Vegetation mat installation method

Abstract

To provide a construction method of a vegetation mat reduced and prevented in erosion and scouring of a back slope by overflow water, and promoting greening of the back slope.SOLUTION: Multiple vegetation mats D formed by integrating nonwoven fabric 1 and lawn 3a on a net material 2 are laid on the back slope of a dike. Pieces of the lawn 3a of adjacent vegetation mats D are set to abut against each other. The vegetation mat has a main part 4 on which the nonwoven fabric 1 and the lawn 3 are integrated to the net 2, and an extended part 5 extending from a circumference of the main part 4 and thinner than the main part 4. The vegetation mats are set in such a way that one extended part 5 of the adjacent two vegetation mats D is spread under the other main part 4.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for constructing a vegetation mat, for example, for preventing erosion of the backfill method of river levees.

Background Art

[0002] When the river water overflows the top edge 91 of the levee during a river flood, the backfill bottom part 93 of the levee is washed out by the overflowing water 92 (Fig. 10(A)). Thereafter, when the erosion of the backfill 94 progresses due to the overflowing water (Fig. 10(B)), the levee breaks (Fig. 10(C)).

[0003] As a countermeasure against the levee breakage caused in this way, it is effective to reduce and prevent the erosion and washing out of the backfill 94 (including the backfill bottom part 93) by the overflowing water 92. For example, the levee reinforcement device of Patent Document 1 attempts to reduce and prevent the above-mentioned erosion and washing out by covering the inner slope surface of the levee with a water shielding sheet made of synthetic resin.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, with the above-mentioned levee reinforcement device, it is difficult to green the backfill 94, and there is room for improvement in terms of landscape aesthetics and environmental protection.

[0006] On the other hand, as shown in Patent Document 2, the applicant has previously proposed a method for constructing a vegetation mat. However, this construction method is assumed to be widely used for greening slopes and flatlands, and is not specialized for application to the backfill of levees that may be affected by overflowing water.

[0007] This invention has been made with the above-mentioned matters in mind, and its purpose is to provide a method for constructing a vegetation mat that can reduce and prevent erosion and scouring of the back slope caused by overflow water, and promote greening of the back slope. [Means for solving the problem]

[0008] To achieve the above objective, the method for constructing vegetation mats according to the present invention involves laying multiple vegetation mats, each composed of a net material, nonwoven fabric, and turf integrated together, on the back slope of the embankment. The vegetation mat has a main body in which nonwoven fabric and grass are integrated into a net material, and an overhanging portion that extends from the periphery of the main body and is thinner than the main body. Two adjacent vegetation mats are installed so that the overhanging portion of one mat is laid under the main body of the other mat, and for two vegetation mats adjacent in the slope length direction, the overhanging portion of the vegetation mat on the slope toe side is laid under the main body of the vegetation mat on the slope shoulder side. The net material and nonwoven fabric constituting the main body extend to the overhanging portion, and a reinforcing net fixed to the top of the embankment is connected to the vegetation mat near the slope shoulder. (Claim 1).

[0009] In the above method for constructing vegetation mats, The reinforcing net is connected to the vegetation mat near the top of the slope, with the insertion length of the reinforcing net into the top of the embankment being greater than the length of the net covering the vegetation mat near the top of the slope. This may be done (Claim 2).

[0010] In the above method for constructing vegetation mats, The grass from adjacent vegetation mats is touching each other. This may be done (Claim 3).

[0011]

[0012]

[0013] [Effects of the Invention]

[0014] The present invention provides a method for constructing a vegetation mat that can reduce and prevent erosion and scouring of the back slope caused by overflow water, and also promote greening of the back slope.

[0015] In other words, in the method of constructing a vegetation mat according to each claim of the present invention, by laying the vegetation mat on the back slope so that the nonwoven fabric prevents the erosion and scouring of the back slope by overflow water, it is possible to reduce and prevent erosion and scouring of the back slope. Furthermore, since turf has a rougher surface than synthetic resin waterproof sheets, etc., by laying the vegetation mat on the back slope so that the turf faces upward, the initial flow velocity of overflow water can be reduced, thereby reducing and preventing the erosion of the back slope soil and scouring of the back slope's tail. Moreover, the turf in the vegetation mat laid on the back slope can also be used to green the back slope. In addition, in the above vegetation mat, the nonwoven fabric and turf can be held in place by a net material to prevent them from being washed away, and by giving this net material an appropriate mesh size, it is easy to avoid hindering the growth of the turf.

[0016] If there are depressions at the joints between multiple vegetation mats laid side by side in the back, the overflow water that flows into these depressions will pull the vegetation mats away from the back, making them more susceptible to being washed away. Section 3 In the method for constructing vegetation mats according to the invention, the grass of adjacent vegetation mats is made to butt against each other, so that depressions are less likely to form at the joints of the vegetation mats, and the erosion of the vegetation mats can be prevented immediately after construction without waiting for the joints of the vegetation mats to be covered with vegetation.

[0017] If a gap forms between the main parts of two adjacent vegetation mats, there is a risk that erosion and suction will occur in that gap due to overflowing water, but Item 1 The method for constructing vegetation mats according to the invention eliminates such gaps, thereby reducing and preventing erosion and suction caused by overflowing water. Furthermore, by making the overhanging portion thinner than the main portion, the step formed at the boundary between the main portion with the overhanging portion laid underneath and the main portion without the overhanging portion is reduced, thereby suppressing the adverse effects caused by this step.

