The Confinement Effect of Different Geogrids—3: The Development of an Index Test for the Omniaxial Testing of the Tensile Properties of Geogrids

Wheel loading is point loading that generates omni-directional horizontal stresses within the engineering fill below the surface and at the interface of this fill with the natural ground. Where the fill is reinforced by geogrids these horizontal stresses are resisted by omni-directional confinement forces in the geogrids. Whilst all geogrids were square-patterned information relevant to these confinement forces could be derived from tensile testing in the two principal directions of the geogrid. However, this does not apply to newer geogrids with triangular apertures. In fact, any uni-directional tensile testing of these products has no relationship to the confinement loads they can generate. Therefore a new test is required to give information on the ability of different geogrids to generate omni-directional confinement loads, such as that introduced at the 9^th International Conference on Geosynthetics in Brazil in May 2010. The test is a modified form of the geomembrane test covered by DIN 61551 in which a circular sample is inflated by water pressure. Since then this test has been applied to a range of different biaxial geogrids of both square and triangular format. Both square and triangular apertures, and both integral and assembled geogrid types have been tested. The results of this testing are reported in this paper and the differences in performance of the different types tested are discussed.