Reinforcement structure for levees and construction method for reinforcement structure for levees

Abstract

To provide an embankment reinforcement structure using a wall that is inserted into the embankment body capable of effectively maintaining the ground resistance of the wall against washing away of the embankment ground during overflow.SOLUTION: A provided embankment reinforcement structure includes: a first wall to be installed on the opposite side of the embankment body from the water area; and a second wall that is inserted at the water area side portion of the embankment. In at least some sections along the length of the embankment, a region having water permeability is formed in the first wall at a position lower than the height of the top of the second wall.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a reinforcing structure for a levee and a construction method of the reinforcing structure for a levee.

Background Art

[0002] In levees such as those along rivers, there are concerns about levee breaches due to cracks and settlements in the levee body caused by earthquakes, and erosion of the levee body due to overtopping during flood surges. As a countermeasure against this, for example, in Patent Document 1, a reinforcing structure for a levee is described in which steel sheet pile walls extending in the continuous direction of the levee body are driven into the berms on both sides in the width direction of the levee body, and the heads of the respective steel sheet pile walls are connected by tie rods. Such a reinforcing structure using double steel sheet pile walls is known to be effective as a liquefaction countermeasure because the two rows of steel sheet pile walls suppress the deformation and movement of soil during an earthquake.

Prior Art Documents

Patent Documents

[0003] [[ID=X]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, regarding the reinforcing structure for a levee using double steel sheet pile walls as described above, although research has progressed as a liquefaction countermeasure during an earthquake, a reasonable structure for improving the strength of the levee when overtopping and scouring occur due to flood surges has not yet been sufficiently proposed. For example, even when scouring occurs, it is conceivable to drive the wall deeper to maintain the ground resistance of the wall body, or to perform ground improvement on the side of the levee body opposite to the water area to suppress the scouring itself, but this is not necessarily preferable from the perspective of economy.

[0005] Therefore, the present invention aims to provide a reinforcing structure for a levee that uses a wall cast into the levee body, which can effectively maintain the ground resistance of the wall against scouring of the levee body ground during overtopping, and a method for constructing such a reinforcing structure for a levee. [Means for solving the problem]

[0006] [1] A reinforcing structure for a levee, comprising a first wall cast on the portion of the levee body opposite to the water body, and a second wall cast on the portion of the levee body facing the water body, wherein in at least a portion of the length of the levee body, a water-permeable area is formed in the first wall at a position lower than the height of the upper end of the second wall. [2] The water-permeable region is formed by the upper end of the first wall being lower than the upper end of the second wall, the reinforcing structure for the embankment according to [1]. [3] The water-permeable region is formed by water-permeable holes formed in the region on the upper end side of the first wall, the reinforcing structure for the embankment according to [1]. [4] A reinforcing structure for a levee according to any one of items [1] to [3], wherein the embedment length of the first wall is longer than the embedment length of the second wall. [5] The reinforcing structure for a levee according to any one of items [1] to [4], further comprising a reinforcing material that covers the embankment constituting the levee between the first wall and the second wall. [6] The reinforcing material is positioned at least in part between the first wall and the second wall, at a position lower than the lower end of the water-permeable area, as described in [5]. [7] The reinforcing structure for a levee according to [6], wherein the reinforcing material is joined at a position lower than the upper end of the first wall. [8] The reinforcing structure for a levee according to any one of items [1] to [7], further comprising a connecting member that connects the first wall and the second wall. [9] The first wall structure is a steel sheet pile wall, a reinforcing structure for a levee according to any one of items [1] to [8].

[10] The water-permeable region is formed by driving a plurality of steel sheet piles constituting the steel sheet pile wall at at least two different upper end heights such that the upper end of the steel sheet pile wall has an uneven shape in the longitudinal direction of the embankment, as described in [9].

[11] The embankment reinforcement structure according to

[10] , wherein the plurality of steel sheet piles include a first steel sheet pile driven so that its upper end is at a first height and a second steel sheet pile driven so that its upper end is at a second height lower than the first height, and the first steel sheet piles are driven on both sides of the second steel sheet pile in the longitudinal direction of the embankment.

[12] The first wall is a first steel sheet pile wall, the second wall is a second steel sheet pile wall with a cap concrete poured over its upper end, and the water-permeable area is formed by either not pouring a cap concrete over the upper end of the first steel sheet pile wall, or by pouring a cap concrete at the upper end of the first steel sheet pile wall that is shorter in height than the cap concrete of the second steel sheet pile wall, as described in [1]. A method for constructing a reinforcing structure for a levee according to any one of paragraphs

[13] , [9] to

[11] , wherein the plurality of steel sheet piles include a first steel sheet pile and a second steel sheet pile, a longitudinal joint member is attached to the upper end of the second steel sheet pile, the joint of the longitudinal joint member is fitted to the first steel sheet pile which is driven in advance and the first steel sheet pile which is driven in subsequently, respectively, and the second steel sheet pile and the longitudinal joint member are driven, and after driving, the longitudinal joint member is removed from the second steel sheet pile, a method for constructing a reinforcing structure for a levee. [Effects of the Invention]

