Comparison between the Interface Interaction of Sand and Clayey Sand with PET Geogrid in Pullout Test Based on Active Length

The large scale pullout test is used to investigate the pullout behavior of the geogrid in the anchorage zone. When pullout force is applied, tensile force gradually transmitted from the front part to end of geogrid. The active length is the part of the geogrid sample on which the activation of interaction mechanism resists against the applied force. In order to investigate more accurately the interaction between soil and geogrid, the geogrid pullout behavior should be evaluated based on the active length. In this study, a series of large scale pullout tests carried out to investigate the distribution of shear stress, pullout interaction coefficient and longitudinal strain of two types of uniaxial PET geogrid with same geometry and different stiffness embedded in two types of sandy soil and sand containing 20% clay based on active length. The results showed that, the pullout force required to move the last transverse bar of geogrid, increased with increasing of vertical effective stress in both type geogrid. Moreover, the active strain of stiffer geogrid embedded in clean sand and clayey was greater than that measured in the more extensible geogrid in both transfer load and pullout stage. At small frontal displacements, increasing the geogrid stiffness decreases the active shear stress in sandy and clayey sand soil. In all pullout tests, the lowest active pullout interaction coefficient occurred at the beginning of the pullout phase.