IMPACT ~ Breach Physical Modelling
Review of
Modelling Work
Undertaken So Far...
IMPACT - Breach Physical Modelling
Summary• Objectives
• General approach and facilities
• Scaling
• Controlling / assessing soil properties
• Data collection
• Test programme
• Test results so far...
IMPACT - Breach Physical Modelling
Objectives
To provide lab data through which:
• Field test data may be compared and scaling issues (between field and lab) analysed
• Breach formation behaviour may be extrapolated from field test data via multiple lab tests showing effect of variation in:
– geometry / sediment size & grading / construction / embankment condition
• Additional data for numerical model comparison and validation
IMPACT - Breach Physical Modelling
General approach and facilities:
General approach:
• Programme of 25 lab tests
– 9 Autumn 2002
– 8 Spring 2003
– 8 Autumn 2003
• Scaling field tests at 1:10 (trying to balance scaling effects)
• Using large scale laboratory facilities to extend data sets as much as possible
IMPACT - Breach Physical Modelling
General approach and facilities:
Facilities:
• Using a large flume (50m x 10m wide)
• Peak discharge >1m3/s (but limited)
• Automated logging of:
– water levels
– flow into flume
– pressure beneath embankment
– u/s vertical velocity profile
– u/s face digital photo shots
– d/s face video footage
Breach Formation
Physical Modelling Flume (earlier model)
Breach Formation
Physical Modelling Flume (dimensions)
10m
50m0.8m
Flow upto 1.25m3
IMPACT - Breach Physical Modelling
Flume
IMPACT - Breach Physical Modelling
Flume
IMPACT - Breach Physical Modelling
Scaling• Range of approaches considered
– Mobile bed modelling
– Sediment entrainment / fall velocities
– Reynolds, Froudian etc.
• For non cohesive, considering different approaches, concluded straight geometric scaling
– 1:10
• Review of scaling later within uncertainty assessment
IMPACT - Breach Physical Modelling
Scaled Sediment
Grain size distribution - Lab Test Series 1
0
10
20
30
40
50
60
70
80
90
100
10 1000 d (microns)
Re
lati
ve
we
igh
t o
f g
rain
s <
d in
%
Target Grading Uniform Grade (250) Steeper Grading (250) Uniform Grade (150)
IMPACT - Breach Physical Modelling
Scaled Sediment
Grain size distribution - Lab Test Series 1
-20
0
20
40
60
80
100
10 1000
d (microns)
Re
lati
ve
we
igh
t o
f g
rain
s <
d i
n
%
Uniform Grade (150) redhill 110chelford 52 Mix redhill110+chelford52mix HST 95+chelford 52 HST 95leighton buzzard da 80 mix leighton buzzard da 80+redhill 110redhill 65 mix redhill 65+redhill110
IMPACT - Breach Physical Modelling
Scaled Sediment
Grain size distribution - Lab Test Series 1
0
10
20
30
40
50
60
70
80
90
100
10 1000d (microns)
Re
lati
ve
we
igh
t o
f g
rain
s <
d
in
%
Target Grading
MIX redhill110+chelford52+leighton buzzard+sand
IMPACT - Breach Physical Modelling
Controlling and Assessing Soil Properties
In order to ensure that field and lab tests are similar we need to consider:
• Soil type
– grading
– permeability
– strength
– cohesion
• Construction properties:
– density
– moisture content
IMPACT - Breach Physical Modelling
Controlling and Assessing Soil Properties
Soil type (grading, strength etc.) is determined through lab analysis of the sample. Properties analysed include:
– grading
– permeability
– proctor
IMPACT - Breach Physical Modelling
Controlling and Assessing Soil Properties
This data permits plotting of the density moisture curve to show optimum compaction.
During construction, optimum compaction is aimed for.
During construction density readings are taken (nuclear density probe) at 9 locations across the bank and at three levels. This permits the degree and consistency of compaction to be identified.
(Test#1 1.79g/cm3; Test#2 1.76g/cm3)
IMPACT - Breach Physical Modelling
Density Measurement - Nuclear Probe
IMPACT - Breach Physical Modelling
Data Collection
Automated logging of:
– water levels
– flow into flume
– pressure beneath embankment
– u/s vertical velocity profile
– u/s face digital photo shots
– d/s face video footage
IMPACT - Breach Physical Modelling
Data Collection
IMPACT - Breach Physical Modelling
Data Collection
IMPACT - Breach Physical Modelling
Data Collection
IMPACT - Breach Physical Modelling
Test Programme
Programme of 25 lab tests
• 9 Autumn 2002
– Non cohesive
– Prior to Autumn 2002 field work
• 8 Spring 2003
– Cohesive
– Prior to Autumn 2003 field work
• 8 Autumn 2003
– TBA (piping?)
– Post Autumn 2003 field work
IMPACT - Breach Physical Modelling
Test Programme - Autumn 2002
• Lab Test#1 Trial / test experiment
• Lab Test#2 Steeper sediment grading - D50 Field Test#2
• Lab Test#3 Repeat Lab Test#2
• Lab Test#4 Breach location (initiate at side of channel)
• Lab Test#5 Scaled grading of Field Test#2
• Lab Test#6 Vary geometry (Crest 2m, Slope 1:2)
• Lab Test#7 Vary geometry (Crest 3m, Slope 1:2)
• Lab Test#8 Steeper grading, different D50
• Lab Test#9 SS Seepage or 2nd D50 variation
IMPACT - Breach Physical Modelling
Test Programme - Spring 2003
Programme to be agreed.
Objectives to:
• Integrate with Norwegian field work
• Integrate with other European and US experimental work
IMPACT - Breach Physical Modelling
Test results so far...• Tests 1-5 completed (probably!)
• Tests 6-9 within next 2-3 weeks
• Steady state seepage an issue
• Data from first tests yet to be processed, however photo and video footage is available...
IMPACT - Breach Physical Modelling
Test results so far...
Breach features noted in Tests 1-3:
• (Seepage and slumping of d/s face)
• Initial vertical cut through bank
– Rapid cut back of d/s face in line with ‘slot’
– Likely significant erosion below ‘bed’ level
• Vertical sides of breach
• Side cracking and slumping
• Upstream slope (face) remains in place as weir for considerable time (flow control)
IMPACT - Breach Physical Modelling
Test results so far...
Still photo series Test 2
Still photo series Test 3
AVI footage Test 2
AVI footage Test 3
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