[0007] According to the above configuration, a permeable region is formed in the first wall, which is constructed on the side of the dam opposite the water body, at a position lower than the upper end of the second wall, which is constructed on the side facing the water body. Because the drop height of the overflow water flowing down from this region is reduced, the force eroding the ground on the side of the first wall opposite the water body is weakened. Therefore, according to the above configuration, the ground resistance of the wall can be effectively maintained against erosion of the dam ground during overflow. The jump water generated when the overflow water flows down from the wall to the top of the dam reduces the energy of the overflow water, and also has the effect of reducing the erosion depth. By maintaining the ground resistance of the wall, the collapse of the entire dam can be prevented. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view showing a reinforcing structure for a levee according to the first embodiment of the present invention. [Figure 2] Figure 1 is a schematic cross-sectional view showing the situation during flooding in the reinforcing structure of the embankment. [Figure 3] This is a schematic cross-sectional view showing the situation during flooding in a reinforcing structure for a levee that does not employ the structure according to the embodiment of the present invention. [Figure 4] This is a cross-sectional view showing a first modified example of a levee reinforcement structure according to the first embodiment of the present invention. [Figure 5] This is a cross-sectional view showing a second modified example of the reinforcing structure for a levee according to the first embodiment of the present invention. [Figure 6] This is a cross-sectional view showing a third modified example of the reinforcing structure for a levee according to the first embodiment of the present invention. [Figure 7] This is a cross-sectional view showing a fourth modified example of the embankment reinforcement structure according to the first embodiment of the present invention. [Figure 8] This figure shows a method for constructing a reinforcing structure for a levee according to the first embodiment of the present invention. [Figure 9] This is a diagram illustrating a second embodiment of the present invention. [Figure 10] This figure illustrates a modified example of a second embodiment of the present invention. [Figure 11] It is a figure showing a construction method of a levee reinforcement structure in a second embodiment of the present invention. [Figure 12] It is a figure for explaining a third embodiment of the present invention. [Figure 13] It is a figure showing another example of a third embodiment of the present invention. [Figure 14] It is a figure showing another example of a third embodiment of the present invention. [Figure 15] It is a cross-sectional view of a levee reinforcement structure according to a fourth embodiment of the present invention. [Figure 16] It is a cross-sectional view of a levee reinforcement structure according to a fifth embodiment of the present invention. [Figure 17] It is a figure showing a modification example regarding the arrangement of reinforcing materials. [Figure 18] It is a figure showing a modification example regarding the arrangement of reinforcing materials. [Figure 19] It is a figure showing a modification example regarding the arrangement of reinforcing materials. [Figure 20] It is a figure showing a modification example regarding the arrangement of reinforcing materials. [Figure 21] It is a figure showing a modification example regarding the arrangement of reinforcing materials. [Figure 22] It is a figure showing a modification example regarding the arrangement of reinforcing materials. [Figure 23] It is a figure showing the flow velocity of overflow water in an example. [Figure 24] It is a figure showing the flow velocity of overflow water in a comparative example. [Figure 25] It is a graph showing the relationship between the ratio of the protruding height of the steel sheet pile wall in an example and a comparative example and the pressure when the overflow water hits the ground surface on the back side of the river.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0010] Figure 1 is a perspective view showing a reinforcing structure for a levee according to a first embodiment of the present invention. In this embodiment, the reinforcing structure 10 for the levee includes a steel sheet pile wall 11, which is a first wall body driven into the river-facing side (opposite side from the river 2, which is the body of water) of the levee body 1; a steel sheet pile wall 12, which is a second wall body driven into the river-facing side (river 2 side) of the levee body 1 and satisfying the planned height; and a tie rod 13, which is a connecting member that connects the steel sheet pile walls 11 and 12. In the illustrated example, the steel sheet pile walls 11 and 12 are each driven into the shoulder portion of the slope, which is the boundary between the slope and the top surface of the levee body 1, or its vicinity. In this embodiment, a tie rod 13 is arranged as the connecting member, but the connecting member is not particularly limited as long as it is a member that connects the steel sheet pile walls 11 and 12 and can transmit tensile force and shear force. For example, the connecting member may be a wall body made of steel material installed perpendicular to each steel sheet pile wall.

[0011] In this embodiment, in the reinforcing structure 10 of the embankment described above, the steel sheet piles constituting each steel sheet pile wall are driven such that the upper end of the steel sheet pile wall 11 is lower than the upper end of the steel sheet pile wall 12. In other words, if the lengths of each steel sheet pile are the same, the steel sheet piles constituting the steel sheet pile wall 11 have a longer embedment length than the steel sheet piles constituting the steel sheet pile wall 12. Alternatively, the steel sheet pile wall 11 is composed of steel sheet piles that are shorter than the steel sheet piles constituting the steel sheet pile wall 12. In the following description, the height of the upper end of the steel sheet pile wall 12 is denoted as the embankment height H. The embankment height H is approximately equal to the top height of the embankment body 1. On the other hand, the height h of the upper end of the steel sheet pile wall 11 is lower than the embankment height H. In the illustrated example, heights H1 and H2 are based on the ground surface G (the boundary between the embankment body and the ground).

