Method for installing scour prevention mats, method for constructing scour prevention structures, and scour prevention mats

Abstract

To provide a method for installing a scouring prevention mat, a method for constructing a scouring prevention structure, and a scouring prevention mat which suspend a scouring prevention mat in a stable attitude while preventing damage ti the scouring prevention mat and can install the scouring prevention mat at a water bottom.SOLUTION: A scouring prevention mat 1 includes a mat body 2 where a hole 3 is formed at its center, and a plurality of suspension parts 6 and 7 which are exposed at prescribed intervals in a circumferential direction in each of an outer edge 4 side and an inner edge 5 side of the mat body 2. In order to construct a scouring prevention structure 36, a scouring prevention mat 1 is suspended and installed at a water bottom using a suspension balance 13 composed of an outer frame 14 suspending the suspension part 6 on the outer edge 4 side of the mat body 2 and an inner frame 15 suspending the suspension part 7 on the inner edge 5 side. Then, a pile-like underwater structure is placed so as to penetrate the hole 3 of the scouring prevention mat 1, and a filter unit 33 where a net body is filled with stone or crushed stone is installed above a clearance between the inner edge 5 of the mat body 2 and the underwater structure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for installing an erosion prevention mat, a method for constructing an erosion prevention work, and an erosion prevention mat.

Background Art

[0002] Conventionally, in the foundations such as piles of offshore wind power generation facilities, levees, and bridge piers, the problem of erosion, where the surrounding sand and mud are sucked out or dug in by the flow of water, has been an issue. This phenomenon is due to the acceleration associated with the local disturbance of the water flow caused by the structure and the generation of vortices. As an erosion prevention work for preventing erosion, there is a method of installing a covering body such as an impermeable sheet or mat in a strip shape on the bottom of the water and installing weights at the joints (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the erosion prevention work of Patent Document 1, since the covering body such as a sheet or mat is made into a strip shape, joint treatment is required, and there is a risk of sand being sucked out from the joints.

[0005] On the other hand, when the mat is laid as a single unit rather than in strips, there are no such problems with seams. However, as underwater structures become larger, the scouring prevention work also needs to be made larger. When laying heavy mats over a large area in the shape of a large circle or polygon, it is difficult to maintain the integrity of the mat itself by suspending it only by its outer edge. In particular, in the case of mats that are difficult to roll up, there is a concern that the covering may be damaged by local bending or shear due to excessive deflection when suspended, or that the scouring prevention mat may tear at the part where the suspension fittings embedded in the mat are located. For this reason, as shown in Figure 14(a), it is necessary to install many suspension fittings 102 on the scouring prevention mat 101 to prevent localized bending. However, when arranging numerous suspension fittings 102 in a grid or staggered pattern within the scour prevention mat 101, and suspending the scour prevention mat 101 in a flat state without bending using a suspension beam 103 as shown in Figure 14(b), there is a concern that the suspension load on the numerous suspension fittings 102 will fluctuate and become significantly uneven in local areas due to water resistance on the underside of the scour prevention mat 101, as well as waves and water currents. Furthermore, the installation work is not easy, as is the connection work with the numerous suspension fittings 102 before lowering them into the water, and the issue of auto-release for simultaneously releasing the suspension fittings 102 remotely from above the water when installing the scour prevention mat 101 on the seabed.

[0006] This invention has been made in view of the aforementioned problems, and its purpose is to provide a method for installing a scour prevention mat, a method for constructing a scour prevention structure, and a scour prevention mat that can be installed on the seabed by being suspended in a stable position while preventing damage to the scour prevention mat. [Means for solving the problem]

[0007] To achieve the aforementioned objective, the first invention is a method for installing a scouring prevention mat on the bottom of a body of water, wherein the scouring prevention mat comprises a mat body with a hole formed in the center, and a plurality of suspension parts exposed at predetermined intervals in the circumferential direction on the outer edge and inner edge sides of the mat body, and the method for installing a scouring prevention mat is characterized by using a suspension beam consisting of an outer frame for suspending the suspension parts exposed on the outer edge side of the mat body and an inner frame for suspending the suspension parts exposed on the inner edge side of the mat body to suspend the scouring prevention mat on the bottom of the water.

[0008] In the first invention, multiple suspension points are provided on both the outer and inner edges of the mat body, which has a hole in the center, and the suspension points are suspended by a suspension beam consisting of an outer frame and an inner frame. This allows the scouring prevention mat to be suspended in a stable position while preventing damage to the mat, compared to the case where numerous suspension fittings are provided inside the mat.

[0009] The aforementioned suspension balance preferably has an auto-release mechanism that releases the suspension after the suspension part has reached the bottom of the water. This allows multiple suspension points to be released remotely from the water without the need for divers, thus improving safety during construction. Even in this case, by suspending the suspension points with a suspension beam consisting of an outer frame and an inner frame, the number of suspension points can be reduced compared to when multiple suspension fittings are installed inside the mat, thus increasing the reliability of preventing release leaks.

[0010] The auto-release mechanism has a movable member that moves circumferentially with respect to the outer frame and the inner frame, respectively, and operates a suspension member that suspends the suspension part depending on the circumferential position of the movable member, and is capable of switching between a state in which the suspension member is hooked onto the suspension part and a state in which it is released from the suspension part, and it is desirable that by moving the movable member circumferentially, the plurality of suspension parts suspended from the outer frame and the plurality of suspension parts suspended from the inner frame can be released all at once. This allows all suspension points to be released quickly and reliably. The moving members are linear or rod-shaped components.

[0011] Preferably, a wire is embedded inside the mat body so as to span the inner and outer edges of the mat body, and the suspension parts are provided at both ends of the wire so as to be exposed on the inner and outer edges of the mat body. This allows the load borne by the suspension point to be transmitted to the wire, thus preventing damage to the mat body near the suspension point. The wire may be a rope or sling made of synthetic fiber or similar material. Furthermore, to prevent damage modes such as the inner and outer wire ends coming loose from the mat, reinforcing materials such as steel strips or reinforcing wires may be placed in a perpendicular direction inside the mat directly above the wire.

[0012] The wire may have one suspension portion at one end that is exposed on the inner edge side of the mat body, and a plurality of suspension portions at the other end that are exposed on the outer edge side of the mat body. This allows the suspension points to be densely arranged on the outer edge of the mat body, thus preventing excessive deformation of the outer edge of the mat body during suspension without increasing the number of suspension points on the inner edge, and thus preventing damage to the mat body.

