Analysis on mechanical behavior and progressive failure of deep-buried marble based on complete stress-strain curves

The mechanical behavior and failure mode of deep-buried rocks are key issues to the safety of deep underground engineering. In this study, a series of acoustic emission (AE) monitored triaxial compression tests on the marble samples were firstly conducted. Then, the effects of confining pressure on the mechanical characteristics were analyzed. Finally, the failure mechanism of the marble was revealed by using micro-computerized tomography (CT) scanning technique. It is found that the elastic modulus of marble samples increases non-linearly with the increase of confining pressure, but Poisson’s ratio decreases exponentially. The shape of deviatoric stress-axial strain curve changes from elastic-brittle to elastic-plastic gradually, and the deviatoric stress-volumetric strain curve changes from compression-dilatancy to complete-compression. The strength and deformation parameters at key points on compressive curves are much correlative with confining pressure, but their sensitivities to confining pressure are different in the pre-peak and post-peak stages. The power function Bieniawski criterion can well describe the strength at the key points in the pre-peak stage. Hoek-Brown and Mohr-Coulomb criteria show a high fitting degree for the strength at zero volumetric strain point and the residual strength in the post-peak stage, respectively. Both crack sketch and micro-CT scanning reveal the change of failure modes of the marble samples from axial splitting to shear failure. The number of microscopically observable cracks decreases first and then increases. The secondary microcracks are detected in the samples under high confining pressure. These results may provide good references to the design and construction of deep rock mass engineering.