Introduction
In opencast mines, the stability of benches (working steps) and dumps (waste overburden heaps) is critical for safe operations. Bench or dump failure can cause large-scale slope collapse, equipment loss, production delays, and even fatalities. DGMS regulations under Coal Mines Regulations 2017, MMR 1961, and DGMS technical circulars (e.g., Tech Circular 02 of 2010 on slope stability) provide detailed guidance to prevent such disasters. This blog explains the causes, prevention methods, case studies, one-liners, descriptive answers, and 20 solved MCQs on this topic — exam-ready for DGMS candidates.

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⚠️ Causes of Bench Failures (H2)

1. Geological Weakness
   • Faults, joints, weak strata, clay seams.
2. Excessive Bench Height or Steep Angle
   • Non-compliance with recommended height/angle (as per DGMS).
3. Water Ingress
   • Rainfall, seepage, inadequate drainage → softens slope material.
4. Overloading by HEMM
   • Heavy trucks/dumpers too close to edge.
5. Improper Dumping Practices
   • Oversteepened OB dumps, lack of terracing.
6. Vibration from Blasting
   • Poor blasting control may trigger slips.

Exam Tip: “What is the safe overall slope angle for coal mine dumps?” → Usually 27°–37° depending on material, DGMS approval needed.

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🛡 Prevention Methods (H2)

• Scientific Design
  • Benches: Height ≤ 10–15 m, Width ≥ HEMM operating width + safety margin.
  • Dumps: Terraced slopes, angle within DGMS norms.
• Drainage & Water Control
  • Garland drains, pumping, surface run-off channels.
• Monitoring Systems
  • Inclinometers, slope monitoring radars, prism survey.
• Dumping Rules
  • Progressive dumping, compaction, no oversteepening.
• Safety Barriers & Berms
  • At dump edges to prevent trucks falling.
• DGMS Compliance
  • Regular geotechnical studies, stability reports, adherence to circulars.

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📑 Case Study Examples (H3)

• Rajmahal OC (Jharkhand, 2016): Dump collapse killed over 20 workers. Cause: weak overburden dump + rainwater infiltration.
• Anjani Opencast (2019): Bench failure due to steep angle & poor drainage.
• Key Lesson: Proper slope design, monitoring, and drainage are life-saving.

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📝 Quick One-Liners

• Bench = working step, Dump = waste heap.
• Bench height ≤ 10–15 m (HEMM-dependent).
• Overall slope angle for dumps: 27°–37°.
• Water is the major trigger for slope failures.
• Garland drains prevent water infiltration.
• Rajmahal disaster (2016) → dump collapse.
• Terracing & compaction improve dump stability.
• DGMS circulars mandate slope monitoring.
• Berms prevent vehicles from toppling.
• Geotechnical study is compulsory for dumps.

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✍️ Descriptive Model Answer
Q: What are the causes and preventive measures of dump and bench failures in opencast mines?
Answer:Bench and dump failures occur due to geological weaknesses, excessive bench height, water ingress, overloading, and improper dumping. Blasting vibrations and rainfall increase risk. To prevent failures, benches must be designed with safe height and width, dumps terraced with proper slope angle, and drainage provided through garland drains and sumps. DGMS requires geotechnical studies, stability monitoring, and safety berms. Proper dumping practices and adherence to circulars (e.g., DGMS Tech Circular 02 of 2010) reduce risk. Conclusion: Bench and dump stability is essential for safe opencast operations and compliance with DGMS exam expectations.

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🎯 20 MCQs – Bench & Dump Failures
Q1 Bench failure in opencast mines mainly occurs due to:
A. Excessive blasting powder
B. Weak strata, water ingress, steep angle
C. Lack of PPE
D. Vehicle breakdown
E. Low manpower
Answer: B.
Solution: Weak strata, water, and steep angle cause slope failure.

Q2 Recommended bench height in opencast mines:
A. 5 m
B. 10–15 m
C. 20 m
D. 25 m
E. 30 m
Answer: B.
Solution: Bench height ≤ 10–15 m for safety.

Q3 Safe overall slope angle for coal OB dumps is around:
A. 10°
B. 27°–37°
C. 45°
D. 55°
E. 60°
Answer: B.
Solution: Dumps must be stable at ~27–37°.
Q4 Major trigger of dump collapse:
A. Heat
B. Rainwater infiltration
C. Manpower shortage
D. Ventilation failure
E. Dust
Answer: B.
Solution: Water weakens dumps → collapse.
Q5 Rajmahal OC dump disaster (2016) caused due to:
A. Gas explosion
B. Weak dump + rain infiltration
C. Fire
D. Winding accident
E. Conveyor belt failure
Answer: B.
Solution: Dump collapse due to weak strata and water.
Q6 Preventive measure against dump failure:
A. Oversteepening dumps
B. Compaction & terracing
C. Random dumping
D. Reducing berms
E. Increasing height beyond limit
Answer: B.
Solution: Compaction & terracing improve stability.
Q7 Slope monitoring method:
A. Drone
B. Inclinometer, radar
C. CCTV
D. Workers’ watch
E. Wind speed meter
Answer: B.
Solution: Instruments detect slope movement.
Q8 DGMS circular on slope stability is:
A. Tech Circular 02 of 2010
B. Tech Circular 05 of 2015
C. Legis Circular 01 of 2019
D. Exam Circular 01 of 2021
E. None
Answer: A.
Solution: Tech Circular 02/2010 covers slope monitoring.
Q9 Water inflow in dumps is prevented by:
A. Barriers
B. Garland drains
C. High bench angle
D. Blasting control
E. Vehicle berms
Answer: B.
Solution: Drains divert water.
Q10 Safety berms prevent:
A. Dump collapse
B. Vehicle edge fall
C. Fire spread
D. Rain inflow
E. Blasting vibration
Answer: B.
Solution: Berms protect trucks from falling.
Q11 The minimum width of a working bench should be: