JPH047767B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a wave-dissipating caisson for a breakwater, and particularly to a wave-dissipating caisson for a breakwater that is highly economical and suitable for use in deep water.

(Prior art and its problems) The breakwaters that have been widely used in the past have disadvantages such as high wave reflectivity and strong wave force. Therefore, as a countermeasure, for example, as shown in the cross-sectional view in Fig. 1, a wave dissipating block 2 is inserted in front of the caisson 1 that forms the breakwater or seawall.
It has been widely practiced to reduce reflected waves and overtopping waves, as well as to reduce wave force. However, in this method, when the water depth is deep, it is necessary to use a large design wave height, so a large number of large wave-dissipating blocks 2 must be used, which is economically disadvantageous. Therefore, this method is mostly used for breakwaters and seawalls in relatively shallow waters.

Therefore, a so-called upright wave-dissipating caisson structure in which the caisson itself has a wave-dissipating mechanism, for example, as shown in Fig. 2, a retarding space 4 having a porous wall or a slit wall 3 is formed on the front side of the port side a of the caisson body. An upright wave-dissipating caisson structure has been proposed. According to this method, the wave-dissipating block 2 described above in FIG.
However, on the other hand, if this structure is to ensure a wave-dissipating function not only for short-period waves but also for long-period waves, the retarding space 4 must be enlarged. . For this reason, not only is it inevitable that the cross-section of the embankment body becomes large, but also a considerably large impact pressure acts on the upper surface of the water retarding chamber that forms the water retarding space 4, as shown by the arrow in the figure. Therefore, there is a major problem in ensuring the strength of the structure. In addition, since the retarding chamber 4 is provided on the port side a, the center of gravity of the embankment is shifted to the port side b, resulting in the undesirable result that a large pressure is applied to the end toe of the caisson 1 on the port side b. It will give rise to Therefore, conventional upright wave-dissipating caisson structures have disadvantages both from an economical and design standpoint.

(Objective of the Invention) The present invention eliminates all the drawbacks of the upright wave-dissipating caisson structure as described above, and provides effective wave-dissipating function and stability even against long-period waves due to the cross section of the dam body which is smaller than the conventional structure. The purpose of this design was to provide a wave-dissipating caisson with excellent economic efficiency. Next, the present invention will be explained in detail based on the drawings.

(Means for Solving the Problems) FIG. 3 is a bird's-eye view showing one box of the wave-dissipating caisson of the present invention, and its features are as follows.

That is, the first is caisson 1 as shown in Figure 3.
The upper surface of the outer side a of the port is made into a gentle slope 5 that rises toward the inner side of the port b, and a plurality of small ridges 6 are provided in parallel on that surface at right angles to the direction of the waves. . The second feature is that an eaves 7 whose upper surface is connected to the gentle slope 5 is provided on the front edge of the caisson body 1 on the outside port side a. Thirdly, on the inner side b of the port of the installation part of the gentle slope 5 of the caisson body 1, there are a plurality of drainage chambers 9 whose tops slightly protrude from the top of the gentle slope 5 and whose top surfaces are open 8.
In addition, a slit 10 is provided on the wall surface on the port side a of the protruding portion, and a drainage hole 11 is provided on the wall surface on the port side b of the drainage chamber 9. Furthermore, at the same time, a wave return 12 is provided on the upper edge of the installation surface of the slit 10 of the drainage chamber 9, connected by the curved surface of the installation surface of the slit 10, and protruding to the outside of the port a.
The back surface of the inner side b of the port of the drainage chamber 9 is made to protrude further upwards than the top end of the front wave return 12, and this part is also provided with a wave return 13 whose upper part has a curved surface and protrudes toward the outer side a of the port. .

(Operation and Effect) If the gentle slope 5 having a plurality of ridges 6 is provided on the port side a of the caisson body 1 as described above, the fourth
As shown in the schematic diagram in Figure a, even when small waves run up during normal times, the energy of the waves is reduced due to wave A running up to the gentle slope 5 and promoting wave breaking based on the collision with the ridge 6. Increase the disappearance. Therefore, it is possible to reduce the reflection of waves without providing a water retarding chamber having slits or porous holes in the upright wall of the caisson body 1 on the port side a as in the conventional case. In addition, the eaves 7 provided on the front edge of the gentle slope 5, which is the second feature, make the gentle slope 5
At the same time as reducing the reflection of long-period waves by increasing the length of By colliding with the coming waves, a large vortex B is generated and the energy of the waves is significantly reduced.
Moreover, in addition to this, the undertow from the top of the gentle slope 5 is caused to fall to a deep place away from the front of the caisson body 1. Therefore, the port outside a of the caisson body 1
The fluid force applied to the foot protection block 14 provided in the ground can be greatly reduced, and its stability can be achieved.

