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|Subsidence due to coal mining is poorly understood by non-specialists. This has led to numerous misconceptions and myths based on limited observations and lack of knowledge. The three most common are: 1. Mine maps are inaccurate. 2. Deep mines are not a problem. 3. If no subsidence has occurred for many years after mining, there is no risk of future subsidence. Maps are important during mining and most are carefully prepared. Future use to evaluate conditions at mine level often includes drilling to confirm what the map shows. Usually, little or no effort is made to tie the surface survey of the property to the mine survey, to conduct a well designed drilling program to confirm the mine map, or to drill test borings vertically. When a mine entry is encountered rather than a coal pillar, or vice versa, and conditions at mine level appear different than anticipated, the first reaction is the mine map is inaccurate. The idea of a safe depth from subsidence is often based on the false premise that mining results in sufficient breakup of the overlying rock strata that bulking compensates for the coal extracted. The safe depth idea first appeared in the literature about 1880 and remained prevalent well into this century. Sadly, it is still encountered. The modern understanding of fragmentation of the immediate mine roof with the overlying beds sagging down on the broken roof rock was first described in 1900. With full extraction mining, either longwall or retreat room and pillar, surface subsidence occurs regardless of the depth of the mine. Subsidence over longwall mines at depths of 2000 feet can be 90 percent of the mined seam thickness. Numerous studies of undermined sites conclude that mining occurred many years ago and since no subsidence has occurred, there is no risk of future movement. This is true if sufficient coal pillars have been left to support the overlying strata. However, every year subsidence occurs over mines that have been closed for 100 years or more. In a study of subsidence incidents over the Pittsburgh Coal, the senior authors found that 50 percent of the incidents occurred above mines that had been closed for at least 50 years and 10 percent over mines closed for at least 80 years.|
Additional chapters/articles from the SME-ICGCM book Proceedings 15th International Conference On Ground Control In Mining
|Practical Aspects Of Mobile Roof Support Usage||Chemical Consolidation For Roadway Surrounding Rock - It&apo||Fortrac® Geogrids For Mine Roof Control||Ground Pressure Control With Use Of Freezing Rocks On The Or||Effect Of Specimen Size On Compressive Strength Of Coal||The Uniaxial Compressive Strength Of Coal: Should It Be Used||Three-Seam Interaction: A Case Study||Computer Modeling Of Rock Mass Geomechanic State In Longwall||The Influence Of Massive Sandstones In The Main Roof On Long||New Laminated Displacement-Discontinuity Program: Fundamenta||Load Determination For Long Cable Bolt Support Using Compute||Subsidence Misconceptions And Myths||Interaction Subsidence In The Sydney Coalfield, Nova Scotia||Identification Of Factors Affecting Horizontal Displacement||Subsidence Control Over Abandoned Mines||Monitoring Subsidence Over Submarine Coal Mines In The Sydne||High Horizontal Stress Effects On Longwall Gate Entry Stabil||Analysis Of Entry Roof Failure And Falls At Springvale Colli||The Effect Of Gas Pressure On Coal Strength||Applications Of Probabilistic Analysis In Mine Ground Contro||Regularities Of Rock Pressure Manifestations In Longwalls In||Design Of Multi-Level Thick Seam Extractions Under Major Aqu||State-Of-The-Art Room-And-Pillar Retreat Mining In The Kitta||Highwall Control At Homestake's Open Cut Mine||Design And Hazard Assessment Of Mine Ore Passes||Geomechanical Support Of Adaptive Mining Technology||Direct Laboratory Tensile Testing Of Select Yielding Rock Bo||Managing A New Technology - An Update Of The UK Rockbolting||Innovative Secondary Support Technologies For Western Mines||Innovation In Control Of Geomechanical State Of Undermined R||Application Of Tomographic Imaging To Stability Assessment||Using Ground Penetrating Radar For Roof Hazard Detection In||Classification Of Large Seismic Events At The Lucky Friday M||Rating Coal Mine Roof Strength From Exploratory Drill Core||Rapid Assessment Of Gateroad Roof Stability By Simple Monito||Geomechanic Monitoring And Distributed Information Systems||Monitoring Roof Beam Lateral Displacement At The Waste Isola||Laboratory Pull Tests Of Resin-Grouted Cable Bolts||Optimizing Secondary Tailgate Support Selection||Performance Evaluation Of A Cable Bolted Yield-Abutment Gate||High Horizontal Movements In Longwall Gate Roads Controlled||Shear Behavior Of Cable Bolt Supports In Horizontal, Bedded||An Evaluation Of Strata Behavior And Tailgate Support Perfor||Two Case Studies Of The Performance Of Rib Supports||Harworth Colliery: Rockbolted Support In Weak Roof At Depth||Problems And Prospects Of Roof Bolting Development At Cuzbas||Design Methods To Control Violent Pillar Failures In Room-An||Design Of Longwall Extractions Under Flooded Abandoned Worki||Effect Of Water On Stability Of Mine Roadways||Weightings And Water Inflows During Longwall Working||Underground Movement Of Rock Mass And Stress Distribution Du||Applications Of New Technologies To The Technical Design And||In-Seam Seismic Tomography Mapping Application To Coal Minin||Application Of Seismic Tomography In Underground Mining||Seismic Tomography For Longwall Stress Analysis||Geostatistical Methods For Hazard Assessment And Site Charac||Estimation Of Long-Term Stability Of Mine Pillars In Undergr||Geotechnical Factors Influencing A Time-Dependent Deformatio||Application Of Computer Programs For Rock Pressure Control||Analysis Of Multiple-Seam Interaction In A Bump-Prone Wester||Optimised Layout And Roadway Support Planning With Integrate||Automated Monitoring Of Rock Slopes And Waste Dumps||The Investigation Of The Rock Mass Stressed-Deformed State U|