عنوان مقاله [English]
Geosynthetics are mainly used to stabilize and reinforce various types of earth structures such as slopes, retaining walls, bridge abutments and foundations. In these cases, the interaction between soil and geosynthetic plays a determinant role. In order to investigate the factors affecting the static, cyclic and post-cyclic pullout behavior of a type of geogrid produced in Iran under the brand name of GPGRID80/30 embedded in uniform sand, an experimental study was carried out using a large scale pullout apparatus. In order to study the monotonic and post-cyclic pullout behavior of geogrid under different conditions, a series of monotonic pullout tests and multistage pullout tests were performed. The effect of vertical effective stress on pullout resistance, the maximum apparent friction coefficient of the surface of the geogrid and soil and deformation along the geogrid was investigated using monotonic tests. In the multistage pullout test, the influence of vertical effective stress, cyclic load amplitude, frequency and number of tensile load cycle on the post-cyclic pullout resistance was studied. The results indicate that with increasing of vertical effective stress the pullout resistance of the geogrid increases and the maximum apparent coefficient of friction decreases. Comparison of the results of the multistage pullout tests with the results of the constant rate pullout tests at the vertical stress of 60 kPa showed that the cyclic loading had no significant effect on the post-cyclic pullout strength compared to static pullout strength of embedded geogrid in the sandy soil, but at vertical effective stresses of 20 and 40kPa, reduction of maximum post-cyclic pullout strength in comparison with pullout strength is more evident. Increasing Effective vertical stress and cyclic load amplitude in the second stage of the multi-stage test enhanced the cumulative displacements along the geogrid sample. Comparison between the loading-unloading tensile stiffness at the end of the second stage and the tensile stiffness at the beginning of the second stage exhibits that the cyclic loading increases the tensile stiffness, and finally at the third stage of the experiment multistage test the tensile stiffness decreases as the displacement increases, until it reaches the corresponding value in the constant-rate displacement test.