Rock fractures in geological conditions are caused not only by applied stress, but also by stress corrosion. Stress corrosion is an environmentally activated chemical process, associated with the fluid-assisted crack growth. Crack growth due to stress corrosion is related to the time-dependent behaviours of rocks and is a crucial factor in determining the stability of underground structures over the long period of time. In this study, constant stress-rate tests including Brazilian tension and three-point flexural tests for the tensile strength, short-beam compression and single-shear tests for the in-plane shear strength, and a torsion test of rectangular section specimens and a circumferentially notched cylindrical specimen test for the out-of-plane shear strength were conducted at a different loading rate from 0.01 to 10 MPa/s using Coconino sandstone. The results show that the rock strength was proportional to the 1/( n +1)th power of the loading rate, where the parameter n indicates the stress corrosion index. The stress corrosion index ( n ) ranged from 34 to 38, with an average value of 36. The stress corrosion indices ( n ) were similar, irrespective of the loading configuration and specimen geometry. The stress corrosion index ( n ) can, therefore, be regarded as a material constant of rocks.
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