JP2013032681A - Rotatable parapet and tsunami disaster preventing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotatable parapet for normally developing wave and tide preventing functions and for reducing the fluid and wave power of tsunami when the tsunami greater than expected come, and a tsunami disaster preventing structure equipped therewith.SOLUTION: A rotatable parapet 10 is installed on a superstructure 22 of a breakwater or a tide wall. It includes an upright wall 11 provided upright on the land side of the superstructure, and a hinge part 13 provided on the superstructure for enabling the turn of the upright wall. The upright wall normally stands upright on the superstructure, and it is turned to the land side with the hinge part as a supporting point when the fluid and wave power of tsunami operate.

Description

  The present invention relates to a rotating parapet installed on a breakwater, a seawall, or the like, and a tsunami disaster prevention structure including the same.

  Coastal structures that reduce tsunami disasters include breakwaters, revetments, seawalls, etc., which build tsunami barriers. In general, it is considered that the higher the barrier, the more effective. When constructing a tsunami breakwater, a hybrid embankment consisting of a caisson body and a foundation mound is often used. The foundation mound is made up of abandoned foundation stones, root hardening and covering blocks. A parapet may be added when installing the superstructure to the caisson body. Patent Document 1 can be cited as a technique for retracting and setting the parapet. Patent Document 2 is cited as a related technique for rotating the barrier.

Japanese Patent Laid-Open No. 2001-207423 Japanese Unexamined Patent Publication No. 2009-57799

  A high barrier increases the action wave force. For this reason, when a tsunami exceeding the design strikes, a structure with a high barrier increases the risk of sliding or falling on the breakwater. On the other hand, the barrier on the hybrid bank is low, and after the tsunami overflows the structure, the mound foundation on the land side may be scoured. When the mound is scoured, the breakwater body works easily to slide and fall.

  Since the tsunami attacks not only one wave but also many other waves, the structure may be destroyed by subsequent waves such as the second and third waves. Countermeasures against excessive design tsunamis are not realistic because they require huge construction costs and construction periods. In addition, a breakwater that has been slid or overturned due to a tsunami exceeding its design requires a lot of cost and time to recover.

  In view of the problems of the prior art as described above, the present invention normally exhibits a wave-proof and tide-proof function, and when a tsunami more than expected hits, it can reduce the fluid force and wave force caused by the tsunami. An object is to provide a parapet and a tsunami disaster prevention structure equipped with the same.

  In order to achieve the above object, the rotary parapet according to the present embodiment is a parapet installed on the superstructure of a breakwater or a tide embankment, provided upright on the land side of the superstructure, A hinge portion provided on the superstructure and capable of rotating the upright wall, and the upright wall normally stands upright on the superstructure, and when hydrodynamic force / wave force due to a tsunami is applied, It turns to the land side using a hinge part as a fulcrum.

  According to this rotating parapet, when an unforeseen tsunami strikes, the fluid force / wave force acts on the upright wall, and the upright wall rotates to the land side with the hinge as a fulcrum. The transmission force to the superstructure by the fluid force / wave force can be reduced. Thereby, destruction of a breakwater or a tide bank can be prevented beforehand. In addition, during normal times, the upright wall functions as a wave and tide.

  The rotating parapet includes a support plate that supports the upright wall at a lower portion of the upright wall and protrudes to the land side from the upper work, and the support plate rotates together with the upright wall with the hinge portion as a fulcrum. It is preferable that the upright wall is kept substantially horizontal by abutting against the land side rear surface of the superstructure when moved.

  By configuring the rotating parapet in this way, the upright wall of the parapet rotates and projects horizontally to the land side only when an excessive design external force is applied due to a tsunami that exceeds the expected level. Scouring the foundation mound behind the breakwater can be effectively prevented.

  Moreover, it is preferable that the upright wall has a counterweight portion, and the resistance moment of the upright wall is adjusted by adjusting the weight of the counterweight portion.

  As described above, the resistance moment can be adjusted by the counterweight portion provided at the base portion or the like of the upright wall, and a structure in which the upright wall rotates only when the design excess external force acts can be realized.

  The tsunami disaster prevention structure according to the present embodiment is characterized in that the above-described rotating parapet is installed in a superstructure of a breakwater or a tide wall.

  According to this tsunami disaster prevention structure, when the surplus tsunami hits, the upright wall of the parapet installed on the land side of the superstructure rotates under the condition where seawater overflows the breakwater or tide embankment, A structure that reduces the tsunami fluid force and the subsequent tsunami force can be realized.

  According to the present invention, a rotating parapet capable of reducing the hydrodynamic force and wave force caused by a tsunami and a tsunami disaster prevention provided with the same, which normally exhibit a wave-proof and tide-proof function and when a tsunami more than expected hits. A structure can be provided.

