A 30-m-long closed-end steel pipe pile group is driven into layered
undrained clay. The pile cap is square, and the nine piles are evenly
spaced. The layout of the pile group is shown in Figure 4.25. The topsoil
layer has a unit weight of 18 kN/m³, undrained cohesion of 100 kN∕m²,
and a thickness of 10 m. The second layer has unit weight of 19 kN∕m³,
undrained cohesion of 150 kN∕m², and it extends to great depth. The
groundwater table is at the ground surface. Determine the ultimate
bearing capacity and pile group efficiency of the pile group.