[0018] Claim Item 1In the method for constructing the vegetation mat according to the invention, the main part of the vegetation mat on the slope side is overlapped from above on the overhanging part of the vegetation mat on the toe side. Therefore, when the river water overflows the top edge of the river embankment, the edge of the vegetation mat does not oppose the overflowing water, and the overflowing water flows smoothly, effectively preventing the vegetation mat from being washed away.

[0019] Claims Item 1 In the method for constructing the vegetation mat according to the invention, when one overhanging part of two adjacent vegetation mats is installed so as to be laid under the other main part, the non-woven fabric constituting one main part of the two vegetation mats and the non-woven fabric constituting the other main part are overlapped, enhancing the function of preventing the suction from the butted part of the lawns. Therefore, even when the end of the lawn is not in a clean straight line shape and is not partially butted, it is expected to prevent the suction from occurring through the gap.

[0020] Among the plurality of vegetation mats laid side by side in the reverse slope method, the vegetation mat near the slope on the most slope side and the top edge of the embankment on the slope side of this vegetation mat often have a significantly different roughness coefficient or a relatively large unevenness (step) is formed between the two. In this case, it is considered that the vegetation mat near the slope is likely to be washed away by the overflowing water. However, Claims Item 1 In the method for constructing the vegetation mat according to the invention, since the reinforcing net is connected to the vegetation mat near the slope, the risk of the vegetation mat near the slope being washed away can be reduced.

[0021] Claims Section 2 In the method for constructing the vegetation mat according to the invention, since the reinforcing net is inserted deeply enough into the top edge of the embankment, it is possible to ensure the prevention of the vegetation mat near the slope from falling out.

Brief Description of the Drawings

[0022] [Figure 1] It is an explanatory diagram schematically showing the method for constructing the vegetation mat according to an embodiment of the present invention. [Figure 2]This is a perspective view showing the structure of the vegetation mat used in the aforementioned vegetation mat installation method. [Figure 3] This is a perspective view showing a schematic configuration of the vegetation mat and its manufacturing method. [Figure 4] (A) to (D) are explanatory diagrams that schematically show the configuration of the method for manufacturing the vegetation mat (standard production method), and (E) to (G) are explanatory diagrams that schematically show the configuration of a modified version of the method for manufacturing the vegetation mat (new production method). [Figure 5] (A) and (B) are longitudinal cross-sectional views that schematically show the overall structure and essential components of the vegetation mat installation method. [Figure 6] (A) to (C) are plan views showing the construction procedure of the vegetation mat construction method related to the comparative example, (D) is a longitudinal section view thereof, and (E) is an explanatory diagram showing how overflow water flows in the back slope after construction. [Figure 7] (A) to (C) are plan views showing the construction procedure of a vegetation mat construction method according to an example of the present invention, (D) is a longitudinal section view thereof, and (E) is an explanatory diagram showing how overflow water flows in the back slope after construction. [Figure 8] (A) is an explanatory diagram showing the overall structure of the test apparatus, (B) is a longitudinal cross-sectional view of the water channel of the test apparatus, (C) is a photograph showing the approximate overall structure of the test apparatus, (D) is a photograph showing the water flow condition of the test specimen, and (E) is a photograph showing the water flow condition upstream of the test specimen in the test apparatus. [Figure 9] (A) is an explanatory diagram of the installation method of the comparative example vegetation mat, (B) and (C) are photographs showing the condition of the seams of the vegetation mats in the comparative example before and after the test, (D) is an explanatory diagram of the installation method of the vegetation mat in this example, and (E) and (F) are photographs showing the condition of the seams of the vegetation mats in this example before and after the test. [Figure 10] (A) to (C) are explanatory diagrams illustrating the process by which a levee breach occurs. [Figure 11] (A) and (B) are explanatory diagrams of the connecting parts of the vegetation mat according to this example and its modified form. [Modes for carrying out the invention]

[0023] Embodiments of the present invention are described below.

[0024] The method for constructing the vegetation mat according to this embodiment involves laying multiple vegetation mats D, shown in Figure 2, in a row horizontally and vertically on the back slope N1 of the river embankment (an example of an embankment) shown in Figure 1.

[0025] The vegetation mat D is, for example, a rectangular shape with a plan view of 1000 mm x 3000 mm or a square shape of 2000 mm x 2000 mm, and is made by integrating a grass mat 3 with a flexible net material 2 on which a nonwoven fabric 1 is placed on the bottom surface (see Figure 2).

[0026] Nonwoven fabric 1 has a nearly rectangular shape when viewed from above, and its chemical fiber basis weight is 30-80 g / m². 2 These components are formed in such a way that they are made using a spunlace method with polyester fibers, coconut mats, and other materials that are highly durable and corrosion-resistant.

[0027] Net material 2 has almost the same shape as nonwoven fabric 1 in plan view, and is formed to have a tensile strength of about 30-80 kN per meter of width and a mesh size of about 5-10 x 5-10 mm. Net material 2 is formed in a grid shape using durable fibers such as nylon, polyester, aramid, carbon, and polyacetal, but it may also be made by knitting a mesh-like body with the same mesh size as above using the filaments of the above fibers. Net material 2 in this example is a geotextile net with a polyester base fabric and an acrylic thermosetting resin covering material.

[0028] The lawn mat 3 consists of multiple pieces of grass 3a and soil 3b held in place by the roots of the grass 3a.