In addition, the third feature of the wave returns 12 and 13 is that the crest height is lower than that of a single wave return structure, making it possible to reduce wave overtopping, and the presence of the slit 10 reduces the wave force acting on the front wave return 12. It has the advantage that the front and rear wave returns 12 and 13 can share and receive the wave force. In addition, a large wave force acts on the wave return 12, but since the length of the slit 10 is short, there is no risk of problems with the strength of the member. Furthermore, the drainage chamber 9 having the drainage hole 11 has a slit 10.
The wave that has overflowed further and the wave that has exceeded the top of the wave return 12 on the front side are received and flowed out little by little to the inner side of the port b. Therefore, the amount of overtopping waves and, by extension, the transmitted waves within the port can be reduced. In addition, particularly in the case of long-period waves, the run-up of waves on the gentle slope 5 becomes high, and the drainage chamber 9 formed by the slit 10
Since the amount of water that overflows to the port increases, the amount of water that returns to the outside of the port a decreases. therefore helps reduce reflections,
Moreover, the fact that there is little return flow is the root hardening block 14.
This will also contribute to improving the stability of the system. Furthermore, since the drain chamber 9 is provided on the inner side of the port b, the center of gravity of the embankment is shifted to the outer side a of the port. This prevents large pressure from being applied between the inner end toe of the caisson and the rubble mound 15, and has the effect of improving the stability of the mound 15. These are also supported by the following explanation. It will be done.

FIG. 5 is a schematic diagram of wave force acting on the wave-dissipating structure of the present invention. The main acting forces when a wave crest hits are the horizontal wave force F ₁ acting on the front upright wall, the wave force F ₂ acting on the gentle slope 5, the wave force F ₃ acting on the front wave return 12, and the wave acting on the rear wave return 13. Force F ₄ , wave forces F ₅ , F ₆ acting on the top and bottom surfaces of the eaves 7, uplift force acting on the bottom bottom surface
It is F _U. Since pressure has the characteristic of acting at right angles to the surface of the member, with respect to the force _F2 acting on the gentle slope 5, only its horizontal component _F2H contributes to sliding, and the downward vertical component _F2V has the same effect as an increase in weight. Moreover, since this component is large, stability in sliding can be ensured even if the embankment is made considerably smaller.

Furthermore, the maximum values of the horizontal wave force F ₁ acting on the front upright wall and the uplift force F _U acting on the bottom surface are thought to act almost simultaneously as in a normal caisson, but other wave force components, especially on the gentle slope 5, are considered to act almost simultaneously. Wave force F ₂ , wave return 12,
As for the wave forces F ₃ and F ₄ acting on wave forces F 3 and F 4 , their respective maximum values occur little by little later than the time when the maximum value of F _U occurs. Therefore, unlike a normal caisson, the total horizontal force in the direction of the port and the total upward vertical force do not act almost simultaneously and increase the overturning moment, and the stability against overturning is extremely high.In turn, this also reduces toe pressure. be effective. Furthermore, the structure of the present invention does not have an upper plate unlike the water retarding chamber 4 of the conventional wave-dissipating caisson illustrated in FIG. Therefore, there is no impact force due to bounce after colliding with the gentle slope 5, which is advantageous from a structural point of view.

As described above, the present invention eliminates the drawbacks of the conventional upright wave-dissipating caisson, and provides effective wave-dissipating function and stability even against long-period waves with a smaller cross-section of the dam body than the conventional one. It is possible to provide a wave-dissipating caisson that allows for economical design while ensuring safety. Furthermore, in addition to the inherent wave-dissipating function of the structure of the present invention, breaking waves and vortices are significantly generated due to the ridges, eaves, etc. as described above. This increases the aeration effect, resulting in a secondary effect that contributes to water quality purification.

Next, the results of experimentally determining the wave-dissipating effect of the present invention using a hydraulic model with a scale of 1/50 will be explained. Figures 6a and b show the wave-dissipating effects of the caisson according to the present invention and a conventional wave-dissipating caisson, using the regular wave reflectance K _R obtained by the input reflection separation method as an index to express the waveforms. Gradient H/L and relative water depth h/L (H: incident wave height at the center position of the structure,
L: incident wave wavelength at the center position of the structure; h: installation water depth at the center position of the structure). The experimental conditions are as follows.

