Pit and Dump Slope Design, Control & Monitoring in Opencast Mines – DGMS Guidelines & 25 MCQs

🧾 DETAILED NOTES

1️⃣ Introduction

Slope stability is one of the most critical aspects of safety in opencast mines. Failure of pit or dump slopes can result in catastrophic accidents, loss of equipment, and production downtime. Proper design, control, and monitoring of these slopes are essential for safe and sustainable mining operations. DGMS has issued several circulars and guidelines emphasizing scientific slope design and regular geotechnical monitoring.

2️⃣ DGMS Safety Concern

DGMS has observed that most slope failures occur due to: Oversteepening of benches, Uncontrolled dumping, Groundwater seepage, and Inadequate monitoring. Hence, slope stability must be based on geotechnical investigation, scientific design, and continuous monitoring using modern instruments.

3️⃣ Legal Framework

Reference	Description
The Mines Act, 1952 – Sec. 23	Safety of persons employed in mines.
CMR 2017 – Regulation 106	Benches, sides, and faces to be of safe design.
CMR 2017 – Regulation 107	Dump stability and waste disposal.
DGMS Circular (Tech.) No. 07/2011	Systematic slope monitoring and investigation.
DGMS Circular (Tech.) No. 02/2010	Geotechnical cell establishment in large opencast mines.

4️⃣ Objectives of Slope Design and Monitoring

Ensure long-term stability of benches and dumps.
Prevent slope failures and accidents.
Optimize excavation geometry for safety and efficiency.
Comply with DGMS statutory provisions.
Protect manpower, machinery, and environment.

5️⃣ Types of Slopes in Opencast Mines

Type	Description
Pit Slopes	Formed during excavation of mineral/overburden benches.
Dump Slopes	Created by disposal of waste overburden or rejects.
Internal Dumps	Placed within mined-out voids.
External Dumps	Located outside the working pit.

6️⃣ Factors Affecting Slope Stability

Geological discontinuities (faults, joints, bedding planes).
Weak or weathered strata.
Groundwater pressure or seepage.
Mining geometry (height, angle, width).
Explosive vibration effects.
Rainfall and erosion.
Load of equipment and material at the crest.

7️⃣ Design of Slopes

Slope design must be based on geotechnical and hydrogeological studies by a competent agency. Design Parameters Include:

Bench height and width based on rock strength.
Overall slope angle for long-term stability.
Catch berms at suitable intervals.
Drainage arrangements to prevent water accumulation.
Slope stability analysis using software (FLAC, SLOPE/W, etc.).

DGMS requires all large opencast mines (>5m³/day output) to have a Geotechnical Cell for design validation.

8️⃣ Control and Monitoring of Slopes

📡 Monitoring Techniques

Method	Instrument	Purpose
Surface Movement	Inclinometer / Prism	Detects slope deformation.
Groundwater Pressure	Piezometer	Measures pore pressure.
Laser/Drone Survey	Lidar/Drone	Periodic slope mapping.
Crack Monitoring	Extensometer	Records widening of cracks.
Remote Monitoring	Radar and LiDAR	Real-time slope tracking.

Manual visual checks should be done daily, and instrumental monitoring weekly or as per design report.

9️⃣ Preventive Measures

Maintain safe bench geometry (height ≤ 10 m, width ≥ 1.5 × height).
Construct proper toe and surface drainage.
Avoid loading at the crest of slopes.
Carry out controlled blasting near weak slopes.
Keep catch ditches at the toe to trap falling debris.
Vegetate and compact dump surfaces to reduce erosion.
Install slope monitoring alarms in high-risk zones.

⚙️ QUICK ONE-LINERS (Revision Points)

Reg. 106 & 107 – Slope and dump safety.
Max slope angle: 28° (OB dumps).
FOS ≥ 1.3 (static condition).
Drainage is vital for slope stability.
Monitoring by geotechnical engineer mandatory.
Piezometer and prism – key instruments.
Dump failures are most common after heavy rain.
Design approval needed from DGMS.
Circular 7/2014 – Slope stability study.
Garland drains prevent toe erosion.

