Evaluation of Hexagonal Multi-Shape, Multi-Axial Geogrids in Unsurfaced Road Applications

Abstract

A full-scale unsurfaced test section was constructed to evaluate the performance of two recently developed innovative geogrids, referred to as NX-1 and NX-2, having a unique combination of hexagonal, trapezoidal, and triangular aperture shapes, rib aspect ratios greater than 1.0, and a coextruded, composite polymer sheet designed to improve aggregate and geogrid interaction. The test section consisted of a 25-cm-thick crushed aggregate surface layer placed over a weak clay subgrade. Simulated truck traffic was applied using a load cart outfitted with a single-axle dual-wheel truck gear. Rutting performance and instrumentation response data gathered from earth pressure cells and single-depth deflectometers were monitored at multiple traffic intervals. It was found that the geogrids improved rutting performance when compared with an unstabilized test item, and NX-1 was found to be the best performer of the two geogrids. Calculated traffic benefit ratios ranged from approximately 1.2 at low levels of rutting up to approximately 13.0 at higher levels of rutting. Instrumentation response data indicated that the geogrids reduced measured pressure and deflection near the surface of the subgrade layer. Pressure response data in the aggregate layer suggested that the geogrids redistributed applied pressure higher in the aggregate layer, effectively changing the measured stress profile with depth.