Double parapet revetment and method for determining the dimensions of double parapet revetment

Abstract

To provide a double parapet revetment having a structure capable of being adapted to increased high tide risk, etc. and being constructed relatively easily, and a method for determining factors of a double parapet revetment capable of objectively determining factors of a parapet.SOLUTION: A double parapet revetment 1 comprises: an existing dam body 2; an existing parapet 3 erected on an upper surface of the dam body 2; and a new parapet 4 provided at a distance behind the existing parapet 3. A method for determining factors of the double parapet revetment 1 determines a gap l between the existing parapet 3 and the new parapet 4 and a height hb of the new parapet 4 from a water surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a double parapet revetment and a method for determining the specifications of the double parapet revetment. [Background technology]

[0002] Seawalls are installed on coasts and riverbanks to prevent erosion damage caused by currents and waves. In order to prevent flooding caused by overtopping waves and overflows during high tides, parapet seawalls, which have a parapet at the top, are sometimes used. In recent years, there have been concerns about storm surges due to rising sea levels caused by global warming and stronger tropical cyclones. If a storm surge occurs and overflows existing seawalls, there is a risk of extensive damage from flooding. For this reason, double parapet seawalls, which have parapets on both the outside (sea side) and inside (land side) of the dam body, are used as seawalls that can reduce the amount of wave overtopping the seawall caused by high tides, etc. (see, for example, Patent Documents 1 and 2). There is no established specific method for determining the parapet specifications of a double parapet revetment, and they are generally determined by conducting hydraulic experiments, etc., with specifications set based on past data, empirical values, etc. However, when attempting to design a double parapet revetment that can adapt to the increasing risk of storm surges due to climate change, past data and empirical values ​​cannot be used, so there is a need to establish a method for objectively determining the parapet specifications. Furthermore, upgrading an existing seawall to a new double parapet seawall requires large-scale seawall improvements, which is extremely costly and time-consuming. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-204529 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-073338 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention aims to propose a double parapet revetment that has a structure that can adapt to increased risks of high tides and can be constructed relatively easily, and a method for determining the specifications of the double parapet revetment that can objectively determine the specifications of the parapet. [Means for solving the problem]

[0005] The double parapet revetment of the present invention, which solves these problems, comprises an existing embankment, an existing parapet erected on the upper surface of the embankment, and a new parapet installed at a distance behind the existing parapet. The distance l between the existing parapet and the new parapet and the height h of the new parapet from the water surface are b is set so as to satisfy Equation 1. It is desirable that the height of the new parapet from the water surface be greater than the height of the existing parapet from the water surface. The method for determining the specifications of a double parapet revetment of the present invention determines the specifications of a double parapet revetment comprising a sea-side parapet provided on the sea side of a cut-off wall and a land-side parapet provided behind the sea-side parapet, and includes the steps of: calculating a first wave overtopping rate, which is a dimensionless wave overtopping rate for the sea-side parapet when the sea-side parapet is provided alone on the cut-off wall; setting a second wave overtopping rate, which is a dimensionless wave overtopping rate for the land-side parapet; and determining the distance l between the sea-side parapet and the land-side parapet and the height h of the land-side parapet from the water surface that satisfy Equation 1 using the first wave overtopping rate and the second wave overtopping rate. b and determining a combination of the interval l and the height h. b If one of these is given, use Equation 1 to determine the value of the other. According to this double parapet revetment and the method for determining the specifications of the double parapet revetment, when renovating an existing revetment into a double parapet revetment, it is possible to construct a structure that can adapt to the increased risk of storm surges due to climate change. It is also possible to achieve the effect of reducing wave overtopping while utilizing the existing revetment. Furthermore, since the adaptation can be achieved by construction only on land, construction costs are lower than those for renovation work that involves construction on water.

