2019 Volume 59 Issue 6 Pages 446-452
Laboratory measurements were conducted to evaluate physical and mechanical properties of sandstone and calcareous concretions which were collected from the wave-cut bench in Iwami-tatamigaura, a natural monument in Shimane, with permission of Agency of Cultural Affairs, Government of Japan. Physical properties such as density, porosity and p-wave velocity of sandstone（concretions）were 2.16～2.21Mg/m3（2.50～2.58Mg/m3）, 10.6～14.9%（2.40～4.82%）and 2.30～2.99 km/s（3.69～4.63 km/s）, respectively. Mechanical properties such as uniaxial compressive strength and tensile strength by Brazilian test of sandstone（concretions）were 18.1～26.7MPa（56.9～128MPa）and 1.52 ～6.04MPa（4.03～10.9MPa）, respectively. Weathering susceptibility index, which is defined as the ratio of porosity to tensile strength, was calculated to be 2.1～7.6×10－2MPa－1 for sandstone and 2.4～6.7×10－3MPa－1 for concretions. Observations of thin sections revealed that carbonate occurs as a matrix in the concretions whereas less carbonate in sandstones with smaller strength. Therefore, the concretions have lower porosity, lower susceptibility of weathering and larger strength than those of the sandstone because of bonding effect by the carbonate.
