A Comparison of the Overburden Loadingin ARMPS and LaModel

Presenter: Ihsan Berk Tulu (WVU) Keith A. Heasley (WVU)

Christopher Mark (NIOSH)

July 27, 201029th 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 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 SFH > 1,000 ft ≥ 2.0 ≥ 1.5* (≥ 2.0**)

H<1,000 ft No Recommendation

Analysis of Retreat Mining Pillar Stability (ARMPS)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Depth of Cover (ft)

AR

MP

S S

F

Satisfactory

Unsatisfactory

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.

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 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 SFH > 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?

ARMPS 2010 – Pressure Arch Loading

ARMPS 2010 – Pressure Arch Loading

Pressure Arch Factor

)))(ln(28.0(1PW

HFPa

ARMPS 2010 – Pressure Arch Loading

ARMPS 2010 – Pressure Arch Loading

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 500 1000 1500 2000 2500

Depth (ft)

AR

MP

S S

tab

ility

Fa

cto

r

Success SqueezeCollapseMulti-Pillar BurstOther Burst

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

Side Gob

Outby BP

AMZOutby

AJ

Inby BP

Active Gob

Inby AJ

Panel Width = 400 ft 330 ft160 ft400 ft

5vH

200

ft

Bar

rie

r P

illar

(B

P)

Ad

jace

nt

Pan

el (

AJ)

Side Gob

Overburden loads calculated on the different areas of the panel.

Load Analyses Results

Development load.

Load Analyses Results Load Analyses - Development

ARMPS 2002

ARMPS 2010

100%

100%

101%

100%

146%

117%

100%

68%

94%

100%

123%

109%LaModel

Bar

rier

Pill

ar

Ad

jac

ent

Pa

nel

Side Gob

Load Analyses Results Load Analyses – Step 2

ARMPS 2002

ARMPS 2010

100%

100%

101%

100%

146%

117%

100%

68%

94%

100%

123%

109%LaModel

Bar

rier

Pill

ar

Ad

jac

ent

Pa

nel

Side Gob

ARMPS 2002

ARMPS 2010

21%

21%

23%

182%

237%

213%

105%

71%

98%

100%

123%

109%LaModel

Side GobB

arri

er P

illar

Ad

jace

nt

Pan

el

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

ARMPS 2002

ARMPS 2010

21%

21%

23%

182%

237%

213%

105%

71%

98%

100%

123%

109%LaModel

Side GobB

arri

er P

illar

Ad

jace

nt

Pan

el

ARMPS 2002

ARMPS 2010

21%

21%

23%

189%

255%

232%

149%

101%

124%

103%

131%

121%LaModel

ARMPS 2002

ARMPS 2010

LaModel 25%

21%

21%

190%

248%

270%

47%

47%

13%

104%

124%

139%

Side GobB

arri

er P

illar

ActiveGob

Ad

jace

nt

Pan

el

Load Analyses Results Load Analyses – Step 4

ARMPS 2002

ARMPS 2010

21%

21%

23%

189%

255%

232%

149%

101%

124%

103%

131%

121%LaModel

ARMPS 2002

ARMPS 2010

LaModel 25%

21%

21%

190%

248%

270%

47%

47%

13%

104%

124%

139%

Side GobB

arri

er P

illar

ActiveGob

Ad

jace

nt

Pan

el

ARMPS 2002

ARMPS 2010

21%

21%

25%

217%

258%

244%

160%

106%

127%

103%

133%

121%LaModel

ARMPS 2002

ARMPS 2010

LaModel 28%

21%

21%

214%

332%

302%

47%

47%

20%

104%

139%

140%

Side GobB

arri

er P

illar

ActiveGob

Sla

b C

ut

Ad

jace

nt

Pan

el

Stability Factor Comparison LaModel – ARMPS

ARMPS 2002 ARMPS 2010 LaModel

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% 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.

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 500 1000 1500 2000 2500

Depth (ft)

AR

MP

S S

tab

ility

Fa

cto

r

Success SqueezeCollapseMulti-Pillar BurstOther Burst

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?