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Hard rock pillar strength estimation an applied empirical approach Lunder, Per John
Abstract
Pillars are present in all hard rock mining operations and in order to effectively design these pillars, an estimate of the pillar strength is required. Two new pillar strength estimation methods for hard rock mine pillars are presented in this thesis. 31 pillar case histories of the database that was used to develop these new formulae were acquired during a cooperative study, entitled “Ground Stability Guidelines for the Extraction of Barrier Pillars in Hard Rock Mines”, between Westmin Resources Ltd. and The Canadian Centre for Mineral and Energy Technology (CANMET). 147 additional case histories were acquired from six documented hard rock pillar case studies in the literature, resulting in a combined database of 178 case histories. The combined database is comprised mainly of massive sulphide pillars with rock mass ratings of between 60% and 85%. Major structural features were not deemed to be an influence in pillar instability. Pillar stressess were calculated using either tributary area theory or numerical modelling methods. The factors determined to influence pillar strength for the combined database therefore are: • the average pillar confinement (which is a function of pillar geometry) • the unconfined compressive strength of the intact pillar material • the stresses that a pillar is subjected to The degree to which a pillar has failed is quantifiable using a pillar stability classification index which ranges from “1” (stable) to “5” (failed). The estimation of pillar stresses is preferably determined using threedimensional numerical modelling, but in some situations two-dimensional numerical modelling or tributary area theory may provide adequate results. It was concluded that the full size unconfined compressive strength of a pillar can be approximated by a strength size factor of 44 percent of the small scale unconfined compressive strength of intact pillar material. Two pillar strength formulae have been developed from the combined pillar database: “The Log-Power Shape Effect Formula” and “The Confinement Formula”. Both of the methods utilize the average pillar confinement. “The Log-Power Shape Effect Formula” is a refined shape effect formula which has a form similar to that proposed by researchers in the past. “The Confinement Formula” has a form that resembles the Mohr-Coulomb shear strength formula. The combined database was analyzed and the predicted strengths from “The Confinement Formula” was compared to the results for existing pillar strength methods (Hedley & Grant (1972), Bieniawski (1975), Salamon & Munro (1967), Obert & Duvall (1967), Hoek & Brown (1980)). “The Confinement Formula” is shown statistically to be the most reliable method of estimating the strength of the pillars that make up the combined database.
Item Metadata
Title |
Hard rock pillar strength estimation an applied empirical approach
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1994
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Description |
Pillars are present in all hard rock mining operations and in order to effectively design these pillars, an
estimate of the pillar strength is required. Two new pillar strength estimation methods for hard rock mine
pillars are presented in this thesis. 31 pillar case histories of the database that was used to develop these new
formulae were acquired during a cooperative study, entitled “Ground Stability Guidelines for the Extraction of
Barrier Pillars in Hard Rock Mines”, between Westmin Resources Ltd. and The Canadian Centre for Mineral
and Energy Technology (CANMET). 147 additional case histories were acquired from six documented hard
rock pillar case studies in the literature, resulting in a combined database of 178 case histories.
The combined database is comprised mainly of massive sulphide pillars with rock mass ratings of
between 60% and 85%. Major structural features were not deemed to be an influence in pillar instability.
Pillar stressess were calculated using either tributary area theory or numerical modelling methods. The factors
determined to influence pillar strength for the combined database therefore are:
• the average pillar confinement (which is a function of pillar geometry)
• the unconfined compressive strength of the intact pillar material
• the stresses that a pillar is subjected to
The degree to which a pillar has failed is quantifiable using a pillar stability classification index which
ranges from “1” (stable) to “5” (failed). The estimation of pillar stresses is preferably determined using threedimensional
numerical modelling, but in some situations two-dimensional numerical modelling or tributary
area theory may provide adequate results. It was concluded that the full size unconfined compressive strength
of a pillar can be approximated by a strength size factor of 44 percent of the small scale unconfined
compressive strength of intact pillar material.
Two pillar strength formulae have been developed from the combined pillar database: “The Log-Power
Shape Effect Formula” and “The Confinement Formula”. Both of the methods utilize the average pillar
confinement. “The Log-Power Shape Effect Formula” is a refined shape effect formula which has a form
similar to that proposed by researchers in the past. “The Confinement Formula” has a form that resembles the
Mohr-Coulomb shear strength formula.
The combined database was analyzed and the predicted strengths from “The Confinement Formula”
was compared to the results for existing pillar strength methods (Hedley & Grant (1972), Bieniawski (1975),
Salamon & Munro (1967), Obert & Duvall (1967), Hoek & Brown (1980)). “The Confinement Formula” is
shown statistically to be the most reliable method of estimating the strength of the pillars that make up the
combined database.
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Extent |
6969648 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-03-03
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0087520
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1994-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.