It is the perspective view (a) and front view (b) which show the rotary parapet by this embodiment. It is a schematic sectional side view of the structure of the breakwater by this embodiment, (a) shows the time of normal time, (b) shows the time of tsunami attack, respectively. FIGS. 2A and 2B are side sectional views similar to FIG. 2, in which FIG. 2A shows the tsunami wave force before rotation of the rotary parapet, and FIG. 2B shows the tsunami wave force after rotation of the rotary parapet. It is a figure for demonstrating roughly the scouring which arises in the foundation mound in the conventional breakwater. It is a figure for demonstrating roughly the scour prevention of the foundation mound by the breakwater of this embodiment. It is a figure for demonstrating the rotational moment and resistance moment which act on the rotation-type parapet of FIG. It is a figure which shows the wave pressure distribution example of the design tsunami (level 1) in this calculation example. It is a figure which shows the wave pressure distribution example of the tsunami (level 2) more than the assumption in this calculation example.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a perspective view (a) and a front view (b) showing a rotary parapet according to the present embodiment.

  As shown in FIGS. 1 (a) and 1 (b), the rotary parapet 10 has an upright wall 11 standing upright at an end on the land side in an upper work 22 such as a breakwater, and supports the upright wall 11 and extends in the horizontal direction. A support plate 12 and a hinge portion 13 provided at an end portion of the upper work 22 are provided. The upright wall 11 is configured to be rotatable together with the support plate 12 with the hinge portion 13 as a fulcrum.

  The upright wall 11 is connected to the support plate 12 at the lower portion of the upright wall 11, and the support plate 12 protrudes in the horizontal direction from the end of the upper work 22 to the land side. The upright wall 11 and the support plate 12 are reinforced by reinforcing ribs 14a and 14b at both left and right ends, and are L-shaped when viewed from the side.

  The hinge portion 13 is constituted by a double tube structure of an inner tube 13a and an outer tube 13b. The outer tube 13b is fixed to a corner portion 22b of the upper work 22, and the inner tube is fixed in the outer pipe 13b fixed to the upper work 22. 13a is rotatable. As shown in FIG. 1B, a pad portion 12a is attached to the lower surface of the support plate 12, and the pad portion 12a is fixed to the inner tube 13a through an opening 13d formed in the outer tube 13b.

  As described above, the hinge portion 13 is integrated with the superstructure 22, and the support plate 12 can be rotated together with the inner tube 13a within the circumferential range of the opening portion 13d. Therefore, the upright wall 11 is also rotatable with respect to the outer tube 13 b of the hinge portion 13.

  The upright wall 11 has a counterweight portion 11a at the lower base, and the resistance force against the tsunami fluid force and wave force can be adjusted by adjusting the weight thereof. The counterweight part 11a can be comprised by adjusting the thickness of a steel plate thickly, for example.

  In addition, the upright wall 11 and the support plate 12 can be comprised from a steel plate, and the inner tube 13a and the outer tube 13b can be comprised from a steel pipe. Further, as shown in FIG. 1B, a differential bar SK is arranged in the concrete in the vicinity of the portion where the hinge portion 13 of the superstructure 22 is provided.

  As described above, the rotary parapet 10 according to the present embodiment has a structure in which the parapet is retracted and installed on the breakwater superstructure 22, and has an L-shaped upright wall 11 and a support plate 12. The connecting portion between the upright wall 11 and the support plate 12 has a hinge structure.

  Next, a breakwater including the rotating parapet 10 of FIG. 1 will be described with reference to FIGS. 2 and 3. 2A and 2B are schematic side sectional views of the structure of the breakwater according to the present embodiment. FIG. 2A shows a normal time and FIG. 2B shows a tsunami attack time. FIG. 3 is a side sectional view similar to FIG. 2, where (a) shows the tsunami wave force before rotation of the rotary parapet, and (b) shows the tsunami wave force after rotation of the rotary parapet. .

  As shown in FIG. 2 (a), the breakwater 20 is installed in a harbor, and a main body 21 made of gravity caisson constructed on a foundation mound M made of foundation rubble ST on the bottom ground G, An upper work 22 provided in the upper part and a rotary parapet 10 of FIG. 1 installed at the rear end inside the harbor on the upper work 22 are configured.

  In addition, in order to prevent scouring, a rooting work NG is disposed around the main body 21 on the foundation mound M, and the foundation mound M is covered with a covering work HF.

  As shown in FIG. 2A, from the normal wave to the normal wave in normal times, the main work 21, the upper work 22, and the rotary parapet 10 of the breakwater 20 are integrated into the wave NA from the outside of the harbor. Prevent entry into.

