In Situ Stress Assessment Based on Width and Depth of Brittle Borehole Breakouts

Book chapter, 2020

Borehole breakouts, as well as breakouts in tunnels and shafts, are a common occurrence, especially under high in situ stresses or stress states with high deviatoric component. Though they can pose a risk to stability, often they are of use, especially in deep boreholes, as they can help to determine to a certain extent the primary in situ stress. Observations have shown that while their depth evolves, their width remains constant. Currently the width only is used in conjunction with the Kirsch analytical solution to establish a linear relationship between the two in plane principal primary stress components. The stress state cannot be fully determined since one equation is available (failure criterion) for two unknowns. A recently proposed numerical tool based on conformal mapping is used in this work to simulate the formation of shear breakouts and investigate the feasibility of the determination of both principal primary in situ stress components, by making use of both the depth and the width of the breakout. Concluding, recommendations are provided for the use of the proposed methodology and limitations of its applicability are discussed.