GB2283265A

GB2283265A - Breakwater caisson

Info

Publication number: GB2283265A
Application number: GB9421276A
Authority: GB
Inventors: Dal-Soo Lee; In-Sik Chun; Woo-Sun Park; Young-Min Oh
Original assignee: Korea Ocean Research and Development Institute (KORDI)
Current assignee: Korea Ocean Research and Development Institute (KORDI)
Priority date: 1993-10-29
Filing date: 1994-10-21
Publication date: 1995-05-03
Anticipated expiration: 2014-10-21
Also published as: GB2283265B; TW294739B; GB9421276D0; JPH07259045A; JP3300729B2; KR950011771A; KR970009830B1

Abstract

A breakwater caisson includes waterways 203 which are generally curved and connect an inlet 201 facing the sea and an outlet 202 formed in the upper surface of the caisson for discharging the seawater entered via the inlet back toward the open sea. This arrangement is intended to reduce overtopping and lessen the disturbance of the water surface of the harbor. The breakwater may further comprise pipe-shaped waterways 213 connecting the generally curved waterway to an outlet 212 located at the rear wall of the caisson for allowing nearly one-way-flow into the harbor when a wave attacks, thereby improving the water quality within the harbor. <IMAGE>

Description

BREAKWATER CAISSON The present invention relates to a breakwater caisson for improving performance of breakwater and water quality in a harbor.

The major function of a breakwater is to directly receive the force of a wave and reflect the received wave back to the open sea. Breakwaters consisting merely of a rubble mound are widely used. Also, a mixed-type breakwater with a caisson placed on the rubble mound situated on the seabed is adopted for use when the water is deep or the force of the wave is strong.

FIGs.lA-lD are cross-sectional diagrams of various conventional mixed-type breakwaters.

FIG.1A is a cross-sectional diagram of a conventional mixed-type breakwater in which the seawater cannot be circulated through the caisson.

Referring to FIG.lA, a rubble mound M is set on a seabed G and a caisson Ca having no wavechamber is set on the rubble mound. By filling the interior with the sand or similarly weighted matter, this type of caisson braces against the impact of a wave by means of a counterweight and has been widely used. The caisson blocks overtopping by reflecting waves 101 at a front side 102, thereby maintaining harbor tranquility behind a rear side 103 of the caisson.

When extraordinarily high waves impact the caisson, part of the waves overtops a top portion 104 thereby protecting the body of caisson against the impact thereof.

However, the breakwater adopting the above caisson without wavechamber causes a severe disturbance in the water's surface caused by the overtopping. Also, the water in the harbor is isolated from the outside seawater to eventually become stagnant and thereby the water quality deteriorates. This is caused by the shortage of oxygen in the harbor water area having very little ebb and flow variations.

FIG.1B is a cross-sectional diagram of a general caisson with wavechamber.

Referring to FIG.lB, a caisson Cb with wavechamber is composed of a base 111 formed on a rubble mound M, a rear wall 112 vertically formed on the base and located on the harbor side, a front perforated-wall 114 having a plurality of holes 113, formed on base 111 at the same height as rear wall 112 and toward the open sea, and a wavechamber 115 between rear wall 112 and front perforated-wall 114. This caisson can decrease the overtopping rate compared with the caisson without wavechamber shown in FIG.1A.

However, in the aspect of a weight distribution of the caisson, the weight of the caisson is more heavily distributed toward the rear wall or harbor side. As a result, the reaction force to the base is severely inclined to the rear wall, a supporting force to an overturning moment occurring in the caisson is reduced when the waves suddenly attack, and stagnation and quality deterioration of harbor water occurs for the same reason as in the case of the caisson without wavechamber of FIG.IA.

FIG.1C is a cross-sectional diagram of a perforated-wall caisson. Via the holes 123, the seawater can be exchanged.

Referring to FIG.1C, holes 123 and 124 are respectively formed in a front perforated-wall 121 and in rear walls 122 of a caisson Cc, thereby providing a structure for exchanging the water in the open sea for the standing water in the harbor. However, with this structure, when the front sea level 125 is higher than rear sea level 126, e.g., when a wave attacks as in the drawing, the water flows via the breakwater from holes 123 in seaward side to holes 124 in the harbor side. Conversely, when the sea level of the front is lower than that of the rear, the water reversely flows from holes 124 in the harbor side to holes 123 in the seaward side. That is, according to a periodical rise and fall of the water level in the front of the breakwater caused by the attacking waves, the direction of the flow of seawater passing through the breakwater caisson also changes periodically.

