It is generally known that physical and mechanical properties of rock materials significantly change by clay mineral content. Therefore, it is considered that clay mineral content or type is one of the factors that greatly affect the rock strength. In order to clarify that effect of only clay mineral content, a series of experiments has been carried out on artificial rock by the use of gypsum specimen mixed with clay minerals. In addition, dry and wet cycle test is conducted to effect of swelling clay mineral on degree of strength reduction. The clay mineral content or type is one of the factors that affect the values of P-wave velocity, uniaxial compressive strength and degree of strength reduction. Comparative tests revealed that the difference in clay mineral content or type in the clay mineral-bearing rock material specimens influences the physical and mechanical properties of rock materials. Furthermore, the results suggested that uniaxial compressive strength of clay mineral-bearing rock materials under dry condition can be evaluated on the basis of interlayer bonding force (i.e. chemical bonds type) in the clay minerals. Our results can be useful and contribution as basis data when evaluating physical and mechanical properties of clay mineral-bearing rock materials.
Hydrothermal alteration, the formation of crushing and weathering zones by volcanic-hydrothermal systems, and weathering over geologic time and historical periods have occurred widely throughout the Pacific Rim region. As a result of these processes, a wide variety of clay minerals occur on the surface and in the crust of the Earth. Hence, the physical and mechanical properties of clay minerals differ, as evidenced by their structures. Therefore, it is very important to notice clay minerals, for instance, resource development, stability evaluation of underground utilization, landslide hazard assessment.
Many researchers have studied the effect of clay mineral on physical and mechanical properties of rock materials. For instance, Kahraman et al. (2016) and Ishida and Tsutsumi (1994) reported that the strength reduction including smectite is closely related to the smectite content. Kohno and Maeda (2010) showed that comparative tests revealed that the smectite content influences the point load index and uniaxial compressive strength of approximately 7% in weight and very small amounts of smectitebearing fine tuff. Furthermore, Kohno and Maeda (2012) showed that clay mineral content or type is one of the factors that greatly affect the rock strength. As above, the clay minerals have some kind of effect on mechanical properties of rock. However, there are following unsolved points: quantitative relationship between clay mineral content and mechanical property of rock, the presence or absence of swelling property of clay mineral, and influence of water content. Furthermore, reports of quantitative evaluation influence of clay minerals content and type, on the physical and mechanical properties of rock have apparently not been published to date.