[0013] In the first invention, for example, the radial distance between the outer frame and the inner frame of the suspension beam can be increased with respect to the radial length from the inner circumference to the outer circumference of the scour prevention mat. This reduces the deflection of the scour prevention mat when suspended, suppressing deformation such as excessive bending, twisting, or torsion. It also reduces resistance to waves and water flow from the side.

[0014] In the first invention, the radial distance between the outer frame and the inner frame of the suspension beam can be reduced with respect to the radial length from the inner circumference to the outer circumference of the scour prevention mat. This increases the deflection of the scour prevention mat when it is suspended, reducing water resistance when it is lowered.

[0015] Furthermore, in the first invention, by providing a rotation mechanism separate from the auto-release mechanism in the outer and inner frames of the suspension beam, the radial distance between the suspension member on the outer frame side and the suspension member on the inner frame side, and the tension of the scour prevention mat can be adjusted.

[0016] The second invention is a method for constructing a scour prevention structure formed on the seabed around an underwater structure, comprising: step a, installing a scour prevention mat on the seabed, the mat having a mat body with a hole formed in the center and a plurality of suspension parts exposed at predetermined intervals in the circumferential direction on the outer edge and inner edge sides of the mat body; step b, driving a pile-shaped underwater structure so as to penetrate the hole in the scour prevention mat; and step c, installing a filter unit with a mesh body filled with stone or crushed stone above the gap between the inner edge of the mat body and the underwater structure, wherein in step a, the scour prevention mat is lowered to the seabed using a suspension beam consisting of an outer frame for suspending the suspension parts exposed on the outer edge side of the mat body and an inner frame for suspending the suspension parts exposed on the inner edge side of the mat body. Note that the filter unit above the gap is an example, and any other unit with sufficient weight and a mechanism to prevent sand from being sucked out may be used instead.

[0017] In the second invention, by driving underwater structures such as foundation piles through holes in a scour prevention mat installed on the seabed, the holes in the mat can be used as markers when driving the underwater structures, enabling efficient construction of scour prevention work. Furthermore, by providing multiple suspension points on both the outer and inner edges of the mat body, which has a hole formed in the center, and suspending the suspension points with a suspension beam consisting of an outer frame and an inner frame, it is possible to suspend the scour prevention mat in a stable position while preventing damage to the mat, compared to the case where many suspension fittings are provided inside the mat.

[0018] The third invention is an anti-scouring mat installed on the bottom of the water around an underwater structure, comprising a mat body with a hole formed in the center, a wire embedded inside the mat body so as to span the inner edge side and the outer edge side of the mat body, and a plurality of hanging parts provided at both ends of the wire and exposed at predetermined intervals in the circumferential direction on each of the outer edge side and the inner edge side of the mat body. The anti-scouring mat is characterized by the above.

[0019] The anti-scouring mat of the third invention embeds a wire so as to span the outer edge side and the inner edge side of the mat body with a hole formed in the center, and provides a plurality of hanging parts on each of the outer edge side and the inner edge side of the wire. By doing so, while ensuring the integrity of the mat body, it is possible to allow a certain amount of deflection and suspend it.

[0020] One of the ends of the wire may be provided with one of the hanging parts exposed on the inner edge side of the mat body, and the other end may be provided with a plurality of the hanging parts exposed on the outer edge side of the mat body. Thereby, the hanging parts can be densely arranged on the outer edge side of the mat body, so that the deformation of the anti-scouring mat during suspension can be suppressed.

Effect of the Invention

[0021] According to the present invention, it is possible to provide a method for installing an anti-scouring mat that can be suspended in a stable posture while preventing damage to the anti-scouring mat and installed on the bottom of the water, a construction method for anti-scouring work, and an anti-scouring mat.

Brief Description of the Drawings

[0022] [Figure 1] (a) is a view of the anti-scouring mat 1 seen from above, and (b) is a cross-sectional view taken along the arrow A-A in (a). [Figure 2] (a) is a perspective view of the suspension balance 13, and (b) is a view of the suspension balance 13 seen from below. [Figure 3] (a) is a view showing the state where the hanging member 19 has come out of the hanging part 6 before and after lifting the anti-scouring mat 1 and after laying, and (b) is a view showing the state where the hanging member 19 has hooked the hanging part 6. [Figure 4] (a) is a diagram showing the state of the scour prevention mat 1 before it is suspended, and (b) is a diagram showing the state of the scour prevention mat 1 after it has been suspended. [Figure 5] (a) is a diagram showing the scour prevention mat 1 installed on the seabed, (b) is a diagram showing the foundation piles 32 driven in, and (c) is a diagram showing the scour prevention work 36 completed. [Figure 6] This diagram shows the scour prevention mat 1e suspended from the suspension beam 13b. [Figure 7] (a) is a diagram showing scour prevention mat 1a, (b) is a diagram showing scour prevention mat 1b, and (c) is a diagram showing scour prevention mat 1c. [Figure 8] (a) and (b) are diagrams showing examples where the distance 26-1 is greater than the length 26-2, (c) and (d) are diagrams showing examples where the distance 26-1 is less than the length 26-2, and (e) and (f) are diagrams showing examples where a mechanism for adjusting the distance 26-1 is provided. [Figure 9] (a) is a view of the scour prevention mat 1d from above, (b) is a view of the suspension beam 13a from above, and (c) is a diagram showing the state in which the suspension member 19a is hooked onto the suspension part 6. [Figure 10] (a) is a diagram showing the scour prevention mat 41 suspended from the suspension beam 47, and (b) and (c) are diagrams showing the scour prevention mat 41 installed on the seabed. [Figure 11] This diagram shows the state in which the scour prevention mat 41a is divided and installed on the ground 31. [Figure 12] (a) is a diagram showing the scour prevention mat 41b suspended from the suspension beam 47a, and (b) is a diagram showing the scour prevention mat 41c suspended from the suspension beam 47a. [Figure 13] (a) is a diagram showing an example in which the folded portion 39 is formed with slits 53 and 54, and (b) is a diagram showing an example in which the folded portion 39 is formed with edge-cutting material 55 and slits 54. [Figure 14] (a) is a view of the scour prevention mat 101 from above, and (b) is a diagram showing the scour prevention mat 101 suspended by the suspension beam 103. [Modes for carrying out the invention]

[0023] Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

[0024] [First Embodiment] Figure 1 shows a scour prevention mat 1. In the first embodiment, the configuration of the scour prevention mat 1, the method of installing the scour prevention mat 1 on the seabed, and the method of constructing a scour prevention structure formed on the seabed around an underwater structure using the scour prevention mat 1 will be described.

