🔹 1. Introduction

Slope stability is a critical safety and economic factor in opencast mines.
A stable slope ensures:

• Safety of workers
  
• Reduced rockfall hazards
  
• Lower stripping ratio
  
• Cost-effective mine design
  

Unstable slopes may fail suddenly, leading to:

• Bench collapse
  
• Rockfall
  
• Slide of massive material
  
• Equipment damage
  
• Fatalities
  

DGMS requires systematic study and monitoring of slopes in all surface mines.

🔹 2. Types of Slopes in Opencast Mines

1) Bench SlopeAngle of each working bench (bench face).

2) Inter-ramp SlopeCombined angle of multiple benches without a catch berm.

3) Overall SlopeAngle from top to bottom of the final pit.

🔹 3. Factors Affecting Slope Stability

⭐ A. Geological Factors

• Joints, faults, bedding planes
  
• Weathered or altered zones
  
• Weak layers within strong strata
  
• Presence of clay seams
  
• Shear zones
  

⭐ B. Hydrogeological Factors

• Groundwater pressure
  
• Rainfall infiltration
  
• Poor drainage
  

⭐ C. Mining Factors

• Blasting intensity
  
• Bench geometry
  
• Height of slope
  
• Excavation method
  

⭐ D. Rock Mass Properties

• RMR (Rock Mass Rating)
  
• UCS (Uniaxial Compressive Strength)
  
• Cohesion & friction angle
  

🔹 4. Types of Slope Failures

⭐ 1) Plane FailureOccurs when a rock block slides along a planar discontinuity.

Conditions:

• Discontinuity dips towards free face
  
• Dip of discontinuity > friction angle
  
• Daylighting of joint
  

⭐ 2) Wedge FailureTwo intersecting joints form a wedge that slides along the line of intersection.

⭐ 3) Circular FailureCommon in soil or weak rock.

Failure surface is circular / rotational.
⭐ 4) Toppling FailureOccurs when steeply dipping slabs rotate and topple forward.

⭐ 5) RockfallSmall, individual rocks fall due to:

• Weathering
  
• Over-steepening
  
• Vibrations
  

⭐ 6) RavellingGradual detachment of small fragments from the slope surface.

🔹 5. Indicators of Potential Slope Failure

• Cracks at crest
  
• Bulging at toe
  
• Increased seepage
  
• Rock noise / popping
  
• Overhang formation
  
• Tension cracks
  

🔹 6. Slope Stability Analysis Methods

⭐ A. Limit Equilibrium Method (LEM)Used for circular failure surfaces.

⭐ B. Kinematic AnalysisFor plane & wedge failures.

⭐ C. Numerical ModellingFLAC, PLAXIS, Phase2D.

⭐ D. Rock Mass ClassificationRMR, SMR, GSI used to evaluate stability.

🔹 7. Factor of Safety (FOS)

FOS=Shear StrengthShear Stress\text{FOS} = \frac{\text{Shear Strength}}{\text{Shear Stress}}FOS=Shear StressShear StrengthMinimum Acceptable Values:

• 1.2 – 1.3 for working slopes
  
• 1.4 – 1.5 for final pit slopes
  

🔹 8. Slope Stabilization Techniques

⭐ 1) BenchingReducing slope height by creating benches.

⭐ 2) Catch BermsCatch falling debris before it reaches bottom.

⭐ 3) Drainage Control

• Horizontal drains
  
• Surface drains
  
• Dewatering wells
  

⭐ 4) Rock Bolting & AnchoringImproves cohesion and interlock.

⭐ 5) Shotcrete / MeshPrevents ravelling and small rockfall.

⭐ 6) ScalingManual removal of loose rock.

⭐ 7) Controlled Blasting Techniques

• Pre-splitting
  
• Cushion blasting
  
• Line drilling
  

⭐ 8) Retaining Walls & Gabions

🔹 9. Slope Monitoring Methods

⭐ Instrumental Monitoring

• Prism reflectors + Total Station
  
• GPS monitoring
  
• Laser scanning
  
• Inclinometers
  
• Extensometers
  
• Piezometers
  

⭐ Visual Monitoring

• Cracks at crest
  
• Rockfall signs
  
• Water seepage
  

⭐ Slope Radar (SSR)Continuous real-time radar monitoring.

