Pile construction method and pile

Abstract

To propose a pile construction method and a pile that can reduce the load on a crane by utilizing the buoyancy of the pile and can reduce the construction labor and costs.SOLUTION: A pile construction method includes an erection step in which a hollow cylindrical pile 2 is erected underwater, and a sinking step in which the pile 2 is sunk. Inside the pile 2, a first floating body portion 41, a second floating body portion 42, and a third floating body portion 43, which impart buoyancy, are formed in this order from a bottom end. The first floating body portion 41 is formed at a predetermined distance from the bottom end of the pile 2, and in the erection step, a top end of the pile 2 is lifted to erect the pile 2, and the buoyancy of the third floating body portion 43 is reduced. In the sinking step, the buoyancy of the first floating body portion 41 is reduced to sink the pile 2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for constructing piles for an offshore structure and to piles used therefor. [Background technology]

[0002] One type of foundation for floating wind power generation facilities is a monopile foundation, which supports the wind turbine tower with a single pile installed on the waterbed. Monopile foundations use either precast piles driven into the waterbed or precast piles buried in boreholes drilled in the waterbed.

[0003] One method of constructing precast piles involves using a crane on a crane ship to suspend the pile, setting it in a pile gripper installed on the crane ship, and using the pile gripper to control the pile's inclination and other aspects while construction is being carried out. For this reason, it is necessary to use a crane ship with sufficient lifting capacity for the precast piles. However, as wind turbine specifications become larger, the weight of the precast piles used in monopile foundations is also increasing, and there is a risk that it will be difficult to secure a crane ship capable of lifting the precast piles.

[0004] If a precast pile is erected while floating on water, the apparent weight of the pile is reduced due to the buoyancy acting on the pile. For example, Patent Document 1 discloses a method of erecting a pile by using a crane to lift one end of a precast pile lying on the water. An inlet with a diameter smaller than the inside diameter of the pile is formed at the bottom end of the precast pile, and by allowing water to flow into the pile through this inlet, the load transmitted to the crane is controlled, allowing for efficient erection work. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-76730 Summary of the Invention [Problem to be solved by the invention]

[0006] In the pile erection method of Patent Document 1, water is introduced into the lower end of a precast pile, causing the weight of the lower end of the pile to exceed the weight of the upper end, thereby rotating the pile and reducing the load on the crane. Therefore, when introducing water into the precast pile, the pile must be tilted in advance so that the water that has flowed into the lower end of the pile remains. Therefore, in the initial stage of erecting a precast pile, the upper end of the precast pile before the water is introduced must be lifted by a crane, and a crane with sufficient lifting capacity must be used. Furthermore, because the water introduced into the precast pile is introduced through an inlet formed at the lower end of the pile, the inflow rate must be controlled by operating a valve installed at the inlet. Therefore, it is difficult to adjust the amount of water introduced depending on the erection of the precast pile.

[0007] The present invention aims to propose a pile construction method and piles that utilize the buoyancy of the piles to reduce the load on the crane and reduce the construction effort and cost. [Means for solving the problem]

[0008] The pile construction method of the present invention, which aims to solve the above-mentioned problems, includes an erection step in which a hollow cylindrical pile is erected in water, and a sinking step in which the pile is sunk. The pile used in the pile construction method of the present invention includes a hollow cylindrical pile main body, a first floating body portion formed inside the pile main body at a predetermined distance from the bottom end of the pile main body, a second floating body portion formed inside the pile main body directly above the first floating body portion, and a third floating body portion formed inside the pile main body directly above the second floating body portion. The weight of the pile main body minus the buoyancy acting on the first floating body portion and the second floating body portion is equal to or less than the lifting capacity of the crane, and the buoyancy acting on the first floating body portion and the third floating body portion can be reduced. In the erection step, the top end of the pile is lifted to erect the pile and the buoyancy of the third floating body portion is reduced, and in the sinking step, the buoyancy of the first floating body portion is reduced to sink the pile.

[0009] This pile construction method allows for the buoyancy of the pile to be adjusted according to the construction stage, making it possible to efficiently erect the pile while reducing the load on the crane by utilizing the buoyancy, thereby reducing the labor and costs involved in constructing the pile.

[0010] Furthermore, if the piles are towed to a predetermined location in a sideways position, a separate barge for transporting the piles is not required. Also, once they are moved to the predetermined location, no reloading work is required. The piles can also be stored floating on the water.

[0011] In the erection process, work to reduce the buoyancy of the third floating body part may be performed when the upper end of the pile is higher than the water surface, or work to reduce the buoyancy of the third floating body part may be performed when the pile is upright.

[0012] If the pile further includes a water passage section that passes through the first floating section, the second floating section, and the third floating section, when the pile is erected, water that flows into the inside of the pile is guided to the lower end without stagnating, so the balance of the pile is adjusted and the load on the crane does not increase.

