TM 5-818-1 / AFM 88-3, Chap. 7
grees (fig 3-3). Approximate values of φ are given as
Thus,
the back-pressure saturated,
consolidated-
undrained triaxial test with pore pressure measurements
follows:
φ = 30 + 0.15 DR for soils with less than 5
is used. If the silt is dilative, the strength is determined
from the consolidated-drained shear test. The strength
percent fines(3-14)
determined from the consolidated-undrained test is used
φ = 25 + 0.15 DR for soils with more than 5
if the silt is contractive. Typical values of the angle of
percent fines(3-15)
internal friction from consolidated-drained tests
commonly range from 27 to 30 degrees for silt and silty
Values of φ = 25 degrees for loose sands and φ = 35
sands and from 30 to 35 degrees for loose and dense
degrees for dense sands are conservative for most
conditions. The consolidated-undrained tests yield 15 to
cases of static loading. If higher values are used, they
25 degrees. The shear strength used for design should
should be justified by results from consolidated- drained
be that obtained from the consolidated-drained tests.
triaxial tests.
(2) Silt tends to be dilative or contractive
depending upon the consolidation stresses applied.
(Courtesy of W. N. Houston and J. K. Mitchell, "Property
Interrelationships in Sensitive Clays , " Journal, Soil
Mechan- ics and Foundations Division , Vol 95, No. SM4,
1969, pp 1037-1062. Reprinted by permission of
American Society of Civil Engineers, New York.)
Figure 3-17. General relationship between sensitivity, liquidity index, and effective overburden pressure.
3-21
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