embankment

Abstract

To improve the strength of an embankment when water overflows through interaction between a wall and a structure installed at a top of an embankment reinforced by using the wall.SOLUTION: An embankment comprises a first wall installed on a water area side part of the embankment, a second wall installed in a portion of the embankment opposite to the water area, and a water-impermeable structure that is installed in an area including at least above the second wall and overhangs horizontally from an outermost edge of the second wall to the side opposite to the water area with an overhang length B of 300 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to embankments. [Background technology]

[0002] There are concerns about river embankments, such as those prone to cracking and subsidence due to earthquakes, and erosion of the embankment due to overflow during floods, which can lead to embankment failure or collapse. To address these concerns, Patent Document 1, for example, describes a reinforcement structure for embankments in which steel sheet pile walls are installed on the shoulders of the embankment on both sides of the width of the embankment, extending in the same direction as the embankment, and the heads of each steel sheet pile wall are connected by tie rods. This type of reinforcement structure using double steel sheet pile walls is known to be effective as a liquefaction countermeasure, as the two rows of steel sheet pile walls suppress soil deformation and movement during an earthquake. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-13451 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, although research into the reinforcement structure of embankments using double steel sheet pile walls as described above has progressed as a measure against liquefaction during earthquakes, it cannot be said that a sufficient number of rational structures have been proposed to improve the strength of embankments in the event of overflow or scouring caused by rising water.For example, the tops of many embankments are maintained as roads or walkways, and structures such as concrete pavements and deck slabs are installed on top of the steel sheet pile walls, but the interaction between these structures and the wall during overflow has not been clarified.

[0005] Therefore, the present invention aims to realize a structure in which the strength of a levee reinforced with a wall body is improved in the event of overflow by the interaction between the wall body and a structure installed on the top part. [Means for solving the problem]

[0006] [1] A levee comprising a first wall cast into the water area side of the levee body, a second wall cast into the opposite side of the levee body from the water area, and an impermeable structure installed in an area including at least the upper part of the second wall and extending horizontally from the outermost edge of the second wall to the opposite side of the water area by an extension length B of more than 300 mm. [2] The embankment described in [1], wherein the overhang length B satisfies equation (i) and equation (ii) including a function f(H) of the embankment height H. TIFF0007817542000001.tif27119 [3] The embankment described in [1], wherein the overhang length B satisfies equations (i) and (iii) including a function f(H) of the embankment height H. TIFF0007817542000002.tif26142 [4] A levee according to [2] or [3], wherein the overhang length B satisfies formula (iv), which further includes the remaining ground length L, which is the distance from the position of the scoured area closest to the second wall to the second wall. TIFF0007817542000003.tif1492 [5] The above-mentioned residual ground length L is defined by the formula (v) using the coefficient β and the passive collapse angle φ of the embankment described in [4]. TIFF0007817542000004.tif15111 [6] The above-mentioned residual ground length L is defined by the formula (vi) using the coefficient β for the embankment described in [4]. TIFF0007817542000005.tif1468 [7] A levee described in any one of [1] to [6], wherein the impermeable structure is a top structure installed on the top surface of the levee body. [8] The embankment described in [7], wherein the crest structure is a paving structure. [9] The embankment described in [8], wherein at least one of the first and second walls and the impermeable portion of the pavement structure are connected by a water-stopping member.

[10] The embankment described in [7], wherein the top structure is a concrete top plate.

[11] A levee described in any one of [1] to [6], wherein the impermeable structure is a protruding member that protrudes from the second wall on the side opposite the water body.

[12] A levee described in any one of [1] to

[11] , wherein at least one of the first and second walls is a steel sheet pile wall.

[13] A wall to be installed in the embankment, a structure installed in an area including at least the upper part of the wall, extending horizontally from the wall on the side opposite the water area by a projection length B of more than 300 mm, including an impermeable portion on the upper surface and a permeable portion on the lower surface, and a water-stopping member connecting the wall and the impermeable portion. A levee equipped with: [Effects of the Invention]