[0025] As shown in Figure 1(a), the scour prevention mat 1 consists of a mat body 2, a wire 8, a suspension part 6, a suspension part 7, etc. The mat body 2 is, for example, an impermeable asphalt (hereinafter referred to as As) mat. The mat body 2 has an outer shape that is approximately circular, with an approximately circular hole 3 formed in the center. The outer and inner shapes of the mat body may be polygonal. The wire 8 is embedded inside the mat body 2 so as to span the inner edge 5 side and the outer edge 4 side of the mat body 2. The suspension part 6 is provided at the end of the wire 8 on the outer edge 4 side of the mat body 2 and is exposed at predetermined intervals in the circumferential direction. The suspension part 7 is provided at the end of the wire 8 on the inner edge 5 side of the mat body 2 and is exposed at predetermined intervals in the circumferential direction. The suspension parts 6 and 7 are, for example, formed by creating an annular shape at the end of the wire 8. The mat body 2 has a plurality of outer edge holes 34 formed between the wires 8 near the outer edge 4. The multiple outer edge holes 34 are located, for example, on a double circle concentric with hole 3.

[0026] As shown in Figure 1(b), the mat body 2 has a reinforcing mesh 10 placed between the lower layer 9 and the upper layer 11 of As. The reinforcing mesh 10 is, for example, a glass fiber tape mesh. The wire 8 is placed between the lower layer 9 and the reinforcing mesh 10. Near the outer edge 4 and inner edge 5 of the mat body 2, reinforcing material 12 is placed between the wire 8 and the upper layer 11 of As. The reinforcing material 12 is placed perpendicular to the wire 8 in a plan view and is, for example, a steel strip.

[0027] The suspension parts 6 and 7 may be fittings or ropes attached to the ends of the wire 8. The reinforcing material 12 may be made of the same material as the wire 8, not limited to strip steel plates. The mat body 2 may be made of other mat-like materials or sheet-like materials, not limited to asphalt mats.

[0028] Figure 2 shows a suspension beam 13. The suspension beam 13 is used to lower the scour prevention mat 1 shown in Figure 1 to the bottom of the water. The suspension beam 13 consists of an outer frame 14 that suspends the suspension part 6 exposed on the outer edge 4 side of the mat body 2, an inner frame 15 that suspends the suspension part 7 exposed on the inner edge 5 side of the mat body 2, a connecting member 16 that connects the outer frame 14 and the inner frame 15, and wires 17 that suspend the outer frame 14 and the inner frame 15. The suspension beam 13 has an auto-release mechanism 22 that releases the connection after the suspension parts 6 and 7 have reached the bottom of the water.

[0029] The auto-release mechanism 22 is provided on both the outer frame 14 and the inner frame 15. The auto-release mechanism 22 consists of a movable member 18, a suspension member 19, a guide 20, etc. The movable member 18 is a member that moves circumferentially relative to the outer frame 14 and the inner frame 15. The movable member 18 is, for example, an annular round steel rod. The suspension member 19 is fixed to the movable member 18 at approximately the same interval as the suspension parts 6 and 7. The guide 20 is fixed to the outer frame 14 and the inner frame 15, and the movable member 18 is inserted through it.

[0030] Figures 3(a) and 3(b) show details of the auto-release mechanism 22, and are enlarged views of area B of the outer frame 14 shown in Figure 2(b). Figure 3(a) shows the state in which the connection with the lifting device has been released from the scour prevention mat 1 before lifting and after laying, while Figure 3(b) shows the state in which it has been connected to the lifting device. As shown in Figure 3, in addition to the moving member 18 and lifting member 19 described above, the auto-release mechanism 22 further includes a hydraulic jack 27, a connecting member 28, a partition plate 29, a partition plate 30, a sling 23, etc.

[0031] The hydraulic jack 27 is fixed at one end to the outer frame 14, and the other end is linked to the movable member 18 by a connecting member 28. The movable member 18 moves circumferentially within the guide 20 (Figure 2(b)) by extending and retracting the hydraulic jack 27. It is desirable to provide the hydraulic jack 27 at multiple locations on the outer frame 14 in order to allow the movable member 18 to rotate smoothly without eccentricity. Furthermore, it is desirable that the inner circumferential surface of the guide 20 be coated with fluororesin or to incorporate an annular ring made of a material with a low coefficient of friction such as fluororesin in order to improve the sliding of the movable member 18.

[0032] The suspension member 19 is, for example, a round steel bent at approximately 90 degrees. The partition plates 29 and 30 are fixed to the outer frame 14 at predetermined intervals, and a portion of the suspension member 19 (a portion approximately parallel to the movable member 18) can be inserted through them. The sling 23 has one end connected to the partition plate 29 and an annular portion 21 at the other end. The auto-release mechanism 22 provided on the inner frame 15 has a similar configuration.

[0033] The auto-release mechanism 22 operates the suspension member 19 based on the circumferential position of the movable member 18, allowing the suspension member 19 to switch between a state where it is hooked onto the suspension parts 6 and 7 via the sling 23 and the annular portion 21, and a state where it is detached from the suspension parts 6 and 7. For example, to put the suspension member 19 into the state where it is hooked onto the suspension part 6, as shown in Figure 3(b), the hydraulic jack 27 is retracted and moved to a predetermined position in the circumferential direction of the movable member 18. At this time, the suspension member 19 also moves together with the movable member 18, and the tip of the suspension member 19 passes through the partition plate 30 and protrudes to the right, and is inserted into or pressed against the partition plate 29. That is, the suspension member 19 is inserted into the partition plates 29 and 30. At this time, the annular portion 21 of the sling 23 that has been passed through the suspension part 6 is passed through the suspension member 19 between the partition plates 29 and 30, thereby connecting the suspension part 6 and the suspension member 19.

