Geoscience Reference
In-Depth Information
3.2. CORRELATION OFS
r
/
σ
VO
WITH
(
N
1
)
60cs
-
Sr
Residualshearstrengthsfromcasehistorieshavealsobeennormalizedwithrespecttothe
initial vertical effective stress,
σ
vo
(e.g., Stark and Mesri, 1992; Ishihara, 1993; Wride
et al., 1999; Olson and Stark, 2002). The use of a normalized shear resistance, S
r
/
σ
vo
,
for sand was usually based on the observation that it provides a reasonable basis for
describingthestress-strainbehavioruptomoderatestrainlevelsinundrainedlaboratory
element tests. In addition, recent studies suggest that the effects of void redistribution,
while affected by numerous factors, may also be better represented by a correlation to
S
r
/
σ
vo
than toS
r
directly.
The values of S
r
/
σ
vo
for the case histories listed in Table 1.1 are plotted as a function
of
N
1
)
60cs
-
Sr
in Figure 1.5. Recommended design relationships for estimating S
r
/
σ
vo
based on median penetration resistances are presented in terms of two different curves:
one curve for conditions where the effects of void redistribution are expected to be neg-
ligible, and the other curve for conditions where the effects of void redistribution could
be significant. These two curves provide guidance for the unavoidable task of having to
estimatetheresidualstrengthsofsoilsthathave
(
N
1
)
60cs
-
Sr
valuesgreaterthanabout14,
which is beyond the range of available case history data. The basis for the form of these
recommended curves isdiscussed below.
(
Theundrainedstress-strainresponseofsaturatedsandforarangeofinitialrelativedensi-
ties
(
D
R
)
indirectsimpleshearloadingisillustratedbytheresultsinFigure1.6forFraser
0.4
Group 1
Recommended Curve
for conditions where
void redistribution effects
are expecte
d
to be negligible
Group 2 &
Group 3
0.3
Recommended Curve
for conditio
n
s where void
redist
r
ibution effects
co
u
ld be significant
0.2
0.1
Seed (1987)
Seed & Harder (1990)
Olson & Stark (2002)
0.0
0
5
10
15
20
25
30
Equivalent Clean Sand SPT Corrected Blowcount, (N
1
)
60cs-Sr
Fig. 1.5. Residual shear strength ratio,S
r
/
σ
vo
,of liquefied soil versus equivalent
clean-sand, SPT corrected blow count for
σ
vo
lessthan 400kPa
