Experimental and Analytical Investigations of the Effect of Hole Size on Borehole Breakout Geometries for Estimation of In Situ Stresses

Borehole breakout is a natural phenomenon in boreholes drilled in rock due to the induced stress concentration. Many researchers have attempted to correlate this phenomenon with in situ stress magnitudes. In this paper, a series of true triaxial tests on sandstone blocks (120 × 120 × 120 mm3) with different diameter pre-drilled holes have been carried out. Results confirmed that breakout geometries (angular span and depth) are dependent on the...