In a permeameter, soil sits on the geotextile and water flows down through both; the hydraulic gradient across the geotextile and the soil just above it is divided by the gradient across the soil higher up. A ratio near 1 means fines are passing or stable, while values that keep rising, commonly above about 3, warn that fines are building up at the fabric. It is run for fine, gap-graded or unstable soils where index tests are not enough.
Gradient ratio climbed to 4 by day five, so that fabric is blinding with this silt.
Also heard as
- GR
- gradient ratio test
Related terms
Clogging
Gradual loss of flow through a geotextile as soil particles or deposits lodge inside its pores.
Blinding
Sealing of a geotextile surface by a thin layer of fine particles that blocks flow across it.
Filtration
Letting water pass across a geotextile while holding back the soil particles it carries.
AOS
Apparent opening size: an index of the largest openings in a geotextile, given as a US sieve number or in millimeters.