JP2020158960A - Reinforcing structure of dam body - Google Patents

Abstract

To provide a reinforcing structure of a dam body capable of suppressing seepage destruction of the dam body, suppressing slide of the dam body by minimizing occurrence of liquefaction inside the dam body, and capable of preventing degradation or dissipation of reinforcement effect causing serious damages.SOLUTION: A dam body 10 has a high impervious part 15 along an upstream slope face 10b, having higher imperviousness than other parts of the dam body 10 and having a predetermined width along the width direction of the dam body 10. A steel-made continuous underground wall 20 is provided in the dam body 10 along the extended direction of the dam body 10. The steel-made continuous underground wall 20 penetrates vertically the high impervious part 15, and an upper end thereof is aligned to an upper surface 10a of the dam body 10, and a lower end is set in a foundation ground S positioned under the dam body.SELECTED DRAWING: Figure 2

Description

The present invention relates to a reinforcing structure of a bank body.

In recent years, many river embankments and reservoir embankments have collapsed due to large-scale earthquakes and localized torrential rains, and several large-scale earthquakes and severe disasters due to climate change are expected. Therefore, seismic reinforcement of the levee body is becoming more important.

Based on this background, techniques for reinforcing embankments (embankments) using steel sheet piles have been proposed (see, for example, Patent Documents 1 to 4 and Non-Patent Documents 1).
In the seismic performance reinforcement structure of the embankment body described in Patent Document 1, a reinforcing plate-like body formed of steel sheet piles in two rows in the longitudinal direction of the substantially central portion of the embankment embankment such as an earth fill dam or a reservoir is provided. It is buried and has a double cutoff structure in which the upper ends of both reinforcing plate-like bodies are connected by connecting members 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 directed. It is fastened to the earth anchor arranged diagonally downward.
In the reinforcement structure of the embankment described in Patent Document 3, at least one row of sheet pile walls having a depth rooted in the supporting ground is continuously formed in the length direction of the embankment by penetrating the embankment inside the embankment excluding the glue edge. A structural skeleton consisting of a sheet pile wall and the ground closed by the sheet pile wall is formed in the ground that constitutes the embankment.
In the reinforcement structure of the embankment 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 substantially top end of the continuous embankment, and the underground steel wall is provided. The body is rooted to a depth shallower than the support layer and to a depth at which the underground steel wall body does not collapse in the event of an earthquake or flood.
Non-Patent Document 1 describes that a water-impervious zone having a predetermined width and higher water-shielding property than other parts of the bank body is provided in the bank body along the slope of the bank body on the upstream side. ..

Japanese Unexamined Patent Publication No. 2003-321826 Japanese Unexamined Patent Publication No. 11-1926 Japanese Unexamined Patent Publication No. 2003-13451 Japanese Unexamined Patent Publication No. 2012-7394

Land improvement project design guideline "Reservoir maintenance" (May 2015) / Supervised by the Development Department, Rural Promotion Bureau, Ministry of Agriculture, Forestry and Fisheries, published by Agricultural and Rural Engineering Association

By the way, osmosis fracture is one of the causes of damage to the embankment, which has a water storage function at all times, such as a pond. This infiltration fracture occurs because the upstream slope on the pond side (water storage side or upstream side) from the full water level to the upper part of the embankment becomes a water leakage entry port into the inside of the embankment that causes infiltration fracture. .. On the upstream slope of the embankment, the water pressure repeatedly decreased due to the vertical movement of the water storage level, the soil particles were sucked out to the water storage side, and erosion was caused by waves for a long period of time. In that case, the embankment body may be locally damaged or destroyed. In addition, a sudden rise in water level due to torrential rain and water supply to the inside of the embankment can also cause water leakage. If the embankment is damaged or destroyed, it becomes difficult to dam the reservoir water.
In addition, when liquefaction occurs inside the basin of the reservoir due to an earthquake or the like, the shear strength of the basin is lost and the basin slips, which may damage or collapse the basin.

