JP2024089833A - Bored pile and method of construction of the same - Google Patents

Abstract

[Problem] We propose a buried pile that utilizes the buoyancy of the pile to reduce the load on the crane and to reduce the labor and cost of construction, and a construction method for the buried pile. [Solution] The buried pile 2 is buried in a borehole formed in the bottom of the water, and comprises a hollow pile body 3, a bottom cover 4 that closes the bottom of the pile body 3, an top cover 5 that closes the top of the pile body 3, and a filling pipe 6 that is piped inside the pile body 3 from the top to the bottom of the pile body 3. A water injection hole 51 for injecting water into the pile body 3 is formed in the head, and the filling pipe 6 is connected to a through hole 32 formed in the bottom of the pile body 3. [Selected Figure] Figure 2

Description

The present invention relates to buried piles that are installed in the bottom of water and a method for installing buried piles.

One type of foundation for floating wind power generation facilities is a monopile foundation, in which a wind turbine tower is supported by a single pile installed on the bottom of the water.
Monopile foundations use driven piles, which are prefabricated piles driven into the water bottom, or buried piles, which are prefabricated piles buried in boreholes formed in the water bottom.
As a method of constructing precast piles, a crane ship's crane may be used to suspend the precast pile, set it on a pile gripper installed on the crane ship, and construction may be performed while controlling the inclination of the pile with the pile gripper. For this reason, it is necessary to use a crane ship with sufficient lifting capacity for the precast piles. On the other hand, as the specifications of wind turbines become larger, the weight of the precast piles used for monopile foundations is also increasing, and there is a risk that a crane ship capable of lifting the precast piles may not be available.
If a prefabricated pile is erected while floating on the water, the apparent weight of the pile is reduced by the buoyancy acting on the pile. For example, Patent Document 1 discloses a method of erecting a pile by lifting one end of a prefabricated pile lying on the water with a crane. An inlet with a diameter smaller than the inner diameter of the pile is formed at the lower end of the prefabricated pile, and by allowing water to flow into the inside of the pile from this inlet, the load transmitted to the crane is controlled, and the pile erection work can be performed efficiently.
If the pile of Patent Document 1 is used as an embedded pile, when filling material is injected around the pile, the filling material may flow into the inside of the pile through the inlet formed at the bottom end of the pile. If the filling material flows into the pile, the amount of filling material injected increases, and as a result, the work and cost of construction increase. In addition, since the water to be flowed into the inside of the pile flows through the inlet formed at the bottom end of the pile, the amount of water to be flowed in must be controlled by operating a valve provided at the inlet. Therefore, it is difficult to adjust the amount of water to be flowed in according to the erection of the pile.

JP 2022-76730 A

The objective of the present invention is to propose a buried pile that utilizes the buoyancy of the pile to reduce the load on the crane and reduce the labor and cost of construction, as well as a construction method for the buried pile.

The buried pile of the present invention for solving the above problems is buried in a borehole formed in the bottom of the water, and includes a hollow pile body, a lower cover that closes the lower part of the pile body, an upper cover that closes the upper part of the pile body, and a filling pipe that is piped from the upper part to the lower part of the pile body inside the pile body. A water injection hole for injecting water into the pile body is formed in the head, and the filling pipe is connected to a through hole formed in the lower part of the pile body.
In addition, the construction method of the buried pile of the present invention includes an erecting process of erecting the buried pile underwater by lifting the upper end side of the buried pile, an insertion process of inserting the buried pile into the borehole, and a filling process of filling the gap between the buried pile and the borehole with filler material, and during the erecting process, water is poured into the inside of the pile body.
According to the buried pile and the method of construction of the buried pile, when erecting the buried pile, water is poured inside, making the lower end of the buried pile heavier, making it easier to erect. In addition, the lower part of the buried pile is closed with a bottom cover, preventing the filler injected into the borehole from flowing into the pile body. Therefore, it is possible to minimize the amount of filler injected, which results in efficient construction and reduced costs.

The top cover is formed with the water inlet and exhaust holes, and the water inlet and exhaust holes are preferably provided with valves, check valves, or blocking caps. In this way, water can be injected and exhausted from the top end of the pile. Also, by forming the water inlet and exhaust holes in the top cover, the effort required for processing the prefabricated pile can be minimized.
Furthermore, if the filling tube is provided with a valve, a check valve or a blocking cap, it is possible to prevent water from flowing into the filling tube.
In addition, during the erection process, by measuring the amount of water injected and controlling the weight of the embedded pile, balance is maintained when erecting the embedded pile, and the weight can be adjusted within the range of the crane capacity.
Furthermore, if the buried pile is towed to a specified location while floating on the water, a steel barge is not required to transport the pile. After the pile is moved to the specified location, no reloading work is required. The buried pile can also be stored while floating on the water.

