Unconfined Versus Confined Testing of Geosynthetics

A theoretical explanation of the confined in-soil behaviour of geosynthetics is presented and compared to standard unconfined load-extension and creep test results. First, it is shown that confined, load-instantaneous geosynthetic extension problems can be successfully described by a pull-out model of a single geosynthetic reinforcement strip in soil. The confined in-soil stiffness of a geosynthetic is derived analytically as a function of the unconfined stiffness and the stiffness of the soil-geosynthetic strip interface. Second, the problem of confined in-soil creep is analysed on the basis of a similar model that takes into account the rheological properties of geosynthetics. Generally, it is shown that the confined in-soil behaviour of geosynthetics can be predicted on the basis of the unconfined properties of geosynthetics and the soil-geosynthetic strip interface stiffness. Practical examples show good agreement between the proposed models and the experimental data.