JP6296017B2 - Gravity breakwater - Google Patents

Description

  The present invention relates to a gravity type breakwater such as a caisson type mixed levee.

  Conventionally, a gravitational breakwater in which a reinforcing support (sliding resistor) is installed on the back side of a dam body made of caisson has been proposed in which the reinforcing support is made of stone. The effect of increasing the sliding resistance has been shown by analysis and experiment (Non-Patent Documents 1 and 2). In addition, a structure in which solidified soil with cement is installed instead of stone (Non-Patent Document 3), a structure in which a support structure such as a steel pipe is vertically embedded in the ground (Patent Document 1), and the like have been proposed. Reinforcing effect has been verified.

JP 2014-101663 A

Supervised by the Ministry of Land, Infrastructure, Transport and Tourism Port Authority, Technical Standards and Explanations of Port Facilities, Volume 2, Japan Port Association, 2007, p.838 Yoshiaki Kikuchi and two others, "Effect of backfilling on the stability of caisson", Report of Port Technology Research Institute, Port Technology Research Institute, Ministry of Transport, June 1998, Vol. 37, No. 2, p.29- 58 Shinsha Hiroshi, 2 others, "Centrifuge model experiment on horizontal resistance of caisson type hybrid dike using solidified soil as backfill", Civil Engineering Society Proceedings C (Geosphere Engineering), 2015, Vol.71 , No.2, p.69-80

  However, among the conventional technologies described above, the gravitational breakwater with the support part made of stone made of stone has a fixed mass and internal friction angle, so the resulting sliding resistance is determined by the installation of the support part for reinforcement. The upper limit is determined by the height. Also, if the covering block installed on the surface of the reinforcing support part peels off when a flow over the top of the breakwater acts, such as a tsunami, stone is likely to be washed away (scouring is likely to occur) There is a problem.

In addition, gravity type breakwaters that consist of a solid support soil for the reinforcement support part are difficult to pass through the water, so when waves or tsunamis occur during a typhoon, the gravel breaker mound, which is the foundation of the levee body, is inside. The flowing water flow is blocked by the reinforcing support, and the lifting pressure (force acting upward on the bottom surface of the dam body) acting on the levee body increases and the stability of the levee body decreases.
In addition, in the case of a gravity breakwater with a structure in which a support structure such as a steel pipe is vertically embedded in the ground, the water flow that flows in the rubble mound is blocked by the support structure, which increases the lifting pressure acting on the dam body. In addition, there is a problem that the material cost is higher than the case of installing stone.

  Therefore, the object of the present invention is to solve the problems of the prior art as described above, to have high sliding resistance against waves with large energy such as tsunami, and to suppress the lifting pressure acting on the levee body, thereby stabilizing the dam body. The object of the present invention is to provide a gravity type breakwater that is highly reliable and can be constructed at low cost.

The gist of the present invention for solving the above problems is as follows.
[1] A rubble mound (1) constructed on the bottom of the water, a dam body (2) installed on the rubble mound (1), and a reinforcing support provided on the back side of the dam body (2) ( 3) Gravity type breakwater provided with a reinforcing support (3) having a unit volume mass in water of 10 kN / m ³ or more and an adhesive strength after curing for 28 days of 10 kN / m ² or more. A reinforced soil layer (4) provided so as to be in contact with the back surface of the dam body (2) and the rubble mound (1), and a back surface of the reinforced soil layer (4) and the rubble mound (1). Gravity type breakwater characterized by comprising a stone layer (5) provided as described above.

[2] In the gravity breakwater of [1] above, the reinforced soil constituting the reinforced soil layer (4) is a mixture of modifiers that cause a hydration reaction in dredged soil and / or earth and sand. Gravity type breakwater.
[3] In the gravity breakwater of [1] or [2] above, the height of the reinforced soil layer (4) on the rubble mound (1) is 1/3 or more of the height of the dam body (2) A gravity-type breakwater characterized by being.
[4] Gravity characterized in that in the gravity type breakwater of any one of [1] to [3], the bottom width of the reinforced soil layer (4) in contact with the top end surface of the rubble mound (1) is 2 m or more. Formula breakwater.
[5] The gravitational breakwater according to any one of [1] to [4], wherein the upper surface of the reinforcing support (3) is covered with a covering block (6).

[6] A method for constructing a gravity breakwater according to any one of the above [1] to [5], wherein the levee body (2) is installed on the rubble mound (1) constructed on the ground of the bottom of the water, On the back side of the levee body (2), stones are stacked at a position away from the dam body (2) to form a stone layer (5), and then between the stone layer (5) and the dam body (2) The reinforcing support (3) including the reinforcing soil layer (4) and the stone layer (5) is constructed by charging and laying the reinforcing soil to form the reinforcing soil layer (4). How to create a gravity breakwater.

