Time-Dependent Load-Reduction Performance of High-Fill Box Culverts Equipped with Top and Side EPS layers

Installing Expanded Polystyrene (EPS) on the top slab of high-fill rigid box culverts reduces crown loads but increases horizontal earth pressures on sidewalls, without significantly alleviating foundation contact pressures. While applying EPS to both the top and sidewalls could theoretically optimize load distribution, the long-term stress redistribution within the soil-culvert system remains unclear. A validated engineering-scale numerical model is employed to investigate the mechanical behavior of high-fill box culverts utilizing a dual EPS configuration. Three conditions, i.e., no load reduction (No-EPS), top slab EPS only (Top-EPS), and top and sidewall EPS (Top-and-side EPS), are compared during the construction phase and over a 50-year service period. Results indicate that the Top-and-side EPS configuration induces soil arching both above the crown and adjacent to the sidewalls. Upon construction completion, this approach reduced vertical earth pressure at the crown center, horizontal earth pressure at the sidewall mid-height, and foundation contact pressure by 24.8%, 36.9%, and 14.5%, respectively, compared to the No-EPS baseline. Over the 50-year service period, soil-culvert stress redistribution exhibited three distinct stages: rapid creep, stress adjustment, and long-term stabilization. Although vertical and horizontal earth pressures increased slightly by 7.2% and 5.5% after 50 years, crown pressure remained below the backfill self-weight, and sidewall pressure stayed significantly below the at-rest earth pressure. These findings demonstrate a pronounced, stable long-term load reduction effect, offering valuable insights for optimizing EPS applications in high-fill box culverts.