Ground engineering · Ground improvement

Geotextile filter criteria calculator

Retention (O95 ≤ B·D85) with B from Cu, permeability kg ≥ ks (critical ×10), and permittivity.

Standard: FHWA NHI-07-092 (Carroll / Christopher & Holtz)

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Diagram for the worked example

B (Cu ≤ 2 or ≥ 8: 1; 2–4: 0.5Cu; 4–8: 8/Cu) = IF(OR(5<=2,5>=8),1,IF(5<=4,0.5*5,8/5)) = 1.6
Max O95 = B D85 = 1.6*0.3 = 0.48 mm
Required kg = 1.000e-5*IF(0=1,10,1) = 1.000e-5 m/s

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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.