In situ Stress at the Lucky Friday Mine (In Four Parts): 1. Reanalysis ofOvercore Measurements from 4250 Level

摘要

U.S. Bureau of Mines researchers reviewed an in situ stress investigationconducted in 1979 at a test site on the 4250 level of the Lucky Friday Mine, Mullan, ID. Although the field measurements of overcore strain were found to be useful, significant deficiencies were found in the stress field estimation procedure. The stress field estimate was then updated to incorporate recent progress in statistical capabilities and new understanding of doorstopper cell stress concentration factors, as well as to correct an error in the original stress solution procedure. Simple models were used to exmaine the possibility that systematic variations in material properties and stress fields existed at the site. These models succeeded in reducing the sum of squared error somewhat, but fell short of completely describing stress variations throughout the test site. This overcore measurement will be supplemented by two others in the second and third reports of this series, and other observations of stress field characteristics in the fourth report. The final report will also characterize the natural in situ stress field in the vicinity of the Lucky Friday Mine.