A full-scale test stope was excavated at the Carr Fork Mine in the early 1980''s (Pariseau et al. 1984). Correlations between measured displacements in borehole extensometers and two-dimensional finite element model estimates were high, R2 over 0.8. These data were short-time estimates corresponding to readings made shortly after each blast. However, some readings more than doubled during the three weeks or so between blasts indicating a significant time effect. A three-dimensional retrospective analysis using an elastic- viscoplastic model indicates the time effect is more complicated than this traditional time-dependent plasticity model. Correlation analogous to the original short-time computations also gave an R2 over 0.8. Regression analyses of two- and three-dimensional calculated extensometer readings on actual time-dependent readings resulted in R2 of 0.6. Reasons for lack of a higher correlation are unclear, but suggest an alternative time-dependent model may be needed.
1 INTRODUCTION This contribution revisits a case study Geomechanics of the Carr Fork Mine Test Stope (Pariseau et al. 1984) with the objective of gaining a better understanding of the noticeable time-dependent behavior of the rock mass that was observed during test stope mining. Copper was the main metal of interest at the mine and occurs mainly as chalcopyrite in a contact metamorphic environment. The mine was scheduled for 10,000 stpd. Location of the mine is shown in Figure 1. Figure 2 is a schematic drawing of mine development. The mine was "metric"; levels are elevations above sea level in meters. The test stope was excavated by a vertical bench retreat method (blast hole, post-fill). Test stoping was the only activity in the mine during the study, so instantaneous effects of face advance and subsequent time-dependent motion were readily distinguished in plots of instrumentation readings versus time. Figure 3 illustrates the test stope geometry.