A 15-m-long closed-end steel pipe pile group is driven into a homoge-

neous 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 pile group

is subjected to a vertical load of 5200 kN. The soil has a unit weight

of 18.5 kN∕m³, cohesion of 100 kN∕m², friction angle of 10 degrees.

The clay layer is 100 m deep, and beneath the clay layer is dense sand.

The groundwater table is at the ground surface. Preliminary laboratory

testing found that the clay’s void ratio is 0.45, compression index is

0.3, swell index is 0.08, and the clay is overconsolidated. The precon-

solidation pressure is 200 kN∕m². Determine the primary consolidation

settlement of the pile group.