The 'primary consolidation' of a clay layer settles because:
Choose the correct answer
Immediate elastic compression of soil grains
Dissipation of excess pore water pressure → effective stress increase → void ratio decrease (water squeezed out)
Erosion of clay particles
Swelling of clay minerals on wetting
Correct Answer
B. Dissipation of excess pore water pressure → effective stress increase → void ratio decrease (water squeezed out)
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Primary consolidation: excess pore water pressure (generated by load application) dissipates through drainage → effective stress increases → volume decreases. Time rate: cv×t/H²_dr (Tv = dimensionless time factor). Final settlement: Δe/(1+e0)×H from oedometer Cc and pressure increment. Complete primary consolidation: u_excess → 0, effective stress = final applied stress. Secondary: continued creep after u=0.
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