Therefore, the seawater exchanging effect is actually confined to the proximity of the narrow area along the breakwater. Also, this going and coming between the inside and outside of the harbor generates small waves in the standing water of the harbor, thereby causing disturbances in the water surface in the harbor. As a result, it is difficult for the area behind the breakwater to be used as a wharf for small seagoing vessels. Also, the breakwater caisson having the above constitution has an empty cavity within the caisson and therefore lacks stability. Whenever the sea levels between the inside and outside of the harbor are different, a flow via the breakwater is generated. Thus, a harbor oscillation can occur when long period waves attack, causing trouble in the cargo operations of ships within the harbor.

FIG.1D is a cross-sectional diagram of a caisson having a plurality of waterways.

Referring to FIG.lD, a caisson Cd is composed of a base 131 which is set on a rubble mound M and has a slope 132 which increases from the front to the upper side of the caisson, and a plurality of sloping portions 133 isolated from base 131 and corresponding to slope 132 of base 131. Also, sloping portions 133 are concentric such that their length is gradually shortened as the distance from the base becomes greater and a constant interval is maintained between each sloping portion. Here, spaces formed between base 131 and the first sloping portion 133 and between the other sloping portions, as shown in FIG.1D, form a plurality of waterways 136 having an inlet 134 at the front of the caisson and an outlet 135 which vertically discharges the sea water passed through waterways 136 and behind the caisson, that is, into the harbor.This structure reduces the maximum horizontal wave force acting on the caisson by having a large hole at the front of the caisson. Also, the structure provides the caisson with a downward thrust when waves attack, thereby reducing the width of the caisson and the weight of the caisson's body.

However, in the aspect of a weight distribution of the caisson, the weight of the caissons having the above constitution is inclined to the rear of the caisson whereby the reaction force of the base is inclined to the rear of the caisson. Also, much of the seawater easily flows into the harbor via waterways 136, thereby causing more severe overtopping and disturbances in the water's surface, compared with the caisson without wavechamber of FIG.1A. As a result, vehicular traffic along the breakwater is difficult so that the rear side of the breakwater cannot be used as a wharf.

To solve one or more the above problems of the conventional breakwater caisson, objects of the present invention are to provide a breakwater caisson for decreasing the occurrence of overtopping, to lessen disturbances in the water surface in the harbor and improve the performance of the breakwater, and to generate an attractive water spout even with relatively small attacking waves.

It is an alternative object of the present invention to provide a breakwater caisson which does not cause a harbor oscillation and improves the water quality inside the harbor water area having very little ebb and flow variations.

To achieve one or more of the above objects of the present invention, there is provided a breakwater caisson comprising an inlet for seawater formed in the front side of the caisson toward the open sea, an outlet for discharging the seawater entered via said inlet toward the open sea, which is formed in the upper surface of the caisson and one or more waterways each for connecting said inlet and outlet, which is generally curved, having an angle below 900 formed between the rear wall at and near the outlet and the upper surface of the caisson, for flowing backward the entered seawater to the open sea.

According to a preferred embodiment of the present invention, the generally curved waterway is composed of two or more arcs having different curvatures or in part of polygon shape. Here, one part of the generally curved waterway is constructed of one or more linear segments and another part of the waterway is constructed of one or more arcs having different curvatures.

According to another preferred embodiment of the present invention, the front part of the caisson is a filled portion for serving as a counterweight against attacking waves.

According to still another preferred embodiment of the present invention, two or more waterways are formed, arranged along the longitudinal direction of the caisson.

According to yet another preferred embodiment of the present invention, the inlet has a seawater inlet angle above 900 formed between the front surface of the caisson and the bottom wall of the waterway in the inlet of the waterway.

According to a further preferred embodiment of the present invention, the area of the outlet of the waterway is less than the area of the inlet.

According to yet still another preferred embodiment, a breakwater caisson comprises one or more pipe-shaped waterways each of whose inlet is at the rear wall of the waterway and whose outlet is at the rear wall of the caisson. Here, so as to reduce the fact that the reaction force of the base caused by the weight of the caisson body inclines toward the rear of the caisson, the area of the outlet of the pipe-shaped waterway may be larger than the area of the inlet.

