Measured by running water along the plane of a specimen squeezed between platens or soil, it is reported in square meters per second. Results drop sharply with normal load, time under load and geotextile intrusion into the core, so the test must copy the design load, gradient and neighboring materials. Design divides the tested value by reduction factors for creep, intrusion and clogging.
Transmissivity at 10,000 psf drops by half, so that geonet won't carry the leachate at the bottom of the cell.
Test with the actual soils or materials against both faces; testing between steel plates flatters the result.
Also heard as
- in-plane flow
- hydraulic transmissivity
- flow capacity
Do not mix it up with
- Permittivity: Permittivity measures flow across the fabric, while transmissivity measures flow along its plane.
Related terms
Geonet
Net of extruded polyethylene ribs that forms a thin, high-flow drainage layer within its own plane.
Geocomposite
Product that combines two or more geosynthetics, most often a geonet core with geotextile bonded on one or both sides.
Drainage
Carrying water along the plane of a geosynthetic to an outlet, as in wall backdrains and leak detection layers.
Permittivity
Rate of water flow across a geotextile per unit head, the basic measure of its cross-plane flow capacity.