[0029] The vegetation mat D consists of a main body 4 in which a nonwoven fabric 1 and a grass mat 3 (grass 3a) are integrated into a net material 2, and an extension 5 that extends from the periphery of the main body 4 and is thinner than the main body 4. In this example, the nonwoven fabric 1 and net material 2 that constitute the main body 4 extend outwards from the main body 4 (towards the extension 5), and this extended portion constitutes the extension 5. It is preferable that the extension 5 includes the net material 2 throughout its entirety, and it may or may not include the nonwoven fabric 1 (whether or not the nonwoven fabric 1 is integrated into the net material 2).

[0030] However, from the standpoint of preventing suction from the seams of the vegetation mats D, it is desirable to provide an overlap between the nonwoven fabrics 1 of adjacent vegetation mats D. For example, it is sufficient if the nonwoven fabric 1 on the underside of the grass mat 3 extends even slightly in the direction of the protruding portion 5, and in this case, the nonwoven fabric 1 does not need to extend to the end of the protruding portion 5 (the entire protruding portion 5). By providing such an overlap, when two adjacent vegetation mats D are installed so that the protruding portion 5 of one is laid under the main body 4 of the other, the nonwoven fabric 1 constituting the main body 4 of one vegetation mat D overlaps with the nonwoven fabric 1 constituting the main body 4 of the other vegetation mat D, thereby enhancing the function of preventing suction from the joints where the grass 3a meet. Therefore, even if the edges of the grass 3a are not in a neat straight shape and do not partially meet, it is expected that suction will not occur from the gaps.

[0031] The protruding portion 5 consists of a peripheral portion 5a, for example, 150 mm wide, formed on one side in the width direction of the vegetation mat D, and a peripheral portion 5b, for example, 100 mm wide, formed on one side in the longitudinal direction of the vegetation mat D.

[0032] Vegetation mat D is manufactured as follows: First, as shown in Figure 4(A), a nonwoven fabric 1 is laid in the field 6, then a flexible net material 2 is placed on top of the nonwoven fabric 1 (Figure 4(B)), and a turf mat 3, which has been grown separately in the field 6, is laid on top of the net material 2 (Figure 4(C)). When the roots of the turf 3a become entangled in the nonwoven fabric 1 and the net material 2 (Figure 4(D)), the turf roots of the turf 3a that have grown under the nonwoven fabric 1 are cut, and the net material 2 together with the nonwoven fabric 1 is peeled off the field 6, thereby completing the manufacture of vegetation mat D (see Figure 3).

[0033] Furthermore, in the above-described method for manufacturing the vegetation mat D, if wooden beams K (see Figure 3) or the like are placed around the periphery of the net material 2 at the start of manufacturing the vegetation mat D, and these wooden beams K or the like are removed when the manufacturing of the vegetation mat D is completed, the vegetation mat D can be provided with an overhanging portion 5 on which the grass mat 3 is not formed.

[0034] Alternatively, the arrangement of the timbers K and other elements described above may be omitted, and the overhang 5 may be formed by breaking up the periphery of the grass mat 3 after the vegetation mat D is manufactured, or by using a brush cutter or similar tool to trim it until the net material 2 is visible. In this case, the roots and rhizomes (underground stems) of the grass 3a entangled in the nonwoven fabric 1, and in some cases, stolons, may be present mainly on the underside of the net material 2, meaning that the overhang 5 may contain grass 3a. Attempting to remove the grass 3a entangled in the nonwoven fabric 1 may damage the nonwoven fabric 1, raising concerns about reduced productivity. For these reasons, the overhang 5 may contain grass 3a to the extent that it does not interfere with the laying of the vegetation mat D.

[0035] According to the manufacturing method for the vegetation mat D having the above configuration, since the nonwoven fabric 1 is formed on the lower surface of the vegetation mat D, the amount of grass roots 3a that penetrate below the vegetation mat D is reduced compared to when the nonwoven fabric 1 is not provided, making it possible to remove the vegetation mat D from the field 6 with less force.

[0036] The nonwoven fabric 1 can be attached to the net material 2 of the vegetation mat D by entangling the roots of the grass 3a of the lawn mat 3 with the nonwoven fabric 1 and net material 2. In addition, it may also be attached using, for example, string or adhesive.

[0037] The method for manufacturing the vegetation mat D is not limited to the above configuration, and may also be the configuration shown below. That is, first, a nonwoven fabric 1 is laid in the field 6, then a flexible net material 2 is placed on top of the nonwoven fabric 1, runners of grass 3a are planted on top of the net material 2 and covered with soil, the roots of the grass 3a become entangled with the nonwoven fabric 1 and the net material 2, and when the runners have grown into the turf mat 3, the net material 2 together with the nonwoven fabric 1 is peeled off from the field 6 while cutting the roots of the grass 3a that have grown under the nonwoven fabric 1.

[0038] Furthermore, as another method for manufacturing the vegetation mat D, the vegetation mat D can also be obtained by spreading the nonwoven fabric 1 on a workbench, for example, placing a flexible net material 2 on top of it, then placing a grass mat 3 on top of that, and integrating these three components by fastening them together with staples or other connecting means such as sewing (neither of which are shown).

[0039] According to this manufacturing method, although the roots of the grass 3a of the grass mat 3 are not intertwined with the nonwoven fabric 1 and the net material 2, these three are integrated by the connecting means. Therefore, when laying the vegetation mat D, by driving anchor members into the overlapping part of one main body 4 and the other overhanging part 5 of adjacent vegetation mats D, the grass mat 3 can be firmly attached to the slope via the nonwoven fabric 1 and the net material 2. Over time, the roots of the grass on the grass mat 3 will intertwine with the nonwoven fabric 1 and the net material 2 and take root on the slope. With this manufacturing method, in addition to using pre-grown grass mats 3, there is no need to wait for the roots of the grass mat 3 to intertwine with the nonwoven fabric 1 and the net material 2, thus further shortening the manufacturing time of the vegetation mat D.

