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 29th International Conference on Ground Control in Mining ARMPS LaModel

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.

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

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.

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.

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.

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.

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.

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 Roof Strong Roof ARMPS SF H<650 ft 1.5 650 ft ≤ H ≤ 1,250 ft 1.5 - [H-650] / 1000 1.4 - [H-650] / 1000 1,250 ft ≤ H ≤ 2,000 ft 0.9 0.8 Barrier Pillar SF H > 1,000 ft ≥ 2.0 ≥ 1.5* (≥ 2.0**) H<1,000 ft No Recommendation

Analysis of Retreat Mining Pillar Stability (ARMPS)

Analysis of Retreat Mining Pillar Stability (ARMPS) Table 1. Recommended ARMPS Stability Factors (Chase et al., 2002). Depth (H) Weak and Intermediate Strength Roof Strong Roof ARMPS SF H<650 ft 1.5 650 ft ≤ H ≤ 1,250 ft 1.5 - [H-650] / 1000 1.4 - [H-650] / 1000 1,250 ft ≤ H ≤ 2,000 ft 0.9 0.8 Barrier Pillar SF H > 1,000 ft ≥ 2.0 ≥ 1.5* (≥ 2.0**) H<1,000 ft No Recommendation Why the lower stability factors may be successful with deeper cover? Actual strength of the large pillars at deeper cover might be higher than the predicted one. ARMPS2002 predicts loads higher than the actual ones.

ARMPS 2010 – Pressure Arch Loading

ARMPS 2010 – Pressure Arch Loading Pressure Arch Factor

ARMPS 2010 – Pressure Arch Loading

ARMPS 2010 – Pressure Arch Loading

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.

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.

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.

LaModel Calibration of the lamination thickness:

LaModel Calculating gob properties based on expected gob loading.

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.

Load Analyses LaModel – ARMPS Deep Cover Database Overburden Depth (ft) Panel Width (ft) Mining Height (ft) Minimum 750 160 3.6 Maximum 2200 940 9 Mean 1260 400 6.9 Standard Deviation 380 156 1.62

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

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

Load Analyses Results Development load.

Load Analyses Results Load Analyses - Development

Load Analyses Results Load Analyses – Step 2

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

Load Analyses Results Load Analyses – Step 3

Load Analyses Results Load Analyses – Step 4

Stability Factor Comparison LaModel – ARMPS Average Stability Factor 1.07 1.51 1.41 Standard Deviation 0.32 0.47 0.25

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%.

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%.

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%.

Stability Factor Comparison LaModel – ARMPS Summary of the Stability Factor comparison. ARMPS 2002 ARMPS 2010 LaModel Correct Failure Classification (%) 38% 52% 76% Correct Success Classification (%) 64% 55% 48% Overall Classification (%) 54% 60%

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.

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

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)

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.

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.

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.

Questions?