🔹 1. Introduction

Drilling is a major unit operation in surface mining and is essential for:

• Blasting
  
• Overburden removal
  
• Ore fragmentation
  
• Sampling and grade control
  
• Bench preparation
  

It determines blast quality, fragmentation, and overall cost of mining.
The quality of drilling directly affects hole deviation, explosive distribution, and shovel productivity.

🔹 2. Types of Drilling Methods in Surface Mining

Surface mines use the following drilling mechanisms:

2.1 Percussive Drilling

The drill bit repeatedly strikes the rock.

Used in:

• Hard rock
  
• Mining quarries
  
• Shallow hole drilling
  

Machines:

• Jackhammers
  
• Top-hammer drills
  

2.2 Rotary Drilling

Rotary motion + weight-on-bit cuts rock using drag bits or roller bits.

Used in:

• Coal, iron ore, limestone
  
• High penetration in soft rocks
  

Types:

• Rotary air blast (RAB)
  
• Rotary hydraulic rigs
  
• Roller-cone (tricone) bits
  

2.3 Rotary Percussive Drilling (Down-The-Hole / DTH)

Percussive hammering occurs at bottom of hole → minimal energy loss.

Best for:

• Hard, competent rock
  
• Deep blasting holes
  
• Large diameter holes
  

2.4 Auger Drilling

Used for:

• Soft, unconsolidated materials
  
• Soil sampling
  
• Overburden
  

🔹 3. Types of Drill Rigs
3.1 Crawler-Mounted Drills

• Medium to large rotary or DTH rigs
  
• Highly stable
  
• Used in open-pit operations
  

3.2 Truck-Mounted Rigs

• Easy relocation
  
• Used for long-distance mine sites
  

3.3 Wagon Rigs

• Light drilling, shallow depths
  
• Used in quarries
  

3.4 Hydraulic Top-Hammer Rigs

• High accuracy
  
• Low deviation
  

3.5 DTH Rigs

• Best for deep benches (up to 20–25 m)
  
• Large hole diameters (100–300 mm)
  

🔹 4. Drilling Parameters
4.1 Burden (B)

Distance between hole and free face.
Critical for uniform fragmentation.Typical values:

• 8–20 times hole diameter
  

4.2 Spacing (S)

Distance between adjacent holes.Typical ratio:S=1.0–1.5×BS = 1.0–1.5 \times BS=1.0–1.5×B
4.3 Hole Diameter

Common diameters:

Material	Diameter
Coal	100–160 mm
Iron Ore	160–250 mm
Limestone	100–200 mm

4.4 Sub-Drilling

Extra depth below the bench floor:Sub-drill=0.3–1.0m\text{Sub-drill} = 0.3–1.0 mSub-drill=0.3–1.0mImproves floor quality.

🔹 5. Penetration Rate (PR)

Penetration rate is:PR=Depth drilledTimePR = \frac{\text{Depth drilled}}{\text{Time}}PR=TimeDepth drilledUnits: m/min or m/hr
5.1 Factors affecting PRRock Properties

✔ Hardness
✔ Abrasiveness
✔ Strength
✔ FracturesMachine Variables

✔ Weight on bit (WOB)
✔ Rotation speed
✔ Air pressure
✔ Bit condition

Bit Parameters

✔ Bit type
✔ Bit wear
✔ Gauge size

Blasting Pattern

✔ Hole inclination
✔ Bench height

Stemming Material

Indirectly affects overall performance by requiring consistent hole condition.
🔹 6. Drilling Patterns Used in Surface Mines
6.1 Square Pattern

• Burden = Spacing
  
• Uniform blasting
  
• Easy to layout
  

6.2 Staggered Pattern

• Spacing ≠ Burden
  
• Better fragmentation
  
• Used widely in hard rock
  

6.3 Line Drilling

• For smooth wall blasting
  
• Holes drilled close together
  

6.4 Ring Drilling

• Used in large-diameter rotary drilling
  
• Deep hole mining and dragline benches
  

🔹 7. Diagrams (Text Format)Drilling Pattern – Square:
O --- O --- O| | |O --- O --- O| | |O --- O --- OStaggered Pattern:
O ----- O ----- O O ----- O ----- OO ----- O ----- O
🔹 8. Common Drilling Problems

