Vibration of base isolated machine foundations has been studied using the Scaled
Boundary Finite Element Method (SBFEM) and the cone model method. The
dynamic stiffness of soil supporting rigid massless foundation was determined. This
stiffness is of complex value. The real part represents the reflected energy of the
restoring and inertial forces while the imaginary part represents the energy dissipated
within the endless extent of the soil as a geometric damping. The effect of geometric
and material properties of soil upon the real and imaginary parts of the dynamic
stiffness was determined and represented in terms of dimensionless charts for the
frequency range of interest. Results have shown that increasing the embedment ratio
has a significant effect on the dynamic stiffness, it increases the dynamic stiffness
considerably. The effect of stiffness ratio(stiffness of isolator/ stiffness of soil) was
demonstrated for isolated machine foundations. The use of soft isolators reduces the
dynamic response of foundation and the soil reaction