In-plane flow is the job of geonets, geocomposites, thick nonwovens and strip drains, rated by transmissivity under the design load. Unlike filtration, where water crosses the fabric, drainage moves water along the layer to a pipe or outlet. A drainage layer that is crushed, clogged or never connected to an outlet only stores water and builds pressure.
Drainage layer behind the wall is fine, but nobody daylighted the outlet, so it's full of water.
Also heard as
- in-plane drainage
- drainage function
Related terms
Transmissivity
In-plane flow capacity of a geosynthetic drainage layer per unit width, under a given gradient and normal load.
Geocomposite
Product that combines two or more geosynthetics, most often a geonet core with geotextile bonded on one or both sides.
Geonet
Net of extruded polyethylene ribs that forms a thin, high-flow drainage layer within its own plane.
Daylight
To bring a drain or drainage layer out to open ground lower down so its water can escape by gravity.