Temporary structure for offshore substructure and foundation construction and construction method using the same

Abstract

According to the present invention, a suction fixed cofferdam is provided, comprising a plate portion, a fixed wall portion extending downward from the plate portion, a cofferdam wall portion extending upward from the plate portion, and a cover detachably coupled to the plate portion; wherein a suction space is formed internally by the plate portion and the fixed wall portion, and a cofferdam space is formed internally by the plate portion and the cofferdam wall portion, and a work passage is formed in the plate portion that communicates the suction space and the cofferdam space and is opened and closed by the cover. A substructure for water surface construction and a temporary structure for foundation construction are provided.

Description

Technology Field

[0001] The present invention relates to a technology for constructing offshore or riverbed structures, and more specifically, to a temporary structure used in the construction of offshore or riverbed structures. Background Technology

[0002] Offshore structures, such as offshore wind jacket support structures, are installed to be fixed to the seabed using either a post-piling or pre-piling method.

[0003] The post-piling method is a foundation type applied to the support structures of the Southwest Sea Offshore Wind Power Demonstration Complex in Korea, in which piles are inserted into the legs of the post-piling jacket. As described in Registered Patent No. 10-1659783, after placing the offshore structure to be constructed on the seabed at the construction site, piles are inserted into the seabed through axial holes formed in the offshore structure. When the post-piling method is applied to the construction of offshore wind turbines, since piles are inserted through the legs provided in the offshore wind jacket support structure, complex processes for the installation of the offshore wind jacket and pile construction occur, and the transition piece placed on the offshore wind jacket support structure must be installed offshore through a separate process after the piles are installed.

[0004] The pre-piling method is a method in which piles are installed in advance on the seabed at the construction site of the offshore structure to be constructed, and the offshore structure is connected to the installed piles. Since the installation of the offshore wind jacket is simple and the connection between the offshore wind jacket support structure and the transition piece does not need to be performed at sea, the construction period can be significantly shortened compared to the post-piling method. However, conventional overseas pre-piling methods require a special type of structure (Pre-piling template), and since Public Patent No. 10-2024-0040978 applies the lower part of the offshore wind jacket as a Pre-piling template, the process is complex and requires a separate structure for precision construction, and the structure used for pile installation is installed by fixing it to the seabed together with the piles. Prior art literature

[0005] Republic of Korea Registered Patent Publication No. 10-1659783 (September 26, 2016) Republic of Korea Published Patent Publication No. 10-2024-0040978 (March 29, 2024) The problem to be solved

[0006] The objective of the present invention is to provide a temporary structure for constructing a water substructure and foundation that can reduce costs while shortening the construction period, and a construction method using the same. means of solving the problem

[0007] In order to achieve the problem to be solved by the present invention as described above, according to one aspect of the present invention, a suction fixed cofferdam is provided, comprising a plate portion, a fixed wall portion extending downward from the plate portion, a cofferdam wall portion extending upward from the plate portion, and a cover detachably coupled to the plate portion; wherein a suction space with an open bottom is formed inside by the plate portion and the fixed wall portion, and a cofferdam space with an open top is formed inside by the plate portion and the cofferdam wall portion, and a work passage is formed in the plate portion that communicates the suction space and the cofferdam space and is opened and closed by the cover. A temporary structure for water substructure and foundation construction is provided.

[0008] In order to achieve the problem to be solved by the present invention as described above, according to another aspect of the present invention, a suction fixing cofferdam is provided, comprising a suction fixing part, a cofferdam part located above the suction fixing part, and a cover detachably coupled to the suction fixing part, wherein the suction fixing part comprises a plate part and a fixed wall part extending downward from the plate part, and the cofferdam part comprises a cofferdam wall in the shape of a tube with open top and bottom ends, and the bottom end of the cofferdam wall is welded to the plate part so that the cofferdam wall forms an integral part of the suction fixing part, and a work passage is formed in the plate part that communicates the internal space of the suction fixing part and the internal space of the cofferdam part and is opened and closed by the cover. A temporary structure for water substructure and foundation construction is provided.

