Abstract: Isotropic compression and conventional triaxial compression experiments are performed on the T2b marble samples taken from Jinping underground laboratory, China, and some issues related to the isotropic compression deformation characteristics, the effect of confining pressure on the post-peak behavior and the pre-peak progressive failure process have been analyzed and discussed. The test results show that the volumetric strain under isotropic compression presents a linear-nonlinear-linear change when subjected to a confining pressure increase. An apparent volume change inflection point (sensitive stress) is observed, which can be related to stress history. There is a brittle-semi brittle-ductile transition trend with increasing confining pressure in the results of the conventional triaxial tests, and the change of the strength is consistent with the change of the isotropic compression curves which is in isotropic pressure vs. volumetric strain plot. Furthermore, the increased confining pressure has an effect on each stage of the progressive failure process, and other stress thresholds of the marble increase approximately linearly with the confining pressure except the crack closure deviatoric stress threshold. The initial crack closure process of the marble occurs twice, one under isotropic compression and the other under the deviatoric stress loading condition. The above results of Jinping T2b marble is valuable for achieving a better understanding the rock failure mechanism and preventing disasters in deep underground engineering.

Key words: Jinping, marble, deformation behaviour, isotropic compression, progressive failure, brittle-ductile transition