In other words, the wave height range is 0.95, which is the wave condition (local equivalent) from normal times to less severe barge times.
~3.60m, with a period of 8~ predominant in the coastal areas of Japan
13 seconds, and the water depth of the structure at high tide level.
This is the result assuming 21.5m and 20.0m at the thousand tide level.

From this result, most of the reflectance K _R of the caisson of the present invention is indicated by the "○" mark in the figure.
It is found that the average value is within the range of 0.2 to 0.5 and is smaller than that of the conventional wave-dissipating caissons indicated by the "x" mark in the figure. Further, in the region where the waveform gradient H/L is small (FIG. 6a) or the relative water depth is small (FIG. 6b), the reflectance K _R becomes considerably large in the case of the conventional wave-dissipating caisson. However, it is recognized that the present invention is not so significantly affected by waveform gradient and relative water depth, and has a better wave-dissipating effect than the conventional method, especially in a region where these parameters are small, that is, for long-period waves.

FIG. 7 shows the results of determining the wave force characteristics of the caisson of the present invention under high wave conditions of the design wave class using the same hydraulic model as in the wave-dissipating effect experiment. In general, in conventional covered levee caissons and wave-dissipating caissons, the horizontal resultant force is applied to the levee body.
F _H (positive direction in the port) and vertical resultant force F _V (positive upward direction)
The maximum positive value of , which acts at approximately the same time, is shown by the broken line in FIG. 7 in the case of the caisson of the present invention
The phase difference between F _H and F _V shown by the dashed line is quite large. Therefore, even if the same horizontal resultant force F _H and vertical resultant force V _H act as in the conventional one, the moment M ₀ around the toe point on the inner side of the port (port side (positive direction of fall) is smaller than that of the conventional one, as shown by the solid line in the figure. Therefore, stability against sliding and overturning is high, and the cross-sectional area and weight of the embankment body itself can be reduced accordingly. Therefore, according to the present invention, it is possible to design an economical breakwater having excellent breakwater functions.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing a conventional wave-dissipating structure using a wave-dissipating block, Fig. 2 is a sectional view showing a conventional structure in which the caisson itself has a wave-dissipating function, and Fig. 3 is an embodiment of the present invention. Bird's-eye view, Figures 4a and 4b are schematic diagrams showing the wave dissipation mechanism of the present invention, Figure 5 is a schematic diagram of the wave force acting on the structure of the present invention, and Figures 6 and 7 are the diagrams of the present invention and the conventional type. FIG. 2 is a diagram showing the results of a comparative experiment regarding the reflectance of a caisson, and a temporal change characteristic diagram regarding the wave force acting on the caisson of the present invention and the moment around the toe point. 1...Caisson body, 2...Wave dissipation block, a
...Outside the port, b...Inside the port, 3...Porous wall or slit wall, 4...Water retarding space, 5...Gentle slope, 6...
Projection, 7...Eave, 8...Top opening, 9...Drainage chamber, 10...Short slit, 11...Drain hole, 1
2, 13... Wave return, 14... Root hardening block,
15...Rubble mound, A...Wave, B...Vortex,
F _U ... Uplift force acting on the bottom surface of the bottom plate, F ₁ ... Wave force acting on the front upright wall, F ₂ ... Wave force acting on the gentle slope, F _2H ...
...Horizontal component of F ₂ , F _2V ...Vertical component of F ₂ , F ₃ , F ₄
...Wave force acting on the front and back waves, F ₅ , F ₆ ...
... Wave force acting on the upper and lower surfaces of the eaves, F _H ... Total horizontal load, F _V ... Total vertical load, M ₀ ... Moment around the toe point on the inner side of the port.

Claims (1)

[Claims] 1. A gentle slope at the front upper part of the outer side of the port that has multiple ridges on its surface that intersect with the direction of wave attack, and an eaves section provided by extending the gentle slope at the front end of this gentle slope outside the port;
A front wave return with a slit in the lower surface protruding from the top of the gentle slope, a rear wave return with a slightly higher top and a distance from the front wave return on the inside of the port, and the front side A wave-dissipating type caisson for a breakwater, characterized in that it is equipped with a drainage chamber having a drainage hole provided on the inner side wall of the port using a compartment between the rear wave return.