The present theoretical analyses about high fill culverts structure stress state mainly focus on the earth pressure acting on the top of culverts

but do not consider the effect of the skin friction between the culvert side walls and the adjacent backfill. In this paper

a mechanical model of culvert-soil under load reduction condition was proposed and formulas for calculating the side wall friction and the foundation contact pressure were also deduced. The theoretical method was compared and calibrated with the numerical simulation. Results show that the soil-side wall friction linearly increases with the depth of the culvert side wall and the increase of fill height. The soil-side wall friction under the load reduction condition is greater than that under the non-load reduction condition at a certain fill height. Although the vertical earth pressure on the top of the culvert is reduced due to the load reduction measure

the horizontal earth pressure on the side of the culvert is increased

as a result

the base pressure is not reduced. It is unreasonable to analyze the culvert performance under load reduction condition without considering the effect of the friction acting on the culvert side wall in present theories.