Study on Pullout Behavior of Uniaxial HDPE Geogrids Under Monotonic and Cyclic Loads

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