Vibro hammer and pile extraction method using the same

Abstract

To enable control of rotational attitude around the Z axis (yaw) of a vibro hammer used for driving pile anchors and the like for mooring offshore structures such as offshore wind power generation facilities, at least underwater.SOLUTION: A vibro hammer 8 is provided with a thruster 15 for controlling at least the rotational attitude (yaw) around the Z axis. Preferably, of the six degrees of freedom, namely, the rotational attitude around the Z axis (yaw), movement in the Z axis direction (heave), the rotational attitude around the Y axis (roll), movement in the Y axis direction (surge), the rotational attitude around the X axis (pitch), and movement in the X axis direction (sway), the vibro hammer 8 is provided with thrusters 15 for controlling a plurality of degrees of freedom including at least the rotational attitude around the Z axis (yaw).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a vibro hammer used to drive pile anchors, steel sheet piles, foundation piles, etc. for mooring offshore structures such as offshore wind power generation facilities, and a pile extraction method using the same. [Background technology]

[0002] In recent years, wind power generation facilities that generate electricity by harnessing natural wind have been attracting attention from the perspective of environmental friendliness and the effective use of natural energy. These wind power generation facilities can be installed on land or on water (mainly offshore), but in Japan, which has mountainous areas behind its coasts, there are few plains along the coast where stable winds can be expected. On the other hand, Japan is surrounded by sea on all sides, and offshore winds suitable for generating electricity are easily available, and there are fewer restrictions on installation, which are some of the advantages. For this reason, many offshore wind power generation facilities have been constructed in recent years.

[0003] To maintain the offshore wind power generation facility in a fixed position above sea level, a mooring rope (chain, wire, etc.) is connected to one end of the floating structure, and the other end is connected to an anchor installed on the seabed for mooring. Pile anchors have traditionally been widely used as one type of anchor. Pile anchor installation methods include the suction method using water pressure, the impact method using a hydraulic hammer, and the vibration method using a vibro hammer. However, the suction method is difficult to apply to soils other than those with low permeability, such as clayey soil, due to the risk of boiling and piping. The impact method using a hydraulic hammer cannot be used to extract pile anchors, so a separate extraction device was required. As a result, the vibration method using a vibro hammer has been widely used for driving and extracting piles underwater (see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-53840 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when constructing offshore wind power generation facilities, if pile anchors are to be driven underwater using a vibro hammer, (1) When the water depth is relatively shallow, even though the position of the vibro hammer can be controlled by operating the crane that suspends the vibro hammer, it is still difficult to control the orientation of the vibro hammer (rotational attitude around the Z axis (yaw)) in a specified direction. (2) In deep waters, if the Vibrohammer is carried away by the tidal current, the position of the Vibrohammer cannot be controlled by crane operation alone, making it difficult to drive the pile anchor in the correct position. If the Vibrohammer is displaced from the water surface to the seabed at an angle of 3° from the vertical at a water depth of 300m, then a tangent of 30° (≒ 15m) will result in a deviation. In addition, the Vibrohammer can sometimes be tilted by the tidal current, making it difficult to drive the pile anchor in the vertical direction.

[0006] On the other hand, when using the vibro hammer to extract a pile anchor, there were problems such as the influence of tidal currents making it difficult to guide the vibro hammer's chuck to the gripping part (chucking plate) of the pile anchor.

[0007] Therefore, the first object of the present invention is to enable the rotational attitude (yaw) of a vibro hammer used to drive pile anchors, steel sheet piles, foundation piles, etc. underwater for mooring offshore structures such as offshore wind power generation facilities to be controlled at least underwater around the Z axis, preferably by controlling multiple degrees of freedom including the rotational attitude (yaw) around the Z axis out of the six degrees of freedom, so that piles can be driven in the correct position and orientation.

[0008] A second object is to enable the pile to be gripped reliably by the vibro hammer when the pile is extracted using the vibro hammer, thereby enabling the extraction work to be carried out efficiently. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention according to claim 1 provides a vibro hammer for use underwater, The vibro hammer is characterized in that the vibro hammer is provided with a thruster for controlling the attitude (yaw) in the rotational direction around at least the Z axis.

[0010] In the invention described in claim 1, the vibro hammer is provided with a thruster for controlling at least the rotational attitude (yaw) around the Z axis. Therefore, by driving the thruster, it becomes possible to control the rotational attitude (yaw) of the vibro hammer around the Z axis, and it becomes possible to drive piles and the like precisely in a predetermined direction.

