In-plane elastic properties of geosynthetics from in-air biaxial tension tests

Geosynthetics experience load simultaneously in each principal material direction in applications such as retaining walls, constructed slopes, roadways, and reinforced granular load transfer platforms. Biaxial loading results in a stiffer load-strain response compared to that observed in uniaxial loading. Load-strain properties of geosynthetics determined from wide-width uniaxial tension tests are unable to account for this effect and are generally regarded as an index test. This paper presents the development of a biaxial testing procedure to provide load-strain response data necessary to determine in-plane linear elastic tensile properties of geosynthetics. These properties consist of two elastic moduli, two dependent in-plane Poisson's ratios and an in-plane shear modulus. The elastic moduli and Poisson's ratios are derived from non-bias biaxial tests where load is applied in the two principal directions of the material. The in-plane shear modulus is determined from biaxial tests on specimens where load is applied on a bias such that the principal material directions are oriented at a 45-degree angle to the test machine directions. The tests are performed on geosynthetics that have been load conditioned such that the subsequent load-strain response is considered to be a resilient response pertinent to repetitive load applications such as geosynthetic reinforced pavements.