Geoscience Reference
In-Depth Information
4. High degree of spatial variability.
5. Potential for further decomposition as a result of changing environmental condi-
tions.
6. High permeability compared with clay.
7. High charge and high specific surface area of the colloidal fraction of peat.
In terms of development, the vast area of peat land and its occurrence close to
or within population centres and existing cropped areas means that some form of
infrastructure development has to be carried out in these areas. This would include
road crossings and, in some instances, housing developments that encroach on the peat
land areas as available land becomes more and more scare. To stimulate agricultural
development, for instance, basic civil engineering structures are required. These would
include irrigation and drainage, water supply, roads, farm buildings etc.
However, just as soil scientists and agriculturalists have, engineers have recognised
that peat land or peat is a very problematic soil that is best avoided as far as possible.
But of course this is no longer an option. To an engineer, peat or organic soils repre-
sent the extreme form of soft soil. They are subject to instabilities, such as localised
sinking and slip failure, and to massive primary and long-term secondary and even
tertiary settlements when subjected to even moderate load increases. In addition, there
is discomfort and difficulty of access to the sites, tremendous variability in material
properties and difficulty in sampling.
As stated above, these materials may also change chemically and biologically with
time. For example, further humification of the organic constituents would alter the
soil's mechanical properties, such as compressibility, shear strength and hydraulic
conductivity. Lowering of ground water may cause shrinking and oxidation of peat,
leading to humification and a consequent increase in permeability and compressibility.
It is obvious that the mechanical properties of peat are very different from those of
the mineral soils (silt and clay) that are familiar to engineering graduates throughout
the world. Thus it is critical to understand fully the characteristics of peat - high water
tables, lack of topographic relief and dynamics in their soil properties - that set them
apart from mineral soils. Criteria based on mineral soils cannot be generally applied
to peat conditions.
However, with the valuable experience gained in peat land development, and
research into the mechanical properties of the material, we are now in better posi-
tion to understand peat and hence develop safer and cheaper engineering design and
construction techniques. In the past, we use to hear tales of 'disappearing roads' or
roads that disappeared 'overnight' in peat swamps. Fortunately, there are now a num-
ber of methods that can be used for infrastructure construction in areas where peat
predominates. These are: excavation and replacement methods; surface reinforcement
and preloading; vertical drains; injection and deep mixing stabilization; cement/stone
columns; and geomaterials or lightweight fill. The preferred method will depend on
working out the best solution considering economic and technical factors, the avail-
able construction time and the target performance standards. Again, this calls for
better and deeper understanding of peat's characteristics to make the construction
more manageable.
