ICGCM Papers:
Analytical and Numerical Modeling Studies
 
 
Numerical Model Calibration for Simulating Coal Pillars, Gob and Overburden Response
29th International Conference on Ground Control in Mining
Numerical Model Calibration for Simulating Coal Pillars, Gob and Overburden Response
by
Essie EsterhuizenChris MarkMichael M. Murphy, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United States
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[Conference] 29th International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Analytical and Numerical Modeling Studies
[Author] Essie EsterhuizenChris MarkMichael M. Murphy, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United States
[Abstract] 

The loading, failure process and ultimate strength of wide pillars used in deep underground mines is poorly understood, mainly because the extreme ground conditions make it difficult to measure the stress-strain behavior of a pillar while it is failing.  Well calibrated numerical models can assist in providing answers to these questions, provided the coal, the overburden and the gob are all modeled with suffuicient accuracy. 

 

A program of model calibration and validation was carried out against observed and measured performance of coal pillars and the overburden in operating mines.  The FLAC3D software package was used to establish realistic coal properties based on laboratory tests on intact coal and matching model results to field data through the Hoek-Brown failure criterion.  The overburden is modeled using the ubiquitous joint approach to simulate bedding and a strain-softening Coulomb material to model the intact rock beds.  Overburden response was calibrated against subsidence measurements and stress distributions measured adjacent to mined panels.  Gob is modeled as a strain hardening material and is based on laboratory tests and matching model results to measured overburden displacements.

 

The model results showed that coal pillar failure can be controlled by the interaction of a number of processes such as interface sliding between the coal and the surrounding rock, the rate of post-peak strength reduction of the coal and the internal shearing of the coal.  Various combinations of these properties can result in widely diverging pillar strengths and failure modes.  Appropriate parameters for matching field observations will be presented.  Overburden response and stress re-distribution is also highly dependent on factors such as the bedding shear strength and rock mass modulus.  The results showed that a basic set of bedded rock properties can be created that will satisfactorily match observed overburden response and load distributions.

 

The paper will demonstrate how the calibration process was carried out, will present appropriate input parameters for modeling coal and rock strata and will present results for a typical retreat mining panel and longwall in weak and strong strata.