A Comparison of the Overburden Loading in ARMPS and LaModel

1. A Comparison of the Overburden Loadingin ARMPS and LaModel ARMPS LaModel Presenter: Ihsan Berk Tulu (WVU) Keith A. Heasley (WVU) Christopher Mark (NIOSH) July 27, 2010 29th International Conference on Ground Control in Mining

2. Outline of Presentation • Introduction • Analysis of Retreat Pillar Mining Program (ARMPS). • ARMPS 2002. • ARMPS 2010 and Pressure Arch Method. • Laminated Model (LaModel) • Calibration of the lamination thickness. • Calibration of the gob stiffness.

3. Outline of Presentation • Load Analyzes LaModel – ARMPS • Methodology used during the load analyzes. • Load Analyzes Results. • Stability Factor Analyzes. • ARMPS 2002 • ARMPS 2010 • LaModel • Summary and Conclusions

4. Introduction • Pillar Recovery accounts for less than 10% of the coal produced from Underground coal mines (1989 to 1996) (Mark et al., 2003). • Also, it accounts for more than 25% of the all ground fatalities (Mark et al., 2003). • MSHA and NIOSH • Global stability through proper pillar design. • Local stability through proper roof support. • Worker safety through proper section management.

5. Introduction • ARMPS and the LaModel programs have been used successfully in the U.S. for designing safe pillar recovery operations for many years. • After Crandall Canyon Mine Disaster (August 6th, 2007) • There is a need for an improved design methodology for deep cover pillar retreat mines. • There is a need for standardized method of calibrating LaModel.

6. Analysis of Retreat Mining Pillar Stability (ARMPS) • ARMPS was originally developed by NIOSH in the mid 1990’s (Mark and Chase, 1997.) to prevent. • Squeezes • Collapses • Bursts • ARMPS consists of three basic calculation steps: • Estimate the applied loads. • Estimate the load bearing capacity of the pillars. • Compare the load to the capacity.

7. Analysis of Retreat Mining Pillar Stability (ARMPS) • Applied loads estimated by ARMPS 2002. • Development loads based on tributary area method. • Abutment loads based on abutment angle concept.

8. Analysis of Retreat Mining Pillar Stability (ARMPS) • ARMPS strength is not coming from the accuracy of its’ calculations. • ARMPS strength is the large data base of retreat mining case histories that it has been calibrated against.

9. Analysis of Retreat Mining Pillar Stability (ARMPS) • First version of the ARMPS (1997), calibrated with 150 cases. • Design stability factor (SF) was 1.5. • Overburden depth deeper than 750 ft SF became less meaningful. • ARMPS 2002 was calibrated with 250 cases.

10. Analysis of Retreat Mining Pillar Stability (ARMPS)

11. Analysis of Retreat Mining Pillar Stability (ARMPS) • Actual strength of the large pillars at deeper cover might be higher than the predicted one. • ARMPS2002 predicts loads higher than the actual ones. Why the lower stability factors may be successful with deeper cover?

12. ARMPS 2010 – Pressure Arch Loading

13. ARMPS 2010 – Pressure Arch Loading • Pressure Arch Factor

14. ARMPS 2010 – Pressure Arch Loading

15. ARMPS 2010 – Pressure Arch Loading

16. LaModel • LaModel program was originally developed in 1993. • It is a Displacement-Discontinuity Variation of the Boundary-Element Method. • Numerical Modeling – Mathematical approximation of the geo-mechanical behavior of the coal and overburden, based on the fundamental laws of physics.

17. LaModel • Natural geologic material does not follow theoretical behavior; It is inhomogeneous, non-isotropic, inelastic. • Models require complex, difficult-to-obtain input information. • Output of the models depends on the input parameters. • Models must be calibrated with reality.

18. LaModel • Calibrating the LaModel for Deep Cover Pillar Retreat Mining : • Calculating the lamination thickness based on the extent of abutment loading. • Calculating coal material properties based on a Mark-Bienawski pillar strength. • Calculating gob properties based on expected gob loading.

