Abstract
Marston & Spangler's equation is generally used to predict a coefficient of vertical earth pressure. It should be, however, separately applied to the convex type earth pressure and the concave type one. And it needs a settlement ratio not to determine easily from the experience. In this paper simple equation will be proposed to predict a vertical earth pressure ratio on the basis of the simple model that does not concern with the arch action generated around a rigid box culvert. It is proved that this equation can give a similar results with one derived from Marston & Spangler's equation and the measured data. Furthermore, since it is possible to apply to predict the reduction of vertical earth pressure by installing large compressible materials over a box culvert, the relationship between soil type and reduction effect will be estimated by the experience of deformability properties against soil classification.
