ICGCM Papers:
Pillar Design Workshop
 
 
Numerical Modeling of Yielding Chain Pillars in Deep Longwall Coal Mines
Pillar Mechanics Workshop Proceedings 2010
Numerical Modeling of Yielding Chain Pillars in Deep Longwall Coal Mines
by
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Ugur Ozbay, Professor Mining Engineering Department Colorado School of Mines Golden, CO Salah Badr, Associate Professor Mining Engineering Department King Abdulaziz University Jeddah, Saudi Arabia
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[Book] Pillar Mechanics Workshop Proceedings 2010
[Topical Area] Pillar Design Workshop
[Author] 
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Ugur Ozbay, Professor Mining Engineering Department Colorado School of Mines Golden, CO Salah Badr, Associate Professor Mining Engineering Department King Abdulaziz University Jeddah, Saudi Arabia
[Abstract] 
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This paper describes a numerical modeling methodology developed for investigating the behavior of yielding of chain pillars in deep longwall coal mines. The methodology is based on first calibrating the material properties of coal using an isolated pillar model and then translating the results to a deep two-entry longwall mine that uses yielding chain pillars. The calibration study results are validated against the commonly used empirical pillar strength formulae and published results of in situ coal pillar tests. A closer analysis of the calibration results show sudden cohesion drops within a region of about 1 to 1.5 mining height distance from the pillar sides as the width to height ratio of these pillars increase beyond 4. The longwall model incorporates two 240 m wide 1,000 m long panels at a depth of 600 m. The coal seam is modeled as a strain softening material to observe its response to loading in both pre- and post-peak states. The model allows monitoring of a width – height ratio 4 chain pillar responses while being subjected to development, headgate, and tailgate loading stages. Full stressstrain behavior of these pillars show that failure initiates within pillar sidewalls under development loading. During headgate loading, the failure propagates further into the pillar and initiates a stable yielding of the pillar. At the time of tailgate loading, the pillar is already in its residual strength state. The validity of the modeling methodology is discussed by comparing the results against the in situ stress measurements taken in an actual longwall mine with similar conditions.