Geogrid Reinforcement of Road Base Aggregate — Measuring the Confinement Benefit

Geogrids are used in flexible pavement construction to reinforce the aggregate base course, usually to stabilize the aggregate over soft subgrade soils. Many researchers, using various large-scale tests, have studied the benefits of base reinforcement geogrids. The wide range of reported findings is likely due to the differences between test procedures and the relatively high cost and extended time required to run the tests, discouraging the study of the various parameters involved. Thus, a relevant, standardized smaller-scale test to quantify base reinforcement is needed. One property—confinement of the base aggregate—is generally recognized to be of primary importance in achieving base reinforcement. A small-scale test has recently been developed that is able to quantify the effects of confinement offered by a geogrid, using out-of-plane loading to create multiaxial stress conditions relevant to base reinforcement. This paper reviews the development of the confinement test, comments on the results as compared to large-scale performance tests, and suggests how the results of confinement testing may be incorporated into design procedures.