Most previous trapdoor stability studies were centered on undrained clay in two dimensions in the past few decades. Very few works were reported for cohesive-frictional soils in two- and three-dimensions. This paper sets out to examine the stability of trapdoors in c-Φ soils under both 2D planar and 3D circular (axisymmetric) conditions using a superposition method that is similar to Terzaghi’s bearing capacity coefficients approach. Using lower bound and upper bound limit analysis with finite elements, the proposed three coefficients (Fc, Fs, and Fγ) are determined with respect to a series of parametric changes of depth ratios and soil internal friction angles. Novel design charts and tables are presented, and several examples are provided to show how to use the three coefficients to evaluate soil stability under planar and circular trapdoors. The numerical results presented in the paper should be of interest to the geotechnical engineering community.