PSI - Issue 82

ScienceDirect Structural Integrity Procedia 00 (2026) 000 – 000 Structural Integrity Procedia 00 (2026) 000 – 000 Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Available online at www.sciencedirect.com ScienceDirect

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Procedia Structural Integrity 82 (2026) 79–83

8th International Conference on Structural Integrity and Durability (ICSID2025) Pressurized granular cavity: stable dynamic equilibrium Koji Uenishi a,b, *, Kohei Shimizu a , Masanao Sekine b a Department of Advanced Energy, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8561, Japan b Department of Aeronautics and Astronautics, The University of Tokyo, 7-3-1 Hongo, Bunkyo 113-8656, Japan 8th International Conference on Structural Integrity and Durability (ICSID2025) Pressurized granular cavity: stable dynamic equilibrium Koji Uenishi a,b, *, Kohei Shimizu a , Masanao Sekine b a Department of Advanced Energy, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8561, Japan b Department of Aeronautics and Astronautics, The University of Tokyo, 7-3-1 Hongo, Bunkyo 113-8656, Japan

© 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers Abstract We study the mechanical stability of a three-dimensional granular medium, in particular, that with a cavity inside the medium. For a preliminary investigation, we prepare a three-dimensional granular medium that is made of glass beads in a transparent tank, and constantly supply compressed air downwards through a nozzle located at some depth from the top surface of this granular medium. With a high-speed video camera, we trace dynamic granular behavior and formation of a pressurized cavity inside the medium. The experimentally taken photographs show that basically, the cavity formed has a teardrop shape with a pointed top and a widened bottom, and once formed, it seems stationary and statically maintained without changing the shape as long as compressed air is supplied. However, contrary to our intuition, instead of being held down and kept stationary, the particles (glass beads) composing the wall of the cavity constantly move from the bottom upwards along the cavity wall due to the action of compressed air and then at the top point of the cavity they fall downwards to the bottom by the effect of gravity (and compressed air). Thus, actually, the pressurized cavity in the granular medium is in a stable dynamic equilibrium state: A steady flow of particles is established, and the particles undergo a cyclic motion to maintain the shape of the cavity. © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers Keywords: Granular flow; Granular collapse; Dynamic equilibrium 1. Introduction We have been investigating dynamic fracture and collapse of granular materials like slope failures (Uenishi and Sakurai, 2015), debris flows and avalanches. So far (Uenishi and Goji, 2018; Uenishi and Xi, 2022; Uenishi and Abstract We study the mechanical stability of a three-dimensional granular medium, in particular, that with a cavity inside the medium. For a preliminary investigation, we prepare a three-dimensional granular medium that is made of glass beads in a transparent tank, and constantly supply compressed air downwards through a nozzle located at some depth from the top surface of this granular medium. With a high-speed video camera, we trace dynamic granular behavior and formation of a pressurized cavity inside the medium. The experimentally taken photographs show that basically, the cavity formed has a teardrop shape with a pointed top and a widened bottom, and once formed, it seems stationary and statically maintained without changing the shape as long as compressed air is supplied. However, contrary to our intuition, instead of being held down and kept stationary, the particles (glass beads) composing the wall of the cavity constantly move from the bottom upwards along the cavity wall due to the action of compressed air and then at the top point of the cavity they fall downwards to the bottom by the effect of gravity (and compressed air). Thus, actually, the pressurized cavity in the granular medium is in a stable dynamic equilibrium state: A steady flow of particles is established, and the particles undergo a cyclic motion to maintain the shape of the cavity. © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers Keywords: Granular flow; Granular collapse; Dynamic equilibrium 1. Introduction We have been investigating dynamic fracture and collapse of granular materials like slope failures (Uenishi and Sakurai, 2015), debris flows and avalanches. So far (Uenishi and Goji, 2018; Uenishi and Xi, 2022; Uenishi and

* Corresponding author. Tel.: +81-4-7136-3824; fax: +81-4-7136-3824. E-mail address: uenishi@k.u-tokyo.ac.jp * Corresponding author. Tel.: +81-4-7136-3824; fax: +81-4-7136-3824. E-mail address: uenishi@k.u-tokyo.ac.jp

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers 2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers

2452-3216 © 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers 10.1016/j.prostr.2026.04.013