[0012] Figure 2 is a schematic cross-sectional view showing the situation during overtopping in the reinforced structure of the embankment shown in Figure 1, and corresponds to the cross-sectional view along line II-II in Figure 1. In the illustrated state, the water level of River 2 rises above the embankment height H, and the overflowing water flows from the river front side over the embankment body 1 to the river back side. This overflowing water causes erosion of the slope of the embankment body 1 and scouring of the ground on the river back side. The depth of ground scouring at this time is denoted as D.

[0013] On the other hand, FIG. 3 is a schematic cross-sectional view showing the situation during overtopping in a levee reinforcement structure that does not adopt the structure according to the embodiment of the present invention. In the example of FIG. 3, as the levee reinforcement structure 90, a steel sheet pile wall 91 driven in the backside part of the levee body 1, a steel sheet pile wall 92 driven in the frontside part of the river, and a connecting member 93 are arranged. Different from the embodiment of the present invention, the heights of the upper ends of the steel sheet pile walls 91 and 92 are the same and equal to the levee height H. At this time, let the scouring depth of the ground occurring on the backside of the river be D'.

[0014] When comparing the example of FIG. 2 and the example of FIG. 3 above, the falling height of the overtopping water in the example of FIG. 2 is the height h of the upper end of the steel sheet pile wall 11, while the falling height of the overtopping water in the example of FIG. 3 is the height of the upper end of the steel sheet pile wall 91, that is, the levee height H. Here, as described above, since the height h of the upper end of the steel sheet pile wall 11 is lower than the levee height H (h < H), the force of the overtopping water with the falling height h scouring the ground in the example of FIG. 2 is weaker than the force of the overtopping water with the falling height H scouring the ground in the example of FIG. 3. Therefore, the scouring depth D in the example of FIG. 2 is shallower than the scouring depth D' in the example of FIG. 3 (D < D'). Therefore, in the example of FIG. 2, scouring of the levee body ground can be suppressed more than in the example of FIG. 3, and the ground resistance to the steel sheet pile wall 11 can be maintained.

[0015] Thus, in the levee reinforcement structure 10 according to the present embodiment, even if overtopping occurs during a flood, scouring of the levee body ground in the backside part of the steel sheet pile wall 11 can be suppressed, and the ground resistance to the steel sheet pile wall 11 can be maintained. Thereby, deformation and displacement of the steel sheet pile walls 11 and 12 can be prevented even during overtopping, and the function of the reinforcement structure 10 can be maintained. In addition, the top end part of the levee body 1 can be easily repaired even if it is washed away.

[0016] In the first embodiment described above, the height h of the upper end of the steel sheet pile wall 11 is lower than the dam height H, thereby forming a region through which overflow water flows during overtopping. In this specification, such a region is also referred to as a water-permeable region. In the first embodiment, as shown in Figure 1, the height h of the upper end of the steel sheet pile wall 11 is lower than the dam height H, which is the height of the upper end of the steel sheet pile wall 12, throughout the entire length (x-direction) of the dam body 1. In other words, in the first embodiment, a water-permeable region is formed in the steel sheet pile wall 11 at a position lower than the dam height H throughout the entire length of the dam body 1.

[0017] Figure 4 is a cross-sectional view showing a first modified example of a reinforcing structure for a levee according to the first embodiment of the present invention. In the example in Figure 4, the embedment length L1 of the steel sheet pile wall 11 on the river-back side is longer than the embedment length L2 of the steel sheet pile wall 12 on the river-front side. As described above, if scouring of the levee body ground is suppressed by making the height h of the upper end of the steel sheet pile wall 11 lower than the levee height H, the stability of the structure consisting of the steel sheet pile walls 11, 12 and tie rods 13 will be improved. Therefore, as in the illustrated example, it is also possible to reduce the amount of steel material required for the steel sheet pile wall by shortening the embedment length of the steel sheet pile wall 12, which is the wall on the river-front side.

[0018] Figures 5 and 6 are cross-sectional views showing second and third modified examples of the reinforcing structure for a levee according to the first embodiment of the present invention. In the example in Figure 5, the steel sheet pile wall 11 on the river-back side is driven into the slope further back from the shoulder of the levee body 1. In the example in Figure 6, the steel sheet pile wall 12 on the river-front side is driven into the shoulder of the river-back side of the levee body 1, and the steel sheet pile wall 11 on the river-back side is driven into the slope further back from there. Thus, in this embodiment, the positions for driving the steel sheet pile walls 11 and 12 are not particularly limited as long as the steel sheet pile wall 11 is driven on the river-back side of the levee body 1 and the steel sheet pile wall 12 is driven on the river-front side of the levee body 1 than the steel sheet pile wall 11, and the steel sheet pile walls may be driven into the slope portion of the levee body 1 as shown in the modified examples in Figures 5 and 6.

