Question

The flow net around a sheet pile wall is shown in the sketch. The properties of the soil are : permeability coefficient = 0.09 m/day (isotropic), specific gravity = 2.70 and void ratio = 0.85. The sheet pile wall and the bottom of the soil are impermeable.

The factor of safety against the occurrence of piping failure is

• A. 3.55
• B. 2.93
• C. 2.60
• D. 0.39

Answer 1

The correct option is C 2.60

Critical hydraulic gradient,

$i_{cr}=\frac{G-1}{1+e}=\frac{2.7-1}{1+0.85}=\frac{34}{37}$

Hydraulic gradient at downstream,

$i=\frac{\left(H/N_d\right)}{\Delta l}=\frac{\left(8.5/8\right)}{3}$

$=\frac{17}{48}$

Factor of safety against piping ;

$=\frac{i_{cr}}{i}=\frac{\left(34/37\right)}{\left(17/48\right)}$

$=2.594$

$\simeq 2.60$