JPH0472922B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a foot protection mound for protecting a caisson of a breakwater, and more particularly to a submerged mound of a high-water deep breakwater.

[Conventional technology]

Traditionally, concrete breakwaters have been built in areas of the coast and shallow seas that are subject to severe erosion by waves.
The tip of the base of the breakwater is eroded by strong frame waves at low water depths and by overlapping waves at high water depths.
This problem is gradually spreading, and accidents leading to the destruction of breakwaters are occurring frequently. Therefore, the mound for foot protection is built long and strong in front of the breakwater body so as not to damage the breakwater itself. Despite such careful construction, most of the breakwater failures were caused by scour at the base of the tip of the breakwater mound.

According to conventional experiments and experience, it has been found that in areas with high water depth, especially in mounds with a depth of 15 m or more, the area at 1/4 wavelength of the maximum wavelength is the area where the most severe scour occurs. In other words, first, the earth and sand near the 1/4 wavelength point are excavated, and this spreads to the surrounding area, and after progressing to a certain extent, a large amount of earth and sand under the mound is suddenly sucked out, and as a result, the stones at the tip of the mound sink, and the stones Some of the structures above, such as wave-dissipating structures and covering blocks, will sink, while others will be scattered. If this phenomenon progresses further, there is a risk of damaging the breakwater body.

This type of mound scouring phenomenon frequently occurs in areas with high water depths of 15 m or deeper, but recently it has become more common in areas with water depths of 20 m to 30 m.
A breakwater with a depth of more than m has been constructed.

Therefore, a strong breakwater is achieved by building a long strong mound in front of the breakwater. In order to do this, it is necessary to construct a mound as long as possible facing the ocean side in accordance with the natural shape of the ground, to fill it with earth to reduce the slope of the mound itself as much as possible, or to build the breakwater itself from deep under the ground. There are methods such as building.

[Problem to be solved by the invention]

However, both methods acknowledge the erosive effects of foot protection and are designed to extend the life of the embankment even if it is eroded, and they also use large amounts of concrete, stone, iron, etc. , construction costs were high.

Therefore, there was a need for a method of constructing breakwaters that would elucidate as much as possible the mechanism of scouring, reduce the amount of stone and concrete used, and prevent scouring at certain points to maintain an equilibrium state.

[Means for Solving the Problem] and [Operation] The present invention was completed by researching the properties of overlapping waves in order to solve the above problem, and its configuration consists of a It is a mound, L/4 x 4/5 from the base of the breakwater.
A submerged frame is installed on the breakwater side from the point (L is the maximum wavelength of waves hitting the shore), and the space between the submerged frame and the breakwater is covered with a concrete structure.

The maximum wavelength here is the wavelength of the maximum wave statistically obtained by continuous observation at each port.
This serves as the basis for strength calculations when constructing breakwaters in the vicinity. The maximum wave is a virtual wave that has a wave height, period, and wavelength equal to the wave height, period, and wavelength of 1/10 of the waves selected from the waves with the highest wave height at a certain point. . In reality, on the San'in Coast, the maximum wave height is 5.0 m and the period is
The maximum wave height on the Ou-Hokuriku coast is 7.0 m, the period is less than 14 seconds, and the wavelength is 306 m.

The sinking frame according to the present invention is a wooden frame in which stones are placed and has been used since ancient times for flood control in rivers and the like. However, concrete blocks came to be used exclusively because of their complicated structure, which required manpower to manufacture, the lack of wood, and their unsuitability for large-scale construction. The present invention uses this sinking frame, and although it may be made of wood like the conventional one, it is preferable to use concrete and assemble it after all the members are cast into a flat plate.

In addition, the tip of the sinking frame should be placed at the part where the sinking frame is installed.
If the maximum wavelength is L, it should stay within L/4 x 4/5, preferably within L/4 x 3/4, more preferably within L/4 x 2/3 from the breakwater.
Only the upper part of the sinking frame is exposed, and crushed stone, natural stone, irregularly shaped blocks having a large number of protrusions, etc. are laid at the tip of the sinking frame, and crushed stones and irregularly shaped blocks are particularly preferred.

There are no particular limitations on the concrete structure that covers the space between the sinking frame and the base of the breakwater, but as has been done in the past, a particularly heavy concrete structure is preferable for the area adjacent to the breakwater. It is also possible to arrange the blocks or to use one having protrusions on the top. In short, it is sufficient to lay concrete blocks that have a weight that will not be blown away by the water pressure applied upward from the bottom surface of the mound by waves.

In the present invention, the main structure refers to the concrete mound covering including the sink frame.

