An oedometer test has been performed on a clay sample of thickness 2 cm. 60% of consolidation has been observed after 15 minutes of loading under double drainage condition. What is the time taken to achieve same degree of consolidation for a 4 m clay layer on field under single drainage ?
- A167 days
- B16·7 days
- C1667 daysCorrect
- D1·6 years
Solution
Concept
Time for the same degree of consolidation
Formula
t₁/t₂ = (Hdr1 / Hdr2)²
Step-by-step solution
1. Lab: thickness 2 cm, double drainage → Hdr = 1 cm. 2. Field: 4 m = 400 cm, single drainage → Hdr = 400 cm. 3. tfield = 15 × (400/1)² = 2.4 × 10⁶ min = 1667 days.
Explanation
For the same degree of consolidation the time factor is the same, so time varies with the square of the drainage path length.
Why the other options are wrong
167 and 16.7 days result from using wrong drainage paths (4 m with double drainage or a 2 m path). 1.6 years (about 584 days) is also wrong.
Shortcut
t ∝ Hdr².
Common mistake
Using 2 m for the field with double drainage.
Correct answer: C) 1667 days