The theory of critical distances applied to fracture of rocks with circular cavities

Abstract

This work presents experimental and theoretical analyses of the fracture behavior of different rocks containing circular holes subjected to uniaxial compressive uniform loads. The experimental critical loads are compared with those derived from the Theory of Critical Distances (TCD) and finite element simulations. The rocks being analyzed are Floresta sandstone, Moleanos limestone, Macael marble and Carrara marble. They were previously characterized under compressive and tensile conditions, obtaining their corresponding Poisson's ratios, Young's moduli and ultimate tensile and compressive strengths. Besides, their fracture properties, specifically their fracture toughnesses and critical distances, were also available from a previous experimental campaign on Single Edge Notched Beam specimens with different notch radii and tested under 4-point-bending conditions. In this paper, prismatic specimens (9 per each type of rock) containing a cylindrical cavity at their center were uniaxially compressed until failure. The fracture pattern was revealed and agrees with previously published cases. The TCD, specifically the Point Method, was applied with the aim of comparing the corresponding fracture load predictions with the experimental ones. Three-dimensional finite element analyses were used to calculate the stress fields. The application of the TCD on the Floresta sandstone and the Moleanos limestone provides reasonable predictions of fracture loads, given their linear-elastic behavior. For the two studied marbles, the resulting predictions are overly conservative despite their quasi-brittle behavior. This may be attributed to complex process zones with intense microcracking that are revealed as white patches prior to failure and generate dust and small fragments after failure.