Dispute Resolution/Improper Compaction Testing 4

[Captain37]

Hello all, I am a heavy/highway contractor and I am preparing a DRB Response. My claim is that the owner project representative improperly tested compaction on embankment we were building in order to cause false negatives (failures). This caused my co. to incur considerable monetary damage. I know that procedure is critical when using a moisture density gauge, but my question is: How critical??? Note: The inspector did not perform proctors on half of the tests taken when the owners specifications outline the specific procedure to follow.....??? Thanks everyone!

 

[BigH]

I would suggest a read of the other thread for some of my comments. As per proctor - Ministry of Highways (MTC - or MOH depending on which government is in office) have a "one point" comparison - that is they take the soil from a sand cone hole, adjust for estimated OMC - then recompact in a mold to get a comparison of volumes (in hole and "at OMC") - of course, there are corrections for different volumes than that required by ASTM D698. Good method, though - I've discussed this on other threads before.

 

[oldestguy]

Ron and BigH:

Have either of you used the USBR Rapid Method of compaction control? It apparently is still standard with US Bureau of Reclamation.

I have an old version (1963) version of the "Earth Manual", where it is detailed, but I see it is now in a 1990 version, still using the "Rapid Method", in part 2 of "Earth Manual".

It takes the on-site sample and develops two added density points (2 percent up and down) from "in place". With that the "Lab Proctor" is determined.

I've never used it, but wonder if it has any following. Jack Hilf wrote a paper on this method back in 1976.

For what it is worth, here are some links dealing with this:

http://www.worldcat.org/oclc/23671411&tab=holdings?loc=54628#tabs

http://www.usbr.gov/pmts/writing/earth/index.html

Part I is available on line.

 

[Ron]

oldestguy...we used something similar for Corps of Engineers work in the late 70's. It got changed during the process though to a full Proctor at each density test location!! A bit of overkill for non-critical dike construction, but that's what they wanted.

The most common breach of these issues that I see routinely is relying on the field technician's visual assessment of whether there has been a change in material. An experienced technician can do a good job..inexperienced one's can run the test but can't spot the anomalies.

 

[woofar]

Hi Oldestguy,

Just to let you know,

The Hilf Rapid Method was used extensively in Australia during the 70s and 80s, It wasn't the norm, but it was well used.

The method has been "resurrected" in the last couple of years and I think it will become very common in the next 5 years or so.

Cheers
Michael

 

[BigH]

Oldest Guy - haven't done it. With the Ontario method, we had a "dipstick" that would permit the volume in the mould to be determined - it also gave the modifications for the blows/layer to be used depending on the volume of the sand cone or the rubber balloon hole. It took an hour to do by one person, but worked rather well.

 

[fattdad]

Late to join the party. I'm a big fan of one-point proctors. I'm not a big fan of the "Ohio" family of curves, however. A small change in grain size can have quite an affect on maximum dry density. As such, if you are really striving for meaningful compaction control it would be perfectly reasonable to take a bulk sample on some periodic basis (every test!!!) and confirm that the sample falls on the laboratory Proctor. IMPORTANT NOTE: This can only be acheived when the one-point is performed dry of optimum.

I have no comment on the other aspects of the specification. For example, I would never specify that the nuke gauge be used at one depth or another. After all, there may be some field justification to vary the penetration depth based on field conditions.

I'm a big fan of proofrolling to evaluate the subgrade to receive fill, but I'm not a fan of proofrolling to demonstrate suitable compaction. Too many soils exhibit favorable dry strength (i.e., pass proofrolling), but when they get wet turn to mud (yeah, that's a technical term). Do your density test, get on the right Proctor and make your conclusion.

For the test that were taken, have you looked at the plots of dry density v. compaction moisture content? I find much information can be gleened by such a plot for each referenced proctor value. I like to do this on a spreadsheet.

Reading your posts, I can sense your frustration. That said, compaction testing is never an exact science as Mother nature never gives us a uniform borrow source (i.e., moisture variation, grain size variation and the like).

Hope this helps. I can tell you have received alot of good information already.

fatt and-getting-older dad

¡papá gordo ain’t no madre flaca!

 

[BigH]

I've said this before, but when using sand as a fill, I would suggest that any test be carried out from a depth of about 3 to 4 inches below the surface of the layer placed - sand, when dried out has a tendency to fluff - also not well compacted due to the traction of the drum. I used to do the test at the surface and if passed, then okay, but if it failed, then I'd dig a small hole some 3 to 4 inches deep and carry out a second test. In effect, when dealing with a uniform sand fill, would suggest that a spec always specify the density of the previous layer rather than recent layer for purposes of acceptance.