Impact of Clay Mineral Type on Rock Properties under Drying and Wetting Cycles

Rocks containing clay minerals exhibit diminished strength and undergo physical and chemical deterioration of their texture due to the presence of these clay minerals. Specifically, rocks containing swelling clay minerals experience a significant decrease in strength when subjected to repeated drying and wetting compared to rocks with non-swelling clay minerals. This study conducted a comprehensive series of experiments (physical, uniaxial compressive, and swelling pressure tests) using artificial soft rock mixed with clay minerals. The primary objective was to elucidate the impact of the types of clay minerals present on the physical properties of rock materials under repeated drying and wetting. The clay minerals investigated in this study included Na-type and Ca-type smectites (swelling clay minerals) and mica (non-swelling clay minerals). The smectite-mixed specimen demonstrated higher swelling pressure than the mica-clay-mineral-mixed specimen. Moreover, the uniaxial compressive strength and P-wave velocity of the specimens were remarkably reduced due to repeated drying and wetting process. Hence, the difference in clay mineral content and type in the clay mineral-bearing rock material specimens directly influences the physical and mechanical properties of rock materials when subjected to dry and wet cycles. Furthermore, the outcomes suggest a close association between the reduction in rock material strength, inclusive of clay minerals, and the swelling pressure observed in the specimen.