Formulation of a New Breach Model for Embankments IMPACT Project Workshop, Wallingford 2002 Breach...
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Transcript of Formulation of a New Breach Model for Embankments IMPACT Project Workshop, Wallingford 2002 Breach...
Formulation of a New Breach Model for Embankments
IMPACT Project Workshop, Wallingford 2002
Breach Formation Theme
Introduction
Do we need a
new model?
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
The HR Breach Model
• Lateral and Longitudinal Breach Growth
• Flow Equations
• Sediment Transport Equations
Lateral Growth (existing models).
• Uniform Erosion
• Constant Shape.
• Top Width Adjustment• Constant bottom width
• Most stable section
• Assuming a shape
• Slope Instability (some)
Breach Growth (Real Cases 1)
Breach Growth (Real Cases 2)
Breach Growth (Real Cases 3)
Breach Growth (Physical Modeling at HR)
Growth Mechanisms
• Continuous Erosion
– Computed using a sediment transport equation.
• Mass Failure
– Shear failure
– Bending failure
Shear Failure (1)
Shear Failure (2)
s
b
WW
HHHdcFOS
tan*'tan)('* 321
Bending Failure (1)
Bending Failure (2)
2012)( /6/)( dMdHHactualt
Longitudinal Breach Growth(New Model)
• The sediment transport continuity equation.
qx
Qs
t
Ap
)1(
Sediment Transport Equations
• Difficult to decide which one?
• Selected Equations:– Yang 1979 (Non Cohesive)– Visser 1998 (Non Cohesive)– Chen and Anderson 1986 (Non Cohesive)
Flow Equations
• Weir Equation• Flow over the crest and on the downstream face
• Bernoulli Equation• Hydraulic calculations on the crest and the
downstream face
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
Composite Embankments (1)
Composite Embankments (2)
• Core Failure Modes:– Sliding– Overturning– Bending
Piping (1)
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
Numerical Model Results
Case Study (1)
Case Study (1) Comparison
Case Study (2) Central
Case Study (2) Side
And .. Finally
• An acceptable approach has been achieved for a new breach model
• More research is needed