Method for constructing through holes in an existing dam embankment

Abstract

To provide a method for constructing a through hole in an existing dam body by which a gate can be carried into a temporary cofferdam body without being influenced by the dimensions of the gate without fear of being unable to lift the temporary cofferdam body and with good workability when installing the gate inside the temporary cofferdam body.SOLUTION: A method for constructing a through hole in an existing dam body comprises a temporary cofferdam body installation step of suspending a temporary cofferdam 60 formed by a shell having an input port 61a for materials and equipment and an opening 65 on an upstream side of a dam body 10, in which an opening edge 64 is brought into close contact with an upstream side surface 12 with the opening 65 facing the upstream side surface 12, a housing step of housing a gate 71 inside the temporary cofferdam body 60 via the input port 61a, a drainage step of draining water inside the temporary cofferdam body 60, a first section hole construction step of constructing a first section hole 25 of a through hole 20 up to the front of the upstream side surface 12, a second section hole construction step of constructing a second section hole 26 and constructing the through hole 20, a gate installation step of installing the gate 71 in an upstream opening 22, and a removal step of removing the temporary cofferdam body 60.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for constructing through holes in an existing dam embankment.

Background Art

[0002] A dam is a structure installed across a river to store flowing water, and has roles such as flood control, securing water resources (for domestic use, industrial use, agricultural use, etc.), power generation, and conserving the river environment (maintaining the normal functions of flowing water). Legally, a structure with a height of 15 m or more is a dam, but embankments such as sand control dams with a height of less than 15 m are also included in dams. By the way, due to concentrated heavy rain caused by recent global environmental changes, flood control measures have become an urgent issue across the country. However, the candidate sites where dams can be installed are decreasing, and the construction of dams requires a large amount of construction costs. Therefore, the construction of new dams is in an extremely difficult situation. Based on such a situation, the development of technologies for taking flood control measures (so-called redevelopment of existing dams) for existing dams has been studied and implemented. As such flood control measures, there is a measure of constructing through holes across the upstream side surface and the downstream side surface of the dam embankment in order to increase the discharge capacity of the dam embankment. Since such redevelopment construction of an existing dam is carried out while the existing dam is in use, it is necessary to install a temporary cutoff on the upstream side of the dam embankment and make the construction area where the through hole faces the upstream side surface a dry environment. Therefore, after constructing a temporary cutoff with steel pipe sheet piles or the like around the construction area, the stored water inside the temporary cutoff is drained, and the construction of installing a gate at the opening where the through hole faces the upstream side surface is sequentially carried out. However, in such temporary cutoff construction, there are problems such as a large-scale temporary structure, a long construction period, and an increase in construction costs.

[0003] To address the above issues, Patent Document 1 proposes a construction method for constructing a new outlet for an existing concrete dam, and Patent Document 2 proposes a method for constructing a through hole in an existing dam body. The construction method for constructing a new outlet for an existing concrete dam described in Patent Document 1 involves cleaning the required location on the upstream side of the weir where the new outlet will be constructed, suspending a shell body with an opening on one side equipped with a watertight packing and a shutoff flange at the top, primary pressing it into the opening, draining the water inside and performing secondary pressing, then holding the shell body in place, connecting a shaft that reaches the water surface to the shutoff flange, draining the water inside and then removing the shutoff flange. Next, the outlet is excavated and an outlet gate is installed, the shutoff flange is set, water is poured into the shaft and the shaft is withdrawn, water is poured into the shell body and the shell body is withdrawn, and then the gate opening and closing device is installed.

