U.S. patent application number 13/140401 was filed with the patent office on 2012-04-12 for method for constructing water barriers and coastal protection.
Invention is credited to Jonas Benjamin Roger Maertens, Marc Van Den Broeck.
Application Number | 20120087735 13/140401 |
Document ID | / |
Family ID | 40934098 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120087735 |
Kind Code |
A1 |
Van Den Broeck; Marc ; et
al. |
April 12, 2012 |
Method for Constructing Water Barriers and Coastal Protection
Abstract
The invention relates to a method for constructing a water
barrier. In the method a core of quarry run is arranged on the
underwater bottom and provided with a protective layer of stones or
concrete blocks, with the proviso that, at least at the position of
the water barrier, the underwater bottom is raised using bottom
material. The method is particularly suitable for constructing a
water barrier for relatively deep water.
Inventors: |
Van Den Broeck; Marc;
(Aalst, BE) ; Maertens; Jonas Benjamin Roger;
(Merelbeke, BE) |
Family ID: |
40934098 |
Appl. No.: |
13/140401 |
Filed: |
December 17, 2009 |
PCT Filed: |
December 17, 2009 |
PCT NO: |
PCT/IB09/08073 |
371 Date: |
December 27, 2011 |
Current U.S.
Class: |
405/117 |
Current CPC
Class: |
E02B 3/06 20130101; Y02A
10/15 20180101; Y02A 10/11 20180101; E02B 3/10 20130101 |
Class at
Publication: |
405/117 |
International
Class: |
E02B 3/10 20060101
E02B003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2008 |
BE |
2008/0683 |
Claims
1. Method for constructing a water barrier, wherein a core of
quarry run is arranged on the underwater bottom and is provided
with a protective layer of stones or concrete blocks, with the
proviso that, at least at the position of the water barrier, the
underwater bottom is raised using bottom material.
2. Method as claimed in claim 1, characterized in that the
underwater bottom is raised with bottom material prior to the core
being arranged.
3. Method as claimed in claim 1 or 2, characterized in that the
underwater bottom is raised to a height such that the average water
depth at the position of the water barrier decreases by 20 to
80%.
4. Method as claimed in any of the foregoing claims, characterized
in that the underwater bottom is raised to a water depth which does
not exceed 50% of the closure depth.
5. Method as claimed in claim 4, characterized in that the
underwater bottom is raised to a water depth which does not exceed
the closure depth.
6. Method as claimed in any of the foregoing claims, characterized
in that the underwater bottom is raised to a level such that the
volume of material required for core and protective layer decreases
by 20 to 80% relative to a water barrier with non-raised underwater
bottom.
7. Method as claimed in any of the foregoing claims, characterized
in that the raised underwater bottom is compacted at least at the
position of the water barrier.
8. Method as claimed in claim 7, characterized in that the raised
underwater bottom is compacted to a saturated density lying between
1.6 ton/m.sup.3 and 2.3 ton/m.sup.3.
9. Method as claimed in any of the foregoing claims, characterized
in that a filter layer is arranged between the raised underwater
bottom and the core.
10. Method as claimed in any of the foregoing claims, characterized
in that the underwater bottom is raised gradually from the natural
level thereof up to a position in the vicinity of the water
barrier, whereby the raising has an inclination.
11. Method as claimed in claim 10, characterized in that the height
of the raising increases at a substantially constant inclination in
the direction of the water barrier.
12. Method as claimed in claim 11, characterized in that the angle
of inclination to the horizontal direction lies between 1:2 and
1:20, more preferably between 1:5 and 1:15, and most preferably
between 1:7 and 1:10.
13. Method as claimed in any of the claims 1-9, characterized in
that the underwater bottom is raised gradually from the natural
level thereof up to a position in the vicinity of the water
barrier, whereby the raising has an average inclination and wherein
this average inclination comprises one or more substantially
horizontal parts.
14. Method as claimed in any of the claims 10-13, characterized in
that the inclination is provided with a plurality of water barriers
which lie substantially in line with the water barrier.
15. Method as claimed in claim 14, characterized in that the crests
of the multiple water barriers lie at increasing height, but do not
exceed the crest height of the water barrier.
Description
[0001] The invention relates to a method for constructing water
barriers and coastal protection, such as in particular breakwaters,
and a water barrier obtained with the method.
[0002] Breakwaters comprise structures erected from relatively hard
rock which are arranged in the sea in order to protect the coastal
area behind. This protection is brought about in that the
breakwater absorbs a significant part of the wave energy of the
incoming waves, whereby the wave reaches the coastal area in
attenuated form. The known rockfill breakwater is generally erected
from a core of quarry run with a heavier protective layer on the
outside, the so-called armour layer. This armour layer generally
comprises larger and heavier stone blocks than the core material.
