“…Kubotera and Yamada (1997, 1998, 2000 showed that indurated volcanic soils and clayey soils that become very hard by air-drying display a vughy microstructure with a small amount of voids whereas the microstructure of the soils that did not show a remarkable hardening was more porous, including microstructure such as crumb microstructure, granular microstructure, and spongy microstructure. On the other hand, Kawai ( 1971) divided the fabric of volcanic ash soils into seven types, and identified the "cemented porous fabric" in which skeleton grains were interconnected by plasma coating and a large amount of voids were observed, as the characteristic of indurated pan layer such as "Masa" around Mt. Fuji.…”