Analytical Modelling of Pull-Out Tests on Geosynthetic Straps

Abstract

2 Terre Armee Internationale, 1 bis, rue du Petit-Clamart - 78140 Velizy-Villacoublay - France ABSTRACT: The reinforcements used in Reinforced Earth structures are most commonly made of ribbed steel strips or of geosynthetic straps. The behaviour of the later is more complex, due to their extensibility. However, the design methods used for the geosynthetic straps are based on a classical friction model. This simple model considers the same design assumptions for the geosynthetic straps as for inextensible reinforcements and does not take into account the strap progressive mobilization. If this is justified for the justification of the structure stability, the detailed behaviour is supposed to be different. To highlight the influence of the synthetic reinforcement extensibility, several pull out tests were carried out on Geostraps developed by Terre Armee Internationale. These tests allow us to monitor the imposed tension as well as the displacements of several points along the strap. Then, back analyses of these results using an analytical model allowed to define the interaction parameters between the soil mass and the synthetic reinforcements. The design methods created for the structures reinforced by metallic reinforcements and thus inextensible were brought to be extrapolated to extensible materials. The difference in behaviour of these two types of reinforcement induces the definition of elongation limits beyond which the behaviour of the structure may be different. In order to adapt and to improve these methods, a better knowledge of the interaction between the soil mass and the reinforcement strips seems necessary. Most of the design methods used for the structures reinforced by geosynthetic straps are developed from the friction models based on the soil/geosynthetic interface friction model (Cambefort type, Fig. 2) and on the tensile-load linear elasticity of the inclusion (resulting from the Hooke's law, Fig. 1). This article presents an analytical method for analysing the pull-out tests on synthetic straps. This method is based on the classic friction laws (Schlosser & Guilloux 1981, Segrestin & Bastick 1996) and permits to reproduce the variation of tensile-load and displacements along the reinforcement strip. Back analysis of the analytical model on the experimental results allows us to validate this analytical development. 2 ANALYTICAL FRICTION MODELS DEVELOPMENT The friction model permits to determine the tensile-load/displacement relationship and the mobilized deformation along a pulled-out reinforcement. The determination