[0040] In the vegetation mat manufacturing method shown in Figures 4(A) to (D), as described above, when the roots of the grass 3a become entangled with the nonwoven fabric 1 and net material 2 (Figure 4(D)), the roots of the grass 3a extending below the nonwoven fabric 1 are cut, and the net material 2 is peeled off from the field 6 together with the nonwoven fabric 1. After this, as shown in Figure 4(E), the rhizomes of the grass 3a are present in the field 6. Therefore, it is also possible to manufacture a new vegetation mat D using the field 6 in this state. Hereafter, this manufacturing method will be called the new production method, and the vegetation mat manufacturing method shown in Figures 4(A) to (D) will be called the standard production method, and the new production method will be explained, including the differences between the two.

[0041] In this new production method, a nonwoven fabric 1 is laid on a field 6 in the state shown in Figure 4(E), as shown in Figure 4(F), then topsoil (soil cover) 3b is placed over it (topsoil covering or covering with soil), and then net material 2 is laid on top of that (Figure 4(G)), and the net material 2 is fixed to the field 6 with fixing members (such as skewers) not shown. In this case as well, once the grass 3a has grown and is sufficiently intertwined with the nonwoven fabric 1 and net material 2, the roots of the grass 3a that have grown under the nonwoven fabric 1 are cut, and the net material 2 is peeled off the field 6 together with the nonwoven fabric 1, thereby completing the production of the vegetation mat D.

[0042] Here, if the relatively lightweight nonwoven fabric 1 were to be lifted by the stems and leaves that grew from the rhizomes of the turf 3a remaining in field 6, the turf 3a would not entangle with either the nonwoven fabric 1 or the net material 2, resulting in insufficient overall integrity of the vegetation mat D. Therefore, the layer of soil 3b placed on top of the nonwoven fabric 1 is given a predetermined thickness (for example, about 10-20 mm) to act as a weight to prevent the nonwoven fabric 1 from being lifted. This makes it easier for the stems and leaves that grew from the rhizomes of the turf 3a remaining in field 6 to penetrate the nonwoven fabric 1, and furthermore, these stems and leaves are more likely to entangle firmly with the nonwoven fabric 1 and the net material 2, thereby increasing the overall integrity of the vegetation mat D. Furthermore, by configuring the structure so that soil 3b is sandwiched between the nonwoven fabric 1 and the net material 2, the soil 3b is well retained by the grass 3a intertwined with the nonwoven fabric 1 and net material 2. This also has the advantage that when the completed vegetation mat D is installed on the riverside and overflow water passes over it, the soil 3b is less likely to be washed away.

[0043] From the perspective of grass growth 3a, it is desirable to mix soil (topdressing) 3b, which is applied to the nonwoven fabric 1, with soil conditioners that have water-retaining properties, such as shirasu and bentonite. Furthermore, by changing the composition, mixture, and thickness of this soil 3b, the permeability (hydropermeability coefficient) of the vegetation mat D can be controlled, making it possible to manufacture products that meet the required hydropermeability coefficient for each riverbank.

[0044] Furthermore, in the standard production method shown in Figures 4(A) to (D), it is necessary to strip 3a of turf grown in a separate field and transport it to field 6 for vegetation mat production. However, the new production method eliminates this extra step, making it possible to manufacture vegetation mat D in a single field 6, meaning that vegetation mat D can be produced with half the field area required by the standard production method.

[0045] In the new production method, as described above, the rhizomes of the turf 3a remaining in field 6 after the vegetation mat D is removed are used. However, their growth may be poor, time-consuming, and of poor quality. Therefore, before placing the nonwoven fabric 1, soil 3b, etc., on the surface of field 6 in the state shown in Figure 4(E), as shown in Figure 4(F), it may be possible to place separately prepared shredded turf (shredded stolons) on top. This allows for vigorous propagation through tillering of the stolons, which may be advantageous in reducing problems such as uneven growth of turf 3a compared to the standard production method that relies solely on the rhizomes remaining in field 6 after the vegetation mat D is removed. Specifically, the following arrangement methods such as (A) and (B) can be considered.

[0046] (A) Using a small cultivator or similar machine, V-grooves with an opening width of about 5 cm and a depth of several centimeters (2-3 cm) are formed in a striped pattern at intervals of, for example, 20-30 cm on the surface of field 6 (field 6 where the rhizomes of turf 3a remain) as shown in Figure 4(E). Loosened turf is then continuously filled into each V-groove in the longitudinal direction and covered with soil. When this arrangement method is adopted, the areas between the V-grooves will eventually be filled with stems and leaves that grow from the rhizomes of turf 3a remaining in field 6, and with stolons of the newly introduced loosened turf, resulting in a surface covered with turf.

[0047] (B) Loosened turf is spread over the entire surface of field 6 (field 6 where the rhizomes of turf 3a remain), as shown in Figure 4(E). Then, the loosened turf is tilled into the soil while tilling the surface of field 6 to a depth of about 5 cm with a tiller, thereby forming a new topsoil layer in field 6 in which the remaining rhizomes and the newly spread loosened turf are distributed almost uniformly, and then the field is compacted. Even when this arrangement method is adopted, field 6 will eventually become entirely covered with turf.

