Geological, Physical, and Mechanical Properties of “ Shirasu ” and its Engineering Classification

Abstract

Shirasu in southern Kyushu is the deposits caused by volcanic activities, and structurally unstable. It is also called “special soil”. This paper contains the descriptions on the formation and constituents of Shirasu, the engineering classification, and the physical and mechanical properties, for estimating the stability of slopes in undisturbed Shirasu and compacted earth fills. Shirasu possesses grains of peculiar shape and surface texture, and its chemical components are composed dominantly of silica and alumina. As for mineral composition volcanic glass greatly surpasses others in quantity. Shirasu deposits can be classified into five distinct groups from the standpoint of soil engineering with its geological aspects in consideration. Physical and mechanical properties are different with the kinds of Shirasu due to engineering classification. Research is needed in order to develop the specification of designs of structures in and of Shirasu and to prevent and decrease in disaster.