Pillar Design Principles in Bord and Pillar Mining – DGMS Exam Guide

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🏗️ Pillar Design Principles – DGMS Exam Notes Introduction In the Bord and Pillar mining method, coal is extracted through a grid pattern of galleries (bords) and square/rectangular blocks called pillars, which act as natural supports.
Proper pillar design is critical for roof stability, worker safety, and maximum recovery of coal. DGMS and CMR 2017 specify strict design and extraction guidelines to avoid collapses or subsidence.

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⚖️ Factors Affecting Pillar Design

1. Depth of Cover:
• Greater depth → higher load on pillars → larger pillar size required.
2. Coal Seam Thickness:
• Thicker seams demand wider pillars for stability.
3. Rock Pressure & Roof Quality:
• Poor roofs require increased pillar size and roof bolting.
4. Panel Layout & Ventilation:
• Proper spacing ensures safety and smooth air circulation.
5. Mining Method:
• Manual vs. mechanized (CM-based) affects pillar strength and layout.

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📐 Design Standards (as per DGMS/CMR 2017 Reg. 107–110)

• Width of Pillar: Usually 1.5–2 times the bord width.
• Minimum Pillar Dimension: Not less than 8 m × 8 m for thin seams.
• Barrier Pillars: Provided between two panels, width depends on depth (approx. 8–30 m).
• Pillar Shape: Preferably square to distribute stress uniformly.
• Factor of Safety (FOS):
• Should be ≥ 1.5 (for working pillars)
• ≥ 2.0 (for barrier pillars)

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🧱 Types of Pillars

1. Working Pillar: Actively supports roof during extraction.
2. Barrier Pillar: Isolates workings or panels to prevent collapse spread.
3. Chain Pillar: Protects main haulages and return airways.
4. Stook Pillar: Remnant of old workings.

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🛠️ Pillar Extraction (Depillaring) Rules

• Extraction to start only after DGMS permission.
• Proper ventilation, roof bolting, and stowing required.
• Split & Fender Method used for controlled extraction.
• Use sand stowing or caving method as per roof condition.

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⚠️ DGMS Circulars on Pillar Safety

• DGMS Tech Circular 02/2010: Stability and support in depillaring areas.
• DGMS Tech Circular 03/2013: Strata monitoring system during pillar extraction.
• DGMS General Circular 05/2016: Barrier width and roof monitoring guidelines.

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⚙️ Quick Revision Notes

• Reg. 107–110 → Pillar design, width, extraction rules.
• Pillar width ↑ as depth ↑.
• FOS ≥ 1.5 for working, ≥ 2.0 for barriers.
• Square pillars → uniform stress.
• Split & Fender → safe depillaring.
• DGMS permission mandatory for extraction.

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🎯 25 DGMS Exam MCQs – Pillar Design Principles

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Q1. The main function of a coal pillar is to:
A. Ventilate mine air
B. Support the roof
C. Store machinery
D. Separate districts
E. Increase haulage
Answer: B.
Solution: Pillars are left to support overlying strata.

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Q2. The factor of safety for a working pillar should not be less than:
A. 1.0
B. 1.5
C. 2.0
D. 2.5
E. 3.0
Answer: B.
Solution: DGMS recommends FOS ≥ 1.5 for working pillars.

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Q3. Minimum dimension of a pillar in thin seams is:
A. 6 × 6 m
B. 8 × 8 m
C. 10 × 10 m
D. 12 × 12 m
E. 5 × 5 m
Answer: B.
Solution: Regulation 107 specifies minimum 8 m × 8 m.

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Q4. Barrier pillars are provided to:
A. Ventilate old workings
B. Prevent collapse spread
C. Improve haulage
D. Increase productivity
E. Store coal
Answer: B.
Solution: Barrier pillars isolate and protect adjacent areas.

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Q5. Pillar shape preferred for stability is:
A. Rectangular
B. Square
C. Irregular
D. Circular
E. Polygonal
Answer: B.
Solution: Square pillars distribute stress evenly.

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Q6. Pillar strength mainly depends on:
A. Seam gradient
B. Depth of cover
C. Air velocity
D. Lighting condition
E. Machine type
Answer: B.
Solution: Overburden weight increases with depth.

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Q7. DGMS permission for depillaring is obtained under:
A. Reg. 107
B. Reg. 111
C. Reg. 110
D. Mines Act 23
E. None
Answer: C.
Solution: Reg. 110 covers extraction and depillaring permission.

