Geoscience Reference
In-Depth Information
methods in peat
6.1 INTRODUCTION
Peat represents the extreme form of soft soil. It is subject to instability, such as localized
sinking and slip failure, and massive primary and long-term settlement 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.
Peat may also change chemically and biologically with time. For example, further
humification of the organic constituents will alter the soil's mechanical properties,
such as compressibility, shear strength and hydraulic conductivity. Lowering of ground
water may cause shrinking and oxidation, leading to humification with a consequent
increase in permeability and compressibility.
Buildings on peat are usually suspended on piles, but the ground around it may still
settle, creating a scenario as depicted in Figure 5.1. Much of this chapter is therefore
devoted to methods of construction for line structures, such as for road embankments,
which are subject not only to instability and settlement, but also to the tremendous
variability in peat soil material properties, as illustrated in Figure 6.1.
Even if failure is avoided, it is inevitable that soft waterlogged soil and peat takes a
long time to settle when loaded due to embankment or soil fill. Under these conditions,
the embankment will settle continually into the ground below, even if the soil does not
fail by displacement. This is illustrated in Figure 6.2. To make matters worse, the
addition of more fill to make up the depression in the embankment will ensure further
settlement.
Where possible, engineers seek to avoid building on this problematic ground.
Avoidance is sometimes possible by changing the location of the construction, as illus-
trated in Figure 6.3. However this is not always possible. In cases where there is no
alternative due to the high demand for land for development, even this less desirable
land has to be developed.
The main purpose of this chapter is to describe some of the methods and recent
technology that have been used to mitigate the challenges faced in construction (in par-
ticular those for line structures such as road embankments) on peat and organic soils.
Some technical details will be presented for the methods described. In must also be
noted that in practice these technologies overlap and are commonly used concurrently.
This chapter gives some insights on the construction methods currently employed
where yet there is no consensus on the best methods of analysis. Undoubtedly con-
struction on peat and organic soils is not easy, but with better understanding it can be
more manageable.
