Topmix Permeable

A permeable design encompasses not just a structural design but also a hydraulic one. This design would be based on many factors such as the design storm event ground permeability and total area to be drained from. This would then normally determine the required thickness of the attenuation layer. (This is basically a storage layer made up of an aggregate with 30-40% voids). It is in this layer that the water would sit, not within the structure of the permeable surface layer so if the water was to freeze it would not have any detrimental effect on this.

Topmix Permeable has an average permeability rate of 36,000mm/hr. The minimum required permeability rates will vary greatly according to local climate conditions, but as an approximate guide, the average permeability required to cope with a 100-year storm event is 300mm/hr. As the permeability rate of this material is so great, there would have to be an unrealistic amount of dirt applied to the surface for the pavement to cease functioning effectively. It is recommended that permeable paving must still be able to function effectively when blocked by up to 95%.

We wouldn't recommend that Topmix Permeable is used in areas which are going to be used for activities such as stockpiling sawdust or in areas where there will be heavy silt loads eg large recycling centres but is suitable for most other applications.

Sinkholes are usually the result of what are known as Karst processes. They happen when a layer of rock underneath the ground is dissolved by acidic water. Before any SuDS design is implemented on a site, a ground investigation report will be carried out. This will highlight any potential issues with the ground conditions that might lead to problems so that they can be rectified before the SuDS system and permeable pavement are installed.