Unsaturated Strength of Tage Tuff and Its Water Retention Drying Curve

Strength loss of sedimentary rocks due to water content changes is an important issue in the civil engineering field. Assuming disasters associated with rainfall and drying, it is important to identify unsaturated strength properties for gradually varying moisture contents. Water retention curves are needed to describe unsaturated strength properties. The high suction acting in the case of rock presents a challenge in identifying the suction. In particular, identifying the water retention drying path is difficult. This study propose a method to identify the drying paths using uniaxial compressive strength and tensile strength of Brazilian test. Uniaxial compression and Brazilian tests were performed on specimens with varying water content in the drying pass to investigate changes in their mechanical properties. Strength and stiffness were found to be approximately halved in the wet condition compared to the dry condition. Simplified Mohr-Coulomb failure criteria are also identified using uniaxial compressive and tensile strength. The cohesion decreases with increasing water content, while the angle of shear resistance is independent of changes in water content. Suction at each saturation level was back-analyzed using the detected cohesion and shear resistance angles to identify the water retention drying curve. The water retention drying curves identified were compared with the water retention wetting curve identified by another method to confirm the validity of the proposed method.