Geoscience Reference
In-Depth Information
Figure 4.10 C
u
vs. depth and
σ
vc
laboratory (
after
Farrel, 1997).
For peat,
λ
cu
for
MalaysiaWest Coast clay fromKlang, for example, is only 0.25 (Chen and Tan, 2003).
In the field, undrained strength is typically determined by vane shear. Plate load,
screw plate and cone penetration tests have been used, but to a lesser extent.
Figure 4.10 shows a plot of undrained strength
C
u
versus consolidation stress,
λ
cu
is generally higher than clay, with values close to 0.50. The
σ
c
.
σ
c
is 0.45.
As shown, the ratio of
C
u
and
C
u
/σ
c
=
0
.
45
(4.1)
Figure 4.11 presents the normalized undrained strength compiled by Edil andWang
(2000). Fibrous and amorphous peats show no perceptible differences and give an
average normalized undrained strength of 0.59, with most of the data falling between
0.5 and 0.7. The organic soils (those with an organic content less than 20%) seem to
have lower normalized undrained strength compared to the peats. These
c
u
/σ
vc
values
appear unusually high compared to the typical values for inorganic clays (0.20 to 0.25).
4.5 EFFECT OF pH ON UNDRAINED SHEAR STRENGTH
Recent investigations have shown that the shear strength is not constant for a given
soil and it changes when the environmental conditions change (Fang, 1997; Fang
and Daniels, 2006). The effects of pore fluid pH on the vane shear strength of various
tropical peaty soils were investigated by Asadi
et al.
(2011a) using the small vane shear
test. In this study, to measure
S
u
, undisturbed samples in small acrylic moulds were
cured under different pH gradients of peat water (Asadi, 2010; Asadi et al, 2011e).
The peat water pH was adjusted using 0.1M HCl or 0.1M NaOH solution for 20
days. Then
S
u
was measured with a standard vane shear apparatus according to BS
