JP4869037B2 - Caisson wave-dissipating structure - Google Patents

Description

  The present invention relates to a caisson wave-dissipating structure as a revetment body installed between a sea side and a land side. Specifically, a wave breaker is arranged on the offshore side of the caisson, and a cut-off dam with a seawater storage part is placed on the land side, and by making this cut-off dam an inclined dam, The present invention relates to a caisson wave-absorbing structure that can effectively suppress overtopping.

  As a revetment body installed between the sea side and the land side, generally a dike body mainly composed of caisson is known (for example, Patent Documents 1 and 2).

  In the caisson wave-dissipating structure disclosed in Patent Document 1, the caisson's top end is made higher than the water surface, and the caisson has a receding parapet, and the caisson's offshore side covers the caisson's top end. A wave-dissipating block of a wave-dissipating work is arranged.

  The caisson wave-dissipating structure disclosed in Patent Document 2 has a structure in which an offshore parapet and a land-side parapet are provided on the top end side of the caisson, and a wave-dissipating work is disposed on the offshore side of the caisson. . A reservoir is formed between the offshore and landside parapets.

Japanese Patent No. 3592116 JP 2000-204529 A

  By the way, in the caisson wave-dissipating structure disclosed in Patent Document 1, the top of the caisson can be designed to be low, but the wave-dissipating wave-dissipating block must be disposed from the offshore side of the caisson including the top of the caisson. Therefore, the number of wave-dissipating blocks is considerably increased, and the work of disposing the wave-dissipating blocks is troublesome.

  In addition, in the caisson wave-dissipating structure disclosed in Patent Document 2, wave waves are driven into a basin formed between an offshore parapet and a landside parapet so that the wave overtopping the landside parapet. The aim is to reduce the waves.

  However, in this structure, in order to reduce overtopping to the land side, the width of the reservoir (the width from the coast to the land side) must be relatively wide, and a large caisson must be laid. In order to solve this, if the width of the reservoir is narrowed, the effect of reducing overtopping will be diminished unless the top height of the land side parapet is increased. Increasing the top height of land-side parapets requires that the strength against waves be taken into account, leading to increased construction costs.

  Accordingly, the present invention solves such a conventional problem, and proposes a caisson wave-dissipating structure that can reduce the construction cost, particularly at a low ceiling, and can obtain an overtopping reduction effect.

In order to solve the above-mentioned problem, a caisson wave-dissipating structure according to the present invention as set forth in claim 1 is constructed by a cut-off bank whose offshore side is an inclined bank for wave-dissipation, and an offshore side that is connected to this. and caisson was, the offshore side of the caisson consists of a wave dissipating Engineering which is sinking, of the cofferdam, the offshore front slopes of Hoshiri the upper Symbol caisson was made lower than the top end of the caisson The sea slope reservoir for overtopping reduction is provided in between, and the slope of the above slope is 20% slope, and in the surface slope of the water mass overtopping the caisson and the seawater reservoir for overtopping reduction, It is characterized in that the energy of the overtopping water mass coming next is reduced by the return flow from the above slope .

  The main body of the caisson wave breaking structure according to the present invention is a cut-off bank formed as an inclined bank and a caisson set off the off-shore side of the cut-off bank. A wave-dissipating work (wave-dissipating block) is set off the caisson to reduce the wave power of the off-shore wave and to suppress the wave. A seawater reservoir is provided between the caisson and the surface slope of the cut-off bank. The seawater storage unit stores the water mass that has passed over the caisson, and attenuates the energy of the overtopping water mass by the return flow of the stored water mass to the sea side.

  A part of the water mass that has passed over the seawater reservoir reaches the top of the cutoff bank along the surface of the cutoff bank, but by providing a seawater storage section from the caisson to the top of the cutoff bank The power of the next water mass that has overwhelmed is weakened due to the long water mass reaching distance and the collision with the water mass descending the surface. The overwhelming water mass is weakest when the slope of the surface slope is 20%. As a result, the amount of water mass (overtopping amount) that passes over the deadline is reduced, and at least the 10-year probability wave can be reliably suppressed below the allowable overtopping amount. Because the caisson is at the low end and its width can be reduced, construction costs can be reduced.

  In the present invention, a seawater storage section is provided between the cut-off bank and the caisson, and the caisson wave-dissipating structure having the cut-off bank as an inclined bank is used, so that even if a low-top end cut-off bank is used, This makes it possible to provide a seawall with excellent economic efficiency.

  Next, a preferred embodiment of the caisson wave absorbing structure according to the present invention will be described in detail with reference to the drawings.

  Example 1 is a case where the present invention is applied to a caisson wave-dissipating structure used for revetment in order to protect facilities such as a power plant laid near a coast from waves.