[0034] Furthermore, in order to remove the suspension member 19 from the suspension section 6, as shown in Figure 3(a), the hydraulic jack 27 is extended to move the circumferential position of the movable member 18, thereby removing the tip of the suspension member 19 from the partition plate 29. Even in this state, the suspension member 19 remains inserted into the partition plate 30. When one end of the suspension member 19 is removed from the partition plate 29, the annular portion 21 of the sling 23 is removed from the suspension member 19. Therefore, by raising the suspension beam 13, the sling 23 can be removed from the suspension section 6.

[0035] Figure 4 is a vertical cross-sectional view of the scour prevention mat 1 and the suspension beam 13. To suspend the scour prevention mat 1 with the suspension beam 13, the suspension beam 13 is positioned above the scour prevention mat 1 as shown in Figure 4(a). Then, as shown in Figure 4(b), the suspension part 6 is hooked to the suspension member 19 of the outer frame 14, and the suspension part 7 is hooked to the suspension member 19 of the inner frame 15 using the sling 23. The radial distance 26-1 between the outer frame 14 and the inner frame 15 of the suspension beam 13 is approximately equal to the radial length 26-2 from the inner circumference 25 to the outer circumference 24 of the scour prevention mat 1 (the length from the end of the suspension part 7 to the end of the suspension part 6). Therefore, the scour prevention mat 1 is suspended from the suspension beam 13 in a moderately flexed state.

[0036] When the scour prevention mat 1 is suspended, the force acting on the suspension parts 6 and 7 is transmitted to the wire 8, and the wire 8 applies a localized lifting force to the mat body 2. The reinforcing material 12 prevents damage to the mat body 2 due to this localized lifting force. In addition, the reinforcing net 10 prevents cracking due to bending of the mat body 2 and prevents the wire from coming loose.

[0037] Figure 5 shows the construction method of the scour prevention structure 36. Figure 5 shows the vertical cross-section at each stage of construction. The scour prevention structure 36 is formed in the seabed ground 31 surrounding the foundation piles 32, which are underwater structures.

[0038] To construct the scour prevention work 36, first, using the crane function of a crane ship or the like, the scour prevention mat 1 is suspended from the lifting beam 13 as shown in Figure 4(b), and lowered to the seabed and allowed to settle. Then, the moving members 18 of the auto-release mechanism 22 of the outer frame 14 and inner frame 15 of the lifting beam 13 are moved in the circumferential direction as shown by arrow C in Figure 2(b). This, along with the rising of the lifting beam 13, causes the slings 23 connected to the multiple lifting parts 6 suspended from the outer frame 14 to detach from the lifting member 19 all at once, and the slings 23 connected to the multiple lifting parts 7 suspended from the inner frame 15 to detach from the lifting member 19 all at once. In other words, the lifting parts 6 and 7 are released from the state in which they are suspended by the lifting member 19. After that, the lifting beam 13 is recovered to the surface of the water along with the slings 23, and the installation of the scour prevention mat 1 on the seabed ground 31 is completed as shown in Figure 5(a).

[0039] Next, using a self-lifting work platform (SEP) or the like, pile-shaped foundation piles 32 are driven through the holes 3 in the scour prevention mat 1, as shown in Figure 5(b). At this time, the holes 3 can be used as markers for the driving positions of the foundation piles 32, but if three or more floats 37 with short ropes for markers are attached to the edge of the holes 3, as shown in Figure 5(a), the driving positions of the foundation piles 32 can be detected more clearly using lights and visible light cameras or acoustic cameras. Alternatively, two or more transponders for underwater positioning devices may be attached to the edge of the holes 3. After the foundation piles 32 have been driven, a filter unit 33 is installed above the gap between the inner edge 5 of the mat body 2 and the foundation piles 32, as shown in Figure 5(c), to complete the construction of the scour prevention work 36. The filter unit 33 is a bag-shaped mesh body filled with stone or crushed stone, and it is preferable to arrange adjacent filter units 33 alternately on top of each other.

[0040] In the scour prevention work 36, sand is drawn out from the ground 31 through multiple outer edge holes 34 (Figure 1(a)) formed near the outer edge 4 of the scour prevention mat 1. This promotes the bending of the outer edge 4 of the scour prevention mat 1 into the ground 31, eliminating gaps through which water flow can penetrate to the underside of the scour prevention mat 1 and preventing the edges of the scour prevention mat 1 from being lifted by water flow.

[0041] As described above, in the first embodiment, the scour prevention mat 1 has multiple suspension parts 6 exposed at predetermined intervals in the circumferential direction on the outer edge 4 side of the mat body 2, which has a hole 3 formed in the center, and suspension parts 7 exposed at predetermined intervals in the circumferential direction on the inner edge 5 side. The scour prevention mat 1 is lowered to the bottom of the water using a suspension beam 13 consisting of an outer frame 14 and an inner frame 15. By suspending the outer edge 4 and inner edge 5 with the suspension beam 13 in this way, the spacing of the suspension devices can be reduced, and the scour prevention mat 1 can be lowered while ensuring the integrity of the mat body 2. For example, if a large number of suspension fittings are provided inside the mat as in the conventional method, the mat is prone to swaying horizontally due to water pressure, waves, or water currents on the bottom surface. However, by providing the suspension parts 6 and 7 at predetermined intervals in the circumferential direction of the mat body 2 and suspending it with the suspension beam 13, the scour prevention mat 1 can be lowered into the water in a stable position, making it easier to position it on the ground 31 at the bottom of the water.

[0042] Furthermore, the suspension beam 13 has an auto-release mechanism 22 that allows the suspension sections 6 and 7 to be released simultaneously from their suspended state. This allows the suspension sections 6 and 7 to be released quickly and reliably by remote operation without the need for divers, thereby improving safety during construction.

[0043] In the first embodiment of the scour prevention mat 1, a wire 8 is embedded inside the mat body 2, spanning both the inner edge 5 and the outer edge 4, and suspension parts 6 and 7 are provided at both ends of the wire 8. This allows the load borne by the suspension parts 6 and 7 when the scour prevention mat 1 is suspended to be transmitted to the wire 8, preventing the mat body 2 from tearing.

[0044] According to the construction method of the scour prevention work 36 of the first embodiment, the foundation piles 32 are driven using the holes 3 of the scour prevention mat 1 as guides, so the scour prevention work 36 can be constructed efficiently.

