In this study, the effect of using geocell as an innovative and effective method for improving loose soils and enhancing the bearing capacity of shallow foundations was investigated. Given the weak geotechnical conditions in Ahvaz and the need to replace costly methods such as pile driving, the objective of the research was to evaluate the performance of geocell and determine its optimal dimensions.Three-dimensional numerical modeling was conducted using PLAXIS 3D software on a concrete foundation with a width of 10 meters and a thickness of 0.8 meters. In this model, the Mohr–Coulomb behavioral model was used for the soil, and geogrid elements with interface properties were applied to simulate the geocell.The analyses were performed in three parametric stages, including variations in installation depth (u/B), layer height (h), and layer width (b/B). The results showed that the use of geocell significantly increased the bearing capacity and noticeably reduced settlement. The best performance was achieved when the geocell was placed at a depth of 0.05B below the foundation base. Increasing the height up to 20 cm and the width up to 1.5B also improved the load–settlement behavior, but further increases were not economically justified.Comparison between the optimized model and the unreinforced model revealed that the bearing capacity more than doubled, and settlement under operational loads was significantly reduced. Ultimately, this research confirms the importance of precise design and the use of geocell as an effective, sustainable, and economical solution in civil engineering projects in regions with weak soils, such as Ahvaz.