[0007] According to the above-mentioned configuration, in a levee where a wall is cast into the levee body, the impermeable structure installed in the area including above the wall extends by a predetermined extension length, so that when overflowing, the point where overflowing water falls on the back side of the river is far from the wall, and the ground bearing capacity of the wall is maintained even in a situation where scouring of the foundation ground occurs. Therefore, with the above-mentioned configuration, the strength of the levee can be improved when overflowing. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view showing the structure of a levee according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the state of the levee shown in FIG. 1 when water overflows. [Figure 3] FIG. 10 is a diagram for explaining a lower limit value of the overhang length. [Figure 4] FIG. 6 is a schematic cross-sectional view showing the structure of a levee according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a schematic cross-sectional view showing the structure of a bank according to a third embodiment of the present invention. [Figure 6]FIG. 10 is a schematic perspective view showing the structure of a bank according to a third embodiment of the present invention. [Figure 7] 10A and 10B are diagrams for explaining an example in which a water-stopping member is provided in an embodiment of the present invention. [Figure 8] 10A and 10B are diagrams for explaining an example in which a water-stopping member is provided in an embodiment of the present invention. DETAILED DESCRIPTION OF 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 drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0010] FIG. 1 is a schematic cross-sectional view showing the structure of a levee according to a first embodiment of the present invention. In this embodiment, a levee 10 includes a steel sheet pile wall 11, which is a first wall structure, installed on the river-front side (the side facing river 2, which is a body of water) of the levee body 1; a steel sheet pile wall 12, which is a second wall structure, installed on the river-back side (the side opposite river 2) of the levee body 1; and a tie rod 13, which is a connecting member connecting the heads of the steel sheet pile walls 11 and 12. The levee body 1 has a slope 1A on the river-front side, a slope 1B on the river-back side, and a top surface 1C. While the tie rod 13 is used as a connecting member in this embodiment, any connecting member may be used as long as it can connect the steel sheet pile walls 11 and 12 and transmit tensile and shear forces. For example, the connecting member may be a steel wall installed perpendicular to each steel sheet pile wall. Alternatively, for example, in the case where the top concrete is poured across the heads of the steel sheet pile walls 11, 12 as a component installed on the top surface, as in the example described below, a separate connecting component does not need to be installed.

[0011] In the above-described embankment 10, a pavement structure 14 is further installed on the top surface 1C of the embankment body 1. The pavement structure 14 is installed to allow the top surface 1C to be used as a road or promenade. It includes, for example, a surface layer and a base layer formed from an asphalt mixture, and a roadbed formed from crushed stone or the like. This pavement structure 14 is an example of a crest structure in this embodiment and is installed to extend a length B from the outermost edge of the steel sheet pile wall 12 on the riverside. Here, the outermost edge refers to the surface of the corrugated portion extending toward the riverside, for example, if the steel sheet pile wall 12 has a corrugated cross section as a whole. If the steel sheet pile wall has a linear cross section, the outermost edge simply refers to the surface on the riverside. The extension length B is the distance from the outermost edge of the steel sheet pile wall 12 on the riverside to the end of the pavement structure 14 on the riverside. For example, if the steel sheet pile wall 12 is constructed of hat-shaped steel sheet piles or U-shaped steel sheet piles and has a corrugated cross section, the part of the corrugated cross section that protrudes toward the riverbank is used as the basis for the overhang distance B. Also, the height of the top surface of the pavement structure 14 above the foundation ground is used as the bank height H.

[0012] Figure 2 shows the state of the levee shown in Figure 1 when water overflows. In the illustrated state, the water level of the river 2 rises and exceeds the height of the top surface of the levee 10, i.e., the top surface of the pavement structure 14, causing overflow. The slope 1B on the backside of the levee body 1 has already been washed away. In this state, the overflow water that reaches the backside of the river overflows the pavement structure 14 falls from the end of the pavement structure 14 and scours the foundation ground. The horizontal distance traveled from the end of the pavement structure 14 to point P where the overflow water reaches the foundation ground is defined as d, and the diameter of the standing vortex generated by the overflow water at point P is defined as R. According to Kenji Noguchi et al., "Large-Scale Model Experiments of Seawall Overtopping and Frontal Scour Caused by Tsunami Run-Up," Coastal Engineering Journal, Vol. 44, pp. 296-300, 1997, the scouring width (on both sides) due to the water flow is proportional to the diameter R of the standing vortex. Therefore, the distance s at which the ground remains on the riverside of the steel sheet pile wall 12 can be expressed by the following equation (1), where the coefficient α is unknown.

[0013]

number

[0014] By ensuring this distance s, the bearing capacity of the ground for the steel sheet pile wall 12 can be maintained even in situations where scouring of the foundation ground occurs on the back side of the river, deformation and displacement of the steel sheet pile walls 11, 12 can be prevented, and the embankment body 1 can be prevented from being washed away on areas other than the back side of the river, thereby maintaining the function of the embankment 10. Therefore, below, based on equation (1), we will consider how to set the overhang length B of the pavement structure 14 to ensure the required distance s.

