🔹 1. Introduction

Blasting is a key operation in surface mining used to fragment hard rock so that excavators, shovels, and loaders can handle it efficiently.
Blasting quality influences:

• Fragmentation
  
• Shovel productivity
  
• Crusher performance
  
• Cost per tonne
  
• Vibration and safety
  

DGMS sets strict regulations for safety, handling explosives, and blasting procedures in surface operations.

🔹 2. Bench Blasting – Basic Concept

A bench is a step-like working level in an open-pit or open-cast mine.
Blasting breaks the rock on a bench so that it can be excavated.
2.1 Bench Geometry

• Bench Height (H): 8–15 m
  
• Bench Width: ≥ 3 × bench height
  
• Face Angle: 60°–70°
  
• Overall Slope: Depends on rock strength
  

Good bench design improves safety, fragmentation, and stability.
2.2 Bench Blasting Layout (Diagram – Text)
Ground Surface--------------------------------------------------------- | Burden (B) |Hole 1 O ----------------------- Free FaceHole 2 O -----------------------Hole 3 O -----------------------

🔹 3. Blast-Hole Parameters

3.1 Burden (B)Distance from blast-hole to free face.
Controls rock movement.Typical value:B=25–40×hole diameterB = 25–40 \times \text{hole diameter}B=25–40×hole diameter
3.2 Spacing (S)Distance between adjacent holes.Typical:S=1.0–1.5×BS = 1.0–1.5 \times BS=1.0–1.5×B
3.3 Stemming (T)Inert material filled at the top of hole to confine explosive gases.

• Usually crushed stone
  
• Stemming length = 0.7 × burden
  

3.4 Sub-Drilling (J)Drilled below bench floor to ensure complete breakage.J=0.3–1.0 mJ = 0.3–1.0 \text{ m}J=0.3–1.0 m
3.5 Hole Diameter (D)100–300 mm depending on equipment and rock type.
3.6 Charge Length (L)Occupied by explosive column.

🔹 4. Types of Blasting Patterns

4.1 Square PatternEqual spacing and burden.
O --- O --- O| | |O --- O --- OUsed for uniform geology.
4.2 Staggered PatternHoles in alternate rows are staggered.
O ----- O ----- O O ----- O ----- OO ----- O ----- OGives better fragmentation

.
4.3 Line Drilling / Smooth Blasting

• Holes drilled close together
  
• For final walls
  
• Minimizes overbreak
  

4.4 VCR (Vertical Crater Retreat)Used in very hard rock or deep pits.

🔹 5. Explosives Used in Surface Mines

Explosive	Features
ANFO	Cheap, good for dry holes
Slurry	Water resistant
Emulsion	High energy, good for wet holes
Heavy ANFO	For higher energy needs
Booster	For priming

🔹 6. Initiation & Delay Patterns

Proper delay timing ensures good fragmentation, reduced vibration, and easier digging.

Delay Systems

• Electric detonators
  
• Non-electric (Nonel)
  
• Electronic detonators
  

Delay Patterns

• V-pattern
  
• Diagonal firing
  
• Row-by-row firing
  
• Staggered delay
  

🔹 7. Factors Affecting Fragmentation

• Burden & spacing
  
• Explosive type
  
• Rock hardness
  
• Hole deviation
  
• VOD (Velocity of Detonation)
  
• Timing sequence
  
• Stemming quality
  

🔹 8. Safety in Blasting (DGMS Guidelines)

• Blasting shelters
  
• Warning signals (Red – 5 mins before blast)
  
