Effect of Defects on Uniaxial Compressive Strength and Point Load Strength for Rock

Uniaxial compressive strength (UCS) and point load strength (PLS or Is(50)) are fundamental mechanical parameters in rock engineering. Investigating the relationship between UCS and PLS is also one of the important research contents in rock mechanics, however, the relationship is usually complex and changeable. This paper explains the complex relationship between UCS and PLS by considering defects that exist in natural rocks. In this study, 48 cylindrical specimens with varying sizes (diameters) and positions of spherical defects were constructed. The impact of these defects on UCS, PLS, crack propagation, and ratio between UCS and PLS were analyzed through numerical tests. The study revealed that both the UCS and PLS decreased with the diameter of defects increased. The positions of defects have an impact on PLS, but not on UCS. Additionally, both the diameter and position of defects affected crack propagation. The ratios between UCS and PLS (initial value 22.28) may vary (from 9.06 to 40.02) depending on the size and position of defects, but remain small when the defect diameter is less than 10 mm. The study also revealed that defects in rock contribute to the complex relationship between UCS and PLS.