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|Since Vicat in 1833, the width to height ratio of a mine pillar has been taken as the fundamental variable in pillar design. From work in the laboratory by many investigators testing rock, Coal and concrete samples, it has been concluded by some that pillars with a width to height ratio of 10 to 1 are indestructible. It has also been concluded that a constrained core exists within the pillar which increases the pillar strength. The role of the roof and floor, if mentioned at all, is often noted in an incidental way. In the present work on laboratory testing of model pillars on concrete, coal, and rock instrumented with special strain gages, it was concluded that the end constraint and not the width to height ratio is the significant variable in determining the pillar strength. In tests where the end constraint is steel, a large compressive stress is produced on the horizontal plane of the pillar, and this effect increases as the width to height ratio is increased, resulting in an increase in pillar strength. If the end constraint is not steel but something with a small Young's modulus, the state of stress in the horizontal plane may be tensile, increasing as the width to height ratio increases, resulting in a decrease in pillar strength. Related to mining, the results are that a large width to height ratio pillar is strong for strong roof and floor and weak for weak roof and floor. That is, the roof and floor and not the width to height ratio determine the pillar strength. The confined core condition should be verified by testing if large pillars are to be used. If there is no confined core or the pillar is in tension, smaller pillar sizes should be used. The final conclusion is that the geometry alone is meaningless in pillar design.|
Additional chapters/articles from the SME-ICGCM book Proceeding of the Fourth Conference on Ground Control in Mining (ICGCM)
|Truss Bolting On-Cycle in Jane Mine Lower Freeport Seam||Design Of A Roof Truss Bolting Plan For Bear Mine||Tension-Torque Relationship For Mechanical Anchored Roof Bol||A Novel System For Automatic Installation Of Cement Grouted||Load Transfer Mechanics In Fully-Grouted Roof Bolts||An Investigation Of Longwall Pillar Stress History||Impact Of Horizontal Load On Shield Supports||Interaction Between Roof And Support On Longwall Faces With||Roof Control With Polyurethane For Recovery Of Kitt Energy?s||First Caving And Its Effects--A Case Study||Staubbekampfung An Schildausbau In Bruchbaustreben (Combatin||Yield Pillar Applications--Impact On Strata Control And Coal||Constraint Is The Prime Variable In Pillar Strength||Massive Pillar Failure--Two Case Studies||Investigations Of Underground Coal Mine Bursts||Destressing Practice In Rockburst-Prone Ground||Statistical Characterization Of Coal-Mine Roof Failure: Sugg||Pillar Design - Continuous Miner Butt Section And Longwall D||Design Factors In Near-Seam Interaction||Remote Sensing For Roof Control And Mine Planning: An Overvi||Design, Construction And Performance Of A Single Pass Lining||Computer Modelling And In Situ Instrumentation Techniques: A||A Sonic Wave Attenuation Technique For Monitoring Of Stress||The Radio Imaging Method (RIM) -- A Means Of Detecting And I||Clay Veins: Their Physical Characteristics. Prediction, and||Evaluation of the Point Load Strength for Soft Rock Classifi||Ground Control Experiences in a High Horizontal Stress Field||Horizontal Stresses and Their Impact on Roof Stability at th||Ground Control Problem Associated with Longwall Mining of De||Geotechnical Aspects of Subsidence over Room and Pillar Mine||Proposed Criteria for Assessing Subsidence Damage to Surface||Surface Subsidence. in Longwall Mining--A Case Stud||An Integrated Approach to the Monitoring and Modeling of Gro|