Scour prevention structure and its construction method

Abstract

To provide an anti-scouring structure and a construction method thereof capable of suppressing suction and leakage of gravel from the bottom and surroundings of a protective block and stabilizing the installation state of multiple protective blocks.SOLUTION: In an anti-scouring structure, multiple first mats (16) are laid on the riverbed (SB) to prevent the suction of gravel from the riverbed (SB). Each first mat (16) is filled inside with a filling material (18). On the multiple first mats (16), bed protection blocks (22) are laid as multiple protective blocks to protect the river bed (SB), and adjacent bed protection blocks (22) are flexibly connected to each other.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a scour prevention structure for preventing scouring of a riverbed, a waterway bottom, a still water pond, or the seabed, and a construction method thereof. [Background technology]

[0002] Many agricultural intake weirs are installed in the mid- to upper reaches of rivers, for example, to facilitate water supply to farm fields. Furthermore, downstream of the weir, the riverbed is often excavated for flood control or aggregate extraction purposes, causing riverbed lowering upstream. When the riverbed lowering reaches the downstream side of the weir, piping and scouring occur, sucking out sand and gravel from the weir bottom and causing the concrete floor (apron) downstream of the weir to collapse, leading to damage to the weir.

[0003] Generally, downstream of a structure such as a weir, a plurality of bed protection blocks are laid as a plurality of protection blocks for protecting the riverbed. The bed protection blocks are arranged in multiple rows along the river width direction. Adjacent bed protection blocks may be flexibly connected by connecting members such as shackles to prevent them from scattering due to flowing water, etc. Alternatively, adjacent bed protection blocks may be configured to interlock with each other so that they are flexibly connected. In addition, the bed protection blocks may be made larger or heavier to prevent them from scattering.

[0004] Incidentally, Patent Document 1 shows a prior art document related to the present invention. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6871583 Summary of the Invention [Problem to be solved by the invention]

[0006] There are gaps of about 5 cm between adjacent protection blocks. If the discharge flow rate from the weir is high, the sand and gravel at the bottom of the blocks is sucked out through the gaps, causing the protection blocks to sink. If the flow begins to fall onto the protection blocks due to the sinking, the suction will progress further, creating a large scour hole immediately downstream of the weir.

[0007] A similar phenomenon occurs immediately downstream of the bed protection blocks (bed protection works) when the water level drops due to lowering of the riverbed downstream of the weir. In this case, the lowered water level downstream of the bed protection works increases the flow velocity, expanding scouring immediately downstream of the bed protection works, causing sand and gravel at the bottom of the bed protection works to leak into scour holes, which then cause the bed protection works to bend (become uneven) and tilt (tilt). The expansion of the scour holes makes the bending and tilting even more pronounced. The gaps between the bed protection blocks widen depending on the angle of bending, making it easier for the sand and gravel at the bottom of the bed protection blocks and surrounding areas to be sucked out. In addition, the tilting increases the flow velocity above the bed protection blocks, further exacerbating the suction. In this way, the tilting spreads to the upstream part of the bed protection works and, when it reaches immediately downstream of the weir, also increases the flow velocity immediately downstream of the weir. This causes scour holes to appear and expand immediately downstream of the weir. If the expansion of the scour hole causes a downflow immediately downstream of the weir, the scour hole will expand further, and combined with the settlement of the bed protection block due to the expansion of scouring immediately downstream of the bed protection work, the lowering of the riverbed downstream of the weir will eventually spread to immediately downstream of the weir.

[0008] The expansion of the scour hole immediately downstream of the weir and the lowering of the riverbed immediately downstream of the weir (subsidence of the bed protection block) as described above can cause piping at the bottom of the weir and leakage of sand and gravel from the bottom of the apron, ultimately leading to damage to the weir.

[0009] Connecting the protection blocks together does not prevent sand and gravel from being sucked out of the gaps between them when the riverbed downstream lowers and the flow velocity increases, so it does not prevent scouring immediately downstream of the weir or damage to the weir. On the other hand, even if the protection blocks are made larger or heavier, they cannot prevent the expansion of scouring immediately downstream of the protection works due to the lowering of the riverbed downstream, and therefore cannot prevent the protection blocks from rolling or being washed away into the scour hole immediately downstream of the protection works, which ultimately leads to the scattering of the protection blocks and scouring immediately downstream of the weir. In other words, connecting the protection blocks together or making them larger or heavier only serves to somewhat delay scouring and riverbed lowering immediately downstream of the weir. Furthermore, adding more protection blocks to replace lost protection blocks simply results in more blocks being washed away and has little effect.