The buried pile and the method for constructing the buried pile of the present invention make it possible to reduce the load on the crane by utilizing the buoyancy of the pile, and also to reduce the labor and costs involved in construction.

1 is a front view showing an embodiment of the floating wind power generation facility according to the present invention. FIG. FIG. 2 is a cross-sectional view showing a buried pile. 1 is a flowchart showing a method for constructing a buried pile. 1A and 1B are side views showing a method for storing buried piles, in which (a) shows the buried piles being unloaded onto the water, and (b) shows the buried piles being stored. 1A and 1B are side views showing the drilling process, in which FIG. 1A shows the template installation state and FIG. 5(b) is a side view showing the excavation step subsequent to FIG. 5(b), where (a) is before excavation and (b) is after excavation. FIG. FIG. 10A and 10B are side views showing the insertion process, in which FIG. 10A shows the time when the buried pile is inserted and FIG. 1A and 1B are side views showing the filling process, in which FIG. 1A shows a filling state and FIG.

In this embodiment, a case will be described where a foundation structure for a floating wind power generation facility 1 is constructed. 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 formed of a so-called monopile foundation in which a support 12 for a wind turbine 11 is supported by a pile foundation 13.
The foundation structure (pile foundation 13) of the floating wind power generation facility 1 is formed by embedding piles (buried piles 2) into boreholes H formed in the water bottom GL (ground G).

The buried pile 2 is shown in Fig. 2. As shown in Fig. 2, the buried pile 2 includes a pile body 3, a lower cover 4, an upper cover 5, a filling pipe 6, and a water injection pipe 7.
The pile body 3 is made of a hollow cylindrical steel pipe. 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 in positions facing each other with the pile body 3 in between. The diameter of the upper part of the pile body 3 decreases toward the upper end. Meanwhile, the other parts of the pile body 3 have the same diameter. A plurality of through holes 32 are formed in the side of the lower part of the pile body 3.

The bottom cover 4 watertightly closes the lower part of the pile main body 3. The bottom cover 4 in this embodiment is made of a circular steel plate, and is fixed (welded) to the lower end of the pile main body 3.
The top cover 5 watertightly closes the top of the pile body 3. In this embodiment, the top cover 5 is made of a circular steel plate and is fixed to the top end of the pile body 3 (by attaching a watertight bolt having a water-stopping function, or the like). The top cover 5 is formed with a water inlet hole 51 and an exhaust hole 52. The water inlet hole 51 communicates with the water inlet pipe 7, and the exhaust hole 52 communicates with the inner space of the pile body 3. The water inlet hole 51 and the exhaust hole 52 are provided with valves (not shown), and by closing the valves, the top end of the pile body 3 is sealed.

The filling pipe 6 is a pipeline for transporting the filling material, and is installed inside the pile body 3 from the top to the bottom of the pile body 3. The upper end of the filling pipe 6 is located below the upper cover 5 inside the pile body 3, and the lower end of the filling pipe 6 communicates with the through hole 32. A check valve (not shown) is provided at the lower end of the filling pipe 6.
The water injection pipe 7 is a pipe for supplying water into the pile body 3, and is arranged inside the pile body 3 from the top to the bottom of the pile body 3. The upper end of the water injection pipe 7 is connected to the water injection hole 51, and the lower end of the water injection pipe 7 opens above the bottom cover 4 in the lower part of the interior of the pile body 3.

The following describes a method for constructing the buried piles 2. Figure 3 shows the steps of the method for constructing the buried piles 2. As shown in Figure 3, the method for constructing the buried piles 2 of this embodiment includes a preparation step S1, an excavation step S2, a pile transport step S3, an erection step S4, an insertion step S5, and a filling step S6.
In the preparation step S1, the buried pile 2 is transported to a predetermined storage location via a barge Bs. The preparation step S1 is shown in Fig. 4(a) and (b). As shown in Fig. 4(a), the buried pile 2 is unloaded from the barge Bs onto the water at the storage location using a crane ship or the like. A cover material (not shown) for preventing adhesion of aquatic organisms is attached to the side of the buried pile 2 that will be submerged in water when lowered onto the water. In addition, the valves of the water injection hole 51 and the exhaust hole 52 are closed to prevent water from entering the buried pile 2. The filling pipe 6 is provided with a check valve to prevent water from entering the filling pipe 6.
The buried pile 2 that has been lowered onto the water is moored while floating on the water, as shown in Fig. 4(b). At this time, the buried pile 2 is moored using a plurality of mooring lines (wires, ropes, etc.) with one end fixed to the bottom of the water. In this embodiment, the mooring line R has one end fixed to the bottom of the water via a sinker block SB provided on the bottom of the water. In addition, a light buoy LB is attached to the sinker block SB. Furthermore, a buoy BU is attached to the mooring line R to prevent the mooring line R from sinking.