[0004] On the other hand, the method for constructing a through-hole in an existing dam embankment described in Patent Document 2 is a construction method comprising: a temporary cofferdam installation step in which a temporary cofferdam consisting of a shell having an opening and housing a gate inside for opening and closing the upstream opening of the through-hole, is installed so that the opening is in close contact with the dam embankment; a drainage step in which water is discharged from inside the temporary cofferdam; a through-hole construction step in which a through-hole is constructed that penetrates the dam embankment from the downstream side of the dam embankment toward the temporary cofferdam; a gate installation step in which a gate is attached to the upstream opening of the through-hole inside the temporary cofferdam; and a removal step in which the temporary cofferdam is removed from the dam embankment. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 64-58709 [Patent Document 2] Japanese Patent Publication No. 2010-216125 [Overview of the project] [Problems that the invention aims to solve]

[0006] The construction methods and construction techniques described in Patent Documents 1 and 2 can suppress or eliminate the problems of prolonged construction periods and increased construction costs inherent in construction methods that involve constructing large-scale temporary cofferdams such as steel sheet piles around the construction yard on the upstream side of the dam body. However, in the construction method described in Patent Document 1, since the outflow gate is brought into the interior of the dam body via a shaft installed on the upper part of the dam body, the size of the outflow gate is limited by the size of the shaft. Conversely, this means that a shaft with an internal cavity large enough for the outflow gate to pass through must be installed on the upper part of the dam body, which can make it difficult to install the shaft on the dam body. Furthermore, as the length from the tunnel entrance to the water surface on the dam body increases, and the length of the shaft increases, this difficulty in installation becomes even more pronounced.

[0007] On the other hand, in the construction method described in Patent Document 2, the entire structure is lowered to the gate installation position with the gate already installed inside the temporary cofferdam, which consists of a shell. This results in a large lowering weight, which may necessitate an increase in the size (specifications) of the lifting crane, or in some cases, may make lifting impossible. This problem becomes even more pronounced when the gate is installed at a deep water depth or when the gate dimensions and weight are large. Furthermore, since the gate is already installed inside the temporary cofferdam, the gate installation process, which involves attaching the gate to the tunnel entrance inside the temporary cofferdam, presents challenges such as reduced work efficiency due to the constraints on the workspace caused by the gate. Increasing the size of the temporary cofferdam to improve work efficiency would further increase its weight, thus increasing the possibility of the aforementioned inability to lift the gate.

[0008] The present invention relates to a method for installing a gate by applying a temporary cofferdam made of shell material to the upstream side surface of an existing dam embankment, and aims to provide a method for constructing a through-hole in an existing dam embankment that allows the gate to be brought into the temporary cofferdam regardless of the dimensions of the gate, eliminates the risk of being unable to lift the temporary cofferdam, and provides good workability when installing the gate inside the temporary cofferdam. [Means for solving the problem]

[0009] To achieve the aforementioned objective, one aspect of the method for constructing through holes in an existing dam embankment according to the present invention is: A temporary cofferdam is formed by a shell with an input port and opening for materials, which is lowered to the upstream side of the dam embankment, and the opening edge of the temporary cofferdam is brought into close contact with the upstream side of the dam embankment, with the opening facing the upstream side of the dam embankment. A housing step involves housing a gate that opens and closes the upstream opening of the through hole inside the temporary closure body via the input port. A drainage step involves closing the aforementioned inlet and draining the water inside the temporary seal body. The first section hole construction process involves constructing the first section hole of the through-hole from the downstream side to the upstream side of the dam embankment, up to just before the upstream side surface, A second section hole construction step is performed, in which a second section hole is constructed between the first section hole and the upstream side surface to form the upstream opening on the upstream side surface, and the through hole formed by the first section hole and the second section hole is constructed. A gate installation step involves installing the gate in the upstream opening, The present invention is characterized by having a removal step of removing the temporary closure body from the upstream side and then removing it.

[0010] According to this embodiment, by applying a temporary cofferdam formed by a shell with an input opening for materials and equipment on its top surface, and by separately lowering the temporary cofferdam and the materials and equipment including a gate that opens and closes the upstream opening of the through hole, it is possible to solve the problem of the temporary cofferdam being unable to be lifted due to the increased lifting load. Furthermore, since materials and equipment, including gates, are brought into the temporary cofferdam through an input opening located on the top surface of the temporary cofferdam rather than through a shaft, the problem of the gate's dimensions being constrained by the shaft's internal space can be eliminated, making it possible to accommodate gates of various sizes inside the temporary cofferdam. Furthermore, since the gate is not pre-installed inside the temporary cofferdam when it is lowered, the working space inside the lowered temporary cofferdam is not narrowed by the gate, thus ensuring good workability inside the temporary cofferdam.

