Geoscience Reference
In-Depth Information
There is, however, a certain class of peats - typically high organic and fibre con-
tent materials with low degree of humification - that do not conform to the concept
of conventional clay compression because of their different solid phase properties and
microstructures. Analysis of the compression of such materials presents certain dif-
ficulties when conventional methods are applied because the curves obtained from
conventional oedometer tests and the behaviour exhibited by them show little similar-
ity to the clay behaviour. The difference becomes particularly apparent at low vertical
stresses, i.e. for surficial peat deposits in early load increments in the laboratory. Pri-
mary consolidation is very rapid, and large secondary and even tertiary compressions
are observed. Analysis of the compression of such materials presents certain difficulties
when conventional methods are applied because the curves obtained from conventional
oedometer tests and the behaviour exhibited by them show little resemblance to the
clay behaviour. Furthermore, such materials also are more prone to decomposition
during oedometer testing. Gas content and additional gas generation may also compli-
cate the interpretation of odometer tests. The behaviour of such peats and the recent
advances in formulating their behaviour have been presented by Edil (1997) and den
Haan (1997).
5.2.1 Compression index,
c
c
and void ratio
Figure 5.6 shows the graph of compression index,
c
c
, versus liquid limit (
LL
) for
various tropical peats. As shown,
c
c
measured in laboratory tests increases with the
liquid limit. Farrell
et al.
(1994) considered that the empirical relationship between
the compression index and the liquid limit suggested by Skempton for organic soils
Figure 5.6
Compression index (
c
c
) vs. liquid limit (
LL
)(
after
Al-Raziqi
et al
., 2003).