[0019] Figure 7 is a cross-sectional view showing a fourth modified example of the reinforcing structure for a levee according to the first embodiment of the present invention. The levee body 1', whose top surface has been eroded by overflow water during overtopping, is shown by a dashed line. In this modified example, a reinforcing material 16 is laid between the steel sheet pile wall 11 and the steel sheet pile wall 12 to cover the embankment that constitutes the levee body 1. The reinforcing material 16 may be made of an impermeable material such as a rubber sheet, or it may be a mesh-like member. Also, the reinforcing material 16 does not have to cover the entire space between the steel sheet pile wall 11 and the steel sheet pile wall 12, but may cover only the area on the river side, for example. The reinforcing material 16 is normally covered by the embankment near the top surface, but when the embankment near the top surface is washed away due to overtopping, it is exposed on the surface of the levee body 1 that is in contact with the overflow water, preventing further washing away of the embankment between the steel sheet pile wall 11 and the steel sheet pile wall 12 below the reinforcing material 16. The reinforcing member 16 may be positioned above the tie rod 13, as shown in the example in Figure 7, or below the tie rod 13, as shown in the examples from Figure 15 onwards.

[0020] By laying the reinforcing material 16 as described above, it is possible to prevent the occurrence of steps due to scouring when water overflows near the steel sheet pile wall 12 on the river side, and to suppress erosion that may occur when overflowing water flows into the embankment between the steel sheet pile wall 11 and the steel sheet pile wall 12. In turn, it is possible to maintain the resistance to water pressure expected of the embankment between the steel sheet pile wall 11 and the steel sheet pile wall 12, and to suppress the decrease in the crest height of the dam body 1 caused by the deformation of the steel sheet pile wall 11 due to the progression of embankment runoff.

[0021] Figure 8 shows a method for constructing a reinforcing structure for a levee according to the first embodiment of the present invention. Figure 8(a) shows a cross-section of the levee body 1 before construction. From this state, first, as shown in Figure 8(b), the top portion of the levee body 1 is excavated. Next, as shown in Figure 8(c), a steel sheet pile wall 11 is driven into the river-facing side of the levee body 1, and a steel sheet pile wall 12 is driven into the river-facing side of the levee body 1. At this time, the upper end of the driven steel sheet pile wall 11 is located near the excavated top of the levee body 1, and the upper end of the driven steel sheet pile wall 12 protrudes upward from the excavated top of the levee body 1. The steel sheet pile walls 11 and 12 are connected by tie rods 13. Finally, as shown in Figure 8(d), the excavated portion of the levee body 1 is backfilled. After backfilling, the upper end of the steel sheet pile wall 11 is embedded inside the levee body 1, and the upper end of the steel sheet pile wall 12 is located near the top of the levee body 1.

[0022] (Second embodiment) Figure 9 is a diagram illustrating a second embodiment of the present invention and is a front view of the steel sheet pile wall 11 on the riverside (the dam body 1 is not shown). In this embodiment as well, the area of ​​water permeability in the steel sheet pile wall 11 on the riverside is formed by the fact that the height h of the upper end of the steel sheet pile wall 11 is lower than the dam height H. However, unlike the first embodiment, the area of ​​water permeability described above is formed only in a portion of the length direction (x direction) of the dam body 1. More specifically, the steel sheet pile wall 11 is formed by a plurality of steel sheet piles 111 driven at at least two different upper end heights such that the upper end has an uneven shape in the length direction of the dam body 1. In the illustrated example, steel sheet piles 111A with an upper end height H and steel sheet piles 111B with an upper end height h are driven alternately one by one.

[0023] In the example above, in a section of the length of the dam body 1 that has a permeable area, that is, in the area where the height of the upper end of the steel sheet pile wall 11 is h, the top of the dam body 1 is partially eroded by the overflowing water during overtopping, and the overflowing water flows down to the riverside from the exposed permeable area. The overflowing water that flows down from the water into this area is affected by the attenuation of energy due to the jump when the water flows from the steel sheet pile wall 12 into the permeable area, and the height of the overflowing water's fall (potential energy) is reduced. This suppresses scouring of the dam body ground on the riverside and maintains the ground resistance to the steel sheet pile wall 11. As a result, deformation and displacement of the steel sheet pile walls 11 and 12 can be prevented even during overtopping, and the function of the reinforcing structure 10 can be maintained.

[0024] Figure 10 is a diagram illustrating a modified example of the second embodiment of the present invention. In the illustrated example, in the steel sheet pile wall 11, steel sheet piles 111A with an upper end height H and steel sheet piles 111B with an upper end height h are driven alternately in a ratio of 2:1. In this way, steel sheet piles 111A and 111B with different upper end heights can be driven alternately in any ratio. At this time, the average of the upper end heights of each steel sheet pile in the steel sheet pile wall 11 is h. ave It is preferable that this is, for example, about 50% to 90% of the dam height H.

[0025] Figure 11 shows a method for constructing a reinforcing structure for a levee according to a second embodiment of the present invention. In the illustrated example, as shown in Figure 11(a), steel sheet pile walls 11 and 12 are driven without excavating the top of the levee body 1. For the steel sheet piles 111A with an upper end height of H that make up the steel sheet pile wall 12 on the river side and the steel sheet pile wall 11 on the river back side, their upper ends are located near the top of the levee body 1, so they can be driven using normal construction methods. On the other hand, for the steel sheet piles 111B with an upper end height of h that make up the steel sheet pile wall 11 on the river back side, a longitudinal joint member 17 is connected to the upper end using a jig 17A, and then driven until the upper end of the longitudinal joint member 17 is near the top of the levee body 1. The longitudinal joint member 17 is a member with a cross-section having joints at both ends, similar to the steel sheet pile 111B, and the joints of the longitudinal joint member 17 can be fitted into the joints of the steel sheet piles 111A that were driven in advance on both sides of the steel sheet pile 111B, and into the joints of the steel sheet piles 111A that are driven in subsequent.

