Written by Jerry Ratzlaff on . Posted in Geotechnical Engineering

Critical hydraulic gradient, abbreviated as $$i_c$$, is the change in height (pressure) to length between any two points.

Critical hydraulic gradient formulas

 $$\large{ i_c = \frac{ \gamma_{sub} }{ \gamma_w } }$$ $$\large{ i_c = \frac{ SG_s \;-\; 1 }{ 1 \;-\; e } }$$

Where:

 Units English Metric $$\large{ i_c }$$ = critical hydraulic gradient $$\large{ dimensionless }$$ $$\large{ \gamma_{sub} }$$  (Greek symbol gamma) = submerged unit weight $$\large{ lbm }$$ $$\large{ N }$$ $$\large{ \gamma_w }$$  (Greek symbol gamma) = unit weight of water $$\large{ \frac{lbm}{ft^3} }$$ $$\large{ \frac{N}{m^3} }$$ $$\large{ SG_s }$$ = specific gravity of soil $$\large{ dimensionless }$$ $$\large{ e }$$ = void ratio $$\large{ dimensionless }$$