The tensile strength and stiffness of a geogrid are the most common variables a designer considers when selecting a product for stabilisation or reinforcement.  While adequate load-transfer from the soil to the geogrid is required for sufficient performance, little guidance is available to select the correct geogrid aperture size based on the soil particle size distribution.  Available guidance often relates the geogrid aperture size to some multiple of the D50 of the soil.  In a uniform soil, the D50 may be an adequate index to characterize the interaction between the geogrid and the soil.  However, this is likely not the case for poorly graded materials.  For example, the required aperture size for a gap-graded soil with 40% gravel and 60% silt based on D50 related guidelines would result in a geogrid with comparatively small aperture size that is not effective for interlocking of the gravel particles.

Reinforced triaxial specimens using geogrids embedded in “transparent” soil will be done as part of this study to investigate the effect of particle size distribution on the soil-geogrid interaction.  Only a single geogrid aperture size will be considered.  The tests will be conducted on specimens prepared with well graded, uniform and gap-graded soils, all with the same D50.  This will allow for the evaluation of the effect of particle size distribution in terms of the impact on peak shear strength of the reinforced soil mass as well as on the observed load-displacement curves.  Digital image correlation will be used to monitor the mechanisms of interaction between the geogrid and grains to determine the governing particle size.

It is hypothesized that the results of the testing program will indicate that the particle size distribution of the fill soil has a considerable effect on the soil-geogrid interaction.  In particular, it is hypothesized that the particle size distribution will affect not only the peak shear strength but also the magnitude of the residual shear strength of the geogrid-reinforced specimens. More importantly, the particle size distribution will affect the thickness of the developed shear band and, consequently, the mode of failure of the tested specimens.