In the drilling step S2, a borehole H is formed to install the buried pile on the bottom of the water. The drilling step is shown in Figures 5 and 6. In the drilling step S2, first, as shown in Figure 5(a), a template T is installed at the position where the buried pile 2 is to be installed. Next, as shown in Figure 5(b), a casing P is installed on the template T. Next, as shown in Figure 6(a), a drilling machine M is installed inside the casing P to drill the borehole H. As the drilling machine M drills the borehole H, the casing P is lowered to prevent the hole wall from collapsing. After the borehole H is formed, the drilling machine M is removed as shown in Figure 6(b).
In the pile transfer step S3, the embedded pile 2 is towed to a predetermined position (construction site) while floating on the water. Figure 7 shows the pile transfer step S3. The embedded pile 2 is towed to the construction site with the wire W extended from the towing vessel Bt attached to a pair of trunnions 31, 31. At this time, a plurality of rotation prevention buoys 33, 33, ... are attached to the side of the pile body 3 to suppress the rotation (mainly rotation around the central axis) of the embedded pile 2 during towing and prevent the towing wire W from being twisted. The plurality of rotation prevention buoys 33, 33, ... are connected by ropes and are provided continuously along the side of the pile body 3. The rotation prevention buoys 33 are fixed to the pile body 3 via a metal band or a magnet.
A tie rod is provided between the boat and the wire to prevent the wire W from twisting.

In the erection process S4, the embedded pile 2 is erected underwater. FIG. 8 shows the erection process S4. In the erection process S4, water is poured into the inside of the pile body 3, and as shown in FIG. 9, the wire W (upper side of the pile body 3) attached to the pair of trunnions 31, 31 is lifted to erect the pile body 2. At this time, the amount of water poured is measured to manage the apparent weight of the embedded pile 2 so as not to exceed the crane capacity. Before starting to pour water, it is recommended to lift the upper side of the pile body 3 and tilt the pile body 3. To pour water into the pile body 3, the valve of the water pouring hole 51 is opened and water is poured from the bottom of the pile body 3 through the water pouring pipe 7. The valve of the exhaust hole 52 is also opened, and the air inside the pile body 3 is exhausted as the water is poured. This makes the lower side of the pile body 3 heavier, making it easier to erect the pile body 3. In this embodiment, pouring fresh water can prevent corrosion inside the pile body 3.

In the insertion step S5, the buried pile 2 is inserted into the borehole H. The insertion step is shown in Fig. 9. In the insertion step, the erected buried pile 2 is inserted into the casing P (borehole H) as shown in Fig. 9(a) and (b). After the buried pile 2 is inserted into the casing P (borehole H), the top cover 5 is removed from the pile body 3.
In the filling step S6, the gap between the buried pile 2 and the borehole H is filled with a filler. FIG. 10 shows the filling step S6. As shown in FIG. 10(a), the filler F is injected from the through hole 32 (see FIG. 2) formed in the lower part of the buried pile 2 through the filling pipe 6. The filler F is pumped through a pressure pipe (not shown) connected to the upper end of the filling pipe 6 and is pumped into the bottom of the borehole H. As the filler F is injected (the upper end surface of the filler rises), the casing P is lifted to fill the gap between the buried material 2 and the borehole H with the filler. After the filler is filled, the template T is removed as shown in FIG. 10(b).

According to the buried pile 2 and the construction method of the buried pile 2 of this embodiment, when erecting the buried pile 2, water is poured inside the buried pile 2, which makes the lower end of the buried pile 2 heavier and tilts the buried pile 2, making it easier to erect the buried pile 2. Furthermore, if the buried pile 2 is erected while an air pocket is secured inside the buried pile 2, it can be erected by utilizing buoyancy even if the weight of the buried pile 2 exceeds the lifting capacity of the crane.
In addition, since the lower part of the buried pile 2 is closed by the bottom cover 4, the filler F injected into the borehole H is prevented from flowing into the pile body 3. Therefore, it is possible to keep the injection amount of the filler F to a minimum, which results in efficient construction and reduced costs.

