Filtration Design

Woven Geotextile Sieve Size vs Soil Particle Retention

A uniform sand has no fines to bridge its own pores, so it needs a tighter fabric than a well-graded soil twice as coarse.

Soil Grading Curve Sieve analysis
mm
mm
mm
mm
mm
%
Candidate Fabric Geotextile
mm
mm

Applied when more than half the soil passes the 0.075 mm sieve.

Maximum Permissible O95

— mm

Coarsest opening the soil grading will tolerate

Grading & Fabric Check

Uniformity Coefficient (Cu)
— ×
Curvature Coefficient (Cc)
— ×
Retention Criterion Multiplier
— × D85
Fabric O95 vs Permissible
— ×
Clogging Ratio (O95/D15)
— ×
Opening Size
— µm

Retention below 1.0 and clogging ratio above about 3 is the window most agency criteria want; a fabric can satisfy retention comfortably and still blind with fines, which is why both numbers appear here. The criterion assumes steady unidirectional flow — reversing flow under wave or tidal loading needs a tighter fabric than this returns. Gap-graded and dispersive soils are outside the range these criteria were fitted on and warrant a filtration test rather than a formula.

Woven Geotextile Sieve Size vs Soil Particle Retention — free, with the formula and a worked example, at Textile School.