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A Comparison of the Overburden Loading in ARMPS and LaModel Presenter: Ihsan Berk Tulu (WVU) Keith A. Heasley (WVU) Christopher Mark (NIOSH) July 27, 2010.

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Presentation on theme: "A Comparison of the Overburden Loading in ARMPS and LaModel Presenter: Ihsan Berk Tulu (WVU) Keith A. Heasley (WVU) Christopher Mark (NIOSH) July 27, 2010."— Presentation transcript:

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

2 Outline of Presentation  Introduction  Analysis of Retreat Pillar Mining Program (ARMPS).  ARMPS  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  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. Table 1. Recommended ARMPS Stability Factors (Chase et al., 2002). Depth (H) Weak and Intermediate Strength RoofStrong Roof ARMPS SF H<650 ft ft ≤ H ≤ 1,250 ft1.5 - [H-650] / [H-650] / ,250 ft ≤ H ≤ 2,000 ft Barrier Pillar SF H > 1,000 ft≥ 2.0≥ 1.5* (≥ 2.0**) H<1,000 ftNo Recommendation

10 Analysis of Retreat Mining Pillar Stability (ARMPS)

11  Actual strength of the large pillars at deeper cover might be higher than the predicted one.  ARMPS2002 predicts loads higher than the actual ones. Table 1. Recommended ARMPS Stability Factors (Chase et al., 2002). Depth (H) Weak and Intermediate Strength RoofStrong Roof ARMPS SF H<650 ft ft ≤ H ≤ 1,250 ft1.5 - [H-650] / [H-650] / ,250 ft ≤ H ≤ 2,000 ft Barrier Pillar SF H > 1,000 ft≥ 2.0≥ 1.5* (≥ 2.0**) H<1,000 ftNo Recommendation Why the lower stability factors may be successful with deeper cover?

12 ARMPS 2010 – Pressure Arch Loading

13  Pressure Arch Factor

14 ARMPS 2010 – Pressure Arch Loading

15

16 LaModel  LaModel program was originally developed in  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 Overburden Depth (ft) Panel Width (ft)Mining Height (ft) Minimum Maximum Mean Standard Deviation

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 ARMPS 2002ARMPS 2010LaModel Average Stability Factor Standard Deviation

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. ARMPS 2002ARMPS 2010LaModel Correct Failure Classification (%) 38%52%76% Correct Success Classification (%) 64%55%48% Overall Classification (%) 54% 60%

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  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  ARMPS 2010 classified the failure cases better than the ARMPS  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?


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