Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 8 GROUND IMPROVEMENT
8.2.3.22 Sand Drain System
Sand drain system
has been introduced since 1930s as the vertical drainage techniquee for soft
ground. In general sand column
are installed in grid pattern with spacing ranges from 2 – 3m center
to center. The common diameter adopted ranges from 200mm to 400mm and the allowable
depth of
treatment can be as deep as 30m. One of the typical examples of sand drain application is the
manmade island for the Kansai Airport Japan in 1990s. The application of sand drain has slowly been
replaced by Prefabricated Vertical Drain due mainly to its speed, ease of construction and relatively
cheaper cost.
Figure
8.4 Typical Schematic Diagram For Vertical Sand
Drain System In Embankment Construction
on Soft Ground
8.2.3.33 Prefabricated Vertical Drain (PVD)
PVD has been widely used as
vertical drainage system. It is a manufactured drain made from
synthetic material. In general, PVD is very thin material, approximately 4mm with a common width
of 100mm. The very thin material would minimize clay
smearing during installation whichh reduces
the efficiency of the
drain. PVD is slowly replacing the use of sand drain because of the cheaper cost
and fast installation. Figure 8.6 shows a picture of a typical PVD available in the market.
Figure 8.5 Prefabricated Vertical Drain
March 2009
8-5