Location

New York, New York

Session Start Date

4-13-2004

Session End Date

4-17-2004

Abstract

Area 1 of Doe Run Company’s Buick North Mine was selected for placement of cemented rockfill (CRF) to “trap” or encapsulate select pillars. This method of “trapping” pillars takes advantage of the passive confinement effect of CRF to increase the post-peak load bearing ability of trapped pillars so that other ore bearing pillars can be extracted while still maintaining local and global mine stability. A total of 73 pillars in this area were extracted from October 1998 thru January 2002. Thirteen of 73 pillars were totally trapped by CRF (i.e., the pillars were totally encased in CRF). Eight of the thirteen pillars trapped with CRF were instrumented with extensometers to monitor deformations that occurred during the extraction process. Of the remaining pillars, 18 were not confined in CRF; and the remaining pillars were partially trapped to some degree (one or more free faces). Data collected from the instruments showed that the rate at which pillars deformed (or converged) slowed and that most of the instrumented pillars were virtually unaffected until the late stages of pillar extraction. Two of the instrumented pillars showed considerable initial vertical strain at the onset of pillar extraction. The rate at which these pillars converged slowed as additionally pillars were extracted. This was attributed to the passive confinement effect of CRF in which this material compacts (the density increases) as the pillar dilates, becomes stiffer, and thus provides an increase in confining pressures or stress that acts to restrict pillar dilation. This study has provided valuable insight into the behavior of trapped roof supporting pillars during the extraction process. Future research is being undertaken to clearly develop procedures to predict the behavior CRF trapped pillars during extraction of other economically valuable pillars.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fifth Conference

Publisher

University of Missouri--Rolla

Publication Date

4-13-2004

Document Version

Final Version

Rights

© 2004 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 13th, 12:00 AM Apr 17th, 12:00 AM

Use of Cemented Rock Fill for Enhanced Pillar Recovery in Area 1 of the Doe Run Company

New York, New York

Area 1 of Doe Run Company’s Buick North Mine was selected for placement of cemented rockfill (CRF) to “trap” or encapsulate select pillars. This method of “trapping” pillars takes advantage of the passive confinement effect of CRF to increase the post-peak load bearing ability of trapped pillars so that other ore bearing pillars can be extracted while still maintaining local and global mine stability. A total of 73 pillars in this area were extracted from October 1998 thru January 2002. Thirteen of 73 pillars were totally trapped by CRF (i.e., the pillars were totally encased in CRF). Eight of the thirteen pillars trapped with CRF were instrumented with extensometers to monitor deformations that occurred during the extraction process. Of the remaining pillars, 18 were not confined in CRF; and the remaining pillars were partially trapped to some degree (one or more free faces). Data collected from the instruments showed that the rate at which pillars deformed (or converged) slowed and that most of the instrumented pillars were virtually unaffected until the late stages of pillar extraction. Two of the instrumented pillars showed considerable initial vertical strain at the onset of pillar extraction. The rate at which these pillars converged slowed as additionally pillars were extracted. This was attributed to the passive confinement effect of CRF in which this material compacts (the density increases) as the pillar dilates, becomes stiffer, and thus provides an increase in confining pressures or stress that acts to restrict pillar dilation. This study has provided valuable insight into the behavior of trapped roof supporting pillars during the extraction process. Future research is being undertaken to clearly develop procedures to predict the behavior CRF trapped pillars during extraction of other economically valuable pillars.