Large-scale laboratory equipment was developed to assess interaction between soil and 3-D honeycomb shaped geocell reinforcement under normal and interface shear stress. An understanding of this interaction is vital in assessing mechanical behavior of geocell-reinforced soil mass. Specifically, the equipment allows evaluation of the load transfer mechanism with the measurements of strains, displacements and loads, including friction and passive resistance on the side surfaces and inside the cells of geocell reinforcement. Additionally, the device visually presents sequence of movement response of each reinforcing cell in the direction of the pulling force, thereby showing the contribution of each cell to the total capacity. Overall, it is concluded that the pullout capacity of geocell reinforcement in cohesionless soils is limited to the seam peel strength at junctions of longitudinal and transverse of geocell strips, which creates the cells in layout of geocell reinforcement. Finally, a theoretical approach was established to predict the pullout capacity of geocell-reinforced soil mass.