Geoscience Reference
In-Depth Information
Figure 4.2
Effective friction angles vs. organic content (
after
Edil, 2003).
4.2.1 Drained shear strength parameters
The
effective friction angle
of peats is typically determined in consolidated undrained
(CU) triaxial compression tests and occasionally in drained direct, ring or simple shear
tests. Drained triaxial tests are seldom performed due to the gross change in specimen
dimensions and shape during the test. Normally, consolidated peats exhibit zero or
small effective cohesion and generally high effective friction angles.
Figure 4.2 gives the reported effective friction angle as a function of organic content
compiled by Edil (2003). In this figure, materials with an organic content less than
approximately 25% are called 'organic soils'. The average effective angle of friction is
53
◦
for the peats and clearly above the average angle of 41
◦
for the organic soils.
Yamaguchi
et al
. (1985) and Farrell and Hebib (1998) report lower friction angles
in triaxial extension tests compared to triaxial compression tests.
4.2.2 Undrained shear strength parameters
Table 4.1 shows shear box test results of various tropical peats from West Malaysia.
The shear strength of peat, as mentioned earlier, is low, with cohesion (
c
) values in
the range 6-17 kPa and angle of internal friction (
φ
) in the range 3-25
◦
. The shear
strength parameters are generally lower with increasing degree of humification (less
fibre content). The angle of friction is also generally higher for the more fibrous
(fibric) peat.
Kazemian
et al
. (2012) have also reported a much higher friction angle for all three
peats; fibrous, hemic and sapric (Figure 4.3). To carry out the consolidated undrained
triaxial test, the authors collected peat from various locations in Selangor, Malaysia,