[0006]

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[0007] The double parapet revetment of the present invention makes it possible to relatively easily construct a structure that can adapt to increased risks of high tides, etc. According to the method for determining the specifications of a double parapet revetment of the present invention, the specifications of the double parapet can be determined objectively. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an overview of a double parapet revetment according to an embodiment of the present invention. [Figure 2] FIG. 1 is a cross-sectional view showing an example of an existing parapet revetment. [Figure 3] 1 is a flowchart showing the steps of a method for determining the specifications of a double parapet revetment according to an embodiment of the present invention. [Figure 4] This is an explanatory diagram of the specifications of the existing parapet. [Figure 5] This is an explanatory diagram of the specifications of the newly constructed parapet. [Figure 6] FIG. 1 is a schematic diagram showing a revetment model used in hydraulic experiments. [Figure 7] 1 is a diagram showing the results of hydraulic experiments, and is a graph showing the relationship between the ratio of the rear parapet height to the wave height H and the dimensionless wave overtopping flow rate. [Figure 8] 1 is a diagram showing the results of hydraulic experiments, and is a graph showing the relationship between the overtopping reduction rate and the dimensionless quantity of each parameter. [Figure 9]FIG. 10 is a graph showing the results of a numerical experiment, illustrating the relationship between the overtopping wave reduction rate and the dimensionless quantity of each parameter. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this embodiment, a double parapet seawall 1 for reducing the amount of wave overtopping a seawall caused by high tides and the like will be described. Fig. 1 shows an overview of the double parapet seawall 1. As shown in Fig. 1, the double parapet seawall 1 comprises an existing embankment body 2, an existing parapet (sea-side parapet) 3 erected on the upper surface of the embankment body 2, and a new parapet (land-side parapet) 4 provided at an interval behind (on the land side of) the existing parapet 3. As shown in FIG. 2, the existing parapet revetment 10 has a parapet (existing parapet 3) that can suppress wave overtopping and overflow at the previous highest tide level TL0. However, if the future highest tide level TL is expected to rise due to the effects of global warming, etc., there is a risk of inundation of land due to wave overtopping and overflow. Therefore, in this embodiment, as shown in FIG. 1, a new parapet 4 is provided on the landward side of the existing parapet 3 to reduce the risk of wave overtopping and overflow and to suppress flooding damage. Note that FIG. 2 is an explanatory diagram showing an example of an existing parapet revetment 10.

[0010] The height of the new parapet 4 from the water surface is made greater than the height of the existing parapet 3 from the water surface. b The distance l between the existing parapet 3 and the existing parapet 3 (the specifications of the double parapet revetment 1) is determined by the following procedure. In this embodiment, the standard height of each parapet is set to the expected tide level of a high tide. The procedure for determining the specifications of a double parapet revetment (newly constructed parapet) is shown in Figure 3. As shown in Figure 2, the method for determining the specifications of a double parapet revetment comprises a first wave overtopping flow rate calculation step S1, a second wave overtopping flow rate setting step S2, an overtopping flow rate reduction rate calculation step S3, and a specification determination step S4. The first wave overtopping flow rate calculation step S1 is a step of calculating the first wave overtopping flow rate q1, which is a dimensionless wave overtopping flow rate for the existing parapet 3 when the existing parapet 3 is installed alone on the cut-off wall 2.* (See Figure 4.) Figure 4 is an explanatory diagram of the specifications of the existing parapet 3. First overtopping flow rate q1 * is calculated using Equation 2.

[0011]

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[0012] The second wave overtopping flow rate setting step S2 is the second wave overtopping flow rate q2 * (See Figure 5.) Figure 5 is an explanatory diagram of the specifications of the new parapet. Second overtopping flow rate q2 * is the allowable overtopping flow rate (target allowable overtopping flow rate) based on wave conditions, etc., and is set according to the purpose of use of the facility, etc. The overtopping flow reduction rate calculation step S3 is performed by calculating the first overtopping flow rate q1 * and the second overtopping flow rate q2 * The target overtopping flow reduction rate (first overtopping flow q1 * Second overtopping flow rate q2 * The overtopping flow reduction rate is shown in Equation 3.

