A comparative study of the trapdoor problem is proposed in this paper involving experimental model tests on one side and a Discrete Element Method modelling on the other side. Most of the past studies related to the arching eŠect and the trapdoor problem were performed under plane strain or axisymetric conditions. The observation of the arching mechanisms is indeed simpliˆed under these special test conditions. In this paper, the trapdoor problem was simulated under three-dimensional testing conditions with a square-shaped trapdoor. The granular layers were made with monodisperse glass beads. The arching mechanisms were experimentally investigated with X-ray Computed Tomography. Based on the images obtained, the propagation in the granular layer of the disturbance due to the displacement of the trapdoor was monitored. On the other side, the intensity of the load transfers in the granular material was evaluated with a force measurement apparatus on the trapdoor. In parallel, a numerical analysis involving the Discrete Element Method was conducted to predict both the qualitative and the quantitative phenomena. The gradual local expansion of the granular layer due to trapdoor displacement and the load transfer amplitudes were very well reproduced. An agreement between the experimental and the numerical results was obtained for small displacements of the trapdoor (high load transfers) as well as for larger displacements of the trapdoor.