JP7320362B2 - Design method for reinforcement structure of cut-off wall - Google Patents

Description

The present invention relates to a reinforcement structure for a bank body.

In recent years, large-scale earthquakes and localized torrential rains have caused many river levees and irrigation levees to burst, and several large-scale earthquakes and climate change are expected to cause severe disasters. Therefore, seismic reinforcement of embankments is becoming more important.

Based on this background, techniques for reinforcing embankments (embankment bodies) using steel sheet piles have been proposed (for example, see Patent Documents 1 to 4 and Non-Patent Document 1).
In the seismic performance reinforcement structure of the embankment described in Patent Document 1, reinforcing plate-like bodies formed of steel sheet piles in two rows and columns in the longitudinal direction of the almost central part of the embankment such as an earthfill dam or reservoir are installed. It has a double coffer structure in which the upper ends of both reinforcing plates are connected by a connecting member at predetermined intervals.
In the liquefaction countermeasure construction method for the embankment structure described in Patent Document 2, a continuous underground wall is constructed near both skirts of the embankment structure, and the head of the continuous underground wall and the lower part of the embankment structure are connected. It is connected with an earth anchor arranged obliquely downward.
In the embankment reinforcement structure described in Patent Document 3, at least one row of sheet pile walls having a depth that penetrates the embankment excluding the toe of the embankment and is embedded in the supporting ground is continuous in the longitudinal direction of the embankment. A structural frame is formed by a sheet pile wall in the ground that constitutes the embankment and the ground closed off by the sheet pile wall.
In the embankment reinforcement structure described in Patent Document 4, one or more rows of underground steel wall bodies are provided along the continuous direction of the embankment within the range of the top end of the continuous embankment, and the underground steel wall The body is embedded to a depth shallower than the bearing layer and to a depth at which the underground steel wall does not collapse when an earthquake or flooding occurs.
Non-Patent Document 1 describes that a water impermeable zone having a higher imperviousness than other parts of the embankment body and having a predetermined width is provided along the slope of the embankment body on the upstream side. .

JP-A-2003-321826 JP-A-11-1926 Japanese Patent Application Laid-Open No. 2003-13451 JP 2012-7394 A

Design guideline for land improvement project "Reservoir maintenance" (May 2015) / Supervised by the Ministry of Agriculture, Forestry and Fisheries Rural Development Bureau Development Department, published by the Society of Agriculture and Rural Engineering

By the way, seepage failure is one of the causes of damage to embankment bodies, such as reservoirs, which have a constant water storage function. This seepage failure occurs because the upstream slope on the reservoir side (reservoir side or upstream side) of the upper part of the levee body always becomes a leak entrance into the levee body, which causes seepage failure. . On the upstream slope of the cut-off wall, repeated dryness and wetness caused by the up-and-down movement of the reservoir water level, suction of soil particles to the reservoir side, and erosion caused by waves occurred for a long period of time. In some cases, the dam body may be locally damaged or destroyed. In addition, a sudden rise in water level due to torrential rain, etc., and the supply of water to the inside of the embankment can also cause water leakage. If the cut-off wall is damaged or destroyed, it will be difficult to dam the reservoir water.
In addition, when liquefaction occurs inside the bank of the reservoir due to an earthquake or the like, the shear strength of the bank is lost, causing the bank to slip, which may damage or collapse the bank.

In the technique described in Non-Patent Document 1, when the embankment body or the foundation ground immediately below the embankment body liquefies during an earthquake, and the crest of the embankment body sinks or is damaged, the stored water overflowing from the reservoir is dammed up. It is not possible.
In the technique described in Patent Document 1, reinforcing plate-shaped bodies are embedded in two rows and columns in the longitudinal direction of the embankment body, and the upper ends of the reinforcing plate-shaped bodies are connected by connecting members at predetermined intervals. However, it is not possible to prevent seepage from the upstream slope, which is the starting point of seepage failure.
In addition, since two rows of reinforcing plates are required, construction costs are high, and if the levee body becomes liquefied, the levee body may slip and be damaged.
The technique described in Patent Literature 2 cannot prevent permeation from the upstream slope, which is the starting point of permeation failure. In addition, since there is no underground continuous wall inside the cut-off wall, it is impossible to dam the accumulated water if the cut-off wall is damaged by liquefaction.
The techniques described in Patent Documents 3 and 4 cannot prevent seepage from the upstream slope, which is the starting point of seepage failure. Also, although the bank can be reinforced with a single row of walls, if the bank is liquefied, the bank may slip and be damaged.
As described in Patent Documents 1, 3 and 4, when the embankment embankment of the reservoir is reinforced with a diaphragm wall, depending on the installation location, liquefaction may occur in the embankment body, and the reinforcement effect is reduced. may decrease or disappear, and there is no technology that takes this possibility into account.

