ABSTRACT: During deep tunneling or mining infrastructure development, the assumed stress state has significant implications on geomechanical design. Remote measurement of the three-dimensional stress state at depth has proven to be a significant challenge and is often assumed using historic tests or implied from the regional tectonic setting. To date, borehole breakout analysis has provided some assistance for the orientation of the stress field, although very little has been done to correlate breakout with stress magnitude. This paper proposes a methodology of predicting stress from acoustic televiewer surveys of breakout geometry. Data from two boreholes at KGHM's Victoria Project in Sudbury, Canada are used to demonstrate the methodology. From material testing and breakout shape characterization, a continuum based, numerical back analysis of breakout was done through the creation of a generic database of stress dependent numerical models. When compared with the in situ breakout profiles, stress magnitudes were estimated as a function of depth along each hole. Results of this analysis relate well in terms of both magnitude and orientation of stress, as compared to other measurements within the Sudbury mining district and regionally throughout the Canadian Shield.
1. INTRODUCTION
In the field of geomechanics, one of the most important considerations during design is the state of stress that exists at the location of a project. Despite this, stress is often the most poorly understood site characteristic, given the current challenges in accurately measuring it. This stems from the fact that stress can't be directly measured, but must be inferred by disturbing the rockmass and recording its response. Although some methods do exist for the prediction of in situ stress, this only provides a point estimate and is often plagued with uncertain results and practical limitations in the field. This is of particular importance as mining companies look to develop deeper and more technically demanding deposits. In these high-risk settings, being able to predict the magnitude of overbreak or ore dilution has direct ramifications throughout a mine's life, from pre-feasibility mine design studies all the way through to site reclamation.
