Environmental Engineering Reference
In-Depth Information
1.5
C
u
C at 1 %/h
1.00 0.10 log
ε
u
1.0
26 clays
0.5
10
3
10
2
1
10
1
10
10
4
10
5
10
2
10
3
Strain rate,
ε
(%/h)
Figure 6.21.
Influence of strain rate on the undrained shear strength (Cu
Su) measured in triaxial
compression (Kulhawy and Mayne, 1990).
6.1.6
Estimation of the undrained strength from the over-consolidation ratio (OCR),
at rest earth pressure coefficient Ko, and effective stress strengths
6.1.6.1
Estimation of undrained strength from OCR
Jamiolkowski et al. (1985) using data from Koutsoftas and Ladd (1984) showed that the
normalised shear strength S
u
/
vc
versus OCR graphs for some soils were close to linear on a
log-log plot. Hence:
S/
′
S(OCR)
m
(6.13)
u c
where
vc
effective vertical stress in the test; S
S
u
/
vc
for normally consolidated clay
(S /
)
′
′
(6.14)
u cOC
or
OCR
m
(S /
)
u cNC
Jamiolkowski et al. (1985) show that for non cemented clays with a plasticity index I
P
less than 60%, m
0.8 and (S
u
/
vc
)
NC
0.23
0.04. So:
0.8
(S /
)
(0.23
0.4) OCR
(6.15)
′
u cOC
This method can be used as an initial estimate of strength, or as a check on other methods.
6.1.6.2
Estimation of undrained strength from effective stress shear parameters
Wroth and Houlsby (1985) give for normally consolidated soils:
3
sin
sin
′
(
)
tc
(6.16)
S
/
0.5743
′
u o
3
−
NC
′
tc
where subscript tc indicates triaxial compression tests, with isotropic consolidation.
