Time dependency for generalized relaxation compliance of rock

The time-dependent behavior of rock is frequently studied in creep tests. However, in rocks with various supports and homogeneity, creep is occasionally accompanied by relaxation in situ. In this study, the behaviors of four types of rocks are analyzed in generalized stress relaxation tests, in which stress and strain are changed simultaneously. To analyze the generalized relaxation behavior, a method for calculating the generalized relaxation compliance (GRC) was proposed. The results showed that GRC is independent of α and stress level, indicating that it can be obtained in a creep test. Furthermore, the GRC was obviously time-dependent and was higher in the Class I rocks than in the Class II rocks investigated in this study. The GRC was related to the logarithm of the time. Finally, an index of the GRC time dependency was proposed, which roughly increases with stress level. The results may quantitative time dependency for many rocks, to predict the failure life in underground engineering.