A square shallow foundation is located at depth of 1 m, in stronger sand. A softer sand layer is located at a depth of 3 m measured below the ground surface. H= 5.0 m and K, 4.0. Find B to carry the 4000 kN load using a factor of safety FS = 3. Assume that the bearing capacity of the top layer exceeds the ultimate bearing capacity. Notes: For the top sand layer, unit weight= 14 kN/m'; d' = 30. For the bottom sand layer, unit weight=11 kN/m2; d'= 22.