About Prefabricated Vertical Drain

At times, Engineers are required to build on sites which are founded on soft compressible soils in the construction of buildings, infrastructures and other structures. In such instances, it would be necessary to improve the soft compressible soils before constructing any structures on them.
Presently, there are various methods available to improve the soft compressible soils. Soil improvement with Prefabricated Vertical Drain (PVD) or sometimes known as wick drains, is among the most economical method to expedite the consolidation process.

The Consolidation Process
In saturated soils such as clay and silty clay, which have a large percentage of voids or pores usually filled with water, large settlement will occur over a long period of time when a load such as a road embankment is placed on top of the soil. The load will result in an initial increase in pore water pressure which will dissipate slowly as the pore water drains off.
During this process called consolidation, the load is gradually transferred to the soil particles as the volume of the voids are reduced and this culminates in the form of settlement.

Acceleration of Consolidation Using Vertical Drains
Due to the very low permeability of clay soil and silty clay soil, the consolidation process will take many years. In order to accelerate and reduce the consolidation time, vertical drains are installed at regular close spacing to the full depth of the compressible layer, to create artificial and shorter horizontal drainage paths for the pore water to drain off. In addition, this will also take advantage of the higher permeability of the soil strata or sand lenses in the horizontal direction. During this accelerated process, the soil will gain an increase in shear strength.
Normally, vertical drains are used in conjunction with pre loading by surcharge with soil or vacuum pressure. In some projects like tank farm, water can also be used as surcharge.

Prefabricated Vertical Drain
. Drain body
a unique high density polyethylene cuspate core or continuous channels polypropylene core to provide high discharge capacity, high tensile and compressive strength
. Filter jacket
a non woven spunbonded polypropelene or polyester fabric with high tensile strength, high permeability and effective filtering properties.
By combining both the features of the unique cores and highly permeable filter jacket, is effective, fast and reliable performance for soil improvement.

Benefits of Using Prefabricated Vertical Drain
. High water discharge capacity to ensure sound safety factor
. The unique and flexible core will not pinch off or flatten when the drains bends and folds during the consolidation of the soils
. High compressive strength of the core to prevent the collapse of the flow path
. Deep installation exceeding 40 m depth
. Light weight
. Customized core and filter jacket to suit particular soil conditions
. Minimum disturbance to the soil during installation
. Fast installation
. Short consolidation period
. Well proven performance in many projects under different soil condition soil conditions

Performance of Prefabricated Vertical Drain
The type of projects where it has been used successfully are :
. Construction of roads, highways and expressways
. Treatment of ex-mining areas for housing development.
. Container yards and harbor construction
. Land reclamation for the construction of airport runways and buildings
. Construction of tank farms
. Commercial development in ex-agriculture land