Question

In a Mohr's diagram, a point above Mohr's envelope indicates

• A. Imaginary condition
• B. Safe condition
• C. Imminent failure condition
• D. Condition of maximum obliquity

Hint:

Remember:
• Below the envelope $\rightarrow$ Safe condition.
• Tangent to the envelope $\rightarrow$ Failure condition.
• Above the envelope $\rightarrow$ Impossible (Imaginary) condition.

Answer 1

The Correct Option is A

Concept: Mohr's failure envelope represents the limiting shear strength of soil. The relationship between the normal stress and shear stress at failure is given by the Mohr-Coulomb criterion \[ \boxed{\tau=c+\sigma\tan\phi} \] where \[ c=\text{Cohesion},\qquad \phi=\text{Angle of internal friction}. \] A Mohr's circle lying below the failure envelope represents a safe condition, touching the envelope represents failure, while a point above the envelope is physically impossible.

Step 1: Interpret the position of the point. A point above the Mohr's failure envelope indicates that the shear stress exceeds the available shear strength. Such a stress state cannot exist in reality.

Step 2: Identify the condition. Hence, a point above the failure envelope represents an \[ \boxed{\text{Imaginary condition}.} \] Therefore, the correct option is \[ \boxed{(A)\;\text{Imaginary condition}.} \]