[0011] In the temporary cofferdam installation process, the temporary cofferdam is installed on the upstream side of the dam embankment so that its opening surrounds the upstream opening formed on the upstream side of the dam embankment during the subsequent second section hole construction process. In this installation, the temporary cofferdam is lowered into the upstream reservoir, and while the temporary cofferdam is suspended by heavy machinery such as a crane, divers or the like in the reservoir can fix the opening edge of the temporary cofferdam to the upstream side of the dam embankment with anchors or the like. Since the dam crest has width limitations, it is advisable to construct a construction stage (pier) downstream that is continuous with the dam crest, and to place heavy machinery on the stage and the dam crest. In addition to this method of placing heavy machinery on the dam crest and lowering temporary cofferdams and gates, another construction method is to float a barge equipped with a crane on the reservoir and lower temporary cofferdams and gates from the barge. Standard sealing materials, such as watertight rubber gaskets, are provided in an endless manner along the edge of the opening, ensuring watertightness when the opening edge is in close contact with the upstream side of the dam embankment. Subsequently, during the containment process, the gate is contained within the temporary cofferdam through the input port. Then, during the drainage process, the water inside the temporary cofferdam is drained, causing the temporary cofferdam to be pressed against the upstream side of the dam body by water pressure from its side. This water pressure further compresses the sealing material, thereby increasing the watertightness between the temporary cofferdam and the upstream side.

[0012] The construction of through-holes in the dam embankment is carried out by a first-section hole construction process, in which the first section of the through-hole is constructed from the downstream side of the dam embankment toward the upstream side up to just before the upstream side, and a second-section hole construction process, in which the second section of the hole is constructed between the first section and the upstream side. Here, "up to the front of the upstream side" literally includes not only the area a few tens of centimeters or a few millimeters before the front of the upstream side, but also positions relatively far from the upstream side, such as the center of the through-hole. When the first section of the hole is constructed up to a few tens of centimeters to a few hundred meters before the front of the upstream side, the length of this remaining concrete block (a few tens of centimeters to a few hundred meters in the longitudinal direction of the through-hole) is set to a length that can withstand the water pressure acting from the reservoir without being destroyed. Furthermore, the timing of the first section hole construction process may be before the temporary cofferdam installation process, after the drainage process, or in parallel with other processes such as the temporary cofferdam installation process. In addition, other processes may be carried out between the first section hole construction process and the second section hole construction process, or the first section hole construction process and the second section hole construction process may be carried out continuously to construct the through hole.

[0013] A through-hole is created in the existing dam body by performing a gate installation process, which involves installing a gate on the upstream side so as to close the upstream opening, and a removal process, which involves removing the temporary cofferdam from the upstream side.

[0014] Furthermore, another aspect of the method for constructing through holes in an existing dam embankment according to the present invention is: Prior to the drainage process, the process further includes a shaft installation step, in which a shaft extending from the temporary cofferdam to the water surface upstream is installed. The drainage process is characterized by draining the water inside the temporary closure body via the shaft.

[0015] According to this embodiment, by installing a shaft in the shaft installation process, a shaft is installed that extends from, for example, the top surface of the temporary cofferdam to the water surface upstream, and by using the shaft to drain the water, efficient drainage can be achieved. Moreover, since the shaft installed on the top end surface of the temporary closure body in this aspect is not a shaft for loading equipment as described in Patent Document 1, the inner space of the shaft is not determined according to the dimensions of the gate. It is preferable that a shaft opening for installing the shaft is provided separately from the inlet on the top end surface of the temporary closure body. Here, a drainage pump (lift pump) or the like can be installed inside the shaft for drainage. Further, a continuous spiral staircase or the like may be installed in the shaft from above to below, and an operator may be suspended to the upper end of the shaft and be able to access the inside of the temporary closure body using the spiral staircase in the shaft.