Concrete elements are also applied. The stone blocks have a
somewhat irregular shape so that the protective layer is
sufficiently porous or permeable for the waves. Because the waves
can partially penetrate the protective layer, the wave energy is
attenuated.
[0003] In addition to attenuating waves, a breakwater protects
against coastal deterioration through erosion, caused by
unfavourable sediment transport from the coastal area to sea. The
breakwater interferes in the natural transport pattern of sediment
such that erosion of the coastal area is prevented, or in any case
reduced.
[0004] Owing to the protective action of a breakwater regular sand
replenishments along the eroded coastline are less necessary. A
drawback of the known water barrier or coastal protection, in
particular breakwater, is that the effect on the sediment transport
along the coastline depends on a large number of parameters, such
as for instance the length of the breakwater and/or the distance
thereof from the coast. At non-optimal ratios problems regularly
occur which can be traced back to unfavourable sediment transport.
The known breakwater can thus for instance cause the formation of
bell-shaped sediment accumulations (so-called `salients`). The
known breakwater is also susceptible to erosion in the vicinity of
the foot of the breakwater, which undermines the stability of the
breakwater.
[0005] The present invention has for its object to provide a method
with which water barriers, and in particular breakwaters, can be
constructed, wherein at least an equivalent protection is provided
as with the known water barrier and wherein the above stated
problems can be at least partly obviated.
[0006] This object is achieved according to the invention by
providing a method for constructing a water barrier of the above
stated type, wherein a core of quarry run is arranged on the
underwater bottom and is provided with a protective layer of stones
or concrete blocks, with the proviso that, at least at the position
of the water barrier, the underwater bottom is raised using bottom
material. With the invented method more bottom material or sediment
is supplied at the position of the water barrier. This is at first
sight unfavourable because the overall amount of bottom material in
the vicinity of the water barrier greatly increases and the chance
of loss of stability and/or undesirable sediment transport
therefore increases. This expectation is further reinforced by
newly supplied bottom material being generally less stable than
bottom material that has already been present for a long time.
Surprisingly however, it has been found that a water barrier
obtained with the invented method is surprisingly stable and causes
less undesirable sediment transport than expected.
[0007] With the inventive method a water barrier is obtained with a
reduced overall height of core and protective layer relative to the
known water barrier. A significant advantage hereof is that the
invented water barrier can be obtained in more economic manner than
the known water barrier. The materials for the core and the
protective layer are generally expensive to purchase and are
moreover often transported by road, this also resulting in high
costs. The water barrier obtained with the invented method in any
case uses a reduced volume of core material relative to the known
water barrier at substantially the same water barrier level,
thereby saving costs. Because the amount of material required for a
water barrier increases sharply along with the depth, the invented
method is particularly suitable for constructing a water barrier
for relatively deep water, which is understood to mean water with a
depth of at least 8 metres, more preferably at least 14 metres, and
most preferably at least 20 metres.
[0008] Another advantage of the method according to the invention
is that the supply of a part of the material for the water barrier
can take place in simple and rapid manner. Although supply of the
bottom material required for raising the underwater bottom can for
instance take place by supplying this bottom material, generally
sand, substantially by road, it is recommended that the bottom
material is dredged in the vicinity, and more preferably in the
immediate vicinity of the water barrier to be constructed. Dredging
is a per se known technique and can for instance be carried out
using a trailing suction hopper dredger. This comprises a drag head
which, together with a suction conduit, is lowered under water at
the rear of the trailing suction hopper dredger until it contacts
the bottom under the influence of its own weight. Through the
forward movement of the trailing suction hopper dredger the drag
head is dragged over the bottom for dredging, wherein the soil is
loosened and suctioned away with water via the suction conduit. If
desired, the suctioned bottom material can be transported
immediately via a transport conduit to the desired location, more
in particular to the vicinity of the water barrier to be
constructed.
[0009] In a preferred embodiment the method according to the
invention is characterized in that the underwater bottom is raised
with bottom material prior to the core being arranged. A more
efficient method is hereby obtained, which moreover provides a
greater reliability. It is thus possible for instance to determine
the height of the raised underwater bottom before the core is
arranged. If desired, the raised part of the underwater bottom can
also be compacted or treated in other manner.
[0010] The underwater bottom can in principle be raised to any
height according to the invention, wherein the stability of the
water barrier remains guaranteed. A water barrier consisting
substantially wholly of bottom material will generally be too
unstable, and cannot therefore fulfill its function properly. In a
preferred embodiment of the method according to the invention the
underwater bottom is raised to a height such that the average water
depth at the position of the water barrier decreases by 20 to 80%,
more preferably by 30 to 70%, and most preferably by 40 to 60%. The
water barrier is found to produce the best results within this
range.
