Study on creep characteristics of granite of deep tunnel affected by joint orientation.

• The effect of loading angle ω on the time-dependent deformation of natural jointed granite subjected to true triaxial stresses was investigated. • The unfavorable combination relationship between joint orientations and true triaxial stresses was investigated. • The stress-structure-controlled time-dependent failure enters the stage dominated by shear cracks earlier than stress-controlled. • Joint orientations most likely to induce the time-dependent disaster in deep tunnel were predicted according to the true triaxial tests of jointed granite. Joints are an important part of rock masses and the spatial relationship between joint orientation and in situ stress (or tunnel axis) has a significant impact on the deformation, strength, and failure behavior of the surrounding rock. To study the influence of joint orientation on creep characteristics of deep hard rock, the true triaxial creep tests were performed in the laboratory on natural jointed granite under different loading angles ω (defined as the angle between the strike of the joint plane and σ 2 -direction) conditions. The test results show that ω has a significant effect on the time-dependent deformation and failure characteristics of the jointed rock. As ω increases, there is a decrease in creep deformation, steady creep rate in the σ 3 -direction, and value of the DI index (used to evaluate the difference in the time-dependent deformation in the σ 2 - and σ 3 -directions). Stress-structure-controlled failure (sliding along the joint plane) occurs when ω ≤ 30°. However, when ω > 30°, the failure of the jointed granite is not affected by joint and stress-controlled failure occurs. The stress-structure-controlled time-dependent failure evolution enters a stage that is dominated by shear cracks earlier than stress-controlled failure according to AE results. In addition, the time-dependent failure went through stages of microcracks initiation and interaction, stable crack growth and unstable crack propagation. And when the time-dependent failure evolution enters the unstable crack propagation stage, the nature of the cracks changed from tensile-dominated to shear-dominated. [ABSTRACT FROM AUTHOR]