The piles are 0.5m in diameter and are spaced at 1m center to center in the group. The undrained shear strength at the base level is 180kPa and the average value of undrained shear strength over the depth of pile is 110kPa. $\alpha$= 0:45. Estimate the capacity of pile group considering factor of safety of 2.5. Also find the efficiency of pile group by converse laberre formula.