  In the gravity breakwater of the present invention, the water flow flowing in the rubble mound (1) can pass through the stone layer (5) as it is and flows to the rear side of the breakwater. However, it is possible to suppress a large lifting pressure from acting on the dam body (2) and to obtain high stability of the dam body (2). Moreover, the reinforcing support portion (3) includes a stone layer (5), and a reinforced soil layer (4) made of reinforced soil having an underwater unit volume mass equal to or greater than that of the stone and having an adhesive force (strength) equal to or greater than a predetermined value. Because of this composite structure, a higher sliding resistance can be obtained as compared with the case where the reinforcing support portion is made of only stone. For this reason, even when a large external force such as a tsunami acts, the stability of the breakwater can be ensured. Normally, the outside of the reinforcing support (3) is covered with a covering block. However, even if a tsunami overflows the breakwater top and the covering block flows out, the reinforcing soil layer (4) has strength. Therefore, scouring is difficult to occur. Moreover, since the support part (3) for reinforcement can be constructed only with stones and reinforced soil, it can be constructed at low cost. Furthermore, since dredged soil generated in large quantities in port construction can be used as the reinforcing soil constituting the reinforced soil layer (4), the dredged soil can be effectively used.

The longitudinal cross-sectional view which shows typically one Embodiment of the gravity type breakwater of this invention A longitudinal sectional view schematically showing an example of a conventional gravity breakwater The longitudinal cross-sectional view which shows typically the gravity type breakwater of the Example of this invention

FIG. 1 is a longitudinal sectional view schematically showing an embodiment of a gravity breakwater according to the present invention.
The gravitational breakwater of the present embodiment includes a rubble mound 1 constructed on the bottom of the water (ground 7), a dam body 2 (dam body) installed on the rubble mound 1, and a back side (wave) of the dam body 2 When the receiving side is the front side, a reinforcing support portion 3 provided on the opposite side) is provided.
When the installation place of the gravity breakwater is a harbor, the front side of the bank 2 is the outside of the port and the back side is the inside of the port. The rubble mound 1 is constructed over the entire length of the breakwater installation site, and a plurality of heavy structures such as caissons are arranged on the dam body 2.

The reinforcing support portion 3 supports the dam body 2 on the back surface side and imparts sliding resistance, and includes a reinforced soil layer 4 provided so as to be in contact with the back surface of the dam body 2 and the rubble mound 1, and this reinforcement. It is composed of a stone layer 5 provided so as to be in contact with the back surface of the soil layer 4 and the rubble mound 1. Here, the stone layer 5 is formed by stacking stone materials such as spar, and the reinforcing soil layer 4 is formed by stacking (laying) reinforcing soil.
The reinforcing soil layer 4 is provided such that the front surface thereof is in contact with the back surface of the bank 2 and the lower end portion 41 is in contact with a part of the top end surface of the rubble mound 1. In constructing the reinforcing support portion 3 as will be described later, a stone layer 5 is first formed at a position away from the dam body 2, and then a reinforced soil layer 4 is formed between the stone layer 5 and the dam body 2. Therefore, the back surface 42 of the reinforced soil layer 4 becomes a downward inclined surface in contact with the slope 52 on the front surface side of the stone layer 5.

The reinforced soil layer 4 is composed of reinforced soil having a unit volume mass in water of 10 kN / m ³ or more and an adhesive strength after curing for 28 days of 10 kN / m ² or more. The adhesive strength of the reinforced soil is calculated by ½ of the uniaxial compressive strength obtained in the uniaxial compression test of soil (JIS A1216: 2009) for the sample (test specimen) after 28 days of curing.
The condition of the reinforced soil is obtained as follows.
The resistance force of the sliding resistor (reinforcing support portion 3 in the present invention) is determined by its mass and the strength of the resistor (here, adhesive force). Therefore, the mass of the reinforcing soil is preferably equal to or higher than that of stone. For this reason, the unit volume mass of the reinforced soil in water shall be 10 kN / m < ³ > or more. Further, since the sliding resistance of the reinforcing support 3 increases as the unit volume mass of the reinforcing soil in water increases, it is preferable from this viewpoint that the unit volume mass of the reinforcing soil in water is larger (for example, 13 kN / m ³ or more). However, about 17 kN / m ³ is a practical upper limit due to restrictions such as the mixing ratio of modifiers in the production of reinforced soil (about 70% is the upper limit for granular materials).