[0011] It has been found that a particularly stable water barrier
is obtained with a method wherein the underwater bottom is raised
to a water depth which does not exceed 50% of the closure depth,
more preferably does not exceed 75% of the closure depth, and most
preferably does not exceed the closure depth. The closure depth is
a term known to the skilled person: when water depths are regularly
measured away from the coastline, there is found to be a minimum
water depth above which the water depths do not change through
time. This depth is called the closure depth. The closure depth can
be determined experimentally or, in the context of the present
patent application, can be derived in simple manner by the
following approximate formula:
d.sub.1=1.75 H.sub.s0.137 (1)
wherein d.sub.1 represents the closure depth and H.sub.s0.137 is
the effective wave height at the position of the water barrier. The
effective wave height is that wave height which is exceeded a
maximum of 12 hours per year and therefore has a maximum occurrence
probability of 0.137%.
[0012] The method according to the invention is preferably
performed in that the underwater bottom is raised to a level such
that the volume of material required for core and protective layer
decreases by 20 to 80% relative to a water barrier with non-raised
underwater bottom, more preferably by 30 to 70%, and most
preferably by 40 to 60%. Statically stable breakwaters, such as of
the above described type, should generally deform only little under
wave attack. A relatively heavy construction is therefore required.
With the method according to the invention a water barrier is
obtained which is lighter per unit volume than the known water
barrier. It is surprising that this has hardly any or no effect on
the stability of the water barrier. An undefended water barrier of
sand would not at first sight appear to be a very obvious solution.
Nature will exert its influence on such a water barrier, deform it
and possibly even level it completely in the course of time. The
water barrier according to the invention comprises a quantity of
weighting material (quarry run and the stones of the protective
layer) which is lower than the known water barrier with the same
water barrier height. Nevertheless, the above stated problems
hardly occur.
[0013] A further preferred embodiment of the method according to
the invention is characterized in that the raised underwater bottom
is compacted at least at the position of the water barrier.
Compaction of the raised water bottom can for instance be performed
by vibration or by pile-driving with a drop weight. It is also
possible and advantageous to provide the raised water bottom with
grout columns for further stabilizing thereof and to make the water
barrier better resistant to earthquakes.
[0014] The raised underwater bottom can in principle be compacted
to any desired saturated density. The saturated density is
understood to mean the density of a volume of material which is
substantially wholly saturated with water. It has been found
advantageous for the raised underwater bottom to be compacted to a
saturated density lying between 1.6 ton/m.sup.3 and 2.3
ton/m.sup.3, more preferably between 1.7 ton/m.sup.3 and 2.2
ton/m.sup.3 and most preferably between 1.9 ton/m.sup.3 and 2.1
ton/m.sup.3.
[0015] It is further advantageous to characterize the method in
that a filter layer is arranged between the raised underwater
bottom and the core. This measure enhances the geotechnical
stability. Soil erosion at the toe of the water barrier, in
particular a breakwater, is hereby reduced. Migration of bottom
material to the core is further countered. Bottom material is in
principle more impermeable than quarry run. Migration may thus
result in a decreasing porosity of the core. The breakwater action
hereby becomes less effective. The present embodiment variant at
least partially avoids this. In some cases the filter layer also
lets through water. A relatively permeable water barrier or
breakwater has a high probability of sanding up, certainly in
sand-rich conditions: waves and current supply sand which then
fills the pores (in the core).
[0016] The water barrier according to the invention can further
comprise multiple filter layers, for instance in the form of a
stone layer between the core and the protective layer. A gradual
transition is hereby obtained between the relatively finer and
coarser materials. If desired, the water barrier can further be
provided with a toe construction for the purpose of supporting the
protective layer in the direction of the inclination of the slope
and with a crown wall on top of the water barrier so that it is
possible to walk thereon.
[0017] The water barrier according to the invention, and in
particular a breakwater according to the invention, can be built
with its crest below or above water. The height position of the
crest of the breakwater relative to the average water level
determines the amount of wave energy which is allowed over the
structure, as well as the degree to which diffraction will occur.
The more wave energy is allowed through, the smaller the wave loads
on the breakwater become. Breakwaters with their crest under water
have the further advantage that they allow through a (large) amount
of wave energy, whereby the load on the breakwater decreases.
[0018] Fully impermeable breakwaters reflect the wave energy or
dissipate the energy in a relatively small stone volume. The
breakwater is here generally loaded more heavily. Such a breakwater
is therefore preferably given a heavier form.