Also, it is desirable that the inlet of the pipeshaped waterway is formed at or near the average sea level in the rear wall of the waterway and the outlet thereof is formed in the rear wall of the caisson and below the water surface by at least as much as the draft of small seagoing vessels.

To achieve another object of the present invention, the present invention provides a breakwater caisson having one or more pipe-shaped waterways which connect an inlet located near the average sea level of the open sea side, and an outlet located on the rear wall toward the harbor and below the water surface by at least as much as the draft of small seagoing vessels.

A breakwater caisson according to the present invention decreases overtopping to thereby lessen a disturbance of the water surface in the harbor, and improves the performance of the breakwater. Also, the caisson of the present invention provides an attractive spouting water display for use as a potential tourism resource, even with relatively small attacking waves.

Another breakwater caisson according to the present invention prevents the harbor oscillation phenomenon while improving water quality inside the harbor.

The above objects and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: FIGs.lA-1D are cross-sectional diagrams of conventional mixed-type breakwater caissons; FIG.2A is a partially cutaway prospective view of a breakwater adopting a caisson according to an embodiment of the present invention; FIG.2B is a cross-sectional diagram of the caisson according to a preferred embodiment of the present invention; FIG.2C is a cross-sectional diagram of the caisson according to another preferred embodiment of the present invention; FIG.2D is a cross-sectional diagrams of the caisson according to still another preferred embodiment of the present invention;; FIGs.3A-3C are photographs of scenes of hydraulic model tests simultaneously adopting the conventional caisson without wavechamber (rear) and the caisson according to the present invention; FIG.4 is a photograph showing overtopping blocking, and a wave breaking, in a hydraulic model test of the caisson according to the present invention; FIG.5A is a graph comparing the conventional breakwater adopting a caisson without wavechamber with the breakwater adopting a caisson according to the present invention in hydraulic model tests for reflection coefficients; FIG.5B is a graph for comparing the conventional breakwater adopting a caisson without wavechamber with the breakwater adopting a caisson according to the present invention in hydraulic model tests for overtopping rate; and FIG.6 is a graph representing the flow rate generated in hydraulic model tests of the caisson according to the present invention.

Referring to the appended drawings, a breakwater caisson according to the present invention will be described in detail below.

FIG.2A is a partially cutaway perspective view of the breakwater adopting a caisson according to an embodiment of the present invention, and FIG.2B is a schematic cross-sectional diagram of the caisson according to a preferred embodiment of the present invention. In FIG.2B, dotted lines representing a seawater inlet and a seawater outlet on the front and upper portions of the caisson, and a dotted line represented at a pipe-shaped waterway, can be represented as a solid line according to the location of the cross-section.

Referring to FIG.2B, a rubble mound M is established on a seabed G and the caisson is built thereon.

An inlet 201 is formed in the front side of caisson toward the open sea and an outlet 202 for discharging the seawater entered via inlet 201 back toward the open sea is formed on the upper side of the caisson. Also, the caisson comprises one or more waterways 203 which is generally curved (hereinafter referred to as " waterway") for connecting inlet 201 and outlet 202. Here, a number of waterways may be provided along the longitudinal direction of the caisson, as shown in FIG.2A. Also, the caisson further comprises a filled portion 208, which is filled with a weighted substance (e.g., sand), formed at the front of the waterway for serving as counterweight against an attacking waves 207.On the other hand, in order to discharge the seawater vertically and back toward the open sea, a seawater discharging angle a formed between the upper side of caisson 204 and the rear wall 205 at and near outlet 202, of waterway 203 is below 900. Also, to increase the stability of the caisson, a seawater intake angle P formed between front wall 206 of the caisson and rear wall 205 (bottom) of the waterway at inlet 201 is preferably above 90". To increase a spouting speed of the seawater to be spouted via outlet 202 of waterway 203, it is desirable that the area of the outlet is less than the area of inlet 201.

On the other hand, the shape of the waterway which is generally curved can be modified into various shapes including that shown in FIG.2B.

FIGs.2C and 2D are schematic cross-sectional diagrams representing another examples of the waterway 203 generally curved.

Referring to FIG.2C, waterway 203a generally curved is in the shape of part of polygon, which is a structure that is convenient for the practical construction of the caisson.