The present invention has been made in view of the above-mentioned circumstances, and is capable of suppressing the seepage failure of a levee body provided near a reservoir and increasing the strength of the levee body itself by lowering the water level inside the levee body. In addition, the embankment body is further reinforced by the rigidity of the diaphragm wall itself, which suppresses slippage of the embankment body and prevents the reduction or disappearance of the reinforcement effect. The object is to provide a reinforcing structure for

In order to achieve the above object, the embankment reinforcement structure of the present invention is a embankment reinforcement structure that reinforces the embankment provided on at least a part of the outer circumference of a reservoir,
Assuming that the reservoir side is the upstream side across the bank,
The bank body has a higher imperviousness than other portions of the bank body along the upstream slope of the bank body on the upstream side and has a predetermined width along the width direction of the bank body. having an aqueous portion,
A steel diaphragm wall is provided on the bank body along the extending direction of the bank body,
The steel diaphragm wall penetrates vertically through the highly impermeable portion, has an upper end aligned with the top end of the embankment body, and has a lower end aligned with the embankment body or the foundation ground located below the embankment body. characterized by being installed.

Here, as the steel diaphragm wall, one formed by connecting a plurality of steel sheet piles is preferably used, but it is not limited to this. For example, a structure formed by connecting a plurality of steel pipe sheet piles or a structure formed by connecting a plurality of steel sheet piles and steel pipe sheet piles may be used.
In addition, "the upper end of the steel diaphragm wall is aligned with the crest of the embankment" means that the upper end of the steel diaphragm wall is located within 1m above or below the crest of the embankment. including being
Also, the highly impermeable portion is formed of a impermeable ground material having a higher imperviousness than a normal ground material such as Hakindo. In many cases, such a highly impermeable portion is already provided on the cut-off wall, but may be newly provided on the cut-off wall.

In the present invention, the steel diaphragm wall has a higher impermeability along the upstream slope of the embankment than other portions of the embankment, and has a predetermined width along the width direction of the embankment. As it penetrates the impermeable part vertically, the upper end is aligned near the top of the embankment body, and the lower end is installed on the embankment body or the foundation ground located below the embankment body, so it is horizontal from the upstream slope. The water that has permeated into the wall is cut off by the steel diaphragm wall and flows downward. Therefore, by forming a difference in the amount of water flow between the high impervious portion and the steel diaphragm wall, the water level inside the levee body behind the steel diaphragm wall (downstream side) is reliably drained first. can be lowered.
In this way, it is possible to lower the groundwater level in the ground inside the levee body inside (downstream side) of the steel diaphragm wall. It is possible to minimize the occurrence of liquefaction in the entire embankment body without reducing the stress, and suppress the slippage of the embankment body by the rigidity of the steel diaphragm wall itself and the shear rigidity of the embankment body itself. , it is possible to prevent the reduction or disappearance of the reinforcement effect, which is a factor that causes serious damage.

In addition, the water that has penetrated horizontally from the upstream slope of the embankment is blocked by the steel diaphragm wall and flows downward. By controlling the water flow inside the levee body and changing its direction downward near the steel underground continuous wall surface, the hydraulic gradient can be reduced. Even in a pond where water is always present, the stability of the cut-off wall can be ensured while keeping construction costs low.
In addition, by arranging the steel diaphragm wall in one row in the width direction of the embankment, the construction period and construction cost can be suppressed.

Further, in the configuration of the present invention, the steel diaphragm wall has a hydraulic conductivity of ks (cm/s), the highly impermeable portion has a hydraulic conductivity of ka (cm/s), and the steel diaphragm wall has a hydraulic conductivity of ka (cm/s). Let c (cm) be the thickness of and a (cm) be the width of the high water impermeability portion at the depth where the steel diaphragm wall penetrates the high water impermeability portion,
A penetration length b (cm) of the steel diaphragm wall to the highly impermeable portion may satisfy the following formula (1).