[0009] In order to achieve the problem to be solved by the present invention as described above, according to another aspect of the present invention, a method for constructing an underwater substructure and foundation using a temporary structure comprising a suction fixed cofferdam having a plate portion in which a work passage is formed, a fixed wall portion extending downward from the plate portion, a cofferdam wall extending upward from the plate portion, and a cover detachably coupled to the plate portion to open and close the work passage, wherein a suction space with an open bottom is formed inside by the plate portion and the fixed wall portion, and a cofferdam space with an open top is formed inside by the plate portion and the cofferdam wall, and the suction space and the cofferdam space are connected by the work passage, the method comprising: a temporary structure immersion step of filling the cofferdam space with water to immerse the temporary structure; and a temporary structure settling step in which a part of the fixed wall portion is penetrated into the seabed by the self-weight of the temporary structure so that the temporary structure is settled. A method for constructing a substructure and foundation is provided, comprising: a step of fixing a temporary structure in which fluid is discharged from a suction space while the temporary structure is in a seated state and the work passage is closed, thereby inserting the entire fixed wall section into the seabed ground by a pressure difference to fix the temporary structure; a step of opening a work passage to open the work passage; a step of installing a pile by inserting it into the seabed ground through the opened work passage; a step of removing a temporary structure by closing the work passage while the pile is installed, and then injecting fluid into the suction space to float the temporary structure to remove it; and a step of installing a substructure and foundation by combining the substructure and foundation with the pile. Effects of the invention

[0010] According to the present invention, all the objectives of the invention described above can be achieved. Specifically, the temporary structure for constructing a substructure and foundation according to the present invention comprises a suction fixing part having a work passage formed therein and a cofferdam part integrally formed with said suction fixing part. Since this allows for the installation of the substructure and foundation after pile installation, the effect of shortening the construction period through pre-piling can be obtained, and since the entire temporary structure can be easily retrieved after the construction of the substructure and foundation, material costs can be reduced. Brief explanation of the drawing

[0011] FIG. 1 is a perspective view of a temporary structure for constructing a water surface substructure and foundation according to one embodiment of the present invention. Figure 2 is a plan view of the temporary structure for the construction of the water substructure and foundation shown in Figure 1. FIG. 3 is an exploded perspective view of a suction-fixed cofferdam provided in a temporary structure for the construction of a water substructure and foundation shown in FIG. 1. FIG. 4 is a longitudinal cross-sectional view of a suction-fixed cofferdam provided in a temporary structure for the construction of a water substructure and foundation shown in FIG. 1. FIG. 5 is a flowchart schematically illustrating a method for constructing a water substructure and foundation according to one embodiment of the present invention. FIGS. 6 to 17 are drawings for explaining each step of the underwater substructure and foundation construction method illustrated in FIG. 5. Specific details for implementing the invention

[0012] Hereinafter, the configuration and operation of an embodiment of the present invention will be described in detail with reference to the drawings.

[0013] FIGS. 1 and FIGS. 2 respectively illustrate a temporary structure for constructing a water surface substructure and a foundation according to an embodiment of the present invention as a perspective view and a plan view. Referring to FIGS. 1 and FIGS. 2, a temporary structure (100) for constructing a water surface substructure and a foundation according to an embodiment of the present invention (hereinafter abbreviated as 'temporary structure') includes a plurality of suction fixing cofferdams (110) and a connecting structure part (190) that connects and integrates the plurality of suction fixing cofferdams (110).

[0014] Multiple suction fixing cofferdams (110) are spaced apart on a plane and connected by a connecting structure (190) to be integrated into a single structure. In this embodiment, there are four suction fixing cofferdams (110), and each of the four suction fixing cofferdams (110) is located at a point corresponding to a vertex of a square. Although this embodiment describes four suction fixing cofferdams (110), there may be two, three, or five or more, and this is also within the scope of the present invention. The positions of the multiple suction fixing cofferdams (110) may be changed according to the construction conditions and environment of the water substructure and foundation. In this embodiment, the temporary structure (100) is described as having multiple suction fixing cofferdams (110), but it may be composed of only one suction fixing cofferdam (110) without a connecting structure (190), and this is also within the scope of the present invention.

[0015] In FIG. 3, a suction fixing cofferdam (110) is shown as an exploded perspective view, and in FIG. 4, a suction fixing cofferdam (110) is shown as a longitudinal cross-sectional view. Referring to FIG. 1 to FIG. 4, the suction fixing cofferdam (110) is in the shape of a tube extending along the height direction overall, and is equipped with a suction fixing part (120), a cofferdam part (140) formed integrally with the suction fixing part (120), and a cover (180) detachably coupled to the suction fixing part (120).

[0016] The suction fixing part (120) comprises a plate part (121) and a fixed wall part (130) formed by extending downward from the plate part (121). Inside the suction fixing part (120), a suction space (120a) is formed by the plate part (121) and the fixed wall part (130).

