This thesis presents an investigation of the effects of water saturation on the effective excitation and system response during building-foundation-soil interaction, using a simple theoretical model. The model consists of a shear wall supported by a rigid circular foundation embedded in a homogenous and isotropic poroelastic half-space. The half-space is fully saturated by a compressible and viscous fluid, and is excited by in-plane wave motion, consisting of plane P and SV waves, or of surface Rayleigh waves. Partial saturation is also considered but in a simplified way. The motion in the soil is described by Biot's theory of wave propagation in fluid saturated porous media. According to this theory, two P-waves (one fast and the other one slow) and one S-wave exist in the medium, which are represent by wave potentials. Helmholtz decomposition and wave function expansion are used to represent the motion in the soil, and a closed form solution of the problem is derived in the frequency domain. Numerical results are presented for the free-field motion, foundation input motion, complex foundation stiffness matrix, and the foundation and building response to incident plane fast P and SV waves, as function of the many model parameters. The presented analysis, which is linear, is of interest for understanding and interpreting the effects of water saturation on the response of the ground and structures to small amplitude (e.g. ambient noise) and to some degree earthquake excitation. An attempt is presented to use this model to explain the observed variation of the apparent frequencies of vibration of Millikan library in Pasadena, California, with heavy rainfall.