CREEP BEHAVIOR OF TUFFACEOUS ROCK AT HIGH TEMPERATURE OBSERVED IN UNCONFINED COMPRESSION TEST

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Geological disposal in soft rocks is expected as one of the most practicable methods for isolation of high-level radioactive wastes. Since the country rock around the deep tunnels tends to be heated for a long term due to continuous collapse of nuclides, creep behavior of the soft rocks of impermeable nature under high temperature should be studied. Under different temperatures from 24℃ to 95℃, a series of unconfined compression tests was conducted on a tuffaceous rock, Ohya stone, at creep stress ratios ranging from 0.6 to 1.0. The results show that the creep behavior is accelerated by high temperatures over 60℃. That is, for higher temperatures, the time to failure is decreased, while the minimum strain rate is increased. A creep model is then presented, in which attention is paid to the change in strain rate with time. Unique relationships between the minimum strain rate and various creep parameters are used, that appear to be dependent on neither creep stress ratio nor temperature. According to the proposed model, the creep failure will not take place if the creep stress ratio is lower than 0.44.
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