To study the failure mechanisms of subgrades and pipelines under load action, a three-dimensional finite element model of a geogrid-reinforced subgrade with underground pipelines was developed and validated. The effect of soil-geogrid interlocking on the geogrid-reinforced soil structure was considered, and the geometric thickness and aperture of the geogrids were accurately modeled. This aimed to simulate the load transfer mechanism of particle interlocking within the geogrid mesh. The effects of three types of geogrid burial depths, geogrid layers, and different loading areas on the underground pipelines was analyzed. The results show that geogrid reinforcement effectively reduces the settlement of pipelines and foundations. As the burial depth of the geogrid increases, the overall settlement of pipelines and foundations shows a decreasing trend, with the minimum settlement occurring when the ratio of the geogrid burial depth to foundation width is 0.3. Increasing the number of reinforcement layers significantly reduces the settlement of buried pipelines and foundations, although the reduction rate decreases with more layers. Comparing cases of load applied vertically and parallel to the pipelines, the maximum circumferential strain around the pipelines remains consistent, but the strain at the bottom of the pipelines significantly decreases. Additionally, the high-stress area within the subgrade moves towards the direction of loading. The inclusion of a geogrid layer helps to form a rigid layer in the reinforced subgrade, redistributing the stress transferred through this layer, dispersing the soil stress distribution, and reducing stress concentration.