Mechanical properties of siliceous mudstone of the Wakkanai formation

Hashiba, Kimihiro*; Fukui, Katsunori*; Sugita, Yutaka ; Sanada, Masanori*

Diatomaceous earth and siliceous rock are widespread in the areas along the Sea of Japan in Hokkaido Prefecture, Akita Prefecture, Noto Peninsula and Oki Islands. To construct underground structures in the siliceous rock mass, it is essential to understand its mechanical properties. In this study, siliceous mudstone of the Wakkanai formation obtained from the deep underground in Horonobe, Hokkaido was applied to various laboratory tests; uniaxial compression test, Brazilian tension test, drying shrinkage test and the test to investigate the time dependent behavior and strength recovery. The testing results showed that water has a huge effect on the deformation and failure of the siliceous mudstone; when the specimen is air dried in room temperature, the axial shrinkage strain reashes 0.9% and the strength is twice larger than that in wet condition. It was found that the siliceous mudstone exhibits the same degree of time dependent behavior and strength recovery as other rocks such as tuff and sandstone.