Mining in a Lateral Stress Field at White Pine
Jack Parker Senior Mine Research Engineer, White Pine Copper Company, Subsidiary of Copper Range Campany, White Pine, Michigan.
The original design of mine open ings and pillars at White Pine was based upon traditional assumptions; i.e., that the principal load is due to the weight of overburden, and that horizontal stresses are equal to one- . third of the vertical. Beginning January, 1964, borehole deformation measurements confirmed suspicions that the principal stress is horizontal and several times greater than the vertical. Vertical stress appears to be directly related to depth, but lateral stresses vary considerably in direction and magnitude. The direction of major principal stress lies parallel to the bedding and is apparently parallel to tension joints. Lateral stresses appear to originate from an igneous intrusive. Mining induces stresses which add to the primitive stresses, in some areas precipitating failure. In this paper, rock failures are illustrated, methods of measurement and typical results are given, and measures to counter or utilize the lateral stresses are described.
Failure, failures, Lower Shale, rock mechanics, U.S. Bureau of Mines, Upper Sandstone, White Pine, Mine, Mines, pillar, Pillars, Rocks, stress