What is the shear strength in kPa in terms of effective stress on a plane within a saturated soil mass at a given point where the total normal stress is 295 kPa and the pore water pressure is 120 kPa. (Take effective cohesion = 12 kPa, Effective angle of internal friction = 45°)
- A120
- B175
- C295
- D187Correct
Solution
Concept
Effective stress shear strength
Formula
τ = c′ + σ′ tan φ′
Step-by-step solution
1. σ′ = 295 − 120 = 175 kPa. 2. τ = 12 + 175 tan45° = 12 + 175 = 187 kPa.
Explanation
σ′ = 295 − 120 = 175 kPa.
Why the other options are wrong
175 is the effective stress, not the strength.
Shortcut
τ = c′ + (σ − u) tanφ′.
Common mistake
Forgetting the cohesion.
Correct answer: D) 187