Asymmetric borehole breakouts at the URL

Investigations into borehole breakouts in brittle rock usually treat the phenomenon as a two-dimensional problem. In these cases, failure is assumed to initiate at the point of maximum tangential stress concentration at the borehole wall. According to linear elastic theory for a circular hole in an elastic medium, the maximum stress concentrations around the hole are diametrically opposed for anisotropic far-field stress conditions. At the 420 Level of the URL, boreholes drilled at angles not coincident with a principal direction typically developed breakouts that were asymmetric, or not diametrically opposed. Numerical modeling of two large-diameter boreholes demonstrates that the asymmetry in azimuth and…