Long-Term Creep Test and Constitutive Equation of Tage Tuff
Two long-term creep tests of Tage tuff were carried out as long as three years. In the tests, specimens were submerged under the water, and creep stress was applied and maintained at 30 % of the peak strength.
The first testing was started in 1994. The result indicated that creep strain
rate was monotonically decreasing with elapsed time approximately proportional
to (elapsed time)−0.9. Trough the testing period, creep strain was increasing
approximately following (elapsed time) 0.1 and did not reach the creep limit to
which creep strain leveled off. The second testing was started in 1997 and the
result was similar to the first one except that creep strain was slightly
smaller than the first. A constitutive equation of variable compliance type was
modified especially focusing on the long-term creep at low stress level.
Experimental results of not only this study but also previous studies were
carefully examined. It was found that the creep strain and strain rate
calculated by the modified equation reasonably well coincided with the
Key Words: Rock, Tuff, Creep, Long-Term Strength, Constitutive Equation, Visco-Elasticity