In the technique described in Non-Patent Document 1 described above, when the embankment or the foundation ground directly under the embankment is liquefied during an earthquake and the top of the embankment sinks or is damaged, the overflowing stored water in 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 a substantially central portion of the bank 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 infiltration from the upstream slope, which is the starting point of infiltration failure.
In addition, since two rows of reinforcing plate-like bodies are required, the construction cost becomes high, and if the bank body is liquefied, the bank body may slip and the bank body may be damaged.
The technique described in Patent Document 2 cannot prevent permeation from the upstream slope, which is the starting point of permeation fracture. Moreover, since there is no continuous underground wall inside the embankment, it is impossible to dam the stored water when the embankment is liquefied and the embankment is damaged.
The techniques described in Patent Documents 3 and 4 cannot prevent permeation from the upstream slope, which is the starting point of permeation fracture. Further, although the bank body can be reinforced with one row of wall bodies, if the bank body is liquefied, the bank body may slip and the bank body may be damaged.
As described in Patent Documents 1, 3 and 4, when the embankment embankment of the reservoir is reinforced with an underground continuous wall, liquefaction may occur inside the embankment depending on the installation location, and the reinforcement effect. There is a possibility that the amount will decrease or disappear, and there is no technology that takes this possibility into consideration.

The present invention has been made in view of the above circumstances, and can suppress the infiltration failure of the embankment body provided in the vicinity of the reservoir, and lower the water level inside the embankment body to increase the strength of the embankment body itself. Reservoir, liquefaction is minimized, and the rigidity of the continuous underground wall itself further reinforces the embankment, which suppresses slippage of the embankment and prevents the reinforcement effect from decreasing or disappearing. It is intended to provide a reinforcing structure for.

In order to achieve the above object, the reinforcing structure of the bank body of the present invention is a reinforcing structure of the bank body provided at least a part of the outer periphery of the reservoir and reinforcing the bank body.
Assuming that the reservoir side is the upstream side across the bank body,
The embankment has a higher water impermeability than other parts of the embankment along the upstream slope of the embankment on the upstream side, and has a predetermined width along the width direction of the embankment. Has an aqueous part,
A steel underground continuous wall is provided on the bank body along the extending direction of the bank body.
The steel underground continuous wall penetrates the highly impermeable portion up and down, and the upper end is aligned with the top end of the embankment body, and the lower end is on the embankment body or the foundation ground located below the embankment body. It is characterized by being installed.

Here, as the steel underground continuous wall, one in which a plurality of steel sheet piles are connected is preferably used, but the present invention is not limited to this. For example, one in which a plurality of steel pipe sheet piles are connected, or one in which a plurality of steel sheet piles and steel pipe sheet piles are connected may be used.
In addition, "the upper end of the continuous steel underground wall is aligned with the top of the embankment" means that the upper end of the continuous steel underground wall is located within 1 m above or below the top of the embankment. Including that.
Further, the highly water-impervious portion is formed of a water-impervious ground material having a higher water-impervious property than a normal ground material such as a blade metal soil. In many cases, such a highly impermeable portion is already provided on the embankment body, but it may be newly provided on the embankment body.

In the present invention, the steel underground continuous wall has a higher water impermeability than other parts of the embankment along the upstream slope of the embankment and has a predetermined width along the width direction of the embankment. It penetrates the water-impervious part up and down, the upper end is aligned near the top of the embankment, and the lower end is installed on the embankment or the foundation ground located below the embankment, so it is horizontal from the upstream slope. The water that has permeated into the water is blocked by a continuous wall in the steel ground and heads downward. Therefore, a difference in the amount of water flow is formed between the highly impermeable portion and the continuous steel underground wall, and the water level in the embankment is raised by ensuring that the water is drained first in the embankment behind (downstream side) the steel underground continuous wall. Can be lowered.
In this way, it is possible to lower the ground ground water level inside the embankment body inside (downstream side) from the continuous steel underground wall, so that the shear strength of the embankment body during an earthquake can be ensured and it is effective inside the embankment body. It is possible to minimize the occurrence of liquefaction in the entire embankment without reducing the stress, and the rigidity of the continuous steel underground wall itself and the shear rigidity of the secured embankment itself suppress the slip of the embankment. , It is possible to prevent a decrease or disappearance of the reinforcing effect, which is a factor causing great damage.

In addition, the water that has permeated horizontally from the upstream slope of the embankment is blocked by the continuous steel underground wall and heads downward, that is, by ensuring the water blocking performance of the continuous steel underground wall. By controlling the water flow inside the embankment and turning downward near the continuous wall surface in the steel ground, the hydraulic gradient can be reduced, so piping inside the embankment can be suppressed, osmotic destruction of the embankment can be suppressed, and storage can be performed. Even in a pond where water is always present, the stability of the embankment can be ensured while keeping the construction cost low.
Further, by arranging the continuous steel underground walls in a row in the width direction of the bank body, the construction period and construction cost can be suppressed.