[0010] Possible measures to prevent damage to structures such as weirs include installing river crossing structures such as ground sills downstream of the weir to restore the tilted bed protection blocks to their original position, or injecting fill concrete between adjacent bed protection blocks. The former method requires the construction of a new river crossing structure similar to the weir, which is costly. Furthermore, scouring and riverbed lowering problems also occur immediately downstream of the ground sills, necessitating the repeated construction of additional ground sills. The latter method eliminates the flexibility of adjacent bed protection blocks, preventing them from adapting to changes in the riverbed topography. Scouring immediately downstream of the bed protection structure can damage the structure and wash away the bed protection blocks from its downstream end, ultimately causing scouring immediately downstream of the weir. Alternatively, to prevent scouring immediately downstream of the weir, frequent backfilling of scour holes immediately downstream of the bed protection structure and repairing the bed protection structure are required, which also increases costs.

[0011] In other words, in response to the drop in downstream water levels and increased flow velocity on the bed protection blocks caused by the lowering of the riverbed downstream of the weir, it is not easy or costly to prevent scouring and riverbed lowering immediately downstream of the apron.

[0012] The above-mentioned scouring problems occur not only in scour prevention structures installed downstream of structures such as weirs, but also in scour prevention structures installed upstream of structures if the flow velocity is fast. They can also occur if the flow velocity is faster than expected when designing a bed protection structure, even if the downstream riverbed has not lowered. They can also occur in scour prevention structures installed on the bottom of a waterway, still water pond, or seabed, regardless of whether they are in a river.

[0013] Therefore, one aspect of the present invention aims to prevent scouring and deterioration of the riverbed and other surrounding areas upstream and downstream of the structure by suppressing the suction and leakage of sand and gravel from the bottom and surrounding areas of protective blocks, etc., and stabilizing the installation state of multiple protective blocks, etc. [Means for solving the problem]

[0014] In order to solve the above-mentioned problems, one embodiment of the present invention provides a scouring prevention structure for preventing scouring of a riverbed, a waterway bottom, a still water pond, or the seabed, and comprises a plurality of first mats that are laid on the riverbed, waterway bottom, still water pond, or seabed and filled with filler material to prevent the suction of sand and gravel from the riverbed, waterway bottom, still water pond, or seabed, and a plurality of protection blocks that are laid on top of the plurality of first mats to protect the riverbed, waterway bottom, still water pond, or seabed and the first mats, and adjacent protection blocks are flexibly connected to each other.

[0015] In order to solve the above-mentioned problems, a construction method for a scour prevention structure according to one embodiment of the present invention includes a filling step of filling a plurality of first mats with filler material; a first laying step of laying the plurality of first mats filled with the filler material on a riverbed, a channel bottom, a still water pond, or the seabed; and a second laying step of laying a plurality of protection blocks for protecting the riverbed, the channel bottom, the still water pond, or the seabed on top of the plurality of first mats that have already been laid.

[0016] A construction method for a scour prevention structure according to one embodiment of the present invention is a method for constructing a scour prevention structure according to one embodiment of the present invention, and includes the following steps: a filling step of filling the interiors of a plurality of first mats and a plurality of second mats that are thicker than the first mats with filler material; a first laying step of laying the plurality of first mats filled with the filler material in a riverbed, a channel bottom, a still water pond, or the seabed; an embedding step of burying the second mats filled with the filler material in the riverbed, a channel bottom, a still water pond, or the seabed so that the second mats filled with the filler material are located at the leading ends of the plurality of first mats; and a second laying step of laying a plurality of protection blocks for protecting the riverbed, channel bottom, or seabed from above the plurality of first mats that have already been buried over to above the above the second mats that have already been buried. [Effects of the Invention]