By pouring water into the buried pile 2, the weight of the buried pile 2 can be adjusted, and the buried pile 2 can be reliably set on the bottom.
By pouring water into the buried pile 2, it is possible to prevent the buried pile 2 from floating up due to the pressure generated when the filler is injected.
In addition, a water inlet hole 51 and an exhaust hole 52 are formed in the upper cover 5, making it possible to inject water and exhaust air from the upper end of the buried pile 2.
Furthermore, if a check valve is provided in the filling pipe 6, it is possible to prevent water from flowing into the filling pipe 6 and the filling material from flowing back.
Furthermore, in the erection process S4, by measuring the amount of water poured in and controlling the apparent weight of the embedded pile 2, it is possible to maintain balance when erecting the embedded pile 2, thereby minimizing the load on the crane.

Since the buried piles 2 are towed to the designated location while floating on the water, no reloading work is required after they are moved to the designated location. Also, there is no limit to the number of piles that can be stored.
In addition, since they can be transported one by one, there is no need to load them onto a crane ship for transport. This means that there is no need to move the crane ship, which is the work vessel, to transport the piles, making it possible to shorten the construction period (construction cycle).
In addition, since the buried piles 2 are stored floating on the water, there is no need to secure a barge or land for storage, which makes it possible to reduce costs.

Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and each of the above-described components can be appropriately modified without departing from the spirit of the present invention.
In the above embodiment, the description has been given of the case where the embedded pile 2 is used for the pile foundation 13 of the floating wind power generation facility 1, but the structure supported by the embedded pile 2 is not limited thereto.
In addition, there is no limitation on the shape of the pile body 3. In addition, the pile body 3 does not necessarily need to have a reduced diameter at its upper end.

In the above embodiment, a case has been described in which the lower cover 4 is fixed to the lower end of the pile main body 3, but the lower cover 4 may also be fixed to the lower part of the pile main body 3 inside the pile main body 3.
Similarly, in the above embodiment, a case has been described in which the upper cover 5 is fixed to the upper end of the pile main body 3, but the upper cover 5 may also be fixed to the upper part of the pile main body 3 inside the pile main body 3.
In addition, in the embodiment, a case has been described in which valves are provided in the water inlet hole 51 and the exhaust hole 52, but the water inlet hole 51 and the exhaust hole 52 may be provided with check valves or blocking caps instead of valves.

In the above embodiment, a check valve is provided in the filling tube 6, but the check valve is not limited to this and may be a valve or a blocking cap, for example, as long as it can prevent water from entering the filling tube 6. When a valve is used, it is sufficient to open it when the filling material F is injected and to keep it closed at other times. Also, when a blocking cap is used, it is sufficient to remove it by the pressure of the filling material F when the filling material F is injected.
The filling tube 6 may be routed through the top cover 5 .
The water injection pipe 7 may be installed as required.
In the above embodiment, fresh water (fresh water) is poured into the pile body 3, but the water poured into the pile body 3 is not limited to this and may be, for example, seawater or desalinated seawater.

Reference Signs List 1 Floating wind power generation facility 2 Buried pile 3 Pile body 31 Trunnion 32 Through hole 4 Lower cover 5 Upper cover 51 Water injection hole 52 Exhaust hole 6 Filling pipe 7 Water injection pipe G Ground GL Water bottom H Borehole

Claims (6)

A buried pile that is buried in a borehole formed in the bottom of the water,
A hollow pile body;
A lower cover that closes the lower part of the pile body;
An upper cover that closes the upper part of the pile body;
A filling pipe is piped from the upper part to the lower part of the pile body inside the pile body,
A water injection hole for injecting water into the pile body is formed in the head portion,
A buried pile, characterized in that the filling pipe is connected to a through hole formed in the lower part of the pile body. The water inlet and exhaust hole are formed in the upper cover,
The buried pile according to claim 1 , wherein the water inlet hole and the exhaust hole are provided with a valve, a check valve or a blocking cap. The buried pile according to claim 1, characterized in that the filling pipe is provided with a valve, a check valve or a blocking cap. A method for constructing a buried pile according to any one of claims 1 to 3 in a water bottom,
A step of erecting the buried pile in water by lifting the upper end side of the buried pile;
An inserting step of inserting the buried pile into the borehole;
A filling step of filling a gap between the buried pile and the borehole with a filler material,
A construction method for a buried pile, characterized in that in the erection process, water is poured into the inside of the pile body. The method for constructing a buried pile according to claim 4, characterized in that the amount of water poured is measured to control the apparent weight of the buried pile. The method for constructing buried piles according to claim 4, further comprising a pile transport step of towing the buried pile to a predetermined position while floating on the water.

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