  On the other hand, when an unexpected tsunami TU exceeding the design as shown in FIG. 3 (a) gets over the superstructure 22 of the breakwater 20, and when an excessive tsunami wave force or fluid force acts on the upright wall 11 of the parapet 10, As shown in FIG. 2B, the upright wall 11 rotates in the rotation direction R with the hinge portion 13 as a fulcrum. At this time, the support plate 12 rotates together with the upright wall 11, hits the back surface 22 a inside the port of the upper work 22, and stops rotating, and the upright wall 11 protrudes inward in the port in the horizontal direction.

  As described above, the parapet 10 after the rotation, as shown in FIGS. 2 (b) and 3 (b), the upright wall 11 rotates and the protruding portion above the upper work 22 disappears, and the tsunami wave Since the force acts only on the main work 21 and the upper work 22 and not on the parapet 10, the force transmitted to the upper work 22 by the tsunami wave force is reduced.

  Next, the effect after the upright wall 11 is rotated as shown in FIGS. 2B and 3B will be described with reference to FIGS. FIG. 4 is a diagram for schematically explaining scouring that occurs in the foundation mound of a conventional breakwater. FIG. 5 is a diagram for schematically explaining scouring prevention of the foundation mound by the breakwater of the present embodiment.

  As shown in Fig. 4, when a tsunami TU hits a conventional breakwater and overflows the superstructure, the wave action causes the caulking work NG and covering work around the lower part of the main work on the foundation mound M inside the port. There was a risk that scouring of the foundation mound M would occur due to HF and rubble ST being washed away. On the other hand, as shown in FIG. 5, the rotating parapet 10 is actuated by the tsunami TU, and the upright wall 11 rotates and projects to the inner side of the port in the horizontal direction. Even if it overflows, the action of the waves does not easily reach the lower part of the main body 21, and the foundation mound M is hardly scoured without the root hardening NG, the covering HF, and the rubble ST not flowing.

  As described above, according to the breakwater 20 provided with the rotating parapet 10 according to the present embodiment, the upright wall 11 is rotated due to an unexpected tsunami attack, so that the superstructure 22 of the fluid force / wave force caused by the tsunami can be obtained. In addition to reducing the transmission force, the upright wall 11 projects horizontally to the inside of the port, thereby preventing the scouring of the foundation mound M caused by the tsunami that overflowed the breakwater. 21 can be prevented from sliding or falling.

  Even if an unexpected tsunami hits the breakwater according to the present embodiment, the transmission force of the fluid force / wave force to the superstructure 22 due to the tsunami can be reduced, so that the main work 21 does not slide or roll. Since the breakwater 20 is not destroyed, its minimum function can be maintained. In addition, the foundation mound scouring prevention effect as described above can effectively prevent the main work 21 from sliding and rolling, and can prevent the breakwater 20 from being destroyed.

  According to the breakwater structure of the present embodiment, a rotating parapet can be integrated with a newly constructed breakwater when the superstructure is manufactured. On the other hand, for the existing breakwater, it is possible to construct a rotating parapet after removing a part of the superstructure.

  In addition, the conventional retracting parapet does not have a function of rotating and rotating, and the rotating barrier is not used on the breakwater. In addition, no structure has been proposed so far that has the function of adjusting the resistance moment by the counterweight and the effect of reducing the wave force only when the design excess external force acts and preventing the foundation mound scouring.

  In addition, the parapet which rotated after the design excess tsunami acts can restore the upright wall to the original state by attaching a winch or the like on the crane ship or the upper work.

  Next, adjustment of the resistance moment with respect to the tsunami wave force by the rotary parapet 10 of the present embodiment will be described with reference to FIG. FIG. 6 is a view for explaining a rotational moment and a resistance moment acting on the rotary parapet of FIG.

  As shown in FIG. 6, the tsunami that rotates the upright wall 11 of the parapet by adjusting the weight of the counterweight portion 11 a provided on the upright wall 11 and the arm lengths L 1 and L 2 that are distances from the fulcrum of the hinge portion 13. Limit wave power can be determined. That is, the product of the weight W1 of the upright wall 11 and the counterweight portion 11a and the arm length L1 functions as the resistance moment M1 with respect to the rotational moment M2 due to the tsunami wave force P and the weight W2 of the support plate 12. The resistance moment M1 and the rotation moment M2 can be obtained by the following equations.

