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Accidents Due to Dump Failure in Opencast Mines – Causes, Prevention & DGMS Guidelines


Accidents Due to Dump Failure in Opencast Mines – Causes, Prevention & DGMS Guidelines

🧾 DETAILED NOTES

1️⃣ Introduction

Dump failures in opencast mines are among the most severe geotechnical hazards leading to property loss, fatalities, and operational disruption. These accidents occur when the stability of overburden (OB) or waste dumps is compromised due to poor construction, weak foundation, or excessive loading beyond design limits. DGMS has issued several circulars under CMR 2017 – Regulation 106 & 107, focusing on dump design, height restriction, and stability monitoring.

2️⃣ Causes of Dump Failure

  • Improper Dump Design: Excessive slope angle, height, or base instability.
  • Weak Foundation Material: Clay, loose soil, or wet strata below dump toe.
  • Water Seepage: Saturation reduces shear strength of dump material.
  • Improper Drainage: Absence of garland drains or toe drains.
  • Overloading: Dumping beyond safe capacity.
  • Vibration: Due to blasting or movement of heavy equipment.
  • Neglected Monitoring: Absence of instruments like piezometers or tiltmeters.

3️⃣ Warning Signs Before Dump Failure

  • Cracks on dump top.
  • Bulging or settlement at dump toe.
  • Sudden increase in slope movement readings.
  • Water seepage at unusual locations.
  • Displacement of berms or haul roads near dump.

4️⃣ DGMS Regulations and Guidelines

  • Reg. 106 of CMR 2017: Construction and maintenance of OB dumps.
  • Reg. 107: Precautions against failure of OB and waste dumps.
  • DGMS Tech. Circular 1 of 2012: Dump slope monitoring and design approval.
  • DGMS Circular 7 of 2014: Guidelines for OB dump stability analysis.
  • Mandatory monitoring: By geotechnical engineers using slope monitoring radar or prism-based systems.

5️⃣ Preventive Measures

  • Design-Approved Dumps: Based on geotechnical investigation and factor of safety (≥ 1.3).
  • Proper Drainage: Garland drains, toe drains, and settling ponds.
  • Bench Formation: Max height 10 m; overall slope < 28°.
  • Dump Compaction: Layer-wise spreading and compaction.
  • Monitoring: Slope stability radar, prisms, or total station.
  • Buffer Zone: No work within 30 m of dump toe unless declared safe.
  • Regular Inspection: Weekly by Mine Manager and Safety Officer.

6️⃣ Case Example (DGMS Report – 2014)

A fatal accident occurred due to dump slide in a coal mine, killing 4 workers. Investigation revealed lack of drainage and steep dump slope beyond design limit. DGMS ordered compliance with Circular 7 of 2014, emphasizing mandatory geotechnical assessment for all OB dumps.

7️⃣ Consequences of Dump Failure

  • Loss of life and property.
  • Damage to haul roads and machinery.
  • Disruption of production.
  • DGMS investigation and legal actions under CMR 2017.

⚙️ QUICK ONE-LINERS (Revision Points)

  • Regulation 106 & 107 of CMR 2017 deal with dump stability.
  • Maximum overall dump slope ≈ 28°.
  • Factor of Safety for dump stability ≥ 1.3.
  • Garland drains prevent water accumulation.
  • Dump design must be approved by competent geotechnical engineer.
  • Failure often begins at dump toe due to weak strata.
  • Monitoring equipment includes prisms, piezometers, and radar.
  • Dump failures are common after heavy rainfall.
  • CMR mandates proper drainage and toe protection.
  • DGMS Circular 7 of 2014 emphasizes dump stability study.

🧮 DESCRIPTIVE MODEL QUESTION

Q. Explain the causes, preventive measures, and DGMS guidelines to prevent dump failures in opencast mines.

Answer:
Dump failures occur due to improper design, poor drainage, and weak foundations. DGMS under Reg. 106 and 107 of CMR 2017 mandates proper construction, design approval, and monitoring of OB dumps. Preventive measures include drainage arrangements, slope angle control (<28°), compaction, and geotechnical monitoring. Regular inspections and safety audits help ensure dump stability and prevent accidents.

