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Time for 50 Percent Clay Consolidation

Hardconsolidationtime factor
A 4 m thick clay layer drains from both its top and bottom faces. Its coefficient of consolidation is cv = 3 × 10⁻³ cm²/s, and the time factor for 50% consolidation is T = 0.197. The time to reach 50% consolidation is most nearly:
  1. A8 days
  2. B30 days
  3. C60 days
  4. D120 days
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Answer: B. 30 days

With drainage at both faces the drainage path is half the layer thickness: Hdr = 4/2 = 2 m = 200 cm. Then t = THdr²/cv = (0.197)(200)²/(3 × 10⁻³) = 2.63 × 10⁶ s ≈ 30 days. Using the full 4 m thickness as the drainage path would quadruple the time to about 120 days.
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