Question

In an Oedometer apparatus, a specimen of fully saturated clay has been consolidated under a vertical pressure of 50 kN/m² and is presently at equilibrium. The effective stress and pore water pressure immediately on increasing the vertical stress to 150 kN/m², respectively, are:

• A. 150 kN/m² and 0
• B. 100 kN/m² and 50 kN/m²
• C. 50 kN/m² and 100 kN/m²
• D. 0 and 150 kN/m²

Hint:

In an Oedometer test, the effective stress is the total vertical stress minus the pore water pressure, which is determined by the change in vertical stress.

Answer 1

The Correct Option is C

The effective stress is the total stress minus the pore water pressure. Initially, the vertical pressure is 50 kN/m², and upon increasing the vertical stress to 150 kN/m², the total stress is 150 kN/m². The pore water pressure is the difference between the initial and final total stress, which is: \[ \text{Pore water pressure} = 150 \, \text{kN/m}^2 - 50 \, \text{kN/m}^2 = 100 \, \text{kN/m}^2. \] Thus, the effective stress is: \[ \text{Effective stress} = 150 \, \text{kN/m}^2 - 100 \, \text{kN/m}^2 = 50 \, \text{kN/m}^2. \] Final Answer: \[ \boxed{50 \, \text{kN/m}^2 \text{ and } 100 \, \text{kN/m}^2}. \]