[0013]

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[0014] The specification determination step S4 determines the distance l between the existing parapet 3 and the new parapet 4 that satisfies Equation 1 using the overtopping flow reduction rate, and the height h of the new parapet 4 from the water surface. b In addition, "H0'" in Equation 1 is the equivalent offshore wave height, which is the wave height of offshore waves before shoaling occurs when "offshore waves change due to shoaling (changes in wave height and wavelength due to water depth) and reach the seawall."

[0015]

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[0016] According to the double parapet revetment 1 of this embodiment, when an existing revetment is renovated into a double parapet revetment 1, a structure that can adapt to the increased risk of high tides due to climate change can be constructed. Furthermore, the effect of reducing wave overtopping can be achieved while utilizing the existing seawall. If the future highest tide level TL is expected to rise compared to the past highest tide level TL0 due to the effects of global warming, etc., there is a risk of land being flooded by wave overtopping and overflow, as shown in Figure 2. However, with the double parapet seawall 1 of this embodiment, the risk of wave overtopping and overflow can be reduced by providing a new parapet 4 on the existing embankment body 2, as shown in Figure 1. Furthermore, since the system can be adapted by only working on the land portion of the embankment body 2, it can be constructed more simply and at lower construction costs than conventional repair work that involves work on water.

[0017] Next, we will explain the hydraulic and numerical experiments conducted to quantitatively evaluate the wave overtopping rate and each parameter of the double parapet revetment. Figure 6 shows the revetment model used in the hydraulic experiment. In this experiment, the wave overtopping flow rate for the double parapet revetment (upright revetment) was measured using a two-dimensional long water tank with a 1 / 20 scale assumed model, a width of 80 cm, and a water depth of 50 cm. The wave overtopping flow rate was measured by measuring the amount of water collected behind the double parapet. In the experimental case, the crown height (height from the water surface) of the front parapet (sea side parapet) was h f 0 to 50 mm, the top height of the rear parapet (land side parapet) (height from the water surface) h b The height of the parapet was set to 100-300 mm, and there was no drainage between the front and rear parapets (see Figure 6). As a comparative example, measurements of the overtopping flow rate were also carried out for a case with only a front parapet. The wave height H of the incident waves was set to a constant 10 cm for both regular and irregular waves, and the target waves were confirmed by an incident test using a horizontal flume with the revetment removed. Table 1 shows the experimental conditions.

[0018] [Table 1]

[0019] Figure 7 shows the results for the case of regular waves with a period of 1.3 seconds and a front parapet height of 50 mm. b and the ratio of wave height H (h b / H) and dimensionless wave overtopping rate q * The experiment shows the relationship between the parapet spacing l and the rear parapet height h b Ratio (l / h b ) was carried out for cases of 1 and 3. As a comparative example (Single), an experiment was also carried out for a single parapet with the same height as the rear parapet. As shown in Figure 7, it was confirmed that the double parapet reduces the overtopping flow rate more than a single parapet. In addition, the larger the parapet spacing (l / h b =3), but the overtopping flow rate tended to be smaller.

[0020] Figure 8 shows the wave overtopping reduction rate, which is expressed as a logarithmic scale on the vertical axis, and the difference in height of the front and rear parapets (h b -h f The graph shows the relationship between the wave overtopping reduction rate and the dimensionless quantities including the wave length, spacing l, incident wave height H, and wavelength L0. As shown in Figure 8, there is a roughly proportional relationship between the wave overtopping reduction rate and the dimensionless quantities of each parameter, and it was confirmed that the wave overtopping rate due to double parapets can be quantitatively evaluated using the incident wave and parapet parameters. The constants (proportionality constants) α and β (the slope and intercept of the dotted line in Figure 8) in Equation 1, which were determined from the results of hydraulic experiments, were α = -7.41 and β = 0.13.

