A sample saturated cohesion less soil tested in a drained

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A sample saturated cohesion less soil tested in a drained triaxial compression test showed an angle of internal friction of 30°. The deviatoric stress at failure for the sample at a confining pressure of 200 kPa is equal to

1. 2000 kPa
2. 400 kPa
3. 600 Kpa
4. 800 kPa

Correct Option: B

σ₁ = σ₃ tan² α + 2c tan α.

α = 45 +	Φ
	2

= 45 +	30	= 60°
	2

c = 0 (cohesionless soil)
∴ σ₁ = σ₃ tan² 60°
Confining pressure/ cell pressure = σ₃ = 200
∴ σ₁ = 200 × 3 = 600 kPa
Deviate stress = σ₁ – σ₃ = 600 – 200 = 400 kPa