Geoscience Reference
In-Depth Information
Table 2.7
Classification of peat on the basis of decomposition on the von Post scale (
after
Karlsson
and Hansbo, 1981).
Designation
Group
Description
Fibrous peat
H1-H4
Low degree of decomposition. Fibrous
structure. Easily recognized plant
structure, primarily of white masses.
Pseudo-fibrous peat
H5-H7
Intermediate degree of decomposition.
Recognizable plant structure.
Amorphous peat
H8-H10
High degree of decomposition. No
visible plant structure. Mushy consistency.
remaining in the hand has a fibrous structure. (Degree of decomposition on the
von Post scale: H1-H4.)
•
Pseudofibrous peat
is moderately humified and has an indistinct to relatively dis-
tinct plant structure. It is usually brown. If a sample is squeezed in the hand, less
than half of the peat mass passes between the fingers. The material remaining in
the hand has a more or less mushy consistency, but with a distinct plant structure
(H5-H7).
•
Amorphous peat
is highly humified and the plant structure is very indistinct or
invisible. It is brown to brown-black in colour. If a sample is squeezed in the hand,
more than half of the peat mass passes between the fingers without any free water
running out. When squeezing, only a few more solid components, such as root
fibres and wood remnants, can be felt. These constitute any material remaining in
the hand (H8-H10).
A Malaysian Soil Classification for organic soils includes the two factors men-
tioned above, i.e. organic content and degree of humification, as shown in Table 2.8.
Peat is also referred to as topogenous or clayey peat and ombrogenous peat.
The former, as its alternative name suggests, is composed of slightly to moderately
decomposed plant matters and fine clastic sediments (mineral matter). The latter is
described as essentially a pile-up of loose trunks, branches and roots (Yogeswaran,
1995). Ombrogenous peat is typically acidic, characterized by low pH.
Table 2.9 shows the other classification of peat mentioned in ASTM according
to fibre content (ASTM D1997), ash content (ASTM D2974), and acidity (ASTM
D2976).
In addition to the organic and fibre content and degree of humification, other index
parameters, such as water content, liquid limits, specific gravity and unit weights are
also useful for peat and organic soils. Hobbs (1986) and Edil (1997) suggested that
the following characteristics should be included in a full description of peat.
1. Colour, which indicates the state of the peat.
2. Degree of humification, which (as described above) represents the degree to which
the organic content has decayed (fibric, hemic, sapric).
3. Water content determined by oven drying method at 105
◦
C.