[0048] In the standard production method shown in Figures 4(A) to (D), the vegetation mat D is basically formed by the roots of the grass 3a intertwining with the net material 2 and nonwoven fabric 1. However, in the new production method employing the arrangement methods in (A) and (B) above, (1) the stolons, which are stronger than the roots of the grass 3a, intertwine with the net material 2 and nonwoven fabric 1, and (2) it becomes possible to include a larger amount of grass 3a roots in the vegetation mat D obtained by peeling it off from the field 6. As a result, the following effects can be obtained: (1) the unity of the vegetation mat D is dramatically improved, resulting in superior durability and resistance to soil erosion, and (2) the vegetation mat D after construction can take hold of a significantly larger number of roots in the soil of the river back slope, and the binding force makes the surface layer of the river back slope stronger.

[0049] The new production method described above utilizes field 6, where some of the rhizomes of the turfgrass 3a remain. However, it is not limited to this; for example, a field where the rhizomes of the turfgrass 3a do not exist could be used by sowing loosened turfgrass in that field.

[0050] When installing vegetation mats D on the back side, anchor members or connecting members are driven into the overlapping section of one main section 4 and the other overhanging section 5 of adjacent vegetation mats D. The overhanging section 5 is, so to speak, the joint between adjacent vegetation mats D, and it is desirable to reinforce it. As an example of this reinforcement, the nonwoven fabric 1 of the nonwoven fabric 1 and net material 2 that make up the overhanging section 5 is reinforced to match the chemical fiber basis weight (30-80 g / m) of the nonwoven fabric 1 that makes up the main section 4. 2 Possible methods include constructing it with a material larger than ), making the mesh size of the net material 2 smaller than the part that makes up the main body 4, and providing two or more layers of nonwoven fabric 1 or net material 2 in the protruding part 5.

[0051] Next, the construction method for vegetation mat D will be explained using Figures 1 and 5. In Figure 1, R represents the direction in which river water flows on the river-facing side of the river embankment. To install vegetation mat D on the back slope N1 of the river embankment, first, as shown in Figure 1, the toe of the back slope (the part that will become the embankment base) is excavated as appropriate, and then, for example, a gabion mat 7 laying method is carried out in the excavated area (other methods such as laying rubble or gabion baskets are also suitable).

[0052] In this case, a net material (an example of a reinforcing net) 8, similar to the net material 2 mentioned above, is laid on the underside of the basket mat 7 over an appropriate width, and its upper edge is made to protrude, for example, by about 1 meter, towards the back side N1 of the top of the basket mat 7.

[0053] On the other hand, as shown in Figures 5(A) and (B), a crushed stone layer S and pavement H are provided at the top of the river embankment from below, and the pavement H has a structure in which an asphalt layer H2 is constructed on top of a subgrade layer H1. In addition, a slope protection structure is provided at the shoulder portion of the river embankment on the back slope N1 side (the portion from the top to the back slope N1), and the slope protection structure in this example is configured by connecting block-shaped protective members G, which are concrete secondary products, in the R direction (see Figure 1).

[0054] As shown in Figures 5(A) and (B), the protective member G is a member that has a longitudinal cross-sectional shape in which one corner of a rectangle is chamfered to have an inclined surface portion G1. Here, when river water overflows the top of a river embankment, the flow velocity change is most likely to occur and erosion is most likely to occur at the end of the horizontal top surface portion G2 on the back slope N1 side. However, in the protective member G of this example, the inclined surface portion G1 is provided in a series on the back slope N1 side of the top surface portion G2 as described above, in order to suppress the occurrence of erosion.

[0055] Then, a net material 9 similar to the net material 2 described above (an example of a reinforcing net) is embedded below the crushed stone layer S and below the protective member G, with its protruding edge 9a on the back side N1 (see Figure 5(B)) protruding.

[0056] Then, multiple vegetation mats D are stretched along the back slope N1 from the downstream side to the upstream side and from the toe side to the crest side, with the peripheral portion 5a (see Figure 2) facing upstream (see Figure 1) and the peripheral portion 5b (see Figure 2) facing towards the slope shoulder (top end).

[0057] At this time, for the vegetation mat D located at the toe end (near the toe) of the back slope N1, the upper part that protrudes from the net material 8 laid beneath the basket mat 7 is overlapped from above, and net pins (an example of an anchor member) 10, or, for example, piles made of synthetic resin (another example of an anchor member) 11, are appropriately driven into the ground between them (see Figure 5(A)). As for the net pins 10, for example, those with multiple (for example, four) insertion parts having a return structure near the base arranged in a row can be used.

[0058] Furthermore, for the vegetation mat D located on the slope shoulder side (near the slope shoulder) of the back slope N1, the protruding edges 9a extending from the net material 9 laid beneath the crushed stone layer S and protective member G are overlapped from above, and net pins 10, stakes 11, etc. are appropriately driven into both (see Figures 5(A) and (B)). If the upper end of the vegetation mat D exceeds the protruding edge 9a due to the length of the vegetation mat D, the length of the vegetation mat D can be adjusted by, for example, cutting the net material 2.

[0059] On the other hand, for vegetation mats D adjacent to each other in the slope length direction of the back slope N1 (from the slope to the slope shoulder, or from the slope shoulder to the slope toe), the main body 4 of the vegetation mat D on the slope shoulder side is overlapped from above onto the upper part (peripheral part 5b) of the overhanging part 5 of the vegetation mat D on the slope toe side, and net pins 10 are driven into the overlapped portion (see Figures 7(A) to (E)). When driving in the net pins 10, a part of the grass 3a of the grass mat 3 of the vegetation mat D on the slope shoulder side may be scraped from the net material 2 to make a hole, and connecting members such as net pins 10 may be driven into the hole to connect the net materials 2 (in this case, the hole will eventually be covered by the runner of grass 3a), or the grass mat 3 of the vegetation mat D on the slope shoulder side may be partially peeled away from the net material 2 and rolled up, the net pins 10 may be driven in in this state, and then the rolled-up grass mat 3 may be placed over it.

