Compaction Testing 1

[Dasovich]

Hello,

Could someone give me some insite about different methods of determining field compaction of building/pipeline subgrades. I know of the nuclear desometer but have also heard that it is not very accurate with crushed rock. Is there anything out there that can quantitatively determine the compaction accurately?

Thanks

 

[Ron]

There are four basic methods of in-place density determination. These are:

Nuclear Density Gage-Can present problems with crushed rock, calcareous materials, and in trenches

Drive Sleeve or Cylinder - Volumetrically accurate but not good for rock or soils containing rock fragments

Sand Cone - Accurate and typical calibration basis test for nuclear, but not accurate in porous materials and/or where vibration is present

Rubber Balloon - Not used much but would be the most accurate for your application

 

[GeoGuy]

Compaction is loosely used to describe how to change the property of soil. You compact to create a useful structure and to make it stiffer. Measure its mechanical property of insitu stiffness or modulus during the compaction process, rather than its physical property of density. By doing so you will more accurately attain the properties you really need.

 

[bb29510]

From my experience, the nuke runs about 97 % accuracy base on a 100% of a sandcone in perfect conditions. So by basing a cone aganst the nuke every 20 test, you are able to be consistion. also the speed of the nuke is more productive compare to other methods. So 97 to 100 is only a three percent differents. On a rock of 141 lbs, that would be about 4 lbs. with this you can add four lbs to the dry weight or just live with the 95 % compaction instead of 99%. What I trying to make you understand is, they are too many variable in gradation, PD, moisture, compaction, thickness of lifts, technician claculations, calcultors round off, to worry about being off two lbs with a nuke. Assume that a nuke is 100% and you sleep better at night. also the gentlemen was right, nukes do not like trenches, pulls moisture out of walls. oh my job daily is running a nuke in the field. remember you can pull ten PD's out of same truck and they will all be different. Allow for a little leadway

 

[dirtsqueezer]

I have about a year's experience using a nuke guage and a sand cone at a testing lab.
I have found the nuke to be very accurate and reliable. It has undergone scrutiny by myself and probably over a hundred different contractors each of whom had their own incentives to see their numbers pass, and it has done the job.
I been testing bottom ash (USCS sand with some gravel) using the sand-cone method for about a year now, and I get extremely consistent results with that, too. An error of two pounds for me would mean a decreace in at least 3% compaction, which would make even a 97% be a potential failing test, and like I said, I don't often have problems.
All of these methods are both based on the consistency of your fill. If you are using manufactured fill like crushed rock, you can expect your tests to be reliable. If you have opted for native material to save on costs, you will basically be relying on the skill, experience, and knowlege of your technician. You will want a straight-arrow testing lab for those jobs to ensure a good result.