[0017] The plate portion (121) is generally in the shape of a flat disc and is arranged horizontally. A work passage (123) and an inflow / outflow passage (125) are formed in the plate portion (121). The work passage (123) is generally located in the center of the plate portion (121). The suction space (120a) communicates with the outside through the work passage (123). The work passage (123) is opened and closed by a cover (180) that is detachably coupled to the suction fixing portion (120). In this embodiment, the work passage (123) is described as being one, but it may be formed in multiple ways, and this is also within the scope of the present invention. The work passage (123) has a size that allows a pile to pass through. The inflow / outflow passage (125) communicates the suction space (120a) with the outside. Fluid passes through the inflow / outflow passage (125). A suction pipe or hose communicating with a suction pump that discharges fluid from the suction space (120a) to the outside may be detachably connected to the inlet / outlet passage (125). Although not illustrated, an opening / closing valve may be installed in the inlet / outlet passage (125) so that the inlet / outlet passage (125) can be opened or closed. In this embodiment, the inlet / outlet passage (125) is described as having two, but the present invention is not limited thereto. The inlet / outlet passage (125) may be formed as one or three or more, and their positions may also be freely adjusted, which is also within the scope of the present invention.

[0018] The fixed wall portion (130) is formed by extending downward from the edge of the plate portion (121). The fixed wall portion (130) is generally perpendicular to the plate portion (121).

[0019] The cofferdam section (140) is positioned above the suction fixing section (120) and formed integrally with the suction fixing section (120). The cofferdam section (140) is provided with a generally cylindrical cofferdam wall (142) that extends along the height direction. The lower end of the cofferdam wall (142) is welded to the edge of the plate section (121) provided in the suction fixing section (120) to be integrally joined. Accordingly, a cofferdam space (144) is formed inside the cofferdam wall (142) by the plate section (121) of the suction fixing section (120) and the cofferdam wall (142). A plurality of inlets (146) are formed in the cofferdam wall (142) and arranged along the circumference direction adjacent to the plate section (121) of the suction fixing section (120). Water from outside the cofferdam wall (142) can flow into the cofferdam space (144) through multiple inlets (146). An opening / closing valve (148) is installed in the cofferdam space (144) to open and close each of the multiple inlets (146).

[0020] The cover (180) is detachably coupled to the work passage (123) to open and close the work passage (123) formed in the plate portion (121) of the suction fixing portion (120).

[0021] Referring to FIGS. 1 and 2, the connecting structure (190) connects and integrates a plurality of spaced-apart suction fixing cofferdams (110). The connecting structure (190) is provided with a plurality of connecting supports (195). Each of the plurality of connecting supports (195) connects two cofferdam walls (142).

[0022] FIG. 5 shows a flowchart schematically illustrating a method for constructing a water substructure and foundation according to an embodiment of the present invention. The method for constructing a water structure illustrated in FIG. 5 includes a temporary structure submersion step (S105), a temporary structure settling step (S110), a temporary structure fixing step (S120), a temporary structure drainage step (S125), a work passage opening step (S130), a work platform installation step (S140), an external pile installation step (S150), an internal pile installation step (S160), a work passage closing step (S170), a work platform removal step (S180), a temporary structure removal step (S190), and a water substructure and foundation installation step (S195). Hereinafter, the method for constructing the underwater substructure and foundation illustrated in FIG. 5 is described as an example in which the underwater substructure and foundation are towed using the temporary structure (100) described with reference to FIG. 1 to 4 to construct an offshore wind jacket support structure.

[0023] In the temporary structure flooding stage (S105), water is filled into the cofferdam space (144) of the temporary structure (100), and the temporary structure (100) is placed on the uppermost layer of soil at the location where the offshore wind jacket support structure is constructed, as shown in FIG. 6. The temporary structure flooding stage (S105) is performed by water flowing from the outside of the temporary structure (100) into the cofferdam space (144) through the inlet (146) of the cofferdam wall (142). After the temporary structure flooding stage (S105) is performed, the temporary structure settling stage (S110) is performed.

