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Construction options

Dependent upon the surface material and use of the surface, the underlying construction usually consists of a combination of :

• Soil, sharp sand, crushed rock.
• One or more layers of different materials e.g. granular and/or geosynthetic layers.
• A permeable geotextile or an impervious geomembrane.

It may also include, if necessary, drainage networks to discharge water entering or flowing through the construction. The report includes typical cross sections for each type of surface.

The outflow from the pervious pavement construction can be achieved in a number of ways:

• Water within the construction is directed to a drainage network either on the subgrade or within the permeable sub-base which conveys it to a suitable outfall or disposal point.
• Water entering the pervious surface infiltrates down into the groundwater through the base of the construction.
• Water is discharged at the base of the construction passing slowly to groundwater and excess waters, which would otherwise fill the construction, are released via a high-level overflow pipe.
• Water is stored in the construction for suitable non-potable use, any excess being disposed of via a high-level overflow pipe.

 

Often pervious areas are required only to handle rainfall landing directly upon their surfaces, but their capacity is such that they may also be used to provide a drainage path for water discharged from adjacent areas, such as roofs or impermeable areas of car park. It is advisable to release any additional waters either onto the surface of the pervious construction, or via a debris trap, in order to prevent clogging of the sub-surface layers. 

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