Variation in strength and creep life of six Japanese rocks

In this paper, variations in strength and creep life are investigated for rocks under various conditions: dry and wet, uniaxial and triaxial, and compressional and tensile. A number of parameters are introduced for this purpose; to assess the time-dependent failure under constant and monotonic loading the following parameters are used: the parameter of time dependency delta, coefficient of creep life a and coefficient of strength beta. delta explains the rate dependency of strength or stress level dependency of creep life. aalpha and beta are related to each other. Variations in beta have been evaluated using data from previous experiments. It is confirmed here that delta, beta and variations in beta determined by creep tests are in most cases identical to those determined using strength tests. Variation in beta in the wet condition is almost the same as that in the dry condition; however, variation in tension increases more than in compression. Under confining pressure, variation in beta is reduced for Neogene sedimentary rocks, and does not appear to change for igneous rock and welded tuff. (C) 2004 Elsevier Ltd. All rights reserved.