A 360-page scholarly monograph that contains a basic yet comprehensive presentation of using the lightweight-fill and compressible-inclusion functions of geofoam to reduce lateral pressures on all types of earth-retaining structures under both gravity and seismic loading. An introduction to using geofoam to reduce vertical earth forces on underground conduits as well as beneath structural slabs constructed on expansive soil and rock is also included. This document reflects Dr. Horvath's more than 30 years of research into this topic, and contains never-before-published material. This document is intended to be of use to both design professionals in practice as well as academic instructors and researchers.