Abstract: Laying expandable polystyrene (EPS) slabs on the top of high-fill box culverts to reduce earth pressure has been used in engineering practice, but the creep of EPS slabs will cause the earth pressure on the box culvert to change over time. The present design theory of box culverts cannot clearly reflect the long-term load reduction effect of EPS slabs and the long-term stress characteristics of box culverts. In this analysis, model tests were carried out to investigate the short-term stress characteristics of the box culvert with EPS slabs, and a numerical model was validated by the model test results. Then the verified numerical simulation method was used to analyze the stress redistribution of the culvert-soil system and the long-term stress characteristics of the high-fill box culvert. On this basis, the mechanical model of the culvert-soil system was proposed, and the calculation method of long-term earth pressure on the top of the culvert was deduced and compared with the numerical simulation results for verification. The research results showed that the earth pressure on the top of the culvert decreased gradually with time, then increased slightly and finally became stable. Compared with the earth pressure at the completion of filling, the long-term earth pressure decreased by 52.12%. The vertical and horizontal earth pressure on the culvert side increased gradually with time and tended to be stable, and the long-term horizontal earth pressure in the upper range of the culvert side increased by 28.32% compared with that when the filling was completed. The foundation contact pressure also increased slightly at first and then tended to be stable. The increase of horizontal earth pressure caused by the creep of EPS slabs should be considered in the design of sidewalls in practical engineering so as to avoid bending failure of box culver sidewalls in the long-term use.

Key words: expandable polystyrene slab, load reduction, box culvert, long-term stress characteristics, creep, load reduction effect