To explore the stress relaxation related strength and failure character of brittle rock, experimental investigations that consist of various kinds of loading paths are conducted on the granite material. For brittle rock material, the relaxation and creep behavior is related to the subcritical growth of cracks. During the experiment, the digital image correlation method is adopted to observe the whole process of crack growth, analysis on the strain distribution character of the studied area in the specimens are carried on too. The experimental results indicate that the failure patterns of granite is related to the stress relaxation path. In detail, distinct stress relaxation behavior can be detected for all the strain relaxation levels. For different loading path, the uniaxial compressive strength shows direct proportion to the stress relaxation history. Besides, the increase in relaxation steps also to contribute to the propagation of subcritical cracks. For all tested specimens, the failure patterns show obvious splitting feature, which reflects the distinguished brittle character of the test material. Furthermore, it is suggested that brittle fracture property of the rock material is intensified as the stress relaxation time increases. In accordance with the present research, it can be concluded that the time dependent behavior is mainly induced by the subcritical growth of crack at the granite material. The present research can provide some increased understanding about the time dependent failure characteristics of brittle rock for the excavation constructions of underground engineering.

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