Sources of variability in small-scale soil-geosynthetic interaction testing
Lateral restraint is the primary mechanism associated with geosynthetic-stabilized road bases. Under traffic loading, the unbound aggregates tend to displace laterally unless they are restrained by the subgrade or by geosynthetic reinforcement. The stabilization of road bases corresponds to small displacement conditions as the end goal is to minimize excessive distress. Thus, the quantification of a small-strain stiffness is fundamental to design structures under serviceability criteria. The soil-geosynthetic composite model (SGC) was developed at the University of Texas at Austin to provide a single parameter that characterizes the soil-geosynthetic composite stiffness (K [subscript SGC]) under small displacements. In this study, the variability sources involved in this experimental characterization were evaluated to quantify their magnitude, to assess their impact on the determination of K [subscript SGC], and to identify strategies to continue to improve the repeatability of test results. The sources of variability were classified into three groups: (1) measuring equipment, (2) testing procedures, and (3) inherent material variability. Modifications in the load measuring equipment and test-specific corrections for the displacement measurements are proposed. The influence of the density/compaction practices on the K [subscript SGC] was also evaluated, and an improved procedure is suggested. Drilled and tubed geogrid-displacement measuring sensors connections are proposed to replace the current steel wire attachments, after confirming that drilling through the geogrid junctions does not alter the product's tensile performance. The variability in the tensile stiffness, J, of geogrid longitudinal ribs, as well as flexural rigidity E · I , of geogrid transverse ribs were evaluated in order to quantify the inherent material variability. A strong correlation was identified between the K [subscript SGC] and J, confirming the adequacy of the SGC model assumptions. In terms of the flexural rigidity, the rib's moment of inertia was identified as a relevant parameter affecting the section's rigidity to flexural loads.