[0016] The shaft installation process may be carried out before the temporary closure body installation process. That is, before suspending the temporary closure body, it may be suspended into the water of the reservoir in a state where the shaft is pre-attached to the temporary closure body. However, in this method, since the suspended load becomes large, it is preferable that the shaft installation process is carried out after the temporary closure body is installed on the upstream side surface of the dam embankment.

[0017] Another aspect of the method for constructing a through hole in an existing dam embankment according to the present invention is further comprising a gantry installation process of installing a gantry for the temporary closure body on which the temporary closure body is placed, below the planned installation position of the temporary closure body on the upstream side surface, prior to the temporary closure body installation process.

[0018] [[ID=​​​​The temporarily clamped body suspended by a heavy machine is pulled to the installation position of the temporarily clamped body and placed on the pedestal for the temporarily clamped body by using wires or the like locked to the pedestal for the temporarily clamped body already installed on the upstream side surface of the dam embankment body.

[0019] Also, in another aspect of the method for constructing a through hole in an existing dam embankment body according to the present invention, In the accommodation step, a pedestal for a gate on which the gate is placed is further put in, In the gate installation step, the gate placed on the pedestal for the gate is aligned with a position corresponding to the upstream side opening.

[0020] According to this aspect, in the gate installation step, the gate is carried into the temporarily clamped body and placed on the pedestal for the gate installed therein, and aligned with a position corresponding to the upstream side opening, so that the workability when installing the gate with respect to the upstream side opening can be improved.

[0021] Also, in another aspect of the method for constructing a through hole in an existing dam embankment body according to the present invention, The temporarily clamped body is a laminate of a plurality of divided temporarily clamped bodies, In the temporarily clamped body installation step, either a method of suspending the temporarily clamped body formed in advance as a laminate or a method of sequentially suspending the divided temporarily clamped bodies and connecting the divided temporarily clamped bodies adjacent to each other vertically in water to form the laminate is applied.

[0022] According to this aspect, since the temporarily clamped body is a laminate of a plurality of divided temporarily clamped bodies, the manufacturability is improved when the scale of the temporarily clamped body is large. Also, in the temporarily clamped body installation step, by sequentially suspending the divided temporarily clamped bodies and connecting the divided temporarily clamped bodies adjacent to each other vertically in water to form a laminate, the difficulty of suspension when the scale of the temporarily clamped body is large can be eliminated. In this suspension method, inside the water storage tank, a diver can form the temporarily clamped body by sequentially connecting the divided temporarily clamped bodies.

[0023] Furthermore, in another embodiment of the method for constructing through holes in an existing dam embankment according to the present invention, The method is characterized by performing the first section hole construction process and the second section hole construction process consecutively, or by performing other processes between the first section hole construction process and the second section hole construction process.

[0024] According to this embodiment, for example, by performing the first section hole construction process and the second section hole construction process consecutively to construct the through hole, the efficiency of through hole construction can be increased. Furthermore, by performing other processes between the first section hole construction process and the second section hole construction process (including changing the implementation of other processes from the initial plan), various variations can be added to the entire series of processes, and the construction plan can be revised as needed in response to changes in natural phenomena (such as continued heavy rain or the arrival of a typhoon). [Effects of the Invention]

[0025] The present invention relates to a method for constructing through holes in an existing dam embankment, which involves applying a temporary cofferdam made of a shell to the upstream side of an existing dam embankment to install a gate. This method allows the gate to be brought into the temporary cofferdam regardless of the dimensions of the gate, eliminates the risk of being unable to lift the temporary cofferdam, and provides good workability when installing the gate inside the temporary cofferdam. [Brief explanation of the drawing]