🧩 25 DGMS-Based MCQs (Dynamic Answers – A–E)

Q1. Dump failures are mainly associated with:

Solution: Dump failures relate to the stability of overburden (OB) or waste dumps, which are features of opencast mines.

Q2. Regulation related to dump construction is:

Solution: Regulation 106 of CMR 2017 specifically details the construction and maintenance of OB dumps.

Q3. Maximum overall slope of OB dump should not exceed:

Solution: DGMS guidelines often specify that the overall dump slope angle should not be steeper than 28 degrees.

Q4. The minimum Factor of Safety (FOS) for dump stability is:

Solution: A minimum Factor of Safety of 1.3 is generally required for long-term geotechnical stability of mine dumps.

Q5. Common cause of dump failure:

Solution: Excessive weight (overloading) and water saturation (poor drainage) are primary triggers for dump failures.

Q6. DGMS Circular 7 of 2014 deals with:

Solution: This circular was issued to provide clear guidelines for the geotechnical assessment and stability analysis of OB dumps.

Q7. Which of the following is an early warning of dump failure?

Solution: All three (cracks, bulging, and seepage) are classic indicators of potential dump instability.

Q8. Ideal compaction technique for dump layers:

Solution: Spreading material in layers and compacting it (e.g., with dozers) increases the density and stability of the dump.

Q9. Maximum height of a single dump bench:

Solution: DGMS guidelines often restrict the height of individual benches to 10m to ensure stability before the next bench is started.

Q10. Dump monitoring is done by:

Solution: Dump stability is a geotechnical subject, requiring assessment and monitoring by a qualified geotechnical engineer.

Q11. Weak foundation increases:

Solution: A weak foundation (like clay or soil) cannot support the weight of the dump, increasing the likelihood of a slip failure.

Q12. Water saturation reduces:

Solution: Water reduces the internal friction (shear strength) and cohesion of the dump material, directly reducing its overall stability.

Q13. Regulation 107 of CMR 2017 emphasizes:

Solution: Regulation 107 is titled "Precautions against failure of overburden dumps, stock-piles and waste-dumps".

Q14. The first indication of dump slide is:

Solution: Physical deformation, such as tension cracks at the top or bulging at the toe, are the earliest visible signs of instability.

Q15. Factor affecting dump stability most:

Solution: Water is the primary destabilizing agent in most dump failures; therefore, drainage is the most critical control measure.

Q16. DGMS mandates inspection of dumps by:

Solution: Regular (often weekly) inspections by competent persons are mandated to check for early signs of failure.

Q17. Instrument used for monitoring slope movement:

Solution: Piezometers (water pressure), Total Stations (surface movement), and others are all part of a geotechnical monitoring system.

Q18. Garland drains are provided:

Solution: Garland (or toe) drains are built at the base of the dump to intercept and drain water seeping from it.

Q19. Dump failure is an example of:

Solution: A dump failure is a classic geotechnical slope stability failure.

Q20. Factor of safety below 1 indicates:

Solution: FOS < 1 means the destabilizing forces are greater than the resisting forces, indicating failure is imminent or in progress.

Q21. Safety distance from dump toe:

Solution: A buffer zone, often 30m or more depending on dump height, is required to protect workers and equipment from potential toe failures.

Q22. Dump failures commonly occur during:

Solution: Heavy rainfall increases water saturation and pore pressure within the dump, significantly reducing its stability.

Q23. Regular monitoring helps in:

Solution: Geotechnical monitoring provides data on movement and pressure, which helps in predicting failures before they become catastrophic.

Q24. Overburden dump design must be:

Solution: DGMS circulars mandate that dump designs must be based on a scientific study by a competent geotechnical engineer or institution.

Q25. Primary purpose of dump drainage:

Solution: Drains are installed to relieve pore water pressure within the dump, which is a major destabilizing force.

🔗 INTERNAL LINKS

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