Strength and Deformation Characteristics of Scoria in Triaxial Compression at Low Confining Stress

Abstract

ABSTRACT Scoria deposit can be found around many volcanoes of the Quarternary epoch in the world. In Japan, Mount Fuji is one of volcanoes, where surface area is widely layered by scoria. From a geotechnical engineering point of view, scoria has many problems because of its physical characteristics by means of its collapsible properties. Since scoria is a non-cohesive material, it is vulnerable to water-induced change and fails easily due to rainfall or snow melting. These are the primary causes of debris flow which frequently occurs in the Mount Fuji area. Typically, this type of debris flow is called “Yukishiro” in Japanese. For better understanding of the shear behavior of scoria within low stress level condition, drained triaxial compression tests were performed on loose dry scoria under low confining pressures (10-80 kPa) which are assumed as representative of the field surface stress conditions. The effects of grain size, dry density ρd and effective confining stress σ′c upon stress-strain behaviour and angle of internal friction φd were investigated. Attention was also paid to level of grain breakage Bg and reproducibility of the test. Grain breakage investigations were carried out on the particle breakage phenomenon, which occurs during testing. Additionally, initial Young's modulus of scoria was identified. As a result, reproducibility of the test is good in terms of stress-strain curves, however volumetric strain versus axial strain exhibits less reproducibility than stress-strain curves. At stress level of 10-80 kPa, it was found that the dependency of φd on σ′c is almost negligible, while there is noticeable dependency of φd on grain size. The effect of grain size on stress-strain relationships was observed. It was also found that grain breakage was noticed at stress level of 10~80 kPa, which describes the dependency scoria parameters on confining stress and the effect of grain size upon Bg-σ′c relationships was also observed.