[0024] In the temporary structure settling stage (S110), the temporary structure submerging stage (S105) is performed so that the temporary structure (100) placed on the uppermost layer of soil settles due to its own weight. FIG. 7 illustrates the state in which the temporary structure (100) settles at a designated location in the sea after the temporary structure settling stage (S110) is performed. Referring to FIG. 7, the temporary structure (100) settles due to its own weight, and the lower part of the fixed wall section (130) provided in the suction fixing cofferdam (110) partially penetrates into the soil layer (A), which is the uppermost layer of the seabed ground. During the process of the temporary structure (100) settling due to its own weight, the air and seawater in the suction space (120a) are discharged to the outside through the inflow / outflow passage (125). The cover (180) is joined to close the work passage (123). With the temporary structure (100) seated as shown in FIG. 7, the temporary structure fixing step (S120) is performed.

[0025] In the temporary structure fixing step (S120), the fixing wall portion (130) provided in the suction fixing cofferdam (110) moves downward so that the temporary structure (100) is fixed to the seabed ground. The temporary structure fixing step (S120) is performed by the state shown in FIG. 7, in which seawater and air are discharged to the outside by a suction pump (not shown) through the inflow / outflow passage (125) from the suction space (120a), thereby forming low pressure in the suction space (120a). FIG. 8 shows the state in which the temporary structure (100) is fixed to the seabed ground after the temporary structure fixing step (S120) is performed. Referring to FIG. 8, the entire fixed wall portion (130) provided in the suction fixed cofferdam (110) is embedded in the soil layer (A) of the seabed ground, and the plate portion (121) provided in the suction fixed cofferdam (110) is in contact with the seabed surface (E). The cover (180) is coupled to close the work passage (123). With the temporary structure (100) fixed to the seabed ground as shown in FIG. 8, the temporary structure drainage step (S125) is performed.

[0026] In the temporary structure drainage step (S125), seawater stored in the cofferdam space (144) is discharged to the outside through a drainage pump (not shown), so that no water remains in the cofferdam space (144) as shown in FIG. 9. After the temporary structure drainage step (S125) is performed, the work passage opening step (S130) is performed.

[0027] In the work passage opening step (S130), the work passage (123) formed in the suction fixing cofferdam (110) is opened. The work passage opening step (S130) is performed by separating the cover (180) in the state shown in FIG. 9. FIG. 10 shows the state in which the work passage (123) is opened after the work passage opening step (S130) is performed. Referring to FIG. 10, the cover (180) is separated so that the work passage (123) is opened in the cofferdam space (144). As shown in FIG. 10, the work table installation step (S140) is performed with the work passage (123) opened in the cofferdam space (144).

[0028] In the work platform installation step (S140), a work platform is installed on the temporary structure (100). The work platform installation step (S140) is performed by installing the work platform in the state shown in FIG. 10. FIG. 11 shows the state in which the work platform is installed on the temporary structure (100) after the work platform installation step (S140) has been performed. Referring to FIG. 11, a work platform (W) is placed and installed on top of the suction fixing cofferdams (110) provided on the temporary structure (100). A work opening (H) is formed on the work platform (W) that communicates with the cofferdam space (144) formed in each of the suction fixing cofferdams (110). As shown in FIG. 11, the external pile installation step (S150) is performed with the work platform (W) installed.

[0029] In the external pile installation step (S150), the external pile is driven into the seabed ground. The external pile installation step (S150) is performed in the state shown in FIG. 11. FIG. 12 shows the state in which the external pile installation step (S150) is being performed and the state in which it is completed. Referring to FIG. 12, as shown on the left, the external pile (P1) is driven through the work opening (H) formed on the work platform (W) and the work passage (123) formed on the suction fixing cofferdam (110) in sequence. As shown on the right, the external pile (P1) is driven through the soil layer (A) in the seabed ground and down to the weathered rock layer (B) located below the soil layer (A) to complete the process. It is preferable that the top of the external pile (P1) protrudes above the top of the work passage (123). As illustrated on the right side of FIG. 12, when the external pile installation step (S150) is completed, the top of the external pile (P1) protrudes upward from the soil layer (A) through the work passage (123). The external pile (P1) is hollow with both ends open. As illustrated on the right side of FIG. 12, when the installation of the external pile (P1) is completed, the internal pile installation step (S160) is performed.

