PVD are installed to create artificial and shorter drainage paths to drain pore water in highly saturated  soil. A PVD can be defined as any prefabricated material or product having the following  characteristics:
1.Ability to be installed vertically into compressible subsurface soil strata under field condition.
2.Ability to permit pore water in the soil to seep into drain.
3.A mean by which the collected pore water can be transmitted up and down the length of the  drain.