Further, in the configuration of the present invention, the hydraulic conductivity of the steel underground continuous wall is ks (cm / s), the hydraulic conductivity of the highly impermeable portion is ka (cm / s), and the steel underground continuous wall. Is c (cm), and the width of the highly impermeable portion at the depth at which the steel underground continuous wall penetrates the highly impermeable portion is a (cm).
The penetration length b (cm) of the steel underground continuous wall to the highly impermeable portion may satisfy the following equation (1).

According to such a configuration, the penetration length b (cm) of the continuous steel underground wall to the highly impermeable portion is determined by the water permeability coefficient ks (cm / s) of the continuous steel underground wall and the high water impermeability. Water permeability coefficient ka (cm / s) of the part, thickness c (cm) of the steel underground continuous wall, width a (cm) of the high water-impervious part at the depth at which the steel underground continuous wall penetrates the high-water-impervious part. ) Can be set.

Further, in the configuration of the present invention, the penetration length of the steel underground continuous wall to the highly water-impervious portion is b (cm), the thickness of the steel underground continuous wall is c (cm), and the above. Assuming that the width of the highly impermeable portion at the depth at which the steel underground continuous wall penetrates the highly impermeable portion is a (cm) and the water permeability coefficient of the highly impermeable portion is ka (cm / s).
The hydraulic conductivity ks (cm / s) of the steel underground continuous wall may satisfy the following equation (2).

According to such a configuration, the water permeability coefficient ks (cm / s) of the continuous steel underground wall is set to the penetration length b (cm) of the continuous steel underground wall to the highly impermeable portion, and the steel underground. The thickness of the continuous wall is c (cm), the width of the highly impermeable portion at the depth at which the continuous steel underground wall penetrates the highly impermeable portion, and the water permeability coefficient ka (cm / s) of the highly impermeable portion. ) Can be set.

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

According to such a configuration, at least a part of the continuous steel underground wall below the portion penetrating the highly impermeable portion has water permeability, so that the portion is more permeable than the highly impermeable portion. In the lower ground below the embankment and the soft layer below it, the increase in water pressure due to water flow can be suppressed and the decrease in effective stress can be suppressed.
Further, in the lower ground supporting the highly impermeable portion, the decrease in the effective stress of the ground can be suppressed to a limited extent, so that the collapse of the highly impermeable portion can be prevented.
Furthermore, it does not obstruct the groundwater flow in the lower natural ground below the bank body.

According to the present invention, it is possible to suppress the permeation fracture of the embankment body and minimize the occurrence of liquefaction inside the embankment body to suppress the slippage of the embankment body and prevent the reduction or disappearance of the reinforcing effect. Can be done.

The reinforcing structure of the embankment body which concerns on embodiment of this invention is schematically shown, and is the schematic perspective view. In the same, (A) is a cross-sectional view of the bank body, and (B) is a view for explaining the amount of water flowing in the highly impermeable portion. It is a schematic diagram for demonstrating the significance of providing a steel underground continuous wall in a bank body. It is a schematic diagram for demonstrating the significance of providing a steel underground continuous wall in a bank body having a highly water-impervious part. It is a perspective view which shows the steel underground continuous wall used for the reinforcement structure of the embankment body which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view schematically showing a reinforcing structure of a bank body according to an embodiment, and FIG. 2 is a cross-sectional view of the bank body and the ground.
First, before explaining the present embodiment, the significance of providing a continuous steel underground wall on the bank body of the pond will be described.
As shown in FIGS. 3A to 3D, assuming that the left side of the bank body 10 is the upstream side, there is a reservoir 11 on the upstream side of the bank body 10, and a part of the stored water of the reservoir 11 is a bank. It gradually penetrates into the inside of the bank body 10 from the upstream slope 10b on the upstream side of the body 10.