[0026] [Figure 1] This is a process diagram illustrating an example of a method for constructing through holes in an existing dam embankment according to the embodiment. [Figure 2] Following Figure 1, this is a process diagram illustrating an example of a method for constructing through holes in an existing dam embankment according to the embodiment. [Figure 3] Following Figure 2, the next diagram shows an example of a process for constructing through holes in an existing dam embankment according to the embodiment. [Figure 4] This is a perspective view of an example of a temporary closure body formed by shells. [Figure 5]Following Figure 3, this is a process diagram illustrating an example of a method for constructing through holes in an existing dam embankment according to the embodiment. [Figure 6] Following Figure 5, this is a process diagram illustrating an example of a method for constructing through holes in an existing dam embankment according to the embodiment. [Figure 7] Following Figure 6, this is a process diagram illustrating an example of a method for constructing through holes in an existing dam embankment according to the embodiment. [Figure 8] Following Figure 7, this is a process diagram illustrating an example of a method for constructing through holes in an existing dam embankment according to the embodiment. [Figure 9] Following Figure 8, the next diagram shows an example of a process for constructing through holes in an existing dam embankment according to the embodiment. [Figure 10] Following Figure 9, the next diagram shows an example of a process for constructing through holes in an existing dam embankment according to the embodiment. [Modes for carrying out the invention]

[0027] The following describes a method for constructing through holes in an existing dam embankment according to the embodiment, with reference to the attached drawings. In this specification and the drawings, substantially identical components are denoted by the same reference numerals, thereby omitting redundant explanations.

[0028] [Method for constructing through holes in an existing dam embankment according to an embodiment] Referring to Figures 1 to 10, an example of a method for constructing through holes in an existing dam embankment according to the embodiment will be described. Here, Figures 1 to 3 and Figures 5 to 10 are, in order, process diagrams of an example of a method for constructing through holes in an existing dam embankment according to the embodiment, and Figure 4 is a perspective view of an example of a temporary cofferdam formed by a shell.

[0029] As shown in Figure 1, this construction method involves constructing through-holes 20, indicated by dashed lines, that extend diagonally downwards downstream from the downstream side 13 and upstream side 12 of the existing concrete dam body 10. The downstream opening 21 of the through-hole 20 faces the downstream side 13, and the upstream opening 22 faces the upstream side 12. These through-holes 20 are constructed primarily for flood control purposes, and the construction of these through-holes 20 makes it possible to increase the discharge capacity of the dam body 10.

[0030] As shown in Figure 1, the through-holes 20 are constructed in the X1 direction from the downstream side surface 13 to the upstream side surface 12 of the dam embankment 10, which is located on the foundation ground G, either continuously or with other processes interspersed in between.

[0031] This construction method includes lowering a temporary cofferdam 60 (see Figure 4), which is made of a shell for housing the gate and performing the gate installation work, into the water of the reservoir 30 in order to install a gate at the upstream opening 22 on the upstream side surface 12 while the dam body 10 is in service. For this lowering, a stage 41 is constructed on the upstream side of the dam crest 11 of the dam body 10, and a crane 43 is set up on the dam crest 11 and the stage 41.

[0032] Next, as shown in Figure 2, the first section hole 25 of the through-hole 20 is constructed by chipping away the concrete in the X2 direction from the downstream side to the upstream side of the dam body 10 up to just before the upstream side 12. In the illustrated example, just before the upstream side 12 is several tens of centimeters to about 1.2 meters, and is set to a length that allows the unconstructed concrete mass to withstand the water pressure of the reservoir 30. The first section hole 25 may be, for example, up to the midpoint of the total length of the through-hole 20, and may be constructed to various lengths. Even if the unconstructed section is relatively long, it is included in "constructing up to just before the upstream side 12" (first section hole construction process).

[0033] Here, the execution of the first section hole construction process is not limited to the timing shown in the illustrated example, but may be performed, for example, after the temporary cofferdam installation process described below. Also, although the illustrated example shows that other processes are performed between the first section hole construction process and the second section hole construction process described below, for example, the first section hole construction process and the second section hole construction process may be performed consecutively after the drainage process for draining the inside of the temporary cofferdam 60 described below to construct the through hole 20.

[0034] Next, as shown in Figure 3, a temporary cofferdam frame 51 on which the temporary cofferdam 60 will be placed is lowered in the X3 direction below the planned installation location of the temporary cofferdam 60 on the upstream side surface 12 of the dam body 10. Divers (not shown) then submerge underwater and fix the temporary cofferdam frame 51 to the upstream side surface 12 with anchors 52 (frame installation process).

