Slope Stability, Design & Monitoring in Opencast Mines – DGMS Guidelines & 25 MCQs

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

🧾 DETAILED NOTES

1️⃣ Introduction

Slope stability is one of the most critical safety aspects in opencast coal and metalliferous mines. Failure of pit or dump slopes can lead to loss of life, damage to machinery, production stoppage, and environmental hazards. DGMS mandates proper design, control, and continuous monitoring of slopes through geotechnical assessments.

2️⃣ Types of Slopes in Opencast Mines

Pit Slopes: Include individual bench faces, bench slopes, and overall pit slope.
Dump Slopes: Formed by external & internal dumping of overburden.

3️⃣ Slope Design Parameters

Design must be prepared by a Qualified Geotechnical Engineer considering Rock Mass Rating (RMR), geological discontinuities, shear strength, water conditions, and excavation depth. Slope design must comply with:

CMR 2017, Reg. 106 & 107
MMR 1961, Reg. 134, 135
DGMS Technical Circulars

4️⃣ Causes of Slope Failure

Weak geological structures (joints, faults).
Excessive bench height or steep slope angles.
Poor drainage & water infiltration.
Overloading of dump tops.
Seismic activity.
Poor blasting practices.
Inadequate geotechnical study.

5️⃣ Slope Control Measures

Bench Design Rules: Maintain safe bench height, provide adequate berms, and create catch berms to retain rolling boulders.

Proper Drainage: Toe drainage, garland drains, and pumping systems to prevent water accumulation in the pit.

Controlled Blasting: Use of pre-split blasting and smooth blasting to avoid over-break.

Dump Stability: Maintain angle of repose, compaction of dumps, proper dumping sequence, and use dozers to maintain slope geometry.

6️⃣ Slope Monitoring Techniques

Visual Monitoring: Daily inspection by supervisors.
Instrumental Monitoring: Slope Stability Radar (SSR), Ground-based LiDAR, Geophones, Inclinometers, Piezometers, Prism monitoring (Total Station), Drones for slope profiling.
Alarms & Alerts: Real-time slope movement detection with warning thresholds.

7️⃣ Geotechnical Cell Requirements

Every large opencast mine must have a Geotechnical Engineer, a slope monitoring team, monitoring instruments, a regular reporting system, and an annual review of slope design.

8️⃣ Emergency Preparedness

Establish exclusion zones, evacuation plans, movement restrictions near unstable slopes, and immediate action when cracks or subsidence are observed.

⚡ QUICK ONE-LINERS (Revision)

Slope stability is crucial for opencast mine safety.
Bench height & angle depend on geotechnical study.
Controlled blasting reduces over-break.
Garland drains prevent water accumulation.
Dump slopes must follow angle of repose.
SSR provides real-time slope monitoring.
Piezometers measure pore water pressure.
Cracks are early signs of slope instability.
Geotechnical engineer must approve slope design.
Monitoring must be continuous in rainy seasons.

🧠 DESCRIPTIVE MODEL Q&A

Q. Explain the design, control, and monitoring requirements of pit and dump slopes in opencast mines according to DGMS standards.

Answer:
The design of pit and dump slopes must be based on a comprehensive geotechnical study that considers geological discontinuities, rock mass rating, water pressure, and excavation depth. Bench height, width, and overall slope angle must comply with CMR 2017 and DGMS guidelines. Control measures include drainage management, controlled blasting, dump compaction, and maintaining the angle of repose. Monitoring must be done using instruments such as SSR, piezometers, inclinometers, and total station. Visual inspections and emergency preparedness are essential to prevent slope failure.

🧮 25 MCQs (Dynamic Answers A–E)

Q1. Slope design is approved by:

Solution: Slope design is a specialized field requiring a qualified Geotechnical Engineer to assess rock mechanics and stability.

Q2. Excess water in slopes leads to:

Solution: Water increases pore pressure and reduces shear strength, leading to slope instability.

Q3. SSR is used for:

Solution: Slope Stability Radar (SSR) is a modern technology for real-time monitoring of slope movement.

Q4. Bench height depends on:

Solution: Bench height is primarily determined by the strength and stability of the rock mass, along with equipment reach.

Q5. Controlled blasting includes:

Solution: Pre-split blasting is a technique used to create a fracture plane along the final wall, minimizing damage to the remaining rock.

Q6. Dump stability depends on:

Solution: The angle of repose is the steepest angle at which loose material (dump) remains stable without sliding.

Q7. Drainage system includes:

Solution: Garland drains are essential for diverting surface water away from the mine pit and dumps.

Q8. Cracks on slopes indicate:

Solution: Tension cracks appearing on the crest or face of a slope are often the first warning sign of movement and potential failure.

Q9. Piezometers measure:

Solution: Piezometers are instruments used to measure pore water pressure within the rock or soil mass.

Q10. Dumps must be:

Solution: Proper compaction of dump material increases its density and shear strength, improving stability.

Q11. Toe failure occurs at:

Solution: Toe failure is a type of slope failure where the sliding surface passes through the toe (bottom) of the slope.

Q12. Slope failures increase during:

Solution: Rainfall during the monsoon season saturates the ground, increasing pore pressure and reducing stability.

Q13. Bench width provides:

Solution: Adequate bench width acts as a catch berm to stop loose rocks falling from upper benches, protecting equipment below.

Q14. Prisms monitored by:

Solution: Reflective prisms installed on slopes are monitored using Robotic Total Stations to detect minute displacements.

Q15. Internal dumps are located:

Solution: Internal dumps (backfilling) are created by dumping overburden into the void created by mineral extraction within the pit.

Q16. Slope failures are:

Solution: With proper monitoring and geotechnical analysis, slope failures can often be predicted before they collapse.

Q17. Drainage helps:

Solution: Removing water from the slope reduces pore water pressure, which increases the effective stress and stability.

Q18. Key slope monitoring tool:

Solution: Inclinometers are used to measure sub-surface lateral displacements within a slope.

Q19. Dump height must be:

Solution: Dump height must strictly adhere to the geotechnical design parameters to ensure stability.

Q20. Slope Stability Radar gives:

Solution: SSR provides continuous, real-time monitoring of slope face movement and issues warnings if thresholds are exceeded.

Q21. DGMS requires slope monitoring:

Solution: Continuous (regular and systematic) monitoring is mandated to detect early signs of instability.

Q22. Toe drains remove:

Solution: Toe drains are specifically designed to collect and remove water seeping from the base of the slope or dump.

Q23. A berm is:

Solution: A berm is the horizontal step or ledge left between benches to improve stability and catch falling material.

Q24. Failure signs include:

Solution: Bulging at the toe or face of a slope is a physical sign of material displacement and potential failure.

Q25. Slope design must be reviewed:

Solution: An annual review of the slope design and monitoring data is required to ensure ongoing safety and validity of the plan.

🔗 INTERNAL LINKS

Related Topic	Read More On...
Geotechnical Cell	DGMS Tech Circular No. 02 of 2020
Dump Management	Accidents Due to Dump Failure
Opencast Safety	Small Opencast Manager Appointment
CMR 2017	CMR 2017 Part 2 - Working & Supervision

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