Compaction

[daviv]

We are backfilling 6 ft at 95% compaction. I have checked with my coworker who said there is no ASTM testing requirement but the common practice is to test the top 8" -12" layer via nuclear gauge. Is he correct or testing frequency is required?

 

[fattdad]

To the best of my knowledge, there are no ASTM testing requirements for anything! ASTM provides standards for testing that are very useful when an engineer specifies required testing for a project. So, maybe your co-worker doesn't want to have this testing. How does he like to manage risk?

I usually go with testing, irrespective of whether there's an ASTM requirement or not.

f-d

¡papá gordo ain’t no madre flaca!

 

[jgailla]

Are you the contractor? If so, the project specifications or geotechnical report should have the testing frequency.
ASTM will only tell you how to do the tests.
It would depend on project specific data on the material and final use, but you should be testing each 12" lift at a minimum about every 2500 square feet.
It is completely pointless to dump 6 feet of fill and then test the top foot.

 

[cvg]

especially with nothing more than a nuke

 

[daviv]

Thanks for the input. To clarify, the backfill serves as a subbase for a 4 in concrete walkway. The contractor is backfilling at 8" lifts. Logically, would it not be safe to assume to achieve 95% on top foot compacted at 8" lift, you would have 95% at the lower layers? So the frequency is a design criteria?

 

[cvg]

unless you were there observing the entire 6 feet high embankment, no - good compaction of the top layer does not indicate that there is good compaction throughout. Especially when you consider variability of soils, moisture content, potentially different equipment or the fact that the contractor pounded the #$!% out of the top lift because he knew you were coming out with the nuke to do the testing. The testing frequency is for quality control / assurance. To assure that you have good quality fill, you need to perform testing. By the way, you need to confirm your nukes with at least one sand cone...

 

[boffintech]

cvg....now you're not suggesting that a contractor wouldn't work all the lifts as much as he would the top lift?! I'm shocked!!!

Remember, contractor's see ALL lifts as being 8" thick even when they are 24" thick.

 

[SirAl]

You should monitor the compaction of intermittent lifts. Adequate compaction of material below grade is important to avoid excessive settlement. Testing frequencies are commonly specified by a local/municipal authority or, on private sites, the project specifications. As the others have indicated, ASTM does not commonly prescribe how often the tests should be done.

 

[polariman]

Yep. Need to test lifts every 18" to 24". However, in this case, have the excavator and tester dig some test pits to test the lower and mid level. Need to excavate using a scraping method as to not to compact too much while excavating. The tester can then dig another 6 to 4 inches to try and get an accurate reading. Still... ...not the best method but will definately give good observation data to back up the compaction. Again, need to test lifts every 18" to 24". Pain in the butt for contractors but has to be done to cya.

 

[DRC1]

Consult your local DOT specs. Most contractors will be familar with those and they will be based upon many years of local experience with the soils in your state.

 

[dicksewerrat]

What happened to sand cone testing? Just bringing the soils testing lab people to the site adds 5-10 to the compaction effort. You have to test about every third lift. You can do a quick check on lower lifts by using a hand probe. You feel the difference of the loose lifts.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com