In this paper numerical program was adopted to investigate the interface effect of shallow strip foundations constructed on homogeneous geogrid reinforced sand. The failure stages in the sand were controlled using the Mohr–Coulomb criterion and a non-associated flow rule. Several parameters including soil type, spacing between interfering footings, and distance between the surface of the earth and first layer of reinforcement are studied. The results indicated that the ultimate bearing capacity of a number of multiple footings in a group becomes always greater than that of a single isolated footing. The best location of interfering footings was determined to achieve the maximum bearing capacity for closely spaced strip footings. The best clear spacing between footings was 0.75 and 1 times the footing width that leads to maximum bearing capacity for closely spaced strip footings in reinforced and unreinforced sand, respectively. The effectiveness of the reinforcement in increasing the bearing capacity of the closely spaced strip footings is achieved when the geogrid layer was placed at a distance 0.5-0.75 times the footing width from the ground surface. Some significant observations on the performance of footinggeogrid systems with change of the parametric values are also studied and presented in this paper.