Abstract
The stability of a circular opening trapdoor in undrained cohesive soils is numerically investigated using three-dimensional (3D) numerical simulations. FLAC3D, a finite difference program using the shear strength reduction method (SSRM), is employed to determine the factor of safety (FoS) solutions that are a function of the depth ratio and the shear strength ratio. Numerical results from the current FoS study suggest that the 3D circular opening results are almost twice larger than those in 2D study. The strong arching effects have been noted for deeper cases, and the corresponding global failure mechanism is observed. The results are compared with published solutions in the literature. Practical examples are used to demonstrate how to use the design charts and equations in practice.