JP7680708B2 - Precast components, flood barriers, and methods for constructing flood barriers - Google Patents

Description

This disclosure relates to precast members, flood barriers, and methods for constructing flood barriers.

Prestressed concrete tanks (hereinafter referred to as PC tanks) have traditionally been used as tanks for storing liquefied gases such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG).

PC tanks have a tank body with a steel outer tank and inner tank, and are configured to prevent liquid from leaking to the outside in the event of damage to the inner tank, etc., by constructing a cylindrical liquid-blocking dike along the outer periphery of the tank body.

One method for constructing this type of flood barrier is to use a precast construction method, in which precast concrete components manufactured in advance at a factory or other facility are transported to the site and connected together, thereby shortening construction time and reducing costs (see, for example, Patent Document 1).

JP 2017-078268 A

In the above precast construction method, multiple precast members are placed at intervals around the circumference of the dike, and weatherstripping concrete is poured between each precast member to form a circular wall body in which each precast member is integrated all around the circumference. The circular wall body is then treated as one lot, and successive lots are stacked on top of each other in the height direction to construct a dike of a specified height.

In this type of precast construction method, adjacent precast members in the circumferential direction remain independent of each other until the inter-filling concrete hardens, and until one lot is integrated all around, the next lot cannot be installed on top of each other in multiple tiers as a measure against wind load. This means that inter-filling concrete must be poured for each lot, which takes time and effort, lengthening the construction period.

In addition, prestress is introduced into the flood barrier using tension members, which are inserted into sheath tubes embedded in the precast members. If the precast members are spaced apart in the circumferential direction, as in the precast construction method described above, the ends of the circumferential sheath tubes between the precast members must be connected with connecting sheath tubes, and watertight connections, such as by heating heat shrink tubing to seal them tightly, must be made to prevent filling concrete from seeping in through these connections, which creates the problem of additional work taking time and effort.

This disclosure has been made in consideration of the above circumstances, and aims to provide a technology for constructing flood barriers that is easy to work with and can shorten the construction period.

The precast member disclosed herein is a precast member that constitutes a cylindrical liquid barrier that surrounds the outer periphery of a liquid storage tank, and includes a main body made of concrete that is rectangular in front view and curved in an arc shape when viewed from above, and an outer cutout portion that cuts out the corner where the curved outer surface of the main body intersects with the circumferential end face, and the outer cutout portion faces the outer cutout portion of another precast member that is adjacently arranged with the circumferential end faces in surface contact with each other, thereby defining an outer recess on the outer periphery of the liquid barrier into which filling concrete can be poured.

It is also preferable that the precast member further includes an outer circumferential reinforcing bar that extends circumferentially within the main body and has an end exposed within the outer cutout, and that the end of the outer circumferential reinforcing bar is joined to the end of the outer circumferential reinforcing bar of the other precast member.

The main body further includes an inner cutout portion cut out of the corner where the curved inner surface and the circumferential end surface of the main body intersect, and the inner cutout portion preferably faces the inner cutout portion of the other precast member to define an inner recess on the inner periphery of the dike into which filling concrete can be poured.

It is also preferable that the precast member further includes an inner circumferential reinforcing bar that extends circumferentially within the main body and has an end exposed within the inner cutout, and the end of the inner circumferential reinforcing bar is joined to the end of the inner circumferential reinforcing bar of the other precast member.

It is also preferable that the structure further includes a circumferential sheath tube extending circumferentially within the main body and into which a circumferential tension member is inserted that can introduce circumferential prestress into the liquid barrier.

It is also preferable that the device further includes a vertical sheath tube extending vertically within the main body and into which a vertical tension member is inserted that can introduce vertical prestress into the dike.

The liquid barrier of the present disclosure is characterized in that it is constructed by rigidly connecting the precast members side by side in the circumferential direction and stacking them vertically to rigidly connect them.