[0015] First, the horizontal movement distance d of the overflow water is expressed by the following equation (2) using the flow velocity v at the time when the overflow water passes the end of the pavement structure 14. Here, g is the acceleration due to gravity. Furthermore, the flow velocity v, the overflow depth h0 at which the maximum water level of the river 2 near the levee 10 exceeds the levee height H, and the critical water depth h at the time when the overflow water passes the end of the pavement structure 14 are calculated. c The relationship between these two is expressed by equation (3). Equation (3) assumes that the flow velocity in the overflow direction, i.e., the direction intersecting with the levee 10, is almost 0 at the maximum water level of the river 2, and calculates the flow velocity v assuming that the overflow depth h0 is equal to the total head. Here, according to Hino Mikio's "Clear Hydraulics" Maruzen Co., Ltd., p. 107, 2001, the critical water depth h in equation (3) is c If we calculate the flow velocity v as 2 / 3 of the overflow depth h0, we get equation (4), and substituting this into equation (2) gives equation (5).

number

[0016] On the other hand, the diameter R of the standing vortex is calculated by the following equation (6): where q is the flow rate of overflow water and the critical water depth h c and the current velocity v. The critical water depth h c is set to 2 / 3 of the overflow depth h0, and q calculated using the flow velocity v calculated in equation (4) is substituted, equation (7) is obtained.

[0017]

number

[0018] Furthermore, experiments were conducted to determine the coefficient α in Equation (1). 50 A model of levee 10 was constructed using a soil material with a thickness of 0.5 mm and a levee height H of 400 mm. The overflow depth h0 was set to 20 mm, 30 mm, and 40 mm, and the diameter R of the standing vortex calculated from equation (7) due to the overflow water was compared with the size of the scoured area measured. The coefficient α was found to be approximately 7. This result is consistent with the results of previous scour experiments. Furthermore, based on past records of river overflows, the overflow depth h0 is approximately 0.6 m at maximum. Therefore, when the coefficient α calculated from equation (5), R calculated from equation (7), and the values ​​of α = 7, h0 = 0.6 (m), and g = 9.8 (m / s) were added to the above equation (1), 2 ) is substituted, equation (8) is obtained. If the minimum condition for the ground to remain on the river side of the steel sheet pile wall 12 is set to s>0, and equation (8) is made into a conditional equation for the overhang length B, equation (9) is obtained.

[0019]

number

[0020] On the other hand, Yuta Mitobe et al., "Numerical Experiments on the Disaster Mitigation Effect of Tsunami Energy Attenuation by Scouring the Toe of the Back Slope of a Coastal Dike," Journal of the Japan Society of Civil Engineers, B2 (Coastal Engineering), Vol. 74, No. 2, I_223-I_228, 2018, found that the scouring width (both sides) L is calculated from the levee height H and the overflow water depth h0. f Equation (10) has been proposed as an empirical formula for calculating the scouring width L calculated using equation (10) with h0 = 0.6 (m) as in the above example. f =4.24H 0.18 Replace αR in equation (1) with h0 = 0.6 (m) and g = 9.8 (m / s 2 ), and s>0, and the condition for the overhang length B is given by Equation (11).

[0021]

number

[0022] As shown in Equation (5), when the levee height H is large, the horizontal movement distance d increases and always exceeds the scour width. Therefore, the values ​​of the right-hand sides of Equations (9) and (11) are less than 0. In this case, the lower limit of the overhang length B is set so that at least the surface of the steel sheet pile does not enter the scour area, so that the steel sheet pile wall is not damaged by turbidity currents containing sediment. According to the inventors' findings, the lower limit of such overhang length B is 300 mm. As shown in Figure 3, for river levees with a typical levee height H of 2 to 6 m and an overflow water depth h0 of 0.2 m or greater, where scouring by overflow occurs, an overhang length of 300 mm or greater is required to prevent the scour-affected area A from reaching the steel sheet pile wall, especially in areas where the overflow water depth h0 is large and the scour depth increases, affecting the stability of the sheet pile. Such an overhang length B exceeds the overhang length of cap concrete typically poured to protect the head of the steel sheet pile wall. Examples of typical overhang lengths using cap concrete are given in the Steel Pipe Pile Association's "Steel Sheet Piles: From Design to Construction," pp. 353-354, 1998, etc., and are approximately 175 mm at most.

[0023] Furthermore, when setting the overhang length B as described above, a crest structure such as the pavement structure 14 is an impermeable material that prevents overflow water from passing from its upper surface to its lower surface during overflow. For example, if a crest structure has an impermeable portion such as a pavement structure or concrete and a permeable portion such as a protective net, only the impermeable portion is treated as the crest structure and the overhang length B is set. However, since it is sufficient that the overflow water does not cause the embankment body 1 to be washed away on the underside of the crest structure, the impermeable portion of the crest structure does not necessarily need to be completely watertight; it is sufficient if it is substantially impermeable.