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Q8. Barrier pillar width increases with:
A. Roof thickness
B. Depth of cover
C. Airflow
D. Manpower
E. Dust load
Answer: B.
Solution: Greater depth = greater width for stability.

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Q9. Chain pillars are used to protect:
A. Surface buildings
B. Haulage and airway
C. Old workings
D. Conveyor belts
E. None
Answer: B.
Solution: Chain pillars support haulage roadways.

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Q10. Pillar extraction is also called:
A. Cutting
B. Depillaring
C. Caving
D. Trimming
E. Notching
Answer: B.
Solution: Removal of pillars = depillaring.

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Q11. The most important parameter in pillar design is:
A. Seam temperature
B. Roof condition
C. Depth of cover
D. Lighting
E. Air density
Answer: C.
Solution: Depth determines load on pillars.

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Q12. Factor of Safety for barrier pillars:
A. 1.0
B. 1.25
C. 1.5
D. 2.0
E. 2.5
Answer: D.
Solution: Barrier FOS ≥ 2.0 per DGMS guidelines.

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Q13. The ratio of pillar width to bord width should not be less than:
A. 1:1
B. 1.5:1
C. 2:1
D. 3:1
E. 1:2
Answer: B.
Solution: Pillar width usually 1.5–2× bord width.

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Q14. In weak roof areas, roof bolting should be done at intervals of:
A. 0.5 m
B. 1 m
C. 1.2 m
D. 1.5 m
E. 2 m
Answer: D.
Solution: 1.5 m interval ensures effective support.

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Q15. The term “stook pillar” refers to:
A. Barrier pillar
B. Old remnant pillar
C. Chain pillar
D. Support pillar
E. Ventilation barrier
Answer: B.
Solution: Stook = remnant of old workings.

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Q16. Roof convergence monitoring is done by:
A. Extensometer
B. Barometer
C. Psychrometer
D. Thermometer
E. Gravimeter
Answer: A.
Solution: Extensometer measures strata movement.

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Q17. Main hazard during depillaring:
A. Flooding
B. Roof fall
C. Gas ignition
D. Haulage
E. Dust
Answer: B.
Solution: Roof fall due to loss of support.

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Q18. DGMS Circular 02/2010 relates to:
A. Transport rules
B. Roof and slope safety
C. Drainage
D. Survey
E. Lighting
Answer: B.
Solution: Circular 02/2010 = slope and roof safety.

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Q19. Factor of Safety calculation involves:
A. Pillar stress and strength
B. Mine temperature
C. Air density
D. Seam dip
E. None
Answer: A.
Solution: FOS = Strength / Induced Stress.

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Q20. Pillar failure is mostly caused by:
A. Overburden pressure
B. Poor drilling
C. Dust load
D. Lighting
E. Explosives
Answer: A.
Solution: High overburden load crushes pillars.

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Q21. Roof bolting pattern should be designed by:
A. Shift in-charge
B. Ventilation officer
C. Manager with support plan approval
D. Surveyor
E. Engineer only
Answer: C.
Solution: Support plan approved by manager & DGMS.

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Q22. Main roof fall in depillaring area occurs when:
A. Extraction exceeds 70%
B. Roof support fails
C. Ventilation low
D. Dust accumulates
E. Roof angle > 30°
Answer: A.
Solution: Beyond 70% extraction, roof pressure increases.

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Q23. Typical bord width in Indian coal mines:
A. 2–3 m
B. 4–5 m
C. 6–8 m
D. 9–10 m
E. 12–15 m
Answer: C.
Solution: 6–8 m commonly used.

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Q24. Stress concentration in pillars is maximum at:
A. Center
B. Corner
C. Roof
D. Floor
E. None
Answer: B.
Solution: Pillar corners experience maximum stress.

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Q25. DGMS emphasizes the use of which system for stress monitoring?
A. Barometric gauge
B. Stress meter / Tell-tale system
C. Flow meter
D. Dust sampler
E. CO sensor
Answer: B.
Solution: Tell-tale or stress meter monitors strata behavior.

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🧩 Conclusion 

 Proper pillar design is the backbone of safe and productive underground coal mining.
DGMS emphasizes scientific assessment of depth, seam properties, and roof behavior.
Accidents due to pillar collapse can be avoided through correct dimensioning, roof support, and continuous monitoring.
For DGMS exams, focus on CMR Reg. 107–110, pillar FOS, and depillaring safety rules.

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