Abstract: Laying soft materials on the top of high-fill box culverts can greatly reduce the vertical earth pressure on the top of the culvert. However, it also leads to a significant increase in horizontal earth pressure and friction on the sidewall of the box culvert, which is likely to cause new structural diseases. In order to improve the stress state of high-fill box culvert, this paper studied the stress characteristics and load reduction effect of box culvert with laying soft materials on the top slab and sidewalls of the culvert through model test. The variation laws of earth pressure on the culvert top, sidewall, and the foundation contact pressure with the fill height were explored by considering two different soft materials (i.e., Sponge and expanded polystyrene (EPS) board). Moreover, the earth pressure coefficients were obtained by the dimensionless of the earth pressure data, which were compared with the existing representative research results of the culverts with laying soft materials on the culvert structures, and the load reduction effect of laying soft materials both on the top slab and sidewalls was proved. The research results show that laying soft materials on the top slab and sidewalls of the culvert can effectively improve the stress state of the box culvert. The soil arch effects generate on the culvert top and sidewalls, the vertical load on the culvert top is transferred to the outside fill of the culvert. Thus, it not only significantly alleviates the earth pressure concentration on the culvert top slab, but also effectively reduces the horizontal earth pressure on the sidewall and the foundation contact pressure.

Key words: box culvert, load reduction, model test, earth pressure, soil arch effect