[0017] According to one aspect of the present invention, tilting of the protection block due to scouring below the protection block can be suppressed, thereby stabilizing the installation state of the protection block. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional side view of a scour prevention structure according to a first embodiment. FIG. [Figure 2] FIG. 2 is a schematic plan view of the scour prevention structure shown in FIG. [Figure 3] FIG. 2 is an enlarged view of part III in FIG. [Figure 4] FIG. 3 is an enlarged view of part IV in FIG. 2. [Figure 5] FIG. 2 is a schematic perspective view of a plurality of first mats. [Figure 6] FIG. 2 is a schematic perspective view of a second mat. [Figure 7] FIG. 2 is a schematic plan view showing a state in which a plurality of first mats extending in the flow direction and a plurality of second mats extending in the flow direction are installed on a riverbed. [Figure 8] FIG. 2 is a schematic plan view showing a state in which a plurality of first mats extending in the river width direction and a plurality of second mats extending in the river width direction are installed on a riverbed. [Figure 9]FIG. 10 is a schematic cross-sectional side view of a scour prevention structure according to a second embodiment. [Figure 10] FIG. 10 is a schematic plan view of the scour prevention structure shown in FIG. 9. [Figure 11] FIG. 10 is an enlarged view of a portion XI in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the specification and claims of this application, the term "riverbed" refers to the riverbed as well as the river slope. The term "waterway bottom" refers to the bottom of various waterways such as agricultural drainage channels and dam spillways as well as the slope of the waterway. The term "seabed" refers to the seabed near the coast as well as the slope of the coast. The term "gravel" refers to sediment and sand. In the drawings, "WD" refers to the river width direction, and "FD" refers to the flow direction.

[0020] [First embodiment] The configuration of a scour prevention structure 10 according to the first embodiment will be described with reference to Figs. 1 to 8. Fig. 1 is a schematic side cross-sectional view of the scour prevention structure 10 according to the first embodiment. Fig. 2 is a schematic plan view of the scour prevention structure 10 shown in Fig. 1. Fig. 3 is an enlarged view of part III in Fig. 1. Fig. 4 is an enlarged view of part IV in Fig. 2. Fig. 5 is a schematic perspective view of a plurality of first mats 16. Fig. 6 is a schematic perspective view of a second mat 20. Fig. 7 is a schematic plan view showing a state in which a plurality of first mats 16 extending in the flow direction and a plurality of second mats 20 extending in the flow direction are installed on the riverbed SB. Fig. 8 is a schematic plan view showing a state in which a plurality of first mats 16 extending in the river width direction and a plurality of second mats 20 extending in the river width direction are installed on the riverbed SB.

[0021] 1 and 2, the scour prevention structure 10 according to the first embodiment is a structure for preventing scouring of the riverbed SB, and is installed immediately downstream of the weir apron 12. The scour prevention structure 10 is located between revetments 14 installed on both sides of the riverbed SB.

[0022] As shown in FIGS. 1 to 5 and 7 , the scour prevention structure 10 includes a plurality of first mats 16 for preventing the suction of sand and gravel from the riverbed SB. The plurality of first mats 16 are laid on the riverbed SB immediately downstream of the apron 12. Each first mat 16 is configured in a net cage shape. Each first mat 16 is formed in a rectangular parallelepiped shape and extends in the flow direction. The plurality of first mats 16 are arranged in multiple rows along the river width direction. A filler material 18 is filled inside each first mat 16. The filler material 18 is, for example, crushed stone, broken granite, gravel, or boulders, and the particle size of the filler material 18 is set to, for example, 20 mm to 200 mm. Note that, within each first mat 16, mesh-like partition members that separate the space may be provided at intervals in the flow direction (longitudinal direction of the first mat 16). The intervals between the partition members are, for example, 250 mm to 500 mm.

[0023] To ensure the abrasion resistance and durability of each first mat 16, the material for each first mat 16 may be a general-purpose fiber such as polyester fiber, nylon fiber, polyethylene fiber, or vinylon fiber, or a high-strength fiber such as ultra-high molecular weight polyethylene fiber, polyarylate fiber, aramid fiber, carbon fiber, or glass fiber. The material for each first mat 16 may be a single material or a composite material. The fiber is preferably filament yarn, which has excellent strength, but spun yarn, slit yarn, or the like may also be used. Knitted nets are primarily used as the material for each first mat 16, and Russell nets are typically used as the knitting method, although knotless or knotted nets may also be used. Other materials such as woven nets, synthetic resin nets, or wire mesh may also be used.

[0024] The diameter (thickness) of the mesh legs of each first mat 16 is set, for example, to 1.0 mm to 8.0 mm. The mesh size of each first mat 16 is set to a size that prevents the fill material 18 from passing through the mesh of each first mat 16 and is set to be equal to or smaller than the average particle size of the gravel in the riverbed SB. The average particle size of the gravel refers to the particle size at 60% of the integrated value of the particle size distribution obtained by a sieving method. Specifically, the mesh size of each first mat 16 is set, for example, to be equal to or smaller than 5 mm to 25 mm.

