Legal Aspects of One-Point Proctors

[DOCPROC]

I want to institute the use of one-point proctors performed in the field for our company. We would use AASHTO T272 (Family of Curves) and ASTM D4959(Direct Heat Moisture Content)as guidelines. We want to use one-points to verify proper proctor selection.

The problem is that I have some managers who are saying that if we don't do everything per ASTM, like we do in the lab, that if a project ever goes to court then we would have a liability issue with the one point proctors.

Does anyone have some suggestions how I approach these managers so that I can get them to buy in to use of one -point proctors?

 

[fattdad]

I'll weigh in, but bear in mind while I do follow ASTM, I also hate being bound by their "Standards". The way I see it, all projects need site-specific moisture-density relations (i.e., Standard Proctor curves) as completed in a laboratory. If you are on a project and the typical soils are sandy silt and clayey sand, you may have a unique Proctor for these two samples. During earthwork, there may be blending or subtile variation that affects both the maximum dry density and the optimum moisture content (as you are likely well aware).

To me the benefit of a one-point Proctor is to pound a point and see if it falls on one or the other of the two curves that you already have. If it's somewhat higher then the dry limb, you may want to sketch in a curve that's roughly parallel to the lab curve and peakes at the line of optimums. You may want to use this fabricated maximum dry density as a basis to either accept or reject the compaction test. If you really have an interpolated maximum dry density that is different from one of your curves, you may make a provisional approval, but submit the sample for a lab curve. If you get another lab curve, you may want to add it to the two proctors you already have and better define the LOO for future tests.

I don't like the wet-density family of curves, even though they're widely used. It's just too easy to make your own family of curves for your local work areas.

It's nice to know you actually care about the adequacy of your field data. I'd rather see quality checks via one-point proctors then somebody just relying on the gray-dirt proctor and the red-dirt proctor, both done to the requirements of the ASTM.

f-d

¡papá gordo ain’t no madre flaca!

 

[msucog]

we typically stay away from them but do use them occassionally. i suppose it's sort of like fattdad mentions and we'll do some confirmatory testing if the check plug doesn't match up to a job proctor. there is usually enough time in the field to complete the proctor for our soils while on site...so no need to leave an open question on the test.

 

[BigH]

As I've detailed in another thread, when I started out in Ontario, we used a method developed by Ontario Ministry of Transportation. We would use a rubber balloon to obtain the soil and to get in situ volume. We would take the soil and adjust by "eye and experience" to pretty well the optimum moisture content and then compact the sample in a proctor mould making blow count adjustments for the actual volume of soil removed. We then get a volume of the soil in the proctor mould. Compare the two volumes for the % compaction. Don't have time now but I'll try to find the previous thread.

 

[fattdad]

Just to add to my earlier post: When doing a one-point proctor you MUST do the point on the dry side of optimum. Recognize that the dry side of the curve is unique, but the wet side is not, as it follows the ZAV (typically at about 90 percent saturation).

I have to comment on BigH's post too: While I'm not familiar with this method, I do like an approach that solves the problem. Whether ASTM has a "Standard" for that approach is irrelavent, if the engineer using the data is standing behind the analysis.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

fattdad - we even had a manufactured "dipstick" that you used to tell you the modifications to make to the blow count depending on the volume of material in the in situ hole!

 

[oldestguy]

Having been in on hundreds of jobs with various methods used, I backed away from trying to use families of curves. Most of the checks against the full curve did not compare. Using material on the dry side might be required, but most of the time it was on the wet side in my experience.

I'd not use it, especially if the job is "touch and go" as to being adequate in meeting specs.

On the other hand, I have modified my ways in later years by calling for much less in the way of degree of compaction, consistent with knowing what the job needs are. For instance, if you are on a paving job and your site has both cut and fill, if your cut area naturally has a clay soil at 85 percent compaction and a Qu of 1.5 t/sf, why would you specify 95 percent compaction at the fill area? Sometimes a common sense approach gets just a good a job at less cost and less fighting.

 

[civilperson]

Use of a one point is good, use of a family of curves is WRONG. When the one point falls off of the plotted/pounded curve, then another M-D curve must be made using the new soil type. The list of proctors done on site will grow everytime a one point is detected that does not apply to previously run M-D curves.

 

[Ron]

I agree with fattdad....use the one point and compare to proctors you already have on the site. It helps you pick the right one. This can be an issue, particularly in alluvium where many soils may "look" alike, but have different moisture-density relationships by several percent.

There was a time when the US Army Corps of Engineers required a FULL proctor with each in-place density test. Kind of reminds me of...

Measure with a micrometer, mark it with a crayon, and cut it with an axe.

 

[DRC1]

I have never seen a contract between an owner and a contractor that based acceptance on one point proctors. I doubt few contractors would tolerate having one point proters as a basis of acceptance. If you are not getting compaction, or it appears the material may not be quite the same, it can tell you if a new proctor is warrented, but I would not rely on it for the value of my max dry density.

 

[fattdad]

use of a family of curves is WRONG.

Completly disagree! Incorrect use of a family of curves is wrong. Here's my perspective: There is little value in some "Ohio" family of curves right here in Virginia. That said, if you are working on a project with LOTS of earthwork, you may end up with six, eight or 10 Proctors during the course of the project. Use these proctors to make YOUR OWN family of curves. Do confirmation testing at a Field density test location via a one-point (on the dry side) and compare it to your family of curves. That's what I consider good practice - nothing wrong with good practice. And, it beats the heck out of the more typical guess work. It's the guess work that ends up causing great pain after the wall falls over, the pavement fails, or the instructrial floor slab cracks.

end of rant. . .

f-d

¡papá gordo ain’t no madre flaca!