A group of nine piles in a  square pattern is embedded in a soil strata comprising dense sand underlying recently filled clay layer, as shown in the figure. The perimeter of an individual pile is 126 cm. The size of pile group is  The recently filled clay has undrained shear strength of 15 kPa and unit weight of 

The negative frictional load (in kN, up to two decimal places) acting on the pile group is _____________