7.9 A 3 m thick clay layer (cu = 60 kN/m² and y = 19.0 kN/m³) is underlain by a weaker clay (c, = 30 kN/m² and y = 18.0 kN/m³) to a large depth. A 2.0 m wide square foundation is placed at 1.5 m depth below the ground level. Determine the maximum column load that can be allowed on the foundation with FS = 3.