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belzer (Materials) (OP)
20 Sep 08 18:55
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 (Geotechnical)
21 Sep 08 9:56
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 (Geotechnical)
24 Sep 08 21:52
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 (Materials)
28 Sep 08 2:40
Can I ask why you are trying to verify the wet density ?
 
Helpful Member!  casimmons (Geotechnical)
2 Oct 08 12:32
wet density = dry density x (1+moisture content)
with moisture content as a decimal
civilperson (Structural)
2 Oct 08 16:28
belzer,
How do you know the % of compaction to use in your check of dry density?
belzer (Materials) (OP)
2 Oct 08 19:02
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 (Geotechnical)
2 Oct 08 20:16
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 (Geotechnical)
2 Oct 08 20:18
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 (Geotechnical)
3 Oct 08 16:22
"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 (Geotechnical)
4 Oct 08 9:19
adjusting proctors doesn't scare me as much as the star that casimmons got. blllttt
mb27 (Civil/Environmental)
22 Dec 08 3:46
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 (Civil/Environmental)
22 Dec 08 7:47
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 (Geotechnical)
22 Dec 08 7:48
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 (Geotechnical)
22 Dec 08 14:31
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 (Civil/Environmental)
22 Dec 08 16:34
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 (Civil/Environmental)
22 Dec 08 16:35
perhaps i should make a thread just for sand cone questions, heh.
woofar (Geotechnical)
22 Dec 08 17:20
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 (Civil/Environmental)
22 Dec 08 20:39
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 (Geotechnical)
23 Dec 08 0:45
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

 
Drumchaser (Civil/Environmental)
23 Dec 08 7:44
Hey woofar

I will not dispute the extensive research program.  Since we all know that research programs are what make the world spin.
I would think Troxler has done some research as well.

Having gone to the Troxler web site (you made me do it)looking up the Troxler 3440, going to the Advanced Operations tab, is the language relating to "oven dried" moisture correction procedures, and pertinent formulae.



As I have stated it should be routine to correlate if moistures vary (%O.D. vs. %M reading from gauge) then corrections are allowed to be dialed in (this model appears to do it for you if the O.D. is input correctly)
Corrections are very rare/uncommon on soils, for us.

As the "manufacturer" states there are materials that will cause false %M in the gauge readings. For us it is usually recycled ACP mixed in with base materials (your term bitumen?)

Rarely have I had to use the two knobs for "moisture correction" on the gauge. But our spec.s do allow it under Test-Method xyz.



 
fattdad (Geotechnical)
23 Dec 08 9:30
Thought #1:  If you want to calibrate your nuke, do a side-by-side sand cone test, as referenced above.  That'll show you the wet/dry density of the in-place soil.

Thought #2:  If you want to determine the "percent compaction" get a bulk sample at the location of your density test.  (Wow!  That'd be a lot of proctor tests, eh?)

Thought #3:  Many field technicians use their nuke gauge like a $5,000.00 rebar.

There is a HUGE problem with folks assigning a Proctor value that confirms their "gut" instinct, i.e., that the soil is dense enough it just must have 95 percent relative compaction.  This is particularly a problem when the soil is below optimum (i.e., with dry strength).

I'm not saying that there should be a proctor for each denstiy test, but for the case of construction failures, the first thing I look for is whether the quality control program included confirmation proctors or one-point confirmations that the proctor that was used was appropriate.

End of rant.

f-d

¡papá gordo ain't no madre flaca!

woofar (Geotechnical)
23 Dec 08 19:02
I can't help myself I just have to keep responding even though we're probably way of track from the original thrust of this thread.

To drumchaser,

We are basically coming from the same line, a few technical differences here and there, but the most important part of testing, as you stated, is the quality of the person doing the assessment.

Your mention of recycled ACP brings up an interesting situation that we encountered last year. We were testing some recycled pavement that was a mixture of bitumen (sprayed bitumen not ACP) and varying ridge gravels. Initially we were testing it with one for one sand replacement testing but the results came out so consistent that we ended up calibrating the nuke to the material and using an assigned proctor value. According to the rules that isn't possible (supposedly).

Assigned values in our part of the world require six initial proctor tests and then updating the value with a new proctor test every third lot(5-10 tests per lot). We were able to do this despite the fact that there were visual(color) variations in the material, although, the material was sourced from the same quarry.


To Fattdad,

We have a similar problem here, although not with lab staff but with construction staff. In Australia, pavements have to pass a density test as well as a proof roll. A proof roll consists of running a fully loaded water truck slowly over each part of the pavement while an inspector walks alongside and looks for any little bit of deflection under the trucks wheels.

A poorly compacted DRY pavement will pass the proof roll but fail the density testing. A well compacted WET pavement will pass the density testing but fail the proof roll. Trying to explain the difference between hardness (dry strength) and density is extremely hard. Most people in the construction side of things just can't grasp the concept.

Also your single point proctor's take me back. That practice got banned here back in the early 90's, unjustly so in my opinion, these days it is either 1 proctor per density test or the aforementioned assigned value. The proctor samples are taken by expanding the field density hole. (Yep that is a lot of proctors, eh!)

Cheers
Michael


 
Drumchaser (Civil/Environmental)
23 Dec 08 20:05
woofar – you make some good points

It is apparent your field and mine are very different. Evidently you are on a different continent. Quite sure your soils have different properties than the ones we have here.

