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Permeable pavement structure & design

Permeable pavement system (PPS) consists of a surface layer, overlying a sub-base layer which rests on existing soil. One or more intermediate layers such as gravel and crushed stone or course fine sand may be included between the surface layer and the sub-base. The essential function of the pavement surface is to support vehicular loads without undue deformation and to allow storm water infiltration to the pavement’s sub-base. The sub-base has a structural role in distributing the pavement’s load to the underlying layers of gravel and soil, but also acts as a water storage layer and is sometimes referred to as the water saturation zone or reservoir course. Filtered storm water may be transported from the pavement structure via infiltration to the underlying soil or be collected in a formal drainage system beneath the pavement surface.
Below is a schematic of a permeable pavement system PPS which includes the pervious concrete blocks, bedding layer course (pea gravel, small stone and sand), geo-textile, layer of gravel and crushed rock and a possible extra geo-textile bottom layer for extra buffering of water quality.

                                                                                     Figure 1 PPS Permeable Pavement System (Tota-Maharaj, 2010)

Advantages of permeable pavements


·         Permeable systems enable pollutants to be trapped by the sub-base or by a geo-textile.

·         Permeable systems are more cost-effective than traditional collection and dispersal systems.

·         Permeable systems can also offer significant environmental advantages, such as natural breakdown of pollutants, replenishment of      aquifers, and the possibility of water harvesting.

Disadvantages of permeable pavements

  • Cost of permeable paving is 2-3 times more than asphalt paving
  • Maintenance is required as grit of gravel can block the open pores.
  • Runoff volume must be considered as this technique must be part of an overall site management. (high water table below pavement)