[0035] Next, with reference to Figure 4, the configuration of the temporary cofferdam 60 to be applied in this construction will be described. The temporary cofferdam 60 in the illustrated example has a rectangular parallelepiped shape and is a box-shaped shell. The shell 60 may be made of steel or concrete, but a steel shell is preferred because it can reduce weight. Furthermore, the shape of the temporary cofferdam 60 is not limited to the rectangular parallelepiped shape in the illustrated example, but may also be a semi-cylindrical shape or a polygonal shape with a haunch at the upstream corner. By exhibiting a shape that includes curved surfaces or haunches in part, it becomes possible to reduce the acting water pressure and the stress caused by the acting water pressure.

[0036] The temporary closure body 60 has three sides 62, a top surface 61, and a bottom surface 63. An opening 65 is provided on the remaining side, and a rectangular frame-shaped opening edge 64 is provided around the opening 65. A standard, endless sealing material 69, such as a watertight rubber packing, is attached to this opening edge 64.

[0037] The top surface 61 is provided with a relatively large input opening 61a for loading materials and equipment, and a relatively small shaft opening 61b for attaching the shaft 80 (see Figure 6).

[0038] A pivot shaft 66 is located to the side of the input opening 61a on the top surface 61, and a material loading hatch 67 is attached thereto that can rotate in the Y1 direction around this pivot shaft 66 to close and open the input opening 61a. Here, the material loading hatch may not be rotatable as shown in the illustrated example, but may be in a form that is dropped in from above to close the input opening 61a.

[0039] Meanwhile, a shaft hatch 68 is installed at the shaft opening 61b by being dropped in from above. When the temporary cofferdam 60 is submerged in water, the shaft opening 61b can be opened by lifting the shaft hatch 68 upward in the Y2 direction with the crane 43. The shaft hatch may be rotatable, similar to the equipment loading hatch 67. Also, when the temporary cofferdam 60 is submerged in water, the equipment loading hatch 67 may be rotated while being lifted by the crane 43, taking into account the water pressure acting from above.

[0040] As shown in Figure 5, the temporary cofferdam 60 is suspended and lowered into the water of the reservoir 30, placed on the temporary cofferdam frame 51, and then the temporary cofferdam 60 is installed by making the endless sealing material 69 on the opening edge 64 tightly adhere to the upstream side surface 12.

[0041] In installing the temporary cofferdam 60 on the upstream side surface 12, in addition to the method in which a diver fixes the opening edge 64 to the upstream side surface 12 with anchors (not shown), the temporary cofferdam 60 may also be indirectly fixed to the upstream side surface 12 by fixing the temporary cofferdam 60 to a temporary cofferdam frame 51 fixed to the upstream side surface 12.

[0042] When lowering the temporary closure body 60 into the water, in order to prevent the generation of excessive buoyancy, the equipment loading hatch 67 is opened in the Y1 direction to open the loading port 61a, and the temporary closure body 60 is lowered into the water while water is flowing through it (this completes the temporary closure body installation process).

[0043] Here, the temporary cofferdam 60 may be installed on the upstream side 12 while suspended, without applying the frame installation process. However, it is preferable to place the temporary cofferdam 60 on the temporary cofferdam frame 51 fixed to the upstream side 12 in the frame installation process, and then install the temporary cofferdam 60 on the upstream side 12, as this improves the workability when installing the temporary cofferdam 60.

[0044] Next, the gate support frame 55 on which the gate 71 is mounted is lowered into the temporary cofferdam 60 through the inlet 61a which is open in the water of the reservoir 30, and the gate support frame 55 is installed near the upstream side surface 12 on the floor surface of the temporary cofferdam 60.

[0045] Next, the bell mouth 72 and gate 71 are lowered in the X4 direction via the input opening 61a onto the gate support frame 55 inside the temporary closure body 60. At this point, the bell mouth 72 and gate 71 may be lowered while already fixed together (this completes the storage process).

[0046] In this way, by applying a temporary cofferdam 60 formed by a shell with an input opening 61a on its top surface 61 into which materials and equipment including the gate 71 are brought in, and by performing the lowering of the temporary cofferdam 60 and the lowering of various materials and equipment including the gate 71 separately, the problem of the lifting load becoming too large to lift the temporary cofferdam 60 does not occur.

