Experimental study on the tensile strength and failure characteristics of transversely isotropic rocks after freeze-thaw cycles

Freeze-thaw (F-T) is a frequent occurrence in cold regions and can weaken the mechanical properties of rocks, thereby severely affecting the safety of rock engineering projects and even causing accidents. In this research, direct tensile tests were conducted to experimentally investigate the influence of the number of F-T cycles (i.e., 0, 10, 20, and 30 times) and the bedding orientation (i.e., 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees) on the tensile strength and failure pattern of transversely isotropic rocks. The results indicate that the tensile strength decreases with the increasing number of F-T cycles and continuously increases with the increasing bedding orientation. The degree of anisotropy in the tensile strength increases with the increasing number of F-T cycles because weakness planes are more sensitive to the effects of F-T cycling and show greater damage than the parent rock. The orientation of the failure plane of the specimens increases with the increasing bedding orientation until a certain orientation is reached, beyond which it decreases rapidly to nearly zero. In addition, a model for the prediction of the tensile strength and failure characteristics of transversely isotropic rocks after F-T cycles is presented based on Nova and Zaninetti's tensile failure theory, and a large quantity of experimental data were adopted for comparison with the theoretical results. It is determined that the proposed model can effectively describe the relationships among the tensile strength properties, bedding orientation, and number of F-T cycles.