The paper describes research into the soil-structure interaction between trees and heavy vegetation and at-grade structures including pavements and slab-on-grade foundation systems. Several areas of distressed pavements and slab-on-grade foundation systems in the North texas area have been documented, with estimates and measurement of soil properties, tree geometry and proximity to the structure, tree concentration, relative elevation surveys and distress patterns to confirm the influence pattern of the root system. Conclusions indicate concentrations of trees tend to have the most significant effects with influence pattrerns occuring radially to approximately the tree drip line. Confirmation of the horizontal and vertical influence pattern is provided by geo-electrical moisture material imaging Resistivity (GMMIR) surveys using soil borings to help characterize the influence patterns of trees. The GMMR plots indicate influences between about 1.2 and 3 meters in depth. Root influence model models were constrcted using unsaturated soil mechanics theory and VOLFLO algorithm. Analysis of these models indicates that the influence of tree roots is a function of the soil type and that the influence at the extreme perimeter of the structure is as significant as the penetration of the tree roots significantly beneath the foundation with differential downword movements wet condition (total soil suction pG=4.3(pF=3.3)) to a desiccated tree condition (total soil suction pG=5.6(pF=4.6)) reducing to approximately 5.1. centimeters (2 inches) or less when the tree roots are at lest 0.6 meters (2 feet) from the struc ure perimeter