According to such a configuration, the penetration length b (cm) of the steel diaphragm wall to the high impermeability portion is the hydraulic conductivity ks (cm / s) of the steel diaphragm wall, the high impermeability Permeability coefficient ka (cm/s) of the part, thickness c (cm) of the steel diaphragm wall, width a (cm ).

Further, in the configuration of the present invention, the penetration length of the steel diaphragm wall to the highly impermeable portion is b (cm), the thickness of the steel diaphragm wall is c (cm), and the thickness of the steel diaphragm wall is c (cm). Let a (cm) be the width of the high impermeability portion at the depth where the steel diaphragm wall penetrates the high impermeability portion, and ka (cm/s) be the hydraulic conductivity of the high impermeability portion,
A permeability coefficient ks (cm/s) of the steel diaphragm wall may satisfy the following formula (2).

According to such a configuration, the permeability coefficient ks (cm/s) of the steel diaphragm wall is set to the penetration length b (cm) of the steel diaphragm wall to the highly impermeable portion, The thickness of the continuous wall is c (cm), the width of the high impermeability portion at the depth where the steel diaphragm wall penetrates the high impermeability portion a (cm), the permeability coefficient of the high impermeability portion ka (cm/s ).

Further, in the configuration of the present invention, at least a portion of the steel diaphragm wall below the portion penetrating the highly impermeable portion may have water permeability.

According to such a configuration, since at least a part of the steel diaphragm wall below the part penetrating the high impermeability part has water permeability, In the ground below the levee body and the soft layer below it, it is possible to suppress the increase in water pressure due to water flow and suppress the decrease in effective stress.
In addition, in the lower ground that supports the highly impermeable portion, it is possible to limit the decrease in the effective stress of the ground, thereby preventing the collapse of the highly impermeable portion.
Furthermore, the groundwater flow in the lower natural ground below the cut-off wall is not hindered.

According to the present invention, it is possible to suppress the seepage failure of the bank body, and to minimize the occurrence of liquefaction inside the bank body, thereby suppressing the slippage of the bank body and preventing the reduction or disappearance of the reinforcement effect. can be done.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic perspective view which shows typically the reinforcement structure of the bank body which concerns on embodiment of this invention. In the same, (A) is a cross-sectional view of the embankment, and (B) is a diagram for explaining the flow rate of the highly impermeable portion. FIG. 4 is a schematic diagram for explaining the significance of providing a steel diaphragm wall in a cut-off wall; FIG. 3 is a schematic diagram for explaining the significance of providing a steel diaphragm wall in a cut-off wall having a highly impervious portion. 1 is a perspective view showing a steel diaphragm wall used in a reinforcement structure for a bank body according to an embodiment of the present invention; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram schematically showing a reinforcing structure for a bank body according to an embodiment, and FIG. 2 is a cross-sectional view of the bank body and the ground.
First, before describing the present embodiment, the significance of providing a steel diaphragm wall in the embankment of a reservoir will be described.
As shown in FIGS. 3( a ) to 3 ( d ), if the left side of the embankment body 10 is the upstream side, there is a reservoir 11 on the upstream side of the embankment body 10 . It gradually penetrates into the inside of the bank body 10 from the upstream slope 10b on the upstream side of the body 10. - 特許庁

As shown in FIG. 3(a), a steel diaphragm wall 20 is driven vertically from the central portion of the crest 10a of the embankment 10 in the width direction (horizontal direction in FIG. 3(a)). is embedded to the foundation ground 12 located directly under the embankment body 10 and the upper end is aligned with the crown 10a, the water in the ground upstream of the steel diaphragm wall 20 inside the embankment body 10 is saturated It becomes easy to liquefy. In addition, below, the liquefaction range is expressed with light ink, and the liquefaction range is indicated by L1 in FIG. 3(a). On the other hand, rainfall permeates the ground downstream of the steel diaphragm wall 20 from the crest 10a. There is nothing to block the liquefaction range.
On the other hand, as shown in FIG. 3(b), when the steel diaphragm wall 20 is driven from the vicinity of the upstream end of the crest 10a of the embankment body 10 (near the upstream slope shoulder) , Since the volume of the ground on the upstream side of the steel diaphragm wall 20 inside the embankment body 10 is smaller than in the case of FIG. can be done.
On the other hand, as shown in FIG. 10, the volume of the ground on the upstream side of the steel diaphragm wall 20 is larger than in the case of FIG. 3(a).
Moreover, as shown in FIG. Since the volume of the ground on the upstream side of the continuous wall 20 is smaller than in the case of FIG. Since 20 protrudes from the upstream slope 10b, there is a problem that the amount of water stored in the reservoir 11 is reduced.

