Knowledge of the in situ stress state is critical for underground rock engineering projects, but direct measurement data are often not available. Although borehole breakouts are only indicative of the in situ stress state, they nevertheless represent a significant data resource. Properties such as breakout orientation, width and depth can all potentially be used to constrain the in situ stress state. In this paper, we present a novel global optimization and associated objective function that uses breakout data to constrain the normalized in situ stress tensor. This tensor is one in which the magnitudes of the three principal stresses are normalized with respect to the difference between the maximum and the minimum principal stresses, and three Tait–Bryan angles describe the principal stress orientations. The efficacy of the scheme is demonstrated by applying it to breakout data obtained from deep mining operations in the Sudbury mining district of Ontario, Canada.
In situ stress is necessary information for the design and construction of underground rock engineering projects. Borehole breakouts are stress-induced borehole diametrical elongations that occur when the induced stress exceeds the local rock strength on the borehole wall. These can be identified and are a potential data source to estimate the in situ stress state.
Due to the high cost and time-consuming process of direct measurement methods, necessary in situ stress data is often not available in most projects. Given the widespread and increasing use of Acoustic Televiewer (ATV) technology to survey boreholes, large amounts of borehole breakout data are available which are indicative of the in situ stress state. Borehole breakout orientation is widely used to estimate the orientations of horizontal principal stresses (Plumb & Hickman 1985; Zoback et al. 1985), but this requires the assumption that one of the principal stresses is vertical. However, this assumption is not valid in many locales, and breakout data are rarely used to estimate in situ stress magnitudes.
