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|A survey of the longwall industry was conducted to examine the performance of modern shield technology. The results of this survey indicate that state-of-the-art shields perform better and last longer than ever before, but premature failures do still occur. In addition, longwalI operators are now using shields longer than ever before and a greater number of fatigue related failures on aging shields are now occurring. A generic assessment of these shield failures is provided, describing the nature of the failures and how widespread they are throughout the industry. An engineering assessment of shield design and factors that cause shield failures is made using both strength of materials and fracture mechanics principles. From this analysis, design practices to improve structural margins of safety and extend the life of the shield are proposed. The existence of unexpected shield failures indicate that current shield performance testing is at times inadequate. Recommendations are made relative to improved shield performance testing protocols including the benefits of testing in an active load frame such as the National Institute for Occupational Safety and Health's (NIOSH) Mine Roof Simulator. Even the most rigorous shield testing procedures, which strive to simulate in-service loading conditions, fail to consider key environmental issues, such as corrosion which is often the cause of structural fatigue failures in modern shields. The survey also indicated that hydraulic failures occur much sooner in the life cycle of a shield than structural failures, and although they can significantly degrade support capability, often go undetected for long periods of time. Methods to detect the hydraulic failures are also provided. The paper concludes with key points to maximizing shield design and life expectancy and ideas for future generation shield designs.|
Additional chapters/articles from the SME-ICGCM book Proceedings - 18th International Conference on Ground Control in Mining
|Pillar Collapse at Welgedacht Colliery, South Africa: A Case||Causes of Massive Directional Roof Falls in Room and Pillar||Catastrophic Collapse Of Highwall Web Pillars And Preventati||Mine Panel Collapse - Two Case Studies||Roof Geology Mapping In Underground Coal Mines||Electromagnetic Seam Wave Mapping Of Roof Rock Conditions Ac||Geological Conditions At Continuous Miner Sections; Examples||The Role Of Engineering And Geology In Analyzing Ground Cont||The Development And Use Of Risk Assessment Techniques To Ass||Time-Dependent Analysis Of Underground Opening Stability||Tekflex As A Sprayon Screen Replacement In An Underground Ha||Tunnel Deformation Monitoring "Action Levels" In Coal Mines||Skin Failure Of Roof And Rib In Underground Coal Mines||Application Of Polyurethane Injection For Rehabilitation Of||Design Considerations For Bump-Prone Longwall Mines||Design Methodology For Standing Secondary Roof Support In Lo||Modern Shield Technology: Better Than Ever But Still Not Per||Shield Monitoring To Forecast Severe Face Weightings At The||Monitoring Of Longwall Seal Behaviour For Permeability And S||Ground Control In South African Coal Mines - A U.S. Perspect||Rock Mechanics Issues In The Trona Patch||Highwall Augering In Ultra-Thick Western Coal Reserves: Uniq||Seismic Events Due To Underground Mining Activities||Control Technology For Roof Drill Operators||Resin Annulus Size Effects On Rebar Bolt Pull Strength And R||Roof Bolt Response To Shear Stress: Laboratory Analysis||Laboratory Study Of Shear Loading And Bolt Load Transfer Mec||Analysis Of Cable Bolt Performance Using Numerical Modeling||Roof Bolting Application In Longwall Mining In Indonesia And||Ground Control Design For Multiple Seam Mining Using Finite||Pillar Design Issues For Underground Stone Mines||Calibration Of The Analysis Of Longwall Pillar Stability (AL||Mine Convergence When Using Mobile Roof Supports In Pillar R||The Advance And Relieve Mining Method: A Horizontal Stress C||Localized Horizontal Stress And Its Effect On Ground Control||Prediction And Control Of Surface Subsidence Over Abandoned||Effects Of Mining On Underground Infrastructures In The Germ||Ground Deformation In The Case Of Underground Mining Of Thic||Prevention Of Time-Dependent Subsidence By Elimination Of Gr|