[0025] The adjacent first mats 16 in the river width direction are connected to each other at points using ropes. The method of connecting the adjacent first mats 16 in the river width direction is not limited to point-connection using ropes, and adjacent first mats 16 may be connected to each other by braiding using ropes, interlocking using fasteners, or other known connecting methods.

[0026] As shown in Figures 1 to 4, 6, and 7, the scour prevention structure 10 includes a plurality of second mats 20 for preventing the suction of sand and gravel from the riverbed SB. The second mats 20 are buried in the riverbed SB so as to be located at the downstream end, i.e., the leading ends, of the first mats 16. Each second mat 20 is configured in a mesh basket shape and is thicker than the first mats 16. Each second mat 20 is formed in a rectangular parallelepiped shape and extends in the flow direction. The second mats 20 are arranged in multiple rows along the river width direction, and the second mats 20 on the downstream side are arranged in two layers. A fill material 18 is filled inside each second mat 20. Note that mesh-like partition members that separate the space inside each second mat 20 may be provided at intervals in the flow direction (the longitudinal direction of the second mats 20).

[0027] To ensure the abrasion resistance and durability of each second mat 20, the same material as that of the first mat 16 is used as the material for each second mat 20. The material for each second mat 20 may be a single material or a composite material. Russell netting is used as the weaving method for each second mat 20, but knotless netting or knotted netting may also be used. Woven fabric netting, synthetic resin netting, wire netting, etc. may also be used as each second mat 20.

[0028] The diameter (thickness) of the mesh legs of each second mat 20 is set to, for example, 1.0 mm to 8.0 mm. The mesh size of each second mat 20 is set to a size that prevents the filler material 18 from passing through the mesh of each second mat 20 and is set to be equal to or smaller than the average particle size of the gravel in the riverbed SB. Specifically, the mesh size of each second mat 20 is set to, for example, 5 mm to 25 mm or smaller.

[0029] The second mats 20 adjacent to each other in the river width direction are connected at points with ropes. The method of connecting the second mats 20 adjacent to each other in the river width direction is not limited to point-connection with ropes, and adjacent second mats 20 may be connected by braiding the rope, by interlocking with fasteners, or by any other known connecting method. Furthermore, the second mats 20 and the first mats 16 adjacent to each other in the flow direction may also be connected by known connecting methods.

[0030] As shown in Fig. 8, each first mat 16 may extend in the river width direction, with multiple first mats 16 arranged in multiple rows along the flow direction. Each second mat 20 may extend in the river width direction, with multiple second mats 20 arranged in multiple rows along the flow direction. In this case, adjacent first mats 16 in the flow direction are connected to each other by a known connecting method such as point-fixing with ropes. Adjacent second mats 20 in the flow direction are connected to each other by a known connecting method such as point-fixing with ropes.

[0031] As shown in Figures 1 to 4, the scour prevention structure 10 includes a plurality of bed protection blocks 22 as a plurality of protection blocks for protecting the riverbed SB. The plurality of bed protection blocks 22 are laid from above the upstream ends of the plurality of first mats 16 to above the downstream ends of the plurality of second mats 20. Each bed protection block 22 is made of, for example, concrete, and the plurality of bed protection blocks 22 are arranged in multiple rows along the river width direction. The interval between adjacent bed protection blocks 22 in the river width direction is set to a gap of, for example, about 5 cm. The interval between adjacent bed protection blocks 22 in the flow direction is set to a gap of, for example, about 5 cm.

[0032] The shape of each bed protection block 22 is shown as a roughly rectangular parallelepiped for ease of explanation, but like existing bed protection blocks, it can be modified into various shapes. In order to stabilize the installation state of each bed protection block 22, the bottom surface of each bed protection block 22 is flat. Furthermore, each bed protection block 22 has a size and weight that will not float up due to the hydrodynamic force of the flowing water at the installation location.

[0033] 3 to 5, connecting reinforcement bars (connecting rings) 24 are embedded in each corner of the upper part of each bed protection block 22. The connecting reinforcement bars 24 of each bed protection block 22 adjacent in the flow direction and / or river width direction are flexibly connected by connecting members 26 such as shackles. In other words, the scour prevention structure 10 is equipped with connecting members 26 that flexibly connect each bed protection block 22 adjacent in the flow direction and / or river width direction.

