Backfill Effects on Circular Foundation Stiffnesses

The dynamic behavior of a structure resting on or embedded in an elastic material is a problem that has been of considerable interest in recent years. The determination of the dynamic soil-structure interaction effects is particularly important in the seismic design of nuclear power plants. The dynamic behavior of these structures has often been adequately described using a lumped parameter model consisting of equivalent mass, stiffness, and damping elements. For cases other then a foundation resting on the surface of an elastic homogeneous half space, numerical procedures, such as the finite element method, are frequently employed to determine these lumped parameters. To the extent that stiffness coefficients may be considered to be independent of frequency, the static had-displacement results of finite element models may be used to determine spring constants for the discrete model. This paper deals with the static load-displacement behavior of circular foundations, embedded in an elastic stratum underlain by a rigid base. Horizontal, rocking and coupled rocking-sliding stiffness are investigated for various backfill conditions.