctor changes...to "facilitate movement on the job".

Those phrases would scare the heck out of me if I were a principal at your firm.

 

[darthsoilsguy2]

adjusting proctors doesn't scare me as much as the star that casimmons got.

 

[mb27]

Maybe I need some clarification, as I'm only a lowly technician, but how does a sand cone really verify the nuke at all? For example, you do a sand cone test, for which the typical hole is 4-6 inches deep (unless there's some other method I'm unaware of), meanwhile a nuke test can read a foot down. Technically, if 8" lifts are placed, you're testing a whole other lift which could be a whole other material with the nuke, while the sand cone is only testing the current lift.

Would a good strategy be to do a 4-6" nuke test to better correlate with the sand cone?

Just curious...I'm on a job currently with the Army Corps of Engineers where sand cones are a requirement. Everyone says it's an ancient and outdated test, but I do honestly see the value in it, so long as the sand cone test goes smoothly. I did search for a thread on the sand cone test alone, but couldn't find one.

 

[Drumchaser]

belzer,mb27

No.s of tests are required,and should be completed.

The preferred method to verify the gauge (in my world) is to run the "oven dried" sample along with the guage readings at several locations.

WC=100(Ww/Ws)
*seldom (but it does happen) the nuke will read a "false" moisture if materials contain salvaged ACP etc.



-----------------------------------------------------------
Being one who has spent lots of time getting to know dirt I always see too many folks getting hung up on the numbers (%proctor, moisture, etc. and so on) and forget that the embankment must be stable and compact.(as easy is this sounds it is routinely lost in the process)

Large embankment job requires many curves or proctors:

* When samples are taken for proctors, put a small portion in a glass jar (mason works great), label the loc., depth etc....later add the other data..ie PI - 22 / 118.8 @ 9.2% optimum moisture.

Due to the fact that you cannot possibly have a proctor for all materials used as embankment (unless you are very lucky) after some time you will have several jars and will be establishing a "family of curves" from this process
and just by looking at the color and properties from the cut/pit locations, be able to quantify materials you do not have a specific moist. dens. curve for.

At least 15-20 jars and curves is reasonable.

As far as adjusting the guage......

You should be familiar with the guage manufacturers recommended procedures..ie standard counts, actual depth of probe hole etc. and so on.
The Troxler owners manual would be of most value to you in these matters.
The spec.s of your project, test methods allowed etc. are crucial.
I have seen some correllations allowed over the years but only with extensive approval and backup (before hand.

Hope this helps you

 

[woofar]

Hi mb27,

I guess this is a little off topic from the original question of this old post, but to answer your questions.

First up the sand cone may be considered ancient but never outdated. When properly performed it is the best true way to assess the field density of a given material.

Properly performed, is the most important part here. Provided extreme care is taken at every point, from the calibration of the pouring sand, digging the hole ensuring that there is zero movement of the plate, right through to the moisture content determination. Every thing must be performed correctly. It can then be used as a benchmark to calibrate your nuclear gauge into that material.

For consistancy you will find that it is best to calibrate your nuke at 1 inch less than your sand cone test. For a six inch sandy use a 5 inch nuke. For an 8 inch sandy use a 7 inch nuke. The depth of your sandy should be the full depth of the layer you are testing, the nuke 1 inch less.

The nuke is actually extremely accurate for wet density measurement but falls down in moisture determination, that is the reason for the calibration. Alternatively, you can use the nuke for wet density determination only, then dig out a moisture sample and determine the oven moisture content of your sample.

What it comes down to is there are NO instant answers that your job foreman is asking for. Sure, in some situations that can be provided but it is nowhere near the norm.

It sounds like what you need is a surly old soily like myself to to quietly explain a few facts of life to these blokes. Don't ever let yourself be browbeaten into giving inferior results and don't ever fall into the trap of trying to estimate the results. When they ask you for a guess tell them that "My best guess is I'll be able to tell you at 7 o'clock tomorrow morning, but if other clients want to talk to me it may not happen till 9 o'clock.

That might sound a bit narcy, and I am not saying that you should be flippant with them but you do need to explain some facts of life to them, Quality results just take time, full stop.