In addition, as shown in FIGS. 4(a) to 4(d), by providing a ground material with high imperviousness such as blade metal soil along the upstream slope 10b, the inside of the embankment 10 has a predetermined width. When the highly impermeable portion 15 is provided, it is possible to prevent part of the water stored in the reservoir 11 from gradually permeating into the bank body 10 from the upstream slope 10b.

As shown in FIG. 4(a), a steel diaphragm wall 20 is driven vertically from the center of the crest 10a of the embankment 10 in the width direction (horizontal direction in FIG. 4(a)). is embedded to the foundation ground 12 located directly under the cut-off wall 10 and the upper end is aligned with the crown 10a (that is, when the steel diaphragm wall 20 does not penetrate the high impermeability portion 15), high impermeability Rainfall penetrates into the ground between the water-based portion 15 and the steel diaphragm wall 20 from the crown 10a, the permeated water due to the rainfall accumulates, and the water in the ground becomes saturated and easily liquefied. The liquefaction range is indicated by L11.
On the other hand, as shown in FIG. penetrates the high water impermeable part 15 vertically, and rainfall does not easily permeate the ground inside the embankment body 10 on the upstream side of the steel diaphragm wall 20, so the water in the ground is not saturated and liquefied. .
On the other hand, as shown in FIG. 4(c), when the steel diaphragm wall 20 is cast from the vicinity of the downstream end of the crest 10a of the embankment body 10, as in the case of FIG. 4(a), , the steel diaphragm wall 20 does not penetrate the highly impermeable portion 15 and is easily liquefied. Furthermore, in FIG. 4(c), the volume of the ground on the upstream side of the steel diaphragm wall 20 inside the embankment body 10 is larger than in the case of FIG. 4(a), so the liquefaction range L13 is It increases beyond the liquefaction range L11 and becomes a problem.
Further, as shown in FIG. 4(d), when the steel diaphragm wall 20 is cast from the substantially central portion in the vertical direction of the upstream slope 10b of the embankment body 10, the upstream side of the steel diaphragm wall 20 In this case, the water in the ground is not saturated and does not liquefy. However, since the steel diaphragm wall 20 protrudes from the upstream slope 10b, there is a problem that the amount of water stored in the reservoir 11 is reduced.

In this way, in order to suppress the liquefaction of the inside of the levee body 10, part of the water stored in the reservoir 11 is suppressed from penetrating into the levee body 10 from the upstream slope 10b of the levee body 10. Therefore, as described above, the highly impermeable portion 15 is provided, and the steel diaphragm wall 20 is provided so as to penetrate the highly impermeable portion 15 from the top end 10a, that is, as shown in FIG. Then, the embankment body 10 can be reinforced.
In this case, the steel diaphragm wall 20 is preferably cast so as to pass through the high impermeability portion 15 from the crown 10a of the embankment body 10 and penetrate the high impermeability portion 15 vertically. The upper end of the steel diaphragm wall 20 may be aligned with the top end 10a of the embankment body 10, or may be within 1 m downward from the top end 10a. Alternatively, the upper end of the steel diaphragm wall 20 may be projected upward from the top end 10a.

Next, the reinforcement structure of the embankment of the present embodiment will be described.
In the present embodiment, an example in which the embankment reinforcing structure of the present invention is applied to the embankment of a valley pond, which is one of reservoirs, will be described. good too.
As shown in FIG. 1, in this embodiment, a valley pond (reservoir) 11 is formed by blocking a valley with a bank 10 . The surroundings of the reservoir 11, except for the embankment body 10, are surrounded by natural ground 12 formed of bedrock, hard ground, and the like.
In FIG. 1, the natural ground 12 around the reservoir 11 is shown in a substantially half elliptical cylindrical shape in plan view, but the shape of the natural ground 12, that is, the shape of the reservoir 11 is not limited to this. Also, the natural ground 12 may be continuous with the slope of the valley.
Moreover, when the reservoir is a plate pond, the outer periphery of the reservoir is surrounded by the bank, but the bank may be provided on at least a part of the outer periphery of the reservoir.
In this case, the portion where the embankment body is not provided is formed by the existing ground such as natural ground and by the embankment body or a protrusion having a height higher than the embankment body. Therefore, the outer circumference of the reservoir is surrounded by the soil structure formed by the bank and the projecting portion. An earthen structure is a structure basically formed mainly of earth, and includes those provided with various facilities and articles made of concrete or the like inside or on the surface thereof.