The strength condition of the reinforced soil was determined based on the following sliding resistance calculation formula.

A case is assumed where a tsunami wave force having a wave height of 10 m is applied to the dam body 2 having a standard size of 19 m on the front side and 17 m on the back side. When the reinforcing support 3 is not provided on the back side of the levee body 2, the sliding resistance is insufficient by 988.85 kN / m in order to satisfy the sliding safety factor of 1.2 or more which is a design standard. In the gravity breakwater of the present invention, when the installation height of the reinforcing support 3 is 12.5 m, the top edge width of the reinforcing earth layer 4 is 21.0 m, and the top edge width of the stone layer 5 is 2 m, the reinforcing earth The underwater unit volume mass is 10 kN / m ³ , the adhesive strength is 10 kN / m ² (uniaxial compressive strength 20 kN / m ² ), the stone unit volume mass in water is 10 kN / m ³ , and the internal friction angle is 40 degrees. The sliding resistance is as follows and satisfies the above-mentioned requirements.

Further, if the uniaxial compressive strength of the reinforced soil is less than 20 kN / m ² , the reinforced soil layer 4 may not be able to support the covering block placed thereon, so the strength is 20 kN / m ² or more. There is a need to.
For the above reasons, the adhesive strength of the reinforced soil after curing for 28 days is set to 10 kN / m ² or more. In addition, since the sliding resistance of the reinforcing support 3 increases as the adhesive strength of the reinforcing soil increases, the adhesive strength of the reinforcing soil is higher from this viewpoint (for example, preferably 30 kN / m ² or more, more preferably 50 kN / m ² or more) is preferable, but usually the height of the reinforced soil layer 4 is set to 1/3 or more of the height of the levee body ^2, so that about 100 kN / m ² may be a practical upper limit. .

Any material can be used as the reinforced soil constituting the reinforced soil layer 4 as long as it satisfies the unit volume mass in water and the adhesive strength as described above, but it develops strength by a hydration reaction. Examples of the reinforced soil include mixed soil obtained by mixing dredged soil and / or a modifying material (hydraulic solidifying material) that causes a hydration reaction. In the present invention, this mixed soil is preferably used as the reinforced soil. it can.
The clay may be subjected to a drying process (for example, sun drying) or a dehydration process (a method of dehydrating and reducing the volume after adding a chemical to agglomerate). The earth and sand may be construction residual soil. The modifying material is not particularly limited as long as it causes a hydration reaction, and examples thereof include steel slag such as cement, lime, and steelmaking slag, and concrete waste, and one or more of these are used. be able to.
The uniaxial compressive strength of the reinforced soil can be adjusted by selecting the type and amount of the modifier.

  Steel slag used as a modifier is blast furnace slow-cooled slag generated in a blast furnace (however, this blast furnace slow-cooled slag is preferably sufficiently aged to prevent elution of sulfide in water), hot metal Steelmaking slag generated in processes such as pretreatment, converter decarburization refining, casting, electric furnace refining, etc. Etc.), ore reduction slag, etc., and two or more of these may be used. Among these slags, steel slag is particularly preferable, and among these, decarburization slag (converter slag) and dephosphorization slag are particularly suitable. In order to obtain a sufficient effect, it is preferable to use a slag having a granular shape.

As the stone material constituting the stone layer 5, natural stone material (sparing stone) is generally used. For example, a concrete block, a carbonate solid block using steel slag as a main raw material, and a hydrated hardened body using steel production slag as a main raw material. Artificial stone materials such as blocks (for example, steel slag hydrated solid bodies) may be used, and one or more of these materials including natural stone materials can be used.
Although the magnitude | size of the stone material which comprises the stone material layer 5 is arbitrary, the thing of about 10-200 kg is used normally.

The installation form of the reinforced soil layer 4 and the stone layer 5 is not particularly limited except for the points described above, but the following installation form is particularly preferable.
As shown in FIG. 1, the reinforced soil layer 4 is provided so that the lower end portion 41 (lower end surface) of the reinforced soil layer 4 is in contact with a part of the top end surface of the rubble mound portion 10 on the back side of the dam body 2. That is, it is preferable that the reinforced soil layer 4 is in contact with the top end face of the rubble mound portion 10 on the surface. The breakage of the reinforcing support portion 3 due to wave force such as a tsunami occurs at a point p where the lower edge of the dam body 2 and the top end surface of the rubble mound 1 are in contact, so that the reinforced soil layer 4 is against the rubble mound portion 10. If the surface is not in contact with the surface (for example, if the reinforced soil layer 4 is not in contact with the rubble mound portion 10 or is in contact with a point), the reinforced soil layer 4 is not resistant to breakage and is reinforced by wave force. The supporting part 3 is easily broken. From this viewpoint, the width w ₁ (lower end width) of the lower end portion 41 of the reinforced soil layer 4 is preferably 2 m or more.