[0045] The auto-release mechanism 22 provided on the suspension beam 13 is not limited to the one described above. For example, the method of hooking the suspension parts 6 and 7 onto the suspension member 19 is not limited to the one shown in Figure 3. Alternatively, both ends of a sling or the like can be passed through the suspension member 19 and hooked onto it, and the sling or the like can be left on the seabed after the suspension beam 13 is retrieved. Alternatively, the suspension parts 6 and 7 can be passed directly through the suspension member 19. The movable member 18 can be any member that moves circumferentially relative to the outer frame 14 or inner frame 15, and may be divided into arcs rather than being a closed annular shape. The hydraulic jack 27 can be any movable or extendable mechanism for remote operation from the water surface for the purpose of eliminating the need for divers, and may be a water pressure jack or the like.

[0046] The suspension beam used in the first embodiment is not limited to the one described above. Figure 6 shows an example using another suspension beam 13b. In the scour prevention mat 1e shown in Figure 6, a suspension part 58 is provided between the suspension part 6 and the suspension part 7 of the mat body 2. The suspension part 58 is preferably anchored to an internal wire 8 and is exposed on the upper side of the mat body 2. In the suspension beam 13b, an intermediate frame 57 is provided between the outer frame 14 and the inner frame 15. The intermediate frame 57 is provided with an auto-release mechanism 22 (Figure 2(b)), similar to the outer frame 14 and the inner frame 15. Note that there may be multiple suspension parts 58 provided in the middle.

[0047] In the example shown in Figure 6, the suspension members 19 of the auto-release mechanism 22, provided on the outer frame 14, middle frame 57, and inner frame 15 of the suspension beam 13b, suspend the suspension parts 6, 58, and 7 of the scour prevention mat 1e, respectively. By providing suspension parts at three points in the radial direction of the scour prevention mat 1e in this way, the deflection of the mat body 2 can be suppressed. Furthermore, when the mat is further enlarged to accommodate the further enlargement of the foundation piles, it may be desirable to have multiple suspension parts 58 or annular middle frames instead of just one.

[0048] In the scour prevention mat 1 described in the first embodiment, the mat body 2, suspension parts 6 and 7, and wire 8 are essential. However, the scour prevention mat used in the scour prevention mat installation method and the scour prevention construction method only needs to have the mat body 2 and suspension parts 6 and 7, and the wire 8 is not essential. In the scour prevention mat installation method and the scour prevention construction method described in the first embodiment, the scour prevention mat of the second embodiment, which will be described later, may also be used.

[0049] Hereinafter, another example of the present invention will be described as the second to seventh embodiments. The second to seventh embodiments will be described in terms of how they differ from the embodiments described so far, and similar components will be denoted by the same reference numerals in the figures, etc., and their descriptions will be omitted. Furthermore, the components described in each embodiment can be combined as needed.

[0050] [Second Embodiment] Figure 7 shows scour prevention mats 1a, 1b, and 1c according to the second embodiment. The scour prevention mats 1a, 1b, and 1c of the second embodiment require a wire embedded inside the mat body 2 so as to span the inner edge 5 side and the outer edge 4 side of the mat body 2.

[0051] In the scour prevention mat 1 shown in Figure 1, if outer edge holes 34 are provided in the mat body 2, the strength near the outer edge 4 of the mat body 2 decreases, increasing the likelihood of cracking. Also, if the circumferential spacing of the suspension parts 6 exposed on the outer edge 4 side of the mat body 2 is large, the mat body 2 will bend significantly when suspended, increasing the likelihood of residual deformation and cracking. The scour prevention mats 1a, 1b, and 1c shown in Figure 7 address these concerns.

[0052] In the scour prevention mat 1a shown in Figure 7(a), annular reinforcing bars or reinforcing wires 35 are embedded in the mat body 2 on the inner side of the outer edge hole 34 formed near the outer edge 4 of the mat body 2. The reinforcing wires 35 may be arranged in one or more layers in a plan view, or placed outside the outer edge hole 34. By embedding the reinforcing wires 35 to complement the crack prevention function of the reinforcing mesh 10 (Figure 1(b)), cracks near the outer edge 4 of the mat body 2 can be prevented even when the outer edge hole 34 is provided. The reinforcing wires 35 are also effective in preventing cracks when the spacing between the wires 8 is wide.

[0053] In the scour prevention mat 1b shown in Figure 7(b), the wire 8a is arranged in a V-shape, with a suspension part 7 provided at one end on the inner edge 5 side of the wire 8a, and suspension parts 6 provided at two ends on the outer edge 4 side. In the scour prevention mat 1c shown in Figure 7(c), the wire 8b is arranged in a Y-shape, with a suspension part 7 provided at one end on the inner edge 5 side of the wire 8b, and suspension parts 6 provided at two ends on the outer edge 4 side. In scour prevention mats 1b and 1c, the circumferential spacing between the suspension parts 6 exposed on the outer edge 4 side of the mat body 2 is reduced, which suppresses the bending of the mat body 2 when suspended, preventing residual deformation and cracking.

[0054] In the scour prevention mats 1a, 1b, and 1c of the second embodiment, similar to the scour prevention mat 1 of the first embodiment, suspension parts 6 and 7 are provided at both ends of wires 8, 8a, and 8b that are embedded inside the mat body 2 so as to span the inner edge 5 side and the outer edge 4 side. This transmits the load borne by the suspension parts 6 and 7 to the wires 8, 8a, and 8b, thereby preventing the mat body 2 from tearing.

[0055] [Third Embodiment] The method for installing the scour prevention mat in the third embodiment differs from the method for installing the scour prevention mat in the first embodiment in that the distance 26-1 between the outer frame 14 and the inner frame 15 of the suspension beam 13 is not approximately equal to the length 26-2 from the inner circumference 25 to the outer circumference 24 of the scour prevention mat 1.

[0056] When the scour prevention mat 1 is suspended from the suspension beam 13 and installed on the seabed, if the deflection of the suspended scour prevention mat 1 is too large, concerns arise regarding the integrity of the mat body 2 due to residual deformation and cracking. Conversely, if the deflection of the suspended scour prevention mat 1 is too small, the mat body 2 will experience significant water resistance during descent underwater, making it prone to swaying, which can cause delays in reaching the bottom and make positioning difficult. Therefore, it is desirable to set the relationship between the distance 26-1 between the outer frame 14 and the inner frame 15 of the suspension beam 13 and the length 26-2 from the inner circumference 25 to the outer circumference 24 of the scour prevention mat 1, taking into consideration the allowable range of deflection of the mat body 2.

