2B - Slope Stability Analysis Slide3

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Slope Stability Analysis: Slide3
Module 2B
When to model in 3D?
1. If pit slope geometry is 3D
2. If failure mechanism is 3D
3. If material strength is anisotropic and not aligned (is oblique) to 2D cross-section
4. If spatial variation in material and other properties is 3D
5. If challenging to identify ‘critical’ or ‘representative’ 2D cross-section
6. If factors of safety of 2D (closely-spaced) cross-sections vary significantly 
• If one chooses most conservative FoS design might be too conservative
• If one chooses least conservative FoS design might be too optimistic
7. If challenging to ‘smear’ influence of discrete support/structural elements
• when supports (such as soil nails) are oriented in different directions or spacing varies
8. If end effects are important
Model Generation Workflow
3
1. Import and 
clean geometry
2. Define 
material 
properties
3. Create 
external 
4. Divide all
5. Assign 
material 
properties
6. Collapse small 
volumes
7. Assign roles to 
surfaces
8. Select 
analysis method
9. Select slip 
surface options
10. Add search 
limits
11. Compute
12. Interpret
13. Additional 
analysis
Interface
• View can be enlarged by double clicking in individual viewport window
• Viewport settings can be customised (View > Display options > Viewports)
LOCKED TOP VIEW ROTATE 
LOCKED FRONT VIEW LOCKED RIGHT VIEW
Model Requirements
The following model parameters need to be defined before Computing a Slide3 model:
• Geometry (import surfaces, volumes, create geometry within Slide3 and Divide All to create 
3D model)
• Loading (if applicable)
• Support (if applicable)
• Groundwater (if applicable)
• Material strengths
• Analysis method
• Search method
• Search limits
Geometry
• Full 3D geometry
• Geometry can be created from scratch 
or imported from a variety of file 
formats
• Boundary surfaces can be interpolated 
from borehole data using the Borehole 
Manager
• Import from Slide
• 2D models can be created in Slide and 
imported into Slide3. The 2D model will 
automatically be converted into an 
equivalent 3D model. You can then 
compare the results to see the effect of 
2D vs 3D. 
3D model of open pit mine
Analysis Methods
The following LE methods have been adapted 
for 3D analysis:
• Bishop (moment equilibrium)
• Janbu (force equilibrium)
• Spencer (force and moment 
equilibrium)
• GLE (force and moment equilibrium 
with interslice force function)
3D critical slip surface
Slip Surfaces & Search Methods
The 3D slip surface shapes which can 
be generated are:
• Spherical 
• Ellipsoidal
• Spline (NEW)
• Mutli-Planar
• Wedge
Spherical slip surface Ellipsoid surface with Spline optimization
Slip Surfaces & Search Methods
Traditional methods
• Grid Search
• Auto Refine
Advanced methods optimized for speed and 
efficiency
• Cuckoo search
• Particle swarm
Slip surfaces can conform to the shape of bedrock 
using an Infinite Strength material
Main: 2D view of slip surface sliding on bedrock 
(infinite strength material)
Top: 3D view of slip surface sliding on bedrock
Loading
Loads can be added as:
• Point loads
• Distributed loads
• Seismic loads
Loads can be applied at any 3D orientation or 
location.
Loads can only be applied once an external 
boundary has been defined. 
Groundwater
Pore pressure can be defined using:
• Water surfaces (water table or piezo line)
• Water pressure grids
• Ru coefficients
• Groundwater > Add Water Surface
Loading & Support Options
Slide3 offers all support types found in Slide2
• End Anchored
• GeoTextile
• Grouted Tieback
• Grouted Tieback with Friction
• Pile/Micro Pile
• Soil Nail
• User Defined
Support can be applied at any 3D orientation
Bolt pattern applied to slope face
Loading & Support Options 
• Loading options include 
• Point Loads
• Distributed Loads
• Seismic Loads
• Loads can be applied at any 3D 
orientation or location
Uniform surcharge load at crest of curved slope 
section
Groundwater Definition
Groundwater pore pressure can be defined using
• Water surfaces (Water Table or Piezo Line)
• Water Pressure Grids
• Ru coefficients
Pore pressure grids from RS3 finite element 
analysis can be imported into Slide3
Water table above ground surface at toe 
creates ponded water
Material Models
• Mohr-Coulomb
• Undrained
• Infinite Strength
• Anisotropic 
Strength
• Shear/Normal 
Function
• C/Phi Function
• Generalized 
Hoek-Brown
• Power Curve 
• Vertical Stress 
Ratio
• Barton-Bandis
• Hyperbolic
• Discrete Function
• Drained-
Undrained
• Generalized 
Anisotropic
• SHANSEP
Slide3 offers a wide variety of strength models for soil and rock:
The Generalized Anisotropic Strength option allows you 
to create virtually any customized anisotropic material 
model incorporating multiple failure criteria applied over 
user-defined 3D orientations. 
Results and Data Interpretation
Global minimum 3D 
surface
Contour any input or 
output data on surface
Show all surfaces, pick 
surfaces, export surfaces
Show results on 2D cutting 
planes
Filter output by safety 
factor
Advanced Features
• Excess Pore Pressure
• Rapid Drawdown Analysis
• Unsaturated Shear Strength
• Anisotropic regions
• Tension cracks
Tension Crack
• If a slip surface intersects a Tension Crack surface, the slip surface will be 
truncated by the Tension Crack surface. 
• The tension crack essentially terminates the slip surface, thereby removing 
the tensile stresses from the calculations. 
