In this paper, influence of different types of soils and geosynthetics on soil/geosynthetics interface behaviouris investigated by direct shear and pullout tests. Three different types of cohesionless soils and three different types of geosynthetics materials are adopted for experimental investigation. A series of large direct shear tests and pullout tests were conducted to investigate the interface behaviour of soil/geosynthetics. The test equipment, soils, and geosynthetics properties are described. The influence of soil particle size (D 50 ) and geosynthetic structure are discussed by analysing tests results. Results are presented and discussed in terms of peak shear resistance, peak pullout resistance, interface friction angle, efficiency factors and interaction coefficient for different soils and geosynthetics. It could be seen that the interface friction angle from both direct shear and pullout tests linearly increases with increase in (D 50 ) of soil. The pullout interaction coefficients (C i ) are found to be in the range of 0.62-1.72 for different tests conditions.

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The paper investigates the behaviour of groups of horizontal square anchor plates in geogrid-reinforced sand using laboratory model tests. The optimum spacing for two anchor plates in unreinforced sand is 3.4 times the anchor width. The unreinforced groups of anchor plates show a clear failure at a displacement of about 5% of the anchor width, whereas this value increases to more than 45% for reinforced groups along with a two-fold increase in uplift capacity. The optimum width and length of the geogrid reinforcement for groups of two anchors is found to be 5 and 9.4 times the width of the anchor plate, respectively. The performance improvement for isolated anchor plates is found to be maximum and gradually reduces with an increase in the number of plates; however, this reduction is much less in groups of two to four. Therefore, the results obtained from the model tests for reinforced groups of two to four anchor plates can be conveniently used to extrapolate the uplift capacity of multiple anchor plate systems in a reinforced soil mass. The model test results show a reasonably good agreement with the three-dimensional (3D) numerical analysis results.