Introduction

💣 Cast Blast Design & Burden Control – DGMS Exam Notes Cast blasting is a specialized technique used in opencast mines to move a large volume of overburden into the adjacent void by blasting energy — thus reducing the cost and time of mechanical excavation.
DGMS highlights design, vibration control, and burden accuracy as key safety parameters under CMR 2017 Reg. 106–115 and related circulars. ⚙️ 1. Concept of Cast Blasting Objective:
To utilize explosive energy for both fragmentation and casting (throwing) of overburden. Applications:

• Dragline and shovel-dumper operations
• High-production coal mines (e.g., NCL, MCL, SCCL)
• Large bench heights (up to 45 m)

Design Goals:

1. Maximize horizontal displacement (casting).
2. Maintain fragment size suitable for dozers.
3. Control vibration, flyrock, and over-digging.

📐 2. Burden & Spacing Design Burden (B): Distance from hole to free face.
Spacing (S): Distance between holes. Typical ratios:

• Burden : Hole depth = 1 : 2.5
• Spacing : Burden = 1.2 – 1.5

Example:
For 10 m hole depth → Burden = 4 m, Spacing ≈ 5 m–6 m. Controlled Burden is critical:

• Too small → Flyrock & over-break.
• Too large → Poor fragmentation & toe problems.

🔩 3. Blast Design Parameters

Parameter	Typical Range	Remarks
Hole dia	150 – 311 mm	Based on HEMM capacity
Bench height	10 – 45 m	Must match dragline reach
Burden	3 – 8 m	Smaller in hard strata
Spacing	4 – 10 m	Depends on burden
Stemming	20 – 30 % of hole depth	Controls flyrock
Sub-drilling	0.3 – 0.6 × burden	Ensures toe break
Powder factor	0.5 – 0.8 kg/m³	Based on rock hardness

🧮 4. Cast Percentage Calculation \text{Cast %} = \frac{\text{Volume thrown beyond the free face}}{\text{Total blasted volume}} \times 100

• Optimum cast = 30–50 %.
• Influenced by burden, spacing, charge distribution, and delay timing.

🔥 5. DGMS Guidelines for Safe Cast Blasting

1. Ensure approved blast design plan.
2. Use delay detonators (≥ 17 ms inter-row delay).
3. Maintain safe vibration levels (≤ 19 mm/s near structures).
4. Record PPV and flyrock distances for each blast.
5. Maintain blast log books per Reg. 115 of CMR 2017.
6. Employ blasting shelters and warning signals.
7. Supervision by competent shot-firer or manager.

🧭 6. Field Example (NCL Jayant Project) Proper burden design (5.5 m) and optimized delay pattern improved cast percentage from 35 % → 48 % while reducing flyrock incidents.
DGMS appreciated the method for vibration control and safety compliance. 📌 Exam-Oriented Quick Notes

• Cast blasting = Controlled overburden movement.
• Optimum burden = 4–6 m; spacing ≈ 1.25 × burden.
• Stemming = 20–30 % of hole depth.
• Cast % = 30–50 %.
• Reg. 106–115 → Blasting regulations.
• Delay detonators & PPV monitoring mandatory.
• Maintain blast log for 5 years.

🎯 25 MCQs – Cast Blast Design & Burden Control (DGMS Pattern)

Q1. Main objective of cast blasting is:
A. Increase fragmentation
B. Reduce flyrock
C. Move overburden by explosive energy
D. Reduce powder factor
E. Increase bench height
Answer: C
Solution: Casting displaces overburden, cutting excavation cost.

