True uniaxial compressive strengths of rock or coal specimens are independent of diameter-to-length ratios
This paper reports that part of the compressive strength of a test specimen of rock or coal in the laboratory or a pillar in a mine comes from physical property strength and, in part, from the constraint provided by the loading stresses. Much confusion in pillar design comes from assigning the total strength change to geometry, as evidenced by the many pillar design equations with width to height as the primary variable. In tests by the U.S. Bureau of Mines, compressive strengths for cylindrical specimens of limestone, marble, sandstone, and coal were independent of the specimen test geometry when the end friction was removed. A conventional uniaxial compressive strength test between two steel platens is actually a uniaxial force and not a uniaxial stress test. The biaxial or triaxial state of stress for much of the test volume changes with the geometry of the test specimen. By removing the end friction supplied by the steel platens to the specimen, a more nearly uniaxial stress state independent of the specimen geometry is produced in the specimen. Pillar design is a constraint and physical property problem rather than a geometry problem. Roof and floor constraint are major factors in pillar design and strength.
- Research Organization:
- Air Force Cambridge Research Center, MA (United States)
- OSTI ID:
- 5790773
- Report Number(s):
- RI-9316
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COAL
COMPRESSION STRENGTH
COAL MINES
PLANNING
SCALE MODELS
SUPPORT PILLARS
DESIGN
CALCULATION METHODS
RESERVOIR ROCK
ROOF BOLTS
STRESS ANALYSIS
CARBONACEOUS MATERIALS
ENERGY SOURCES
EQUIPMENT
FOSSIL FUELS
FUELS
MATERIALS
MECHANICAL PROPERTIES
MINES
MINING EQUIPMENT
STRUCTURAL MODELS
UNDERGROUND FACILITIES
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