Filtration
Letting water pass across a geotextile while holding back the soil particles it carries.
A filter geotextile has to meet three demands at once: openings small enough to retain the soil, permeability high enough for the flow, and pores that will not clog over the life of the job. Designers compare AOS with the soil's grain sizes, check permittivity against the soil's permeability and run gradient ratio tests on problem soils. Filtration is the job of the fabric around drains, under riprap and behind walls.
It's a filtration job, so pick the fabric off the soil gradation, not off the price list.
Also heard as
- filter
- filter function
Related terms
AOS
Apparent opening size: an index of the largest openings in a geotextile, given as a US sieve number or in millimeters.
Permittivity
Rate of water flow across a geotextile per unit head, the basic measure of its cross-plane flow capacity.
Gradient ratio
Laboratory ratio that shows whether a soil and geotextile pair is starting to clog under steady seepage.
Clogging
Gradual loss of flow through a geotextile as soil particles or deposits lodge inside its pores.
Piping
Soil particles washing through a filter or out of an embankment, leaving voids and channels behind.