1. Design of Chain Pillars for Longwall Workings
MINE PORTAL TEAM
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2. Introduction Differences Between ‘Normal Coal Pillar’ & ‘Chain Pillar’
Dimensions
Loading
Pillar Design Technique: Three Step Concept
Determine Expected Load on Pillar
Predict the Pillar Strength
Determine F.O.S

3. Comparison of Empirical Pillar Strength Formulae
Formulae Selected: 1. Greenwald Formula (1939) 2. Mark and Bineiawski (1997) 3. Galvin and Salamon (1967) 4. Bineiawski (1968) 5. Bunting (1911) 6. Holland (1964) 7. Salamon & Munro 8. Holland & Gaddy (1956) 9. Bunschinger(1876)

4. Comparison of Empirical Pillar Strength Formulae
Effect of Pillar Shape: -For the Same cross section area, the Rectangular Pillar (W/L<1) are weaker than Square Pillars - Greenwald Predicts Highest Strength and The Holland and Gaddy Lowest
Effect of Pillar Width: -Pillar Strength increases with increase in pillar width -Holland and Salamon & Munro Formula are quite close in their prediction
Effect of W/H ratio: - Three Prediction Groups: (a) Lower- Holland & Gaddy, Salamon & Munro, Holland and Bauschinger; (b) Medium- Bunting, Bieniawski, Greenwald, (c) Heigher- Galvin and Salamon

5. Comparison of Empirical Pillar Strength Formulae
Effect of Pillar Height -Strength of Pillar Decreases with Increase in Pillar Height
Effect of Pillar Length - Pillar Strength increases with increase in pillar length but increase is not significant w.r.t increase in width
Effect of θ - Square Pillars are more stable than Parallel-Piped or a Diamond Shaped Pillar

6. Comparison of Empirical Pillar Strength Formulae
(i) Effect of Pillar Shape
(ii) Effect of Pillar Width
After Du Xinzhi et. al.

7. Comparison of Empirical Pillar Strength Formulae
(iii) Effect of W/H ratio
(iv)Effect of Pillar Height
After Du Xinzhi et. al.

8. Comparison of Empirical Pillar Strength Formulae
(v) Effect of Pillar Length
(vi)Effect of Cross-Cut Angle
After Du Xinzhi et. al.

9. Different Approaches for Chain Pillar Design
Analytical Method ( Carr-Wilson)
Empirical, From field Measurements (Mark and Bieniawski)
Numerical (Hsiung and Peng)
ALPS: Analysis of Longwall Pillar Stability

10. Numerical Method-Hsiung Peng
Simple Formula based on 3-D Finite Element
Reliability of the result depends on Longwall panel simulation
Total applied load includes the front abutment load, side abutment load, and Overburden load
Method assumes that the UCS of pillar yield zone is equal to zero and supported only by confinement stress
Method has fixed internal Friction angle 37 degree( A point of weakness, as effect of confinement stress on the pillar strength is governed by the internal friction angle)
Effect of the assumption is negligible because in solid pillars only a small % of the total applied stress is borne by yield zone

11. Empirical Method (Mark- Bieniawski)
Special Feature of this Method: Calculates abutment load using field data(s), for development, Head gate loading, and Tailgate loading
Pillar Strength is calculated by Bieniawski formula
Result is in the from of ALPS-SF
For Higher CMMR value (75) ALPS-SF= 0.7 is adequate
For Lower CMMR Value (35) ALPS-SF= 1.3 is required
Experience shows Method works quite well upto moderate depths only
Negligible effect of UCS on Chain Pillar Strength

12. Carr-Wilson Approach Based on Wilson’s core model
Method Simulates the stress Distribution within the pillar
Method Considers the Progressive failure theory of Wilson[1977]
The failure will begin from the corners

13. CASE-STUDY- TML Mine, Iran (Tabas Coalfields)
Table1: Geometrical Parameters of TML mine
Parameters
Value
Pillar Height
3.2 m
Crosscut width
4.5 m
Pillar Length
40 m
Entry Width
Overburden Depth
45 m
Number of Entries 2
Effect of the assumption is negligible because in solid pillars only a small % of the total applied stress is borne by yield zone

