Netlon Strip Drains

A geocomposite strip drain is a prefabricated subsoil drainage element that replaces the stone-and-pipe French drain. The product comprises an extruded two-dimensional HDPE geonet core, nominally 500 g/m² and 4.5 mm thick under 2 kPa load, encased in a needle-punched nonwoven polypropylene filter sleeve. The core provides an open, high-void drainage path along the length of the strip; the geotextile sleeve filters incoming water, holding back fines while allowing free passage of flow. Supplied in standard widths of 100, 200, 250, 300 and 333 mm in rolls up to 25 m, the drain arrives on site as a finished component requiring no aggregate, no bedding and no assembly. On South African sites the product is still widely referred to as a netlon strip drain, a term inherited from the extruded plastic mesh drains that first introduced the technique locally.

Drainage performance is measured rather than assumed. In-plane water flow capacity is tested to EN ISO 12958 at a hydraulic gradient of i = 1.0 across a range of normal loads, giving the designer real values to work from instead of a nominal rating: 1.40 l/s/m in the machine direction at 20 kPa, falling to 1.09 l/s/m at 200 kPa and 1.02 l/s/m at 300 kPa. Cross-machine values are lower, at 0.80 and 0.57 l/s/m respectively, which matters when the drain is installed against a curved or irregular face. Note that flow values quoted above 200 kPa fall outside the scope of EN ISO 12958 and should be treated as indicative. The complete product meets the requirements of COTO (2020) Table A3.1.5-3 for geocomposite strip drains, the reference table used by South African road authorities for this product class, and the core carries a maximum service temperature of 85 °C.

The filter sleeve is available in two grades, and the choice is a design decision rather than a price one. The standard grade offers 10/10 kN/m tensile strength to SANS 1525 / EN ISO 10319, 1.7 kN CBR puncture resistance to SANS 12236, and higher water flow at 77 l/s/m² under a 50 mm head - suited to backdrainage behind retaining walls, basements and lift pits, where installation conditions are controlled and flow capacity is the governing requirement. The heavy-duty grade steps up to 15/15 kN/m tensile, 2.6 kN CBR puncture, and a dynamic cone drop of 17 mm against 28 mm for the standard grade, at some cost to flow at 54 l/s/m². Specify the heavy-duty grade where the drain will be placed against rock or shotcrete, backfilled with angular or coarse material, or subjected to rough handling during installation. Both grades are staple-fibre needle-punched nonwovens manufactured from virgin polypropylene, share a pore size of O90 = 70 micron to SANS 12956, and resist the chemical and biological conditions normally encountered in soils. Filter compatibility should be confirmed against the site's actual particle size distribution before specifying.

Typical applications include backdrainage to retaining walls, basement and lift-pit walls, road and highway edge drains, cutting and embankment drainage, sports field and landscape drainage, and the dewatering of soft saturated soils. A version with an integral 250-micron damp-proof course layer, bonded to the geotextile on one face, is available for use against structural walls where the drain must both collect water and act as a barrier against moisture transfer into the structure. DPC widths of 100, 150, 225, 300, 340 and 450 mm can be matched to the drain width, and wider DPC than drain is available where the detail requires it. Non-standard widths, lengths, and alternative woven or nonwoven geotextile grades are produced to order.