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.

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

### Where:

$$\large{ i_c }$$ = critical hydraulic gradient

$$\large{ \gamma_{sub} }$$  (Greek symbol gamma) = submerged unit weight

$$\large{ \gamma_w }$$  (Greek symbol gamma) = unit weight of water

$$\large{ G_s }$$ = specific gravity of soil

$$\large{ e }$$ = void ratio