The method of constructing a flood barrier of the present disclosure is a method of constructing a flood barrier using the precast members, which is characterized in that a plurality of the precast members are arranged in a circumferential direction so that their circumferential end faces are in surface contact with each other, and adjacent precast members are temporarily connected to form a single stage of annular wall that is integrated all around, and a wall formation process of stacking the annular walls in a plurality of stages to form a cylindrical wall, and a pouring process of pouring the filler concrete into the cylindrical wall all at once are repeated at least once, and a permanent circumferential tensioning member is provided in the cylindrical wall formed to a predetermined height to tension it, thereby introducing prestress.

In addition, in the wall formation process, when temporarily connecting adjacent precast members in the circumferential direction, it is preferable to provide temporary circumferential tension members in the annular wall body and tension the annular wall body to integrate the entire circumference.

The technology disclosed herein allows for the construction of flood barriers with excellent workability and shortened construction times.

FIG. 2 is a schematic vertical cross-sectional view showing a portion of the PC tank according to the present embodiment. FIG. 2 is a schematic perspective view showing the PC tank according to the present embodiment. FIG. 2 is a schematic perspective view showing a precast member according to the present embodiment. A schematic cross-sectional view illustrating the procedure for vertically connecting precast members according to this embodiment. A schematic cross-sectional view illustrating the procedure for connecting precast members in the circumferential direction in this embodiment. FIG. 1 is a schematic diagram illustrating a method for constructing a flood barrier using precast members according to this embodiment. FIG. 1 is a schematic diagram illustrating a method for constructing a flood barrier using precast members according to this embodiment. FIG. 1 is a schematic diagram illustrating a method for constructing a flood barrier using precast members according to this embodiment. FIG. 1 is a schematic diagram illustrating a method for constructing a flood barrier using precast members according to this embodiment. FIG. 1 is a schematic diagram illustrating a method for constructing a flood barrier using precast members according to this embodiment. FIG. 11 is a schematic perspective view showing a precast member according to another embodiment.

The precast members, the flood barrier, and the method for constructing the flood barrier according to this embodiment will be described below with reference to the attached drawings. Identical parts are given the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[PC Tank]
FIG. 1 is a schematic vertical cross-sectional view showing a part of a PC tank 1 according to this embodiment, and FIG. 2 is a schematic perspective view showing the PC tank 1 according to this embodiment.

The PC tank 1 shown in Figures 1 and 2 is an aboveground tank that stores liquefied gases such as LNG and LPG. Note that the material stored in the PC tank 1 may be liquids other than liquefied gases, such as liquefied hydrogen, but the following description will use LNG as an example.

As shown in FIG. 1, the PC tank 1 comprises a tank body 2, a bottom slab 5, multiple piles 6, and a liquid retaining dike 10 surrounding the outer periphery of the tank body 2. Note that the multiple piles 6 are not required, and the bottom slab 5 can be supported directly on the ground depending on the specific size of the PC tank 1, ground conditions, etc.

The tank body 2 is hollow and generally cylindrical with closed top and bottom, and has an inner tank 3 for storing LNG, and an outer tank 4 surrounding the inner tank 3. The inner tank 3 and the outer tank 4 are made of, for example, steel plates. A heat insulating material is interposed between the inner tank 3 and the outer tank 4, and the LNG is kept cold between the inner tank 3 and the outer tank 4.

The base slab 5 is, for example, a reinforced concrete structure, and is formed in a roughly disk-like shape. In the illustrated example, the base slab 5 is supported by multiple piles 6 buried in the ground, but the piles 6 may be omitted depending on the ground conditions, etc. The tank body 2 and the liquid retaining dike 10 are installed on the upper surface of the base slab 5.

The liquid barrier 10 is a cylindrical prestressed concrete wall rising from the base slab 5, and is constructed in a generally cylindrical shape with an open top so as to surround the outer periphery of the tank body 2. The liquid barrier 10 is provided with outer reinforcing bars 13A consisting of multiple outer circumferential reinforcing bars 11A and multiple outer vertical reinforcing bars 12A combined in a lattice pattern. The liquid barrier 10 is also provided with inner reinforcing bars 13B consisting of multiple inner circumferential reinforcing bars 11B and multiple inner vertical reinforcing bars 12B combined in a lattice pattern.

