This paper investigates the structural behavior and soil–structure interaction mechanism of a three-sided culvert (TSC) at service and ultimate load levels. Field measurements were used to verify a two-dimensional (2D) finite-element model (FEM) and evaluate the backfill height at which the TSC would fail. In addition, experimental data available in the literature of an arched TSC segment loaded to failure was adopted to verify a three-dimensional (3D) FEM for the analysis at the ultimate limit state (ULS). The results demonstrated that the Canadian Highway Bridge Design Code overestimates the earth pressures on the top slab. It was also found that the connection at the sidewall base does not behave as a perfect hinge. Finally, the nonlinearity of the reinforced concrete (RC) was evaluated throughout the loading spectrum and it was concluded that simplifying the behavior of RC using a linear-elastic model is only adequate at the service load levels.