"The Bureau of Mines, under a cooperative agreement with Callahan Mining Corp., measured rock displacement at the 4,750-ft level of the 5,100-ft-deep rectangular, timbered caladay shaft in northern Idaho. Displacements were measured with multiple-position borehole extensometers installed 4 ft above the face and timber extensometers installed with the timber sets. This report presents the displacement data along with preliminary, qualitative observations of rock behavior. The measured displacements showed an instantaneous response to shaft sinking and significant time dependency. The relative magnitudes of displacement measured at the shaft walls were heavily influenced by local geologic structure and distance from the shaft bottom." - NIOSHTIC-2

NIOSHTIC no. 10005852

National Institute for Occupational Safety and Health