DELAYED FAILURE IN ROCK LOADED IN UNIAXIAL COMPRESSION

The long-term response to sustained compressive loading of two crystalline hard rocks of the Canadian Shield has been investigated. Static fatigue tests conducted on granite and anorthosite have shown that in a humid environment the long-term strengths of these crystalline igneous rocks could be less than 60 percent of their dry instantaneous strengths. The particular case of a nuclear fuel waste vault located at a depth of one kilometer is considered. Considering a service life of 1,000 years, a vault one kilometer deep in granite could suffer time-dependent spalling in highly stressed regions of the rock where the maximum principal stress exceeds about 130 MPa. Anorthosite has a lower instantaneous strength than granite and it is sensitive to static fatigue as well. A vault in anorthosite would be subject to time-dependent spalling of the perimeter rock in places where the maximum principal stress is above 80 MPa.