Referring to FIG.2D, waterway 203b which is generally curved is composed of arcs having varying radii for forming the rear wall of the waterway, such as, rl, r2 and r3, that is, having different curvatures. Here, the front wall of the waterway may be similarly composed of two or more arcs having radii such as rl , r2 and r3'. This constitution is necessary for increasing a stability and resistance to the sliding of the caisson or for controlling the spouting rate of the waterway Also, in the waterway, the inlet vicinity or outlet vicinity of the walls may be composed of linear segments as shown in FIG.2C and the remaining parts of the walls may be composed of arcs having different curvatures as shown in FIGs.2B or 2D.On the contrary, in the waterway, the inlet vicinity or outlet vicinity of the walls may be composed of one or more arcs having different curvatures and the remaining parts of the walls may be composed of linear segments. That is, the generally curved waterway may be composed of one or more linear segments as shown in FIG.2C and one or more arcs having different curvatures as shown in FIG.2B or 2D.

The breakwater caisson having the above constitution divides the wave volume due to attacking wave 207 along the front wall of the breakwater by receiving the front portion of the water inside waterway 203 via inlet 201, thereby reducing the sea level rise forward (open sea side) of the caisson.

Also, a wall of jettisoned water spouting via outlet 202 of waterway 203 collides against the water attempting to pass over the front of the caisson, thereby blocking the overtopping into the harbor and reducing the disturbance of the water surface in the harbor. Thus, the waves are partially destroyed in midair, thereby having the effect of additional wave energy dissipation beyond the capacity of the body of the caisson and additional reduction of reflection coefficient.

Here, the reflection coefficient is the ratio of reflected wave height to incident wave height. The overtopping is a phenomenon in which the incident waves pass over the breakwater. The overtopping rate is the amount of water overtopping a one meter section of the caisson per unit time. Such reductions in reflection coefficient and the overtopping rate are widely used as an index for measuring improvement of the performance of breakwater.

FIGs. 3A-3C are photographs of the scenes of hydraulic model tests simultaneously adopting the conventional caisson without wavechamber (rear) and the caisson according to the present invention. Here, a wave tank is partitioned into two with a transparent acrylic plate.

Referring to FIG.3A, the breakwater caisson according to the present invention divides the seawater in front of the attacking waves in a vertical plane in front of the caisson by receiving inflowing seawater into the interior of the waterway via inlet 201, thereby reducing the water level rise in front of the caisson. On the contrary, the conventional caisson without wavechamber exhibits a higher water level rise due to the attacking wave.

Referring to FIG.3B, in the case of the caisson according to the present invention, a jettisoned wall of water spouts via the outlet of the waterway and collides against the water passing over the front of the caisson, thereby blocking the overtopping into the harbor and dissipating the wave energy in midair.

However, in the case of the conventional caisson without wavechamber, the incident wave overtops the front of the caisson unimpeded. Accordingly, as shown in FIG.3C, the overtopping rate is much less in the caisson according to the present invention. On the other hand, a large amount of water is overtopped in the conventional caisson without wavechamber.

FIG.4 is a photograph showing scenes of overtopping blocking and destroying of a wave in a hydraulic model test of the caisson according to the present invention. Referring to FIG.4, the performance of the breakwater using the caisson according to the present invention is improved by the waterway for making the entered seawater flow backward. Also, an appealing spout of seawater is created by the generally curved waterway even when an incident wave is not overly large.

FIG.5A is a graph for comparing the reflection coefficients of the conventional breakwaters adopting a caisson without wavechamber with those of the breakwaters adopting a caisson according to the present invention through hydraulic model tests.

FIG.5B is a graph for comparing the overtopping rates of the conventional breakwaters adopting a caisson without wavechamber with those of the breakwaters adopting a caisson according to the present invention through hydraulic model tests.

Referring to the graph of FIG.5A, the horizontal axis represents the model wave period in the depth of 50cm in hydraulic model test, and the vertical axis represents the reflection coefficient. Reference characters Al and A2 represent the breakwaters adopting the caisson according to the present invention when the wave height of the model wave is 7cm and 13cm, respectively. Also, reference characters A3 and A4 represent the breakwater adopting the conventional caisson without wavechamber when the wave height of the model wave is 7cm and 13cm, respectively.