  As shown in FIG. 1, a caisson wave breaking structure 10 according to the present invention includes a cut-off bank 20 that is an inclined bank, a caisson 30 that is set on the offshore side so as to be connected thereto, and an offshore side of the caisson 30. It is comprised with the wave-dissipating work 40 laid in.

  The caisson 30 is directly laid on the sea floor, but if it can be set and fixed on a number of rubble mounds, a steel frame is attached to the bottom of the caisson 30 instead of the rubble mound. It is also possible to sink the gantry with the caisson 30 on the sea floor.

  The caisson 30 has a top edge width (width toward the land side) of about 13 m. P is the standard level and T.W. It is set higher by 2.0 m than P.

  A wave absorber 40 is laid on the offshore side of the caisson 30. This wave-dissipating work 40 is constructed by stacking known wave-dissipating blocks in consideration of the slope of the slope, and the top end thereof is substantially equal to the top end of the caisson 30.

  Although the slope of the wave-dissipating work 40 is arbitrary, in order to make the number of wave-dissipating blocks set as economical as possible, a slope of (1: 4/3) is preferable in this example. Moreover, wave breakage can be expected by using this slope. The top end 42 of the wave breaker 40 is substantially equal to the top end height of the top end 32 of the caisson 30, and the width thereof is wider than the top end width of the caisson 30. It is because it leads to the wave extinction to the following wave accompanying the collapse of the wave when the wave gets over the top of the wave extinguishing work 40.

  A deadline 20 is laid on the land side of the caisson 30. The cut-off dam 20 is mainly constructed by laminating rocks made of crushed rocks from near the seabed.

  The cut-off dam 20 is a levee body of sufficient length provided along the shoreline or the land side so that facilities, such as a power plant, can be protected. The cut-off bank 20 is an inclined type cut-off bank 20 as described above, and the cut-off bank 20 between the slope 23 of the surface slope 22 and the land side surface of the caisson 30 is seawater in which a predetermined water depth is secured. The storage unit 50 is used. Therefore, the slope 23 of the surface slope 22 is made lower than the top end of the caisson 30 by a predetermined length. In addition, the width of the seawater reservoir 50 (the length from the land side surface of the caisson 30 to the buttock 23) and the water depth of the seawater reservoir 50 are designed in consideration of the magnitude of the overwhelming wave and its flow rate. Has been.

  Reaching the water mass from the start end of the caisson 30 to the top end (the ridge crest) 60 of the cut-off dam 20 by providing the seawater reservoir 50 for overtopping reduction between the caisson 30 and the slope 23 of the surface slope 22 Since the distance can be increased, the energy of the overtopping water mass reaching the top end of the cut-off bank 20 is also attenuated, and the overtopping amount from the cut-off bank 20 can be reduced.

  This is because the head wave of the overwhelming wave collapses in the seawater storage unit 50 and needs to have a width that can suppress the wave force of the subsequent overtopping wave, and the water depth reaches beyond the caisson 30. This is because the amount can be temporarily secured.

  In this example, the water depth from the top end 32 of the caisson 30 is ensured to be (TP + 1.0) m with respect to the top end 32 of the caisson 30. And the width | variety of the seawater storage part 50 shall be about 25.0 m in this example. By setting it as the seawater storage part 50 with such a capacity | capacitance, the sufficient storage effect can be anticipated also in the wave of a 10-year probability wave so that it may mention later.

  In order to reinforce the bottom part (bottom face) of the seawater storage part 50, a tension concrete 52 is cast on the bottom part by a predetermined thickness. In this example, concrete is driven to a thickness of about 300 mm.

  The front slope 22 is designed to have an appropriate slope. As will be described later, this takes into account the wave overtopping effect, and the rock formation is laid so as to have a slope (20% slope) of (1: 2.0). Further, in order to increase the strength of the cut-off bank 20 against this slope, the concrete slope is covered with a concrete structure. In this example, in order to construct a concrete structure efficiently with respect to the surface slope 22, the filling concrete 24 is used. In other words, the bag formwork filled with concrete and quilted is laid on the entire surface surface 22 so that the thickness thereof is about 300 mm, so that the surface surface 22 is covered with the filling concrete 24. .

  The filling concrete 24 and the tension concrete 52 are laid so as to be flush with each other, and further, the portion of the hull 23 which is the boundary between the seawater storage portion 50 and the surface slope 22 is protected from waves. Therefore, a sheet-like filter unit (for example, a 4t type filter unit) 26 is laid.

  The top end (top) of the deadline 20 is covered by a three-sided winding (not shown) to protect it from overtopping water mass, and the top height is high considering the allowable overtopping flow rate with a 30-year probability wave. It has become. In other words, the deadline 20 is set at a crest height so that the overtopping amount (allowable overtopping amount) at the time of the 30-year probability wave invasion is less than or equal to the damage limit value of the deadline 20.

