Fracture toughness testing of rock at elevated temperatures and pressures

Fracture toughness tests were done on Kimachi sandstone and Inada granite using two types of core based specimens. In addition to the measurement at ambient conditions, fracture toughness was also determined at elevated temperatures, confining pressures and wet conditions. Elevated temperatures appear to make the rock tougher causing the fracture toughness to increase substantially. Increasing confining pressure also increases the fracture toughness as the pressure causes closure of some pre-existing microcracks and discontinuities. Water content was found to cause reduction of fracture toughness particularly in sandstone. This effect is supposed to be due to the increase in pore pressure.