SOIL PREPARATION

CHAPTER 6

6.4.5.2 INSTALLATION Installation starts with a good lay-out plan, drawn to scale, of the final drainage system design that will allow the exact placing of pipes and other components such as manholes and outlets. These days a plan drawn on an image of the land (as background) created by remote sensing is possible and also preferable. The plan should be kept in a safe place as a reference when other actions are carried out on the land. Installation can either be done manually, i.e. trenches are dug and pipes are laid by hand, or mechanically, in which case a part (Figure 6.7) or the whole operation (Figure 6.8) can be done by machines. Machines used to install drain pipes include back-hoes, wheel diggers and ‘trenchless’ machines that install plastic drain pipes behind a ripper. Mechanical installations are much faster, more accurate and cheaper than manual methods. According to Reinders et al. (2016), there are contractors who claim to be able to install 4 000 m of pipe per day. Construction work should be conducted when the water table is at its lowest during the dry season (Figure 6.9). This will help to ensure that soil compaction by tractors and other equipment is kept to a minimum, and soil permeability is not decreased as a consequence. Soil compaction due to heavy vehicle traffic is also the reason why it is better to drain the soil before it is deep tilled. The sequence of drainage and deep tillage will, however, be decided by the depth of the drain pipes. If the drain pipes are shallower than 120 cm, it will normally not be possible to install the drainage system before deep tillage. Excavations and installation should start at the discharge end of the drainage system and progress backwards. Access wells should be equipped with tight-fitting lids as a safety precaution, while outlet pipes must be provided with grids to keep vermin out.

FIGURE 6.7: Machine used to cut a furrow for the installation of drain pipes (Photo: J.E. Hoffman, Stellenbosch University).

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