Page 170 - RoadCem Manual - PCT BV

6.2.3 Crown Height
Crown height is the vertical distance from the bottom of the side drain to the finished road level at centre line. It needs to be sufficiently great to allow proper internal drainage of the pavement layers. Economical ways to achieve sufficient crown height include the use of material from the side drain and road reserve, a common procedure where scrapers/motor graders are used for construction. Maintaining sufficient crown height through cuttings is of particular importance, owing to the unfavorable drainage conditions in such areas.
Figure 6.1 Drainage. Figure 6.2 Damaged drainage.
This may result in a considerable increase in the quantity of earthworks. Alternatives, such as subsurface filter drains, should be considered as a last resort because of cost and maintenance implications. The traffic safety aspects of large crown heights should be taken into account by moving the side drain further away from the shoulder break point.
In areas where in situ soils are considered to be self-draining, such as in sandy areas and desert-type areas, priority should be given to providing good side support within a low embankment profile and shallow side slopes (typically 1:6 or 1:8) rather than a large crown height and relatively steep side slopes.
6.2.4 Seepage and subsurface drains
Unfortunately, inadequate surface and subsurface drainage are typical deficiencies associated with cut- and-fill pavement sections for roads, as shown in figure 6.3. Such deficiencies can affect the pavement by erosion, decreasing soil support or initiating creep or failure of the downhill fill or slope. They should be addressed during construction rather than waiting until failures occur because it is much more expensive to undertake remedial works.
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