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

The factor of safety against piping is the ratio of critical hydraulic gradient (ic) to the exit gradient (ie). ic = (G-1)/(1+e) = (2.7-1)/(1+0.85) = 0.919. The exit gradient ie = delta_h / (nf * l), where delta_h is head loss and l is length of the last flow element. Based on the flow net, calculating the ratio yields approximately 2.60.