Study on the Features of Critical Arch in Granular Materials by the Developed Trapdoor Apparatus

This paper experimentally discusses events being relevant to the arching effect in granular materials by the developed trapdoor apparatus. A focus on the features of stable arch at two moments when an arch is on the verge of collapse in addition to the time after the collapse. The critical arch for a granular medium is the last stable arch belonging to a trapdoor with maximum possible width at a particular base angle. The maximum trapdoor width is observed 4.7 to 8.67 times the average particles diameter depending on the internal friction angle and base angle values. The critical arch has the maximum width in proportion to previous run, whereas its height not only increases but will get smaller. After arch collapses, particles remained in the test box, are approximately located on the horizontal rails symmetrical. Besides, their arrangement remains almost constant compared to early one.