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NSERC/COSIA Industrial Research Chair in
Oil Sands Tailings Geotechnique
Development of an integrated tailings simulation model using System
Dynamics and GoldSim
Tony Zheng
• Introduction: System Dynamics and Causal
Loop Diagrams (CLD)
• Case Study: Soil Water Dynamics of Tailings Cap
- Part I: Modelling Process
- Part II: Results
• Concluding Remarks
2
Agenda
The Modelling Universe
3
Finite Element
Finite Difference
GEOTECHNICAL ENGINEERING
SOCIAL-ECONOMIC , ENVIRONMENT AND BUSINESS
Discrete Element
System Dynamics- Global Rules- Global Dynamics
Discrete Event- Global Rules- Local Dynamics
Agent Based- Local Rules- Local Dynamics
Hybrid Models
System Dynamics + Finite Difference
Stochastic
Non-Linearity
MY THESIS(Bobashev, 2015)
– Developed by Jay Forrester at MIT’s Sloan
Business School in the 50s:
To model complex inter-relationships between
elements within a system or multiple systems.
- Feedbacks, Feedbacks and Feedbacks
– Applications in Public Health, Management
Consulting, Water Resource Management,
Public Policy, International Relations, Defense
and Securities etc.
What is System Dynamics?
4
5
System Dynamics Modelling Process
Mental Model (s)
System Dynamics and Causal Loop Diagrams (CLD)
Simple Model
Detailed Model
Amount of Time Spent in the Real World
DiagramsQualitative
Quantitative
Transition
A Simple Example of Causal Loop Diagrams
6Modified from Sternman, 2000
R R: Reinforcing R
BB: Balancing
B
A Simple Example of Causal Loop Diagrams
7Modified from Sternman, 2000
Population
BR
R
B
B
R
A Simple Example of Causal Loop Diagrams
8 Modified from Sternman, 2000
Population ?
Soil Water Dynamics of Tailings Cap
Part I: Model Building Process
Part II: Simulation and Analysis
Case Study
10
Step 0 – Conceptualization
Coarse Sand Tailings Cap
Thickened Tailings
Evaporation
Run-Off
Precipitation
Upward Consolidation
Flux
3 m
50 m
11
Step 1: Pick the Governing Equations
Van Ganutchen - Maulem (1980) ; Wilson et al (1997); Huang et al (2011)
Vol Water Content
Hydraulic Conductivity
Relative Saturation
Inter-Layer Transmission Rate
Evaporation-Suction Model
Actual Evaporation Rate
Step 2: List relevant variables; identify the stock(s) and flows
Step 3: Construct the preliminary CLD;Identify feedbacks; discuss and debate
Step 4: Use the Bull’s Eye Diagram to identify the boundary of the model / system
EXOGENOUS
ENDOGENOUS
AE/PE Ratio
Suction Head
Vol Water Content
Unsat K
Water
Storage
PrecipitationPotential
Evaporation
Temperature
Void Ratio
Saturated K
Infiltration Rate
Rel Humidity
of Soil
Run-off
Thickness
Rel Humidity of Air
Consolidation Flux
EXCLUDEDSnowmeltVapour Transport
DiffusionFreeze/Thaw
OsmosisLateral
Flow
15
Step 5: Build the partial CLD; add polarity signs and identify feedback structures
15
Negative (Balancing) Loop
- Suction-Driven
- Dominates when
evaporation >
precipitation
Positive (Reinforcing) Loop
- Infiltration-Saturation Driven
- Dominates when
precipitation > evaporation
or when wetting front arrives
16
Step 6: Transform CLDs into GoldSim
16
17
Step 7: Validation
0
50
100
150
200
250
300
350
400
450
0 50 100 150 200 250 300 350 400So
il W
ater
Sto
rage
(m
m)
Time (days)
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40 50 60 70
Ch
ange
in S
oil
Wat
er S
tora
ge (
mm
)
Time (Days)
Measured
GoldSim
Step 7: Run and validate simple models under a variety of conditions and different materials.
Dynamic Boundary Condition
Extreme Conditions
Step 8: Visualization and User Interface
User Input Model Overview
Layer Setup
Real-Time Simulation Results
User sees what the
modeler sees
Step 9: Go back to the Bull’s Eye Diagram if required as part of the iterative and participatory modelling process
Final Steps
Step 10: Parameter Estimation (Case Study)
Step 11: Simulation and Sensitivity Analysis (Case Study)
20
Case Study
Soil Water Dynamics of Tailings Cap
Part I: Model Building Process
Part II: Simulation and Analysis
Global Dynamics– Total Water Storage
21
Vary Saturated Hydraulic Conductivity of CST
Initial SC of TT = 60%
10-Year
22
Global Dynamics– Total Water Storage
Vary Initial SC of TTSame CST Ks in all scenarios
23
Global Dynamics– Cumulative Runoff
What is the minimum initial SC of TT required to prevent consolidation release water from daylighting at the surface?
24
Local Dynamics - Layer 4 (Depth: 52 cm)
Dashed Line: Higher KsSolid Line: Lower Ks
Arrival of Wetting Front
Un-Saturated Quasi-Saturated
• Why System Dynamics?
– Feedback Structures
– Rigorous Qualitative Process
– Foster thinking and shared understanding
through participatory modelling exercises
– Ability to model soft variables
Concluding Remarks
25
• Limitations
– Poor Capture of Spatial Variation
– Over-Simplification
– Over-Complexity
– Complacency?
Concluding Remarks
26
27
Acknowledgements
- Dr Nicholas Beier
Software Support:
FSCA (Dr Silawat Jeeravipoolvarn)