[0013] If the second floating body portion is formed so that its upper end surface coincides with the waterline when the pile body is erected to reduce the buoyancy of the first floating body portion, the erected pile will be set up in a balanced manner, thereby preventing the pile from rotating due to buoyancy when it is sunk.

[0014] The first floating body portion, the second floating body portion, and the third floating body portion may be spaces formed by partitioning the inside of the pile main body and having openable and closable water holes formed therein to allow water to flow in, so that buoyancy can be reduced by allowing water to flow in. The first floating body portion, the second floating body portion, and the third floating body portion may be bags that are inflated with pressurized gas and can reduce buoyancy by venting the gas, or may be solid bodies that are detachably provided inside the pile main body. [Effects of the Invention]

[0015] According to the pile construction method and pile of the present invention, when constructing piles for underwater structures, the buoyancy of the piles can be utilized to reduce the load on the crane, and construction work and costs can be reduced. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a front view showing a floating wind power generation facility according to an embodiment of the present invention. [Figure 2] FIG. [Figure 3] 1 is a flowchart showing a pile construction method. [Figure 4] FIG. [Figure 5](a) is a side view showing the erection process, and (b) is a side view of the erection process following (a). [Figure 6] FIG. [Figure 7] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] In this embodiment, construction of a foundation structure for a floating wind power generation facility 1 will be described. Fig. 1 shows the floating wind power generation facility 1 of this embodiment. As shown in Fig. 1, the floating wind power generation facility 1 of this embodiment is made up of a so-called monopile foundation in which columns 12 of a wind turbine 11 are supported on pile foundations 13. The foundation structure (pile foundations 13) for the floating wind power generation facility 1 is formed by sinking piles into the water bottom GL (ground G).

[0018] Figure 2 shows the pile 2. As shown in Figure 2, the pile 2 is mainly formed of a pile body 3 made of a hollow cylindrical steel pipe with an outer diameter of 10 m or more. A pair of trunnions 31, 31 are fixed to the side of the pile body 3. The pair of trunnions 31, 31 are arranged above the center in the height direction, facing each other with the pile body 3 in between. The pile 2 can be erected underwater using a crane or the like by fastening a wire to the trunnions 31, 31. Note that the dimensions of the steel pipe that constitutes the pile 2 are not limited. Furthermore, the pile 2 is not limited to a steel pipe.

[0019] A floating body portion 4 is formed inside the pile main body 3. The floating body portion 4 includes, in order from the lower end side of the pile main body 3, a first floating body portion 41, a second floating body portion 42, and a third floating body portion 43. The first floating body portion 41 is formed at a position spaced a predetermined distance from the lower end of the pile main body 3. The second floating body portion 42 is formed directly above the first floating body portion 41, and the third floating body portion 43 is formed directly above the second floating body portion 42.

[0020] In this embodiment, the first floating body portion 41, the second floating body portion 42, and the third floating body portion 43 are formed by disposing a bag inflated with pressurized gas inside the pile main body 3. The bag has an exhaust port, and the buoyancy of the first floating body portion 41, the second floating body portion 42, and the third floating body portion 43 is reduced by exhausting the internal gas through the exhaust port. The second floating body portion 42 is formed so that its upper end surface coincides with the waterline when the pile main body 3 is erected and the buoyancy of the first floating body portion 41 and the third floating body portion 43 is reduced. In addition, the buoyancy of the floating body portion 4 is set so that the weight obtained by subtracting the buoyancy force F acting on the first floating body portion 41 and the second floating body portion 42 from the weight mg of the pile main body 3 is equal to or less than the lifting capacity of the crane used to erect the pile 2.

[0021] A water-passing section 5 is formed inside the pile main body 3. In this embodiment, the water-passing section 5 is made of a pipe that extends from the lower end of the first floating body section 41 to the upper end of the third floating body section 43. In other words, the water-passing section 5 passes through the first floating body section 41, the second floating body section 42, and the third floating body section 43, and enables the movement of fluids such as water between one end and the other end of the pile main body 3 (between the upper and lower ends of the floating body sections 4).

[0022] The pile construction method of this embodiment will be described below. Figure 3 shows the steps of the pile construction method for the pile 2. As shown in Figure 3, the pile construction is performed by a pile transporting process S1, an erecting process S2, a positioning process S3, and a sinking process S4.

[0023] In the pile transfer step S1, the pile 2, which is laid on its side, is towed to a predetermined position (construction site) while floating on the water. Figure 4 shows the pile transfer step S1. The pile 2 is towed to the construction site with a wire W extended from the towing vessel Bt and attached to a pair of trunnions 31, 31. At this time, if necessary, multiple anti-rotation floats 32 or the like are attached to the side of the pile body 3 to suppress rotation of the pile 2 (mainly rotation around the central axis) during towing and prevent twisting of the towing wire W.