The flood barrier 10 is equipped with multiple circumferential tension members 14 and multiple vertical tension members 15. These tension members 14, 15 may be, for example, PC steel materials such as PC steel wires and PC steel bars.

The circumferential tension members 14 extend around the entire circumference of the dike 10, and multiple members are provided at a predetermined interval in the vertical direction. The circumferential tension members 14 are inserted into circumferential sheath tubes 17 that extend circumferentially within the dike 10. When the circumferential tension members 14 are tensioned, circumferential prestress is introduced into the dike 10, and a predetermined compressive stress is applied to the concrete. This makes it possible to counter the circumferential tensile force acting on the dike 10 due to the liquid pressure when LNG leaks from the tank body 2, ensuring the liquid-tightness of the dike 10. After the circumferential tension members 14 are tensioned, a filler such as mortar is filled into the circumferential sheath tube 17.

The vertical tension members 15 are tension members arranged vertically within the dike 10, and multiple tension members are provided at a predetermined interval in the circumferential direction. The vertical tension members 15 are inserted into the vertical sheath tube 18 that extends vertically within the dike 10. When the vertical tension members 15 are tensioned, vertical prestress is introduced into the dike 10, making it possible to counteract the liquid pressure in the event of an LNG leak. In addition, during normal times when there is no leakage, a vertical bending moment due to the circumferential prestress acts on the dike 10, but by introducing vertical prestress, it becomes possible to counteract this bending moment as well. After the vertical tension members 15 are tensioned, a filler such as mortar is filled into the vertical sheath tube 18.

In this embodiment, the flood barrier 10 is composed of precast concrete members 20. Specifically, as shown in FIG. 2, the flood barrier 10 is constructed by arranging a number of precast members 20 side by side in the circumferential direction and stacking them vertically. Vertical joints 19A made of filler concrete, which will be described in detail later, are formed between each of the precast members 20 adjacent in the circumferential direction, and horizontal joints 19B made of mortar or the like are formed between each of the precast members 20 adjacent in the vertical direction. Details of the precast members 20 according to this embodiment are described below.

[Precast components]
Fig. 3 is a schematic perspective view showing the precast members 20 according to the present embodiment. Fig. 4 is a schematic cross-sectional view illustrating a procedure for vertically connecting the precast members 20 according to the present embodiment. Fig. 5 is a schematic cross-sectional view illustrating a procedure for circumferentially connecting the precast members 20 according to the present embodiment.

As shown in FIG. 3, the precast member 20 has a plate-shaped main body 21 that is approximately rectangular when viewed from the front and curved in an arc when viewed from above, a number of circumferential sheath tubes 17, a number of vertical sheath tubes 18, outer reinforcing bars 13A, and inner reinforcing bars 13B.

The main body 21 is constructed in advance at a factory or the like by pouring and filling concrete into a formwork so that the sheath pipes 17, 18 and the reinforcing bars 13A, 13B are integrally formed. In the following, the outer curved side of the main body 21 is simply referred to as the outside, and the inner curved side is simply referred to as the inside.

The multiple circumferential sheath tubes 17 are embedded in the main body 21 at a predetermined interval in the vertical direction. One end of the circumferential sheath tube 17 in the tube axis direction opens into one end face 22A of the main body 21, and the other end of the circumferential sheath tube 17 in the tube axis direction opens into the other end face 22B of the main body 21. The number of circumferential sheath tubes 17 is not limited to the illustrated example, and may be an optimal number depending on the construction conditions, etc.

The vertical sheath tubes 18 are embedded in the main body 21 at a predetermined interval in the circumferential direction. The upper end openings of the vertical sheath tubes 18 are located on the upper surface 23A side of the main body 21, and the lower end openings of the vertical sheath tubes 18 are located on the lower surface 23B side of the main body 21. Here, the upper and lower ends of the vertical sheath tubes 18 may each be provided with a socket-shaped male and female coupler that can be fitted in order to easily connect to the vertical sheath tubes 18 of other precast members 20 stacked on the upper tier. The vertical sheath tubes 18 are preferably embedded inside the circumferential sheath tubes 17 of the main body 21. The number of vertical sheath tubes 18 is not limited to the illustrated example, and may be the optimal number depending on the construction conditions, etc.