[0024] In the above equations (9) and (11), the minimum condition for the ground to remain on the riverside of the steel sheet pile wall 12 is set to s>0, but to be on the safe side, a lower limit value L for the distance s at which the ground remains on the riverside of the steel sheet pile wall 12 may be set, as in the example described below. In this case, the right-hand sides of equations (9) and (11) are set as a function f(H) of the bank height H, and the condition of the following equation (12) is set.

[0025]

number

[0026] As a first example, let us consider the range in which passive resistance is exerted in the ground at the embedded part of the steel sheet pile wall 12. According to the Steel Pipe Pile Association's "Steel Sheet Piles: From Design to Construction," 1998, the depth of the first fixed point is calculated from the theory of beams on an elastic bed under the condition that the head of the pile embedded in the ground does not rotate, and the lower limit value L is calculated as the distance from the pile to the point where the line extending the passive collapse angle φ from that depth intersects with the base plate surface, as shown in the following formula (13). Here, β is β=(E s / 4EI) 1 / 4 is a coefficient calculated as E s is the deformation modulus, and E and I are the Young's modulus and moment of inertia of the steel sheet pile.

[0027]

number

[0028] As a second example, according to the Architectural Institute of Japan's "Guidelines for the Design of Building Foundations" p. 277, 2019, the horizontal resistance of piles near sloping ground can be designed ignoring the effects of the slope if the distance to the slope is greater than 2.5 / β. If we consider this slope as the area where the foundation ground has disappeared due to scouring caused by overflow water, the lower limit L mentioned above can be calculated as in the following formula (14). Note that β is the same as in the first example, β = (k h D / 4EI) 1 / 4 is a coefficient calculated as follows:

[0029]

number

[0030] FIG. 4 is a schematic cross-sectional view showing the structure of a levee according to a second embodiment of the present invention. In the levee 20 according to this embodiment, a concrete top plate 24 is installed as a crest structure. The heads of the steel sheet pile walls 11, 12 are embedded in the concrete top plate 24. As already mentioned, in this case, a separate connecting member does not need to be installed between the steel sheet pile walls 11, 12. The remaining configuration is the same as in the first embodiment, so a detailed description will be omitted. In this embodiment, too, the overhang length B, which is the distance from the outermost edge of the steel sheet pile wall 12 on the riverside to the end of the concrete top plate 24 on the riverside, is set according to the above-mentioned formula (9), formula (11), or formula (12) depending on the levee height H. This allows the bearing capacity of the steel sheet pile wall 12 to be maintained even when scouring of the foundation ground occurs on the riverside.

[0031] 5 and 6 are schematic cross-sectional and perspective views showing the structure of a levee according to a third embodiment of the present invention. The perspective view in FIG. 6 is a perspective view showing the levee body 1. In this embodiment, instead of an impermeable crest structure, an impermeable overhanging member 35 is installed along the slope from the cap concrete 34 poured at the top of the steel sheet pile wall 12 to the backside of the river. The overhanging member 35 is formed, for example, of a steel plate, a concrete plate, or a resin plate. Even when the impermeable structure installed in the area above the steel sheet pile wall 12 of the levee body 1 is not a crest structure, as in this embodiment, the bearing capacity of the steel sheet pile wall 12 can be maintained even when scouring of the foundation ground occurs on the backside of the river by setting the horizontal overhang length B of the overhanging member 35 to satisfy Equation (9), Equation (11), Equation (12), or Equation (13) in relation to the levee height H.

[0032] 7 and 8 are diagrams illustrating an example in which a water-stopping member is provided in an embodiment of the present invention. Fig. 7 shows an example of a levee 40 in which steel sheet pile walls 11, 12 are cast into a levee body 1 as in the first embodiment, and a paving structure 14 is installed as a crest structure. In the levee 40, a water-stopping member 46 connects the top of the steel sheet pile wall 11 on the riverside to the paving structure 14.

[0033] As described above, the pavement structure 14 is an impermeable structure in that overflow water does not penetrate from its upper surface to its lower surface during overflow. However, the pavement structure 14 includes, for example, a surface layer and base layer formed from an asphalt mixture from the surface side, and a subgrade formed from crushed stone or other materials, and the subgrade portion is not necessarily impermeable. In other words, although overflow water does not penetrate from its upper surface to its lower surface, it may penetrate from the river front side to the river back side through the connection between the pavement structure 14 and the steel sheet piles or the underside of the subgrade portion of the pavement structure 14. If overflow water penetrates between the pavement structure 14 and the steel sheet pile walls 11 and 12 in this way, the pavement structure 14 will eventually lift off the steel sheet pile walls 11 and 12, causing the top surface 1C of the embankment 1 to collapse. This would negate the effect of the pavement structure 14 in preventing overflow water from falling to the point P, thereby preserving the ground on the river back side of the steel sheet pile wall 12, as described above.

