Introduction

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Highwall Mining is an advanced surface mining technique designed to extract coal that remains beyond the reach of conventional opencast methods. It bridges the gap between opencast and underground mining, improving resource recovery, safety, and environmental sustainability. The system was introduced in the U.S. in the early 1980s and has since been adapted in Indian mines under CMPDI and CIL supervision.

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🧭 1. Concept of Highwall Mining 

 Highwall Mining operates at the final wall (highwall) of an opencast mine. Instead of leaving the remaining coal unmined, this system drives continuous miner-type machines horizontally into the coal seam through small openings.

• Entry size: 3.5–4.5 m (height) × 5–6 m (width)
• Penetration depth: up to 400 m
• Output per day: 1,500–2,000 tonnes (depending on seam thickness and geology)

It’s also called a remote-controlled mining system because no operator enters the seam; all operations are controlled from outside.

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🏗️ 2. Evolution of Highwall Mining

Era	Development
1960s	Early auger mining concept in the U.S.
1980s	Introduction of Highwall Miner (HWM) by Addcar & Superior Coal Co.
1990s	Automated pushbeam systems developed
2000s	Highwall mining introduced in India (CMPDI, NCL, SECL)
2010s	Advanced tele-remote monitoring and slope sensors
2020s	Focus on sustainable extraction and DGMS safety integration

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⚙️ 3. Working Principle 

 Highwall Mining uses a continuous miner module mounted on a base crawler.
The machine cuts coal with a rotating cutter head and conveys it through pushbeams using a chain conveyor system. The cut coal travels through the pushbeam train to the feeder breaker, which loads coal into trucks or conveyors. Major Subsystems:

1. Cutter Head & Conveyor Module
2. Pushbeam Train (Extendable Conveyor Tubes)
3. Tractor or Launch Vehicle
4. Control Cabin & Monitoring Sensors

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⚡ 4. Advantages of Highwall Mining

• Higher recovery from final highwall (up to 80%)
• No underground workforce exposure
• Lower cost compared to underground mining
• Faster deployment and mobility
• Suitable for steep seams and multi-seam operations

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⚠️ 5. Limitations

• Restricted to competent roof and dry conditions
• Limited penetration (400–500 m max)
• Requires skilled operation & real-time monitoring
• Risk of cavity collapse if pillar design is poor

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📘 6. DGMS Guidelines & Indian Adoption DGMS allows Highwall Mining under strict safety standards as per:

• Coal Mines Regulations (CMR 2017) – Reg. 99–104 (Safety, Support & Inspection)
• DGMS Tech Circular No. 01 of 2015 – Safety in Highwall Mining operations
• CMPDI Guidelines (2013) – Site selection, slope design, and monitoring requirements

Highwall Mining has been successfully implemented at:

• SECL Sharda Mine
• NCL Dudhichua Project
• MCL Lajkura OCP
• SCCL Ramagundam Project

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📌 7. Important Parameters (DGMS Focus)

Parameter	Typical Range
Seam Thickness	2.5–6.0 m
Dip	<10° preferred
Web Pillar Width	7–12 m
Barrier Pillar Width	25–40 m
Maximum Penetration	300–400 m
Recovery	50–80% of residual coal
Safety Factor	≥ 1.5 for pillar design

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⚡ Quick One-Liners (Revision Points)

• Highwall Mining = bridge between opencast & underground.
• Max penetration: 300–400 m.
• Web pillars: 7–12 m.
• Barrier pillars: 25–40 m.
• DGMS Circular: Tech Circular 01/2015.
• Controlled from surface → no person inside coal seam.
• Safe for steep seams <10° dip.

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✍️ Descriptive Model Answer

 Q: Explain the concept and advantages of Highwall Mining.

 Answer:
Highwall Mining is a remotely operated surface mining system used to recover residual coal beyond the economic limit of opencast mines. It employs a continuous miner and pushbeam system to cut coal and transport it outside the seam without man entry. Advantages:

• Enhanced recovery (up to 80%)
• Reduced environmental footprint
• Lower operating cost
• No underground workforce exposure
• Applicable for steep, thin seams

DGMS mandates slope stability analysis, remote monitoring, and approved operation plans for all HWM projects in India.

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🎯 25 MCQs – Highwall Mining Basics (DGMS Exam Format) 

Q1. Highwall Mining is mainly applied in:
A. Deep underground mines
B. End walls of opencast mines
C. Shaft sinking
D. Longwall panels
E. None
Answer: B.
Solution: It’s done from the final highwall of an opencast mine.

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Q2. Maximum penetration depth in modern HWM is:
A. 50 m
B. 150 m
C. 300–400 m
D. 700 m
E. Unlimited
Answer: C.
Solution: Pushbeam train limits penetration to 300–400 m.

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Q3. Highwall Mining combines features of:
A. Underground & longwall mining
B. Opencast & auger mining
C. Hydraulic & solution mining
D. Borehole & longwall
E. None
Answer: B.
Solution: It evolved from auger mining.

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Q4. Cutter module of a HWM resembles:
A. Shovel
B. Continuous miner
C. Dragline
D. Dozer
E. Drill jumbo
Answer: B.
Solution: It cuts coal like a continuous miner.

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Q5. Major advantage of HWM over underground mining:
A. Lower recovery
B. Higher cost
C. No human entry in seam
D. High manual labour
E. None
Answer: C.

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Q6. DGMS Tech Circular 01/2015 relates to:
A. Fire precautions
B. Ventilation standards
C. Highwall Mining safety
D. Blasting rules
E. Survey regulations
Answer: C.

