Considering the high seismicity of Iran, the study of seismic force's effects on the foundations' bearing capacity is always of interest to researchers. The current study investigated the bearing capacity of a shallow foundation reinforced with geogrid using the limit analysis method in static and seismic modes. The Optum G2 software is used for this purpose. An attempt has been made to calculate the static and seismic bearing capacity of the foundation by conducting a parametric study on the geogrid length (1B, 2B, 3B, 4B, and 5B), geogrid burial depth (0.1B, 0.2B, 0.5B, 0.7B, 0.9B, 1.1B, and 1.8B), geogrid layers distance (0.1B, 0.2B, 0.4B, 0.6B, and 0.8B) and the number of geogrid layers (1, 2, 3 and 4). Also, these analyses were performed on different internal friction angles of sandy soil (25, 30, 35, and 40 degrees) and various foundation depths (0, 0.3B, and 0.5B). The results show that the effective length of geogrid is estimated to be between 2B and 3B. Also, the geogrid's maximum effective depth is between 0.7B and 1.1B. The optimal distance of geogrid layers was estimated between 0.2B and 0.6B. Also, the optimal number of geogrid layers varies from 2 to 4, depending on the soil's internal friction angle and the foundation's burial depth. The seismic bearing capacity of the foundation estimated to be less than the static condition, and the percentage decrease of the seismic bearing capacity of the foundation compared to the static mode was varied between 7% and 20%.
