Time-dependent failure characteristics of natural jointed granite of deep tunnel under different dip angles conditions

To investigate the time-dependent characteristics of jointed rock masses, a series of single-step true triaxial creep tests were conducted on natural jointed granite samples under different dip angles conditions. The results showed that the time-dependent failure of jointed granite behave as two different forms, namely, stress-controlled and stress-structure-controlled failure. When the dip angle of joint is less than 70° or greater than 77°, stress-controlled failure was the predominate mode. Otherwise, stress-structure-controlled failure occurred. There are similarities and differences in the evolution mechanisms of these two types of time-dependent failure. Similarly, the acoustic emission (AE) count rate demonstrated multiple peaks in both types of time-dependent failure processes. Differently, for stress-controlled failure, tensile microcracks and large-scale shear cracks develop alternately until the ultimate failure is reached, but for stress-structure-controlled failure, tensile cracks are dominant in the early stage and followed by plenty of shear cracks in the later stage.