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Pillar failure analysis and in situ stress determinations at the Fletcher Mine Near Bunker, Missouri.

Authors
Horino-FG; Aggson-JR
Source
NTIS: PB 279 705, 1978; :1-19
Link
NIOSHTIC No.
10007834
Abstract
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.
Keywords
Mining-industry; Rock-mechanics; Compression-tests; Structural-analysis; Laboratory-testing; Ground-control; Ground-stability; Failure-analysis; Gravitational-forces
Publication Date
19780101
Document Type
IH; Report of Investigation
Fiscal Year
1978
NTIS Accession No.
PB-279705
NTIS Price
A03
Identifying No.
RI 8278
NIOSH Division
DRC
Source Name
NTIS: PB 279 705
State
MO; CO
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