Visualization and sequence photo of tertiary creep under confining pressure

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It is essential for underground development to understand the failure process of rock subjected to tri-axial compression. Therefore, we developed a transparent tri-axial vessel made of an acrylic acid resin, and succeeded in observing the failure process of rock specimens in tri-axial compression test. In this study, tri-axial creep tests of Tage tuff were also conducted within the transparent vessel.A creep test usually requires longer time than a compression test and it is not feasible to take a photograph continuously at every predetermined time interval. Therefore, in this study, the photographing system was developed which cooperated with the existing loading and measuring apparatuses. This system made it possible to take a series of photographs of a specimen in the tertiary creep region. Photographs taken in a tri-axial test were processed to obtain axial and lateral deformations by the computer program developed in this study.After careful examination of axial and lateral deformations, it was found that the creep strain (axial strain) just before failure was nearly equal to the cross sectional width of the stress-strain curve at the creep stress level, and that not only axial but also lateral strain-rates in the tertiary creep region were inversely proportional to the residual time up to the failure. And it was also found that ratio of the lateral and axial strain increases in the tertiary creep region were similar to those of the tri-axial compression test just after the strength failure point.