G-PFEM Numerical Study of the Downward Trapdoor Problem

The downward trapdoor provides a valuable framework for investigating stress distribution and ground movement during tunnel excavation. Numerous efforts have been made to devise analytical methods based on experimental observations. The area above the trapdoor experiences gravitational flow, and it becomes an active soil pressure condition with the lowering of the trapdoor. Due to the substantial discontinuous movement between the trapdoor and the adjacent stationary support, significantly discontinuous deformations arise at the boundary between the active zone above the trapdoor and the stationary zone. This complexity renders the trapdoor problem challenging by traditional continuum analysis methods. To confront this challenge, the present study employs the Particle Finite Element Method for geotechnical applications (G-PFEM) to simulate the downward trapdoor problem. The effectiveness of this approach is demonstrated by replicating a model experiment included in the literature. The simulation captures the gravitational flow of the surrounding ground as the trapdoor descends, and the numerical results, encompassing stress distributions, ground displacements, and surface settlements, closely correspond to experimental data. Moreover, to underscore the advantages of employing G-PFEM, a larger displacement is applied to the trapdoor. The results indicate significant changes in ground displacement and corresponding earth pressure as the trapdoor displacement increases, ultimately leading to substantial slope failure like large deformation.