As shown in FIG. 3A, a steel underground continuous wall 20 is vertically driven from the central portion in the width direction (horizontal direction in FIG. 3A) of the top end 10a of the bank body 10, and the lower end thereof. When the foundation ground 12 located directly below the embankment body 10 is rooted and the upper end is aligned with the top end 10a, the water in the ground upstream of the steel underground continuous wall 20 is saturated inside the embankment body 10. It becomes easy to liquefy. In the following, the liquefaction range is represented by light ink, and in FIG. 3A, the liquefaction range is indicated by L1. On the other hand, the ground downstream of the steel underground continuous wall 20 is infiltrated with rainfall from the top 10a, but the infiltrated water due to the rainfall is discharged to the outside of the embankment on the downstream side of the steel underground continuous wall 20. There is nothing to prevent it, and it does not fall within the liquefaction range.
On the other hand, as shown in FIG. 3B, when the steel underground continuous wall 20 is driven from the vicinity of the upstream end of the top end 10a of the embankment 10 (near the upstream side of the shoulder). Since the volume of the ground on the upstream side of the steel underground continuous wall 20 inside the embankment 10 is smaller than that in the case of FIG. 3A, the liquefaction range L2 should be reduced from the liquefaction range L1. Can be done.
On the other hand, as shown in FIG. 3C, when the steel underground continuous wall 20 is driven from the vicinity of the downstream end of the top end 10a of the embankment 10 (near the downstream side of the shoulder), the embankment body Since the volume of the ground on the upstream side of the steel underground continuous wall 20 inside 10 is larger than that in the case of FIG. 3A, the liquefaction range L3 is larger than the liquefaction range L1 and causes a problem.
Further, as shown in FIG. 3D, when the steel underground continuous wall 20 is driven from the substantially central portion in the vertical direction of the upstream slope 10b of the bank body 10, the steel ground is inside the bank body 10. Since the volume of the ground on the upstream side of the continuous wall 20 is smaller than that in the case of FIG. 3B, the liquefaction range L4 can be further reduced from the liquefaction range L2, but the steel underground continuous wall Since 20 protrudes from the upstream slope 10b, there is a problem that the amount of water stored in the reservoir 11 decreases.

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

As shown in FIG. 4A, a steel underground continuous wall 20 is vertically driven from the central portion in the width direction (horizontal direction in FIG. 4A) of the top end 10a of the bank body 10, and the lower end thereof. When the foundation ground 12 located directly below the bank body 10 is rooted and the upper end is aligned with the top end 10a (that is, when the steel underground continuous wall 20 does not penetrate the high water-impervious portion 15), the high-impervious part is high. Rainfall permeates into the ground between the water-based portion 15 and the steel underground continuous wall 20 from the top end 10a, and the permeated water due to the rainfall accumulates, and the water in the ground is saturated and easily liquefied. The liquefaction range is indicated by L11.
On the other hand, as shown in FIG. 4B, when the steel underground continuous wall 20 is driven from the vicinity of the upstream end of the top end 10a of the bank body 10, the steel underground continuous wall 20 is placed. Penetrates the highly impermeable portion 15 up and down, and rainfall does not easily penetrate into the ground inside the embankment 10 on the upstream side of the steel underground continuous wall 20, so that the water in the ground is not saturated and does not liquefy. ..
On the other hand, as shown in FIG. 4C, when the steel underground continuous wall 20 is driven from the vicinity of the downstream end of the top end 10a of the bank body 10, the same as in the case of FIG. 4A. , The steel underground continuous wall 20 does not penetrate the highly impermeable portion 15, and is easily liquefied. Further, in FIG. 4 (c), the volume of the ground on the upstream side of the steel underground continuous wall 20 inside the bank body 10 is larger than that in the case of FIG. 4 (a), so that the liquefaction range L13 is set. It increases from the liquefaction range L11 and becomes a problem.
Further, as shown in FIG. 4D, when the steel underground continuous wall 20 is driven from the substantially central portion in the vertical direction of the upstream slope 10b of the bank body 10, the steel underground continuous wall 20 is on the upstream side. Then, the water in the ground is not saturated and does not liquefy. However, since the steel underground continuous wall 20 projects from the upstream slope 10b, there is a problem that the amount of water stored in the reservoir 11 decreases.

In this way, in order to suppress the liquefaction inside the bank body 10, it is possible to prevent a part of the stored water of the reservoir 11 from permeating into the inside of the bank body 10 from the upstream slope 10b of the bank body 10. Therefore, as described above, the high impermeable portion 15 is provided, and the steel underground continuous wall 20 is provided so as to penetrate the high impermeable portion 15 from the top end 10a, that is, as shown in FIG. 4 (b). The bank body 10 may be reinforced.
In this case, it is preferable that the steel underground continuous wall 20 is driven from the top end 10a of the bank body 10 through the upper surface of the high impermeable portion 15 so as to vertically penetrate the high impermeable portion 15. The upper end of the steel underground continuous wall 20 may be aligned with the top end 10a of the bank body 10 or may be within 1 m below the top end 10a. Further, the upper end of the steel underground continuous wall 20 may be projected above the top end 10a.