[0057] Figure 8 is a vertical cross-sectional view of the scour prevention mat 1 and the suspension beam. Each figure in Figure 8 corresponds to the left half of each figure in Figure 4. In the example shown in Figure 8(a), the distance 26-1 between the outer frame 14 and the inner frame 15 is greater than the length 26-2 from the inner circumference 25 to the outer circumference 24. In this case, as shown in Figure 8(b), the deflection of the scour prevention mat 1 when suspended is reduced, so the twisting and torsion of the mat body 2 is reduced, and the integrity of the mat body 2 can be ensured.

[0058] In the example shown in Figure 8(c), the distance 26-1 between the outer frame 14 and the inner frame 15 is smaller than the length 26-2 from the inner circumference 25 to the outer circumference 24. In this case, as shown in Figure 8(d), the deflection of the scour prevention mat 1 increases when suspended, allowing the water resistance on the lower surface of the mat body 2 to be released in the direction of the arrow during underwater descent, thus shortening construction time and making positioning easier.

[0059] Thus, in the installation method of the scour prevention mat 1 according to the third embodiment, the relationship between the radial length 26-2 from the inner circumference 25 to the outer circumference 24 of the scour prevention mat 1 and the radial distance 26-1 between the outer frame 14 and inner frame 15 of the suspension beam is appropriately set. This prevents damage to the mat body 2 during construction and improves workability.

[0060] Furthermore, in the example shown in Figures 8(e) and 8(f), the outer frame 14b and inner frame 15b of the suspension beam are polygonal, and a rotation mechanism such as a lever 38 is provided on the outer frame 14b and inner frame 15b in addition to the auto-release mechanism. By adjusting the angle of the suspension member 19b with this rotation mechanism, the radial distance 26-1 between the suspension member 19 of the outer frame 14b and the suspension member 19b of the inner frame 15b can be adjusted. In addition, by pre-setting the radial distance 26-1 determined by the degree of rotation of the rotation mechanism, it becomes possible to adjust the tension and deflection of the scour prevention mat 1 when it is suspended.

[0061] [Fourth Embodiment] Figure 9 shows the scour prevention mat 1d and the suspension beam 13a. The method of installing the scour prevention mat 1d on the seabed in the fourth embodiment differs from the method of installing the scour prevention mat 1 on the seabed in the first embodiment in that the outer shape of the scour prevention mat 1d and the suspension beam 13a are polygonal in plan view.

[0062] As shown in Figure 9(a), the mat body 2a of the scour prevention mat 1d is, for example, octagonal in shape. The scour prevention mat 1d has V-shaped wires 8a arranged in the same way as the scour prevention mat 1b shown in Figure 7(b), but the arrangement of the wires is not limited to this.

[0063] As shown in Figure 9(b), the suspension beam 13a has an outer frame 14a and an inner frame 15a that are octagonal in shape, similar to the mat body 2a. The suspension beam 13a has an auto-release mechanism 22a that releases the suspension parts 6 and 7 from the suspended state.

[0064] The auto-release mechanism 22a is provided on both the outer frame 14a and the inner frame 15a. The auto-release mechanism 22a consists of a movable member 18a, a suspension member 19a, a pulley 20a, etc. The movable member 18a is a member that moves in the circumferential direction relative to the outer frame 14a and the inner frame 15a. The movable member 18a is, for example, a wire. The suspension member 19a is arranged at approximately the same interval as the suspension parts 6 and 7. A pulley 20a is fixed near the corners of the outer frame 14a and the inner frame 15a, and the movable member 18a is hooked onto the pulley 20a.

[0065] The movable member 18a moves circumferentially along the pulley 20a by pulling one end upward as shown by arrow E. The auto-release mechanism 22a operates the suspension member 19a together with the movable member 18a, and can switch between a state in which the suspension member 19a is hooked onto the suspension parts 6 and 7 and a state in which it is detached from the suspension parts 6 and 7, depending on the position of the movable member 18a.

[0066] Figure 9(c) is a diagram showing details of the auto-release mechanism 22a, and is an enlarged view of the area F of the outer frame 14 shown in Figure 9(b). The suspension member 19a consists of, for example, a pin 191 with a head and a sub-wire 192, and the head of the pin 191 is connected to the movable member 18a via the sub-wire 192. The movable member 18a is passed through a guide 20 fixed to the outer frame 14 or inner frame 15. Although not shown in the diagram, the sub-wire 192 portion may also be replaced with a steel lever or the like, and the suspension member 19a may be released by rotating or moving the lever.

[0067] To get the suspension member 19a hooked onto the suspension section 6, the pin 191 of the suspension member 19a is inserted into the partition plates 29 and 30. At this time, the annular portion 21 of the sling 23, which is passed through the suspension section 6, is passed through the suspension member 19a between the partition plates 29 and 30, thereby connecting the suspension section 6 and the suspension member 19a. To get the suspension member 19a detached from the suspension section 6, the movable member 18a is moved to the left in Figure 9(c) by pulling it up from the water or by using the lifting force to inflate a balloon by blowing air from the water to make it float, thereby removing the pin 191 from the partition plates 29 and 30. At this time, the annular portion 21 of the sling 23 is removed from the pin 191, so the sling 23 can be removed from the suspension section 6 by raising the suspension beam 13a.

[0068] In the installation method of the scour prevention mat 1d of the fourth embodiment, the scour prevention mat 1d, in which multiple suspension parts 6 and 7 are exposed, is lowered by a suspension beam 13a consisting of an outer frame 14a and an inner frame 15a, and an auto-release mechanism 22a is provided that allows each part to be released collectively once the scour prevention mat 1d has reached the bottom, thereby achieving the same effect as the installation method of the scour prevention mat 1 of the first embodiment.

[0069] Furthermore, the scour prevention mat 1d, the outer frame 14a and inner frame 15a of the suspension beam 13a may be polygonal in shape other than octagonal. The auto-release mechanism of the suspension beam 13a is not particularly limited, as in the first embodiment.

[0070] [Fifth Embodiment] Figure 10 shows a scour prevention mat 41 and its installation method according to the fifth embodiment. In the fifth embodiment, the scour prevention mat 41 shown in Figure 10 is installed on the seabed ground 31.