The outer reinforcing bars 13A are embedded outside the circumferential sheath tube 17 of the main body 21. Specifically, the outer reinforcing bars 13A are formed by combining multiple outer circumferential reinforcing bars 11A and multiple outer vertical reinforcing bars 12A in a lattice pattern. Both ends of the outer circumferential reinforcing bars 11A are exposed in the outer cutouts 24A and 24B described below. The lower ends of the outer vertical reinforcing bars 12A are arranged to protrude downward by a predetermined amount from the lower surface 23B of the main body 21. The number of each reinforcing bar 11A and 12A is not limited to the illustrated example, and may be an optimal number depending on the construction conditions, etc.

The inner reinforcing bars 13B are embedded inside the vertical sheath tube 18 of the main body 21. Specifically, the inner reinforcing bars 13B are formed by combining multiple inner circumferential bars 11B and multiple inner vertical bars 12B in a lattice pattern. Both ends of the inner circumferential bars 11B are exposed in the inner cutouts 26A, 26B described below. The lower ends of the inner vertical bars 12B are arranged to protrude downward by a predetermined amount from the lower surface 23B of the main body 21. The number of each reinforcing bar 11B, 12B is not limited to the illustrated example, and may be an optimal number depending on the construction conditions, etc.

The main body 21 has a plurality of outer cylindrical holes 28A and inner cylindrical holes 28B recessed downward from the upper surface 23A to a predetermined depth. The outer cylindrical holes 28A are formed coaxially with the outer vertical reinforcing bars 12A, and the inner cylindrical holes 28B are formed coaxially with the inner vertical reinforcing bars 12B. The diameter of each cylindrical hole 28A, 28B is formed to be larger than the reinforcing bar diameter of each vertical reinforcing bar 12A, 12B, and the vertical reinforcing bars 12A, 12B of other precast members 20 stacked on the upper tier are inserted into each cylindrical hole 28A, 28B.

Specifically, as shown in FIG. 4, a cylindrical coupler C is provided at the upper end of the vertical reinforcing bars 12A, 12B located at the bottom side of the cylindrical holes 28A, 28B. When stacking the precast members 20', the lower end side of the vertical reinforcing bars 12A', 12B' of the precast member 20' is inserted into the cylindrical holes 28A, 28B of the lower precast member 20 and fitted into the coupler C, so that the upper and lower vertical reinforcing bars 12A, 12A', 12B, 12B' are joined to each other. The filler M, such as mortar, to be filled between the upper and lower precast members 20, 20' may be provided in advance on the upper surface 23A of the lower precast member 20, or may be poured and filled after the upper precast member 20' is stacked. When the filler M solidifies, the upper and lower precast members 20, 20' are integrated (rigidly connected).

As shown in FIG. 3, a pair of outer cutouts 24A, 24B that are approximately L-shaped in top view are provided at two corners where the outer surface 22C of the main body 21 intersects with the end faces 22A, 22B. A pair of inner cutouts 26A, 26B that are approximately L-shaped in top view are provided at two corners where the inner surface 22D of the main body 21 intersects with the end faces 22A, 22B. These outer cutouts 24A, 24B and inner cutouts 26A, 26B are provided over the entire height of the main body 21.

The ends of the outer circumferential reinforcing bars 11A are exposed in the internal spaces of the outer cutouts 24A and 24B, and the ends of the inner circumferential reinforcing bars 11B are exposed in the internal spaces of the inner cutouts 26A and 26B. These circumferential reinforcing bars 11A and 11B are joined to the circumferential reinforcing bars 11A and 11B of other precast members 20 that are arranged adjacently in the circumferential direction. The joining of the circumferential reinforcing bars 11A and 11B to each other may be any of mechanical joints, lap joints, and gas pressure welding joints.

