On the pullout resistance of geosynthetics

Abstract

Pullout tests are reported on geosynthetic test specimens embedded in a relatively dense, coarse sand sample. The tests are displacement controlled and are performed at different vertical effective stresses. Tests are reported for a smooth and textured geomembrane and for geogrids of a high and low junction strength. Behaviour is compared with an inextensible, rough sheet. Pullout resistance is governed by progressive tensile strain in the geosynthetic which is a result of relative displacement between it and the soil. Values of interface bond that are described by an interaction factor vary significantly and are stress dependent. Both types of geogrid and the textured geomembrane exhibit a similar response to loading at small displacement, and mobilize a much larger interaction factor than the smooth geomembrane. A rationale is suggested for selection of appropriate values in design. L'on prCsente les rCsultats d'essais d'arrachement sur des specimens gCosynthCtiques enfouis dans un Cchantillon de sable grossier relativement dense. Les essais sont faits ii dCplacement contr616, et sont rCalisCs h diffCrentes contraintes verticales. L'on prCsente les rksultats d'essais sur des gComembranes lisses et texturCes, et pour des gCogrilles h forte et h faible rCsistance aux joints. Le comportement est compare h celui d'une feuille rugueuse inextensible. La risistance h I'arrachement est rCgie par la dCformation progressive en traction dans le spCcimen gCosynthCtique, laquelle rCsulte du dCplacement relatif entre le spCcimen et le sol. Les valeurs des liens 21 l'interface, qui sont dCcrits par un facteur d'interaction, varient de f a~o n significative et dCpendent de la contrainte. Les deux types de gCogrille et la gComembrane texturCe montrent une rCaction similaire ii un chargement h faible deformation et mobilisent un facteur d'interaction beaucoup plus grand que la gComembrane lisse. Une approche est suggCrCe pour choisir des valeurs appropriCes dans le calcul. Mots clCs : essais d'arrachement, gCogrille, gkomembrane, frottement ii l'interface, sol armC. [Traduit par la rCdaction] Can. Geotech.

Bearing force mobilisation in pull-out tests on geogrids

“…Pull-out tests have been commonly employed to address the problem of soil-grid interaction and several works on the pull-out behaviour of geogrids can be found in the literature (Jewell, 1980;Dyer, 1985;Palmeira and Milligan, 1989;Fannin and Raju, 1993;Alfaro et al, 1995;Lopes and Ladeira, 1996;Ochiai et al, 1996;Lopes and Lopes, 1999, for instance). In most of the cases studied the soil material is granular and dense, but the geogrids may present very different geometrical characteristics and mechanical properties, as well as different load-strain-time responses.…”

Load-strain-displacement response of geosynthetics in monotonic and cyclic pullout

“…No significant variation of the maximum pullout resistance (p m ) in a displacement-controlled test has been observed for relatively slow rates of displacement (r d ) less than 6 mm/min (Farrag et al 1993), and in the range 0.25-1 mm/min (Fannin and Raju 1993). Therefore, displacement-controlled tests reported for comparative purposes in this study were performed at r d = 0.5 mm/min (see Fig.…”

“…Confining stress is applied to the top of the soil sample by a stress-controlled boundary comprising a flexible bag filled with water; all other boundaries act as rigid plates. Details of the apparatus are reported by Fannin and Raju (1993).…”

“…Values of interaction factor may be determined experimentally from pullout tests, performed under displacement or load control, to simulate various loading conditions in the field. Displacement-controlled tests are typically performed at a constant rate of displacement (Juran and Chen 1988;Palmeira and Milligan 1989;Berg and Swan 1991;Farrag et al 1993;Fannin and Raju 1993), at rates of displacement between 0.1 and 20 mm/min, with relatively slow rates of about 1 mm/min being preferred. Load-controlled tests are reported for conditions of constant load (Kutara et al 1988;Collin and Berg 1993), a constant rate of loading, cyclic loading (Yasuda et al 1992), or a slow repeated loading (Hanna and Touhamia 1991).…”

“…Displacementcontrolled tests show that pullout resistance is mobilized through progressive strain of the geosynthetic specimen. In testing at relatively low confining stress, failure occurs by a continued displacement of the test specimen in pullout at constant strain (Fannin and Raju 1993), whereas at higher confining stress the failure mechanism involves a pullout that is associated with continued tensile extension of the specimen. The interaction factor, F * α, established for static loading from constant-rate-of-displacement (monotonic) testing is governed by the magnitude of relative displacement at the test specimen -soil sample interface.…”