Q2. Ideal cast percentage in dragline mines is:
A. 10–20 %
B. 25–35 %
C. 30–50 %
D. 60–80 %
E. > 80 %
Answer: C Q3. Typical burden-to-spacing ratio is:
A. 1 : 1
B. 1 : 1.2–1.5
C. 1 : 2
D. 1 : 3
E. 1 : 0.5
Answer: B Q4. Sub-drilling ensures:
A. Smooth wall
B. Toe breakage
C. Less vibration
D. Reduced stemming
E. Smaller burden
Answer: B Q5. Stemming should be about:
A. 10 %
B. 15 %
C. 20–30 %
D. 40 %
E. None
Answer: C Q6. Optimum powder factor in cast blasting is:
A. 0.3 kg/m³
B. 0.5–0.8 kg/m³
C. 1.5 kg/m³
D. 2.0 kg/m³
E. 3.0 kg/m³
Answer: B Q7. Excessive burden causes:
A. Flyrock
B. Back-break
C. Poor fragmentation
D. Smooth wall
E. High vibration
Answer: C Q8. DGMS regulation governing blasting in opencast mines:
A. Reg. 100
B. Reg. 106–115
C. Reg. 121
D. Reg. 130
E. Reg. 140
Answer: B Q9. The minimum stemming length for a 20 m hole is about:
A. 2 m
B. 3 m
C. 4–6 m
D. 8 m
E. 10 m
Answer: C Q10. Flyrock can be reduced by:
A. Increasing stemming
B. Reducing burden
C. Increasing spacing
D. Decreasing sub-drilling
E. Reducing hole depth
Answer: A Q11. Inter-row delay recommended by DGMS:
A. 1 ms
B. 5 ms
C. 17–25 ms
D. 50 ms
E. 100 ms
Answer: C Q12. PPV stands for:
A. Peak Pressure Variation
B. Peak Particle Velocity
C. Powder Pressure Value
D. Pulse Power Variation
E. None
Answer: B Q13. Recording blast data is mandatory for:
A. 1 month
B. 3 months
C. 1 year
D. 5 years
E. 10 years
Answer: D Q14. Flyrock risk increases with:
A. Large burden
B. Small burden
C. Proper stemming
D. Low charge per hole
E. High inter-row delay
Answer: B Q15. Sub-drilling depth = ___ × burden.
A. 0.1–0.2
B. 0.3–0.6
C. 0.8–1.0
D. 1.5
E. 2.0
Answer: B Q16. Powder factor indicates:
A. Explosive per delay
B. Explosive per unit volume
C. Rock density
D. Delay interval
E. Bench width
Answer: B Q17. Cast blasting mainly applies to:
A. Underground mines
B. Quarries
C. Opencast dragline mines
D. Tunnel drives
E. None
Answer: C Q18. Stemming material should be:
A. Loose soil
B. Coarse drill cuttings
C. Sand & clay mix
D. Explosive residue
E. Water
Answer: B Q19. Flyrock distance should not exceed:
A. 100 m
B. 300 m
C. 500 m
D. 1000 m
E. 1500 m
Answer: C Q20. Effective burden control helps in:
A. Reducing vibration
B. Ensuring uniform fragmentation
C. Preventing over-dig
D. All of the above
E. None
Answer: D Q21. DGMS requires warning signals to be given:
A. 30 s before firing
B. 1 min before firing
C. 5 min before firing
D. 10 min before firing
E. None
Answer: C Q22. Over-drilling increases:
A. Flyrock
B. Toe breakage
C. Slope stability
D. Fragmentation only
E. None
Answer: A Q23. Delay detonators are preferred to:
A. Instantaneous detonators
B. Electric detonators
C. Non-el detonators
D. Shock tubes
E. Cord relays
Answer: A Q24. The best indicator of blast efficiency is:
A. Vibration level
B. Fragmentation uniformity
C. Flyrock distance
D. Bench width
E. Noise level
Answer: B Q25. DGMS requires supervision during blasting by:
A. Mate
B. Overman
C. Manager or shot-firer
D. Surveyor
E. Time-keeper
Answer: C 🧩                                     Conclusion 

Proper cast blast design and accurate burden control are essential for safe and economical overburden removal.

Adhering to DGMS regulations ensures reduced vibration, improved slope stability, and higher productivity.
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