Geoscience Reference
In-Depth Information
5.1 INTRODUCTION
When a soil is subjected to an increase in compressive stress due to foundation load
the resulting soil compression (generally called settlement) generally consists of elastic
compression (immediate settlement), primary compression (consolidation settlement)
and secondary compression. Compared with mineral soils, peat soils are highly organic
and highly compressible. Their compression or settlement process may take a consid-
erably longer amount of time. Peat generally possesses low undrained strength and
high compressibility. Buildings on peat are usually supported on piles, but the ground
around them may still settle, creating a scenario as depicted in Figure 5.1.
Fibrous peat has high organic and fibre content with a low degree of humification.
The behaviour of fibrous peat is different from mineral soil because of different phase
properties and microstructure (Edil, 2003). Landva and Pheeney (1980) described
fibrous peat particles as consisting of fragments of long stems, thin leaves, rootlets,
cell walls and fibres, often very large.
Since fibrous peat has hollow perforated cellular structures (Figure 5.2) and a net-
work of fibrous elements in vertical and horizontal sections, it is most likely to have very
low shear strength and high compressibility, and the long-term consolidation of peat
results in a large deformation. Peat lands have presented difficult subsurface conditions
for the construction of roads, dikes, housing developments, storage facilities, industrial
parks and so on, including high initial costs and/or continued maintenance operations
for years (Colley, 1950; Hanrahan and Rogers, 1981). Peat soils are geotechnically
problematic soils as the compression and settlement processes may take a consid-
erably longer time, which increases when the ground water level decreases. Besides
settlement, stability problems during construction, such as localized bearing failures
and slip failures need to be considered (Duraisamy
et al
., 2009).
One of the towns in Malaysia that is badly affected by land subsidence on peat is
Sibuin Sarawak. The problem is mainly caused by either uncontrolled land filling or
ground water lowering due to over-drainage (or both). A substantial part of the town
centre is currently in a state of disrepair, with rows of residential housing units being
abandoned altogether, due to excessive ground subsidence. Ground subsidence has
also resulted in negative gradients to drainage, resulting in unhealthy water stagnation
in many parts of the town. Much of the town is also prone to flooding, both locally
as well as regionally. The regular occurrence of flooding is, however, the very basis on
which the peat soils are geologically formed and sustained (Figure 5.3).
