🔹 1. Introduction

Bench design is one of the most fundamental components of surface mine planning.
A properly designed bench ensures:

• Safety of workers & equipment
  
• Efficient excavation and loading
  
• Optimal slope stability
  
• Reduced stripping cost
  
• Higher productivity
  

DGMS mandates strict guidelines for bench dimensions to avoid slope instability and accidents.
🔹 2. What is a Bench?

A bench is a horizontal working step in a surface mine created during excavation.A bench consists of:

• Bench Height (H)
  
• Bench Width (W)
  
• Bench Slope (Face Angle)
  
• Toe & Crest
  
• Catch Berm
  

Each parameter affects stability and safety.
🔹 3. Bench Height (H)

Bench height is the vertical distance between two successive working levels.

📌 Typical Bench Height: 8–15 mIdeal depends on:

• Rock hardness
  
• Excavator/shovel reach
  
• Stability
  
• Fragmentation requirements
  

DGMS Guidelines:

• Bench height must not exceed the safe reach of excavating equipment.
  
• In hard rock, heights may be higher only if slope stability study supports it.
  

⭐ Factors Affecting Bench Height

Factor	Effect
Rock hardness	Higher height in hard rock
Equipment size	Bigger shovels → higher benches
Desired fragmentation	Lower bench → finer fragmentation
Safety	Lower benches safer in soft/weak rocks

🔹 4. Bench Width (W)

Bench width is the horizontal distance between two vertical faces.📌 General Rule:W=3H
(minimum)W = 3H \quad \text{(minimum)}W=3H(minimum)Example: Bench height = 10 m
Bench width = 30 m minimumPurpose of Bench Width:

• Space for equipment movement
  
• Safety zone
  
• Placement of drilling & blasting equipment
  
• Catchment of falling rock
  

🔹 5. Bench Face Angle

Face angle = Angle at which bench wall is designed.📌 Typical Range:

• Hard rock: 70°–80°
  
• Soft rock: 55°–65°
  

Bench face must be stable under:

• Blasting vibrations
  
• Water seepage
  
• Geological structures
  

🔹 6. Catch Berms / Safety Berms

A catch berm is a horizontal ledge between benches designed to catch falling debris.📌 Functions:

• Stops rolling boulders
  
• Provides safety buffer
  
• Reduces overall slope height
  

Width of Berm:8–12 m (varies with bench height)

🔹 7. Overall Slope Angle

Overall slope = Angle from bottom to top considering all benches + berms.Factors influencing overall slope:

• Rock Mass Rating (RMR)
  
• Geological discontinuities
  
• Rainfall & water inflow
  
• Height of pit
  
• Bench configuration
  

Steeper slopes reduce waste removal cost but increase instability risk.

🔹 8. Bench Geometry Diagram (Text Format)

Crest /\ / \-----------/----\---------------- Bench 1 (Height H) | | | | | | Face Angle----------\______\------------- Bench 2 (Berm Width W) Toe
🔹 9. Bench Design Standards 

(DGMS + Good Practice)

✔ Must minimize rockfall hazard

✔ Should allow safe machine movement

✔ Proper drainage to avoid pore pressure✔ Adequate berms at intervals

✔ Avoid undercutting

✔ Maintain slope monitoring

✔ No steep benching in weak strata without studies

🔹 10. Factors Affecting Bench Stability1️⃣ Geological Structures

• Faults, joints, bedding planes
  
• Weak zones
  
• Shear zones
  

2️⃣ Rock Strength

• UCS
  
• RMR
  
• Weathering
  

3️⃣ Water

• Rainfall
  
• Groundwater pressure
  
• Poor drainage
  

4️⃣ Blasting

• Excessive blasting → overbreak → slope failure
  

5️⃣ Equipment

• Longer equipment → wider benches
  

🔹 11. Table: Recommended Bench Parameters

Parameter	Hard Rock	Soft Rock
Bench Height	10–15 m	6–10 m
Bench Width	3 × H	3 × H
Face Angle	70–80°	55–65°
Berm Width	8–12 m	10–15 m

