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RE: Proctor Tests

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I attended a seminar on soil compaction a number of years ago - the speaker said he feels that Modified Proctor is more reliable and should be what the industry should standardize on. But he said that currently it is best to check with local practices/ local standards (DOT's, etc), to see what method is most commonly used in the area or to use what the geotech recommends.
Modified Proctor compares well with heavy compaction equipment and Standard Proctor compares well with light rollers or tamping. Thus, Modified is often used on large civil projects and Standard is often used for smaller projects. As Tom noted, 95% Standard Proctor is considered to approximately relate to 90% Modified Proctor; 100% Standard Proctor is not hard to achieve in the field but 100% Modified Proctor  is much harder to achieve.
One soil's report I got recommended Standard Proctor for cohesive soils and Modified Proctor for granular soils but did not give a basis for these recommendations.

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)


From: THunt(--nospam--at) [mailto:THunt(--nospam--at)]
Sent: Thursday, January 27, 2005 8:06 AM
To: seaint(--nospam--at)
Cc: seaint(--nospam--at)
Subject: Re: Proctor Tests


I remember looking into this a long time ago when we called for modified proctors and received standard proctors from the lab.  As I remember, the standard proctor and the modified proctor are very similar laboratory tests with the standard proctor using more energy (a larger or heavier hammer?).  Both can be used however the desired or accepted percent compaction will be different depending on the test method.  I do not believe there is a direct correlation but if I remember right a 90% standard proctor is roughly about the same as a 95% modified proctor.  With this in mind, I seem to also remember that the standard proctor correlates better with field compaction when using very large rollers whereas the modified proctor correlates better when using smaller rollers, plate compactors, and powder-puffs.  As already suggested, best to check with a real geotech.

Thomas Hunt, S.E.
ABS Consulting


01/26/2005 07:47 PM

Please respond to

Proctor Tests

Are there are guidelines for when you should specify a standard Proctor and when you should specify a Modified Proctor? 
Is it  based on type or magnitude of loading? 

Gail Kelley