An approximation model to evaluate the limiting soil resistance beneath the cutting curb during sinking of an open caisson is investigated

in which the shape and embedment depth of the cutting curb are considered. And then a typical slip line field for this problem is presented approximately with Prandtl failure mechanism; and the formulas of bearing capacity factors are derived for the plane strain problem and axisymmetric one of a circular open caisson

respectively. For the plane strain problem

the bearing capacity factor Nγ is composed of two parts: one part is caused by the tread of cutting curb; and the other one is the inclined plane

and the former

as well as the other bearing capacity factors

Nc and Nq

are identical with the results derived from Prandtl failure mechanism when the embedment depth of cutting curb is not considered. The embedment depth and width of tread and taper angle of the cutting curb exert a major influence on the limiting soil resistance. If neglecting these influence factors

the evaluated value of the limiting soil resistance would be significantly small. This study shows that the values of bearing capacity factors increase significantly with the increase of the embedment depth or taper angle of cutting curb. And it also shows that the taper angle has a more significant influence on the limiting soil resistance when the strength of soil is relatively high.