Damage Evolution and Infrared Precursory Characteristics of Sandstone Containing Stress-Relief Holes

To investigate how the diameter of stress-relief holes affects the load-bearing capacity and damage evolution of sandstone, intact Qing sandstone specimens and specimens containing holes with diameters of 6, 8, 10, and 12 mm were comparatively evaluated. The relationships between hole diameter and mechanical response were examined using uniaxial compression stress-strain curves, failure photographs, acoustic-emission (AE) ring counts, and energy-evolution curves. The peak strength of the intact specimens was 30.95 MPa, and the peak strengths of the four holed groups were 18.73, 18.68, 17.34 and 15.32 MPa, respectively. The elastic modulus of the undamaged specimen was 4.80 GPa; that of the specimen with a 12-mm hole was 1.60 GPa. The maximum strain of the holed specimen exceeded that of the undamaged specimen, and therefore, a reduction in load-bearing capacity was accompanied by an increase in pre-peak deformation. Failure photographs showed that regions adjacent to the holes participated in the formation of the main cracks; longitudinal cracks, inclined cracks, and branching cracks developed in the holed specimens. AE activity generally intensified with loading, but neither the peak ring count nor the cumulative count varied monotonically with hole diameter. In the latter stages of loading, the energy curves showed decreasing releasable elastic strain energy and increasing dissipated energy. The possible relationship between hole-wall damage and infrared anomalies is discussed, and the dependence of infrared precursors on hole diameter is identified as requiring validation with synchronous temperature-field data. These results provide experimental reference for damage identification in holed sandstone and for evaluating load-bearing constraints in the design of pressure-relief holes.