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Q7. Optimum web pillar width (m):
A. 2–4
B. 7–12
C. 20–25
D. 40
E. 50
Answer: B.

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Q8. Maximum seam dip for efficient HWM operation:
A. 5°
B. <10°
C. 15°
D. 20°
E. >25°
Answer: B.

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Q9. Barrier pillar width (m):
A. 10
B. 15
C. 25–40
D. 50–60
E. 5
Answer: C.

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Q10. CMPDI first demonstrated HWM at:
A. Dudhichua
B. Lajkura
C. Sharda Mine
D. Jayant Project
E. Kusmunda
Answer: A.

Q11. The Highwall Mining system primarily uses which technology for cutting and conveying coal?
A. Drill & blast
B. Chain conveyor with pushbeam system
C. Belt conveyor inside the seam
D. Hydraulic slurry transport
E. Shuttle cars
Answer: B.
Solution: The pushbeam system conveys coal using chain conveyors from the cutter head to the surface.

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Q12. Which of the following ensures slope safety in Highwall Mining operations?
A. Visual inspection only
B. Rock mass rating system
C. Slope stability radar and geotechnical monitoring
D. Daily drilling
E. Water sprinkling
Answer: C.
Solution: Modern HWM uses radar and geotechnical sensors to monitor slope movement in real-time.

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Q13. DGMS mandates pre-operational approval for HWM under which regulation?
A. CMR 2017, Reg. 99
B. CMR 2017, Reg. 124
C. CMR 2017, Reg. 104
D. CMR 2017, Reg. 170
E. CMR 2017, Reg. 178
Answer: A.
Solution: Regulation 99 covers approval and inspection of mine plans, including mechanized systems like HWM.

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Q14. The pushbeam length in HWM is typically:
A. 1 m
B. 2 m
C. 6 m
D. 10 m
E. 12 m
Answer: C.
Solution: Each pushbeam is around 6 m and forms the extendable train of the system.

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Q15. For slope safety, the bench angle for Highwall operation should generally be:
A. 30°
B. 45°
C. ≤ 60° (depending on rock stability)
D. 75°
E. 90°
Answer: C.
Solution: The overall bench angle should not exceed 60°, depending on rock condition and design study.

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Q16. Which of the following instruments is used for real-time monitoring in HWM?
A. Theodolite
B. Tiltmeter
C. Slope stability radar (SSR)
D. Altimeter
E. Tachometer
Answer: C.
Solution: SSR provides continuous slope movement data to prevent wall failures.

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Q17. What is the usual method for coal transport from feeder breaker in HWM?
A. Underground belt
B. Road dumpers or surface conveyor
C. Hydraulic pipes
D. Tramming cars
E. None
Answer: B.
Solution: Coal is fed to dumpers or conveyor systems at the surface for dispatch.

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Q18. The cutter head in a HWM machine is powered by:
A. Hydraulic system
B. Diesel engine
C. Electric motor
D. Pneumatic pressure
E. Manual drive
Answer: C.
Solution: The cutter head operates with high-power electric motors.

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Q19. Barrier pillars in HWM act as:
A. Coal extraction points
B. Fire suppression zones
C. Safety barriers preventing highwall failure
D. Roof support lines
E. Access tunnels
Answer: C.
Solution: Barrier pillars isolate extraction zones and prevent slope failure.

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Q20. What is the approximate safety factor recommended for pillar design in HWM?
A. 1.0
B. 1.2
C. ≥1.5
D. 2.0
E. 0.9
Answer: C.
Solution: DGMS recommends a minimum safety factor of 1.5 for stability assurance.

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Q21. Which DGMS document provides slope safety guidance for HWM?
A. Tech Circular 02 of 2010
B. Tech Circular 01 of 2015
C. Rescue Rules 1985
D. CMR 2017, Reg. 105
E. Mines Act 1952, Sec. 19
Answer: B.
Solution: Tech Circular 01 of 2015 gives specific HWM safety protocols.

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Q22. HWM is most efficient when the seam thickness is:
A. <1 m
B. 2.5–6 m
C. 8–12 m
D. >15 m
E. Variable
Answer: B.
Solution: Optimal for medium-thick seams of 2.5–6 m thickness.

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Q23. Which of the following helps in determining the optimal web pillar design?
A. RQD values only
B. Empirical formula + numerical modeling
C. Guesswork
D. Rock mass visual observation
E. None
Answer: B.
Solution: DGMS requires numerical modeling using software like FLAC3D or Phase2.

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Q24. What does the Launch Vehicle do in HWM?
A. Drills holes
B. Pushes and retrieves pushbeams
C. Pumps coal slurry
D. Operates ventilation
E. Supports the face
Answer: B.
Solution: The launch vehicle feeds and retrieves pushbeams during operation.

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Q25. The key DGMS requirement for Highwall Mining projects before approval is:
A. Manual inspection only
B. Geotechnical study, slope analysis & risk assessment
C. Manager’s signature only
D. Local council approval
E. None
Answer: B.
Solution: DGMS mandates full geotechnical and risk assessment before operation.

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                    ✅ Conclusion

Highwall Mining stands as a strategic, semi-mechanized method ensuring optimum coal recovery while meeting DGMS safety and operational standards.
By integrating remote systems, geotechnical monitoring, and efficient design, this method maximizes productivity while reducing risk — a must-know topic for every DGMS First & Second Class Manager candidate.

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