Plasticity Index: LL-PL Liquidity Index: LI = (W-PL)/ (LL - PL) Consistency Index: CI = (LL - W)/ (LL - PL) Activity (A) of a soil is the PI divided by the percent of clay-sized particles (less than 2 µm) present. Where, LL=liquid limit, PL = plastic limit, W = natural water content