[0024] In the erection process S2, the pile 2 is erected in the water. Figure 5 shows the erection process S2. In the erection process S2, as shown in Figures 5(a) and 5(b), the wire W attached to the trunnions 31, 31 is lifted to lift the upper end of the pile 2 and erect (stand upright) the pile 2. The tension acting on the wire W is equal to the pile weight mg minus the buoyancy F. When lifting of the pile 2 begins, the positional relationship between the point of action of the buoyancy F1 caused by the floating body part 4 (distance b1 from the trunnion 31, which is the hanging point) and the center of gravity of the pile 2 (distance a from the trunnion 31 to the point of action of the pile weight mg) is b1·F1=a·mg (see Figure 5(a)).

[0025] In the erection process S2, the wire W is lifted, and when the upper end of the pile 2 is elevated above the water surface, the gas inside the third floating body portion 43 is evacuated to reduce the buoyancy of the third floating body portion 43. By lifting the upper end of the pile 2, the water on the upper end side of the pile 2 (the water that entered from the top of the pile when the pile 2 was laid on its side) moves to the lower end side of the pile 2 via the water passage portion 5. At this time, the buoyancy F2 of the first floating body portion 41 and the second floating body portion 42 ensures a submerged length L (submerged length L that ensures a predetermined clearance) at which the pile 2 does not contact the bottom surface of the water. Note that air trapped below the first floating body portion 41 inside the pile main body 3 is evacuated from the upper end of the pile main body 3 via the water passage portion 5.

[0026] In the positioning step S3, the pile 2 is moved to a sinking position. The positioning step S3 is shown in Figure 6. In the positioning step S3, as shown in Figure 6, the erected pile 2 is moved laterally so as not to exceed the crane capacity and while maintaining the submerged length of the pile 2.

[0027] In the sinking process S4, the pile 2 is sunk and made to land on the seabed. The sinking process S4 is shown in FIG. 7. In the sinking process S4, the gas inside the first floating body 41 is exhausted to reduce the buoyancy of the first floating body 41, and the pile 2 is sunk. The air inside the first floating body 41 is exhausted from the upper end of the pile body 3 through the water passage 5. The acting point of the buoyancy F3 when the buoyancy of the first floating body 41 is reduced (the distance b3 from the trunnion 31 which is the suspension point) moves closer to the trunnion 31 side than in the state of FIG. 6 (b3 < b2), and the buoyancy moment b3·F3 < the self-weight moment a·mg. In the state of FIG. 7, since the pile weight mg > the buoyancy F2, if the pile is vertical, the pile 2 can be sunk. Also, even when the pile 2 is tilted due to the influence of waves or the like, since the buoyancy moment b3·F3 < the self-weight moment a·mg, the pile 2 can be sunk. That is, the buoyancy moment b3·F3 does not exceed the self-weight moment a·mg of the pile 2, and in order to suppress the rotation of the pile 2 during the sinking of the pile 2, the pile 2 can be lowered to the seabed GL in a standing state. Since it is more stable when b3·F3 is smaller, it is preferable that when the buoyancy of the first floating body 41 is reduced, the upper end of the second floating body 42 substantially coincides with the waterline position of the pile 2.

[0028] According to the pile 2 and the construction method of the pile 2 of the present embodiment, since the buoyancy of the pile 2 can be adjusted according to the construction stage, while reducing the load on the crane by using the buoyancy, the pile 2 can be efficiently erected. More specifically, in the erection process S2, the first floating body 41 secures, together with the second floating body 42, the buoyancy for preventing the lower end of the pile 2 from contacting the seabed GL when erecting the pile 2. Also, in the sinking process S4, the second floating body 42 secures alone the minimum buoyancy necessary for keeping the pile 2 vertical when sinking the pile 2. Further, in the pile transfer process S1, the third floating body 43 secures, together with the first floating body 41 and the second floating body 42, the buoyancy necessary for the horizontally laid pile 2. Thus, by appropriately adjusting the buoyancy by the floating body 4, it becomes possible to reduce the labor and cost of the construction of the pile 2.

[0029] In the method for constructing the piles 2 of this embodiment, the piles 2 are towed to a predetermined position in a sideways state, so that no reloading work is required after they have been moved to the predetermined position. Furthermore, the piles 2 can be stored without a limit on the number of piles that can be stored by floating them on water. Furthermore, since the piles 2 can be transported one by one, there is no need to load them onto a crane ship for transportation. Therefore, there is no need to move the crane ship, which is a work ship, to transport the piles, and the construction period (construction cycle) can be shortened.

