Civil Engineering Reference
In-Depth Information
60
q
c
p
a
p
a
s
′
vo
q
c
1
=
High compressibility
G
0
/
q
c
Increasing
cementation
and/or
ageing
10
0% A.C. Monteray
1% A.C. Monteray
2% A.C. Monteray
Alabama residual soil
Utah tailings
Quiou
Kidd
Massey
Alaska
Ticino
Toyoura
Low compressibility
A.C. = Artificially cemented
(% by weight)
1
10
100
q
c
1
1000
q
c
and
σ
v
0
. (After Fahey, 1998.)
Figure 5.20
Correlation of
G
0
,
Ohsaki and Iwasaki (1973) and other workers, that may be expressed as
G
0
120
N
0
.
8
p
a
≈
(5.25)
For vertical loading, strain levels are such that the small strain modulus may be used
directly in estimating settlements (Mandolini and Viggiani, 1997), or possibly reduced
by up to 50% where fewer piles are used (such as in piled rafts).
For horizontal loading, higher strains will occur in the soil and lower shear modu-
lus values will be appropriate, perhaps a factor of 2 lower than for vertical loading.
Randolph (1981) has suggested the simple, but conservative, correlation of
G
p
a
≈
10
N
(5.26)
at working load levels, which is 15 to 20% of the
G
0
correlation in equation (5.25).
Alternatively for laterally loaded piles, the soil shear modulus may be taken as varying
from zero at the ground surface (where the strains are highest) up to the full value
taken for vertical loading, at a depth equal to the critical pile length.
