Dilatant stresses at the interface of granular fills and geogrid strip reinforcements

Design guidelines for geosynthetic-reinforced soil walls recommend the use of densely compacted granular soils as select fills. The prevailing construction practices employ two reinforcement layouts. In one, geosynthetics are laid out continuously throughout the length of reinforced area ( sheet reinforcement): this layout is usually associated with wrap-around and modular block-type facing units. In the other, geosynthetics are laid out discretely ( strip reinforcement): this is usually associated with panel-type facing units. These two reinforcement layouts interact differently with densely compacted granular fills, which are inherently dilatant. Sheet reinforcement corresponds to a free dilatancy condition whereas strip reinforcement corresponds to a restrained dilatancy condition. The effect of restrained dilatancy results in an increase in normal stresses or mobilization of dilatant stresses at the soil - reinforcement interface during reinforcement pullout and in turn generates additional localized compressive stresses in the surrounding granular fill. This has a generally positive influence because it enhances the pullout resistance of the reinforcement and also raises the effective stresses, resulting in an increase in the shear strength of the granular fill and thus improving the internal stability of reinforced soil walls. This paper presents an extension to earlier work by Alfaro et al. on the pullout interaction mechanisms of geogrid strip reinforcements. It examines the mobilization of dilatant stresses at the soil - reinforcement interface during reinforcement pullout. The study shows that it is essential to take into account the influence of dilatant stresses in the internal stability analysis of reinforced soil walls that use geogrid strip reinforcements.