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13.3.6.1 Drainage Layers in the Pavement The sub-surface drainage system often includes a (permeable) drainage layer in the pavement. Its function is to quickly remove water entering the pavement layers, either through infiltration to the groundwater or to a sub-surface drainage system, before any damage to the road can be initiated. It is common practice […]

Sometimes it is desirable to combine surface water runoff collection and sub-surface seepage water into one, combined, drainage system. Typically, such systems are in the form of lateral trench drains (see Section 13.4.1) that are open to the surface. These are the traditional means of draining roads and continue to be used on lower — […]

Although they may not be considered as part of the drainage system, a pervious type of asphalt treated surface layer, known as porous asphalt, has become common in Europe in recent years. The main advantages attributed to porous asphalt layers are noise reduction, improvement of skid resistance in wet weather, and enhancement of runoff water […]

A rather common subsurface drainage system used to remove the infiltrated/seepage water from the pavement structures is by providing a permeable layer. Permeable layers should be at least 10-15 cm thick and extend under the full width of the roadway. They can be used under both concrete (PCC) and asphalt (AC) pave­ment surfaces. Permeable bases […]

In drainage design, an undamaged asphalt surface is considered almost impervious. However, water can infiltrate into the structure through cracks and joints (see Chap­ter 5, Sections 5.3 and 5.4.2). Also, shoulders and slopes with higher permeability and high water tables can allow significant amounts of water into the structure. Whether the water arrives via cracks […]

Subsurface drainage is made up of different parts but all are linked directly with the surface drainage system and all are, fundamentally, taking care of groundwater or water that infiltrates through the pavement surface. 13.3.4.1 Drainage Regime Part of the rainfall-runoff infiltrates into the ground and continues as subsurface flow. Part of this may, in […]

The surface drainage system should remove all flow of rainwater from the road’s sur­face, and from the highway slopes as well as the runoff from adjacent land. Surface drainage systems are also important in the proper management of polluted runoff and in minimizing environmental impacts. The surface drainage can be divided into transverse drainage and […]

The drainage system employed in a road construction will depend on factors such as: • The importance of the road; • The amount of traffic; Fig. 13.2 A horizontal alignment designed to lead water away from sensitive areas • The zone (rural or populated); • The sensitivity of the groundwater; and • The sensitivity of […]

13.3.1 Road Alignment and Routing For new roads, before drainage can be considered, the routing of the road must be fixed. Road routing is a complex procedure that involves very many factors including social, economic, engineering and environmental criteria as well as pub­lic acceptance. However, proper selection of the road corridor is one of the […]

There are two aspects, which must be addressed in answering the question: “Why is road drainage so important?”. They are: • A road’s infrastructure is an engineering work, aimed at the establishment of a platform on which vehicle circulation is possible under safe conditions, with proper traffic flow, utility, and economy, independent of the region’s […]