[0021] Additionally, using 3D fluid analysis software, vertical 2D numerical experiments were conducted under analysis conditions similar to those of the hydraulic experiments, and many more cases were examined. Figure 9 shows the relationship between the wave overtopping reduction rate and the dimensionless quantities of each parameter. As shown in Figure 9, in the numerical experiments, just like the results of the hydraulic experiments, the wave overtopping reduction rate and the dimensionless quantities of each parameter showed a roughly proportional relationship, confirming the effectiveness of the double parapet. Furthermore, the slope of the regression curve was the same as in the hydraulic experiments. From the above results, it was confirmed that by using Equation 1, it is possible to determine the parapet specifications according to the wave height and wavelength.

[0022] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described components can be appropriately modified without departing from the spirit of the present invention. In the above embodiment, the distance l between the sea-side parapet and the land-side parapet and the height h of the land-side parapet from the water surface are b However, if the distance l between the sea-side parapet and the land-side parapet is determined based on the shape of the cut-off wall and the site conditions, the height h of the land-side parapet corresponding to the distance l can be determined using Equation 1. b Similarly, the height of the land-side parapet h b If is predetermined, the height h b The interval l according to the above can be determined using Equation 1. In the above embodiment, a case where a new parapet 4 is constructed on the land side of an existing parapet 3 for an existing embankment 2 is described, but the method for determining the specifications of a double parapet revetment in this embodiment may also be used when determining the specifications when constructing a new double parapet revetment (sea-side parapet and land-side parapet). [Explanation of symbols]

[0023] 1 Double parapet revetment 2 Embankment body 3 Existing parapet (sea side parapet) 4 New parapet (land side parapet)

Claims

1. A double parapet revetment comprising an existing embankment body, an existing parapet erected on the upper surface of the embankment body, and a new parapet installed at a distance behind the existing parapet, The distance l between the existing parapet and the new parapet and the height h of the new parapet from the water surface ｂ is set to satisfy Equation 1. [Equation 1]

2. 2. The double parapet revetment according to claim 1, wherein the height of the new parapet from the water surface is greater than the height of the existing parapet from the water surface.

3. A method for determining the specifications of a double parapet revetment, which comprises a sea-side parapet provided on the sea side of a cut-off wall and a land-side parapet provided behind the sea-side parapet, a step of calculating a first wave overtopping rate, which is a dimensionless wave overtopping rate for the sea-side parapet when the sea-side parapet is provided alone on the cut-off wall; setting a second wave overtopping flow rate which is a dimensionless wave overtopping flow rate for the land-side parapet; The distance l between the sea-side parapet and the land-side parapet and the height h of the land-side parapet from the water surface satisfy Equation 1 using the first wave overtopping rate and the second wave overtopping rate. ｂ and a step of determining a combination of the above. [Equation 2]

4. When a new parapet is installed behind an existing parapet on an existing embankment with a distance l, the height h of the new parapet from the water surface is ｂ A method for determining the dimensions of a double parapet revetment, a step of calculating a first wave overtopping rate, which is a dimensionless wave overtopping rate for the existing parapet when the existing parapet is provided alone on the cut-off wall; setting a second wave overtopping flow rate which is a dimensionless wave overtopping flow rate for the newly constructed parapet; The height h of the new parapet from the water surface that satisfies Equation 1 using the first wave overtopping flow rate and the second wave overtopping flow rate ｂ A method for determining the specifications of a double parapet revetment, comprising: [Equation 3]

5. Behind the existing parapet installed on the existing embankment, there is a height h from the water surface. ｂ A method for determining the dimensions of a double parapet revetment that determines the distance l between the existing parapet and the new parapet when a new parapet is constructed, a step of calculating a first wave overtopping rate, which is a dimensionless wave overtopping rate for the existing parapet when the existing parapet is provided alone on the cut-off wall; setting a second wave overtopping flow rate which is a dimensionless wave overtopping flow rate for the newly constructed parapet; and determining the spacing l that satisfies Equation 1 using the first wave overtopping rate and the second wave overtopping rate. [Equation 4]

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