How Wickdrain Functions
How WICKDRAIN vertical drain functions
WICKDRAIN prefabricated vertical drain has two components – a core which serves as a water conduit and a geotextile filter fabric which allows water to pass into the core while restricting the movement of soil particles which might clog the core.
The fabric
The WICKDRAIN filter material uses a strong, tough, permeable nonwoven filter fabric of 100% polypropylene specifically designed for drainage. Its continuous filaments are arranged preferentially in the length and width directions of the sheet and thermally bonded. WICKDRAIN filter fabric resists mildew, rotting, insects and chemicals normally encountered in a subsurface drainage system. It is dimensionally stable, wet or dry, has good tear and puncture resistance and will not shrink, grow or unravel.
WICKDRAIN fabric has a unique structure that enhances its function as a filter fabric. It has a large number of openings with a range of opening sizes throughout its structure instead of a few openings of fixed size as in woven fabrics. Its bonded fabrics create a tortuous pathway resembling that of a well graded aggregate filter rather than a simple, straight line exit for soil particles. Because of its unique structure, the filter fabric has both high permeability and the ability to restrict the movement of most soil particles, while allowing the very fine silts to flow into and out of the drain. The initial removal of very fine silts from the soil is beneficial because this leaves the larger particles to form a highly permeable soil network against the fabric. The soil network restricts the further movement of fine soil particles and helps to develop a graded soil filter. This soil filter effectively stops piping of soil and prevents other fine particles from entering the drain. The fabric filter, being more permeable than the soil filter and the natural soil, does not restrict the flow of water into the drain.
The effectiveness of the filter fabric has been proven in government and commercial projects in a wide range of soil types. Its effectiveness has also been confirmed by extensive laboratory tests at the Colorado State University Engineering Research Center. Tests were run with soil mixtures of fine sand, silts and clays which simulated actual systems. Under these conditions, the tests confirmed that, after the initial passage of fine silts through the filter there was:
a)No measurable migration of soil fines within the soil filter or into the drain, and
b)No measurable pressure drop across the filter indicating no reduction of water flow through the fabric. Scanning electron microscopy confirmed that there was no clogging of the fabric.
The core
The WICKDRAIN core is a strong, tough structural member of extruded from 100% polypropylene specifically designed for vertical drain systems. A total of 38 longitudinal grooves distributed on both sides of the core provide discharge passages for water flowing to the surface. The core is dimensionally stable when wet, has good puncture and collapse resistance and will not shrink or rot
Wickdrain