As shown in FIG. 5(A), when connecting the precast members 20, 20' in the circumferential direction, the end face 22A of the main body 21 and the end face 22B' of the main body 21' are brought into surface contact with each other. When the end faces 22A, 22B' are brought into surface contact, the outer cutouts 24A, 24B' and the inner cutouts 26A, 26B' face each other, thereby defining an outer recess 25 and an inner recess 27 between each of the precast members 20, 20'.

When constructing the flood barrier 10, a number of precast members 20, 20' are sequentially arranged in a circumferential direction and connected to form one lot of annular wall. Since the end faces 22A, 22B' of adjacent precast members 20, 20' are in surface contact with each other, the ends of the circumferential reinforcing bars 11A, 11A', 11B, 11B' exposed in the recesses 25, 27 can be fastened together with temporary bolts such as mechanical joints, or temporary circumferential tension members 14' (e.g., tension members with fewer numbers than the permanent circumferential tension members 14) are inserted into the circumferential sheath tube 17 for temporary tensioning, or buried bolts previously installed in the precast members 20, 20' are fastened with nuts to form an integrated periphery.

In other words, the precast members 20, 20'... for one lot can be easily integrated all around with temporary bolts or tension members 14' without pouring filler concrete between each precast member 20, 20'. This makes it possible to install the next lot of precast members 20 in multiple stages without pouring filler concrete between each precast member as in the conventional technology, and effectively improves workability. In addition, the end faces 22A, 22B' of each precast member 20, 20' are brought into surface contact, and a watertight connection can be made by sandwiching a seal ring or the like at the end of the circumferential sheath tube 17, 17'. This also makes it possible to reduce incidental work required in the conventional technology when connecting sheath tubes, such as the work of connecting the sheath tubes with a connecting sheath tube and sealing the heat shrink tube.

Once multiple lots have been installed in multiple tiers, formwork (not shown) is placed on the outside and inside between each precast member 20, 20', as shown in Figure 5 (B), and filler concrete 30, 31 is poured into the outside recess 25 and the inside recess 27, respectively. At this time, the outside filler concrete 30 and the inside filler concrete 31 can be applied vertically together for multiple lots at once. In other words, there is no longer a need to pour filler concrete for each lot as in the conventional technology, making it possible to significantly shorten the construction period for the flood control embankment 10.

In addition, by pouring the outer filler concrete 30 into the outer recess 25 to introduce circumferential prestress, a compression area that can withstand the liquid pressure in the event of an LNG leak is secured in the outer peripheral portion between each precast member 20, 20'. This makes it possible to reliably improve the liquid-tightness of the liquid retaining dike 10. Here, the outer filler concrete 30 should be formed so that the recess amount from the outer surface 22C of the outer cutout portions 24A, 24B is 10 cm or more, and a compression area thickness of 10 cm or more as stipulated in the LNG aboveground storage tank guidelines can be secured.

In addition, by pouring inner filler concrete 31 into the inner recess 27 and burying the circumferential reinforcing bars 11B, the strength of the entire floodgate 10 can be effectively improved. This makes it possible to withstand circumferential tensile forces and bending moments without significantly increasing the number of tendons 14, 15, simplifying the structure and reducing costs.

[How to build a flood barrier]
Next, a method for constructing a flood barrier 10 using the precast members 20 according to this embodiment will be described with reference to Figures 6 to 10. Note that, although the following description will be given starting from a state where the construction of the base slab 5 has been completed, the construction method of the present disclosure may or may not include the construction of the base slab 5.

In the first step shown in FIG. 6, multiple precast members 20 are arranged in a circumferential direction on the top surface of the base plate 5. At this time, adjacent precast members 20 are arranged with their end faces 22A, 22B in surface contact with each other. Once multiple precast members 20 are arranged in a ring shape, the ends of the circumferential reinforcing bars 11A, 11B exposed in the recesses 25, 27 are fastened together with temporary bolts such as mechanical joints, or a temporary circumferential tension member 14' (see FIG. 5(A)) is inserted into the circumferential sheath tube 17 and temporarily tensioned to form a ring-shaped wall W1 that is integrated all around. The first step corresponds to a part of the wall formation step of this disclosure.

