A comprehensive laboratory research program to investigate geogrid reinforcement of granular base layers of flexible pavements was carried out at the University of Waterloo and involved repeated load tests on varying thicknesses of reinforced and unreinforced granular bases. Other controlled variables included reinforcement location and subgrade strength. The purpose of this paper is to explain geogrid reinforcement mechanisms in granular base applications through analysis of stress, strain, and deflection measurements. The results of that research are first compared with fabric reinforcement and failure criteria. For high-deformation systems both fabric and grid can be effective in tension membrane action, but for low-deformation systems the interlock and confining action of a grid is required to provide effective reinforcement. The waterloo work showed that permanent deformation of both types of systems can be significantly reduced by using geogrid reinforcement in the granular base. The reinforcement mechanisms involved with geogrid reinforcement of granular bases, and how the stress-strain-deflection response of the structure varies, are discussed. It is concluded that, for optimum effect, geogrid reinforcement should be placed at the base-subgrade interface of thin base sections and near the midpoint of thicker bases. Moreover, the zone of such placement should not involve elastic tensile strains in the grid that are greater than 0.2 Percent. Under these conditions, geogrid reinforcement can be highly effective in reinforcing the granular base material and thereby extend the life of a structure.
Abstract