We sample the (soils) source at varying depths and locations (and colors), and have a full blown multi-point proctor, L.L., P.I. (linear bar if appl.) etc.  Our spec.s require a minimum of 95% - 98% of the Da depending on the P.I. of the materials. In this area the native soils are mongrel (that is to say they may change 20 FT away.
There is no way to run a proctor and series of lab tests for all the differing soils we will encounter. (Projects with 400K to 1 million CY)

"A well compacted WET pavement will pass the density testing but fail the proof roll."

Sounds like you were/are working with sand (low P.I. matl.s)



----------------------------------------------------------------------------------------------------------------------fatdad

1)We have a test method for and do occasionally use the sand cone.
2)I would agree there are technicians that have no business operating a gauge.
    
 "confirmation  proctors or one-point confirmations that the proctor that was used was appropriate"

3)Your confirmations / expectations far exceed that of our normal industry standards.   
 
darthsoilsguy2 (Geotechnical)
24 Dec 08 14:12
woven geotextile is crap! geogrid works better!

Yarrr!!!!
pirate
Threadjackin Pirate
 
woofar (Geotechnical)
24 Dec 08 18:56


OK, I'll bite!

You're not only off topic and out of line, your contention is fundamentally flawed. You are
comparing two great products that are used for totally different applications. Your statement
is the equivalent of saying, concrete is better than asphalt.

The stupidity of such comparisons is mind boggling.

Go Away!!!




 
mb27 (Civil/Environmental)
29 Dec 08 0:13
I guess I'm not fully versed in the area of one-point proctors.  Are they only performed in the area of a nuke test?  IE, is it the same as doing a sand cone to verify a nuke gauge, only simpler and faster?  And how close or far away do the numbers have to be to verify or negate your gauge's numbers?
woofar (Geotechnical)
29 Dec 08 2:29


Hi mb27,

The proctor test determines the Maximum Lab Dry Density(MLDD).

On a project job you can develop a library of proctor curves for each different material type. Then, when you do a Field Density test in a certain material, you can knock out a single proctor point at estimated optimum and then match the single point with the correct curve from your library. This method also requires a visual comparison, thus, the jars of material that Drumchaser mentioned earlier in this thread.

How you go about the determination of the MLDD has no bearing on the comparison between a sand cone and a nuke.

Reading back on what I have just written, I realise that my point may not be totally clear, if that is the case then please post back.

Cheers
Michael


 
mb27 (Civil/Environmental)
29 Dec 08 7:15
I get comparing it to the proctor library, I just wasn't sure if it was intended to be another way to verify the nuke.  From what you're saying, it's more of a guide to which proctor to use and not an indicator of compaction.
dirtsqueezer (Geotechnical)
31 Dec 08 11:55

Woofar,

Perhaps some direction on where to find your info?  But I bet I'd still think you're crazy.  There is a procedure for testing trench backfill that involves taking a standard in the ditch, but besides that I know no 'adjustment' for site-specific testing.  The test gives the same numbers as a sand cone; how do adjust that?  I'm just speechless.  Trust your gauge.  That's all I can say.  


-d
woofar (Geotechnical)
31 Dec 08 19:38


Hi Dirtsqueezer, I will address your post point by point



.....Perhaps some direction on where to find your info?

Did the link I provided in my earlier post not work for you? If that is the case, then please let me Know.



.....But I bet I'd still think you're crazy.

Yes, my wife and my friends would tend to agree with you there, but only as a general observation, never when discussing technical matters.



.....There is a procedure for testing trench backfill that involves taking a standard in the ditch, but besides that I know no 'adjustment' for site-specific testing.

Yes, you do need to do a new standard count when testing in a trench. You have to take a new standard count whenever the conditions for a changed background radiation exist.



.....The test gives the same numbers as a sand cone how do adjust that?

I have done many thousands of such correlations and the only place that the numbers match is in the wet density determination. In the moisture determination there is always variability. The reasons for this variability are many and varied and you can find a full explanation of this at the aforementioned link.


.....I'm just speechless.  

Can't help you there.



.....Trust your gauge.  That's all I can say.

I agree totally, the gauge is very trustworthy, however, like any tool, it does have it's limitations and to use it correctly you must fully understand those limitations.


Cheers
Michael


 
WHEngineer (Geotechnical)
14 Jan 09 16:53
Just a note pertaining to the question of moisture correction.  Most nuclear density gauges measure water content by counting "slow neutrons" which lose energy through interaction with water molecules.  The density testing is only concerned with free moisture (which can be burned off in oven drying).  In areas where bound water is present in the matrix, the nuclear desity gauge will give incorrect moisture values.  We have a large percentage of these materials in the SE USA, which include minerals such as mica and montmorillinite clays.  In our area, the wet density is generally measured with a nuke gauge and we burn off moisture samples separately.  Troxler has a good application bulletin on its website that describes this problem and methods to correct moisture readings.
Ron (Structural)
17 Jan 09 22:01
I would fire a technician or engineer (and have done so) for "adjusting" numbers, for any reason other than a valid calibration factor.  That is the type of activity that makes it difficult for legitimate testing laboratories to compete against such practices and demeans the entire profession.

Properly obtained and validated data are extremely important to the evaluation process.  We can deal with correct data, whatever its course.  We cannot evaluate incorrect data and the consequences of such can be dire.  

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