Further, the height h of the reinforced soil layer 4 on the rubble mound 1 (the height of the top end portion 40) is the highest from the functional surface as a sliding resistance body, the height H of the dam body 2 (from the rubble mound 1). It is preferable that it is 1/3 or more of the height of the levee body.
The width w ₂ (top edge width) of the top end portion 40 of the reinforced soil layer 4 ensures the reinforcing effect by the reinforced soil layer 4, while the cross section of the reinforced soil layer 4 becomes large and the creation cost increases. From the viewpoint of suppression, it is preferably about 10 to 20 m.

The stone layer 5 is preferably provided so that the lower surface of the stone layer is in contact with a part of the top end face and the side end face of the rubble mound portion 10 and the bottom portion 8 behind the rubble mound 1. Thereby, the water flow flowing through the rubble mound 1 can flow into the stone layer 5 particularly smoothly.
The width w ₃ (top edge width) of the top 50 of the stone layer 5 ensures the stability of the stone layer 5 while suppressing an increase in the creation cost due to a large cross section of the stone layer 5. Therefore, it is preferable to be about 2 to 5 m.

  The slope of the slopes 51 and 52 on the back side and the front side of the stone layer 5 is preferably about 1: 1.2 to 1: 1.5. If the slopes of the slopes 51 and 52 are greater than 1: 1.2, the stone material may collapse depending on the internal friction angle of the stone material. On the other hand, if the slopes of the slopes 51 and 52 are smaller than 1: 1.5, the cross section of the stone layer 5 becomes large, so that the creation cost increases.

Although not shown, the upper surface of the reinforcing support 3 is usually covered with a covering block 6 (see FIG. 5) in order to prevent outflow of the reinforcing soil and the stone constituting the reinforcing support 3 (the reinforcing soil layer 4 and the stone layer 5). 3) and the upper surface of the rubble mound portion on the front side of the dam body 2 is also covered with a covering block or a root block (see FIG. 3).
It should be noted that the size of the levee body 2 and the rubble mound 1 that supports it differs depending on the water depth of the sea area where it is installed and the assumed wave height, etc. -The width between the back surfaces is about 10-20 m, the height is about 15-25 m, and the rubble mound 1 has a width (width between the front surface and the back surface) of about 40-60 m and a thickness of about 3-10 m. Many.

For comparison, FIG. 2 (longitudinal sectional view) shows a conventional gravity breakwater in which the reinforcing support portion is made of only stone (sparing stone).
In the gravity breakwater of the present invention, the water flow flowing in the rubble mound 1 can flow directly through the stone layer 5 to the back side of the breakwater, so that even when a typhoon wave or tsunami acts on the dam body 2 The action of a large lifting pressure is suppressed, and the high stability of the levee body 2 is obtained. In addition, the reinforcing support 3 is a composite of the stone layer 5 and the reinforcing soil layer 4 made of the reinforcing soil having the above-described unit volume mass in water equal to or greater than that of the stone and having an adhesive force (strength) equal to or greater than a predetermined value. Due to the structure, it is possible to obtain a higher sliding resistance as compared with a reinforcing support portion made of only stone as shown in FIG. That is, the reinforced soil layer 4 made of the reinforced soil having a unit volume mass in water equal to or greater than that of the stone and having an adhesive strength of 10 kN / m ² or more has a higher sliding resistance than the reinforced layer made of only the stone. Since the support part 3 is a composite structure of the reinforced soil layer 4 and the stone layer 5, a high sliding resistance can be obtained. Normally, the outer side of the reinforcing support 3 is covered with the covering block 6. However, even when a tsunami overflows the breakwater top and the covering block 6 flows out, the reinforcing soil layer 4 has strength. Therefore, there is an advantage that scouring hardly occurs.

  When constructing the gravitational breakwater of the present invention as described above, first, a rubble mound 1 is constructed on the bottom 7 of the bottom of the water over the entire length of the breakwater installation place, and a plurality of heavy structures such as caissons are formed thereon. The bank 2 is installed side by side. Next, in constructing the reinforcing support 3, first, a stone layer 5 is formed by stacking stone materials at a position slightly away from the bank body 2 on the back side of the bank body 2, and then the stone layer 5 and the bank The reinforcing soil layer 4 is formed by introducing and laying the reinforcing soil between the body 2 and the body 2. As a result, the reinforcing support portion 3 including the reinforcing soil layer 4 and the stone layer 5 as shown in FIG. 1 is constructed. Furthermore, normally, while covering the upper surface of the reinforcement structure part 3 with the covering block 6, the upper surface of the rubble mound part of the front side of the dam body 2 is also covered with a covering block or a root block.