[0060] Similarly, when laying multiple vegetation mats D from the downstream side (see Figure 1) to the upstream side (see Figure 1) of the back method N1, the main body 4 of the upstream vegetation mat D is overlapped from above onto the peripheral portion 5a of the downstream vegetation mat D, and connecting members such as net pins 10 are driven into the overlapping portion.

[0061] According to the above-described method for constructing the vegetation mat D, the vegetation mat D used in this method is a highly shape-retaining vegetation mat D in which the strong surface rhizomes of the grass mat 3 are firmly intertwined with the nonwoven fabric 1 and net material 2. Since adjacent vegetation mats D are overlapped and fixed to the backing N1 with net pins 10, stakes 11, etc., the grass mats 3, whose four sides are essentially connected to each other, can be firmly attached to the backing N1 via the nonwoven fabric 1 and net material 2, and over time the grass mats 3 will firmly take root in the backing N1.

[0062] Therefore, uniform greening and vegetation can be ensured across the entire back embankment N1. Furthermore, even if river water overflows the top of the river embankment immediately after the installation of the vegetation mat D, the vegetation mat D will not easily collapse or peel off due to the overflowing water. Thus, it exerts its protective function for back embankment N1 from the moment of installation, which is not only aesthetically pleasing but also effectively reduces and prevents erosion and scouring of back embankment N1 caused by overflowing water.

[0063] In particular, for adjacent vegetation mats D, the main portion 4 of the vegetation mat D on the slope shoulder side and upstream side is overlapped from above onto the overhang portion 5 of the vegetation mat D on the slope toe side and downstream side. Therefore, when river water overflows the top of the river embankment, the edges of the vegetation mat D do not resist the overflowing water, allowing the overflowing water to flow smoothly, and effectively preventing the vegetation mat D from being washed away.

[0064] Furthermore, a nonwoven fabric 1 is formed on the underside of the vegetation mat D. This nonwoven fabric 1, like the grass mat 3, has an anti-suction effect that prevents soil from being drawn out from the underside of the vegetation mat D by flowing water during floods, etc. Therefore, even if there are areas where the grass mat 3 is missing from the vegetation mat D, for example, due to insufficient growth of grass 3a at the time of construction, or due to the expansion of the area where grass 3a is missing after construction due to the invasion of weeds (including the replacement of grass with clump-like plants) or the decline of grass 3a, the nonwoven fabric 1 can prevent soil from being drawn out from those areas and compensate for the function of the missing grass 3a. In addition, the nonwoven fabric 1 can also prevent soil and sand from being drawn out from the underside of the protruding parts 5 where grass mat 3 is not formed, or from the joints of the vegetation mat D.

[0065] Furthermore, by also providing the nonwoven fabric 1 to the protruding portion 5, it is possible to prevent soil from being sucked out through gaps when the lawn mats 3 are joined together, even if the edges of the lawn mats 3 are not straight and gaps are created between the lawn mats 3.

[0066] Furthermore, when using the new production method in which loosened turf is also placed in field 6 where the rhizomes of turf 3a remain to obtain the vegetation mat D, the net material 2 and the nonwoven fabric 1 are firmly integrated by the stolons, thus further improving the overall effect of preventing soil erosion in the vegetation mat D.

[0067] Furthermore, in order to obtain the above-mentioned anti-suction effect, it is desirable that the nonwoven fabric 1 has multiple holes or gaps that are impermeable to soil and sand forming the backing N1, and that allow the rhizomes of the grass 3a of the grass mat 3 to pass through to some extent.

[0068] Furthermore, since the nonwoven fabric 1 is impermeable to soil and sand, it can suppress and hinder the growth of weeds that have been blown in from the surrounding area onto the vegetation mat D after installation, and ultimately prevent weed intrusion.

[0069] Furthermore, because the turf mat 3 (turf 3a) has a rougher surface than synthetic resin waterproof sheets, etc., by laying the vegetation mat D on the back slope N1 with the turf facing upwards, the initial flow velocity of overflow water can be reduced, which in turn can reduce or prevent the erosion of the back slope soil and the scouring of the back slope's tail.

[0070] Furthermore, in the vegetation mat D of this example, the nonwoven fabric 1 and the grass mat 3 (grass 3a) can be held in place by the net material 2 to prevent them from being washed away, and by giving the net material 2 an appropriate mesh size, it is easy to avoid hindering the growth of the grass 3a.

[0071] Here, if there are depressions (see Figure 6(E)) at the joints of multiple vegetation mats D laid side by side on the back side N1, the overflow water that flows into these depressions will pull the vegetation mats away from the back side, making them prone to being washed away. However, in this example, the grass mats 3 of adjacent vegetation mats D are made to butt against each other, so depressions are less likely to form at the joints of the vegetation mats D, and consequently, the washing away of the vegetation mats D can be prevented.

[0072] Furthermore, if a gap occurs between the main body 4 of two adjacent vegetation mats D (see Figure 6(E)), there is a risk of erosion and suction by overflowing water in that gap. However, the construction method of the vegetation mat in this example eliminates such gaps, thereby reducing and preventing erosion and suction by overflowing water. Moreover, by making the overhanging portion 5 thinner than the main body 4, the step formed at the boundary between the main body 4 with the overhanging portion 5 laid on the lower side and the main body 4 without the overhanging portion 5 is reduced, thereby suppressing the adverse effects of that step.