M1 = L1 × W1 (1)
M2 = L2 × W2 + h × P (2)
However,
L1: Arm length W1 from the fulcrum of the hinge portion 13 to the upright wall 11: Weight W1 of the upright wall 11 (including the counterweight portion 11a)
L2: Arm length from the fulcrum of the hinge portion 13 to the center of gravity of the support plate 12 W2: Weight of the support plate 12 h: Average action height P due to tsunami wave force P (having wave pressure distribution in the height direction) P: Tsunami Wave power

  If the resistance moment M1 is greater than the rotation moment M2 (M1> M2), the upright wall 11 does not rotate with respect to the tsunami wave force P, but the rotation moment M2 is greater than the resistance moment M1 (or both are equal). And (M2 ≧ M1), the rotation starts. Therefore, if the tsunami wave force P, the working height h, and the support plate weight W2 are constant, the resistance moment M1 can be adjusted by adjusting the weight of the counterweight portion 11a and the arm lengths L1 and L2, and the upright The tsunami limit wave force that the wall 11 rotates can be determined. In particular, if the arm lengths L1 and L2 are also constant, the arm lengths L1 and L2 are adjusted according to the weight of the counterweight portion 11a.

(Calculation example)
As a structural design example for the breakwater in this embodiment, the sliding safety factor and the fall safety factor for the following specifications were calculated. Each safety factor is 1.2 or more for the design tsunami (level 1), and each safety factor is 1.0 or more for the tsunami (level 2) that is higher than expected. Design tsunami (level 1) is assumed to be tsunami height 3.0m, tsunami (level 2) is assumed to be tsunami height 4.0m. The caisson and parapet specifications are shown in Tables 1 and 2, respectively. FIG. 7 shows a wave pressure distribution example of the design tsunami (level 1) in this calculation example. FIG. 8 shows an example of the wave pressure distribution of a tsunami (level 2) that is higher than expected in this calculation example. Table 3 shows the calculation results of this calculation example.

  As shown in Table 3 and FIG. 7, in this calculation example, the parapet does not rotate for the design tsunami (level 1) because the resistance moment of the parapet is larger than the rotational moment of the tsunami wave force. The sliding safety factor and the falling safety factor are both 1.2 or more, and the breakwater is stable.

  Further, as shown in Table 3 and FIG. 8, for a tsunami more than expected (level 2), the parapet rotates because the resistance moment of the parapet is smaller than the rotational moment of the tsunami wave force. If the parapet does not rotate like a normal breakwater, both the sliding safety factor and the falling safety factor will be less than 1.0 for the tsunami (level 2) higher than expected. On the other hand, in the example in which the parapet rotates, the breakwater is stable because the sliding safety factor and the falling safety factor both exceed 1.0.

  As described above, the modes for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, in the present embodiment, the rotary parapet is installed on the breakwater to form a tsunami disaster prevention structure, but the present invention is not limited to this, and may be installed on a tide bank or a revetment.

  In this embodiment, when the upright wall 11 of the parapet 10 rotates together with the support plate 12, the upright wall 11 protrudes inward in the harbor in the horizontal direction. If the effect of preventing scouring is obtained, it may be inclined to some extent up and down.

  In addition, the structure in which the upright wall rotates is constituted by a double-pipe hinge structure. However, the present invention is not limited to this, and other rotating structures may be used.

  The weight of the counterweight portion 11a can be adjusted by adjusting the thickness of the steel plate. However, the present invention is not limited to this, and other means may be used. For example, the counterweight portion 11a is heavy. You may make it comprise a steel plate etc. (weight) so that attachment or detachment is possible.

DESCRIPTION OF SYMBOLS 10 Rotating parapet 11 Upright wall 11a Counterweight part 12 Supporting plate 13 Hinge part 20 Breakwater 21 Main body work 22 Superstructure G Submarine ground M Foundation mound TU Tsunami

Claims (4)

A parapet installed on the superstructure of a breakwater or a tide embankment,
An upright wall provided upright on the land side of the superstructure,
A hinge portion provided in the upper work and capable of rotating the upright wall;
The rotating parapet is characterized in that the upright wall normally stands upright on the superstructure, and rotates to the land side with the hinge portion as a fulcrum when hydrodynamic force or wave force is applied by a tsunami. A support plate that supports the upright wall at the bottom of the upright wall and protrudes to the land side from the upper work;
The said support plate keeps the said upright wall substantially horizontal by contact | abutting to the land side back surface of the said superstructure when it rotates with the said upright wall with the said hinge part as a fulcrum. The described rotating parapet. The upright wall has a counterweight portion;
The rotary parapet according to claim 1 or 2, wherein a resistance moment of the upright wall is adjusted by adjusting a weight of the counterweight portion.   A tsunami disaster prevention structure characterized in that the rotary parapet according to any one of claims 1 to 3 is installed in a superstructure of a breakwater or a tide wall.