[0019] A further preferred embodiment of the method according to
the invention is characterized in that the underwater bottom is
raised gradually from the natural level thereof up to a position in
the vicinity of the water barrier, whereby the raising has an
inclination. The present variant has the advantage that the waves
already at least partially lose their energy well before the water
barrier. Model tests have moreover shown that sediment transport to
the area between water barrier and coastline occurs to lesser
extent. It is further advantageous here when the height of the
raising increases at a substantially constant inclination in the
direction of the water barrier. The best results are achieved when
the angle of inclination to the horizontal direction lies between
1:2 and 1:20, more preferably between 1:5 and 1:15, and most
preferably between 1:7 and 1:10. The underwater bottom is
preferably raised gradually from the natural level thereof up to a
position in the vicinity of the water barrier, whereby the raising
has an average inclination but wherein this average inclination
comprises one or more horizontal parts. The horizontal parts
preferably have a length which is about 2 to 3 times the raised
water depth at that position.
[0020] In order to further support the favourable effect of the
inclination, in a preferred embodiment of the method the
inclination is provided with a plurality of water barriers which
are positioned at a mutual distance from each other and which lie
substantially in line with the water barrier. The crests of the
multiple water barriers preferably lie at increasing height in the
direction of the water barrier, with the proviso that the crest
heights of the water barriers do not exceed that of the water
barrier.
[0021] The invention will now be further elucidated with reference
to the accompanying figures, without otherwise being limited
thereto. In the figures:
[0022] FIG. 1 shows a schematic cross-section of a first embodiment
of a water barrier according to the invention; and
[0023] FIG. 2 shows a schematic cross-section of a second
embodiment of a water barrier according to the invention.
[0024] Referring to FIG. 1, a water barrier 1 embodied as
breakwater is shown which is obtained using the method according to
the invention. The shown embodiment of water barrier 1 is obtained
by raising the existing underwater bottom 3, at least at the
position of water barrier 1, with bottom material 4 supplied from
elsewhere and subsequently arranging a core of quarry run 2
thereon, for instance by pouring it onto the supplied bottom
material 4. The core of quarry run 2 is provided with an
approximately 2 m thick protective layer 5 constructed from stones
6. A filter layer 8 of a granular material, with a stone size
between 5 and 75 mm, is arranged between the raised water bottom 4
and core 2. It is likewise possible to apply a geotextile with a
typical thickness of between 2 and 5 mm.
[0025] In the variant shown in FIG. 1 the top of the water barrier
protrudes above water surface 7, although it is also possible for
the top to lie below the water surface 7, for instance in order to
conceal the breakwater from view. An existing water bottom at 14 m
below water level 7 can for instance be raised to an average of for
instance 5 m below water level 7 using the invented method. The
underwater bottom is here thus raised to a height at which the
water depth is reduced from -14 m to -5 m, therefore by about 65%.
In the given example a prior art water barrier, which is arranged
directly onto the existing underwater bottom, is at least
approximately 14 m high. With the method according to the invention
the overall height of core 2 and protective layer 6 amounts
approximately to at least only 9 m, this corresponding to a height
reduction of about 65%.
[0026] It is advantageous when underwater bottom 3 is raised
gradually from the natural level thereof up to a position in the
vicinity of water barrier 1, whereby the height of raising 4
increases at a substantially constant inclination 9 in the
direction of water barrier 1. In the shown example the angle of
inclination 10 to the horizontal direction lies between 1:10 and
1:20.
[0027] The raising 4 can extend over a relatively great distance on
the sea side of water barrier 1 (the left-hand side in FIG. 1). In
a preferred variant (not shown) inclination 9 is provided with a
plurality of water barriers which lie substantially in line with
water barrier 1 and which are obtained in the same way as water
barrier 1. The crests of the water barriers herein lie at
increasing height in the direction of water barrier 1 as seen from
the sea side, wherein they do not however exceed the crest height
of water barrier 1.
[0028] Referring to FIG. 2, another embodiment of a water barrier 1
is shown, which is likewise obtained using the method according to
the invention. The shown embodiment of water barrier 1 is obtained
by raising the existing underwater bottom 3, at least at the
position of water barrier 1, using bottom material 4 supplied from
elsewhere and subsequently arranging a core of quarry run (2, 2a,
2b) thereon, the central part 2a of which consists of coarser rocks
and the right-hand part of which consists partially of even coarser
rocks 2b. The core (2, 2a, 2b) is poured onto the supplied bottom
material 4 in a number of operations. The core (2, 2a, 2b) is then
provided with a protective layer 5, approximately 2 m thick and
constructed from stones 6. A filter layer 8 with a thickness of 5
to 75 mm is arranged between the raised underwater bottom 4 and
core 2. The parts (2a, 2b) provide for a locally increased porosity
of core layer (2, 2a, 2b), whereby the wave energy is better
dissipated locally. This variant further has a raising 4 with two
substantially horizontal terraces (9a, 9b) and two parts (9c, 9d)
which have an incline. Such a structure has a favourable influence
on the breakwater action and the stability of water barrier 1.
[0029] The invention is by no means limited to the above described
exemplary embodiments, and many variants are possible within the
scope of protection of the appended claims.
* * * * *