Mechanical properties and fracture characteristics of pre-holed rocks subjected to uniaxial loading: A comparative analysis of five hole shapes

Abstract

This study systematically investigates the influence of hole shape on mechanical properties and fracture characteristics of rocks containing a hole under uniaxial loading. First, combined with digital image correlation (DIC) and acoustic emission (AE) equipment, quantities of uniaxial compression tests on brittle prismatic sandstone samples containing a circular, inverted U-shaped, trapezoid, rectangular or square hole were conducted to study the strength, deformation and fracture characteristics. After that, the analytical solutions of stress for the five types of holes were derived using complex variable function theory. The experimental results suggest that the mechanical properties of the samples are greatly weakened by the existence of the holes, and the degradation degree depends on the hole shape. The stability order of these holes is ranked as: circle > inverted U-shape > trapezoidal > square > rectangle. According to the formation mechanism and sequence, four types of cracks, namely, primary tensile cracks, slabbing fractures, remote cracks and shear cracks, are formed around all the holes, but the crack sequence, initiation location and propagation characteristics of each hole are slightly different. The variation of AE signals matches well with the fracture evolution. The shear failure mode results from the coalescence of the shear cracks and V-shaped notches. Theoretical analysis shows that crack development mechanism can be well interpreted by the stress distributions around the holes. Moreover, the length of the primary tensile cracks is theoretically solved and compared, which is agreeable with the measured result.