Use of waste materials can help alleviate problems related to landfilling them and also preserve fast dwindling natural granular materials. Waste foundry sand (WFS) can be a promising candidate as a backfill material in the construction of mechanically stabilised earth (MSE) walls. In the design of such MSE structures, the interaction properties between WFS and geogrid reinforcement are important input parameters. In the present study, interaction properties of a wide range of different polyester (PET) uniaxial geogrids with WFS in two common modes- direct shear and pullout- were evaluated using large-size interface direct shear and pullout tests. In the pullout mode, interaction of geogrid embedded in WFS under axial and transverse pullout were studied. The direct shear interface coefficients of four PET geogrids with WFS were found to be in the range observed in conventional fill materials. Higher axial and transverse pullout resistance factors were observed for geogrids with higher tensile strength and higher opening area ratio. Empirical equations were proposed to estimate the axial and transverse pullout resistances of geogrids at two pullout displacements. Finally, sensitivity analyses were carried out to identify the parameters significantly influencing the axial and transverse pullout resistances of geogrids in WFS. © 2022 ICE Publishing. All rights reserved.