As shown in FIG. 2(A), in the present embodiment, the embankment body 10 is formed to have a trapezoidal cross section, and the bottom of the embankment body 10 is the surface (upper surface) of the soft layer S1 that constitutes the surface layer of the foundation ground S. However, it is not limited to this, and the bottom of the bank 10 may be installed so as to dig into the surface of the soft layer S1. In this case, the bottom of the bank 10 is the surface of the soft layer S1. It may be parallel or slanted. Moreover, the surface of the soft layer S1 on which the bank body 10 is installed may be inclined with respect to the horizontal plane. A support layer S2 is provided below the soft layer S1, and the foundation ground S is formed by the soft layer S1 and the support layer S2.
Moreover, although the reservoir 11 has a circular shape in plan view in the present embodiment, it is not limited to this. For example, it may have an elliptical shape, an elliptical shape, a polygonal shape, or the like in plan view.

Assuming that the reservoir 11 side (left side in FIG. 2(A)) across the bank 10 is the upstream side, the bank 10 along the upstream slope 10b on the upstream side is more impermeable than other parts of the bank 10. is high and has a highly impervious portion 15 having a predetermined width a along the width direction of the bank body 10 (horizontal direction in FIG. 2(A)). Here, "another portion of the bank body 10" refers to a portion of the ground constituting the bank body 10 and excluding the highly impermeable portion 15. As shown in FIG.
The highly impermeable portion 15 is formed in a cross-sectional parallelogram shape by ground material with high impermeability such as blade metal soil, but the cross-sectional shape of the highly impermeable portion 15 is not limited to the parallelogram shape. Instead, the steel diaphragm wall 20 may have a shape that allows it to vertically penetrate the highly impermeable portion 15 inside the bank body 10 .
In the present embodiment, the upper surface of the highly impervious portion 15 occupies approximately half of the upstream side of the crest 10a of the bank body 10 and is flush with the crest 10a. In addition, the sloped surface on the upstream side of the highly impervious portion 15 constitutes substantially the entire upstream slope 10b of the bank body 10 . Therefore, it is possible to prevent part of the water stored in the reservoir 11 from gradually permeating into the bank body 10 from the upstream slope 10b.

In this embodiment, the highly impermeable portion 15 is provided on the existing embankment body 10, but the present invention is not limited to this. For example, a part of the highly impermeable portion 15 may be replaced with a new ground material with high impermeability such as blade metal soil, or a highly impermeable ground material may be added to the highly impermeable portion 15 . Furthermore, when constructing the embankment body 10 as a new construction, the highly impervious portion 15 may be constructed as a new construction.

Further, the embankment 10 is provided with a steel diaphragm wall 20 along the extending direction of the embankment 10 (the direction perpendicular to the paper surface in FIG. 2(A)).
That is, inside the embankment body 10, a steel diaphragm wall 20 is continuously installed in a straight line in a plan view along the extending direction (longitudinal direction) of the embankment body 10 (see FIG. 1). ). That is, the steel diaphragm wall 20 is continuously installed in a straight line from one longitudinal end to the other longitudinal end of the embankment body 10 of the reservoir 11 .
Furthermore, the steel diaphragm wall 20 is driven vertically from a position closer to the upstream side than the central portion in the width direction of the bank body 10 , that is, from the vicinity of the slope shoulder on the upstream side of the bank body 10 .

In addition, the steel diaphragm wall 20 vertically penetrates the high impermeability portion 15, and the upper end is aligned with the top end 10a of the embankment body 10 (the upper surface of the impermeability portion 15), and the lower end is aligned with the embankment body 10. and below the weak layer S1. The lower end of the steel diaphragm wall 20 is preferably embedded in the support layer S2 in consideration of earthquake resistance. It may be placed on the soft layer S1 or may simply be applied to the upper surface of the support layer S2.