[0026] After the steel sheet pile walls 11 and 12 are driven in as described above, if the longitudinal joint member 17 is pulled out and removed as shown in Figure 11(b), the steel sheet piles 111 with an upper end height of h that make up the steel sheet pile wall 11 can be embedded inside the embankment 1 without excavating the embankment 1. Although the tie rods 13 are not shown in Figure 11, if the tie rods 13 are connected to the steel sheet piles with an upper end height of H that make up the steel sheet pile wall 11 and to the steel sheet pile wall 12, respectively, the tie rods 13 can also be installed without excavating the embankment 1.

[0027] (Third embodiment) Figure 12 is a diagram illustrating a third embodiment of the present invention and is a front view of the steel sheet pile wall 11 on the riverside (the embankment 1 is not shown). In this embodiment, the permeable area of ​​the steel sheet pile wall 11 on the riverside is formed by water passage holes 14 formed in the upper end region of at least a portion of the steel sheet piles 111 that constitute the steel sheet pile wall 11. The water passage holes 14 form a permeable area of ​​the steel sheet pile wall 11 at a position lower than the embankment height H in a portion of the length direction (x direction) of the embankment 1. By setting the size and number of water passage holes 14 so that these permeable areas occupy, for example, 10% to 50% of the area of ​​the steel sheet pile wall 11 above the ground surface G, this embodiment, as in the first and second embodiments described above, can suppress scouring of the embankment ground on the riverside during overflow and maintain ground resistance to the steel sheet pile wall 11.

[0028] Furthermore, this embodiment offers construction advantages. Since the height of the upper end of the steel sheet pile 111, in which the water passage holes 14 are formed, is approximately the same as the dam height H, the steel sheet pile walls 11 and 12 can be driven without excavating the dam body 1. When water overtops the dam, the top of the dam body 1 is eroded by the overflowing water, and the overflowing water flows down to the riverside through the exposed water passage holes 14.

[0029] Figures 13 and 14 show another example of a third embodiment of the present invention. In the illustrated example, the water-permeable region of the steel sheet pile wall 11 on the riverside is formed by a perforated plate 15 incorporated into the upper end region of at least a portion of the steel sheet piles 111 that constitute the steel sheet pile wall 11. The perforated plate 15 is a material such as perforated metal or mesh, and a portion of the steel sheet pile 111 is either perforated or cut out and fitted with the perforated plate. The perforated plate 15 may be incorporated into all of the steel sheet piles 111, as in the example in Figure 13, or into some of the steel sheet piles 111, as in the example in Figure 14.

[0030] (Fourth embodiment) Figure 15 is a cross-sectional view of a reinforcing structure for a levee according to a fourth embodiment of the present invention. In this embodiment, the reinforcing member 16, as described above with reference to Figure 7, is joined at a position lower than the upper end of the steel sheet pile wall 11 on the river-back side. In the illustrated example, the reinforcing member 16 is arranged almost horizontally, and if the height of the steel sheet pile wall 12 on the river-front side is H1 and the height of the steel sheet pile wall 11 on the river-back side is H2, then H1 > H2 > 0. By joining the reinforcing member 16 at a position lower than the upper end of the steel sheet pile wall 11, an appropriate height difference of H2 is created between the reinforcing member 16 and the upper end of the steel sheet pile wall 11 on the river-back side, after the embankment near the top is washed away, backflow occurs in the overflow water flowing along the exposed reinforcing member 16. Here, backflow occurs when overflow water flowing from the riverfront side to the riverback side along the reinforcing material 16 is partially pushed back to the riverfront side as it passes over the steel sheet pile wall 11 on the riverback side, resulting in a flow in the opposite direction to the flow of overflow water from the riverfront side to the riverback side. Backflow causes energy loss in the overflow water, further weakening the scouring force on the ground as the overflow water flows down to the riverback side after passing over the steel sheet pile wall 11.

[0031] (Fifth embodiment) Figure 16 is a cross-sectional view of a reinforcing structure for a levee according to the fifth embodiment of the present invention. In this embodiment, similar to the fourth embodiment described above, the reinforcing member 16 is joined at a position lower than the upper end of the steel sheet pile wall 11 on the river-back side, and a difference in height between the river-front and river-back wall bodies is created by the cap concrete 18A and 18B. More specifically, in this embodiment, the first wall body cast on the river-back side is composed of a steel sheet pile wall 11 and cap concrete 18B cast on the upper end of the steel sheet pile wall 11. On the other hand, the second wall body cast on the river-front side is composed of a steel sheet pile wall 12 and cap concrete 18A cast on the upper end of the steel sheet pile wall 12. In the illustrated example, the upper ends of the steel sheet pile walls 11 and 12 are at the same height, but a difference in wall body height is created because the height of the cap concrete 18B on the river-back side is smaller than the cap concrete 18A on the river-front side. In other words, in this embodiment, the permeable area formed in the river-back wall at a position lower than the dam height H is formed by the difference in height between the cap concretes 18A and 18B. In other examples, the permeable area may be formed by pouring cap concrete 18A at the upper end of the river-front steel sheet pile wall 12, while not pouring cap concrete at the upper end of the river-back steel sheet pile wall 11.

