Prefabricated vertical drains

Preloading is one of the most common ground improvement techniques for soft clay. The modern application of the preloading method is combined almost always with the use of vertical drains or prefabricated vertical drains (PVDs). PVDs have been used successfully in many soil improvement and land reclamation projects in the world (Hansbo, 1979, 2005; Holtz, 1987; Holtz et al., 1991; Balasubramaniam et al., 1995; Bergado et al., 1990, 1993a, 1993b, 1996, 2002; Li and Rowe, 2001; Chu et al., 2004; 2009a; Choa et al., 2005; Bo et al., 2003; 2005; Arulrajah et al., 2004; Indraratna et al., 2005; Seah, 2006; Kitazume, 2007; Varaksin and Yee, 2007). Therefore, the theories, design, and construction methods for PVDs have become the core technical issues in the preloading or consolidation method. In recent years, PVDs or their variations have also been used for other purposes such as for dissipation of pore water pressures for liqueable sand (Towhata, 2008; Chu et al., 2009a) or in environmental engineering for vapour extraction system (Schaefer et al., 1997; Collazos et al., 2002).