DYNAMIC STIFFNESS OF FOUNDATIONS ON FLUID-FILLED POROELASTIC STRATUM

The finite-element technique presented in the companion paper is applied to the calculation of the static and dynamic stiffnesses of rigid strip and circular foundations on a fluid-filled poroelastic stratum. A simplified approximate method is also proposed for the estimation of the dynamic stiffnesses. In this approximation, the two-phase medium is replaced by a single-phase solid. The shear-wave velocity of the equivalent solid is set equal to that of the solid skeleton. In the case of vertical excitation, the pressure-wave velocity is taken equal to the velocity of the slow dilatational wave of the mixture, while the average of the velocities of the fast and slow dilatational waves of the mixture is used in the cases of horizontal excitation and rocking. Stiffness and damping coefficients are computed and compared with those obtained by the approximate method. The effects of seepage forces on the dynamic stiffnesses are examined.