A space generates inside the ground by tunnel excavation and so the stress inside the ground surrounding the tunnel would change. This re-arrangement of stress has been investigated by so-called "trapdoor experiment". This research analyses numerical simulations of a bed of granular material having a moveable trapdoor over part of the underlying boundary using the discrete element method (DEM). Kikumoto & Kishida (2003) measured the vertical stresses on a trapdoor and the adjacent boundaries in tests using Toyoura sand to represent natural ground. The DEM model provided a good simulation of the vertical stresses measured on the trapdoor when it was moved downward and also the vertical stresses on the boundaries adjacent to the trapdoor. Next the gravitational flow of the sand was calculated when the trapdoor was suddenly removed; it was found that there was a complex dynamic response in the vertical stress on the boundary immediately adjacent to the opening created, but only modest changes further away. The motivation for these DEM simulations was to gain a better understanding of the processes involved in tunnel construction when there is a partial collapse of the face, or the roof, near the tunnel face.

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As a part of countermeasures against powder dust explosions, induced voltages in a loop antenna and voltages in a storage tank in the event of electrostatic discharge (ESD) were measured for the detection of ESD inside a storage tank. As a result of a full-scale experiment using a pneumatic conveying system for powders, it was possible to detect induced voltages due to ESD even if conductive electromagnetic noises existed. It was not possible to detect a precursory phenomenon before an incendiary ESD, such as bulking brush discharge occurring, because the high-level induced voltage due to a presumed incendiary ESD occurred suddenly without any precursory phenomenon. However, the continuous monitoring of induced voltages is considered useful to prevent electrostatic accidents because it is possible to decrease the probability of explosion accidents due to ESD by neutralizing charged powders with a static eliminator when a presumed incendiary ESD is detected.

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[in Japanese]

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[in Japanese]

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