Question

Calculate the maximum exit gradient for soil with a specific gravity of 2.5 and porosity of 0.35 to prevent piping failure.

• A. 0.92
• B. 1.15
• C. 0.75
• D. 1.50

Hint:

Remember: $i_c = \frac{G-1}{1+e}$ (use void ratio, not porosity directly).

Answer 1

The Correct Option is B

Solution: Step 1: Concept
Piping failure occurs when the upward seepage force becomes equal to the submerged weight of soil particles. The limiting condition is defined by the critical hydraulic gradient. Step 2: Formula
The formula for critical hydraulic gradient is: \[ i_c = (G - 1)(1 - n) \] where:
\(G\) = Specific gravity of soil solids
\(n\) = Porosity Step 3: Given Data
Specific gravity, \(G = 2.5\)
Porosity, \(n = 0.35\) Step 4: Calculation
Substitute the values in the formula: \[ i_c = (2.5 - 1)(1 - 0.35) \] \[ i_c = 1.5 \times 0.65 \] \[ i_c = 0.975 \] Step 5: Final Answer
The calculated critical hydraulic gradient is \(0.975\).
The closest value among the given options is: \[ \boxed{0.92} \] Therefore, the correct answer is (A) 0.92.