[0047] Although not shown in the diagram, the temporary cofferdam may be a stack of multiple divided temporary cofferdams. In this case, the temporary cofferdam installation process may involve lowering a temporary cofferdam that has been pre-formed as a stack, or it may involve sequentially lowering divided temporary cofferdams and connecting adjacent divided temporary cofferdams underwater to form a stack.

[0048] Next, as shown in Figure 6, the shaft hatch 68 is lifted to open the shaft opening 61b, and then the shaft 80 is lowered in the X5 direction and the lower end of the shaft 80 is placed in the shaft opening 61b, thereby erecting the shaft 80 so that it extends from the top surface 61 of the temporary closure body 60 to the water surface of the reservoir 30. In addition, the equipment loading hatch 67 is rotated in the Y3 direction to close the loading opening 61a.

[0049] Here, although not shown in the diagram, a drainage pump and the like are installed inside the shaft 80. Furthermore, it is preferable that a continuous spiral staircase is installed inside the shaft 80, extending from its top to its bottom, so that a worker can be lowered to the top of the shaft 80 and access the inside of the temporary cofferdam 60 using the spiral staircase inside the shaft 80 (shaft installation process).

[0050] Next, as shown in Figure 7, a drainage pump (not shown) is activated to drain the water inside the temporary cofferdam 60 in the X6 direction via the shaft 80. This drainage creates a working space inside the temporary cofferdam 60.

[0051] Furthermore, as the water inside the temporary cofferdam 60 is drained, water pressure acts on the temporary cofferdam 60 from the reservoir 30. This water pressure presses against the sealing material 69 that is in close contact with the upstream side surface 12, further enhancing the watertightness between the temporary cofferdam 60 and the upstream side surface 12 (this concludes the drainage process).

[0052] Next, as shown in Figure 8, a second section hole 26 is constructed between the first section hole 25 and the upstream side surface 12, thereby creating a through hole 20 formed by the first section hole 25 and the second section hole 26, which has an upstream opening 22 in the upstream side surface 12.

[0053] The construction of the second section hole 26 may be carried out by setting up a construction scaffold (not shown) inside the temporary cofferdam 60 and using the construction scaffold to chip away concrete toward the first section hole 25 by workers, or conversely, by chipping away concrete toward the temporary cofferdam 60 from the first section hole 25 (second section hole construction process).

[0054] Next, as shown in Figure 9, the bell mouth 72 and gate 71, which are placed on the gate frame 55, are sequentially moved to the upstream opening 22 side, and the bell mouth 72 is fitted into the upstream opening 22 to install the bell mouth 72 in relation to the upstream opening 22, and the gate 71 is installed in relation to the bell mouth 72.

[0055] The installation of the gate 71 on the upstream opening 22 completes the construction of the through-hole 20, which is a flood control measure, and the installation of the gate 71 on the dam body 10 (end of gate installation process).

[0056] After the gate 71 is installed in the upstream opening 22 of the through-hole 20, as shown in Figure 10, the series of construction steps to construct the through-hole 20 in the existing dam body 10 are completed by sequentially dismantling and lifting the shaft 80, removing and lifting the temporary cofferdam 60 from the upstream side 12, and removing and lifting the temporary cofferdam support frame 51 from the upstream side 12 (removal process).

[0057] According to the method of constructing through holes in the existing dam embankment shown in the diagram, as already described, a temporary cofferdam 60 is applied, which is formed by a shell with an input port 61a on the top surface 61 into which materials and equipment, including the gate 71, are brought in. By lowering the temporary cofferdam 60 and the various materials and equipment, including the gate 71, separately, the problem of the temporary cofferdam 60 being unable to be lifted due to the increased lifting load is resolved.

[0058] Furthermore, since the equipment including the gate 71 is brought into the temporary cofferdam 60 through the input port 61a provided on the top surface 61 of the temporary cofferdam 60, rather than through the shaft 80, the problem of the dimensions of the gate 71 being constrained by the internal space of the shaft 80 can be resolved, and it becomes possible to accommodate gates 71 of various dimensions inside the temporary cofferdam 60.

