Geoscience Reference
In-Depth Information
Figure 1.11
Worldwide distribution of peat (
after
Parish
et al
., 2008).
As mentioned above, soils with an organic content greater than 20% are generally
termed organic soils. The organic content is essentially the remains of plants whose rate
of accumulation is faster that the rate of decay. The precise definition of peat, however,
varies between the disciplines of soil science and engineering. Soil scientists define peat
as soil with an organic content greater than 35%. To a geotechnical engineer, all soils
with organic content greater than 20%are known as organic soil and peat is an organic
soil with an organic content of more than 75% (see further definition in Chapter 2).
The engineering definition is essentially based on the mechanical properties of the soil.
It is generally recognized that when a soil possesses greater than 20% organic content
the mechanical criteria of conventional mineral soil (silt and clay) can no longer be
generally applied. To avoid further confusion, we will generally term all organic soils
as peat in this topic - in other words, the terms
peat
and
organic soil
will be used
interchangeably. One main reason for this is that many reference sources about soil
distribution are based on agricultural science, whose definition of peat is different from
that of engineering. The worldwide distribution of peat is shown in Figure 1.11.
In temperate region, such as in Canada, Europe and the USA, peat deposits are
termed bogs and fens. These are pits or basins filled with organic material. Bogs are
typically covered with live moss. Thoroughly decomposed peat is sometimes called
muck. Swamps are larger than bogs and may contain a wide variety of materials.
Slow streams or lakes typically feed them. A noteworthy example is the Everglades in
Florida, USA.
In tropical countries like Malaysia and Indonesia, peat is generally termed either
basin or valley peat. Basin peat is usually found on the inward edge of mangrove
swamps along a coastal plain. Individual peat bodies may range from a few to 100,000
hectares and they generally have a dome-shaped surface. The peat is generally clas-
sified as ombrogenous or rain-fed peat, and is poor in nutrients. Due to coastal and
