In Situ Determination of Rock Behavior by Overcore Stress Relief Method, Physical Property Measurements, and Initial Deformation Method.
This Bureau of Mines report describes the fieldwork and subsequent analysis to determine physical properties, stress distribution, and several aspects of rock behavior as a necessary evaluation for a typical mine opening. All work was done at a test site on the 3300 level, Crescent Mine, Coeur d'Alene Mining District, Idaho. Free field stress beyond the influence of the opening was also determined. Conventional overcore technique with the three- component borehole deformation gage developed by the Bureau of Mines was used in three drill holes. Three field verification tests were performed using a gage newly developed by the Spokane Mining Research Center in an approach herein termed "initial deformation method." Use of this method validated that aspect of overcore theory which predicts that similar deformation effect occurs in the wall rock around the perimeter of an opening in rock under stress. Also described are all drilling procedures and performances.