Transcript A Comparison of Homogeneous and Multi-layered Berm Breakwaters with Respect to Overtopping and Stability

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., 2008
1 of 17
Homogeneous Berm Breakwater Investigations by
Lykke Andersen (2006)
B
Erosion
-hb
hs
Deposition
Initial profile
Gc
Recession
(Rec)
Rc
hf
d
Reshaped profile
R
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., 2008
2 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., 2008
3 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., 2008
4 of 17
Multi-Layer Berm Breakwaters (Icelandic Type)
• 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.
II
I
II
IV
III
VI
III
V
Not covered in detail in study 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., 2008
5 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., 2008
6 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., 2008
7 of 17
Lykke Andersen (2006) Overtopping Formula
for 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., 2008
8 of 17
Evaluation of Overtopping Formula – Other Data
2 Additional data sets homogenous berm breakwater:
Good agreement
for the few other
data sets
available as well.
3 Additional data sets multi-layer berm breakwater:
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS
WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 2008
9 of 17
New Model Tests
Studying Stability and Overtopping of Different Berm Breakwaters Types (Low Crest)
Multilayer Berm and Low Crest
6.3 m
Prototype conditions (model tests at scale 1:50):
.3
:1
.5
1:1
IV
III
1:
1.
3
IV
I
II
III
5
.
1:1II
Landward
.5
1 :1
1:
V
1:
VI
1.
3
1.
3
V
Hybrid Berm and Low Crest
6.3 m
Seeward
12 m
10 m
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
100
3
1.
.5 I+II+III
1 :1
.5
1:1
I+II+III
1:
90
1:
1.
3
IV+V
Landward
.5
1 :1
IV+V
1:
1:
VI
IV+V
1.
3
1.
3
80
70
60
50
Homogeneous Berm and Low Crest
40
6.3 m
30
20
10
Seeward
3
1.
I+II+III
+IV+V
1:
0
0
5
10
15
W [t]
20
25
12 m
10 m
Layer I
Layer II
Layer III
Layer IV
Layer V
5m
Units Passing [%]
•
•
•
•
•
10 m
1
5m
Seeward
12 m
5m
Same stones but study influence of amount
of sorting on stability and overtopping!!
.5
1:1
.5
1 :1
I+II+III
+IV+V
1:
1.
3
Landward
.5
1 :1
1:
VI
1:
1.
3
1.
3
30
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS
WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 2008
10 of 17
New Model Tests
Studying Stability and Overtopping of Different Berm Breakwaters Types (High Crest)
Multi-layer Berm and High Crest
Multilayer Berm and Low Crest
3
1.
1: III
I
6.3 m
III
1:
1.
27
IV
Landward
5
:1.
IV 1
II
1:
1
1.
3
V
1:
VI
Seeward
12 m
10 m
.5
1:1
.5
1:1
II
5m
Seeward
12 m
5m
13.3 m
3.5 m
.3
:1
Landward
.5
1:1
1.
3
1.
3
1.
3
.5
1:1
I+II+III
1:
1.
3
IV+V
Landward
.5
1 :1
IV+V
1:
1:
VI
IV+V
1.
3
1.
3
Homogeneous Berm and Low Crest
3.5 m
.5
1:1
.5 I+II+III
1 :1
.5
1:1
1:
1.
3
1:
10 m
3
1.
1:
VI
20 m
Seeward
12 m
5m
1:
I+II+III
+IV+V
1.
27
Wide Homogeneous Berm and High Crest (Add. Volume)
13.3 m
1:
6.3 m
1:
6.3 m
I+II+III
+IV+V
1:
1.
27
Landward
.5
1:1
Seeward
1:
VI
1:
1.
3
1.
3
12 m
10 m
.5
1:1
1.5
3
1.
1:
I+II+III
+IV+V
5m
1:
V
Hybrid Berm and Low Crest
5m
13.3 m
5m
12 m
I+II+III
+IV+V
Landward
.5
1 :1
V
3.5 m
3
1.
1:
1.
3
VI
Homogeneous Berm and High Crest
Seeward
IV
III
1:
IV
I
II
III
1.
3
V
Seeward
.5
1:1
5
.
1:1II
3
1.
I+II+III
+IV+V
1:
.5
1:1
.5
1 :1
I+II+III
+IV+V
1:
1.
3
Landward
.5
1 :1
1:
VI
1:
1.
3
1.
3
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS
WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 2008
11 of 17
Recession Results
Influence 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., 2008
12 of 17
Recession Results
Comparison with Lykke Andersen (2006) formula
Low Crest
•
•
High Crest
High Crest & Wide Berm
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.
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS
WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 2008
13 of 17
Overtopping Results
Influence 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., 2008
14 of 17
Overtopping Results
Comparison 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., 2008
15 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., 2008
16 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
A COMPARISON OF HOMOGENEOUS AND MULTI-LAYERED BERM BREAKWATERS
WITH RESPECT TO OVERTOPPING AND STABILITY
Lykke Andersen, Skals & Burcharth
ICCE2008, Hamburg, Sep., 2008
17 of 17