Evaluation of creep mechanical behavior of deep-buried marble under triaxial cyclic loading

摘要

Triaxial compression experiments were carried out on deep-buried marble specimens to investigate their short-term and creep mechanical behavior under cyclic loading. First, based on the results of short-term triaxial experiments, the elastic, plastic, and strength behaviors of marble were analyzed. The results show that for the same confining pressure, the elastic modulus of marble remains basically constant at the lower axial deviatoric level but decreases slowly after yielding strength; in contrast, the plastic modulus reduces rapidly with the increase of axial deviatoric stress. However, the elastic and plastic moduli of the tested marble were quite independent of the confining pressure. The relationship between axial deviatoric stress and plastic deformation of marble can be described well by the interface model. The peak strength of marble under higher stress increases with the confining pressure, which can be better described in accordance with the Mohr-Coulomb criterion. And then, in accordance with the experimental results of marble creep under triaxial cyclic loading, the instant elastic and plastic strains, and the visco-elastic and visco-plastic strains were all separated successfully, which provided a better foundation for constructing a visco-elasto-plastic creep model of rock. The creep strain rate of marble under different deviatoric stresses is analyzed, which shows that the steady-state creep rate of marble increases nonlinearly with the increase of axial deviatoric stress. In the end, the creep mechanical behavior of marble under cyclic loading is theoretically analyzed using the creep model. The results show that Burgers creep model can describe the creep behavior of marble under the loading condition satisfactorily but is inadequate to describe the creep behavior of marble under the unloading condition. Therefore, by adopting the fundamental hypothesis of visco-plastic mechanics, a visco-elasto-plastic creep model of rock material is constructed, which can describe the unloading creep behavior of marble better than Burgers creep model. The creep model curve agrees very well with the experimental results, which verifies the proposed visco-elasto-plastic creep model.