Referring to FIG.5A, in both cases (7cm and 13cm) of the present invention, the reflection coefficient of the breakwater adopting the caisson according to the present invention is less than the reflection coefficient of the breakwater adopting the conventional caisson without wavechamber. Therefore, the breakwater adopting the caisson according to the present invention causes the conditions of the sea in front of the breakwater to deteriorate, less than the breakwater adopting the conventional caisson without wavechamber.

In FIG.5B, the horizontal axis of the graph represents the model wave period and the vertical axis represents the overtopping rate for 13cm wave height.

Reference character B1 is a case of the breakwater adopting the caisson according to the present invention, and reference character B2 is a case of the breakwater adopting the conventional caisson without wavechamber. Referring to FIG.5B, for any wave period, the overtopping rate of the breakwater adopting the caisson according to the present invention is much less than that adopting the conventional caisson without wavechamber, thereby demonstrating the excellent properties of the caisson according to the present invention in view of the capacity of breakwater for reducing wave overtopping.

As described above, in the case of the caisson having a plurality of waterways as shown in FIG.1D, the degree of water surface disturbance is much more extreme compared with the caisson without wavechamber of FIG.1A. Therefore, the overtopping rate of the breakwater adopting the caisson according to the present invention is much less than the overtopping rate of the breakwater adopting the caisson having a plurality of waterways and has an excellent effect on harbor tranquility.

Comparing the caisson according to the present invention with the conventional perforated-wall caisson with wavechamber in view of the overturning of the caisson, the front of the conventional perforatedwall caisson with wavechamber is composed of the empty cavity of a wavechamber 115 whereby the supporting force to overturning is weak. However, since the front of the caisson according to the present invention is composed of a filled portion 208 which is located farthest away from a rear corner 209 of the caisson, a moment acting in the reverse direction with respect to the overturning moment is generated. As a result, the self-supporting force to the overturning is increased, thereby improving the stability of the caisson.

Referring to FIG.2B, the breakwater caisson according to the present invention further comprises a waterway 213 in the shape of a pipe (hereinafter referred to as a "pipe-shaped waterway") whose inlet 210 is at rear wall 205 of waterway 203 and whose outlet 212 is at rear wall 211 of the caisson, that is, for connecting rear wall 205 of waterway 203 and rear wall 211 of the caisson. Here, one pipe-shaped waterway can be desirably constructed for every waterway or a proper number of pipe-shaped waterways can be desirably constructed within a caisson, according to the characteristic of water flow. Also, in order to reduce the degree to which the reaction force of the base, caused by the weight of the caisson, inclines to the rear of the caisson, the area of outlet 212 in pipe-shaped waterway 213 can be larger than the area of inlets 210.Furthermore, it is desirable that inlet 210 is formed at or near the average (calm) water level 215 on a vertical plane at rear wall 205 of waterway 203, so as to properly control the flow of the water from the harbor into the waterway and vice versa.

The horizontal component of wave force is actually the largest near average water level 215 on rear wall 205 of the waterway when a wave attacks.

Thus, if inlet 210 of pipe-shaped waterway 213 is constructed near the average water level, the horizontal wave force acting on the body of the breakwater is decreased to thereby increase the stability of the caisson body. Also, it is desirable that outlet 212 of pipe-shaped waterway 213 formed in rear wall 211 of the caisson is below the water surface at least as much as a draft of small seagoing vessels.

The breakwater caisson according to the present invention causes a flow of seawater due to the difference of the sea level between raised water level 215 in waterway 203 and rear water level 214 of the caisson when a wave attacks, which flows into the harbor via pipe-shaped waterway 213. Here, a slight raising of the water level at the rear of the breakwater forms a flow from the rear of the breakwater to the entrance of the harbor, thereby continuously exchanging the water of the harbor with the water of the open sea which has much oxygen even in the harbor water area having very small tidal range. That is, the water condition of the harbor is more like a slowly flowing river than a pond. As a result, the self-cleaning capacity of the harbor is improved by preventing the deterioration of the water quality, for example, eutrophication.

