The rate of consolidation:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 2009
Detailed Explanation
The rate of consolidation is controlled by how easily water can flow out of the clay, i.e. by the permeability k, through the coefficient of consolidation:
\[ c_v = \frac{k}{m_v\,\gamma_w} \]
Permeability itself depends on the viscosity of water: \( k \propto \gamma_w/\mu \).
Why “increases with increase in temperature” Is Correct
When temperature rises, the viscosity μ of water falls (water at 30 °C is about 20% less viscous than at 20 °C). Lower viscosity gives higher permeability, a higher cv, and so a faster rate of consolidation. That is why permeability and cv values are usually corrected to a standard temperature of 27 °C (IS) or 20 °C.
Why the Other Options Are Wrong
- A. increases with decrease in temperature: Lower temperature makes water more viscous, which slows flow and consolidation.
- C. is independent of temperature: Temperature affects the viscosity of the pore water, so the rate does depend on it.
- D. All the above: The options contradict each other, so they cannot all be true.
Key Point
Temperature ↑ → viscosity ↓ → k ↑ → cv ↑ → faster consolidation.
Key Concepts for Students
- Permeability correction: k_T1/k_T2 = μ_T2/μ_T1.
- The amount of primary consolidation is not much affected by temperature; the rate is.
- Clays consolidate far more slowly than sands because of their very low permeability.
Practice more: this is question 22 in Soil Consolidation MCQs – Part 2. Try the whole set and check every answer instantly.