[0032] Furthermore, the configuration of the cap concrete 18A and 18B as described above does not necessarily have to be adopted in a form in which the reinforcing material 16 is positioned lower than the lower end of the water-permeable area, as in the example in Figure 16. In other embodiments described above, specifically, for example, in cases where the reinforcing material 16 is not provided, or in cases where the reinforcing material 16 is joined to the upper end of the steel sheet pile wall 11 on the river-back side, the water-permeable area may be formed by the difference in height between the cap concrete 18A and 18B, or by pouring only the cap concrete 18A on the river-front side.

[0033] (Variations regarding the arrangement of reinforcing materials) Figures 17 to 22 show modified examples of the arrangement of the reinforcing members 16 for the fourth and fifth embodiments described above. In the illustrated examples, the arrangement of the reinforcing members 16 is changed in the fourth embodiment, but the arrangement of the reinforcing members 16 may be changed similarly in the fifth embodiment. In the examples described below, the reinforcing members 16A to 16F are positioned lower than the permeable area (the upper end of the steel sheet pile wall 11 in the illustrated examples) in at least a portion between the steel sheet pile wall 11 and the steel sheet pile wall 12. In such cases as well, by generating a backflow of overflow water that flows along the reinforcing members 16 that are exposed after the embankment near the top has been washed away, the force that scours the ground when the overflow water flows down to the riverside can be further weakened.

[0034] In the example shown in Figure 17, the reinforcing member 16A is positioned at an angle such that it decreases in elevation from the steel sheet pile wall 11 on the river-back side to the steel sheet pile wall 12 on the river-front side. The position where the reinforcing member 16A is attached to the steel sheet pile wall 12 on the river-front side is lower than the upper end of the steel sheet pile wall 11 on the river-back side (height difference H2). In the illustrated example, the reinforcing member 16A is attached to a position lower than the upper end of the steel sheet pile wall 11 on the river-back side as well, but the reinforcing member 16A may also be attached to the upper end of the steel sheet pile wall 11 on the river-back side.

[0035] In the example shown in Figure 18, the reinforcing member 16B is positioned at an angle such that it decreases in elevation from the steel sheet pile wall 12 on the river side towards the steel sheet pile wall 11 on the river side. The reinforcing member 16B is installed at a position lower than the upper end of the steel sheet pile wall 11 on the river side (height difference H2). In the illustrated example, the position where the reinforcing member 16B is installed on the steel sheet pile wall 12 on the river side is also lower than the upper end of the steel sheet pile wall 11 on the river side, but the position where the reinforcing member 16B is installed on the steel sheet pile wall 12 on the river side may be the same as or higher than the upper end of the steel sheet pile wall 11 on the river side.

[0036] In the example shown in Figure 19, the reinforcing members 16C are arranged in a stepped manner, becoming lower from the steel sheet pile wall 12 on the river-facing side towards the steel sheet pile wall 11 on the river-back side. The reinforcing members 16C are installed at a position lower than the upper end of the steel sheet pile wall 11 on the river-back side (height difference H2). In the illustrated example, the position where the reinforcing members 16C are installed on the steel sheet pile wall 12 on the river-facing side is also lower than the upper end of the steel sheet pile wall 11 on the river-back side, but the position where the reinforcing members 16C are installed on the steel sheet pile wall 12 on the river-facing side may be the same as or higher than the upper end of the steel sheet pile wall 11 on the river-back side.

[0037] In the example shown in Figure 20, the reinforcing member 16D is positioned to form a stepped recess near the middle of the steel sheet pile walls 11 and 12. The lowest part of the reinforcing member 16D is lower than the upper end of the steel sheet pile wall 11 on the riverside side (height difference H2). In the illustrated example, the attachment point of the reinforcing member 16D to the steel sheet pile wall 11 on the riverside side is also lower than the upper end of the steel sheet pile wall 11, but the reinforcing member 16D may also be attached to the upper end of the steel sheet pile wall 11.

[0038] In the example shown in Figure 21, the reinforcing member 16E is positioned to form a recess including an inclined surface near the middle of the steel sheet pile walls 11 and 12. The lowest part of the reinforcing member 16E is lower than the upper end of the steel sheet pile wall 11 on the riverside side (height difference H2). In the illustrated example, the attachment position of the reinforcing member 16E to the steel sheet pile wall 11 on the riverside side is also lower than the upper end of the steel sheet pile wall 11, but the reinforcing member 16E may also be attached to the upper end of the steel sheet pile wall 11.