[0073] Among the multiple vegetation mats D laid in a row along the back slope N1, the roughness coefficient of the vegetation mat D closest to the slope shoulder and the top of the embankment on the slope shoulder side of this vegetation mat D often differ significantly, or relatively large irregularities (steps) are formed between them. In this case, the vegetation mat D near the slope shoulder is likely to be eroded and washed away by overflowing water. However, in the construction method of the vegetation mats in this example, the net material 9 is connected to the vegetation mat D near the slope shoulder, thus reducing the risk of the vegetation mat D near the slope shoulder being washed away. The same applies to the vegetation mat D near the toe of the slope that is connected to the net material 8.

[0074] Furthermore, in the vegetation mat construction method of this example, the net material 9 is connected to the vegetation mat D near the slope crest by covering it from above, and the length of the net material 9 inserted into the top of the embankment is made greater than the length of the net material 9 covering the vegetation mat D near the slope crest. By inserting the net material 9 sufficiently deep into the top of the embankment in this way, it becomes difficult for it to be pulled out, thus ensuring that the vegetation mat D near the slope crest does not fall out. The same applies to the net material 8 installed to prevent the vegetation mat D near the toe of the slope from falling out. However, there are differences in the way the net material 9 on the slope crest side and the net material 8 on the toe side are installed (direction, etc.), and the net material 9 on the slope crest side is more likely to be pulled out by the force of overflowing water, so it is preferable to insert the net material 9 on the slope crest side deeper than the net material 8 on the toe side.

[0075] Furthermore, as shown in Figure 5(B), the net material 9 is fixed in a bent state from the portion laid on the protective member G toward the crushed stone layer S, making it less likely to be pulled out by overflowing water (shear force) compared to when it is fixed in a straight state.

[0076] As described above, in the vegetation mat construction method of this example, by covering at least the upstream portion of the vegetation mat D near the slope shoulder with net material 9 and at least the downstream portion of the vegetation mat D near the slope toe with net material 8, it is possible to prevent the peeling or washing away of both vegetation mats D due to overflow water. Furthermore, if peeling or washing away of the vegetation mat D near the slope shoulder and slope toe occurs, there is a risk that this will trigger a chain reaction of peeling or washing away of the vegetation mats D connected to these points. However, in this example, it is possible to prevent the peeling of the vegetation mat D near the slope shoulder and slope toe, which would be the starting point for such a chain reaction of peeling of vegetation mats D, thereby ensuring the protection of the back slope N1 and the reliability of greening.

[0077] In the construction method for the vegetation mat D consisting of the above configuration, the installation of the vegetation mat D onto the back slope N1 may be done using a crane or by hand, depending on the weight of the vegetation mat D. If a crane can be used at the site, it is possible to handle increased weight by making the vegetation mat D longer. In this case, the vegetation mat D can be manufactured so that its length in the longitudinal direction corresponds to the length (slope length) of the construction area (back slope N1) (3m or more, for example, 15m), rolled up and transported to the site, and then installed using a crane so that its longitudinal direction aligns with the longitudinal direction of the construction area. In this case, multiple vegetation mats D only need to be placed in the short direction (horizontal direction) of the vegetation mat D, eliminating the need to join vegetation mats D in the longitudinal direction (vertical direction). In this case, while it is still necessary to connect adjacent vegetation mats D in the horizontal direction (the shorter side of the vegetation mat D), it is no longer necessary to join the vegetation mats D in the vertical direction, which is highly effective in preventing the vegetation mats D from peeling off or being washed away.

[0078] The following describes a test conducted to confirm how differences in the configuration of the joints of vegetation mats laid in parallel along the back slope N1 affect erosion by overflow water. The test apparatus used in this test was constructed by installing a test specimen 16 in a part of a waterway 15 having a slope as shown in Figure 8(A) and a cross-section as shown in Figure 8(B). The test specimen 16 was constructed by placing a cage mat and an anti-erosion material inside a long member (bench flume) that was roughly U-shaped in longitudinal cross-section, filling it with rubble and crushed stone, filling it with topsoil, and then installing a vegetation mat. Figure 8(C) is a photograph showing approximately the entire test apparatus, Figure 8(D) is a photograph showing the water flow condition of the test specimen 16, and Figure 8(E) is a photograph showing the water flow condition upstream of the test specimen 16 in the test apparatus.

[0079] Then, for each of the 16 test specimens, water was continuously passed through them for 24 hours at a flow velocity of 3.5 to 4.0 m / s using the above-described test apparatus, in two cases: one where the vegetation mat was installed to correspond to the comparative examples in Figures 6(A) to (E), and another where the vegetation mat was installed to correspond to the present example in Figures 7(A) to (E). The condition of the joints was then checked.

[0080] As shown in Figure 9(A), when a vegetation mat is installed (corresponding to the comparative examples in Figures 6(A) to (E)), areas where there is no grass mat are formed at the seams, as shown in Figure 9(B), and it was confirmed that erosion occurs, as shown in Figure 9(C).

[0081] In contrast, when a vegetation mat is installed as shown in Figure 9(D) (corresponding to the example in Figures 7(A) to (E)), it was confirmed that no areas without grass mats are formed at the seams, as shown in Figure 9(E), and that erosion is prevented, as shown in Figure 9(F).

[0082] From the above tests, it can be seen that this example, in which grass mat 3 is placed at the joints of vegetation mat D, is effective in preventing erosion.

