Angle of Internal Friction for Cohesive Soil Multiple Choice Question
(A) Zero
(B) 30°
(C) 15°
(D) 45°
Explanation
Cohesive soils, such as clay, derive their shear strength primarily from cohesion rather than frictional resistance between particles. In the Mohr-Coulomb failure criterion, the shear strength (τ) of soil is expressed as:
τ = c + σ tan(ϕ)
Where:
- c = cohesion
- σ = normal stress
- ϕ = angle of internal friction
For purely cohesive soils, the angle of internal friction (ϕ) is assumed to be zero, meaning the shear strength depends entirely on cohesion.
Key Notes
- In purely cohesive soils like clay, the angle of internal friction is theoretically zero, as their strength comes from cohesion rather than particle friction.
- In real-world scenarios, natural clays may exhibit a small ϕ (e.g., 5°–15°) due to minor granular interactions, but for design simplification, ϕ = 0° is often assumed.
- The Mohr-Coulomb criterion is widely used in geotechnical engineering to analyze soil shear strength and stability.
- Understanding the properties of cohesive soils is critical for designing foundations, retaining walls, and other structures in civil engineering.
Note: The assumption of a zero angle of internal friction for cohesive soils simplifies design calculations and ensures safe structural analysis in geotechnical applications.
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