Next, the reinforcing structure of the bank body of the present embodiment will be described.
In the present embodiment, an example in which the reinforcing structure of the embankment body of the present invention is applied to the embankment body of the valley pond, which is one of the reservoirs, will be described, but it is applied to the embankment body of the dish pond, which is one of the reservoirs. May be good.
As shown in FIG. 1, in the present embodiment, the valley pond (reservoir) 11 is formed by blocking the valley with the bank body 10. Except for the embankment 10, the reservoir 11 is surrounded by the ground 12 formed by rock, hard ground, and the like.
In FIG. 1, the ground 12 around the pond 11 is shown in a substantially half elliptical cylinder shape in a plan view, but the shape of the ground 12, that is, the shape of the pond 11 is not limited to this. Further, the ground 12 may also be continuous with the slope of the valley.
Further, when the reservoir is a dish pond, the outer circumference of the reservoir is surrounded by the embankment body, but the embankment body may be provided at least a part of the outer circumference of the reservoir.
In this case, the portion where the embankment body is not provided is formed by an existing ground such as a ground and a protrusion having a height of the embankment body or higher. Therefore, the outer circumference of the pond will be surrounded by the soil structure formed by the embankment and the protrusion. The soil structure is basically a structure formed mainly of soil, and includes a structure in which various facilities and articles made of concrete or the like are provided inside or on the surface thereof.

As shown in FIG. 2A, in the present embodiment, the bank body 10 is formed in a trapezoidal cross section, and the bottom portion of the bank body 10 is the surface (upper surface) of the soft layer S1 constituting the surface layer portion of the foundation ground S. However, the bottom surface of the bank body 10 may be installed so as to bite from the surface of the soft layer S1. In this case, the bottom surface of the bank body 10 is the surface of the soft layer S1. It may be parallel or inclined. Further, the surface of the soft layer S1 on which the bank body 10 is installed may be inclined with respect to the horizontal plane. There is a support layer S2 below the soft layer S1, and the foundation ground S is composed of the soft layer S1 and the support layer S2.
Further, in the present embodiment, the reservoir 11 has a circular shape in a plan view, but the present invention is not limited to this. For example, it may have an elliptical shape in a plan view, an oval shape, a polygonal shape, or the like.

Assuming that the pond 11 side (the left side in FIG. 2A) is the upstream side with the bank body 10 in between, the bank body 10 is more water-impervious than the other parts of the bank body 10 along the upstream slope 10b on the upstream side. Has a high water-impervious portion 15 having a predetermined width a along the width direction (left-right direction in FIG. 2A) of the bank body 10. Here, the "other part of the bank body 10" means a part of the ground constituting the bank body 10 excluding the highly impermeable portion 15.
The high water-impervious portion 15 is formed in a cross-sectional parallel quadrilateral shape by a highly water-impervious ground material such as blade metal soil, but the cross-sectional shape of the high water-impervious portion 15 is limited to the parallel quadrilateral shape. The shape may be such that the steel underground continuous wall 20 can penetrate the highly impermeable portion 15 vertically inside the embankment body 10.
In the present embodiment, the upper surface of the highly impermeable portion 15 occupies approximately half of the upstream side of the top end 10a of the bank body 10 and is flush with the top end 10a. Further, the inclined surface on the upstream side of the highly impermeable portion 15 constitutes almost the entire area of the upstream slope 10b of the bank body 10. Therefore, it is possible to prevent a part of the stored water stored in the reservoir 11 from gradually infiltrating from the upstream slope 10b into the inside of the bank body 10.

In the present embodiment, the highly impermeable portion 15 is provided on the existing bank body 10, but the present invention is not limited to this. For example, a part of the high water-impervious portion 15 may be replaced with a new ground material having a high water-imperme such as a blade metal soil, or a ground material having a high water-imperme may be added to the high water-impervious part 15. Further, when the bank body 10 is newly constructed, the highly impermeable portion 15 may be newly constructed.

Further, the bank body 10 is provided with a steel underground continuous wall 20 along the extending direction of the bank body 10 (direction orthogonal to the paper surface in FIG. 2A).
That is, inside the embankment body 10, steel underground continuous walls 20 are 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 underground continuous wall 20 is continuously installed in a straight line from one end to the other end of the bank body 10 of the reservoir 11 in the longitudinal direction.
Further, the steel underground continuous wall 20 is vertically driven 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 shoulder on the upstream side of the bank body 10.

