A soil with a cohesion of 25 kPa has a normal stress of 39 kPa and a shear stress of 56 kPa at the point of failure. The angle of internal friction for the soil is most nearly:.

39⁰

Explanation:

We have cohesion c = 25kpa

Then the normal stress = 39kpa

Shear stress = 56kpa

This question is asking us to find the angle of internal friction

Shear stress at the time of failure = cohesion C + normal stresstanΦ

56 = 25 + 39tanΦ

Φ = angle if refractive index

Φ = 38.48⁰

This is approximately 39⁰

Therefore in answer to this question, the angle of internal friction for the soil is nearly 39⁰

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