[0039] In the example shown in Figure 22, the reinforcing member 16F is positioned to form a convex portion including an inclined surface near the midpoint of the steel sheet pile walls 11 and 12. The reinforcing member 16F is installed at a position lower than the upper end of the steel sheet pile wall 11 on the riverside side (height difference H2). In the illustrated example, the highest part of the reinforcing member 16F is lower than the upper end of the steel sheet pile wall 11, but the highest part of the reinforcing member 16F may be at the same level as or higher than the upper end of the steel sheet pile wall 11 on the riverside side.

[0040] (Results of the first experiment) The following describes the results of the first experiment, which analyzed the erosion of the levee body due to overflow using a model experimental apparatus. In a model experimental apparatus that modeled the levee at a 1 / 15 scale, the height of the upper end of the wall cast on the river-facing side of the levee body was set lower than the height of the wall cast on the river-facing side to generate overflow from the river-facing side. Specifically, the levee body was set to a height of 400 mm from the ground surface. In the example, the upper end of the wall on the river-facing side was set to a height of 400 mm from the ground surface, and the upper end of the wall on the river-facing side was set to a height of 250 mm from the ground surface. In the comparative example, the upper ends of both walls were set to a height of 400 mm from the ground surface. In the example, the height of the upper end of the wall (250 mm) is approximately 60% of the levee height (400 mm).

[0041] In both the example and comparative example described above, when overflow was generated from the river-facing side, the overflowing water eroded the slope on the river-facing side, causing scouring of the foundation ground. One hour after the start of overflow, the scouring depth was measured to be 40 mm in the example and 100 mm in the comparative example. This result indicates that by reducing the drop height of the overflowing water through the difference in the height of the upper end of the wall, the force of the overflowing water scouring the ground is weakened, suppressing scouring and maintaining the ground resistance of the wall.

[0042] (Results of the second experiment) Next, we will explain the results of a second experiment in which we calculated the pressure when overflowing water hits the ground surface on the river's back side using the Volume of Fluid (VOF) method, specifically the interfacial capture method for multiphase flow. For the calculation, we assumed an overflow depth of 0.4m, a flow velocity of 1.0m / s, and a flow rate of 0.4m for a levee with a height of 6.0m, a head width of 6.0m, and a slope width of 12.0m (slope gradient of 1:2). 3The experiment assumed an overflow occurring at a rate of / s. On the river-facing side, a steel sheet pile wall with an upper end height equal to the dam height was installed, and on the river-back side, a steel sheet pile wall with an upper end height less than the dam height was installed, and it was assumed that the embankment on the river-back side had already been washed away below the steel sheet pile wall on the river-back side. Furthermore, reinforcing material was installed almost horizontally from a position 1.2m below the upper end of the steel sheet pile wall on the river-facing side to the steel sheet pile wall on the river-back side, and it was assumed that the erosion of the embankment in the area between the steel sheet pile walls was suppressed by the height of the reinforcing material. In the experiment, the height difference between the reinforcing material and the steel sheet pile wall on the river-facing side was defined as H1, and the height difference between the reinforcing material and the steel sheet pile wall on the river-back side was defined as H2, and the pressure of the overflowing water was calculated by setting the heights H1 and H2 as shown in Table 1 below.

[0043] [Table 1]

[0044] Of the examples shown in Table 1, Example 1 is an example in which the upper end of the wall on the river-back side is lower than the upper end of the wall on the river-front side, but the reinforcing material is installed at the same height as the upper end of the wall on the river-back side (corresponding to the example in Figure 7). Examples 2 and 3 are examples in which the upper end of the wall on the river-back side is lower than the upper end of the wall on the river-front side, and the reinforcing material is installed at a position lower than the upper end of the wall on the river-back side (corresponding to the example in Figure 15). Comparative Example 1 is an example in which the upper end of the wall on the river-back side and the upper end of the wall on the river-front side are at the same height (corresponding to the example in Figure 3, excluding the reinforcing material).

[0045] Figure 23 shows the flow velocity of the overflow water in Example 2. In this example, backflow occurs when the overflow water, which has flowed along the reinforcing material, goes over the steel sheet piles on the riverside, causing a decrease in the flow velocity of the overflow water that flows over the steel sheet piles and down to the riverside. The decrease in flow velocity indicates an energy loss of the overflow water, which reduces the pressure when the overflow water hits the ground surface on the riverside, weakening the force that scouring the ground.

[0046] On the other hand, Figure 24 shows the flow velocity of the overflowing water in Comparative Example 1. In this example, the difference in height between the steel sheet pile walls on the river-facing and river-backward sides is small, and the height difference between the reinforcing material and the upper end of the steel sheet pile wall on the river-backward side is large, so the decrease in flow velocity of the overflowing water due to backflow, as in the example in Figure 23, does not occur. More specifically, as the water depth in the region between the steel sheet pile walls increases, the flow of the overflowing water separates into internal and surface flows, and vortices are generated in the internal flow while vortices and backflow are not generated in the surface flow, so there is no decrease in flow velocity, i.e., no energy loss occurs.