7, multiple precast members 20 are stacked on top of the annular wall W1 and arranged in a circumferential direction, and the same work as in the first step is performed to form an annular wall W2 in which each precast member 20 is integrated all around. At this time, the upper and lower precast members 20 adjacent in the vertical direction are integrated by the filler M poured between them. The second step may be performed only once, or may be performed multiple times to stack the annular walls W1, W2, etc. in three or more layers. The number of layers to stack the annular walls W1, W2, etc. may be determined appropriately depending on the construction conditions, such as the height and outer diameter of the liquid barrier 10 and the dimensions of the precast members 20. The second step corresponds to a part of the wall formation step of the present disclosure.

As shown in FIG. 8, if the cylindrical wall body WC is constructed by stacking the annular walls W1, 2, 3, etc. in multiple stages (three stages in the illustrated example), in the third step, the filling concrete 30, 31 is poured vertically in multiple stages into the outer recess 25 and the inner recess 27 at once. When the filling concrete 30, 31 hardens, the precast members 20 adjacent in the circumferential direction are rigidly connected to each other. Here, the order in which the outer and inner filling concrete 30, 31 are poured is not particularly limited, and one may be poured first, or they may be poured simultaneously. The third step corresponds to the pouring step of this disclosure.

After the fourth step shown in FIG. 9, the second and third steps described above are repeated an appropriate number of times to stack the annular walls W4, 5, etc., thereby building up the cylindrical wall body WC in the vertical direction. The number of times the second and third steps are repeated may be determined appropriately depending on the height of the liquid barrier 10 to be constructed, etc. Once the cylindrical wall body WC has been built to the desired height, the process moves to the final step. Note that if the cylindrical wall body WC is to be stacked all at once to the height of the liquid barrier 10 in the second step described above, after the third step, the fourth step may be omitted and the process may move directly to the final step.

In the final step shown in Figure 10, the temporary circumferential tension member 14' in the circumferential sheath tube 17 (see Figure 3) is replaced with the permanent circumferential tension member 14, and the permanent vertical tension member 15 is inserted into the vertical sheath tube 18 (see Figure 3). These tension members 14, 15 are tensioned to introduce circumferential and vertical prestress into the dike 10. Once prestress has been introduced, mortar or other filler is filled into each sheath tube 17, 18, completing the construction of the dike 10.

The flood barrier 10 completed in this way has a full cross-sectional compression area including the interfacial concrete 30, 31, which can reliably improve the liquid-tightness of the flood barrier 10. In addition, since the interfacial concrete 30, 31 can be applied in multiple layers at once, it is possible to reliably improve workability and shorten the construction period.

[others]
The present disclosure is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present disclosure.

For example, as shown in FIG. 11, one end face 22A of the main body 21 may have a convex portion 29A extending in the vertical direction, and the other end face 22B of the main body 21 may have a concave groove 29B extending in the vertical direction, and when the precast members 20 are arranged side by side in the circumferential direction, these convex portions 29A and concave grooves 29B may be configured to fit together. With this configuration, it is possible to stably connect each precast member 20 in the circumferential direction.

Although the precast member 20 has been described as having both the outer recess 25 and the inner recess 27, it may be configured to have only the outer recess 25. In this case, too, the liquid-tightness of the dike 10 can be effectively ensured by forming a compressed area on the outer periphery of the dike 10. Also, it may be configured so that only the filling concrete 30, 31 is poured without exposing the circumferential reinforcing bars 11A, 11B in each recess 25, 27.

Furthermore, the application of this disclosure is not limited to the liquid retaining dike 10 of the PC tank 1, but can also be widely applied to the construction of other concrete structures.

