study on pullout behavior of uniaxial hdpe geogrids under monotonic and cyclic loads

abstract: this paper presents the results of pullout tests on uniaxial geogrid embedded in silica sand under monotonic and cyclic pullout forces. the new testing device as a recently developed automated pullout test device for soil-geogrid strength and deformation behavior investigation is capable of applying load/displacement controlled monotonic/cyclic forces at different rates/frequencies and wave shapes, through a computer closed-loop system. two grades of extruded hdpe uniaxial geogrids and uniform silica sand are used throughout the experiments. the effects of vertical surcharge, sand relative density, extensibility of reinforcement and cyclic pullout loads are investigated on the pullout resistance, nodal displacement distributions, post-cyclic pullout resistance and cyclic accumulated displacement of the geogrid. tell-tale type transducers are implemented along the geogrid at several points to measure the relative displacements along the geogrid embedded length. in monotonic tests, decrease in relative displacement between soil and geogrid by increase of vertical stress and sand relative density are the main conclusions structural stiffness of geogrid has a direct effect on pullout resistance in different surcharges. in cyclic tests it is observed that the variation of post-cyclic strength ranges from minus 10% to plus 20% of monotonic strength values and cyclic accumulated displacements are increased as normal pressure increase, but no practical specific comment can be made at this stage on the post-cyclic strength of geogrids embedded in silica sand. it is also observed that in loose sand condition, the cyclic accumulated displacements are considerably smaller as compared to dense sand condition.