Experimental and DEM investigation of geogrid–soil interaction under pullout loads

Geogrid–soil interaction is a key issue to describe geogrid reinforcement mechanisms. In order to investigate the geogrid–soil interface behaviour, both experimental and numerical pullout tests have been carried out with modified geogrid samples embedded in granular soil. In the laboratory tests, two different failure modes have been observed depending on the number of geogrid transverse members in this study. Obviously, the maximum pullout resistance increased with increasing number of geogrid transverse members. In the numerical investigations, discrete element software PFC2D has been used. The geogrid–soil interaction under pullout loads has been investigated not only by the qualitative force distributions along the geogrid and in the specimen but also by the quantitative geogrid force, displacement and strain distributions along the geogrid with different numbers of geogrid transverse members. The numerically obtained contributions of transverse members to the total pullout resistance have been used to explain the different failure modes in the laboratory pullout tests. Based on the Fourier Series Approximation (FSA) method, reorientations of contacts and forces in the specimen were presented at different clamp displacements. Moreover, normal stress distributions in the geogrid plane, which is a decisive parameter that can only be evaluated indirectly in the experimental pullout tests, have been obtained directly using the FSA method in the numerical modelling. The experimental and DEM investigation results in this study provide researchers an improved understanding of the geogrid–soil interaction under pullout loads.