🧮 DESCRIPTIVE MODEL QUESTION

Q. Explain the design, control, and monitoring measures of pit and dump slopes in opencast mines as per DGMS guidelines.

Answer:
According to DGMS Circulars 07/2011 and 02/2010, all mechanized opencast mines must design slopes scientifically based on geotechnical investigations. Pit and dump slopes must have safe bench geometry, proper drainage, and catch ditches. Monitoring instruments like piezometers, inclinometers, and extensometers should be installed to detect early movement. Dump slopes must be compacted and vegetated to prevent erosion. All slope monitoring data should be analyzed by a Geotechnical Cell and records maintained for DGMS inspection. This ensures safe mining operations and prevents slope failures.

🧩 25 DGMS-Based MCQs (5 Options Each)

Q1. Regulation dealing with slope stability in opencast mines:

Solution: Regulation 106 of CMR 2017 specifically addresses the safety of sides (pit slopes) and benches.

Q2. Maximum overall slope angle for OB dump:

Solution: 28° is the commonly accepted safe overall slope angle for overburden dumps under standard conditions.

Q3. Factor of safety for slope design should be:

Solution: A minimum Factor of Safety of 1.3 is required for long-term static stability.

Q4. The key DGMS circular for slope stability:

Solution: DGMS Technical Circular 7 of 2014 provides comprehensive guidelines for dump stability analysis.

Q5. Instrument used for slope movement detection:

Solution: Piezometers (water), Extensometers (cracks), and Inclinometers (sub-surface movement) are all used.

Q6. Primary cause of slope failure:

Solution: Geotechnical weakness (weak strata) and high water pressure (poor drainage) are the primary drivers of slope instability.

Q7. FOS under seismic condition must be at least:

Solution: Under dynamic (seismic/earthquake) loading, a slightly lower FOS of 1.1 is often considered acceptable.

Q8. Bench height in coal mines should not exceed:

Solution: 10 m is a common maximum bench height for OB dumps, though pit bench height depends on the excavator's reach.

Q9. Bench width must be:

Solution: The width must be adequate for the largest machinery, typically 3 times its width for safe two-way passage.

Q10. DGMS mandates slope monitoring by:

Solution: Slope stability is a specialized field requiring a qualified Geotechnical Engineer.

Q11. Cracks on slope indicate:

Solution: Tension cracks are a clear visual warning sign that the slope is under stress and may be failing.

Q12. Slope failure often occurs after:

Solution: Rainfall (saturation) and overloading are both major triggers that reduce stability and can cause failure.

Q13. The purpose of garland drains is:

Solution: Garland drains are built around the dump to intercept surface runoff water and divert it away from the slope.

Q14. Safe dump height depends on:

Solution: All these geotechnical factors must be considered in designing a safe dump height.

Q15. Visual monitoring frequency should be:

Solution: Daily visual checks by competent persons are essential, supplemented by weekly instrumental monitoring.

Q16. Instrument measuring pore pressure:

Solution: Piezometers are specifically designed to measure pore water pressure within soil or rock.

Q17. Dump failures are categorized under:

Solution: Slope stability is a core subject of geotechnical engineering.

Q18. Stability analysis is performed by:

Solution: Only a qualified geotechnical engineer has the expertise to conduct slope stability analysis.

Q19. Regulation 107 relates to:

Solution: Regulation 107 of CMR 2017 is titled "Precautions against failure of overburden dumps..."

Q20. Real-time slope monitoring can use:

Solution: All these technologies (LiDAR, Radar, robotic Total Stations with prisms) are used for advanced, real-time monitoring.

Q21. Catch drain purpose:

Solution: Catch drains are built on benches or at the top of slopes to catch and divert surface runoff before it erodes the slope face.

Q22. DGMS requires geotechnical report to be:

Solution: Geotechnical reports/plans must be prepared, filed (often annually or with modifications), and are subject to review/approval by DGMS.

Q23. Overburden dump must be designed by:

Solution: Safe dump design is a specialized task requiring a qualified geotechnical engineer or institution.

Q24. CMR 2017 came into force replacing:

Solution: The Coal Mines Regulations, 2017, superseded the earlier Coal Mines Regulations, 1957.

Q25. Slope stability factor of safety less than 1 means:

Solution: FOS < 1 indicates that the forces causing failure are greater than the forces resisting failure, meaning the slope is unstable.

🔗 INTERNAL LINKS

Related Topic	Read More On...
Geotechnical Cell	DGMS Tech Circular No. 02 of 2020
Opencast Safety	Small Opencast Manager Appointment
Dump Management	Accidents Due to Dump Failure
Risk Assessment	DGMS Campaign on "Risk Calculator"

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