Plaspave

Non Infiltration or Tanked

 

The Non Infiltration/Tanked paving system is employed in situations where the existing sub-grade has low permeability such as a heavy clay soil where there is little opportunity for infiltration. It is also used where the sub-grade is of low strength and liable to damage by the introduction of additional water. This system allows for the complete capture of all the water falling on the paved area. This is achieved by placing an impermeable flexible geomembrane on top of the sub-grade and up the sides of the permeable sub-base to effectively create an underground tanked reservoir.




Non-Infiltration/Tanked paving systems are particularly suitable for contaminated sites as it prevents pollutants from infiltrating the sub-grade from where they are eventually washed into the groundwater. The stored water can also be re-used for not-potable purposes such as irrigation, car washing or toilet flushing. See Rainwater Harvesting.

PIPE OUTLETS AND OUTFLOW

Pipe outlets from Non-Infiltration/Tanked paving systems penetrate the impermeable flexible membrane. To ensure watertight connection, proprietary ‘top-hat’ seal systems should be employed.

Non-Infiltration/Tanked paving system design assumes that the system outflow rate is restricted to the accepted ‘Greenfield’ run off rate of 5 - 7 Litres/sec/hectare. This minimises the impact on drainage networks and water courses during storm events. This discharge rate can be accommodated using a 100mm diameter pipe with the flow restricted by proprietary flow control systems. The spacing and location of outlet pipes will be dictated by site layout and available points of discharge. Outlets to the urban drainage system may need permission from the Local Authority/ Environment Agency.

CAPPING LAYER

For Non-Infiltration/Tanked paving systems, it is necessary to lay a layer of capping material below the impermeable flexible geomembrane to provide a firm working platform for the
overlying construction layers. Two types of capping material are recommended for use in the Specification for Highway Works (2007), 6F1 (finer material) and 6F2 (courser material).
If 6F2 material is used it will be necessary to blind the surface with fine material to prevent puncturing the impermeable geomembrane.