In addition, of the steel diaphragm wall 20, at least part of the portion below the portion penetrating the highly impervious portion 15 (the portion penetrating the portion of height b in FIG. 2(A)) has water permeability. For example, below the portion penetrating the high water impermeable portion 15 of the steel diaphragm wall 20 and forming the lower part of the embankment body 10, the steel ground provided in the soft layer S1 A water permeation hole 17 (see FIG. 5) is provided at the lower end of the diaphragm wall 20 .

The steel diaphragm wall 20 is formed by connecting a plurality of hat-shaped steel sheet piles 16, as shown in FIG.
The steel sheet pile 16 includes a web 16a, flanges 16b formed at both ends of the web 16a, and an arm 16c formed at the end of the flange 16b opposite to the web 16a. A joint 16d is formed in the portion.
Adjacent steel sheet piles 16, 16 are connected by fitting joints 16d, 16d to each other, whereby a steel diaphragm wall 20 is formed.
The steel sheet piles constituting the steel diaphragm wall 20 are not limited to hat-shaped steel sheet piles, and may be U-shaped steel sheet piles or straight steel sheet piles. Further, the steel diaphragm wall 20 is not limited to steel sheet piles, and may be composed of steel pipe piles or steel pipe sheet piles, or may be composed of a combination thereof.

The web 16a is integrally formed by an upper web 16a1 and a lower web 16a2, and the lower web 16a2 is provided with a plurality (a large number) of elliptical or circular water permeable holes 17 vertically and horizontally at predetermined intervals. The upper web 16a1 is not provided with the water permeable holes 17. As shown in FIG.
Then, the lower portion having the lower web 16a2 provided with the water permeable holes 17 is the above-described water permeable portion.

In addition, the portion having water permeability is not limited to this, and although not shown, for example, in a steel diaphragm wall formed by connecting a plurality of steel sheet piles, a predetermined number of steel sheet piles By forming the steel sheet pile shorter than the other steel sheet piles, an opening corresponding to the width of the steel sheet pile is formed in a part of the lower end portion of the steel diaphragm wall, and this opening can be used as the above-described portion having water permeability. good.

In this embodiment, as shown in FIG. 2(A), part of the water stored in the reservoir 11 permeates horizontally from the upstream slope 10b of the embankment body 10. Water is cut off by the intermediate wall 20 and goes downward, and then passes through the permeable hole 17 (see FIG. 5) provided at the lower end of the steel diaphragm wall 20 to the back side of the steel diaphragm wall 20. flows into the soft layer S1. In addition, in FIG. 2A, the flow of water is indicated by thick arrows.
Therefore, as shown in FIG. 2(B), in the cross section of the embankment body 10, the total amount of water flowing through the right-angled triangular portion, which is part of the highly impervious portion 15, of the steel diaphragm wall 20 is By making the portion opposite to the right-angled triangle portion larger than the total flow rate of water permeation, a difference in water flow rate is formed between the highly impermeable portion 15 and the steel diaphragm wall 20, and the steel diaphragm wall is formed. The water level in the bank body 10 behind 20 (downstream side) can be reliably drained first and the water level in the bank body 10 can be lowered.
That is, by satisfying the following formula (3), a water flow rate difference is formed between the highly impermeable portion 15 and the steel diaphragm wall 20, and the water level in the cut-off wall 10 can be lowered.

In the above equation (3), the left side is the water head difference (dx) and the streamline length at each height of the right triangle (a/b x ) and the hydraulic conductivity ka of the highly impermeable portion (Hakinedo) 15, and the right side is the total flow rate determined from the hydraulic head It is the total flow rate determined from the difference (b), the thickness of the steel diaphragm wall 20 as the streamline length (c), and the hydraulic conductivity ks of the steel diaphragm wall 20 . In the left side of equation (3), a is the width of the high impermeability portion 15 at the depth where the steel diaphragm wall 20 penetrates the high impermeability portion 15 (the height of the embankment body 10 Of the two surfaces perpendicular to the highly impermeable portion 15 in the width direction, the horizontal distance from the lowest end of the surface in contact with the highly impermeable portion 15 located on the upstream side to the upstream slope 10b), b is steel It is the penetration length (the distance from the lowest end to the top end 10a) of the continuous wall 20 during manufacturing to the highly water impermeable portion 15. In the above formula, as the projected cross-sectional area in the direction of flow perpendicular to the flow when obtaining the total flow, the depth direction (extending direction of the bank) is a unit length, and the height direction is the right triangle part. The same item b is used for the steel diaphragm wall, and the left side and the right side are the same items, so they are omitted.

