If the total stress = 100 kPa, hydrostatic pore water pressure = 30 kPa and excess pore water pressure during undrained shearing = 10 kPa, then the effective stress is
- A100 kPa
- B70 kPa
- C60 kPaCorrect
- DNone of these
Solution
Concept
Terzaghi's principle
Formula
σ′ = σ − u
Step-by-step solution
1. u = 30 + 10 = 40 kPa. 2. σ′ = 100 − 40 = 60 kPa.
Explanation
Excess pore pressure adds to the hydrostatic pressure.
Why the other options are wrong
Other values forget one of the pressures.
Shortcut
σ′ = σ − (u₀ + Δu).
Correct answer: C) 60 kPa