Experimental study on shear and creep behaviour of green tuff at high temperatures

The long-term stability of soft rock under high temperature conditions is very important to the safety of high-level radioactive waste (HLW) disposal. This study presents a series of triaxial compression tests and triaxial creep tests on green tuff in a temperature range of 20-80 °C. Repeated tests showed that the influence of temperature was more apparent on the peak strength and creep failure time than on the residual strength and volume change. The thermal effect on creep failure time was significant and became more prominent in higher creep stress. A linear correlation between the creep failure time and the minimum axial steady-strain rate at different temperatures was obtained. A thermal reversion behaviour, in which the peak shear strength and the creep rupture time of soft rocks are not monotonic functions of temperature, was observed. X-ray diffraction analysis showed that neither zeolite reduction nor hydrothermal alteration was the reason for thermal reversion.