failing compaction efforts in silty/sandy material

[kurtjfred]

Hi all. Newbie here and first post ever. Working in Southern Cal and getting my ass kicked trying to achieve 95% compaction on some very silty/sandy material in trench backfill. County inspection is using a caltrans wet density test with a nuke gauge and not getting results until following day at soonest. Working deep in some places (almost 20') and having to close up streets at end of each day. Can anyone explain to me with great detail the methods and differences between the dry density and wet density testing methods. Or can you direct me to someplace online that I can get a thorough education on the differences. I would like to learn every possible detail about them, even their history and development. Thanks in advance for any help.

 

[geomtl]

by the time you have a few proctor values in a native material (or a fill if fairly uniform) you should be able to estimate the insitu density value pretty good based on the moisture content and the way in which it packs. You should also know by this point if the material needs water just by looking at it.

Do you use an estimated value during the day, if so are you generally ok the next day when the test comes back or do you have to repack the material.

The above method will not work if you have hugely varying soils.

Just to make sure you understand the proctor curve soils have an optimum moisture content where the maximum compaction (density) can be obtained. There is only one moisture content at which you can obtain the maximum density. Therefore, by looking at the moisture content, the density values from the nuke (density values not % of your proctor) during the day you will be able to get a pretty good handle on how the compaction is being done.

i,e if my tech calls me from the field and tells me that he is getting 99% of modified proctor on a 0-3/4" crushed limestone with 2% moisture content, I suspect that the proctor he is using may be too low. (in this area optimum for this type of material is between 5 and 7%). A simple analogy but gives an idea of how to treat the nuke machine, i.e if the proctor value inputted is incorrect you will have a very difficult time attaining the 95%, or you will be attaining over 100%, which also should not occur if using the modified proctor.

 

[msucog]

i don't see the practicality of the method described. field proctor and in-place drive rings only take a few hours. once the proctor is nailed down, you can use it each time you run across that particular soil and can be confirmed with a check plug run near optimum moisture. you can run a few density tests per hour. around here, contractors and owners aren't going to wait until the next day for a density test result...and i agree with them. they might be running 10-15 scrapers and if a test comes up failing the next day, it'd be under many feet of fill by then. given, my techs should know whether the tests will fail (other than marginal results) before they run the test...but we still must have test results to back up our observations and/or recommendations.
we discuss wet densities between us (engineer and techs) while waiting for final results to come back but i would not say pass/fail based on that...soils and in-situ moistures are too variable around here. densities from 80-125pcf with moistures <10% to >45%.

 

[kurtjfred]

You guys are confirming my complaints! BUTT!!! The county is pounding a curve on EVERY test taken. Every time that nuke gauge hits the ground, they take a sample and go back to the lab and pound out a curve on it.
The guys in the lab are pissed about having to pound out this many, they know what the damn soil is in place once they run the numbers. The soil is not varying that much. Some sandier and some siltier. But I don't have results in writing until (at the soonest) the following day. They ARE NOT doing any lab work on site. They are not doing any curves before hand.
What does the ASTM & ANSI specs dictate? Can I insist that they come before hand and take a sample and pound the curve the day before so they can give me the results from the nuke gauge as they poke the damn thing in the ground? Like I said, with the survey stakes sitting here next to the trench, we can return to the same exact location within inches. I cannot force them to take a sand cone by the way.
On a different note, I have worked with silt in the past and it is by far the most contriversial regarding moisture. I call it a spike instead of a curve when you pound a curve on it. I have a speedy moisture meter with me but feel we are getting the moisture close enough by vision. I am considering some type of vibration along with the weight might help. I stated before, I don't think you can fail due to over optimum moisture per the spec, although it may be detrimental to have too much water on a practical view. If anyone has any experience and advice putting a silty material back together, I would very much appreciate any input.

 

[msucog]

from my experience with silts, more than 3% wet will knock you down below 95% standard Proctor max dry density. some micaceous silts will do the same at about 2% wet (maybe less). same goes for it being too dry of optimum. i personally wouldn't rely on wet density...but again, the soil is variable here where i'm at. wish i could offer more help.

 

[emmgjld]

kurtjfred

As they are pounding a proctor for every test, sounds similar to the Corps of Engineers in the Colorado Springs area. My father had many choice comments regarding the fiasco which developed. My condolences.

