Question

For medium silt whose average grain size is 0.16 mm, Lacey’s silt factor is likely to be

• A. 0.30
• B. 0.45
• C. 0.70
• D. 1.32

Hint:

Lacey's silt factor is directly dependent on the square root of the mean particle size (in mm). This is a key parameter in canal design in alluvial soils.

Answer 1

The Correct Option is C

Lacey’s silt factor \( f \) is given by the empirical formula: \[ f = 1.76 \sqrt{d} \] where \( d \) is the average grain size in mm. Given: \[ d = 0.16\ \text{mm} \] \[ f = 1.76 \sqrt{0.16} = 1.76 \times 0.4 = 0.704 \] So, Lacey’s silt factor \( f \approx 0.70 \).