Understanding the physical mechanisms controlling the rate of macroscopic fracture propagation in intact rock under near-surface environmental conditions requires insight from time-dependent laboratory experiments. Recently designed static loading frames with integrated climate chambers are used to conduct constant load (up to 100 days) in uniaxial compression (UCS) and single edge notch three point bending (SENB) tests. Stability under stress- or strain-controlled loading conditions is ensured with the introduction of a hydraulic accumulator in line with the load application system and once the load target is reached, the accumulator acts as a spring to maintain a near-constant pressure on the hydraulic line (± 0.5 kN and ± 0.02 mm at 1000 kN load). The apparatus can also control the climate with an environmental chamber surrounding the loaded sample for temperature ranges over -20 to + 150 °C (± 0.3 °C), and relative humidity ranges over 10 – 80% (± 2.5%). Compressive tests performed on 115 mm long cylinders of Herrnhoz Granite, the same material used for long-term SENB tests with the new apparatus, are presented. A significant degree of cracking can be observed in the Acoustic Emission data during the load relaxation phase, indicating readily observable progressive failure characteristics of the specimen. This result gives us confidence to investigate time dependent damage evolution in crystalline rocks with the new apparatus.


The degradation of underground excavations as a result of:


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