  The land side of the deadline 20 becomes the ground level of the facility through the back slope 62. The slope of the back slope 62 is also a slope that takes into account the ease of laying work, and in this example is a 20% slope of (1: 2.0).

  An example of the size of the above-described deadline 20 structure will be described next. The ceiling height of the cut-off bank 20 is (TP + 10.0) m with respect to the level surface, and the horizontal length of the surface slope 22 of the cut-off bank 20 is 17.0 m. The bank width of the top (top) 60 is 18 m. The bank width is related to the above-mentioned damage limit value, so it cannot be made too narrow, but in some cases, the bank width can be designed to be about 10 m.

  Now, in the caisson wave-absorbing structure 10 according to the present invention configured as described above, first, the relationship between the seawater reservoir 50 and the amount of overtopping will be described with reference to FIGS. 2 and 3.

  FIG. 2 shows the relationship between the wave absorber 40 and the caisson 30 and the water depth of the seawater reservoir 50. As shown in FIG. 2, when the water depth of the seawater reservoir 50 with respect to the top of the caisson 30 is based on the level surface (TP), the depth from the level surface (TP + α) is the water depth. It becomes. When α is 1.5 m, the top depth of the caisson 30 is (TP + 2.0) m, so the actual water depth is 0.5 m. Therefore, the smaller the α, the deeper the water depth.

  FIG. 3 shows the relationship between this water depth (m) in the seawater reservoir 50 and the overtopping amount (water amount per second per meter) from the deadline 20 at that time. As the amount of overtopping, we consider waves of 10-year probability waves and waves of 30-year probability waves.

  Here, 10-year stochastic waves and 30-year stochastic waves are a kind of numerical calculation program that replaces hydraulic model experiments on waves, and are specialized software for numerical analysis of wave fields related to Navier-Stokes wave-resistant design. Software was used for analysis. In fact, the planned high water level of the tide level W. This is a value when L (High Water Level) is (TP + 0.46) m. At this time, the offshore wave height of the 10-year probability wave is 7.3 m, and the offshore wave height of the 30-year probability wave is 8.9 m.

  Although it changes depending on how much the width of the seawater reservoir 50 is set, there is a wave breaker 40 off the caisson 30 as shown in FIG. 1, and the width of the seawater reservoir 50 is about twice that of the caisson 30 ( Actually, it is a predicted value (analyzed value) when it is set to about 25 m which is slightly less than twice.

  As the water depth of the seawater reservoir 50 increases, the overtopping amount does not decrease, but an appropriate water depth value exists as is apparent from FIG. In the case of a 30-year probability wave as shown by the curve La, the amount of overtopping tends to increase as the water depth increases. In the case of a 10-year probability wave, the water depth is about 1.0 m as shown by the curve Lb. However, the amount of overtopping is the smallest, and the amount of overtopping tends to increase as the water depth increases.

  Therefore, in the present invention, the depth of the seawater reservoir 50 is selected in the vicinity of (TP + 1.0) m from the top of the caisson 30.

  In order to reduce the overtopping amount, in addition to the width and depth of the seawater reservoir 50, the slope of the cut-off bank 20 and the top height are further related. FIG. 4 and FIG. 5 show the relationship between the slope of the surface slope 22 of the cut-off bank 20 and the amount of wave overtopping, and three slopes were selected as the slope as shown in FIG. The slope slope SLa of the front slope 22 is (1: 3.0), the slope slope SLb is (1: 2.0), and the slope slope SLc is (1: 1.5). is there.

  FIG. 5 shows the amount of overtopping when the slope slopes SLa, SLb, and SLc are obtained. Curve Lc is an analysis value of a 30-year probability wave, and when the slope is 20% (1: 2.0), the overtopping amount (m3 / m / sec) from the cut-off bank 20 is the smallest. It has been found. Further, in the case of a 10-year probability wave, as shown by the curve Ld, it can be seen that in this case also, the overtopping amount is small when the slope is 20% (1: 2.0).

  When such slope slope SLb = (1: 2.0), the amount of overtopping from the cut-off bank 20 decreases because part of the waves are captured by the seawater reservoir 50 and not captured. The water mass climbs the surface slope 22 and tries to exceed the cut-off bank 20, but the water mass that has not passed the cut-off bank 20 tries to return to the offshore side through the seawater storage unit 50 again. The return water mass (return flow) collides with the next wave water mass in the seawater reservoir 50 or the slope of the surface slope 22. As a result of the reduction (reduction) of the energy of waves approaching by this collision, it is considered that the water mass can effectively prevent the water mass from reaching the top 60 of the cut-off bank 20 and overtopping.

  If the slope is tight, the water mass returns too quickly, and if the slope is slow, the next wave of water reaches the surface slope 22 before the water mass begins to return. It is because it is thought that the diminishing effect on the water mass of water will fade.

