formulation of a new breach model for embankments impact project workshop, wallingford 2002 breach...
TRANSCRIPT
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Formulation of a New Breach Model for Embankments
IMPACT Project Workshop, Wallingford 2002
Breach Formation Theme
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Introduction
Do we need a
new model?
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The PhD Project
• Started on 1st of October 1998
• Ended on the 31st of January 2002
• Objectives:– Improve the understanding of the process
embankment breaching.– Develop a model based on that understanding
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The HR Breach Model
• Lateral and Longitudinal Breach Growth
• Flow Equations
• Sediment Transport Equations
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Lateral Growth (existing models).
• Uniform Erosion
• Constant Shape.
• Top Width Adjustment• Constant bottom width
• Most stable section
• Assuming a shape
• Slope Instability (some)
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Breach Growth (Real Cases 1)
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Breach Growth (Real Cases 2)
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Breach Growth (Real Cases 3)
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Breach Growth (Physical Modeling at HR)
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Growth Mechanisms
• Continuous Erosion
– Computed using a sediment transport equation.
• Mass Failure
– Shear failure
– Bending failure
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Shear Failure (1)
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Shear Failure (2)
s
b
WW
HHHdcFOS
tan*'tan)('* 321
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Bending Failure (1)
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Bending Failure (2)
2012)( /6/)( dMdHHactualt
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Longitudinal Breach Growth(New Model)
• The sediment transport continuity equation.
qx
Qs
t
Ap
)1(
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Sediment Transport Equations
• Difficult to decide which one?
• Selected Equations:– Yang 1979 (Non Cohesive)– Visser 1998 (Non Cohesive)– Chen and Anderson 1986 (Non Cohesive)
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Flow Equations
• Weir Equation• Flow over the crest and on the downstream face
• Bernoulli Equation• Hydraulic calculations on the crest and the
downstream face
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Material Uncertainty
Factor of Stability Probability Distribution Functions
0
0.25
0.5
0.75
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Factor of stability
Pro
bab
ity o
f fai
lure
Poor
Good
V. Good
DeterministicApproachEqual Probability
low
er li
mit
Up
pet
lim
it
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Composite Embankments (1)
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Composite Embankments (2)
• Core Failure Modes:– Sliding– Overturning– Bending
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Piping (1)
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Piping (2)
• Processes– Flow through the pipe– Pipe widening and deepening– Failure of the material above the pipe– Failure of the top of the dam– Similar processes to overtopping
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Numerical Model Results
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Case Study (1)
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Case Study (1) Comparison
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Case Study (2) Central
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Case Study (2) Side
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And .. Finally
• An acceptable approach has been achieved for a new breach model
• More research is needed