[0034] Next, a construction method for the scour prevention structure according to the first embodiment will be described with reference to FIGS.

[0035] 1 and 2, the construction method for a scour prevention structure according to the first embodiment is a method for constructing a scour prevention structure 10 on a riverbed SB, and includes a filling step, a first laying step, a burying step, a second laying step, and a connecting step. The specific contents of the construction method for a scour prevention structure according to the first embodiment are as follows.

[0036] As shown in Figures 5 and 6, a filling device is used to fill the interiors of a plurality of first mats 16 and a plurality of second mats 20 with fill material 18 (filling process). A backhoe or other construction machinery is used to fill the fill material 18, and a backhoe, crane, or other construction machinery is used to lift the first mats 16 and second mats 20. Before filling each first mat 16 with fill material 18, one end of each first mat 16 is left open, and after filling each first mat 16 with fill material 18, the end of each first mat 16 is closed with a mesh-like lid member. Similarly, before filling each second mat 20 with fill material 18, the end of each second mat 20 is left open, and after filling each second mat 20 with fill material 18, the end of each second mat 20 is closed with a mesh-like lid member.

[0037] 7 and 8, a plurality of first mats 16 filled with filler material 18 are laid on the riverbed SB immediately downstream of the apron 12 by a construction machine such as a backhoe or a crane (first laying step). After or before laying the plurality of first mats 16, a worker connects adjacent first mats 16 together.

[0038] Furthermore, after the area is excavated to a predetermined depth using a construction machine or the like so that the second mats 20 filled with the filler material 18 are located at the downstream end side, i.e., the leading ends, of the first mats 16, the second mats 20 are installed (buried) in the riverbed SB by the construction machine (burial process). After or before burying the second mats 20, a worker connects adjacent second mats 20 to each other and each second mat 20 to each first mat 16.

[0039] 1 and 2, a construction machine is used to lay a plurality of bed protection blocks 22 from above the upstream ends of a plurality of first mats 16 to above the downstream ends of a plurality of second mats 20 (second laying process). Furthermore, as shown in FIGS. 3 and 4, workers flexibly connect the connecting reinforcement 24 of adjacent bed protection blocks 22 with connecting members 26 (connecting process). This completes the construction of the scour prevention structure 10.

[0040] Next, the effects of the first embodiment will be described.

[0041] A plurality of bed protection blocks 22 are laid from above the upstream ends of a plurality of first mats 16 to above the downstream ends of a plurality of second mats 20. Therefore, even if adjacent bed protection blocks 22 bend and the gap between the adjacent bed protection blocks 22 widens, it is possible to prevent the suction of gravel from the riverbed SB through the gap. In particular, because the mesh size of each first mat 16 is set to be equal to or smaller than the average particle size of the gravel in the riverbed SB, it is possible to sufficiently prevent the suction of gravel from the riverbed SB through the gap between adjacent bed protection blocks 22. This prevents the bed protection blocks 22 from tilting due to the suction of gravel below them, thereby stabilizing the installation state of the plurality of bed protection blocks 22.

[0042] Furthermore, the second mats 20 are buried in the riverbed SB so as to be located on the downstream end side of the first mats 16. Therefore, the second mats 20 act as anchors (weights) and are less likely to roll up from the riverbed SB, stabilizing not only the installed state of the second mats 20 but also the installed state of the first mats 16. This further stabilizes the installed state of the bed protection blocks 22. Furthermore, even if scouring occurs downstream of the second mat 20, the second mat 20, first mat 16, and bed protection blocks 22 will remain horizontal as long as the amount of scouring is approximately twice the thickness of the second mat 20. Even if the amount of scouring exceeds this, the second mat 20 will sink evenly in the river width direction due to its own weight, and will hold the riverbed material at the bottom of the second mats 20 and first mats 16 on the upstream side, preventing the scouring from spreading and stabilizing the riverbed.

[0043] Therefore, according to the first embodiment, scouring immediately downstream of the weir installed on the riverbed SB can be prevented, and damage to the weir, such as the collapse of the apron 12, can be avoided.

[0044] Second Embodiment The configuration of a scour prevention structure 28 according to a second embodiment will be described with reference to Fig. 9 to Fig. 11. Fig. 9 is a schematic side cross-sectional view of the scour prevention structure 28 according to the second embodiment. Fig. 10 is a schematic plan view of the scour prevention structure 28 shown in Fig. 9. Fig. 11 is an enlarged view of part XI in Fig. 9.

