SOIL PREPARATION

CHAPTER 6

TABLE 6.1: Summary of drain pipes and envelope materials that are available Item Material Pipe Drains • Unglazed clay pipes • Glazed clay pipes • Pitch fibre pipes • Cement pipes (for soils with no sulphates in the soil water) • Double wall perforated pipe manufactured of high density polyethylene (HDPE) • Single wall slotted HDPE pipe • Single or double walled HDPE pipe available in three nominal diameters, viz . 75 mm, 110 mm and 160 mm • Smooth PVC pipes with grooves (6 m lengths) • Corrugated PVC pipes with grooves (in rolls)

Envelope material Mineral •

Gravel or coarse sand, free of shale and dust

Coal ash

•

• Crushed stone of 5-15 mm particle size, free of dust Synthetic • Glass fibre • Styromull • Geotextiles (Figure 6.6) Organic • Coconut fibre • Straw

FIGURE 6.6: Drainage pipe covered by geotextile to prevent clogging of pipe perforations (Photo: J.E. Hoffman, Stellenbosch University). Access wells can be built of bricks, but ready-made manholes are also available commercially. Modern, cost-effective installation practices are, however, moving away from access wells. These structures present obstacles to tractors and other implements, they silt up, and can even be a safety hazard when lids are removed or damaged. Mechanised installation methods are used without any access wells and can be done much faster and safer than manual installation of drain pipes (Reinders et al. , 2016).

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