• Hole deviation
  
• Bit wear
  
• Over-drilling
  
• Under-drilling
  
• Collar slippage
  
• Rig instability
  
• Hard bands in rock
  
• Water inholes
  

🔹 9. 25 MCQs (DGMS Exam Pattern)
1) Penetration rate is expressed in —

a) m²/s
b) kg/m
c) m/min or m/hr
d) rpm
e) N/m
Answer: c
2) DTH stands for —

a) Down-the-handle
b) Drill-to-hole
c) Down-the-hole
d) Drill-through-hole
e) Down-hole-hammer
Answer: c
3) Burden is distance between hole and —

a) Adjacent hole
b) Drill collar
c) Free face
d) Bench floor
e) Blast shelter
Answer: c
4) Sub-drilling improves —

a) Bench height
b) Hole collar
c) Floor level quality
d) Ore grade
e) VOD
Answer: c
5) Tricone bits are used in —

a) Jackhammers
b) Rotary drilling
c) Augers
d) DTH
e) None
Answer: b
6) DTH drilling generates —

a) Weak blows
b) High deviation
c) Excess mud
d) Strong percussive action at hole bottom
e) None
Answer: d
7) Drilling pattern that gives best fragmentation —

a) Line
b) Square
c) Staggered
d) Single row
e) None
Answer: c
8) Hole diameter for coal benches —

a) 50 mm
b) 75 mm
c) 100–160 mm
d) 300 mm
e) None
Answer: c
9) Air pressure affects —

a) Blast design
b) Bench width
c) Penetration rate
d) Truck speed
e) Ore density
Answer: c
10) Drilling deviation increases when —

a) ROP is low
b) Rock is fractured
c) Bit is new
d) Hole is vertical
e) None
Answer: b
11) Primary drilling method in hard rock —

a) Augur
b) Drag-bit
c) DTH
d) Cable tool
e) None
Answer: c
12) Rotary drills work best in —

a) Hard granite
b) Soft to medium rocks
c) Iron ore
d) Placer deposits
e) None
Answer: b
13) Line drilling is used for —

a) Deep holes
b) Production blasting
c) Smooth wall blasting
d) Dragline benches
e) None
Answer: c
14) Bit wear increases when rock is —

a) Soft
b) Weak
c) Highly abrasive
d) Sandy
e) Shaly
Answer: c
15) DTH performance depends on —

a) Water level
b) Humidity
c) Air pressure
d) Bus voltage
e) None
Answer: c
16) Weight on bit affects —

a) Bench width
b) Truck cycle time
c) Drilling penetration
d) Fragment size
e) None
Answer: c
17) Blast holes in surface mines are generally —a) Horizontal
b) Inclined 55°
c) Vertical
d) Inverted
e) None
Answer: c
18) Collar slippage occurs when —

a) Hole is dry
b) Collar is loose
c) Tricone bit is new
d) Bench is flat
e) None
Answer: b
19) DTH bits are —a) Drag bits
b) Percussive bits
c) Roller bits
d) Chisel bits
e) None
Answer: b
20) Drilling accuracy depends on —

a) Truck payload
b) Bench width
c) Blasting crew
d) Rig stability
e) None
Answer: d
21) Over-drilling leads to —

a) Blasting misfire
b) Increased explosives usage
c) Protection of floor
d) Reduced fragmentation
e) None
Answer: b
22) Bit gauge refers to —

a) Hole depth
b) Drill RPM
c) Bit diameter
d) Cutting speed
e) Air velocity
Answer: c
23) Wagon drills are used for —

a) 30 m benches
b) Small depth drilling
c) Very wide benches
d) Deep hole mining
e) None
Answer: b
24) Drilling pattern planning is part of —

a) Explosive manufacturing
b) Blast design
c) Truck scheduling
d) Crusher design
e) None
Answer: b
25) High WOB in soft rock causes —

a) Low ROP
b) Bit jamming
c) Better sampling
d) Lower RPM
e) None
Answer: b
                   🔚 Conclusion

Drilling is the backbone of surface mining operations.
The choice of drill rig, drilling pattern, and penetration rate directly influences fragmentation quality, shovel productivity, and overall cost.
Proper blast-hole design and adherence to DGMS guidelines ensure safety and efficiency.

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