Effects of water saturation on the strength and loading-rate dependence of andesite

Abstract

Water saturation conditions in the rock masses around underground openings vary with place and time. For the long-term stability assessment of underground structures, it is essential to understand the effect of water on the time-dependent behavior of rocks. In this study, the effects of water saturation on the loading-rate dependence of strength, which is one of the time-dependent characteristics of rocks, were investigated both theoretically and via experiments. First, the effects of loading rate and water saturation on rock strength and its variability were clarified by means of a theory that is based on both stochastic and rate processes. Next, alternating loading-rate tests were conducted on Sanjome andesite using uniaxial compression testing under various water saturation conditions. The test results showed that the rock strength increases with a decrease in water saturation and that an increase in strength accompanied by a tenfold increase in loading rate is almost constant under various water saturation conditions. All of the test results were consistently explained by our theory of the dependence of rock strength and its variability under different loading rates and water saturation conditions. It was also found that the dependence of strength on the loading rate is equivalent to that on the water saturation, and that the strength obtained from a test could be converted to one under an arbitrary loading rate and water saturation condition. In addition, we proposed a constitutive equation based on these theoretical and experimental results that could reproduce the loading-rate dependence of stress-strain curves under various water saturation conditions using a single set of constants.