Page 177 - RoadCem Manual - PCT BV

• Drifts are designed to provide a firm driving surface in the riverbed, where traffic can pass when water levels are moderate.
• Vented drift sometimes named fords, causeways or Irish bridges, (larger structures are called low level bridges) allow water to pass through openings, but can withstand overtopping without damage. Openings in vented drifts should, like culverts, be made large enough, preferably not less than 0.9 m so that cleaning during future maintenance is made easier and the risk of blockage is minimized.
Figure 6.12 Low level drift. Figure 6.13 Vented drift.
A common feature of all low level structures is that they require proper foundations and anchoring, as well as scour protection to the road prism.
Figure 6.14 Inadequate culvert. Figure 6.15 Banks of pipe.
6.5.3 Culverts
Types: Culverts are constructed on roads using a variety of methods and materials. Examples include corrugated plastic pipes, steel pipes or arches, pre-cast or concrete pipes, boxes, arches or half arches (“shelverts”), reinforced concrete slabs resting on blockwork in a box culvert profile and wooden culverts in a box or circular profile.
LOCATION
Wherever possible, culverts should be located in the original stream bed with the invert following the grade of the natural chanell.
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