Use of Proctors
Use of Proctors
(OP)
Is there a limit to the amount of field compaction tests for any given proctor?
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RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
There is no limit to the number of field density tests that are referenced to any given Proctor. There is a compelling need to confirm that you are using the correct Proctor for every field density test; however. The one-point method is great for doing this - providing that the one-point is done BELOW the optimum moisture content. (If a one-point is done above the optimum, you can't properly interpret which unique curve it belongs to.)
Basing your selection of the correct Proctor only on "what it looks like" is a dangerous practice. It takes surprising little change in sand/silt/clay content to affect the maximum dry density. Refer to the 1988 ASTM publication "Compaction Control and the Index Unit Weight" by Steve J. Poulos (my former boss) for more information.
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
GODsRebel, note having a compaction of vover 100% does NOT indicate that the Proctor is incorrect or that the material has changed. Percent compaction is just a ratio of measured density to a laboratory density that was determined in a specific manor.
RE: Use of Proctors
RE: Use of Proctors
RE: Use of Proctors
Keep in mind that there is variation in the proctor method. Just by the allowable tolerance of the mold volume (+/- 0.0005 cf) there could be a difference of up to about 3 percent. (calced from 4.22lbs in mold sizes of 0.0338 and 0.0328 cf, 15% moisture). Then add in all the other possible variations that may be included. Heck, the 5% variation of moisture listed in the precision section (between labs, i.e. could be lab oven, and field lab oven) of the laboratory moisture (ASTM D 2216) can account for a greater than 0.5% difference in the dry density of the sample.
RE: Use of Proctors
RE: Use of Proctors
On the flip side.
About 15 years ago, My father sent me a copy of a review of a large project (A water filtration plant, if I recall) in Colorado Springs which was in litigation. Not Ours!
Hundreds of density tests had been taken.
The soils were complicated.
I believe there were over 60 proctors. Very few one-point checks.
Many proctors did not have a sieve analysis run and recorded with the test.
Apparently, every time the soil looked different, a proctor was run. The supervision was not as frequent.
Many of the proctors differed from previous by only 1-1/2 to 2-1/2 pcf.
Several of the Proctor Curves were significantly over a reasonable Zero Air Voids Curve.
Many of the proctors were obviously very similar, to almost identical with earlier proctors. But, without sieves, who knew?
The reviewing Engineer for litigation concluded that:
The tester had lost track of what he had.
Too many Proctors and how to sort them out???
Many Proctors differing from previous by only 1-1/2 to 2-1/2 pcf may very well be within the normal range of field sampling and laboratory testing. [See Precision & Bias Section in ASTM]
[Over 1/2 of the proctors should have been one-point checks]
A significant number of the Proctor tests were not valid (over Zero Air Voids Curve).
Supervision was worse than poor.
!!!Take it to heart and don't let it happen to you!!!
RE: Use of Proctors
Years ago, Onatario had a comparison method for relative compaction - you did your in situ density test (rubber balloon or sand cone). The material that comes out of the hole is then "adjusted" to be near optimum moisture. You then recompact it into the proctor mould and measure the volume. Compare its volume to the hole's volume and you get the relative compaction. There were adjustments to be made on the blow counts per each layer of the recompaction in the mould depending on the volume of the field hole.
As much as everyone (generally clients, contractors and even engineers) think that they are experts on compaction (it is SO simple), it is amazing that in many handbooks (Fang for instance) the largest chapter is on compaction. And Monihan (NJNIT) has written a pretty good book just on compaction.
RE: Use of Proctors
Big H has probably the best point. It's not just matching a compaction result to a proctor. It is an overal program. Inspecting the borrow pits and sampling, Doing laboratory multiple point proctors. doing sieves moisture content and limit tests, having the engineer review and accept the material and coordinating the work with the contractor. I have seen jobs where several pits, each with approved proctors, have been pulled out of simultaniously to go in the same fill. Note that Proctor A + Proctor B does not equal Proctor A+B. Also I have jobs where stanard proctor is required and proctors in the lab were modified because nobody comminicated (or vice versa) Note that it is very easy to get in excess of 100% standard proctor.
Also rember that if you are testing with a nuclear gauge, the toal density is the average density of the lift (up to 12 inches)but the moisture is a backscatter measurement in the top 2-3 inches so unexpected high or low readings should be checked prior to acceptance or rejection.
Proctors are multi point tests that require 3 days to perform. One point proctors are performed in the lab to cross check the test. One points, even done by experineced technicians can be way off. I would not recomend using one pointers for feild inspection.
If the project does not have a testing plan for eathwork, use the states DOT's practices. A.) They are probably the largest owner contracting for earthwork B.) They have refined a system for that area over the years and C.) Most earthwork contractors are familar with it.
That said one of my pet peeves in civil engineering is compaction testing. I have yet to figure out quanataively what compaction tests say about bearing capacity or settlement pediction. So if we arbitarily accept (and the acceptance value seems rather arbitary to me)of 95% and we have 92%, how do we know the fill won't perform as intendend? On the other hand if we have 98% how do we know it is enough?
RE: Use of Proctors
RE: Use of Proctors
I know if the Maximum Dry density MDD are not close its easy to tell by your dry density and if the soil is different (ie clay till and sand) you can tell be moisture content MC). But if your soils are similar, it comes down to feel.
For complex jobs that use borepit material, it should have be test pitted and samples taken for sieves,proctors before hand.
I think this post shows how important experience is for the field testing as there is no right or wrong answer, everyone has good input.
RE: Use of Proctors
RE: Use of Proctors
f-d
RE: Use of Proctors
RE: Use of Proctors
Well whose fault is that? Chapter 17 of the IBC requires certain inspections for various structural elements of projects. The power to enforce the competence level of those performing the testing, observation, and reporting is in the hands of design professional of record. If you guys started rejecting some of the bullshit work produced by these idiots, some of whom are my coworkers, things would change. But if you get a number of nearly illiterate nonsensical reports from a job and don’t call the lab and say something like, “What IS this load of non-sense you are sending me?” then the sadness you refer to is never going to change.