Concept Total stress = Effective stress + Pore pressure When loading is done initially Total pressure increases. The decrease in soil volume by squeezing out of the pore water on account of gradual dissipation of excess hydrostatic pressure induced by an imposed total stress is called consolidation. Total Consolidation of soil is divided into i) Primary consolidation Primary consolidation begins when soil is fully saturated. (In a saturated soil mass if an increase in effective stress is Δσ1, then initially it will be taken by pore water, Hence increase in pore pressure (Excess Pore Pressure (u) = Δσ1 ) Primary consolidation is complete when the expulsion of pore water stops. (u = 0). (i.e. decrease in pore water pressure). At this stage, primary consolidation is complete for Δσ1. If the further load continues to act then effective stress increases causing secondary consolidation. ii) Secondary consolidation After completion of primary consolidation when the expulsion of pore water is stopped and load continues to act, then at a very slow rate further volume change may be recorded which is due to plastic readjustment of solids. ∴Correct sequence is i) Increase in Total stress ii) Increase in pore water pressure iii) Decrease in pore water pressure (u = 0) iv) Increase in effective stress.