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|The depletion of thicker coal reserves has resulted in the thinner seams being economically attractive. Surface protection against subsidence limits the extraction ratio to 50% for the room and pillar method as a "no subsidence condition". That rule was developed for pillars with smaller width/height ratio because seams mined at the time were commonly 6 feet thick. Over time pillar ribs deteriorate around the pillar perimeter and thus decrease the area of the pillar. Using 50% extraction as the no subsidence condition in the squat pillar category (below 42 in with w/h > 7) causes unnecessary losses of reserves because squat pillars are stronger. In this paper a method is presented for design of long-term pillars. Based on the analysis of pillar deterioration and field observations, an increase of the "no subsidence" extraction rate to 60% for squat pillars is proposed.|
Additional chapters/articles from the SME-ICGCM book Proceedings 20th International Conference On Ground Control In Mining
|Hydraulic Fracturing Of Sandstone And Longwall Roof Control||Status Of Longwall Research In CSIRO||Longwall Moves At Twentymile Recovery Mesh System||Risk Assessment Of Geotechnical Factors Associated With Unde||Load And Deflection Response Of Ventilation Stoppings To Lon||The Stress And Failure Paths Followed By Coal Mine Roofs Dur||Simulated Materials Modeling And Analysis Of The Overburden||Sizing Of Final Stumps For Safer Pillar Extraction||Evaluation Of Mobile Roof Support Technologies||FDM Prediction Of A Yield Pillar Performance In Conjunction||Extraction Ratio In Thin Seams Assuring No Surface Subsidenc||Improving Roof Control At A South African Coal Mine||In-Situ Investigation Into The Causes Of Falls Of Roof In So||Failure Characteristics Of Roof Falls At An Underground Ston||Determination Of Limitation Of Roof Layer Separation (LRLS)||The Integration Of Geology And Engineering In Ground Control||Worldwide Implementation Of Continuous Miner System - Integr||Effect Of Face Advance Rates On The Characteristics Of Subsi||The Response Of A High Order Stream To Shallow Cover Longwal||SDPS For Windows: An Integrated Approach To Ground Deformati||Development Of A Remote Reading Dual-Height Telltale System||Enhanced Surface Control For Roof And Rib Support||Long Term Stability Of Mine Workings In Soft Floor Environme||Visualization Of Geostructure By Mechanical Data Logging Of||A Step Towards Understanding The Behaviour Of Wider Roadways||Research And Application Of Combined Reinforcement System||Estimation Of In-Situ Stress At Ikeshima Colliery Using AE A||Typical Complete Stress-Strain Curves Of Coal||Analysis Of Roof Bolt Systems||Effects Of Bedding Plane Sliding And Separation And Tensione||Systems Used In Coal Mining Development In Long Tendon Reinf||Determination And IT-Supported Evaluation Of Rock Mechanical||Tensioned Cable Bolts As Primary Support: Update||Determination Of Basis For The Double Use Of Rectangular Roc||Cost Preventive System To Control Unstable Roof In Main Line||Injection Techniques for Cost-effective Stabilization of Bri||An Analysis of Rock Failure Around a Deep Longwall Using Mic||Numerical Simulation on Microseismicity Due to Mining at One||Investigation of Seismicity Near Appin, NSW, and its Associa||Effects of Bolt Spacing, Bolt Length, and Roof Span on Bolt||Evaluation of Instrumented Cable and Rebar Bolts as Ground S||Application of the Coal Mining Roof Rating System in South A||Roof Instability Rating (RIR) System and Its Application at||Updating the NlOSH Support Technology Optimization Program (||Mistakes, Misconceptions, and Key Points Regarding Secondary||Non-Destructive Testing on Fully Grouted Rockbolts||Visual Recognition of the Load of Roof-Bolts by an Indicator||A New Rockbolt Axial Load Measuring Device||A New Approach to the Integrity Testing of Ground Anchorages||A Lineament Analysis Case Study of the Fola Coal Co., LLC. N||Analyses of Valley Fill Slope Stability - Three Case Studies||Modeling of Joint and Fracture Distributions in Rock Mass Be|