Triaxial Testing Machine for Properties of Rocks in Water Circumstance at Elevated Temperature and Results of Tests by Using It

Abstract

We made the machine testing the mechanical properties of rocks in wet conditions under confining pressure for estimating drillability of geothermal reservoir or stability analysis of underground structure in disposal of nuclear waste in deep rock mass becuase effect of temperature on mechanical properties of rocks might be different between in dry condition and in water circumstance.
In this paper are described the results of triaxial compression tests of INADA granite in water circumstance at elevated temperature. Maximum temperature is 250°C and maximum confining pressure 300 kgf/cm². Specimens were exposed to pressurized water without sealing in order to investigate the effect of both pore pressure, which is equal to confining pressure, and chemical reaction of hot water.
Main results obtained in this study are summarized as follows:
1) Effect of confining pressure which is equal to pore pressure is negligible. Therefore, law of effective stress can explain the mechanical behavior of the granite.
2) In pressurized water, both stress of strength failure and Young's Modulus are almost identical with those at room temperature when temperature is below 100°C, remarkable decrease of both stress of strength failure and Young's modules ocurred with temperature.
3) In comparison with dry condition, decrease of stress of strength failure is much larger in wet condition of pressurized water especially when temperature is larger than 100°C.
4) As mechanism of deterioration of grante in pressurized water at elevated temperature, it is suggested that chemical reaction such as solution of minerals is important in addition to thermal stress caused by differential thermal expansion of different minerals or anisotropy of thermal expansion of each mineral.