In the geological disposal of radioactive waste, it is imperative to perform long-term assessments of the shielding efficacy and mechanical stability of the surrounding rock. Numerous investigations into the timedependent characteristics of various rock types have been undertaken to predict the long-term mechanical response of rocks. However, the time-dependent behaviors of diatomaceous earth, such as the strain-rate dependency of strength and creep behavior, remain unclear. In this study, constant-strain-rate and creep tests on diatomaceous earth specimens under undrained conditions and a confining pressure of 10 MPa, at both ambient (25 °C) and elevated (80 °C) temperatures were conducted. Although variations in strength (maximum differential stress) were observed between tests conducted at different temperatures, it is inconclusive as to whether the strength variations were primarily induced by temperature variations, as the unintentional deviation in water content between specimens used in the constant-strain-rate tests at 80 °C and 25 °C might have exerted some effects. The strain-rate dependency of strength and the creep behavior of diatomaceous earth were obtained, and a constitutive equation of the variable-compliance type, which accounts for the time-dependent behaviors of rocks, was applied to the obtained experimental results. Formulating an improved constitutive equation through further triaxial compression tests is an issue in the future.
