Assuring ground control safety in many mining and tunneling projects depends, at least in part, on an understanding of in situ stress conditions that will be encountered. Yet it is rarely practical to conduct more than a very limited number of stress measurements. Stresses along the route of a proposed excavation are typically interpolated from available measurements, often assuming a linear variation of stress with depth (or elevation). However, projects where multiple stress measurements are conducted often report more complex variations of in situ stress, usually in apparent relationship to geologic structures. These structures often include lithologies of contrasting elastic properties. A method is proposed for estimating stresses in these cases by first back-calculating regional loads from available stress measurements and then modeling the distribution of stress throughout the rock mass. The method has been successfully applied to a set of in situ stress measurements from the Coeur d'' Alene Mining District of northern Idaho, USA. Results provided new insights into district stress conditions and the distribution of rockburst hazards along mine drifts and between various mines. This success should transfer readily to suitable deep tunneling projects.
The safety of miners is too often compromised by failures of ground through any of a number of mechanisms, most of which are influenced by the state of in situ stress. Thus, a better understanding of how in situ stress varies and how these variations control the location and severity of hazards was sought as part of a research program conducted by the Office for Mine Safety and Health of the National Institute for Occupational Safety and Health (NIOSH). The proposed method for modeling in situ stress variation described in this paper is one product of this program.
