One point proctor method

[Snatch]

I am working on an earthwork project, which consist of a cut and fill operation. The specification for filling requires a compaction 95% Maximum Dry Density with +/- 2% Optimum moisture content. The geo-technical engineer for the contractor is suggesting using one point proctor method to determine the optimum moisture content and maximum dry density. Is this a reliable method and what are the typical problems associated with this method?

Thanks
Snatch

 

[SirAl]

I would surmise that the site has variable soils present and that intermixing of different soils are expected.

There may be a number of lab (5-point) Proctors required, 1 for each soil type present. Performing one-point proctors with each in-place density/moisture test will aid the tester in selecting the appropriate lab proctor for determination of % compaction and applicable OMC. (The one point Proctor at natural moisture content should plot on the laboratory 5-point curve if the materials are the same).

There are limitations. A one-point could plot on or near the curve of more than 1 lab 5-point Proctor curve. There are other field techniques available to help the tester select the proper lab Proctor reference values. In the end, it often falls on the judgement of the tester.

I suggest you do a search of the Eng-Tips site. This topic has been discussed in the past and you may find other comments that may be helpful in this regard.

 

[DRC1]

The one point procter is Fast & Cheap. However, it is not as acurrate or does give you as much information as a proper proctor. It is okay if you run into a situation where you have a sudden change on the job and you need to run a fill in. You don't want to stop the job but you need some compaction guidance quickly. Also if you are considering several borrow sites you can do a one point procter to give you an idea of which sites warrent a closer look.
However do not run a fill operation on a one point procter. (even for the emergency work get a full proctor as soon as it is possible.) A one point procter is not accurate and does not conform to ASTM. If there is a problem with the fill it will because you approved a fill that did not meet the proper standard. The cost of a full proctor vs a one point proctor is a few bucks. The cost of replacing a fill can be substantial, especially if something is on it.

 

[DBNodurf]

One-point "Proctors" are only useful to determine whether or not the correct curve is being used for testing, and/or to interpolate between curves where multiple soils are present on which moisture-density relationships have been determined, and where mixing will occur. In the latter case, you should plot all the Proctor curves on one sheet of graph paper so the one-point "Proctor" can be plotted and the probable curve roughed in order to estimate %relative compaction.

In the former case, if the one-point "Proctor" (aka checkpoint or check plug) is very far from any previously obtained moisture-density relationships, then a new moisture-density relationship should be determined for the soil represented by the check point.

D. Bruce Nothdurft, MSCE, PE, PG, M.ASCE, etc, etc,...
Principal Engineer/Geologist
Atlantic Geoscience & Engineering
Charlotte, NC