The gravity type breakwater of the present invention as shown in FIG. 3 was installed in the sea area of envy average high tide surface +0.5 m and water depth 16.5 m. In this gravity type breakwater, the thickness of the rubble mound 1 was 3 m, and the dike body 2 was 19 m in width and 19 m in height to the top of the parapet. The installation height of the reinforcing soil layer 4 was 6.5 m from the top of the rubble mound 1, the top width of the reinforcing soil layer 4 was 11 m, and the top width of the stone layer 5 was 2 m. The slope of the stone layer 5 was set to 1: 1.5. In order to ensure that sliding resistance can be exerted even with a small amount of reinforced soil, the unit volume mass in water is preferably greater than that of stone. In this embodiment, steelmaking slag (modifier) is mixed with the clay and 70 volumes of clay is obtained. %, Mixed soil made of steelmaking slag 30% by volume was used. As a result of the indoor blending test, this mixed soil had a unit volume mass in water of 11.0 kN / m ³ and a uniaxial compressive strength after curing on the 28th of 120 kN / m ² (adhesive strength 60 kN / m ² ).

Assuming a tsunami with a wave height of 10 m, the sliding resistance is 3292.57 kN / m against the resultant wave force of 2724.12 kN / m (of which the sliding resistance of the reinforced soil layer 4 is 1012.38 kN / m) The sliding safety factor of 1.2, which is a design standard, was satisfied.
Calculation for the case where a reinforcing support (stone layer) consisting only of stone (underwater unit volume mass 10.0 kN / m ³ , internal friction angle φ = 40 °) is provided as in the conventional gravity breakwater shown in FIG. As a result, when the installation height of the reinforcing support portion is 6.5 m, the upper limit of the sliding resistance is 971.52 kN / m, and the safety factor of 1.2 is satisfied even if the width of the reinforcing support portion is widened. As a result, it was impossible to obtain the necessary sliding resistance. On the other hand, in the case of the gravity breakwater according to the present invention, the composite structure of the reinforcing soil layer 4 and the stone layer 5 can secure the required sliding resistance even if the cross section of the reinforcing support 3 is made smaller. Conceivable.

DESCRIPTION OF SYMBOLS 1 Rubble mound 2 Dike body 3 Reinforcement support part 4 Reinforcement soil layer 5 Stone layer 6 Covering block 7 Ground 8 Water bottom part 10 Rubble mound part 40 Top end part 41 Lower end part 42 Back surface 50 Top end part 51,52 Slope

Claims (6)

A rubble mound (1) constructed on the bottom of the water, a dam body (2) installed on the rubble mound (1), and a reinforcing support (3) provided on the back side of the dam body (2) A gravitational breakwater equipped,
The reinforcing support (3) is made of reinforced soil having a unit volume mass in water of 10 kN / m ³ or more and an adhesive strength after curing for 28 days of 10 kN / m ² or more. A reinforced soil layer (4) provided in contact with the rubble mound (1), and a stone layer (5) provided in contact with the rear surface of the reinforced stone layer (4) and the rubble mound (1). A gravity breakwater.   The gravitational breakwater according to claim 1, wherein the reinforced soil constituting the reinforced soil layer (4) is a mixture of a modifying material that causes a hydration reaction in dredged soil and / or earth and sand.   The gravity breakwater according to claim 1 or 2, wherein the height of the reinforced soil layer (4) on the rubble mound (1) is not less than 1/3 of the height of the dam body (2). .   The gravity type breakwater according to any one of claims 1 to 3, wherein the bottom width of the reinforcing soil layer (4) in contact with the top end surface of the rubble mound (1) is 2 m or more.   The gravity type breakwater according to any one of claims 1 to 4, wherein the upper surface of the reinforcing support (3) is covered with a covering block (6). A method for constructing a gravity breakwater according to any one of claims 1 to 5,
After installing the levee body (2) on the rubble mound (1) constructed on the bottom of the water, the stone material is piled up at a position away from the dam body (2) on the back side of the dam body (2). The layer (5) is formed, and then the reinforced soil layer (4) is formed by introducing and laying the reinforced soil between the stone layer (5) and the dam body (2) to form the reinforced soil layer (4). And a reinforcing support (3) provided with a stone layer (5).

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