In the present embodiment, the hydraulic conductivity of the steel diaphragm wall 20 is ks (cm/s), the hydraulic permeability of the highly impermeable portion 15 is ka (cm/s), and the steel diaphragm wall 20 is Assuming that the thickness is c (cm) and the width of the high impermeability portion 15 at the depth where the steel diaphragm wall 20 penetrates the high impermeability portion 15 is a (cm), the height of the steel diaphragm wall 20 is The penetrating length b (cm) to the impervious portion 15 is set based on the above equation (3) so as to satisfy the following equation (1).

For example, the hydraulic conductivity ks of a steel diaphragm wall (steel sheet pile): 1 × 10 ^-6 (cm / s),
Plate thickness of steel diaphragm wall (steel sheet pile plate thickness) c: 1.08 (cm),
Permeability coefficient ka of highly impermeable part (Hakin soil): 5 × 10 ^-5 (cm / s),
If the width of the highly impermeable portion at the depth where the steel diaphragm wall penetrates the highly impermeable portion is a: 250 (cm),
Penetration length b>102.48 (cm) to the highly impervious portion of the steel diaphragm wall. In other words, the penetration length b (cm) of the steel diaphragm wall to the highly impervious portion should be set longer than 102.48 (cm).
The permeability coefficient of the highly impermeable part is the maximum value of the impermeable coefficient of the impermeable material compacted on site (Land improvement project design guideline "Reservoir maintenance", Ministry of Agriculture, Forestry and Fisheries).

Further, in the present embodiment, the penetration length of the steel diaphragm wall to the highly impervious portion is b (cm), the thickness of the steel diaphragm wall is c (cm), the steel diaphragm wall is If the width of the highly impermeable portion at the depth where the wall penetrates the highly impermeable portion is a (cm), and the permeability coefficient of the highly impermeable portion is ka (cm/s), the permeability coefficient of the steel diaphragm wall is ks (cm/s) is set so as to satisfy the following expression (2) based on the above expression (3) or (1).

For example, plate thickness of steel diaphragm wall (steel sheet pile plate thickness) c: 1.08 (cm),
Penetration length b to the highly impervious portion of the steel diaphragm wall: 200 (cm),
Hydraulic coefficient ka of highly impervious part (hagane soil): 5 × 10 ^-5 (cm/s)
If the width of the highly impermeable portion at the depth where the steel diaphragm wall penetrates the highly impermeable portion is a: 250 (cm),
The permeability coefficient ks (cm/s) of the steel diaphragm wall is less than 1.14×10 ⁻⁶ (cm/s). In other words, the hydraulic conductivity ks required for the steel diaphragm wall should be set lower than 1.14×10 ⁻⁶ (cm/s).
The permeability coefficient of the highly impervious portion is the same as above.

As described above, according to the present embodiment, the steel diaphragm wall 20 along the upstream slope 10b of the cut-off wall 10 has a higher water impermeability than other portions of the cut-off wall 10, and The foundation ground S vertically penetrates the highly water impermeable portion 15 having a predetermined width along the width direction of the dam 10, the upper end is aligned with the top end 10a of the dam body 10, and the lower end is located below the dam body 10. , the water penetrating horizontally from the upstream slope 10b is blocked by the steel diaphragm wall 20 and flows downward. Therefore, by forming a water flow rate difference between the high impervious portion 15 and the steel diaphragm wall 20, the water is reliably discharged first in the cut-off wall 10 behind (downstream side) the steel diaphragm wall 20. It is possible to drain water and lower the water level in the bank body 10. - 特許庁
In this way, since the groundwater level in the ground inside the levee body inside (downstream side) of the steel diaphragm wall 20 can be lowered, the shear strength of the levee body 10 can be secured, and the It is possible to minimize the occurrence of liquefaction in the entire embankment body without reducing the effective stress, and prevent the embankment body 10 from slipping due to the rigidity of the steel diaphragm wall itself and the secured shear rigidity of the embankment body itself. It can be suppressed and prevent the decrease or disappearance of the reinforcing effect.