Further, the steel underground continuous wall 20 penetrates the high impermeable portion 15 vertically, and the upper end is aligned with the top end 10a of the embankment body 10 (the upper surface of the highly impermeable portion 15), and the lower end is the embankment body 10. It is embedded in the support layer S2 located below and below the soft layer S1. The lower end of the steel underground continuous wall 20 is preferably rooted in the support layer S2 in consideration of earthquake resistance, but when only infiltration failure is considered, it may be installed at or near the bottom of the bank body 10. It may be installed on the soft layer S1 or simply applied to the upper surface of the support layer S2.

Further, at least a part of the steel underground continuous wall 20 below the portion penetrating the highly impermeable portion 15 (the portion penetrating the portion having the height b in FIG. 2A). Has water permeability. For example, a steel material provided in the lower ground of the embankment body, which is below the portion penetrating the highly impermeable portion 15 of the steel underground continuous wall 20 and constitutes the lower part of the embankment body 10, and the soft layer S1. A water permeation hole 17 (see FIG. 5) is provided at the lower end of the underground continuous wall 20.

As shown in FIG. 5, the steel underground continuous wall 20 is formed by connecting a plurality of hat-shaped steel sheet piles 16.
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 an end of the flange 16b opposite to the web 16a, and the tip of the arm 16c. A joint 16d is formed in the portion.
The adjacent steel sheet piles 16 and 16 are connected to each other by fitting the joints 16d and 16d to each other, whereby the steel underground continuous wall 20 is formed.
The steel sheet pile constituting the steel underground continuous wall 20 is not limited to the hat-shaped steel sheet pile, and may be a U-shaped steel sheet pile or a straight steel sheet pile. Further, the steel underground continuous wall 20 is not limited to the steel sheet pile, and may be composed of a steel pipe pile or a steel pipe sheet pile, or may be composed by combining these.

The web 16a is integrally formed by the upper web 16a1 and the lower web 16a2, and the lower web 16a2 is provided with a plurality (many) elliptical or circular water permeation holes 17 at predetermined intervals in the vertical and horizontal directions. The upper web 16a1 is not provided with a water permeation hole 17.
The lower portion having the lower web 16a2 provided with the water permeable hole 17 is the portion having the above-mentioned water permeability.

Further, the portion having water permeability is not limited to this, and the illustration is omitted, but for example, in a steel underground continuous wall formed by connecting a plurality of steel sheet piles, a predetermined number of steel sheet piles are formed. By forming it shorter than other steel sheet piles, an opening corresponding to the width of the steel sheet pile is formed in a part of the lower end of the continuous steel underground wall, and this opening can also be used as the portion having the above-mentioned water permeability. Good.

In the present embodiment, as shown in FIG. 2 (A), a part of the stored water of the reservoir 11 permeates horizontally from the upstream slope 10b of the embankment body 10, and this permeated water is made of steel. Water is blocked by the intermediate continuous wall 20 and heads downward, and further, through a water permeation hole 17 (see FIG. 5) provided at the lower end of the steel underground continuous wall 20, the back side of the steel underground continuous wall 20. Flows into the soft layer S1 of. In FIG. 2A, the flow of water is indicated by a thick arrow.
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 a part of the highly impermeable portion 15 is measured by the steel underground continuous wall 20. By increasing the amount of water flowing through the portion facing the right triangle portion, a difference in the amount of flowing water is formed between the highly impermeable portion 15 and the steel underground continuous wall 20 to form a steel underground continuous wall. It is possible to surely drain the water in the embankment body 10 behind (downstream side) 20 and lower the water level in the embankment body 10.
That is, by satisfying the following equation (3), a difference in the amount of flowing water can be formed between the highly impermeable portion 15 and the steel underground continuous wall 20, and the water level in the embankment 10 can be lowered.

In the above equation (3), the left side is the head difference (dx) and the streamline length (a / b · x) at each height of the right triangle portion, assuming that water flows in the horizontal direction in the right triangle portion. ) And the water permeation coefficient ka of the highly impermeable portion (blade metal soil) 15. The right side is the head when water flows in the horizontal direction on the continuous steel underground wall 20. The difference (b) is the total amount of flowing water determined by the streamline length (c) of the thickness of the steel underground continuous wall 20 and the water permeation coefficient ks of the steel underground continuous wall 20. In addition, in the left side of the formula (3), a is the width of the high impermeable portion 15 at the depth at which the steel underground continuous wall 20 penetrates the high impermeable portion 15 (the embankment body 10 of the steel underground continuous wall 20). Of the two surfaces orthogonal to the high impermeable portion 15 in the width direction of, the horizontal distance from the lowermost end of the surface in contact with the high impermeable portion 15 located on the upstream side to the upstream slope 10b), b is steel. It is the penetration length of the continuous wall 20 in the ground production to the highly impermeable portion 15 (distance from the lowermost end portion to the top end 10a). Further, in the above equation, the projected cross-sectional area in the flowing water direction, which is orthogonal to the flowing water when calculating the total amount of flowing water, is the unit length in the depth direction (extending direction of the bank body) and the height direction is the right triangle portion. It is the same b in the continuous wall part in the steel ground, and it is omitted because it is the same item on the left side and the right side.

