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Author:
chandra obula reddy
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2002-06-18 |
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1. In carrying out a UU test on saturated clay, what
is the significance of confining pressure.
2. What the is the confining pressure one should apply
in testing for Unconsolidated undrained test. (Is it
the total overburden pressure or the effectiveoverburden pressure.
3. Does the free standing water depth affect the
confining pressure to be applied.
4. What is the effective stress at a point H belowmudline for the following
a. With zero free standing water depth
b. with a free standing water of Z (from water levelto soil)
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Follow-up:
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Author:
Paul W. Mayne
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2002-06-18 |
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Dear Chandra,
Best to avoid the UU altogether as UU = useless, unreliable.
Sure, its an easy test to run, but gives scattered results
that make it impossible to utilize in a strength analysis.
See Terzaghi Lecture by Chuck Ladd (1991, ASCE Journal of
Geotech Engrg.). If you run a CIUC test, you will benefit
from getting info on the effective stress strength envelope
(effective friction angle = phi') plus some info on total
stress parameter (su = undrained shear strength). The latter
will be too high a mode for general strength, but you can
reduce to an equivalent "average" or "representative" direct
simple shear strength by method of Kulhawy (Predictive Soil
Mechanics, 1993, Thomas Telford) or taking 2/3 value to reduce
from CIUC to DSS.
On the effective stresses below the mudline, both the total
overburden & the hydrostatic increase by same amount, so the
effective overburden (vertical) stress remains the same.
Sincerely
Paul
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Follow-ups:
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Subject:
tri-axial test 