Biaxial Creep Test Study on the Influence of Structural Anisotropy on Rheological Behavior of Hard Rock

AbstractRheological characteristics are one of most important properties needed to be considered in the design and construction for the long-term stability and serviceability of underground structures in the rock mass. To date, although extensive studies on the rheological properties of rocks are available in the literature, most of the existing studies reported the strain-time data for the axial deformation through the compression rheological method and did not mention the lateral deformation, and mainly focused on the soft rocks at shallow depth. Thus, very limited attention has been paid to the rheological properties of deep and hard rock, neglecting the effects of structural anisotropy on the rheological properties. This paper presents a comprehensive, in-depth study of the rheological behaviors of super-deep hard rock, considering the effects of structural anisotropy by using the uniaxial and biaxial creep tests. The results revealed that significant creep behavior can be observed in the hard rock specimens under high stress in the in situ conditions, and the strain-time behavior of hard rock exhibited brittle failure. The strain-time curves of hard rock exhibited two obvious phases of instantaneous creep and steady-state creep, without the phase of accelerated creep. Moreover, it was observed that the rheological behaviors, including the instantaneous modulus, transient creep duration, axial and lateral creep deformations, steady-state creep rate, volumetric strain, and contraction ratio are strongly affected by the structural anisotropy. Based on the experimental data, empirical models of the parameters governing creep behavior have been established.