19th U.S. Symposium on Rock Mechanics (USRMS),
Permission to Distribute - American Rock Mechanics Association
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A method is described for determining total stresses and mining-induced displacements around openings in a tabular orebody. In the boundary element formulation of the solution procedure, each excavation is divided into a number of rectangular segments, and distributions of various types of singularities are imposed over the segments to produce traction-free conditions on the boundary elements representing the excavation surfaces. The method of analysis and the singularities used exploit the parallelism and proximity of the boundaries of excavations in a tabular orebody, while the distributions of singularities imposed on segments take account of optimum distributions suggested by previous two-dimensional analysis of tabular orebody extraction. Stresses and displacements around a disc-shaped crack, calculated from an analytical solution for this problem, are compared with the results for the same problem calculated with the boundary element program, to demonstrate the validity of the solution procedure. Analysis of other excavation geometries, and comparison with results from independent three-dimensional analyses of these excavation shapes, indicate that the method of analysis is satisfactory for openings where the span/height ratio is greater than 5.
The mining of tabular or lenticular orebodies typically generates openings whose dimensions in the plane of the orebody are much greater than the thickness or the stratigraphic width of the orebody. For mining methods such as open stoping or cut-and-fill stoping in inclined tabular orebodies, or room and pillar mining in flat lying deposits, pillar support is designed to control mining--induced displacements in and around the mining area. Economic design of pillar support implies leaving the minimum amount of pillar support consistent with achieving stability of the country rock. Alternatively, if temporary pillar support is to be removed, the problem may be to determine the most acceptable stress path, of a number of alternatives, to satisfy various operational requirements.
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