 

[BigH]

kurtjfred: back to the point I made earlier. Who is requiring that his people run all these tests? Can you not talk to his superior to work out a more practical resolution to the problem? "BOHICA" might better describe the situation you are in rather than it being my normal "handle".

 

[DarthSoilsGuy]

kurtjfred,

you can purchase individual ASTMs at the ASTM website if you have the reference number. (i.e. ASTM D698 is the standard Proctor test). since it's giving you so much heat, i would buy the ones listed in the project specs that apply to compaction testing if you don't have them already. I would be surprised if ASTM were to make judgment calls (or poor judgment calls in your case) with regards to frequency of testing and reporting turnaround time. But, you should know them since it is costing you money now and who knows, maybe you'll find some information to help defend other testing issues that may come up.

i agree with BigH about looking for some consideration up the chain of command. from what you've presented, you're not asking for leniency but reason.

also if this thing is truly slowing down the project and costing real money (as opposed to being a good scapegoat for the contractors and labor), you should look into hiring a reputable testing firm to provide compaction testing. Have the firm test in the exact locations that the county is testing as well as some additional locations. Offer to distribute the results to the owner and design team. it would be best if they could give the results to the county before the county officially tells you the results. you still might not get passing results, but you'll at least get them immediately with some feedback of what to do about it and can repair/retest. i'm going to speculate that any tester who is comfortable telling you the results tomorrow or the day after isn't too concerned with getting things fixed, just redone. that kind of move will probably ruffle some bureacratic feathers, but if someone tries to state that only the county test numbers will be valid, immediately look puzzled and ask why would there be any difference. if you choose this route, do the testing firm and yourself a favor and let them know the project history.

 

[msucog]

county bureacratics can be tough. i've had county inspectors tell me to take a hike when our density test results came back <85% at the pavement subgrade simply because he had proofrolled the area with a offroad haul truck and HE said it was okay. all i can do is document our side and let the other side play out. you might gain some ground by "negotiating" with the county. explain to them that if the project can be hurried along with faster testing, then they would look like champs by finishing a job ahead of schedule. just make sure to go the extra mile (get 99% where 95% is required) so that you don't get caught up in fighting over who's results are correct (96% versus 94% where 95% is required). you might even help yourself if you can make it sound like another testing method was the county's idea ("hey county people, we're over here trying to get this project done on schedule but are not making as much headway since we're waiting so long on test results to come back. do you guys have another test method that might be acceptable for the sake of finishing the job ahead of schedule? i've heard of drive ring or sand cone methods but would like some input from you guys since we're here to satisfy your requirements.")--it might work even though it's sort of kissing up...there again, it might not. the other option is to suck it up and be frustrated at the slow progress.

 

[DRC1]

If you google caltrans and the test number, you get the proceedure. It is a funky test. It is definately a caltrans test, not ASTM. Sort like quick procters but not really. First the test does not measure a proctor value - It computes the relative density andmeasures the wet density. i only read this for five minutes, but this is my take - they are assigning a relative density to the compaction and computing the wet density both in the lab and in the field. ibelieve they are controlling the limits of moisture, but I am not sure how. Any way Yes you can make them do sand cones because the test requires the field testing be done by sand cone. Does not even mention nukes. It is a pretty fussy test so a lot is dependant on the lab technician. It seems you do a sand cone and then take a 35 lb sample to the lab where a 3 point test is run, but every thing works in terms of relative compaction and wet weight.
In short this is really different from what I have seen, but A.) does not sound like they are doing it right and
B) Does not sound like it is the best method for this job.
I would suggest you talk to someone at a CalTrans lab to get some background on this.
Good Luck!

 

[emmgjld]

DRC1

Is the CalTran method really any different than the ASTM D5080-00 TEST METHOD FOR Rapid Determination of Percent Compaction, I mentioned in the above post??

In theory, if the water content is being checked and reasonably under control, this should work. Just a lot of work.

 

[cvg]

I posted the test method previously - it is a Caltrans standard:

http://www.dot.ca.gov/hq/esc/ctms/CT216Oct2006.pdf

 

[civilperson]

CalTrans has a unique method which has little or no correlation to ASTM D698 or any other test method. I can not see any provisions for nuclear gauge results. Truly a bureaucratic boondoggle.

 

[DRC1]

The other point I got out of it is that it measures relative density, not a proctor value. If you are trying to coralate a wet density to what is thought to be 95% proctor(dry density) and you are really trying to acheive 95% relative density, that could be part of the problem.