Parking Garage Supported on Structural Fill

The site of the 10‐story parking garage contained soft to medium consistency residual silty clays overlying carbonate rock formations. This rock contains numerous solution cavities and fracture zones with angles of dip varying from 30°–75°. The rock surface is extremely variable. Surficial soils were incapable of supporting structural loads and deep foundations including drilled caissons and steel H‐piles were evaluated for support of the structure. The potential for extra costs with caissons and H‐piles due to unpredictable bearing grades indicated these solutions to be unacceptable. Excavation of the residual soils to the surface of rock or minimum required depths for settlement considerations, and replacement with compact structural fill was recommended for building support utilizing shallow spread foundations. An allowable bearing pressure of 8 ksf $(400\mathrm{kN}/m^2)$ was utilized for design. This method provided an economical foundation solution and minimal extra costs to the owner.