Then, in the present embodiment, the water permeability coefficient of the steel underground continuous wall 20 is ks (cm / s), the water permeability coefficient of the highly impermeable portion 15 is ka (cm / s), and the steel underground continuous wall 20 Assuming that the thickness is c (cm) and the width of the high water-impervious portion 15 at the depth at which the steel underground continuous wall 20 penetrates the high water-impervious part 15 is a (cm), the height of the steel underground continuous wall 20 is high. The penetration length b (cm) to the water-impervious portion 15 is set so as to satisfy the following equation (1) based on the above equation (3).

For example, the hydraulic conductivity of a continuous steel underground wall (steel sheet pile) ks: 1 × ^10-6 (cm / s),
Steel underground continuous wall plate thickness (steel sheet pile plate thickness) c: 1.08 (cm),
Permeability coefficient ka of highly impermeable part (blade metal soil): 5 × ^10-5 (cm / s),
Assuming that the width of the highly impermeable portion a: 250 (cm) at the depth at which the continuous steel underground wall penetrates the highly impermeable portion,
The penetration length b> 102.48 (cm) to the highly impermeable portion of the steel underground continuous wall. That is, the penetration length b (cm) of the steel underground continuous wall to the highly impermeable portion may be set longer than 102.48 (cm).
The hydraulic conductivity of the highly impermeable portion was set to the maximum value of the hydraulic conductivity in the state of being compacted at the site as an impermeable material (land improvement project design guideline "reservoir maintenance", Ministry of Agriculture, Forestry and Fisheries).

Further, in the present embodiment, the penetration length of the continuous steel underground wall to the highly impermeable portion is b (cm), the thickness of the continuous steel underground wall is c (cm), and the continuous steel underground wall is continuous. Assuming that the width of the highly impermeable portion at the depth at which the wall penetrates the highly impermeable portion is a (cm) and the water permeability coefficient of the highly impermeable portion is ka (cm / s), the water permeability coefficient ks of the continuous steel underground wall (Cm / s) is set so as to satisfy the following equation (2) based on the above equation (3) or (1).

For example, plate thickness of continuous steel underground wall (steel sheet pile plate thickness) c: 1.08 (cm),
Penetration length b: 200 (cm), through the highly impermeable part of the steel underground continuous wall,
Permeability coefficient ka of highly impermeable part (blade metal soil): 5 × ^10-5 (cm / s)
Assuming that the width of the highly impermeable portion a: 250 (cm) at the depth at which the continuous steel underground wall penetrates the highly impermeable portion,
The hydraulic conductivity of the continuous steel underground wall is ks (cm / s) <1.14 × ^10-6 (cm / s). That is, the hydraulic conductivity ks required for a continuous steel underground wall may be set lower than 1.14 × ^10-6 (cm / s).
The hydraulic conductivity of the highly impermeable portion is the same as above.

As described above, according to the present embodiment, the steel underground continuous wall 20 has a higher water impermeability than the other parts of the embankment body 10 along the upstream slope 10b of the embankment body 10, and the embankment body. The foundation ground S which penetrates the highly impermeable portion 15 having a predetermined width along the width direction of 10 up and down, has the upper end aligned with the top end 10a of the embankment body 10, and the lower end is located below the embankment body 10. Since it is installed (rooted) in the support layer S2 of the above, the water that has permeated in the horizontal direction from the upstream slope 10b is blocked by the steel underground continuous wall 20 and heads downward. Therefore, a difference in water flow is formed between the highly impermeable portion 15 and the steel underground continuous wall 20, and the embankment body 10 behind (downstream side) the steel underground continuous wall 20 is surely first. It can be drained and the water level in the embankment 10 can be lowered.
In this way, the ground ground water level inside the embankment body inside (downstream side) the steel underground continuous wall 20 can be lowered, so that the shear strength of the embankment body 10 can be ensured and the inside of the embankment body 10 can be lowered. It is possible to minimize the occurrence of liquefaction in the entire embankment without reducing the effective stress, and the slip of the embankment 10 can be prevented by the rigidity of the continuous steel underground wall itself and the shear rigidity of the secured embankment itself. It can be suppressed and the reduction or disappearance of the reinforcing effect can be prevented.

