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soil density after compaction

soil density after compaction

(OP)
I am involved with a project in which fill material had been placed several months ago in a greenbelt area. The compaction specification arrived at by others was 95 percent of the standard proctor density, which was achieved at the time. It is now contended, though, that the compaction of the soil placed was lower than this, and the contractor would like to re-test the material that has been placed.

The soil has been re-vegetated, and has been exposed to many wetting/drying events do to the length of time that has lapsed since placement. The total fill placed is at most 3 feet. The soils placed were clayey sand (A-2-6) with a fines content of about 30 percent.

I think everyone in this project understands that there is a certain amount of variability inherent to the placement of fill, but I am looking to resources to turn to that would maybe help explain a lower compaction at the surface should it be the case that the new test results are different. Can anyone help with this?

RE: soil density after compaction

Unless the site has experienced frost action, I'd not expect any change.

RE: soil density after compaction

The biggest post-placement vulnerability occurs in the near surface. It's the result of frost action or it's the result of dynamic forces acting on the properly-placed fill after it gets wet. The nice thing about a dry density standard is once acheived variation in moisture content alone will have zero affect. Unless, of course somebody tries to compact those very soils after the moisture content increases. Now, nobody would remobilize the compaction equipment, but they may drive on it. . They may use the placed fill for construction staging. . . The contractor may use it for his/her benefit - i.e., not the benetif of the owner.

If the project has not been turned over to the owner, the contractor's obligation to deliver as specified remains.

f-d

ípapß gordo ainÆt no madre flaca!

RE: soil density after compaction

correct on the most likely effect near the surface - the only times that one might see the dry density be lower is when the soil is expansive. Being expansive, it will "increase in volume" and the soil structure would expand (hence less soil mass per unit volume) - taking out the water content, you would still have a "lighter" soil. Conversely, if the soil shrunk - - but for most soils, there should be little change as oldestguy pointed out.

The question I have is who thinks that the compaction wasn't achieved? Was it not tested by a reliable geotechnical/testing firm or a similar entity hired by the contractor? If it was tested, what is the "observation" that the material might have "lost" compaction? - and if this is landscaping type area only, what is the difference if it is 93% or 95% or 98%? Unless you are anticipating placing structures it would seem to me to be a moot point other than contractual issues. There seems to be a strong "fixation" on 95%. Can anyone really tell the difference of behaviour of 94% compared to 95% - or 95% to 96%?

RE: soil density after compaction

BigH...ya beat me to it! Potential expansion of the clayey material. Agree with your other points as well.

RE: soil density after compaction

we need more detail about why it was contended, and by whom.... if the compaction is contended, is the soil classification you quoted representing all the fill also suspect... When you say 'Contractor would like to retest' is this the same contractor that placed the fill or is this a contractor placing work on the fill and happens to be contractually separated from the grader. is the surface the only area of contention or is it the entire fil?...Did the earthwork contractor plant the grass immediately after getting to grade or was there time for other trades to do wheelies in it with equipment.... Was the compaction questioned after the site was stripped again and heavy equipment hit it again.... Getting Owners and their consultants wrapped up in finger-pointing between trades is why the GC prime contract structure was created.

Compaction is the controlled disturbance of soil to achieve desirable engineering properties.
There is no soil which cannot be uncompacted by uncontrolled disturbance when left unprotected by overlying layers.


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