A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND...
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Transcript of A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND...
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20081 of 17
A Comparison of Homogeneous and Multi-Layered Berm Breakwaters with Respect to Overtopping and Stability
ICCE2008, Hamburg, Germany
Lykke Andersen, T., Aalborg University, Denmark
Skals, K. T., Niras, Denmark
Burcharth, H. F., Aalborg University, Denmark
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20082 of 17
Homogeneous Berm Breakwater Investigations by Lykke Andersen (2006)
Recession(Rec)
Erosion
Deposition
Initial profile
Reshaped profile
hf
Rc
hs
B
-hb
d
R
Gc
hb is negative when the berm level is higher than the still water level.
Berm recession, wave overtopping and wave reflection measured for a large number of cross sections and sea states. In total approximately 700 model tests performed.
Recession and overtopping formulae were also established.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20083 of 17
Lykke Andersen (2006) Recession Formula for Homogenous Berm Breakwaters
Geometrical
considerations
Geometrical
considerations
Parameters included:• Influence of stability index and wave period• Influence of vertical wave skewness• Influence of water depth• Influence of front slope• Influence of berm elevation. • Influence of number of waves• Influence of stone gradation
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20084 of 17
Lykke Andersen (2006) Recession Formula for Homogenous Berm Breakwaters
• Some of the other data sets available show same amount of scatter as observed for the present data.
• Other data sets show much more and in some cases also a bias. This deviation could not be addressed.
90% confidence band:
Lykke Andersen (2006) data
All data (12 additional data sets, mainly homogenous)
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20085 of 17
Multi-Layer Berm Breakwaters (Icelandic Type)
Not covered in detail in study by Lykke Andersen (2006)
I
II
IIIIV
II
V
III
VI
• In a multi-layer berm breakwater the armour stones are separated in several stone classes.
• The largest stones are placed where they add most to the total stability of the structure.
• On a multi-layer berm breakwater very limited damage is accepted.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20086 of 17
Multi-Layer Berm Breakwaters (Icelandic Type)
• The parameter depends on
the stone size.
• Lykke Andersen (2006) proposed to apply the stone size (Dn,50) of the largest class in the berm when using the recession and overtopping formulae.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20087 of 17
Lykke Andersen (2006) Recession Formula
Comparison of calculated recession from the Lykke
Andersen (2006) formula and measured recession data from
other researchers.
Includes multi-layer data
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20088 of 17
Lykke Andersen (2006) Overtopping Formulafor Homogenous Berm Breakwaters
fH0 defined as in the recession formula
Initial profile parameters B and Gc have to be adjusted to match a profile with initial front slopes 1:1.25 as given by Lykke Andersen (2006).
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 20089 of 17
Evaluation of Overtopping Formula – Other Data2 Additional data sets homogenous berm breakwater:
3 Additional data sets multi-layer berm breakwater:
Good agreement for the few other data sets available as well.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200810 of 17
New Model Tests Studying Stability and Overtopping of Different Berm Breakwaters Types (Low Crest)
Prototype conditions (model tests at scale 1:50):• Water depth: 20 m
• Tested wave heights (Hm0): 4-11 m
• Deep water peak wave steepness (s0p): 0.02 & 0.04
• Based on a real quarry yield from Keilisnes in Iceland.