14. CASE-STUDY- TML Mine, Iran (Tabas Coalfields)
Table2: Geo-Mechanical Parameters of TML Mine
Parameters
Value
In-Situ Strength of Coal
6.62 MPa
Young’s Modulus of Coal
3,682 Mpa
Young’s Modulus of Immediate Roof
3,682 MPa
Young’s Modulus of Floor
Young’s Modulus of Main Roof
35,344 MPa
Internal Friction Angle of main Roof
26 Degree
Unit Weight of overburden
26.5 kN/m^3
Abutment Angle
21 Degree

15. CASE-STUDY- TML Mine, Iran (Tabas Coalfields)
Pillar Width:
ALPS- 3.3 m (Considering AlPS-SF= 1.3)
Hsiung Peng: 10.6 m
Analytical Method- CWOH: 2.7 m (Instead of Using Carr-Wilson’s approach, a new combined approach CWOH, i.e. Carr-Wilson Oraee Hosseini ,is used here. This approach calculates the overburden + abutment load by Wilson’s method and prediction of Pillar strength by Oraee Hossieni Formula)

16. CASE-STUDY- TML Mine, Iran (Tabas Coalfields)
Sensitivity Analysis of Pillar Width with Variations in Mine Depth

17. Conclusions
Holland and Gaddy Predicts lowest strength while Greenwald Predicts highest Strength
Pillar Width rather than the Pillar length is the controlling factor in Pillar strength
Squat Pillars (W/H>4) have greater Strength potential than Slender Pillars (W/H<4)
Chain pillar design is less influenced by UCS of coal
The Calculated width of chain Pillar by Hsuing-Peng Formula is very high
As Alps is a credible method so width calculated by ALPS and CWOH is quite close to APLS so both methods can be taken for design consideration and also TML is a shallow depth mine so lager width of Pillar is not necessary.
Effect of the assumption is negligible because in solid pillars only a small % of the total applied stress is borne by yield zone

18. Loading Conditions:
Abutment Loading: Activity 5 srrt(H) where, H is depth of working

19. References
Oraee Kazeem, Oraee Behdeen, and Bangian, Amir H.,(2010), “Design Optimization of Longwall Chain Pillars”, In: Proceedings of the 29th International Conference on the Ground Control in Mining(ICGCM), Morgantown, W.V.
Oraee, K., Hosseini, N., and Gholinejad, M., (2009), “Coal Pillar Strength Based on the Ground Reaction Curve- A New Approach”, In: Proceedings of the 28th International Conference on Ground Control in Mining, Morgantown, W.V.,pp 21-24
Peng S.,S., and Hsiung S.,M., (1985), “Chain Pillar Design For U.S.Longwall Panels”, Mining Science and Technology, Elsevier Science Publishers, 2(1985) pp
Oraee, K., Hosseini, N., Gholinejad, M., (2010), “Optimization of Chain Pillars in Longwall Mining Method”, In: Proceedings of the 29th International Conference on the Ground Control in Mining(ICGCM), Morangtown, W.V.
Mark, C.,(2001), “Overview of Ground Control Research for Underground Coal Mines in The United States”, In: Proceedings of the 17th Mining Congress and Exhibition of Turkey (IMCET 2001), Ankara, Turkey, pp 3-10
Mark, C., (2006), “The Evolution of Intelligent Coal Pillar Design: ”, In: Proceedings of the 25th International Conference on the Ground Control in Mining(ICGCM), morgantown, W.V, pp
Gale, W., J., (1998)“Coal Pillar Design issues in Longwall Mining”, (1998), In: The Proceedings of Coal Operators Conference, University of Wollongong & The Australian Institute of Mining and Metallurgy, 1998, pp
Peng, S.,S., Morsy, K., Lu, Jun, Du, Xinzhi, (2008)“Coal Pillar Design Formulae Review and Analysis, (2008), ”, In: Proceedings of the 27th International Conference on the Ground Control in Mining(ICGCM), Morgantown, W.V.
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20. References
Mark, C., (1999), The State of The Art in Coal Pillar Design, In: Proceedings SME Annual Meeting,1999 Denver, Colorado, pp 1-8
Mark, C., and Chase, F., E.,(1997) “Analysis of Retreat Mining Pillar Stability(ARMPS)”, NIOSH Document: Technology News , URL: (Retrieved: 14th Aug 2011)
Hartman, Howard, L., (2000), “SME Mining Engineering Handbook”, Published by: Society of Mining, Metallurgy, and Exploration, Inc. (SME), Littleton Colorado, pp 2260.
Hudson, John A., and Harrison, John P., “Engineering Rock Mechanics: An Introduction to the Principles”,(1997), Published by: Pergamon- An Imprint of Elsevier Science.
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