Evaluation of rock pillar failure mechanisms under uniaxial compression: impact of joint number and joint angle

Experimental and discrete element methods were used to investigate the effects of joint number and joint angle on the failure behavior of rock pillars under the uniaxial compressive test. Gypsum samples with dimensions of 200 mm x 200 mm x 50 mm were prepared. The model material had a tensile strength of 1 MPa. Embedded notches with a length of 6 cm were utilized within the samples to determine its compressive strength. In constant notch length, the number of notches was one, two, and three. In the experimental test, the angle of the diagonal plane related to the horizontal axis was 0 degrees, 30 degrees, 60 degrees, and 90 degrees. In the numerical test, the angles of the diagonal plane related to the horizontal axis were 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees. The axial load was applied to the model at a rate of 0.05 mm/min. The results show that the failure process was mostly governed by both the non-persistent notch angle and notch number. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behavior of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the notch angle. The strength of samples increases by increasing both the notch angle and notch number. The failure pattern and failure strength are similar in both methods, i.e., the experimental testing and the numerical simulation methods.