[0083] It should be noted that the present invention is not limited in any way to the embodiments described above, and can be implemented in various ways without departing from the spirit of the invention. For example, the following modifications can be given.

[0084] In the above embodiment, a vegetation mat D with a nonwoven fabric 1 pre-integrated is used for installation. However, the invention is not limited to this, and the nonwoven fabric 1 may first be stretched on the back surface N1, and then the pre-integrated flexible net material 2 and grass mat 3 may be stretched over the nonwoven fabric 1 using fastening means such as staples or sewing.

[0085] In this case, to attach the nonwoven fabric 1 to the backing N1, for example, the edges or other appropriate parts of the nonwoven fabric 1 can be anchored to the net material 8, 9, etc., and this anchoring can also be used for attaching the net material 2 and the grass mat 3.

[0086] As described above, the nonwoven fabric 1 may or may not be provided on the protruding section 5. If provided, it can enhance the effect of preventing the erosion of the back-facing N1 soil, and if not provided, it is advantageous for the growth of the turf 3a.

[0087] As described above, for two adjacent vegetation mats D, if the main body 4 of the vegetation mat D on the slope shoulder side or upstream side is superimposed from above onto the overhang 5 of the vegetation mat D on the slope toe side or downstream side, when river water overflows the top of the river embankment, the edges of each vegetation mat D do not resist the overflowing water, allowing the overflowing water to flow smoothly, and effectively preventing the vegetation mats D from being washed away. In this case, as shown in Figure 11(A), there is always an overhang 5 below the joint of the vegetation mats D, and by providing nonwoven fabric 1 on the overhang 5, the effect of preventing suction can be reliably obtained. Furthermore, in this case, as shown in Figure 11(A), the height of the connecting part of the vegetation mats D is higher on the slope shoulder side or upstream side and lower on the slope toe side or downstream side, so even if the flow velocity of the overflowing water changes due to this change in height, it is less likely to become a force that pulls the vegetation mats D out, which is advantageous.

[0088] However, this is not the only option; for example, as shown in Figure 11(B), for two adjacent vegetation mats D, the overhang portion 5 of the vegetation mat D on the slope shoulder side or upstream side may be superimposed from above onto the main portion 4 of the vegetation mat D on the slope toe side or downstream side.

[0089] Furthermore, in the above embodiment, as shown in Figure 2, the overhangs 5 ​​are provided only on two adjacent sides of the main body 4, which is rectangular in plan view. However, the overhangs 5 ​​are not limited to this, and may be provided on three or four sides of the main body 4, which is rectangular in plan view. That is, when arranging multiple vegetation mats D vertically and horizontally, it is ideal to overlap them so that in the vertical direction the vegetation mat D on the slope shoulder side is higher than the vegetation mat D on the slope toe side, and in the horizontal direction the vegetation mat D on the upstream side is higher than the vegetation mat D on the downstream side. To lay the vegetation mats D in this ideal manner, if there are overhangs 5 ​​on two sides, and the vegetation mat D shown in Figure 2 is for the left bank, then a vegetation mat D for the right bank may be needed in which the peripheral portion 5a in Figure 2 is provided on the left side of the main body 4 instead of the right side (or the peripheral portion 5b in Figure 2 is provided on the back side of the main body 4 instead of the front side). In other words, two types of vegetation mats D with peripheral portions 5a and 5b in a mirror image relationship are needed. In contrast, if the protruding sections 5 are provided on three or four sides of the main section 4, they can be used interchangeably for the left bank and the right bank without distinction, meaning that only one type of vegetation mat D will suffice.

[0090] Furthermore, if the protruding portion 5 is provided on three or four sides, in order to bring adjacent vegetation mats D's grass mats 3 together, the protruding portion 5 of one of the vegetation mats D may be folded towards the lower surface of the main body 4, or it may be cut off.

[0091] Needless to say, the modifications described herein may be combined as appropriate. [Explanation of Symbols]

[0092] 1 Nonwoven fabric 2 Netting 3. Lawn mat 3a grass 3b soil 4 Main part 5 Overhang 5a Peripheral portion 5b Peripheral portion 6 fields 7 Basket Mat 8 Netting 9 Netting 9a Projecting edge 10 Net Pins 11 stake 15 waterways 16 Specimen 91 Top surface 92 Overflow water 93 Back of the buttocks 94 Secret Method D Vegetation mat G Protective component G1 Slope section G2 Top section K-shaped timber N1 Reverse Method R: Direction of river water flow

Claims

1. Multiple vegetation mats, constructed by integrating nonwoven fabric and turf onto a net material, are laid in a row on the back slope of the embankment. The vegetation mat has a main body in which nonwoven fabric and grass are integrated into a net material, and an overhanging part that extends from the periphery of the main body and is thinner than the main body. The two adjacent vegetation mats are installed so that the protruding portion of one mat is laid under the main body of the other mat. For two adjacent vegetation mats along the slope, they are installed such that the overhang of the vegetation mat on the slope toe side is laid beneath the main body of the vegetation mat on the slope shoulder side. The net material and the nonwoven fabric constituting the main body extend to the protruding portion. A method for constructing vegetation mats, in which reinforcing nets fixed to the top of the embankment are connected to vegetation mats near the slope shoulder.

2. The reinforcing net is connected to the vegetation mat near the shoulder of the slope by covering it from above, The method for constructing a vegetation mat according to claim 1, wherein the length of the reinforcing net inserted into the top of the embankment is greater than the length of the net covering the vegetation mat near the shoulder of the slope.

3. The method for installing a vegetation mat according to claim 1 or 2, wherein the grass of adjacent vegetation mats is butted against each other.

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