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RE: Proctor Tests
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Proctor Tests
- From: "Foy, Warren" <Warren.Foy(--nospam--at)mhgrp.com>
- Date: Mon, 31 Jan 2005 09:55:32 -0500
other bit of caution. Be cautious of over compaction. Often, in
order to obtain the specified in-place dry density, it is necessary for the soil
to be drier that it will be when it reached it's equilibrium in-situ moisture
content. When the moisture content equalizes, the soil
(even non-expansive soils) has the potential to expand. I have
seen floor slabs and even building heave upward as much as
You are correct that I had the right
philosophy but got parts of it backyards. The grey matter just keeps on
Thomas Hunt, S.E.
01/31/2005 06:03 AM
I think you have it backwards. As I recall, a standard
Proctor (ASTM D698) uses a 5.5 lb hammer dropped 12" with the sample
being compacted in three lifts. The modified Proctor (ASTM D 1557) uses
a 10 lb hammer dropped 18" with the sample being compacted in 5 lifts.
The modified Proctor produces a higher compactive effort (56,000
ft-lb/ft3) than the standard Proctor (12,400 ft-lb/ft3). (OK, I didn't
recall all this, I looked it up). The point is that a modified Proctor
will produce a higher maximum density with a lower optimum moisture content
than a standard Proctor. I have heard that as a rule of thumb, 95% of a
standard Proctor is close to 90% of a modified Proctor.
Thursday, January 27, 2005 10:06 AM
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.
01/26/2005 07:47 PM
Are there are guidelines for
when you should specify a standard Proctor and when you should specify a
based on type or magnitude of loading?