[0071] As shown in Figure 10(a), the scour prevention mat 41 has a rectangular mat body 42 with a hole in the center. The mat body 42 has suspension sections 43 exposed at predetermined intervals along one side. The mat body 42 has multiple bent sections 39 parallel to the side on which the suspension sections 43 are provided. The mat body 42 has reinforcing material 44 embedded near the outer edge and reinforcing material 45 embedded near the inner edge. The suspension beam 47 is, for example, a rod-shaped steel material with the required rigidity. The suspension beam 47 suspends the suspension sections 43 of the scour prevention mat 41.

[0072] To install the scouring prevention mat 41 on the seabed 31, the scouring prevention mat 41 is suspended vertically from the suspension beam 47 as shown in Figure 10(a), and then lowered into the water using the suspension beam 47 as shown in Figure 10(b). Once the lower end of the scouring prevention mat 41 touches the seabed 31, the suspension beam 47 is moved horizontally as shown in Figure 10(c) to bend the scouring prevention mat 41 and install it along the seabed 31. Once the entire surface of the scouring prevention mat 41 is installed on the seabed 31, the suspension part 43 is released from the suspension beam 47 using an auto-release mechanism or the like (not shown).

[0073] In the fifth embodiment, since the mat body 42 has a bent portion 39, local bending does not occur in areas other than the bent portion 39. By using a scour prevention mat 41 having a bent portion 39, the scour prevention mat 41 suspended vertically can be installed on the seabed ground 31 while bending it.

[0074] In the fifth embodiment, a scour prevention mat 41 with holes formed in the mat body 42 is shown, but the holes are not essential. Figure 11 shows the scour prevention mat 41a installed on the ground 31. In the scour prevention mat 41a shown in Figure 11, no holes are formed in the center of the mat body 42a, but suspension parts 43 are exposed at predetermined intervals along one side, and multiple bent lines 39 are formed parallel to the side on which the suspension parts 43 are provided. The scour prevention mat 41a can be installed on the ground 31 in the same way as the scour prevention mat 41 using a suspension beam 47.

[0075] To construct a scour prevention structure using scour prevention mats 41a, first, the first scour prevention mat 41a-1 is placed on the bottom ground 31. Next, the second scour prevention mat 41a-2 is placed parallel to the first scour prevention mat 41a-1, with a gap between them. Then, the third scour prevention mat 41a-3 is placed so as to overlap one end of the first two scour prevention mats 41a-1 and 41a-2, and the fourth scour prevention mat 41a-4 is placed so as to overlap the other end. The foundation piles 32 may be driven in before or after the scour prevention mats 41a are laid.

[0076] [Sixth Embodiment] Figure 12 shows a method for installing scour prevention mats on the seabed using structural steel 49 as a weight. In the sixth embodiment, scour prevention mats 41b and 41c are installed on the seabed using structural steel 49 as a weight.

[0077] In the examples shown in Figures 12(a) and 12(b), the same suspension beam 47a is used in both cases. The suspension beam 47a is made of, for example, rod-shaped steel materials arranged in a grid pattern, and auto-release slings 48 are provided on the underside of two opposing sides. The slings 48 are placed, for example, at two locations near both ends on each side of the suspension beam 47a.

[0078] The scour prevention mat 41b used in the example shown in Figure 12(a) is a scour prevention mat 41 shown in Figure 10, with suspension parts 43 provided on two opposing sides of the mat body 42. To install the scour prevention mat 41b on the seabed, as shown in Figure 12(a), the suspension parts 43 of the scour prevention mat 41b are attached to a structural steel 49, the structural steel 49 is attached to a suspension beam 47a with a sling 48, and the scour prevention mat 41b is suspended from the suspension beam 47a. Once the scour prevention mat 41b, which has been lowered into the water, has reached the bottom, an auto-release mechanism (not shown) is used to release the sling 48 from the suspension beam 47a. The structural steel 49 is placed on top of both ends of the scour prevention mat 41b and functions as a weight.

[0079] The scour prevention mat 41c used in the example shown in Figure 12(b) is a scour prevention mat 41 shown in Figure 10, with structural steel 49 attached to two opposing sides of the mat body 42. To install the scour prevention mat 41b on the seabed, as shown in Figure 12(b), the structural steel 49 of the scour prevention mat 41c is attached to a suspension beam 47a with a sling 48, and the scour prevention mat 41c is suspended horizontally from the suspension beam 47a. Once the scour prevention mat 41c, which has been lowered into the water, has reached the bottom, the sling 48 is released from the suspension beam 47a using an auto-release mechanism (not shown). The structural steel 49 functions as a weight for the scour prevention mat 41c. Note that the structural steel 49 may not be a single piece on one side, but may be divided.

[0080] In the sixth embodiment, since the mat body 42 has a bent section 39, when it is suspended by the suspension beam 47a, local bending does not occur in areas other than the bent section 39, and the scour prevention mats 41b and 41c can be lowered and installed on the seabed in a flexed state. In addition, by placing the shaped steel 49 as weights on two sides of the scour prevention mats 41b and 41c installed on the seabed, the mat body 42 can be prevented from being curled up by the water flow.

[0081] [Seventh Embodiment] Figure 13 is a cross-sectional view of the scour prevention mat 41. Figure 13 shows a cross-section of the scour prevention mat 41 in a direction perpendicular to the extension direction of the folded portion 39. In the seventh embodiment, a method for forming the folded portion 39 of the scour prevention mat 41 will be described.

[0082] The mat body 42 shown in Figures 13(a) and 13(b) is formed by pouring the lower layer 51 of As, installing wires 56 and reinforcing nets 50 on the upper surface of the lower layer 51 of As, and then pouring the upper layer 52 of As.

[0083] In the example shown in Figure 13(a), the broken line section 39 is formed by slits 53 and 54. Slit 53 is formed simultaneously with the removal of the mat body 42 by fixing a convex separation frame to the bottom frame of the formwork when the lower layer 51 of As is poured. Slit 54 is formed by placing a rod-shaped separation frame on the upper surface of the reinforcing mesh 50 when the upper layer 52 of As is poured, and removing the separation frame from the upper layer 52 of As either before or after the removal of the mat body 42.

[0084] In the example shown in Figure 13(b), the folded section 39 is formed by an edge-cutting material 55 and a slit 54. The edge-cutting material 55 is placed on the release paper that serves as a formwork at the bottom when the As lower layer 51 is cast. The edge-cutting material 55 can be, for example, heat-resistant cardboard, plated steel, stainless steel, or aluminum. In order to ensure anchoring to the As lower layer 51, it is desirable that the edge-cutting material 55 has an L-shaped cross-section and anchoring protrusions at the inner corners. The slit 54 is formed in the same manner as in the example shown in Figure 13(a).

