Environmental Engineering Reference
In-Depth Information
3.4.4
Soil Strength Measurements
General
Selection of Test Method
A number of factors required for the selection of the method for testing soils, including the
following:
Loading conditions: static or dynamic.
●
Loading duration in the field: long-term (drained conditions) or short-term
(undrained conditions).
●
Parameter desired: peak or ultimate (residual) strength.
●
Material suitability for undisturbed sampling and the necessity or desirability
for
in situ
testing.
●
Orientation of the field failure surface with that in the test; some cases are
shown in
Figure 3.47
and
Figure 3.48.
Stability analysis is often improperly
based on compression tests only, whereas direct shear and extension tests are
often required. Their strength values may differ significantly from the com-
pressive parameters.
●
Testing Methods Summarized
Soil laboratory static strength tests —
Table 3.19.
●
In situ
static strength tests —
Table 3.20.
●
Laboratory dynamic strength tests —
Table 3.33.
●
Triaxial tension type
active
σ
1
K
0
s
Z
b
σ
3
S
P
T
Active pressure = P
A
= K
A
s
Z
d
Triaxial compression
passive
a
Passive
(a)
Active
ε
(c)
Triaxial compression
Triaxial tension
type
σ
1
R
d
C
W
1
a
σ
3
S
Direct shear
σ
N
l
1
S
a
σ
1
W
2
σ
3
l
2
σ
3
σ
1
σ
3
σ
1
σ
1
σ
3
b
d
σ
1
S
Active
point - a
Passive
point-d
C
S
σ
N
σ
N
S
L
σ
N
Passive
Active
(b)
(d)
W
2
I
2
+
R
Σ
S
−
L
Σ
resisting forces and masses
Factor of safety =
=
Σ
active driving forces and masses
W
1
I
1
FIGURE 3.47
Probable natural stress and strain restraint conditions: (a) Retaining wall influence of lateral yielding on
stresses. (b) Mass slide of excavated slope. Influence of lateral yielding. (c) Stress-strain relations
corresponding to lateral yield conditions in (b). (d) Angle of friction relations corresponding to lateral yield
conditions in (b). (From Burmister, D. M., ASTM Special Technical Publication No. 131, 1953. Reprinted with
permission of the American Society for Testing and Materials.)
