An experiment using the rings of 34 mm in thickness

50 mm in external diameter

and 8-30 mm in internal diameter was designed via the ring test

to analyze the stress characteristics around the hole. Strain gauges were used to record the strain changing around the hole during the test

and the mechanical properties of specimens were studied. The results indicate that the peak load of the specimens decreases with the increase of internal diameter. Both the discs and ring specimens with relatively small internal diameters have abrupt failure when they reach the first peak load. However

when the diameter is greater than 16 mm

there is no clearly defined stress drop after the first peak stress

but a distinct stress drop after the second peak stress is reached. The stress at the weakest point in the ring specimen is a structural parameter rather than a material parameter

and it changes with different internal diameters. The Hobbs’ equation based on elastic mechanics may not be suitable for determining the tensile strength of rock. Rock specimen needs adequate tensile deformation to fail until it reaches the limit stress. The failure of the borehole in the rock may be evaluated by the tensile deformation instead of tensile strength. The results provide important reference for mechanical characteristics of rock under compression-tension stresses.