[0045] As shown in Figures 9 and 10, the scour prevention structure 28 according to the second embodiment is a structure for preventing scouring of the riverbed SB, and is installed immediately downstream of the weir apron 12. The scour prevention structure 28 is located between revetments 14 installed on both sides of the riverbed SB. The scour prevention structure 28 has a similar configuration to the scour prevention structure 10 (see Figures 1 and 2) described above, and only those points of the configuration of the scour prevention structure 28 that differ from the configuration of the scour prevention structure 10 will be described. For ease of explanation, members that have the same functions as the members described in the first embodiment will be denoted by the same reference numerals, and their description will not be repeated.

[0046] As shown in Figure 11, one of the bed protection blocks 22 adjacent in the flow direction and / or river width direction has a convex portion 30 formed on the top of the other bed protection block 22, protruding towards the other bed protection block 22. The other of the bed protection blocks 22 adjacent in the flow direction and / or river width direction has a concave portion 32 formed on the top of the other bed protection block 22, recessed on the opposite side to the one bed protection block 22, that can fit into the convex portion 30 of the one bed protection block 22. Furthermore, each connecting member 26 is located below the convex portion 30 of one of the bed protection blocks 22 adjacent to each other.

[0047] The scour prevention structure 28 can be constructed on the riverbed SB by the same method as the construction method for the scour prevention structure according to the first embodiment.

[0048] Next, the effects of the second embodiment will be described.

[0049] The second embodiment provides the same effects as the first embodiment described above. Additionally, the second embodiment provides the following additional effects.

[0050] The engagement between the convex portion 30 of one of the adjacent first bed protection blocks 22 and the concave portion of the other bed protection block 22 makes it difficult for gravel flowing down from the upper side of the bed protection block 22 to reach the first mat 16 and the second mat 20. This reduces wear on the first mat 16 and the second mat 20 caused by gravel flowing down from the upper side of the bed protection block 22, improving the durability of the first mat 16 and the second mat 20.

[0051] Since each connecting member 26 is located below the convex portion 30 of one of the adjacent bed protection blocks 22, it is possible to reduce wear of the connecting member 26 due to gravel flowing down from the upper side of the bed protection block 22. This makes it possible to improve the durability of the connecting member 26.

[0052] Other Embodiments The technical concept applied to the scour prevention structure 10 (28) installed immediately downstream of the weir apron 12 may also be applied to scour prevention structures installed downstream of structures other than weirs, or upstream of structures including weirs. Also, the technical concept applied to the scour prevention structure 10 (28) may also be applied to scour prevention structures installed on the bottom of a waterway, a still water basin, or the seabed.

[0053] 〔summary〕 The scouring prevention structure according to aspect 1 of the present invention is a scouring prevention structure for preventing scouring of a riverbed, a waterway bottom, a still water pond or the seabed, and comprises a plurality of first mats that are laid on the riverbed, waterway bottom, still water pond or the seabed and filled with filler material to prevent the suction of sand and gravel from the riverbed, waterway bottom, still water pond or the seabed, and a plurality of protection blocks that are laid on top of the plurality of first mats and protect the riverbed, waterway bottom, still water pond or the seabed, and adjacent protection blocks are flexibly connected to each other.

[0054] According to the above configuration, the plurality of protective blocks are laid on top of the plurality of first mats. Therefore, even if adjacent protective blocks bend and the gap between the adjacent protective blocks widens, it is possible to prevent the suction of sand and gravel from the riverbed or the like through the gap. This makes it possible to suppress the tilting (tilting) of the protective blocks due to the suction of sand and gravel below the protective blocks, and stabilize the installation state of the plurality of protective blocks. Therefore, it is possible to prevent scouring immediately downstream of structures such as weirs installed on the riverbed or the like, and avoid damage to the structures.

[0055] A scouring prevention structure according to a second aspect of the present invention is the same as that of the first aspect, and further comprises a second mat that is buried in the riverbed, waterway bottom, still water pond, or seabed so as to be located at the tip side of the plurality of first mats, is thicker than the first mats, has the fill material filled inside, and prevents sand and gravel from being sucked out from the riverbed, waterway bottom, still water pond, or seabed, and the plurality of protective blocks may be laid from the upper side of the plurality of first mats to the upper side of the second mat.