 

[dirtsqueezer]

I am disturbed. I've run a Troxler gauge for ...8? years now and it has always proven accurate. You shouldn't need to adjust for anything, unless you have bituminous materials in your dirt. Verify with the sand cone is a great idea; I ran sand cones in tandem with Troxler shots and the two fit perfectly. But don't adjust your numbers. Once you stray to the Dark Side, "forever will it rule your destiny".

Watch out. Trust your numbers.

 

[mb27]

Missouri isn't much on sand cones. I've probably run more in 2 months than anyone else in our company (granted, we had to do 40 sum-odd test pits where 2-6 sand cones per hole were normal). We had a QA (our competition) test along side us with their nuke, and he said he's been in this business for 17 years and only ever seen the sand cone once. And by once, i mean one time, that's it.

 

[mb27]

perhaps i should make a thread just for sand cone questions, heh.

 

[woofar]

Hi Dirtsqueezer,

You certainly do need to adjust, take a look at our testing manual at this site.

http://www.mainroads.qld.gov.au/web/partnersCR.nsf/DOCINDEX/Nuclear+Gauge+Testing+Manual

In particular, click on the Test Methods link and scroll down to Test Method N01,Test Method N02 and Test Method N03.

Admittedly it is fairly tedious reading, but there is a lot of good information there.

Cheers
Michael

 

[Drumchaser]

First hand knowledge.

Again...your nuke gauge manual (comes with the machine) has very relevant text and applicable formulae (used too, anyway) manufacturers recommended instruction is a good place to start. If you do not run your standard counts and know how to operate the gauge, you are erroneous from the start.

Having spent more than 20 years playing with a Troxler on soils, treated and non-treated base courses, and ACP, (asphaltic concrete pavement) I always ran oven dried samples when a new material entered the scope, as a verification to quality assurance as well as backup if there were any "questions" to the gauges stability etc. (some folks do not take care of the gauge) Oven drieds always matched the gauge very closely.

"falls down in moisture determination" ????????????????
Never came across this episode

The gauges I have seen/used are always very reliable (if used properly)

To reiterate my earlier point....getting lost in the numbers is common conundrum.

Once you have used the gauge for some time, and somewhat begin too know your soil properties....you will see that the big part of the reason the gauge, (or any test) is used, is to bring forth the equipment, materials, and labor necessary to achieve a density controlled embankment.--------- Compactive effort.--------------------

Do not misunderstand, the required number of tests for a given lift, or quantity of soils is important.
Soils are not an exact science...sometimes your fill area is stable and tight and the density will not pass. ( your proctor is not as representative of the area as you thought)
Sometimes your lift is pumping and nasty, but the density passes. So see, you can't always have the correct proctor input into the gauge for a given area/qty. of materials....hence the "family of curves". (earlier comment in this thread)
Dirt is very frustrating at times to say this least. It takes /took much suffering to get a clear picture.

The type of embankment to be placed has a lot to do with your program. Is it all mostly low P.I.? High P.I.? Silty? Sandy? Wet, with disking required to dry it out? Dry? Lots of water truck/tanker action to establish the required moisture content?

Is your cut (pit area(s) full of roots that require picking out before compaction begins (if you are watching…)
If the equipment is there, the compactive effort is there (lift thickness not exceeding 10-12”) and the embankment is processed as needed, you are heading in the correct direction.
If they are hogging the dirt in (large lifts, minimal compactive effort, with no drying if req’d. and no addition of moisture if req’d) you have problems.
-Regardless of what the cone, gauge, sun dial etc. says.-

 

[woofar]

Hi Drumchaser,

"falls down in moisture determination" ????????????????
Never came across this episode.

That is not just a theory of mine, that is a proven and documented fact. Documented by our department who have been doing a very extensive research program that has been ongoing for the past 30 years. It has also been documented by the nuke gauge manufacturers. That is the reason that they provide the offset function in the gauges, so that you can apply the required density and moisture biases.

Take a look at our testing manual which I put a link to in my previous post. Compliance with that document is the legal requirement for any soil laboratory in Queensland. Upwards of over 500 laboratories.

We only calibrate into manufactured gravels or insitu material that is very consistent. For all other materials we do a proctor for every density test, sometimes a sand replacement and sometimes we use the nuke unbiased to get a wet density figure and then dig out an oven moisture content.

Cheers
Michael