[0047] Figure 25 is a graph showing the relationship between the ratio of the protruding heights of the steel sheet pile walls (H2 / H1) and the pressure of the overflowing water in the examples and comparative examples. As shown in the graph, the pressure, which was 8.5 kPa in Example 1 where H2 / H1=0, becomes lower in Example 2 (3 kPa) where H2 / H1=0.25 and in Example 3 (6.5 kPa) where H2 / H1=0.6 than in Example 1. This is because energy loss occurs due to the backflow of the overflowing water, as shown in Figure 23. On the other hand, in Comparative Example 1 where H2 / H1=1, the pressure is 12 kPa, which is higher than in Example 1. This is because, as shown in Figure 24, there is no energy loss due to the backflow of the overflowing water, and the height of the overflowing water drop is greater than in each example because the height of the upper end of the wall on the river-back side is the same as the height of the upper end of the wall on the river-front side.

[0048] The second experimental results described above demonstrate that lowering the upper end of the wall on the river-back side to a lower level than the upper end of the wall on the river-front side is effective in creating a permeable area and suppressing soil erosion caused by overflow water. Furthermore, installing reinforcing materials at a position lower than the upper end of the wall on the river-back side can further suppress soil erosion caused by overflow water. Note that the appropriate value of H2 / H1 varies depending on the flow velocity of the overflow water, etc., and is not limited to the values ​​in the above example, but should be set appropriately based on the shape of the embankment and predictions of overflow occurrence.

[0049] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these will naturally also be understood to fall within the technical scope of the present invention. [Explanation of Symbols]

[0050] 1...Dam body, 2...River, 10...Reinforcement structure, 11,12...Steel sheet pile wall, 111,111A,111B...Steel sheet pile, 13...Tie rod, 14...Water passage hole, 15...Perforated plate, 16,16A,16B,16C,16D,16E,16F...Reinforcement material, 17...Longitudinal joint member, 17A...Jig, 18A,18B...Copper concrete.

Claims

1. A first wall body to be constructed on the part of the dam body opposite to the water body, A second wall is constructed on the water-side portion of the aforementioned dam body. Equipped with, In at least a portion of the lengthwise section of the embankment, a region that allows water to pass through the first wall is formed at a position lower than the height of the upper end of the second wall, The embedment length of the first wall is longer than the embedment length of the second wall. Reinforcement structure for the embankment.

2. A first wall body is constructed on the part of the dam body opposite to the water body, A second wall is constructed on the water-side portion of the aforementioned dam body. Equipped with, In at least a portion of the lengthwise section of the embankment, a region that allows water to pass through the first wall is formed at a position lower than the height of the upper end of the second wall, The first wall and the second wall further comprise a reinforcing material that covers the embankment constituting the dam body, The reinforcing material is positioned at least a portion between the first wall and the second wall, at a position lower than the lower end of the water-permeable region. Reinforcement structure for the embankment.

3. The reinforcing material is joined to the embankment according to claim 2, wherein the reinforcing material is joined to a position lower than the upper end of the first wall.

4. A first wall body is constructed on the part of the dam body opposite to the water body, A second wall is constructed on the water-side portion of the aforementioned dam body. Equipped with, In at least a portion of the lengthwise section of the embankment, a region that allows water to pass through the first wall is formed at a position lower than the height of the upper end of the second wall, The first wall structure is a steel sheet pile wall, The water-permeable region is formed by driving multiple steel sheet piles constituting the steel sheet pile wall at at least two different upper end heights such that the upper end of the steel sheet pile wall has an uneven shape in the longitudinal direction of the embankment. Reinforcement structure for the embankment.

5. The plurality of steel sheet piles include a first steel sheet pile driven so that its upper end is at a first height, and a second steel sheet pile driven so that its upper end is at a second height lower than the first height. The levee reinforcement structure according to claim 4, wherein the first steel sheet piles are driven on both sides of the second steel sheet pile along the length of the levee body.

6. A first wall body is constructed on the part of the dam body opposite to the water body, A second wall is constructed on the water-side portion of the aforementioned dam body. Equipped with, In at least a portion of the lengthwise section of the embankment, a region that allows water to pass through the first wall is formed at a position lower than the height of the upper end of the second wall, The first wall is a first steel sheet pile wall, The second wall is a second steel sheet pile wall with a cap concrete layer laid at its upper end. The water-permeable region is formed by either not pouring cap concrete on the upper end of the first steel sheet pile wall, or by pouring cap concrete on the upper end of the first steel sheet pile wall that is shorter in height than the cap concrete of the second steel sheet pile wall. Reinforcement structure for the embankment.

7. A method for constructing a reinforcing structure for a levee, comprising a first wall driven into the portion of the levee body opposite to the water body and a second wall driven into the portion of the levee body on the water body side, wherein a water-permeable region is formed in the first wall at a position lower than the height of the upper end of the second wall in at least a portion of the length of the levee body, and the first wall is a steel sheet pile wall, The plurality of steel sheet piles constituting the steel sheet pile wall include a first steel sheet pile and a second steel sheet pile, A method for constructing a reinforcing structure for a levee, comprising: attaching a longitudinal joint member to the upper end of the second steel sheet pile; fitting the joint of the longitudinal joint member to the first steel sheet pile which has been driven in advance and the first steel sheet pile which will be driven in subsequently, thereby driving in the second steel sheet pile and the longitudinal joint member; and removing the longitudinal joint member from the second steel sheet pile after driving in.

Images