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|Probably the most expensive but least well understood roof falls in underground coal mining, are those that occur ahead of the powered supports in the centre of longwall face. Even small roof cavities result in the dilution of the ROM product and large cavities can stop the face for days if not weeks and the incurred cash flow losses can be catastrophic. Expensive and time-consuming remedial measures (e.g. PUR, cavity filling, removal of stone from the AFC by hand) are required and equipment wear and damage can be significant when the need to blast and convey stone is also considered. Through four major research projects within the Australian coal industry and numerous consulting assignments, the author has spent the best part of fifteen years attempting to identify and defme the various geotechnical and operational factors that determine whether a major roof cavity occurs ahead of the powered supports or a normal goaf fall occurs just behind them, the difference in operational outcome being enormous. The paper presents a condensed summary of the overall technical findings covering such issues as roof fall mechanisms, the measured influence of cover depth, periodic weighting of massive strata units and its quantification, the role of cut-throughs in chain pillars, face width and height, the role of the powered support and the influence (both positive and negative) of mine site operations. The big picture outcome is the view that high production longwall extraction is well-suited to certain geotechnical environments, is marginal in others and under certain conditions is fatally flawed and beyond the control of mine operators, although fortunately the latter category is a relatively rare situation. Various risk-based research findings in this regard will be given as a basis for future discussion.|
Additional chapters/articles from the SME-ICGCM book 24th International Conference on Ground Control in Mining (ICGCM) 24th
|Keynote Address at the 23rd International Conference on Grou||Analysis and Design of Rib Support (ADRS) a Rib Support Desi||Evaluation of the Impact of Standing Support on Ground Behav||Half a Career Trying to Understand Why the Roof Along the Lo||Forecasting Roof Falls with Monitoring Technologies - A Look||Analysis of Seismic Source Parameters of Roof Falls in Time||A System to Provide Early Warning on Impending Goaf||Outcomes of the Landmark Longwall Automation Project with Re||Application of Phenolic Foam in Longwall Mining||Multiple Seam Mining Interactions: Case Histories from the H||Analysis of Entry Stability Associated with Multi-seam Minin||Failure Mechanics of Multiple Seam Mining Interactions||Engineering Classification of Ultra-close Multiple Seam Roof||Definition of Ultra-close Multiple-seams and its Ground Pres||Depillaring and Roof Bolting Practices at Quinsam Coal Mine||Seam Structure - An Important Criterion for Coal Pillar Desi||Mitigating Longwall Subsidence Effects on a Large Industrial||Impacts of Longwall Mining on Hydrology, Soil Moisture, and||Basics on the Dimensioning and the Extraction of Shaft Safet||Modeling the Arc-effect of a Coal Mine Roof||Recent Advances in Numerical Simulation of Cutter Roof Failu||Test Method for Assessing Water Degradation Potential of Coa||Geotechnical Strata Characterisation Using Geophysical Boreh||A Method for Quantitative Void/Fracture Detection and Estima||Implication of Highly Anisotropic Horizontal Stresses on Ent||Ground Control of a Mine Stope in Weak Rocks Subjected to Hi||Analysis of Highwall Mining Stability - The Effect of Multip||Highwall Mining in a Multiple-seam, Western United States Se||The Slope Stability Assessment in the Wall Overlooking the S||Numerical Modeling as a Tool to Predict Pillar Condition and||Development and Testing of a New Roof Prop||Stability Mapping System||Using Foaming Grout to Stabilize a Ventilation Raise in Very||Roof Control and Roadway Support Design in the #9 Coal Seam,||Non-confirmation Mathematics for Wall Rock Classification fo||The Influence of the First Layer Thickness of Immediate Roof||Studies on Distribution Pattern of and Methane Migration Mec||Development of a New Roof Bolt Technology to Improve Gate- R||Improved Pull out Strength of Fully Grouted Roof Bolts throu||Experimental and Numerical Methodology Assessment of Load Tr||An Investigation into the Support Systems in South African C||Investigation of Fully Grouted Roof Bolts Installed Under In||Development of the Laboratory Short Encapsulation Pull Test||A Resin Quality Testing Procedure for Collieries||Determination of Load Transfer Characteristics of Gloved Res||Fully Grouted Torque Tension Bolts Successfully Support Pitt||Shear Bond Characteristics in Grouted Cable Bolts||Overcoring Techniques to Assess in Situ Corrosion of Galvani||Development of a Laboratory Facility for Testing Shear Perfo||Mechanical Response of Split-Set Rock Bolts in Squeezing Gro||Mechanisms of Rib Sloughing and Methods of Controlling Thick||Supporting Method of the Bolted Strata in Large Deformation||Assessment of Ground Conditions Near a Mine Portal Using Gro||Detection of Abandoned Mines and Air Passages/Burning Center||Detecting Abandoned Coal Mine Entries by High Resolution Ear|