  When the slope is set to 20% slope (1: 2.0), which is such an intermediate value, the slope construction is relatively easy and the slope construction work of the cut-off bank 20 becomes relatively easy. Along with this, secondary effects such as shortening of the slope construction work time can be obtained.

  Next, the top edge height and overtopping amount of the deadline 20 will be considered. It is clear that the overtopping decreases as the top 60 of the pier 20 increases. However, it is not economical. Therefore, an optimum top height that is excellent in economic efficiency and can reduce overtopping is required as an economic design.

  FIG. 6 shows the relationship between the top height of the cut-off bank 20 and the overtopping amount for realizing economic design. The top height of the deadline 20 is set on the basis of the overtopping amount at the time of 30-year probability wave invasion as described above. According to the above numerical analysis, the allowable overtopping amount in the 30-year probability wave is set. The (flow rate) was 0.05 m3 / m / sec. Curve Le is the analysis value of 30-year probability wave. When the ceiling height of the cut-off bank 20 is 9.5 m, overtopping of the 30-year probability wave cannot be prevented, but the ceiling height is up to 10.0 m. If the carry is carried out, the overtopping amount of the 30-year probability wave can be suppressed below the allowable overtopping amount. Further carryover will reduce the amount of overtopping for a while.

  On the other hand, the amount of overtopping of the 10-year probability wave at the top of 9.5 m is 0.01 or less as shown by the curve Lf. It turned out that it is not influenced by the edge height. Therefore, as a result of analysis, it can be said that the minimum value of the top height of the cut-off bank 20 that can be most economically designed when a 30-year probability wave is also expected is around 10.0 m. Therefore, in the case of FIG. 1, the ceiling height of the cut-off bank 20 is selected to be 10.0 m. If the overtopping amount due to the 30-year probability wave can be reduced, the bank width of the top 60 of the deadline 20 can be designed to be narrow.

  In this way, by making the cut-off bank 20 an inclined bank, and providing the seawater storage section 50 having a sufficient width between the caisson 30 and the surface slope 22 on the offshore side of the cut-off bank 20, Since the energy of the water masses of waves that have passed over the caisson 30 can be effectively suppressed, even waves such as 30-year probability waves can be reduced as much as possible.

  In the first embodiment, the present invention is applied to a coastal wave breakwater embankment where an industrial facility such as a power plant is laid. However, the present invention is not limited to the place where it is applied. Moreover, although the rock formation was used as the structure of the cut-off bank 20, it is not restricted to this. The slope of the slope on the offshore side of the wave-dissipating work 40 is obtained from the relationship with the offshore wave, and is merely an example.

  The present invention can be applied to a wave-dissipating structure for a wave-dissipating embankment on a coastline where an industrial facility such as a power plant is laid.

It is principal part sectional drawing which shows an example of the caisson wave-absorbing structure 10 which concerns on this invention. It is explanatory drawing which shows the relationship between the caisson 30 and the water depth of the seawater storage part 50. FIG. It is a curve figure which shows the relationship between the water depth of the seawater storage part 50, and the amount of overtopping. It is explanatory drawing of the slope of the deadline. It is a curve figure which shows the relationship between the slope of the deadline 20, and the amount of overtopping. It is a curve figure which shows the relationship between the top edge height of the deadline 20, and the amount of overtopping.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Caisson wave-dissipating structure 20 ... Cut-off bank 22 ... Surface slope 24 ... Filled concrete 30 ... Caisson 40 ... Wave-dissipating work 50 ... Seawater storage part 52. ..Upholstered concrete 60 ...

Claims (4)

It consists of a cut-off bank whose offshore side is an inclined bank for wave-dissipation, a caisson submerged on the offshore side to be connected to this, and a wave breaker submerged on the offshore side of this caisson,
The out of deadline Tsutsumi, overtopping reduce seawater reservoir between the Hoshiri upper Symbol caisson was made lower than the top end of the caisson table slopes of offshore is provided,
The slope of the above-mentioned slope is 20% slope, and in that face slope, the water mass that overwent the caisson and the overtopping reduction seawater storage part will come next by the return flow from the above slope A caisson wave-dissipating structure characterized by reducing the energy of the overtopping water mass . The caisson wave-extinguishing structure according to claim 1, wherein the overtopping reduction seawater storage section has a water depth to obtain a predetermined amount of stored seawater. The caisson wave breaking structure according to claim 1, wherein the width of the overtopping-reduction seawater storage portion is selected in consideration of the reach of the overtopping water mass reaching the top of the deadline. The caisson wave-extinguishing structure according to claim 1, wherein the top edge of the cut-off bank has a top-end height such that the amount of overtopping at the time of a 30-year probability wave invasion falls below the damage limit value of the cut-off bank. body.

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