A Study on the Bio-treatment Technique of Ground Improvement with Urease Microorganisms Which Live in Japan

Soil improvement techniques using microorganisms have recently been focused on as the low cost and environmentally friendly technique (Mitchell and Santamaria in J Geotech Geoenviron Eng 131:1222–1233, 2005; De Jong et al. in Bio-soils interdisciplinary science and engineering initiative: meeting societal needs through international transforming research, 85 pp, 2007) for practical use in Japan. Sporosarcina pasteurii is mainly used for this technique in almost all researches. But it has not yet been clarified how much this microorganism affects the environment in Japan because it is imported from the USA. In this paper, three laboratory tests were carried out to examine urease microorganisms which live in Japan for this bio-treatment technique. Results revealed that the urease microorganisms were found in all natural beach rocks from Okinawa that these microorganisms could reproduce calcium carbonates in soil. Especially microorganisms picked up from Yomitan Beach show a high rate of productivity of calcite to help the treatment. It was also found that the unconfirmed compression strength of the specimen treated with microorganism from Yomitan Beach showed almost the same strength as the one with S. Pastuerii. Therefore this microorganism is useful for the bio-treatment technique, instead of S. pasteurii.