[0030] In the internal pile installation step (S160), the internal pile is driven into the seabed ground. The internal pile installation step (S160) is performed in the state shown on the right side of FIG. 12. FIG. 13 shows the state in which the internal pile installation step (S160) is being performed and the state in which it is completed. Referring to FIG. 13, as shown on the left, the internal pile (P2) passes through the working hole (H) formed on the work platform (W) and is inserted into the external pile (P1) that has been internally excavated by the RCD (Reverse Circulation Drill) equipment, and as shown on the right, the internal pile (P2) is driven into the soft rock layer (C) located below the weathered rock layer (B) in the seabed ground to complete the process. As illustrated on the right side of FIG. 13, when the inner pile installation step (S160) is completed, the upper end of the inner pile (P2) is positioned within the outer pile (P1) at a certain distance from the upper end of the outer pile (P1), and the lower end of the inner pile (P2) is positioned protruding downward from the lower end of the outer pile (P1). The inner pile (P2) is a hollow type with both ends open. As illustrated on the right side of FIG. 13, when the installation of the inner pile (P2) is completed, the work passage closing step (S170) is performed. Although not illustrated, grouting is performed on the outer pile (P1) and the inner pile (P2) before the work passage closing step (S170) is performed.

[0031] In the work passage closing step (S170), the work passage (123) is closed. The work passage closing step (S170) is performed when the installation of the inner pile (P2) is completed, as shown on the right side of FIG. 13. FIG. 14 shows the work passage (123) formed in the suction fixing cofferdam (110) closed after the work passage closing step (S170) is performed. Referring to FIG. 14, the work passage (123) is closed by attaching the cover (180). Before the work passage closing step (S170) is performed and the work passage (123) is closed by the cover (180), a bolt piece (F) is connected to the top of the outer pile (P1) protruding above the work passage (123) by a joining operation such as welding. As shown in FIG. 14, the work table removal step (S180) is performed with the work passage (123) closed.

[0032] In the workbench removal step (S180), the workbench (W) is removed. The workbench removal step (S180) is performed in the state shown in FIG. 14. FIG. 15 shows the state in which the workbench (W) has been removed after the workbench removal step (S180) is performed. In the state shown in FIG. 15, the temporary structure removal step (S190) is performed.

[0033] In the temporary structure removal step (S190), the temporary structure (100) is removed. The temporary structure removal step (S190) is performed in the state shown in FIG. 15. The temporary structure removal step (S190) is performed by injecting an external fluid through the inflow / outflow passage (125) to float the temporary structure (100). After the temporary structure removal step (S190) is performed and the temporary structure (100) is removed, only the external pile (P1) and the internal pile (P2) remain installed on the seabed ground, as shown in FIG. 16. In the state shown in FIG. 16, the surface structure installation step (S195) is performed.

[0034] In the stage of installing the underwater substructure and foundation (S195), the underwater substructure and foundation are installed. The stage of installing the underwater substructure and foundation (S195) is performed in the state shown in FIG. 16. FIG. 17 shows the state in which the underwater substructure and foundation are installed after the stage of installing the underwater substructure and foundation (S195) is performed. Referring to FIG. 17, the lower end of the leg provided on the offshore wind jacket (J) is inserted into the upper end of the outer pile (P1). A bolt piece (K) provided on the leg of the offshore wind jacket (J) is bolted together with a bolt piece (F) provided on the upper end of the outer pile (P1) of the temporary structure (100).

[0035] Although the present invention has been described through the above embodiments, the present invention is not limited thereto. The above embodiments may be modified or changed without departing from the spirit and scope of the present invention, and those skilled in the art will understand that such modifications and changes are also within the scope of the present invention. Explanation of the symbols

[0036] 100: Temporary structure 110: Suction fixed cofferdam 120: Suction fixing part 120a: Suction space 121: Panel 123: Work passage 125: Entrance / Exit Passage 130: Fixed Wall 140: Cofferdam section 142: Cofferdam wall 144: Cofferdam space 146: Inlet 148: Inlet shut-off valve 180: Cover 190: Connecting structure 195: Connecting support A: Soil layer B: Weathered rock layer C: Soft rock layer E: Seafloor W: Workbench H: Workhole P1: External pile P2: Internal pile J: Offshore wind jacket

