Geoscience Reference
In-Depth Information
Figure 4.13 K
o
vs. organic content (
after
Edil andWang, 2000).
of excess pore pressure generated by cyclic loading undrained strength is not improved
very much.
4.7
K
o
BEHAVIOUR
K
o
represents the one-dimensional lateral earth pressure coefficient under confined
conditions in which no lateral strain is permitted, in other words, the at-rest condition.
Several reports of laboratory measurements of
K
o
are available in the literature. The
K
o
data collected by Edil and Wang (2000) are plotted in Figure 4.13 as a function
of
N
(loss on ignition), i.e. organic content. Figure 4.13 does not reveal a trend with
respect to
N
; however, it is clear that the average
K
o
for amorphous peats (0.53) is
higher than the average value for fibrous peats (0.34).
The
K
o
data presented above pertains to normally loaded specimens. During
unloading,
K
o
becomes greater than that during loading, as would be expected of
overconsolidated soils. Schmidt (1966) proposed the following formula to relate
K
o
(
rb
)
(during rebound) to
K
o
(
nc
)
(during normal loading):
K
o(nc)
(OCR)
α
K
o(rb)
=
(4.2)
where OCR is the overconsolidation ratio (the ratio of the maximum past stress to the
current stress) and
α
is an empirical coefficient. Several values have been proposed for
α
including sin
φ
(Mayne and Kulhawy, 1982), based on an extensive review of inorganic
soils. Another commonly used value for
α
is 0.5 for inorganic soils. Similar data for
peats and organic soils are limited. Kanmuri
et al
. (1998) report a value of 0.5 for
α
for a fibrous peat based on numerous tests in a
K
o
-consolidation triaxial apparatus.
Edil and Dhowian (1981) reported much lower values for
α
(0.09 to 0.18) for a range