[0056] According to the above configuration, the second mat, which is thicker than the first mat, is buried in the riverbed or the like so as to be located at the tip end of the plurality of first mats. The plurality of protective blocks are laid from the upper side of the plurality of first mats to the upper side of the plurality of second mats. This makes it difficult for the second mat to lift up from the riverbed or the like, thereby stabilizing not only the installation state of the second mat but also the installation state of the plurality of first mats. This makes it possible to further stabilize the installation state of the plurality of protective blocks.

[0057] A scouring prevention structure according to aspect 3 of the present invention is the same as that according to aspect 2, wherein each of the first mats and the second mats is configured in a wire basket shape, and the mesh size of each of the first mats and the second mats may be equal to or smaller than the average particle size of the sand and gravel in the riverbed, channel bottom, still water pond, or seabed.

[0058] According to the above configuration, the mesh size of each first mat and second mat is smaller than the average particle size of gravel in riverbeds, etc., so that it is possible to sufficiently prevent gravel in riverbeds, etc. from being sucked out through the gaps between adjacent protective blocks.

[0059] A scouring prevention structure according to aspect 4 of the present invention may be such that, in any of aspects 1 to 3, a convex portion is formed on the top of one of the adjacent protective blocks so as to protrude toward the other protective block, and a concave portion capable of engaging with the convex portion of the one protective block is formed on the top of the other protective block so as to be recessed on the opposite side to the one protective block.

[0060] According to the above configuration, the engagement between the convex portion of one protective block and the concave portion of the other protective block makes it difficult for gravel flowing down from above the protective blocks to reach the first mat, thereby reducing wear on the first mat caused by gravel flowing down from above the protective blocks and improving the durability of the first mat.

[0061] The scouring prevention structure according to aspect 5 of the present invention is the same as in aspect 4, and includes connecting members that flexibly connect adjacent protective blocks, and each connecting member may be located below the convex portion of one of the protective blocks.

[0062] According to the above configuration, since each connecting member is located below the protrusion of one of the protective blocks, sand and gravel flowing down from above the protective block are less likely to reach the connecting members, thereby reducing wear on the connecting members due to sand and gravel flowing down from above the protective block and improving the durability of the connecting members.

[0063] A construction method for a scour prevention structure according to aspect 6 of the present invention is a method for constructing the scour prevention structure according to aspect 1, and includes a filling step of filling a plurality of first mats with filler material, a first laying step of laying the plurality of first mats filled with the filler material on a riverbed, a channel bottom, a still water pond, or the seabed, and a second laying step of laying a plurality of protection blocks for protecting the riverbed, the channel bottom, the still water pond, or the seabed on top of the plurality of first mats that have already been laid.

[0064] According to the above configuration, a plurality of the first mats are laid on the riverbed, etc., and a plurality of the protection blocks are laid on top of the plurality of first mats that have already been laid. Therefore, even if adjacent protection blocks bend and the gaps between the adjacent protection blocks widen, it is possible to prevent the suction of sand and gravel from the riverbed, waterway bottom, still water pond, or seabed through the gaps. This prevents the protection blocks from tilting (sloping) due to the suction of sand and gravel directly below the protection blocks, and stabilizes the installation state of the plurality of protection blocks.

[0065] A construction method for a scour prevention structure according to a seventh aspect of the present invention is a method for constructing the scour prevention structure according to the second aspect, and includes the following steps: a filling step of filling the interiors of a plurality of first mats and a second mat thicker than the first mats with filler material; a first laying step of laying the plurality of first mats filled with filler material in a riverbed, channel bottom, still water pond, or seabed; an embedding step of burying the second mats filled with filler material in the riverbed, channel bottom, still water pond, or seabed so that the second mats filled with filler material are located at the leading ends of the plurality of first mats; and a second laying step of laying a plurality of protection blocks for protecting the riverbed, channel bottom, still water pond, or seabed from above the plurality of first mats that have already been buried and laid over above the already laid second mat.

[0066] According to the above configuration, the plurality of protection blocks are laid from above the plurality of first mats already laid to above the plurality of second mats already laid. Therefore, even if adjacent protection blocks bend and the gaps between the adjacent protection blocks widen, it is possible to prevent the suction of sand and gravel from the riverbed, waterway bottom, still water pond, or seabed through the gaps. This prevents the protection blocks from tilting (sloping) due to the suction of sand and gravel from the bottom and surrounding areas of the protection blocks, thereby stabilizing the installation state of the plurality of protection blocks.