Here, a characteristic of flow rate varies according to a relative position between the position (height) of inlet 210 of pipe-shaped waterway 213 and rear water level 214. FIG.6 shows the variation of flow rate characteristic. In FIG.6, the horizontal axis represents the period of a 13cm-high model wave and the vertical axis represents a net flow rate into the harbor via one pipe-shaped waterway whose diameter is 3.2cm. Reference characters C, D and E represent the height (vertical position) of inlet 210 in waterway 203. Specifically, reference character D is the case where the inlet is located at the height of average water level 215. Reference characters C and E are the cases where the inlet is located slightly above and slightly below the average water level, respectively.Referring to FIG.6, the flow rate is less at ''C'l when the wave period is short and at "E" when the wave period is long. However, the flow rate is great at "D" at all times. Thus, the height of the inlet can be suitably determined according to the necessary flow rate.

Comparing the characteristic of the breakwater adopting the caisson having a pipe-shaped waterway with the conventional perforated-wall caisson breakwater, as described above, the harbor oscillation can be caused by the inflowing of a long period wave via the breakwater, and the seawater exchanging effect is limited to the narrow water region near the breakwater in the case of the conventional perforatedwall caisson breakwater. On the contrary, the breakwater adopting the breakwater caisson according to the present embodiment comprises a pipe-shaped waterway whose inlet is located near the average water level, thereby short-periodically raising and lowering the water level in front of the caisson even when the long period wave component is included in the attacking wave trains. As a result, the flow of the long period wave component is filtered out so that harbor oscillation is not generated. Also, backward flow is limited so that the inflow of seawater having a high oxygen content occurs into the harbor. Thus, the water quality improving effect can be widely extended throughout the region of the harbor. Also, in the case of the conventional perforated-wall caisson breakwater, the inflow and outflow through the breakwater provide small secondary waves in the harbor, thereby causing disturbances in the water surface within the harbor. Thus, it is difficult for the rear side of the breakwater to be used as a wharf for small seagoing vessels. However, the breakwater adopting the breakwater caisson according to the present embodiment limits the backward flowing.As a result, the amplitude of the waves secondarily generated in the harbor is decreased to approximately one half that of the waves generated when adopting the conventional perforated-wall caisson breakwater.

Accordingly, the problem of water surface disturbance within the harbor is shortened. Furthermore, when outlet 212 of pipe-shaped waterway 213 is located below the water surface by at least as much as a draft of small seagoing vessels, a rolling of the vessels caused by the speed of the out flowing water within the harbor can be prevented. Also, along with the prevention of a rolling of the vessels, the function of reducing of overtopping provides small seagoing vessels with suitable wharf conditions.

Comparing the caisson having the pipe-shaped waterway according to the present invention with the conventional caisson with wavechamber of FIG.1B and the caisson having a plurality of waterways of FIG.1D in a view of the weight distribution, the weight of the conventional caisson is inclined to the rear thereof whereby the reaction force to the base is excessively inclined to the rear. On the other hand, the caisson according to the present invention has empty spaces caused by pipe-shaped waterway 213, thereby decreasing an imbalance of the reaction force to the base. Furthermore, if the area of outlet 212 of pipe-shaped waterway 213 is designed to be larger than the area of inlet 210, the imbalance of the reaction force of the footing base can be further lowered.

As above, the pipe-shaped waterway is described only in the caisson having the generally curved waterway. However, the pipe-shaped waterway can be adopted in a caisson having various shapes. For example, if the pipe-shaped waterway is applied to the caisson without wavechamber of FIG.lA, the inlet of the pipe-shaped waterway is to be located at front wall 102 of the caisson and the outlet is to be located at rear wall 103. If the pipe-shaped waterway is applied to the caisson with wavechamber of FIG.1B, the inlet of the pipe-shaped waterway is to be located at rear wall 112 toward wavechamber 115 of the caisson with wavechamber and the outlet is to be located at rear wall 112 toward harbor 116.Also, if the pipeshaped waterway is applied to the caisson having a plurality of waterways, the inlet of the pipe-shaped waterway is to be located at a slope 132 of a base 131 and the outlet is to be located at a rear wall 137 of base 131. A breakwater caisson according to the present embodiment having the pipe-shaped waterway applied to the caissons of various forms further comprises one or more pipe-shaped waterways connecting an inlet located near the average sea level of the wall toward the open sea while contacting with the seawater and an outlet located below the water surface by at least as much as a draft of small seagoing vessels, on the caisson's rear wall toward the harbor.

As described above, the breakwater caisson according to one aspect of the present invention provides for the water of the attacking waves to be divided by a waterway and the overtopping is reduced by the spouting water via the outlet of the waterway, thereby decreasing the overtopping and lessening the disturbance of the water surface within the harbor.

