Pillar Failure Analysis and In Situ Stress Determinations at the Fletcher Mine Near Bunker, Missouri

Details

• Personal Author:
  Aggson JR ; Horino FG
• Description:
  A rock mechanics program (composed of laboratory and field tests) was initiated by the Bureau of Mines in an effort to determine the causes of pillar instability at the Fletcher Mine, near Bunker, Missouri. Compressive strength, young's modulus, shear strength, and the angle and coefficient of internal friction were determined on drill cores obtained from 16 different locations in the mine. Results of the laboratory tests showed that highly mineralized zones and brecciated zones in pillars could significantly affect pillar strengths and stability in locations where extraction ratios exceeded the normal design ratio of approximately 78%. High-angle fractures that were present in some locations also may have contributed to pillar deterioration. In the field tests, in situ stress determinations were made in one pillar to establish the pillar-loading conditions and to evaluate the stability of the pillar. Continued monitoring of stresses in the pillar showed a gradual decrease in compressive stress, indicating that the pillar was probably in the postfailure state. A second stress determination was made in a vertical hole in the underlying igneous rock that was exposed on one section of the mine. Horizontal stresses were compressive and larger than would be expected from gravity loading. [Description provided by NIOSH]
• Subjects:
  Laboratories Mining Occupational Health Safety
• Keywords:
  Mining-industry; Rock-mechanics; Compression-tests; Structural-analysis; Laboratory-testing; Ground-control; Ground-stability; Failure-analysis; Gravitational-forces
• Series:
  Mining Publications
• Subseries:
  Report of Investigations
• Document Type:
  Text
• Genre:
  Conference Publications ; Case Report
• Place as Subject:
  Colorado ; Missouri ; OSHA Region 7 ; OSHA Region 8
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DRC - Denver Research Center
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-19
• NIOSHTIC Number:
  nn:10007834
• NTIS Accession Number:
  PB279705
• Citation:
  NTIS: PB 279 705, 1978; :1-19
• Federal Fiscal Year:
  1978
• Peer Reviewed:
  False
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:65b84d2081e99928ca95c33fded7cd719145f8063bde430e85d993b23c323f83303c755c8ffaa6609e771c8299c67e15c2c6e716b7c2570a7cde6df47f074180
• Download URL:
  https://stacks.cdc.gov/view/cdc/237136/cdc_237136_DS1.pdf
• File Type:
  [PDF - 7.06 MB ]