An Experimental Study on Creep Behavior of Transversely Isotropic Composite Rock under Conventional Triaxial Compression

The time-dependent deformation behavior of hard-soft composite rock has a significant effect on tunnel excavation. In this article, a method to prepare hard-soft composite rock specimens with orientations ranging from 0 degrees to 90 degrees is presented. The influences of the dip angle on the long-term deformation and failure behaviors of an artificial transversely isotropic rock specimen were investigated by a series of creep experiments. The test results show that the creep failure strengths of the specimens first decreased and then increased with an increasing dip angle. The composite rocks displayed remarkable creep characteristics. The axial instantaneous deformation increased linearly with an increasing deviatoric stress, but the creep strain displayed a nonlinear trend. The instantaneous modulus first decreased in the range of 0 degrees to 30 degrees and then increased in the range of 45 degrees to 90 degrees with the increase of dip angle; however, the creep strain showed an opposite result. The steady-state creep rate increased nonlinearly with an increasing deviatoric stress. The dip angle had a significant effect on the steady-state creep rate. Moreover, the creep failure modes of the rock-like specimens, which were dependent on the dip angle, were compared.