Subsidence Misconceptions And Myths

Gray, Richard E.
Organization: International Conference on Ground Control in Mining
Pages: 10
Publication Date: Jan 1, 1996
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.
Full Article Download:
(2964 kb)

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
FortracĀ® 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