• Safe blasting zone
  
• Proper stemming
  
• Avoiding misfires
  
• Overbreak control
  
• Use of suitable explosives in wet holes
  
• Supervision by shot-firer with valid certificate
  

🔥 9. Common Blasting Problems

• Flyrock
  
• Overbreak
  
• Backbreak
  
• Poor fragmentation
  
• High vibration
  
• Misfire
  
• Excessive boulders
  
• Underbreak
  

🔥 10. 25 MCQs (DGMS Pattern) with Answers
1) Burden is measured from —

a) Adjacent hole

b) Topsoil
c) Hole to free face
d) Bottom of bench
e) Stemming plug
Answer: c
2) Stemming is used to —

a) Increase hole depth
b) Reduce hole deviation
c) Confine explosive gases
d) Increase density
e) Raise burden
Answer: c
3) Typical bench height in surface mines —

a) 2–4 m
b) 4–6 m
c) 8–15 m
d) 20–30 m
e) None
Answer: c
4) Sub-drilling ensures —

a) More explosive
b) Clean floor breakage
c) High dilution
d) Wet holes
e) None
Answer: b
5) Hole diameter for surface blasting —

a) 50 mm
b) 100–300 mm
c) 400 mm
d) 25 mm
e) None
Answer: b
6) Square pattern is used for —

a) Gold
b) Granite
c) Uniform geology
d) Deep blasting
e) None
Answer: c
7) Staggered pattern improves —

a) Sub-drilling
b) Fragmentation
c) Bench stability
d) Topsoil removal
e) None
Answer: b
8) ANFO is unsuitable in —

a) Dry holes
b) Air-blast
c) Wet holes
d) Hard rock
e) VCR blasting
Answer: c
9) Emulsion explosives are —

a) Not water resistant
b) Cheap
c) Highly water resistant
d) Weak
e) None
Answer: c
10) Delay detonators reduce —

a) Bench height
b) Spacing
c) Vibration
d) Air blast
e) None
Answer: c
11) Flyrock is caused by —

a) Low stemming
b) Wrong timing
c) Excess explosive
d) All of these
e) None
Answer: d
12) VOD refers to —

a) Volume of dust
b) Ventilation
c) Velocity of detonation
d) Velocity of drill
e) Volume of det cord
Answer: c
13) Best fragmentation achieved with —

a) Single hole
b) Same row timing
c) Correct burden, spacing & timing
d) High stemming
e) No delay
Answer: c
14) Smooth blasting requires —

a) High explosives
b) No spacing
c) Line drilling
d) No sub-drill
e) None
Answer: c
15) Column charge occupies —

a) Entire hole
b) Top portion
c) Lower portion of hole
d) Stem section
e) None
Answer: c
16) A misfire refers to —

a) Quick blast
b) Small blast
c) Incomplete detonation
d) High muckpile
e) None
Answer: c
17) DGMS requires blasting shelters to be —

a) Optional
b) Mandatory
c) Only in underground
d) For small holes only
e) None
Answer: b
18) Major blasting hazard —

a) Flooding
b) Roof fall
c) Flyrock
d) Manriding
e) None
Answer: c
19) Stemming material should be —

a) Wood
b) Sand
c) Crushed inert stone
d) Coal dust
e) Clay only
Answer: c
20) Backbreak occurs due to —

a) Weak explosive
b) Excess burden
c) High spacing
d) Low sub-drill
e) None
Answer: b
21) Bench width depends on —

a) Blast size
b) Equipment size
c) Explosive density
d) Hole depth
e) None
Answer: b
22) Air blast is —

a) Gas emission
b) Shock pressure wave in air
c) Diesel exhaust
d) Cutter noise
e) None
Answer: b
23) Poor fragmentation leads to —

a) High shovel productivity
b) Low crusher output
c) High safety
d) Low blasting cost
e) None
Answer: b
24) Delay timing is used to —

a) Increase density
b) Increase vibration
c) Control rock throw
d) Remove stemming
e) None
Answer: c
25) Blast design is mainly the function of —

a) Truck size
b) Loader bucket
c) Rock mass & hole geometry
d) Haul road
e) None
Answer: c
                         🔚 Conclusion

Blasting in surface mines is a precise scientific operation involving the right combination of drilling patterns, bench design, explosive selection, and timing.
Correct blast engineering ensures better fragmentation, improved productivity, and reduced hazards as per DGMS norms.

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