[0034] Therefore, in the example of Figure 7, a water-stopping member 46 such as swelling rubber is used to connect the top of the steel sheet pile wall 11 to the impermeable portion of the pavement structure 14, preventing overflow water from passing between the pavement structure 14 and the steel sheet pile walls 11, 12. This makes it possible to maintain the functionality of the portion of the top structure that protrudes into the river, even when the top structure, like the pavement structure 14, includes a partially impermeable layer. Note that the water-stopping member may also connect the top of the steel sheet pile wall 12 to the impermeable portion of the pavement structure 14.

[0035] In the example of Figure 8, in a levee 50 in which only the steel sheet pile wall 11 on the river-front side is installed, the steel sheet pile wall 11 and the impermeable portion of the pavement structure 14 are connected by a water-stopping member 46. As a result, the portion of the pavement structure 14 that protrudes from the outermost edge of the steel sheet pile wall 11 on the river-front side by a length B moves the point P (see Figure 2) where overflow water falls away, thereby preserving the ground on the river-front side of the steel sheet pile wall 11 and maintaining the reinforcing effect of the steel sheet pile wall 11 on the embankment body 1. Note that the protrusion length B in this case is also calculated in the same way as in the example described in the first embodiment above.

[0036] Furthermore, for example, as explained above in the second and third embodiments, if the impermeable structures installed in the area including above the steel sheet pile wall include a concrete top plate and a concrete cap, and the head of the steel sheet pile wall is embedded in these structures, overflow water will not flow between the steel sheet pile wall and the structure, and therefore the above-mentioned water-stopping member is not necessary.

[0037] According to the embodiment of the present invention as described above, in a levee in which walls (steel sheet pile walls 11, 12) are cast into the embankment body 1, an impermeable structure (a paving structure 14 or a concrete top plate 24, which is a top structure, or an overhanging member 35) is installed in an area including above the wall, and by making this structure overhang on the back side of the wall by a predetermined overhang length B, the point P of overflow water on the back side of the river in the event of overflow can be moved away from the wall, and the ground bearing capacity of the wall can be maintained even in situations where scouring of the foundation ground occurs.

[0038] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0039] 10, 20, 30, 40, 50... embankment, 1... embankment body, 1A... slope, 1B... slope, 1C... top surface, 2... river, 11, 12... steel sheet pile wall, 13... tie rod, 14... pavement structure, 24... top slab concrete, 34... cap concrete, 35... overhanging member, 46... water-stopping member.

Claims

1. a first wall body to be cast in the water area side portion of the embankment body; a second wall body installed on a portion of the embankment body opposite to the water area; A structure that is installed in an area including at least the upper part of the second wall, extends horizontally from the outermost edge of the second wall to the side opposite the water area by a projection length B of 300 mm or more, includes an impermeable portion on the upper surface side, and includes a permeable portion on the lower surface side; a water-stopping member connecting a head portion of at least one of the first and second walls to the impermeable portion; A levee equipped with:

2. The embankment according to claim 1 , wherein the overhang length B satisfies equations (i) and (ii) including a function f(H) of the embankment height H.

3. The overhang length B satisfies the formula (i) and the formula (iii) including the function f(H) of the bank height H. The embankment according to claim 1.

4. A levee as described in claim 2 or claim 3, wherein the overhang length B further satisfies formula (iv), which further includes a lower limit value L of the distance over which ground remains on the opposite side of the second wall from the water area.

5. The embankment according to claim 4, wherein the lower limit value L is defined by equation (v) using a coefficient β and a passive collapse angle φ.

6. The embankment according to claim 4 , wherein the lower limit value L is defined by equation (vi) using a coefficient β.

7. The embankment according to any one of claims 1 to 6, wherein the impermeable portion is a top structure installed on the top surface of the embankment body.

8. The embankment according to claim 7 , wherein the top structure is a paving structure.

9. The embankment according to any one of claims 1 to 8, wherein at least one of the first and second wall bodies is a steel sheet pile wall.

10. A wall to be installed on the embankment, A structure that is installed in an area including at least the upper part of the wall, extends horizontally from the wall on the side opposite the water area by a projection length B of more than 300 mm, includes an impermeable portion on the upper surface side, and includes a permeable portion on the lower surface side; a water-stopping member connecting the head of the wall body and the impermeable portion; A levee equipped with:

Images