Soil improvement and construction methods in peat - Geotechnics of Organic Soils and Peat - page 143

Figure 6.20 Dynamic replacement to form sand columns.
of work is carried out until completion of the installation of a DR column, as shown
in Figure 6.20.
This method seems to work well for soft silty clay, but its application to peat is
yet to be proven.
6.4.7 Sand drains and sand/stone columns
Kurihara et al . (1994) reported the favourable performance of the central Hokkaido
expressway, built on peat using sand drains as shown in Figure 6.21. The sand drain-
treated sections were found to experience smaller post-construction settlement over
five years of operation compared with the untreated section. They also concluded that
the sand compaction pile would be more expensive in this respect.
Very weak surficial zones of peat may not have adequate strength to provide lateral
support to the sand or stone columns. The use of geotextile and synthetic fibres has
been suggested to remedy this problem (Al-Refeai, 1992).
6.4.8 Vibrated concrete column
In this technique concrete columns are created in situ . A vibrator penetrates the weak
subsoil until it reaches the proposed bearing stratum. Concrete is then pumped as
the vibrator is withdrawn. By re-vibrating the concrete at the base and top, bulbous
ends are formed which enhance base resistance and form pile caps at the surface.
The embankment above the piles is reinforced with geogrid layers to promote load
transfer to the columns. An example of this application is given by Maddison et al .
(1996).
6.5 PILE SUPPORT
Piles may be described as long, slender concrete, steel or timber members that can be
used in transferring loads through weak/unstable soil to ground of higher load-bearing
capacity.