Comparison Between Monotonic, Cyclic and Post-Cyclic Pullout Behavior of a PET Geogrid Embedded in Clean Sand and Clayey Sand

A series of monotonic and multistage pullout tests were performed using a large pullout apparatus to study the monotonic, cyclic and post-cyclic pullout behavior of a uniaxial woven geogrid under different conditions. The monotonic and multistage pullout tests were performed for clean sand and sand containing 10% and 20% clay. The effect of vertical effective stress on the pullout resistance and deformation along the geogrid was investigated using monotonic testing. In the multistage pullout test, the influence of vertical effective stress, cyclic load amplitude and the frequency and the number of tensile load cycles on the post-cyclic pullout resistance and deformation during the cyclic stage was studied. The monotonic test results indicated that an increase in clay content increased the pullout resistance at the lower effective vertical stress (20 kPa), while at higher vertical stresses (40 and 60 kPa), this effect was insignificant. Moreover, when a geogrid was embedded in clean sand and 20% clayey sand, the post-cyclic peak pullout resistance was slightly lower than the values attained in monotonic tests at a vertical effective stress of 20 kPa. The reductions varied from 3.5 to 8% for clean sand and 5.5 to 7% for 20% clayey sand. An increase in the cyclic load amplitude had no effect on the post-cyclic resistance of the geogrid-embedded in clean sand, but post-cyclic resistance of geogrid embedded in 20% clayey sand decreases with increasing cyclic load amplitude.