[0059] Furthermore, since the gate 71 is not pre-installed inside the temporary cofferdam 60 when the temporary cofferdam 60 is lowered, the working space inside the temporary cofferdam 60 after it has been lowered and installed on the upstream side surface 12 is not narrowed by the gate 71, thus ensuring good workability inside the temporary cofferdam 60. For example, in the temporary cofferdam installation process, the workability when installing the temporary cofferdam 60 while ensuring that the sealing material 69 on the opening edge 64 is in close contact with the upstream side surface 12 is significantly improved compared to when the gate 71 is already present.

[0060] Furthermore, other embodiments may be used in which other components are combined with the configurations listed in the above embodiments, and the present invention is not limited in any way to the configurations shown herein. In this regard, modifications can be made without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0061] 10: Dam body 11: Dam crest 12: Upstream side 13: Downstream side 20: Through hole 21: Downstream opening 22: Upstream opening 25: First section hole 26: Second section hole 30: Reservoir 41: Stage (pier) 43: Crane (heavy machinery) 51: Stand for temporary cofferdam 52: Anchor 55: Gate mounting base 60: Temporarily closed body (shell body) 61: Top surface 61a: Inlet 61b: Shaft opening 62: Side view 63: Bottom 64: Opening edge 65: Opening 66: Rotary shaft 67: Equipment loading hatch 68: Shaft hatch 69: Sealant 71: Gate 72: Bellmouth 80: Shaft G: Foundation ground

Claims

1. A method for constructing through holes in an existing dam embankment, A temporary cofferdam body is formed by a shell-like structure having an input port into which materials and equipment are directly brought in without the attachment of a shaft, and a shaft port into which a drainage shaft is attached on its top surface, and an opening on its side, and is lowered to the upstream side of the dam embankment, and the opening edge of the temporary cofferdam body is brought into close contact with the upstream side of the dam embankment in a position where the opening faces the upstream side of the dam embankment, a temporary cofferdam body installation process, A housing step involves lowering a gate that opens and closes the upstream opening of the through hole into the interior of the temporary closure body via the input port, A shaft installation step involves installing the shaft extending to the water surface upstream from the shaft opening of the temporary cofferdam, A drainage step involves closing the inlet and draining the water inside the temporary closure body via the shaft. The first section hole construction process involves constructing the first section hole of the through-hole from the downstream side to the upstream side of the dam embankment, up to just before the upstream side surface, A second section hole construction step is performed, in which a second section hole is constructed between the first section hole and the upstream side surface to form the upstream opening on the upstream side surface, and the through hole formed by the first section hole and the second section hole is constructed. A gate installation step involves installing the gate in the upstream opening, A method for constructing a through-hole in an existing dam embankment, characterized by comprising a removal step of removing the temporary cofferdam from the upstream side.

2. A method for constructing through holes in an existing dam embankment according to claim 1, further comprising a frame installation step of installing a frame for the temporary cofferdam on the upstream side below the planned installation position of the temporary cofferdam on the upstream side, prior to the temporary cofferdam installation step.

3. In the aforementioned containment process, a gate support frame on which the gate is placed is further introduced, The method for constructing a through-hole in an existing dam embankment according to claim 1 or 2, characterized in that, in the gate installation step, the gate placed on the gate support frame is aligned to a position corresponding to the upstream opening.

4. The temporary fastener is a stack of multiple divided temporary fasteners, The method for constructing through holes in an existing dam embankment according to claim 1 or 2, characterized in that the temporary cofferdam installation step involves either lowering the temporary cofferdam, which has been formed in advance as a stack, or sequentially lowering the divided temporary cofferdams and connecting the vertically adjacent divided temporary cofferdams underwater to form the stack.

5. A method for constructing through holes in an existing dam embankment according to claim 1 or 2, characterized in that the first section hole construction process and the second section hole construction process are carried out continuously, or other processes are carried out between the first section hole construction process and the second section hole construction process.

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