This paper present an experimental study of the trapdoor problem in 3-dimensions using X-ray computed tomography. Trapdoor tests were performed on layers of glass beads of different sizes. Different trapdoor shapes varying from square to rectangular shape were also tested. The trapdoor tests were analyzed in terms of load transfer (force) and in terms of propagation of the disturbance created in the layer by the trapdoor movement. The results revealed the existence of a transition between a 2-dimesional behavior and a 3-dimensional behavior in the trapdoor problem, as the aspect ratio of the trapdoor increased.