A pit of 6.4 m deep is to be excavated in a fine sand stratum completely saturated up to the ground surface. The saturated unit weight of the sand was obtained as 20.3 kN/m3. To stabilize the bottom of the excavation (prevent boiling), it was decided to drive steel sheet piles to cut as cutoff walls that encircle the excavation. Determine the total length of the sheet pile wall to provide a factor of safety of 1.5 against sand boiling. Assume specific gravity of soil, Gs = 2.7 and unit weight of water,γ w = 9.81 kN/m3.