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Field measurement of rock displacement and support pressure at 5,955-ft level during sinking of deep circular shaft in northern Idaho
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1984
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Description:"The Bureau of Mines, under a cooperative agreement with Hecla Mining Company, is conducting a rock mechanics study of the 6,200-ft-deep circular, concrete-lined silver shaft in northern Idaho. The objective of the project was to instrument and evaluate lining behavior and rock deformation when a deep shaft is constructed in a high in situ stress field and anistropic rock mass. Rock mass displacements were monitored with multiple-position borehole extensometers. Liner stress and strain were measured with concrete pressure cells and embedment strain gauges. Field data from the 5,955-ft test level show that rock displacement is controlled by rock mass anisotropy. Liner stress and strain levels reflect the high in situ stress field as well as nearby station and raise construction. Maximum stresses measured in the lining, as a result of shaft excavation, are about one-third of its compressive strength. Continued monitoring and preliminary analysis of the data indicate that concrete-lined, circular shafts are stable for the high, unequal horizontal stress fields and rock anisotropy encountered in deep-level mining." - NIOSHTIC-2
NIOSHTIC no. 10004148
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