1...PC tank, 2...tank body, 3...inner tank, 4...outer tank, 5...bottom slab, 6...pile, 10...levee, 11A, 11B...circumferential rebar, 12A, 12B...vertical rebar, 13A, 13B...reinforcing rebar, 14...circumferential tension member, 15...vertical tension member, 17...circumferential sheath tube, 18...vertical sheath tube, 20...precast member, 21...main body, 22A, 22B...end face, 22C, 22D...side face, 24A, 24B...outer cutout, 25...outer recess, 26A, 26B...inner cutout, 27...inner recess, 28A, 28B...cylindrical hole

Claims (9)

A precast member constituting a cylindrical liquid barrier surrounding the outer periphery of a liquid storage tank,
A main body made of concrete that is rectangular in front view and curved in an arc in top view;
an outer cutout portion formed by cutting out a corner portion where the curved outer surface of the main body portion and a circumferential end surface intersect ;
a circumferential sheath tube extending circumferentially within the main body and into which a circumferential tendon capable of introducing circumferential prestress into the dike is inserted ,
This precast member is characterized in that the outer cutout portion faces the outer cutout portion of another precast member that is arranged adjacently with its circumferential end faces in face contact with each other, thereby defining an outer recess on the outer periphery of the liquid retaining embankment into which filling concrete can be poured. The steel structure further includes an outer circumferential reinforcing bar extending circumferentially within the body portion and having an end exposed within the outer cutout portion,
2. The precast member according to claim 1, wherein ends of the outer circumferential bars are joined to ends of outer circumferential bars of the other precast member. The curved inner surface of the main body and a circumferential end surface of the main body are intersected by a corner portion, and the curved inner surface and the circumferential end surface of the main body are cut out by the inner cutout portion.
A precast member as described in claim 1 or 2, wherein the inner cutout portion faces the inner cutout portion of the other precast member, thereby defining an inner recess on the inner circumference side of the liquid retaining wall into which filling concrete can be poured. The steel structure further includes an inner circumferential reinforcing bar extending circumferentially within the main body portion and having an end exposed within the inner cutout portion,
4. The precast member according to claim 3, wherein ends of the inner circumferential bars are joined to ends of inner circumferential bars of the other precast member. A precast member as described in any one of claims 1 to 4 , further comprising a vertical sheath tube extending vertically within the main body and into which a vertical tension member capable of introducing vertical prestress into the floodwall is inserted. A vertical reinforcing bar extending vertically within the main body and having a lower end protruding downward by a predetermined amount from the lower surface of the main body;
A cylindrical hole recessed downward from the upper surface of the main body by a predetermined depth and formed coaxially with the vertical reinforcing bar, in which an upper end of the vertical reinforcing bar is disposed;
a cylindrical coupler provided at an upper end of the vertical reinforcing bar located within the cylindrical hole,
The coupler is fitted with a lower end side of another vertical reinforcing bar protruding downward from a second other precast member arranged on the upper surface of the main body, thereby connecting the vertical reinforcing bar and the other vertical reinforcing bar.
A precast component according to any one of claims 1 to 5. A flood barrier constructed by rigidly connecting the precast members according to any one of claims 1 to 6 side by side in the circumferential direction and stacking and rigidly connecting them vertically. A method for constructing a flood barrier using the precast members according to any one of claims 1 to 6, comprising the steps of:
a wall forming process in which a plurality of the precast members are arranged in a circumferential direction, and their circumferential end faces are brought into surface contact with each other, and adjacent precast members are temporarily connected in the circumferential direction to form a single stage of annular wall body that is integrated all around, and the annular wall body is stacked up in a plurality of stages to form a cylindrical wall body;
A pouring step of pouring the filling concrete into the cylindrical wall body at once. This step is repeated at least once.
A method for constructing a flood barrier, comprising the steps of: providing a permanent circumferential tension member on the cylindrical wall formed to a predetermined height to tension the wall, thereby introducing prestress. A method for constructing a liquid retaining wall as described in claim 8, in which, in the wall formation process, when temporarily connecting circumferentially adjacent precast members, the annular wall is integrated all around by providing temporary circumferential tensioning members in the annular wall and tensioning it.

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