In order to describe the variation of vertical earth pressure against culverts for different types of unsaturated soils under steady infiltration, the earth pressure coefficient at a sliding surface considering soil arching effect was derived by assuming the minor principal stress trajectory and Mohr stress circle. Based on the effective stress strength equation of unsaturated soils, the suction stress theory, and the vertical force equilibrium of a horizontal thin layer element, this study then respectively presented iterative solutions of vertical earth pressure against positive-buried/trench-buried culverts in unsaturated soils under steady infiltration along with providing application steps. Comparative validations and method extensions were also performed. Finally, simplified practical formulations of vertical earth pressure were introduced according to distribution laws of suction stress with depth. The results show that iterative solutions of vertical earth pressure against culverts can reasonably address comprehensive influences of soil type, water evaporation, rainfall infiltration, and soil arching effect. Moreover, these iterative solutions and their applicability to culverts in unsaturated soils are verified by comparing with the data of field measurements and theoretical calculations reported in the literature. Practical formulations of vertical earth pressure against culverts can be expressed explicitly with high accuracy, and they are readily to be adopted to estimate primary culvert loads under different steady infiltrations. Vertical earth pressure against culverts in sands could be determined as saturated soils due to ignoring the effect of unsaturated characteristics. The suction stress can be simplified as a linear profile with depth for culverts in silts and clays. The negative soil arching effect of a positive-buried culvert increases the vertical earth pressure, whereas the positive soil arching effect of a trench-buried culvert reduces the vertical earth pressure.