Uncovering Failure and Cracking Behaviors of Double-Flawed Sandstone Under Compressive-Shear Loading Using Digital Image Correlation (DIC) Technique

Abstract

The coalescence of flaws provides valuable insights into the failure behaviors of rock masses, which is a critical issue in rock engineering. In this study, a series of compressive-shear tests were conducted on sandstone specimens containing double flaws. The failure and cracking behaviors of specimens with different geometric configurations under various loading conditions were analyzed using the digital image correlation (DIC) technique. The strain and displacement fields effectively demonstrate crack propagation and coalescence, accompanied by the axial load–displacement curve. The results revealed the effect of eccentric and overlapping distance of double flaws on the compressive-shear bearing capacity. The relative displacement method (RDM) was applied to analyze the crack characteristics in this study. Based on the relative displacement behaviors of the cracks, five typical types of crack modes were identified, including tensile mode, shear mode, mixed-I mode, mixed-II mode, and mixed-III mode. Both wing cracks initiated from flaw outer tips and anti-wing cracks generated from flaw inner tips were classified as a tensile mode or mode-I, dominated by normal relative displacement. In contrast, the secondary cracks were categorized as either shear mode or mode-III, which are dominated by tangential relative displacement. The geometry configurations of flaws affected both the coalescent mode and cracking path, which in turn influenced the failure mode of specimens. This study identified and summarized eight types of coalescent modes between double flaws. The findings presented in this paper contribute to a better understanding of the failure behavior of rock masses containing flaws subjected to compressive-shear loads.