• Maximum stone size: 30t
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30
Un
its P
assi
ng [%
]
W [t]
Layer I
Layer II
Layer III
Layer IV
Layer V
Same stones but study influence of amount of sorting on stability and overtopping!! 5
m
12 m
I
IIIII IV
IVII
III
VI
V
Multilayer Berm and Low Crest
Seeward Landward
10
m
V
1:1.5
1:1.5
1:1.3
1:1.3
1:1.3
1:1.3
1:1.5
I+II+III
IV+V VI
1:1.3
1:1.5
I+II+III
IV+V
IV+V
I+II+III+IV+V VI
1:1.3
1:1.5
I+II+III+IV+V
6.3 m
5 m
12 m
Hybrid Berm and Low Crest
Seeward Landward
10
m 1:1.5
1:1.5
1:1.3
1:1.3
1:1.3
6.3 m
5 m
12 m
Seeward Landward
10
m 1:1.5
1:1.5
1:1.3
1:1.3
1:1.3
6.3 m
Homogeneous Berm and Low Crest
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200811 of 17
New Model Tests Studying Stability and Overtopping of Different Berm Breakwaters Types (High Crest)
5 m
12 m
I
IIIII IV
IVII
III
VI
V
Multilayer Berm and Low Crest
Seeward Landward
10
m
V
1:1.5
1:1.5
1:1.3
1:1.3
1:1.3
1:1.3
1:1.5
I+II+III
IV+V VI
1:1.3
1:1.5
I+II+III
IV+V
IV+V
I+II+III+IV+V VI
1:1.3
1:1.5
I+II+III+IV+V
6.3 m
5 m
12 m
Hybrid Berm and Low Crest
Seeward Landward
10
m 1:1.5
1:1.5
1:1.3
1:1.3
1:1.3
6.3 m
5 m
12 m
Seeward Landward
10
m 1:1.5
1:1.5
1:1.3
1:1.3
1:1.3
6.3 m
Homogeneous Berm and Low Crest
I
IIIII IV
IVII
III
VI
V
V
1:1.51:1.27
1:1.5
3.5 m
VI
1:1.27
1:1.5
I+II+III+IV+V
I+II+III+IV+V
VI
1:1.27
1:1.5
I+II+III+IV+V
I+II+III+IV+V
5 m
12 m
Seeward Landward1
3.3
m1:1.5
1:1.3
1:1.3
1:1.3
Multi-layer Berm and High Crest
1:1.5
3.5 m
5 m
12 m
Seeward Landward
13.
3 m
1:1.5
1:1.3
1:1.3
1:1.3
Homogeneous Berm and High Crest
1:1.5
3.5 m
5 m
20 m
Seeward Landward
13.
3 m
1:1.5
1:1.3
1:1.3
1:1.3
Wide Homogeneous Berm and High Crest (Add. Volume)
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200812 of 17
Recession ResultsInfluence of Berm Type and Comparison to Lykke Andersen (2006) formula
• The multi-layer and hybrid berm breakwaters performs quite similar in terms of recession, i.e. the number of stone classes in the berm can be reduced from 5 to 2 without significantly influencing the stability. This is important as it is easier and cheaper to construct.
• The homogenous berm breakwater gives significantly more recession.
• Wave height for which berm recession starts is well predicted by the formula.
• The test results for the homogenous berm breakwater shows a slower development of recession with wave height compared to that given by the formula while the multi-layer and hybrid is well described by the formula.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200813 of 17
Recession ResultsComparison with Lykke Andersen (2006) formula
• Recession calculations are very reliable for the tested multi-layer and hybrid berm breakwaters with start of berm recession estimated very well. Note that front side erosion might start before recession of the berm.
• Recession calculations for the homogenous berm breakwaters are unexpectedly somewhat conservative in many cases. Might be due to a small fraction (around 10%) of very large stones which is not described by fg = Dn,85 / Dn,15.
Low Crest High Crest High Crest & Wide Berm
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200814 of 17
Overtopping ResultsInfluence of Berm Type
• Investigated range of overtopping discharges corresponds to prototype discharges in the range 0.03 l/sm to 100 l/sm.
• Homogenous berm breakwater gives slightly more overtopping than the more stable multi-layered types.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200815 of 17
Overtopping ResultsComparison with Lykke Andersen (2006) formula
Low Crest High Crest High Crest & Wide Berm
• Overtopping prediction by the formula seems reliable for all tested cross-sections but with a slightly conservative bias.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200816 of 17
Overall Conclusions Related to Application of Lykke Andersen (2006) Design Formulae
• Recession seems well predicted by the Lykke Andersen (2006) formula for multi-layer berm breakwaters.
• Recession for the tested homogenous berm breakwaters shows in many cases less recession than indicated by the Lykke Andersen (2006) formula. However, start of damage is well predicted by the formula. The reason for this deviation was not completely clear but could be due to a small fraction of very large stones included in the berm stones.
• Overtopping is for all cases in good agreement with the formula of Lykke Andersen (2006).
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 200817 of 17
Overall Conclusions Related to Sorting of Armour Stones
What do we get out of sorting the stones in the berm?
• The homogenous berm breakwater gives slightly more overtopping than the more stable multi-layer and hybrid types.
• Recession is significantly smaller for the multi-layered berm breakwaters compared to the homogenous berm breakwater but the failure mode is less ductile.
• It seems as the number of stone classes in the berm can be reduced from 5 to 2 without significantly influencing berm recession and overtopping performance. This means a structure that is significant easier to construct and cheaper.
Thank you for your attention