In addition, the water that has permeated horizontally from the upstream slope 10b of the bank body 10 is blocked by the steel underground continuous wall 20 and heads downward, that is, the steel underground continuous wall 20 guarantees the water stopping performance. By doing so, the water flow in the embankment 10 can be controlled, the direction can be changed downward in the vicinity of the continuous wall surface in the steel ground, and the hydraulic gradient can be reduced. Therefore, the piping in the embankment 10 can be suppressed and the embankment body can be suppressed. In addition to being able to suppress the infiltration destruction of No. 10, even in the pond 11 where the stored water is always present, the stability of the embankment body can be ensured while keeping the construction cost low.
Further, by arranging the steel underground continuous walls 20 in a row in the width direction of the bank body 10, the construction period and construction cost can be suppressed.

Further, even if the bank body 10 is damaged, the steel underground continuous wall 20 functions like a fail-safe, and the stored water in the reservoir 11 can be dammed up.
Further, since at least a part of the steel underground continuous wall 20 below the portion penetrating the highly impermeable portion 15 has water permeability, the bank below the highly impermeable portion 15 In the lower part of the body and the ground that is the soft layer S1 below it, the increase in water pressure due to the water flow can be suppressed and the decrease in effective stress can be suppressed.
Further, in the lower ground (soft layer S1) that supports the highly impermeable portion 15, the decrease in the effective stress of the ground can be suppressed to a limited extent, so that the collapse of the highly impermeable portion 15 can be prevented, and further, the embankment body 10 It does not obstruct the groundwater flow in the lower ground (soft layer S1) below.

In the present embodiment, as shown in FIG. 2A, the steel underground continuous wall 20 is driven from the vicinity of the shoulder on the upstream side of the embankment 10, and the highly impermeable portion 15 is moved up and down. Although it was penetrated, the casting position of the steel underground continuous wall 20 is not limited to the vicinity of the shoulder. For example, it may be driven from the central portion in the width direction of the top end 10a of the bank body 10 to penetrate the highly impermeable portion 15 vertically. In short, the steel underground continuous wall 20 may be driven from the top end 10a of the embankment body 10 so that the highly impermeable portion 15 penetrates vertically inside the embankment body 10.

10 Embankment body 10a Top end 10b Upstream slope 11 Reservoir 20 Steel underground continuous wall S Foundation ground S1 Soft layer S2 Support layer

Claims (4)

It is a reinforcement structure of the embankment body that reinforces the embankment body provided at least a part of the outer circumference of the reservoir.
Assuming that the reservoir side is the upstream side across the bank body,
The embankment has a higher water impermeability than other parts of the embankment along the upstream slope of the embankment on the upstream side, and has a predetermined width along the width direction of the embankment. Has an aqueous part,
A steel underground continuous wall is provided on the bank body along the extending direction of the bank body.
The steel underground continuous wall penetrates the highly impermeable portion up and down, and the upper end is aligned with the top end of the embankment body, and the lower end is on the embankment body or the foundation ground located below the embankment body. Reinforcement structure of the embankment, which is characterized by being installed. The hydraulic conductivity of the steel underground continuous wall is ks (cm / s), the hydraulic conductivity of the highly impermeable portion is ka (cm / s), and the thickness of the steel underground continuous wall is c (cm). Assuming that the width of the highly impermeable portion at the depth at which the steel underground continuous wall penetrates the highly impermeable portion is a (cm).
The reinforcing structure for a bank body according to claim 1, wherein the penetration length b (cm) of the steel underground continuous wall into the highly impermeable portion satisfies the following equation (1).

The penetration length of the steel underground continuous wall to the highly impermeable portion is b (cm), the thickness of the steel underground continuous wall is c (cm), and the steel underground continuous wall is the height. Assuming that the width of the highly impermeable portion at the depth penetrating the impermeable portion is a (cm) and the water permeability coefficient of the highly impermeable portion is ka (cm / s).
The reinforcing structure of a bank body according to claim 1, wherein the hydraulic conductivity ks (cm / s) of the steel underground continuous wall satisfies the following equation (2).

Any of claims 1 to 3, wherein at least a part of the steel underground continuous wall below the portion penetrating the highly impermeable portion has water permeability. Reinforcement structure of the embankment body described in item 1.

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