Factors affecting the pullout behaviour of extruded geogrids embedded in compacted granular soil

In order to study the factors affecting the behaviour of reinforcement geogrids embedded in granular compacted soils, a large scale pullout test apparatus has been designed. More than 40 pullout tests have been performed, at constant displacement rate, on three different HDPE extruded geogrids embedded in a compacted granular soil by varying the specimen lengths and the applied vertical effective pressures. The different geogrids used in the research have been tested using unconfined tensile tests performed at different speeds, and, in particular, at the same speed of the pullout tests; granular soil have been characterized through classification, Proctor and shear tests. The pullout test results showed the influence of the different parameters studied on pullout behaviour. Moreover, on the basis of the test results it was possible to evaluate the peak and the residual pullout resistance and the apparent coefficient of friction mobilized in the same conditions.