The breakwater of the present invention is suitable for high water depth and upright type, but it can also be used for breakwaters with sloping slopes and shallow breakwaters.

[Effect]

Assuming that the maximum wavelength of the present invention is L, the submerged frame is sunk at a point closer to the caisson than L/4 x 4/5 from the base of the caisson toward the ocean, as shown in the results of conventional experiments. Scouring is 1/ of the maximum wavelength
The work progresses from 4 points, and the area between the 1/4 point and the sinking frame is relatively deeply scoured. However, the stones in front of the sinking frame are scattered by the returning waves and become integrated with the ground soil, forming a ground that is not scoured by the returning waves.
Furthermore, due to the weight of the entire sinking frame, the water permeability of the crushed stones filled in this sinking frame, and the structure that prevents them from moving relative to each other, the phenomenon of integration of stones with the ground soil remains at the top of the sinking frame, and this state The scouring stops at this point, and an equilibrium state is achieved in which not only the base of the sinking frame but also the sinking frame itself does not move at all.

〔Example〕

FIG. 1 is a sectional view when the present invention is implemented using an experimental apparatus with a scale of 1/50. In the drawing, the part indicated by the broken line is the 1/4 point of the maximum wavelength, and since the experimental equipment only sent the maximum wave of about 216 cm, the 1/4 point was about 54 cm. 1 is a caisson, 2 is a water surface, and 3 is crushed stone. A large weight block 4 was installed in front of the caisson base. In this embodiment, a concrete block having a horizontal protrusion on the upper surface is used, but any heavy concrete block may be used, such as a rectangular one or one having an upward protrusion. 5 is a long block, which is used in combination with side pieces extending alternately from both sides. Reference numeral 6 denotes a hole for releasing water pressure, which was provided in the center of the main body, and the diameter of the hole was larger on the bottom surface than on the top surface, in order to discharge the pressure water that had entered into the crushed stone 3. The drawing shows a cross section of the center of the hole. Reference numeral 7 denotes a shoe provided on the lower surface of the side piece, which stabilizes the long block 5 embedded in the crushed stone 4. Although the long block 5 has a slope of 1:2, it is also possible to make the slope even steeper to about 1:1.5. Reference numeral 8 denotes a root stop block for preventing the long block 5 from sliding down. A sediment 9 was buried adjacent to this root stop block 8. In this example, the sinking frame 9 was a square type with horizontal bars on the bottom and sides, and the inside was filled with crushed stone. The tip of this sinking frame 9 was 31 cm from the breakwater. A frame stone was further laid in front of the sinking frame 9, and the area in front of the 1/4 point of the maximum wavelength was left as it was. That is, in FIG. 1, the part indicated by the two-dot chain line is the initial ground.

When artificial waves with a wavelength of 216 cm were sent continuously for about 10 hours, scouring started at the 1/4 point (the broken line in Figure 1), and then deep scouring occurred between the 1/4 point and sink frame 9. It was done. However, according to the present invention, due to the effect of the sinking frame, the scoured soil, crushed stones scattered by returning waves, and ground soil were integrated further forward of the 1/4 point, forming an integrated ground 10. Therefore, due to this integrated ground 10, the returning waves also lost their scour power, and the topography as shown by the solid line in Figure 1 reached equilibrium, and the sinking frame remained stable forever.

On the other hand, it was the same as the previous example except that the same experimental equipment was used, no sinking frame was used, any covered area was sloped more gently than 1:3, and up to 1/4 of the maximum wavelength was covered with various concrete blocks. When an experiment was conducted using this method, it was found that the area where the integrated ground was formed was endlessly eroded, crushed stone was scoured, and concrete blocks were scattered.

〔effect〕

According to the present invention, the scouring of the breakwater mound is stopped to the extent that no damage is caused and does not proceed any further, so the durability of the breakwater is improved, repair is easy, and the foundation for protecting the base of the breakwater is improved. It is also economically advantageous because the amount of materials such as cement and iron used in the compaction structure can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view showing one embodiment of the present invention. In the drawing, the symbols 1 are caton, 2 is water surface, 3 is crushed stone, 4 is weight block, 5 is long block, 6
is a hole, 7 is a shoe, 8 is a root block, 9 is a sinking frame,
10 is an integrated ground.

Claims (1)

[Claims] 1. A mound built to protect the base of the main caisson of the breakwater, which is located L/4 from the base of the breakwater.
A submersible frame was placed on the breakwater side from the point x4/5 (L is the maximum wavelength of waves hitting the coast), and the space between the submersible frame and the breakwater was covered with a concrete structure. A characteristic mound for high water and deep breakwaters.