🔹 10. Text Diagram – Slope Failure Types

Plane Failure: Wedge Failure: Circular Failure:
\ | \ / ______ \ | \ / / \ \____| \__/ /________\
Toppling Failure:
| | | |\ | | | | \ | | | | \__ (Toppling)

🔥  25 MCQs (DGMS Pattern) with Solutions
1) Plane failure occurs along —

a) Circular arc
b) Planar discontinuity
c) Random blocks
d) Clay seam
e) None
Answer: b
2) Wedge failure is caused by —

a) 1 joint only
b) Intersection of two joints
c) Soft soil
d) Water inflow
e) None
Answer: b
3) Circular failure is common in —

a) Hard rock
b) Soil and weak rock
c) Coal pillars
d) Iron ore benches
e) None
Answer: b
4) Toppling failure occurs when —

a) Rocks dip away
b) Rocks dip steeply toward the face
c) Deep cracks
d) No joints
e) None

Answer: b
5) Slope stability factor of safety is —

a) Strength ÷ Height
b) Width ÷ Depth
c) Strength ÷ Stress
d) Height ÷ Angle
e) None
Answer: c
6) Minimum FOS for final pit slopes —

a) 1.0
b) 1.1
c) 1.4–1.5
d) 2.0
e) None
Answer: c
7) Drainage improves stability by reducing —

a) Friction
b) Pore pressure
c) Cohesion
d) Tensile strength
e) None
Answer: b
8) Pre-splitting is a —

a) Loading technique
b) Controlled blasting method
c) Pumping system
d) Surveying method
e) None
Answer: b
9) RMR stands for —

a) Rock Machine Rating
b) Rock Mass Rating
c) Resistivity Mining Ratio
d) Rock Mechanical Resistance
e) None
Answer: b
10) Slope failure signs include —

a) Dry cracks
b) Bulging at toe
c) Good fragmentation
d) Constant seepage
e) None
Answer: b
11) A catch berm is used to —

a) Raise toe
b) Store water
c) Stop falling rocks
d) Strengthen pit floor
e) None
Answer: c
12) SSR is used for —

a) Blasting
b) Real-time slope monitoring
c) Haulage control
d) Lighting
e) None
Answer: b
13) Slope stability is affected by —

a) Tire pressure
b) Bench illumination
c) Geological structures
d) Uniform blasting
e) None
Answer: c
14) Excessive blasting causes —

a) Better slope
b) Overbreak
c) Stronger wall
d) Lower vibration
e) None
Answer: b
15) Drainage holes are also called —

a) Window holes
b) Horizontal drains
c) Drill holes
d) Core holes
e) None
Answer: b
16) Most dangerous slope failure —

a) Ravelling
b) Rockfall
c) Wedge failure in large benches
d) Scaling
e) None
Answer: c
17) Slope monitoring instrument —

a) Vibrator
b) Total Station
c) Shovel
d) Dozer
e) None
Answer: b
18) Circular failure surface shape —

a) Straight

b) Zigzag
c) Arc-like
d) Vertical
e) None
Answer: c
19) Water seepage leads to —

a) Slope strengthening
b) Weakening of rock mass
c) Hardening
d) Better fragmentation
e) None
Answer: b
20) Controlled blasting reduces —

a) Strength
b) Damage to slope
c) Height
d) Haul distance
e) None
Answer: b
21) Clay seams reduce —

a) Pore pressure
b) Density
c) Friction angle
d) Bench width
e) None
Answer: c
22) Excessive rainfall leads to —

a) Better slope
b) Drainage failure
c) Higher friction
d) Strong rock
e) None
Answer: b
23) Radar monitoring detects —

a) Light
b) Heat
c) Slope movement
d) Gas
e) None
Answer: c
24) Toppling failure is identified by —

a) Vertical slabs
b) Forward-leaning blocks
c) Backward rotation
d) Loose soil
e) None
Answer: b
25) Slope failure prevention starts with —

a) Extra blasting
b) Removing drainage
c) Proper bench design
d) Random excavation
e) None
Answer: c
                        🔚 Conclusion

Slope stability is essential for ensuring the safety, economy, and longevity of opencast mines.
By understanding geological structures, water conditions, blasting impacts, and adopting stabilization techniques such as:

• Drainage
  
• Benching
  
• Controlled blasting
  
• Bolting & meshing
  
• Monitoring instruments
  

…operators can prevent catastrophic failures and ensure smooth, safe mining operations.

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