[0067] In addition, the second mat is buried in the riverbed or the like so as to be located on the tip side of the plurality of first mats. This makes it difficult for the first mat to lift up from the riverbed or the like, stabilizing not only the installation state of the second mat but also the installation state of the plurality of first mats. This makes it possible to further stabilize the installation state of the plurality of protection blocks.

[0068] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0069] 10: Scour prevention structure (scour prevention structure according to the first embodiment), 12: Apron, 14: Revetment, 16: First mat, 20: Second mat, 18: Filling material, 22: Bed protection block (protection block), 24: Connecting reinforcement, 26: Connecting member, 28: Scour prevention structure (scour prevention structure according to the second embodiment), 30: Convex portion, 32: Concave portion

Claims

1. A scour prevention structure for preventing scouring of a riverbed, a waterway bottom, a still water pond, or the seabed, a plurality of first mats that are laid on a riverbed, a waterway bottom, a still water pond, or a seabed and filled with a filler material to prevent the suction of sand and gravel from the riverbed, the waterway bottom, the still water pond, or the seabed; a plurality of protection blocks laid on top of the plurality of first mats to protect a riverbed, a waterway bottom, a still water pond, or an ocean bottom; Adjacent protection blocks are flexibly connected to each other, A scour prevention structure in which a convex portion is formed on the top of one of adjacent protective blocks so as to protrude toward the other protective block, and a concave portion that can fit into the convex portion of the one protective block is formed on the top of the other protective block so as to be recessed on the opposite side to the one protective block.

2. A scour prevention structure for preventing scouring of a riverbed, a waterway bottom, a still water pond, or the seabed, a plurality of first mats that are laid on a riverbed, a waterway bottom, a still water pond, or a seabed and filled with a filler material to prevent the suction of sand and gravel from the riverbed, the waterway bottom, the still water pond, or the seabed; a plurality of protection blocks laid on top of the plurality of first mats to protect a riverbed, a waterway bottom, a still water pond, or an ocean bottom; Adjacent protection blocks are flexibly connected to each other, a second mat that is buried in the riverbed, waterway bottom, still water pond, or seabed so as to be located on the tip side of the plurality of first mats, is thicker than the first mats, is filled with the fill material, and prevents sand and gravel from being sucked out from the riverbed, waterway bottom, still water pond, or seabed; A scour prevention structure, wherein the plurality of protection blocks are laid from the upper side of the plurality of first mats to the upper side of the plurality of second mats.

3. 3. The scouring prevention structure according to claim 2, wherein each of the first mats and the second mats is configured in a mesh basket shape, and the mesh size of each of the first mats and the second mats is equal to or smaller than the average particle size of gravel in a riverbed, a channel bottom, a still water pond, or the seabed.

4. 4. The scour prevention structure according to claim 2 or 3, wherein a convex portion is formed on an upper portion of one of adjacent protective blocks so as to protrude toward the other protective block, and a concave portion capable of fitting with the convex portion of the one protective block is formed on an upper portion of the other protective block so as to be recessed on the opposite side to the one protective block.

5. a connecting member that flexibly connects adjacent protection blocks to each other; The scour prevention structure according to claim 1 or 4, wherein each connecting member is located below the protruding portion of the one of the protection blocks.

6. A method for constructing the scour prevention structure according to claim 1, comprising: a filling step of filling a filler material into the plurality of first mats; a first laying step of laying a plurality of the first mats filled with the filler material on a riverbed, a waterway bottom, a still water pond, or the seabed; a second laying step of laying a plurality of protection blocks for protecting a riverbed, a waterway bottom, a still water pond, or the seabed on top of the plurality of first mats that have already been laid.

7. A method for constructing the scour prevention structure according to claim 2, comprising: a filling step of filling a filler material into the interior of each of the first mats and a second mat that is thicker than the first mats; a first laying step of laying a plurality of the first mats filled with the filler material on a riverbed, a waterway bottom, a still water pond, or the seabed; an embedding step of embedding the second mat in a riverbed, a waterway bottom, a still water pond, or the seabed so that the second mat filled with the filler material is located on the tip side of the plurality of first mats; a second laying step of laying a plurality of protection blocks for protecting a riverbed, a waterway bottom, a still water pond, or the seabed from above the plurality of first mats that have already been buried to above the second mat that has already been buried.

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