[0085] Note that the cross-sectional shapes of slits 53 and 54 are not limited to those shown in Figure 13. For example, the rod-shaped separation frame forming slit 54 may have a trapezoidal cross-section with a lower base shorter than the upper base to facilitate removal from the upper As layer 52. Also, at the location of the broken line section 39, a suction prevention sheet (not shown) is placed to prevent sand from being sucked upward from slits 53 and 54.

[0086] Thus, in the seventh embodiment, by providing slits 53, 54 and edge-cutting material 55 in the mat body 42, a scour prevention mat 41 that can be bent at the fold line portion 39 can be manufactured.

[0087] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but the present invention is not limited to these examples. It will be obvious to those skilled in the art that various modifications or alterations can be conceived within the scope of the technical idea disclosed herein, and these will naturally also fall within the technical scope of the present invention.

[0088] For example, the scour prevention mat of the present invention shown in Figures 1(a), 7, and 9(a), and the installation method of the scour prevention mat described in the first, third, and fourth embodiments can also be applied when the scour prevention mat is laid after the foundation piles 32 are driven in, and the filter unit 33 is installed to carry out scour prevention work. In the installation method of the scour prevention mat of the present invention, the suspension beam may be released from the state in which it is suspending the suspension part by diver work, and a lever that applies the principle of leverage may be used for diver operation. [Explanation of Symbols]

[0089] 1, 1a, 1b, 1c, 1d, 41, 41a, 41a-1, 41a-2, 41a-3, 41a-4, 41b, 41c... Scrap prevention mats 2, 2a, 42, 42a... Mat body 3……hole 4...Outer edge 5… Common-law marriage 6, 7, 43, 58... Suspension section 8, 8a, 8b, 17, 56… wire 9, 51……As lower layer 10, 50... Reinforcement net 11, 52……As upper layer 12, 44, 45... Reinforcement materials 13, 13a, 13b, 47, 47a... Hanging balance 14, 14a, 14b... Outer frame 15, 15a, 15b... inner frame 16… Connecting material 18, 18a... Movable member 19, 19a, 19b... Suspension members 20... Guide 20a... Pulley 21... Ring section 22, 22a... Auto-release mechanism 23, 48... Sling 24...Outer perimeter 25……Inner circumference 26-1.......distance 26-2... Length 27... Hydraulic jack 28… Connecting member 29, 30... Partition board 31……ground 32… Foundation piles 33………Filter Unit 34... outer pore 35… Reinforcement wire 36...Scouring prevention work 37... Float 38... Lever 39... Broken line section 49……Shaped steel 53, 54... Slit 55… Edge-cutting material 57...Middle frame

Claims

1. A method for installing erosion prevention mats on the bottom of a body of water, Scrap prevention mats are The mat body has a hole formed in the center, On the outer and inner edges of the mat body, there are multiple suspension parts exposed at predetermined intervals in the circumferential direction, It is equipped with, A method for installing a scour prevention mat, characterized by lowering the scour prevention mat to the bottom of the water using a suspension beam comprising an outer frame for suspending the suspension portion exposed on the outer edge side of the mat body and an inner frame for suspending the suspension portion exposed on the inner edge side of the mat body.

2. The method for installing a scour prevention mat according to claim 1, characterized in that the aforementioned suspension beam has an auto-release mechanism that releases the suspension part after it has settled on the seabed.

3. The auto-release mechanism has a movable member that moves circumferentially relative to the outer frame and the inner frame, and operates a suspension member that suspends the suspension part depending on the circumferential position of the movable member, and can switch between a state in which the suspension member is hooked onto the suspension part and a state in which it is detached from the suspension part. The method for installing a scour prevention mat according to claim 2, characterized in that by moving the movable member in the circumferential direction, the plurality of suspension parts suspended from the outer frame and the plurality of suspension parts suspended from the inner frame can be released collectively.

4. A wire is embedded inside the mat body so as to span the inner and outer edges of the mat body. The method for installing a scour prevention mat according to claim 1, characterized in that the suspension portion is provided at both ends of the wire and is exposed on the inner and outer edges of the mat body.

5. The method for installing a scour prevention mat according to claim 4, characterized in that the wire has one suspension portion at one end that is exposed on the inner edge side of the mat body, and a plurality of suspension portions at the other end that are exposed on the outer edge side of the mat body.

6. The method for installing a scour prevention mat according to claim 1, characterized in that the radial distance between the outer frame and the inner frame of the suspension beam is large compared to the radial length from the inner circumference to the outer circumference of the scour prevention mat.

7. The method for installing a scour prevention mat according to claim 1, characterized in that the radial distance between the outer frame and the inner frame of the suspension beam is small compared to the radial length from the inner circumference to the outer circumference of the scour prevention mat.

8. A method for constructing scour prevention structures formed on the seabed around underwater structures, Step a of installing a scour prevention mat on the bottom of a body of water, the mat having a hole formed in the center and a plurality of suspension parts exposed at predetermined intervals in the circumferential direction on the outer edge and inner edge of the mat body, Step b involves driving a pile-shaped underwater structure so as to penetrate the holes in the aforementioned scouring prevention mat, Step c involves installing a filter unit, in which a mesh body is filled with stone or crushed stone, above the gap between the inner edge of the mat body and the underwater structure. It is equipped with, A method for constructing a scour prevention structure, characterized in that, in step a, the scour prevention mat is lowered to the bottom of the water using a suspension beam consisting of an outer frame for suspending the suspension portion exposed on the outer edge side of the mat body and an inner frame for suspending the suspension portion exposed on the inner edge side of the mat body.

9. A scour prevention mat installed on the seabed around an underwater structure, The mat body has a hole formed in the center, A wire is embedded inside the mat body so as to span the inner and outer edges of the mat body, Multiple suspension parts are provided at both ends of the wire, and are exposed at predetermined intervals in the circumferential direction on the outer and inner edges of the mat body, A scour prevention mat characterized by having the following features.

10. The scour prevention mat according to claim 9, characterized in that the wire has one suspension portion at one end that is exposed on the inner edge side of the mat body, and a plurality of suspension portions at the other end that are exposed on the outer edge side of the mat body.

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