Thus, the performance of the breakwater is increased.

Also, the filled portion provided at the front of the caisson improves the stability against overturning.

Also, the breakwater caisson of another aspect of the present invention has the inlet of a pipe-shaped waterway located near the average water level, thereby limiting the backward flow. Thus, the water quality improving effect can be widely extended into the harbor. The breakwater caisson which is a kind of perforated-wall caisson breakwater filters out long period component of waves so that harbor oscillation is not generated. Also, when the outlet of the pipeshaped waterway is located below the water surface by at least as much as a draft of the small seagoing vessels, rolling of the ships caused by the flowing speed of the out flowing water within the harbor can be prevented, thereby providing a suitable condition for a wharf. Also, the empty space for pipe-shaped waterway 213 decreases the imbalance of the reaction force to the base. Furthermore, if the area of outlet 212 of pipe-shaped waterway 213 is designed to be larger than the area of inlet 210, the imbalance of the reaction force of the base can be further lowered.

In this document, the word "caisson" means a structure supported from the sea floor for protecting a habor from waves, and will be understood in this broad sense.

In this document, one typical or average depth of a small seagoing vessel is around 4 metres.

Figures 3a-3c and 4 of Korean application 22735 (from which priority is claimed) are incorporated herein by reference.

As described above, the present invention has been described through a preferred embodiment.

However, the present invention is not limited to the preferred embodiment and various modifications are possible within the limits of the technology of the present invention, as understood by one skilled in the art.

Claims

CLAIMS:

1. A breakwater caisson comprising: an inlet for seawater formed in the seaward side of the caisson toward the open sea; an outlet for discharging the seawater entered via said inlet, formed above the inlet; and at least one waterway connecting said inlet and outlet, the waterways and outlet being shaped to direct the entered seawater backwards to the open sea.

2. A breakwater caisson according to claim 1 in which the outlet is formed in the upper surface of the caisson, and the waterway is generally curved, and forms at its rear wall near said upper surface an angle of less than 900 with said upper surface.

3. A breakwater caisson as claimed in any preceding claim, wherein said waterway comprises two or more arcs having different curvatures.

4. A breakwater caisson as claimed in any preceding claim, wherein said waterway comprises two or more linear segments.

5. A breakwater caisson as claimed in any preceding claim, wherein one or more linear segments are provided in part of said waterway and one or more arcs having different curvatures are provided in the remaining parts thereof.

6. A breakwater caisson as claimed in any preceding claim, wherein the front part of the caisson has a filled portion for serving as a counterweight in case of a wave attack.

7. A breakwater caisson as claimed in any preceding claim, wherein said waterways are two or more in the number and are arranged along the longitudinal direction of the caisson.

8. A breakwater caisson as claimed in any preceding claim, wherein said inlet of the waterway has a seawater inlet angle of above 900 formed between the front surface of the caisson and the bottom wall of the waterway.

9. A breakwater caisson as claimed in any preceding claim, wherein the area of said outlet of the waterway is less than the area of the inlet.

10. A breakwater caisson as claimed in any preceding claim, further comprising at least one waterway in the shape of a pipe whose inlet is formed in the rear wall of said waterway and whose outlet is formed in the rear wall of the caisson.

11. A breakwater caisson as claimed in claim 10, wherein the area of the outlet of said pipe-shaped waterway is larger than the area of the inlet of the same.

12. A breakwater caisson as claimed in claim 10 or claim 11, wherein the inlet of said pipe-shaped waterway is formed at or near an average water level in the rear wall of the waterway.

13. A breakwater caisson as claimed in any of claims 10 to 13, wherein the outlet of said pipeshaped waterway is formed in the rear wall of the caisson, below a water surface by at least as much as the draft of small seagoing vessels.

14. A breakwater caisson comprising: an inlet which is located near the average water level of the wall toward the open sea; an outlet which is located below the water surface and the level of the inlet in the rear wall toward the harbor; and at least one waterway conduit connecting said inlet and outlet.

15. A breakwater caisson according to claim 14 in which the outlet is located at a depth at least that of a small seagoing vessel beneath the level of the inlet.

16. A breakwater caisson according to claim 14 or claim 15 in which the outlet is located at least 4 metres below the level of the inlet.