[0030] Since it is equipped with a water passage section 5 that penetrates the first floating section 41, the second floating section 42 and the third floating section 43, when the pile 2 is erected, the water that flows into the inside of the pile 2 is guided to the lower end without stagnating, so the balance of the pile 2 is adjusted and the load on the crane does not increase.

[0031] The second floating body portion 42 is formed so that its upper end surface coincides with the waterline when the pile 2 is erected to reduce the buoyancy of the first floating body portion 41, so that the erected pile 2 stands in a balanced manner and the pile 2 is prevented from rotating due to buoyancy when it is sunk.

[0032] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and each of the above-described components can be appropriately modified within the scope of the present invention. In the above embodiment, the pile 2 is used as the pile foundation 13 of the floating wind power generation facility 1, but the structure supported by the pile 2 is not limited. In addition, the shape of the pile main body 3 is not limited.

[0033] In the above embodiment, in the erection process S2, the buoyancy of the third floating body part 43 is reduced when the head of the pile 2 is positioned higher than the water surface WL, but the buoyancy of the third floating body part 43 may also be reduced when the pile 2 is made upright.

[0034] In the embodiment, the first floating body portion 41, the second floating body portion 42, and the third floating body portion 43 are described as being made of bags inflated by pressurized gas, but the configurations of the first floating body portion 41, the second floating body portion 42, and the third floating body portion 43 are not limited thereto. For example, the first floating body portion 41, the second floating body portion 42, and the third floating body portion 43 may be solid bodies (e.g., made of foamed resin) that are detachably provided inside the pile main body 3. When the floating body portion 4 is made of a solid body, it is desirable to form a groove on the side of the solid body as the water passage portion 5.

[0035] Furthermore, the first floating body portion 41, the second floating body portion 42, and the third floating body portion 43 may be spaces formed by dividing the inside of the pile main body 3 with partition walls. In this case, each partition wall is formed with an openable water passage hole that allows water to flow in, and the first floating body portion 21, the second floating body portion 22, and the third floating body portion 23 can reduce their buoyancy by letting water in through the water passage hole. [Explanation of symbols]

[0036] 1. Floating wind power generation facility 2 stakes 3 Pile body 31 Trunnion 4 Floating body section 41 First floating body section 42 Second floating body section 43 Third Floating Body Section 5 Water flow section Bt Towing Vessel G Ground GL underwater L Submerged length W Wire WL water surface

Claims

1. an erection process of erecting a pile made of a hollow cylindrical body underwater; A pile construction method comprising: a sinking step of sinking the pile; A first floating body portion, a second floating body portion, and a third floating body portion that impart buoyancy to the pile are formed in this order from the lower end side inside the pile, The first floating body portion is formed at a position spaced a predetermined distance from the lower end of the pile, In the erection process, the upper end side of the pile is lifted to erect the pile, and the buoyancy of the third floating body part is reduced. A pile construction method, characterized in that in the sinking step, the pile is sinked by performing work to reduce the buoyancy of the first floating body section.

2. 2. The pile installation method according to claim 1, further comprising a pile transporting step of towing the pile in a horizontally laid state while floating on the water to a predetermined position.

3. 2. A pile construction method as described in claim 1, characterized in that, in the erection process, work is carried out to reduce the buoyancy of the third floating body section when the upper end of the pile reaches a position higher than the water surface.

4. 2. The pile construction method according to claim 1, wherein in the erection step, work is carried out to reduce the buoyancy of the third floating body section when the pile is erected upright.

5. A pile that can be erected underwater using a crane, A pile main body consisting of a hollow cylindrical body; A first floating body portion formed inside the pile main body at a position spaced a predetermined distance from the lower end of the pile main body; A second floating body portion formed directly above the first floating body portion inside the pile main body; a third floating body portion formed directly above the second floating body portion inside the pile main body, a weight obtained by subtracting the buoyancy acting on the first floating body portion and the second floating body portion from the weight of the pile body is equal to or less than the lifting capacity of the crane; A pile capable of reducing the buoyancy acting on the first floating body portion and the buoyancy acting on the third floating body portion.

6. The pile according to claim 5 , further comprising a water-passing portion passing through the first floating portion, the second floating portion, and the third floating portion.

7. The pile according to claim 5, characterized in that the second floating body portion is formed so that its upper end surface coincides with the waterline when the pile body is erected to reduce the buoyancy of the first floating body portion.

8. The pile described in claim 5, characterized in that the first floating body portion, the second floating body portion and the third floating body portion are formed by partitioning the interior of the pile main body, and are spaces formed with openable and closable water passage holes that allow water to flow in.

9. The pile according to claim 5, wherein the first floating body portion and the third floating body portion are formed of bags inflated with pressurized gas, and buoyancy is reduced by discharging the gas.

10. The pile according to claim 5 , wherein the first floating body portion and the third floating body portion are solid bodies removably provided inside the pile main body.

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