Geoscience Reference
In-Depth Information
100
Clean Sands
Silty Sands; FC = 6 to 9%
Silty Sands; FC > 9%
80
60
40
20
(
)
60
N
1
D
R
=
C
d
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7 0.8
Median Grain Size, D
50
(mm)
Fig. 1.9. Variations of theparameter C
d
withD
R
(values of relative density, N
1
, FC, and
D
50
arefromCubrinovski and Ishihara, 1999)
m
=
0
.
7836
−
0
.
5208D
R
(1.6)
C
1
=
0
.
64 to1
.
55
(1.7)
σ
vo
=
in which q
c1
is the corrected (to
1 atmosphere) CPT tip resistance and q
c1N
is
the normalized corrected CPT tip resistance
,K
o
is the lateral earth
pressure coefficient at rest, and P
a
is atmospheric pressure. The variation in the relation-
ship between q
c1N
and D
R
described by the above equations is similar to the variation
observed between
(
q
c1N
=
q
c1
/
P
a
)
N
1
)
60
and D
R
,as illustrated inFigure 1.9.
Theaboveq
c1N
-D
R
and
(
N
1
)
60
-D
R
correlationswereusedbyIdrissandBoulanger(2003)
to maintain consistency between SPT- and CPT-based liquefaction triggering correla-
tions for clean sands. A value of C
d
=
(
46 was used for the SPT relationship and values
of C
1
=
45 were used for the CPT relationship. These values, for
example,indicatethataD
R
ofabout81%correspondsto
0
.
9 with K
o
=
0
.
(
N
1
)
60cs
=
30andq
c1N
=
175.
The resulting CPT expression was also shown to be closely approximated as
0
.
264
D
R
=
0
.
478
(
q
c1N
)
−
1
.
063
(1.8)
which simplifies the computation of D
R
fora specified q
c1N
.
