Environmental Engineering Reference
In-Depth Information
TABLE 3.21
Triaxial Test Methods
a
Test
To Measure
Procedure
_
,
_
Consolidated-drained (CD) or (S)
Effective stress parameters
φ
Specimen permitted to drain and
compression test
consolidate under confining
pressure until
u
0.
Deviator stress applied slowly
to failure while specimen
drains during deformation
b
Consolidated-undrained (CU) or
Total stress parameters
φ
,
c
Specimen permitted to drain and
(R) compression test
consolidate under confining
pressure until
u
0.
Deviator stress applied slowly
to failure, but specimen
drainage not permitted
_
,
_
Effective stress parameters
φ
Pore pressures are measured
during test (see Pore-Pressure
Parameters)
CK
0
U
test
s
u
See Notes
c
and
d
below
Unconsolidated-undrained (UU)
Undrained strength
s
u
Confining pressure applied but
or (Q) compression test
no drainage or consolidation
permitted to reduce test time.
Deviator stress applied slowly
to failure with no drainage
permitted
Extension tests as CD, CU, UU
Lateral shear strength
Maintain confining pressure
constant and reduce axial stress,
or maintain axial stress constant
and increase confining
pressure until failure
Plane strain compression or
Parameter
φ
in cohesionless
Modified triaxial apparatus in
extension test
granular soils
which specimen can strain only
in axial direction and one lateral
direction while its
dimension remains fixed in the
other lateral direction
a
See
Table 3.19
for comments on test results and test comparisons.
b
Backpressure is applied to the pore water to simulate
in situ
pore-water pressures, or to saturate partially sat-
urated specimens.
c
CK
o
U
test: specimen anisotropically consolidated with lateral pressure at
K
0
p
o
and vertical pressure at
p
o
.
d
SHANSEP procedure (Ladd and Foott, 1974) attempts to minimize the effects of sample disturbance and
assumes normalized behavior of clay. Specimens are consolidated to
p
c
stresses higher than
p
o
, rebounded to
selected values of OCR, and then tested in undrained shear to establish the relationship between
s
u
/
p
o
vs.
OCR for different modes of failure. Normalized behavior requires this relationship to be independent of
p
c
.
The
s
u
profile is then calculated front the values of
p
o
and OCR vs. depth (Baligh et al., 1980).
Apparatus
The test apparatus is illustrated in
Figure 3.51.
Procedure
The specimen is trimmed to fit into the shear box between two plates, which can be per-
vious or impervious, depending upon the drainage conditions desired, and a normal load
applied which remains constant throughout the test. The test is normally run as a consol-
idated drained (CD) test (sample permitted to consolidate under the normal load), but it
