Influence of geologic structures on stress variation and the potential for rockbursting in mines with particular reference to the Lucky Friday Mine, Idaho.

摘要

A numerical modeling procedure is proposed for inferring in situ stress conditions in geologic structures from scattered measurements and numerical stress analyses. Stress analyses are used to estimate the pattern of in situ stress that is induced through a geologic structure for a number of residual, body, and boundary load sources. These patterns are then superposed in a manner that best fits the available stress measurements.; This approach is applied to the problem of evaluating the effect of stress variation on rockbursting in the Coeur d'Alène Mining District of northern Idaho. Deep mines in the district are seismically active and have suffered many damaging and dangerous rockbursts. These mines provided sites for four reliable stress determinations, as well as observations of breakouts in a number of bored raises (circular vertical openings) that indicated horizontal stress directions at these locations.; A simple in situ stress model has been constructed based on large-scale geologic features and overcore stress measurements. Statistical measures show that the resulting model provides a significantly better fit to the available data than previous efforts, all of which have postulated a linear relationship between stress and depth. This model accurately projected breakout orientations at locations far from the stress measurement sites, suggesting that the model is generally applicable to the region and not restricted to the stress measurement sites. Moreover, the model was generally consistent with behavior documented in site studies, indicating that the proposed markers for rockburst hazard are causal, not just coincident, indicators.; This analysis underlines the value of considering how in situ stress might vary through a geologic structure and demonstrates that residual stress can be a significant element of a stress model. Finally, the exercise demonstrates that the proposed method for developing a stress model provides practically useful information and that the resulting model can be generally applicable to geologically complex situations.