🔥  25 MCQs (DGMS Pattern) with Solutions
1) Bench height in surface mines is typically —a) 2–4 m
b) 4–6 m
c) 8–15 m
d) 20–25 m
e) None
Answer: c
2) Minimum bench width =

a) H
b) 2H
c) 3H
d) 5H
e) None
Answer: c
3) Catch berm function —

a) Support blasting
b) Increase gradient
c) Catch falling rocks
d) Fire protection
e) None
Answer: c
4) Bench face angle in hard rock —

a) 20°
b) 40°
c) 70°–80°
d) 90°
e) None
Answer: c
5) Overall slope angle depends on —

a) Roof bolts
b) Coal grade
c) Rock mass properties
d) Explosive charge
e) None
Answer: c
6) Bench height is controlled by —

a) Truck size
b) Excavator reach
c) Conveyor width
d) Powder factor
e) None
Answer: b
7) Large bench width ensures —

a) Lower capacity
b) Safe movement of machinery
c) High dust
d) High vibration
e) None
Answer: b
8) Water seepage affects —

a) Fuel cost
b) Lighting
c) Bench stability
d) Powder factor
e) None
Answer: c
9) A bench is —

a) Support
b) Haul road
c) Working step in opencast mine
d) Loading point
e) None
Answer: c
10) Berm width typically —

a) 1 m
b) 2 m
c) 8–12 m
d) 40 m
e) None
Answer: c
11) Face angle in soft rock —

a) 55°–65°
b) 90°
c) 20°
d) 10°
e) None
Answer: a
12) Bench width ensures —

a) Poor stability
b) Drill & shovel placement
c) More accidents
d) No drainage
e) None
Answer: b
13) Excess blasting leads to —

a) Good stability
b) Overbreak & slope failure
c) Lower cost
d) High safety
e) None
Answer: b
14) Overall slope angle affects —

a) Conveyor length
b) Stripping cost
c) Roof bolts
d) Gas emission
e) None
Answer: b
15) Toe of bench is —

a) Top edge
b) Bottom edge
c) Drill pattern
d) Haul road
e) None
Answer: b
16) Crest of bench is —

a) Bottom
b) Middle
c) Top edge
d) Side wall
e) None
Answer: c
17) Berms must be —

a) Weak
b) Properly maintained
c) Random
d) Removed
e) None
Answer: b
18) Stability increases with —

a) Higher water
b) Weak rock
c) Broader bench width
d) Faults
e) None
Answer: c
19) Steeper slopes reduce —

a) Production
b) Waste removal
c) Safety
d) Strength
e) None
Answer: b
20) Bench height in soft formations —

a) 20 m
b) 6–10 m
c) 1–2 m
d) 50 m
e) None
Answer: b
21) Slope failure is caused by —

a) Strong strata
b) Good drainage
c) Faults & joints
d) Controlled blasting
e) None
Answer: c
22) Bench geometry is essential for —

a) Lighting
b) Safe and productive mining
c) Coal grading
d) Sampling
e) None
Answer: b
23) Berm angle should be —

a) Vertical
b) Gentle to stop rolling rocks
c) 90°
d) No berms needed
e) None
Answer: b
24) Bench design depends on —

a) Gas content
b) Water pH
c) Geology & mining method
d) Conveyor placement
e) None
Answer: c
25) DGMS requires bench parameters to ensure —

a) High coal grade
b) Fast blasting
c) Safety of workers & equipment
d) More explosives
e) None
Answer: c
                                    🔚 Conclusion

Bench design is critical for safe, efficient, and economical surface mining.
The correct combination of bench height, width, face angle, berm design, and drainage ensures:

• Stable slopes
  
• Minimal rockfall hazards
  
• Smooth equipment movement
  
• Compliance with DGMS safety rules
  

Scientific bench design reduces accidents and enhances productivity.

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