19. LaModel • Calibration of the lamination thickness:

20. LaModel • Calculating gob properties based on expected gob loading.

21. Load Analyses LaModel – ARMPS • Deep Cover Database: As part of the research to improve ARMPS and LaModel programs, a database of deep cover retreat mining case studies was developed (Heasley, 2010) • 52 Cases from 11 different mines. • 7 mines from Central Appalachian coal fields. • 4 mines from Western coal fields. • 31 successful cases. • 21 unsuccessful cases.

22. Load Analyses LaModel – ARMPS • Deep Cover Database

23. Load Analyses LaModel – ARMPS • Methodology Used During the Load Analyses. • Ideal mine geometry is used for each cases. • Model with average panel dimensions from 52 case histories. • Each cases were divided into the four steps. • Step 1: Development only • Step 2: Step 1 + Side Gob • Step 3: Step 2 + Active Gob • Step 4: Step 3 + Slab Cut

24. Load Analyses LaModel – ARMPS • Overburden loads calculated on the different areas of the panel.

25. Load Analyses Results • Development load.

26. Load Analyses Results • Load Analyses - Development

27. Load Analyses Results • Load Analyses – Step 2

28. Load Analyses Results • Step 2 Loads on AMZ: Development +Initial side Abutment Load + Load Transfer from the barriers (if barrier pillar yields.)

29. Load Analyses Results • Load Analyses – Step 3

30. Load Analyses Results • Load Analyses – Step 4

31. Stability Factor Comparison LaModel – ARMPS

32. Stability Factor Comparison LaModel – ARMPS • ARMPS 2002 failure and success comparison. • 38% of the unsuccessful (failure) case histories and 64% of the successful case histories are correctly classified. • Overall classification accuracy is 54%.

33. Stability Factor Comparison LaModel – ARMPS • ARMPS 2010 failure and success comparison. • 52% of the unsuccessful (failure) case histories and 55% of the successful case histories are correctly classified. • Overall classification accuracy is 54%.

34. Stability Factor Comparison LaModel – ARMPS • LaModel failure and success comparison. • 76% of the unsuccessful (failure) case histories and 48% of the successful case histories are correctly classified. • Overall classification accuracy is 60%.

35. Stability Factor Comparison LaModel – ARMPS • Summary of the Stability Factor comparison.

36. Summary and Conclusions • After Crandall Canyon Mine Disaster (August 6th, 2007) • NIOSH improved ARMPS program (Mark, 2010). • Dr. Heasley (WVU) proposed standardized method of calibrating the LaModel and improved LaModel. • Overburden load distributions calculated by ARMPS 2002, ARMPS 2010 and LaModel are analyzed and compared.

37. Summary and Conclusions • ARMPS 2002 vs. ARMPS 2010. • Depth effect eliminated.

38. Summary and Conclusions • If LaModel is calibrated as proposed by Heasley (2010). • Extend of the abutment zone calculated by LaModel matches the one used by ARMPS. • 2-D Magnitude of the abutment load calculated by LaModel also matches with the one calculated by ARMPS. • LaModel calculated the active gob load less than the ARMPS. (3-D scenario at the active line)

39. Summary and Conclusions • LaModel distributes the overburden loads based on: • Bending stiffness of the laminated overburden and relative stiffness's and the failure strengths of the production and barrier pillars. • Overburden load distribution calculated by LaModel might be much closer to ARMPS 2010 with strain softening material model.

40. Summary and Conclusions • Stability Factor comparison based on the old and new designs. • Overall classification of the failure and success are same for both ARMPS 2002 and ARMPS 2010. • ARMPS 2010 classified the failure cases better than the ARMPS 2002. • LaModel may be considered to classify the case histories slightly better than ARMPS 2010.

41. Summary and Conclusions • Future studies to improve the ARMPS and LaModel for deep cover pillar recovery operations. • Abutment extend need to be investigated. • Load distribution need to be investigated. • Abutment angle concept need to be improved. • Load transfer from the barrier pillars need to be investigated.

42. Questions?