The strength of a soil is usually identified by:
Try it first: pick an option, then read the explanation.
Correct answer: C. Ultimate shear stress
Asked in SSC JE 2015
Detailed Explanation
As in Q283, soils fail by shearing along surfaces. Their strength is therefore quoted as the maximum shear stress they can carry before failure.
Why “Ultimate shear stress” Is Correct
The ultimate shear stress on the failure plane, τf = c + σ tan φ, is the soil's shear strength. That is how soil strength is identified.
Why the Other Options Are Wrong
- A. Direct tensile stress: Soils have negligible tensile strength.
- B. Direct compressive stress: Compressive strength is used only as an index for clays (qu).
- D. Effective stress: Effective stress controls strength, but it is not itself the strength.
Key Point
Strength of soil = ultimate shear stress, τf.
Key Concepts for Students
- Peak strength vs residual strength after large displacement.
- Undrained strength cu for clays in the short term.
- Effective-stress parameters for long-term design.
Practice more: this is question 41 in Shear Strength of Soils MCQs – Part 3. Try the whole set and check every answer instantly.