Symmetry
• If model geometry is symmetric and the 
material model is not anisotropic, it can be 
expected that the critical slip surface is 
symmetric
• This symmetry can be enforced in engine 
computations by enabling the symmetry 
option within project settings
Slide2 Section Cut
Results – Interpretation
Review
• Global minimum/s (for all analysis methods calculated)
• Show all slip surfaces (to ensure adequate coverage across area of interest)
• Surface safety maps (readily highlights low FOS areas)
• Column Viewer (check for tension, review material properties assigned to column bases)
• Contour plots e.g. of stress, strength, pore pressure, etc. (validate results)
• Use Slide2 Section Creator (to compare results with 2D)
• Import and overlay monitoring data if available (reconcile results with slope monitoring data)
Results – Global Minimum
Results – Show All Surfaces
Interpretation – Surface Safety Map
Interpretation – Surface Safety Map
FOS = 1.48
~ 800 slip surfaces FOS = 1.33
~ 5000 slip surfaces
The number of slip surfaces calculated will have an impact on the results. 
Interpretation – Column Viewer
Interpretation – Contour Plots
Interpretation – Slide2 Comparison
Interpretation – Slide2 Comparison
3D FOS
2D FOS
Calibration with Radar Monitoring Data
Probabilistic Analysis
Probabilistic analysis uses distribution of material strength/s to see 
the range in FOS values that are calculated from combinations of 
different strengths sampled from within the distribution.
Sampling methods: 
• Monte-Carlo: Input distribution is sampled at random
• Latin-Hypercube: Distribution is divided into sections and 
each section is sampled, to ensure distribution is covered
• Response Surface: FOS is predicted using a small number of 
strategically placed samples 
Analysis types:
• Global Minimum: The global minimum surface for a 
deterministic analysis is used. The new samples are input, 
and the FOS is calculated using that same surface
• Overall Slope: For each simulation (new sample), the slip 
surface search is repeated, and new global minimums may 
be found
• Multiple Minima: The surfaces searched in the deterministic 
analysis to determine the global minimum are used, and the 
samples are changed for each surface
𝑃𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝐹𝑎𝑖𝑙𝑖𝑢𝑟𝑒 𝑃𝐹 =
# 𝑜𝑓 𝑠𝑖𝑚𝑢𝑙𝑎𝑡𝑖𝑜𝑛𝑠 𝑤𝑖𝑡ℎ 𝐹𝑆 < 1
𝑇𝑜𝑡𝑎𝑙 # 𝑜𝑓 𝑠𝑖𝑚𝑢𝑙𝑎𝑡𝑖𝑜𝑛𝑠Back Analysis
• Activate the Probabilistic Analysis in Project Settings to complete a back 
analysis in Slide3
• Enter the distribution of material strengths for each material to be back 
analysed 
Back Analysis – Example
Initial FOS = 1.66 View Scatter Plot in Results
Back Analysis – Example
Select combination of material strength that is estimated to provide a FOS < 1
Back Analysis – Example
Modify material parameters in new Slide3 model Back analysed FOS = 0.96
Simple Methods to Importing and 
Extruding Slide 2D Models
Introduction
The model analyzes the slope stability of a soil (yellow) with a weak layer 
(green) to see the effect of geometry
• The factor of safety is affected by the size of model and the loading force
Example Model 1
Base model with continuous loading 
200 m
95 m
Example Model 2
Base model with centered load
200 m
95 m
20 m
10 m
Step 3: Applying New Loading
The resulted model should look like below
Results Comparison
Slide3 Example 1: GLE FS 1.03 Slide3 Example 2: GLE FS 1.1Slide2 result : GLE FS 1.01
Base Normal Stress Contours
Model Creation by Importing Geometry 
Files (DXF, STL)
Open Pit
Geometry and Geology of the open pit 
mine
Step 5: Check Results
Interpret > Refresh Results
Slope Limits
Using Slope limits option, find the 
factor of safety on the opposite 
side of the pit
End of Module
	Slide 1: Slope Stability Analysis: Slide3
	Slide 2: When to model in 3D?
	Slide 3: Model Generation Workflow
	Slide 7: Interface
	Slide 8: Model Requirements
	Slide 9: Geometry
	Slide 10: Analysis Methods
	Slide 11: Slip Surfaces & Search Methods
	Slide 12: Slip Surfaces & Search Methods
	Slide 13: Loading
	Slide 14: Groundwater
	Slide 15: Loading & Support Options
	Slide 16: Loading & Support Options 
	Slide 17: Groundwater Definition
	Slide 18: Material Models
	Slide 19: Results and Data Interpretation
	Slide 20: Advanced Features
	Slide 21: Tension Crack
	Slide 22: Symmetry
	Slide 23: Slide2 Section Cut
	Slide 24: Results – Interpretation
	Slide 25: Results – Global Minimum
	Slide 26: Results – Show All Surfaces
	Slide 27: Interpretation – Surface Safety Map
	Slide 28: Interpretation – Surface Safety Map
	Slide 29: Interpretation – Column Viewer
	Slide 30: Interpretation – Contour Plots
	Slide 31: Interpretation – Slide2 Comparison
	Slide 32: Interpretation – Slide2 Comparison
	Slide 33: Calibration with Radar Monitoring Data
	Slide 34: Probabilistic Analysis
	Slide 35: Back Analysis
	Slide 36: Back Analysis – Example
	Slide 37: Back Analysis – Example
	Slide 38: Back Analysis – Example
	Slide 39: Simple Methods to Importing and Extruding Slide 2D Models
	Slide 40: Introduction
	Slide 41: Example Model 1
	Slide 42: Example Model 2
	Slide 43: Step 3: Applying New Loading
	Slide 44: Results Comparison
	Slide 45: Model Creation by Importing Geometry Files (DXF, STL)
	Slide 46: Open Pit
	Slide 47: Step 5: Check Results
	Slide 48: Slope Limits
	Slide 49: End of Module