Dr. Shunta Shiraishi: Tiny Air Bubbles during Earthquakes

Tiny air bubbles prevent seismic liquefaction…Niigata Earthquake in 1964 is the subject of another Japanese veteran Shunta Shiraishi of Tashi Fudohsan Co., Ltd. Shunta Shiraishi writes “Countless tiny air bubbles in ground water remain semi-permanently at the positions where they are first held in the clusters of soil grains and prevent seismic liquefaction of ground by lowering the saturation degree of ground water. It was first recognized at Niigata Earthquake of 1964 that the ground of fine sand surrounding the pneumatic-caisson foundations of Bandai Bridge were not liquefied. A considerable amount of the compressed air leaked out of the pneumatic caissons when they had been built in 1927 remained in the ground water around the pneumatic caissons for 37 years since then, and prevented the liquefaction of the ground around the pneumatic caissons. The structures founded on 305 pneumatic caissons were not damaged beyond repair by the violent Hyogoken-Nambu Earthquake of 1995 where the maximum horizontal acceleration of ground movement was at the record high value of 818 gal. Conceptual inexpensive methods using small equipment for preventing seismic liquefaction of ground by lowering the saturation degree of ground water are proposed in place of the expensive methods using large equipment to compact the loose ground. Dr. Shiraishi acknowledge the following persons in his papers, Professor A. Asaoka of Nagoya University for his information quoted in his paper (1992), Dr. T. Asama of JPTA who compiled the report (1996), Dr. T. Sakai of Kiso Jiban Consultants, Inc. who helped RGRI (1987) for the author and Dr. Y. Yoshimi (1994) who was past-President of the Japanese Society of Geotechnical Engineering.