Prefabricated Vertical Drains
Prefabricated vertical drain (PVD) or wick drain is a soil improvement method commonly used to speed up the consolidation of soft foundation. The installation of PVD is normally followed by the placing of a temporary surcharge or preloading embankment which causes water to be squeezed out through the PVD.
The machine consists of excavator, stitcher and mandrel. The excavator is used as a base carrier in installing vertical drains into the ground. Its hydraulic system controls the up-and-down movement of the mandrel through a stitcher along with a system of cylinders and pulleys attached to it. The stitcher pushes the mandrel into the ground at the required depth of installation. The mandrel houses the drain and drives it to the ground until it reaches the required depth of embedment. Once it reaches the required depth, the mandrel is removed from the ground, leaving the drain anchored at the depth by a steel plate.
The materials used are the drains and anchor plates. The drain itself is a flat plastic core with drainage channels wrapped in a filter fabric which allows the water to pass through the drain, thus, creating a shortened path for drainage. It can be fabricated in to different sizes depending on the soil and site conditions. The other material is the anchor plate which is made up of steel and is connected to the base of the drain. Along with the mandrel and the drain, it is driven down to the ground at the required depth. Once the required depth is reached, the anchor plate locks itself at the depth to ensure that the drain is secure while the mandrel is removed.
This video shows how drains are drilled into the soil with the use of the machine. This is done repeatedly until the desired number of drains are inserted into the ground.