In addition, since the water that has penetrated horizontally from the upstream slope 10b of the embankment body 10 is blocked by the steel diaphragm wall 20 and flows downward, the steel diaphragm wall 20 guarantees water stopping performance. By doing so, the water flow in the levee body 10 can be controlled, and the direction can be changed downward in the vicinity of the steel underground continuous wall surface to reduce the hydraulic gradient, so piping in the levee body 10 can be suppressed, It is possible to suppress seepage failure of 10 and secure the stability of the embankment body while keeping the construction cost low even in the pond 11 where there is always retained water.
In addition, by arranging the steel diaphragm wall 20 in one row in the width direction of the cut-off wall 10, the construction period and construction cost can be suppressed.

Furthermore, even if the bank body 10 is damaged, the steel diaphragm wall 20 functions like a fail-safe, making it possible to dam the water stored in the reservoir 11 .
In addition, since at least a portion of the steel diaphragm wall 20 below the portion penetrating the highly impermeable portion 15 has water permeability, the embankment below the highly impermeable portion 15 In the subbody ground and the ground forming the soft layer S1 below it, it is possible to suppress the increase in water pressure due to the water flow and suppress the decrease in effective stress.
In addition, in the lower ground (soft layer S1) that supports the highly impermeable portion 15, it is possible to limit the decrease in the effective stress of the ground, so that the highly impermeable portion 15 can be prevented from collapsing. The groundwater flow in the lower ground (soft layer S1) is not hindered.

In addition, in this embodiment, as shown in FIG. Although the steel diaphragm wall 20 is penetrated, the placement position of the steel diaphragm wall 20 is not limited to the vicinity of the slope shoulder. For example, the high water impervious portion 15 may be penetrated vertically by driving from the widthwise central portion of the top end 10a of the bank body 10 . In short, the steel diaphragm wall 20 should be cast from the top end 10a of the bank body 10 so that the highly impermeable portion 15 penetrates vertically inside the bank body 10. As shown in FIG.

10 Bank body 10a Crown 10b Upstream slope 11 Reservoir 20 Steel diaphragm wall S Foundation ground S1 Soft layer S2 Bearing layer

Claims (2)

A design method for designing a reinforcement structure for a bank body that reinforces a bank body provided on at least a part of the outer circumference of a reservoir, comprising:
The reinforcing structure is
Assuming that the reservoir side is the upstream side across the bank,
The bank body has a higher imperviousness than other portions of the bank body along the upstream slope of the bank body on the upstream side and has a predetermined width along the width direction of the bank body. having an aqueous portion,
A row of steel diaphragm walls is provided on the bank body along the extending direction of the bank body in the width direction of the bank body,
The steel diaphragm wall vertically penetrates the high water impermeability portion inside the bank body, has an upper end aligned with the top end of the bank body, and has a lower end on the bank body or below the bank body. It is installed on the foundation ground located in
ks (cm/s) is the permeability coefficient of the steel diaphragm wall, ka (cm/s) is the permeability coefficient of the highly impervious portion, c (cm) is the thickness of the steel diaphragm wall, Assuming that the width of the high water impermeable portion at the depth where the steel diaphragm wall penetrates the high water impermeable portion is a (cm),
A method for designing a reinforcement structure for a bank body, characterized in that the penetration length b (cm) of the steel diaphragm wall to the highly impermeable portion is set so as to satisfy the following formula (1).

A design method for designing a reinforcement structure for a bank body that reinforces a bank body provided on at least a part of the outer circumference of a reservoir, comprising:
The reinforcing structure is
Assuming that the reservoir side is the upstream side across the bank,
The bank body has a higher imperviousness than other portions of the bank body along the upstream slope of the bank body on the upstream side and has a predetermined width along the width direction of the bank body. having an aqueous portion,
A row of steel diaphragm walls is provided on the bank body along the extending direction of the bank body in the width direction of the bank body,
The steel diaphragm wall vertically penetrates the high water impermeability portion inside the bank body, has an upper end aligned with the top end of the bank body, and has a lower end on the bank body or below the bank body. It is installed on the foundation ground located in
The penetration length of the steel diaphragm wall to the high impervious portion is b (cm), the thickness of the steel diaphragm wall is c (cm), and the steel diaphragm wall is the high water impermeable portion. Assuming that the width of the highly impermeable portion at the depth penetrating the impermeable portion is a (cm) and the permeability coefficient of the highly impermeable portion is ka (cm/s),
A method for designing a reinforcement structure for a cut-off wall, characterized in that the permeability coefficient ks (cm/s) of the steel diaphragm wall is set so as to satisfy the following formula (2).

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