Foundation Impedance Functions: Theory Versus Experiment

Forced-haimonic-vibration tests, using an eccentric-mass shaker, were conducted on two small but different concrete foundations. One foundation (Cholame 1E), located in central California, consisted of a 4-in.-(10-cm-) thick, 50-in.- (1.27-m-) square slab with corner piers embedded in moderately stiff alluvial deposits. The other foundation (Station 6), a 6-in.- (15-cm-) thick, 48‐in.‐×45‐in.‐(1.22‐m‐×1.14‐m‐) rectangular slab, rested directly on softer deposits in the Imperial Valley of southern California. Experimental foundation-impedance functions, computed from the vibration-response data, were similar to theoretical predictions for Station 6; however, significant differences were observed between the experimental and theoretical impedance functions for Cholame 1E. These differences probably resulted from overestimation of the shear-wave velocities of the top layers of soil directly underneath the Cholame IE foundation, and to a lesser extent from the use of a simple embedded disk to model the foundation geometry.