Page 169 - RoadCem Manual - PCT BV

6. Drainage
Like water we look for the easiest solution
6.1 General
Drainage is probably the most dominant factor affecting the performance of roads. When roads fail it is often because of inadequacies in drainage. This results in the ingress of water into the road structure, structural damage and costly repairs. In addition, surface water can form a road safety hazard by causing aquaplaning.
Unfortunately, many roads have evolved with inadequate initial engineering and drainage design. Even with properly engineered roads, on-site inspection is often necessary to correct any unforeseen conditions during construction. Such an approach is more cost-effective than maintaining or correcting deficiencies after the road has been in service for several years.
Two inter-related aspects of drainage require careful consideration during construction, namely:
• Internal drainage of the pavement which seeks to avoid the entrapment of water by allowing it to permeate through and drain out of the pavement structure.
• External drainage which seeks to divert water away from, and prevent its ingress into the pavement structure through measures such as the construction of sealed shoulders, side drains, etc.
6.2 Internal Drainage 6.2.1 General
Internal drainage involves measures to minimise moisture contents in the embankment and pavement layers and importantly to prevent unwanted movement of water within the pavement structure. Internal drainage is vital for the satisfactory performance of earthworks and pavement layers made of natural soils and gravel.
6.2.2 Permeability of pavement layers
Each layer in pavement and earthworks should be more permeable than the overlying layer in order to prevent any water entering the structure from being trapped. With RoadCem the road pavement design and construction ensures that this is always the case since it consist of one bound layer which is almost impermeable with extremely low water permeability. The sub base layer, under the RoadCem treated layer will almost always have a higher water permeability. But, it is always advisable to provide cross-fall in all earthworks and layer works for water to escape from the pavement structure and in doing so alleviate potential water retention problems. Under severe conditions, especially where there is risk of water seeping into the pavement structure, consideration should be given to installing subsurface drainage systems or, better still, to increase the height of the road in such areas.
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