Claims

Claim 1 Multiple suction-fixed cofferdams spaced apart horizontally; A temporary structure for water surface substructure and foundation construction, comprising a connecting structure that integrally connects the plurality of suction fixed cofferdams, wherein each of the plurality of suction fixed cofferdams comprises a plate portion, a fixed wall portion extending downward from the edge of the plate portion, a cofferdam wall extending upward from the edge of the plate portion, a cover detachably coupled to the plate portion, and an opening / closing valve for opening / closing an inlet formed adjacent to the plate portion in the cofferdam wall; wherein the connecting structure comprises a plurality of connecting supports connected to the cofferdam wall; wherein a suction space with an open bottom is formed inside by the plate portion and the fixed wall portion, and a cofferdam space with an open top is formed inside by the plate portion and the cofferdam wall; wherein a work passage is formed in the plate portion to communicate the suction space and the cofferdam space and is opened / closed by the cover, and wherein the cofferdam space communicates with the outside through the inlet when the inlet is opened by the opening / closing valve. Claim 2 delete Claim 3 In claim 1, the work passage is formed in a plurality of portions on the plate, and the cover is formed in a plurality of portions corresponding to the plurality of work passages, a temporary structure for water substructure and foundation construction. Claim 4 A temporary structure for water surface substructure and foundation construction according to claim 1, wherein an inflow / outflow passage connecting the suction space and the cofferdam space is further formed in the plate portion. Claim 5 delete Claim 6 Multiple suction-fixed cofferdams spaced apart horizontally; The apparatus includes a connecting structure that integrally connects the plurality of suction fixing cofferdams, wherein each of the plurality of suction fixing cofferdams comprises a suction fixing part, a cofferdam part located above the suction fixing part, and a cover detachably coupled to the suction fixing part; the suction fixing part comprises a plate part and a fixed wall part extending downward from the edge of the plate part; the cofferdam part comprises a cylindrical cofferdam wall with open top and bottom ends, and an opening / closing valve for opening and closing an inlet formed adjacent to the plate part in the cofferdam wall; the cofferdam wall extends upward from the edge of the plate part, and the bottom end of the cofferdam wall is welded to the plate part so that the cofferdam wall forms an integral part of the suction fixing part; the connecting structure comprises a plurality of connecting supports connected to the cofferdam wall, and the plate part connects the internal space of the suction fixing part and the internal space of the cofferdam part, and by the cover A temporary structure for water substructure and foundation construction, wherein an openable and closable work passage is formed, and when the inlet is opened by the opening and closing valve, the internal space of the cofferdam wall communicates with the outside. Claim 7 A method for constructing an underwater substructure and foundation using a temporary structure comprising a suction fixed cofferdam having a plate portion forming a work passage, a fixed wall portion extending downward from the edge of the plate portion, a cofferdam wall portion extending upward from the edge of the plate portion, and a cover detachably coupled to the plate portion to open and close the work passage, wherein a suction space with an open bottom is formed internally by the plate portion and the fixed wall portion, and a cofferdam space with an open top is formed internally by the plate portion and the cofferdam wall portion, and the suction space and the cofferdam space are connected by the work passage, the method comprising: a temporary structure submerging step of filling the cofferdam space with water to submerge the temporary structure; a temporary structure settling step in which a part of the fixed wall portion is penetrated into the seabed by the self-weight of the temporary structure so that the temporary structure is settled; and a method comprising discharging fluid from the suction space with the work passage closed in a state in which the temporary structure is settled so that the entire fixed wall portion is inserted into the seabed ground by a pressure difference so that the plate portion is inserted into the seabed A method for constructing a water substructure and foundation, comprising: a step of fixing the water substructure in a state where the water substructure is fixed in contact with the ground; a step of draining water from the cofferdam space while the water substructure is fixed; a step of opening the work passage while the water is drained from the cofferdam space; a step of installing a pile by inserting it into the seabed ground through the opened work passage; a step of removing the water substructure by closing the work passage while the pile is installed and then injecting fluid into the suction space to float the water substructure; and a step of installing the water substructure and foundation by combining the water substructure and foundation with the pile, wherein the step of flooding the water substructure is performed by water from outside the cofferdam wall flowing into the cofferdam space through an inlet formed in the cofferdam wall. Claim 8 A method for constructing a water substructure and foundation according to claim 7, wherein the pile installation step comprises an external pile installation step of installing a hollow external pile and an internal pile installation step of installing an internal pile by inserting it through the external pile. Claim 9 A method for constructing a water substructure and foundation according to claim 8, wherein the external pile installation step is performed by pile driving. Claim 10 A method for constructing an underwater substructure and foundation according to claim 8, wherein the inner pile installation step is performed by inserting the inner pile after the outer pile is internally excavated by an RCD (Reverse Circulation Drill) device. Claim 11 A method for constructing a water substructure and foundation according to claim 8, wherein the upper end of the outer pile protrudes upward from the seabed through the work passage, and the upper end of the inner pile is located below the upper end of the outer pile. Claim 12 delete Claim 13 delete

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