[0011] The present invention according to claim 2 provides a vibrohammer according to claim 1, which is equipped with thrusters for controlling a plurality of degrees of freedom including at least the rotational attitude about the Z axis (yaw) out of six degrees of freedom: rotational attitude about the Z axis (yaw), movement in the Z axis direction (heave), rotational attitude about the Y axis (roll), movement in the Y axis direction (surge), rotational attitude about the X axis (pitch), and movement in the X axis direction (sway).

[0012] The invention described in claim 2 above is provided with thrusters for controlling multiple degrees of freedom, including at least the rotational attitude (yaw) around the Z axis, out of the six degrees of freedom. In deep water, the vibrohammer is swept away by the influence of tidal currents, making position control and attitude control difficult. Therefore, by providing thrusters for controlling multiple degrees of freedom, including the rotational attitude (yaw) around the Z axis, out of the six degrees of freedom, and most preferably all six degrees of freedom, it becomes possible to drive piles and the like into predetermined positions in the correct orientation and vertically with high precision.

[0013] According to a third aspect of the present invention, there is provided a vibro hammer according to the second aspect, wherein a rotary thruster capable of rotating 360° is used as the thruster.

[0014] In the invention described in claim 3 above, a propeller is equipped on a pod that rotates 360 degrees, and by using this, it is possible to control with many degrees of freedom while reducing the number of thrusters to be installed.

[0015] The present invention according to claim 4 provides a method for extracting a pile driven into the bottom of water using the vibro hammer according to any one of claims 1 to 3, The pile is provided with a chucking plate at the center of the upper end of the pile to be clamped by a pair of left and right chucks of the vibro hammer, and a funnel-shaped guide cone that widens upward is provided on the periphery of the upper end of the pile, a relatively long guide bar extending in the vertical direction is provided on one side of a pair of left and right chucks of the vibro hammer, and a relatively short guide bar extending in the vertical direction is provided on the other side of the chucks, A first step of bringing a tip of the long guide bar of the vibro hammer into contact with a guide cone of a pile; a second step of positioning the vibro hammer at an upper position of the pile by guiding the long guide bar to the center of the pile using the guide cone while the tip of the long guide bar is in contact with the guide cone; a third step of moving the vibro hammer downward from that state to insert the long guide bar and the short guide bar into the inside of the pile while straddling the chucking plate, thereby guiding the pair of left and right chucks to a position where they can clamp the chucking plate; A method for extracting piles using a vibro hammer is provided, which comprises a fourth step of clamping the chucking plate with a pair of left and right chucks of the vibro hammer, and then extracting the pile by moving it upward while applying vibration.

[0016] The invention of claim 4 enables efficient extraction work using the vibro hammer. Specifically, as a preliminary step, a chucking plate for clamping the pile with a pair of left and right chucks of the vibro hammer is provided at the center of the top end of the pile, a funnel-shaped guide cone that widens upward is provided around the periphery of the top end of the pile, a relatively long guide bar that extends vertically is provided on one side of the pair of left and right chucks of the vibro hammer, and a relatively short guide bar that extends vertically is provided on the other side of the chucks.

[0017] Then, the tip of the long guide bar of the vibro hammer is brought into contact with the guide cone of the pile (first step), and while the tip of the long guide bar is in contact with the guide cone, the long guide bar is guided by the guide cone to the center of the pile, thereby positioning the vibro hammer at the upper position of the pile (second step).

[0018] Next, from that state, the vibro hammer is moved downward, causing the long guide bar and short guide bar to be inserted into the inside of the pile while straddling the chucking plate, thereby guiding the pair of left and right chucks to a position where they can clamp the chucking plate (third step).After the chucking plate is clamped by the pair of left and right chucks of the vibro hammer, the pile is pulled out by moving it upward while applying vibration (fourth step). [Effects of the Invention]

[0019] As explained in detail above, according to the present invention, with regard to a vibro hammer used to drive pile anchors, steel sheet piles, foundation piles, etc. underwater for mooring offshore structures such as offshore wind power generation facilities, it is possible to drive piles, etc. in the correct position and orientation by controlling at least the rotational attitude (yaw) of the vibro hammer around the Z axis underwater, or preferably by controlling multiple degrees of freedom including the rotational attitude (yaw) around the Z axis out of the six degrees of freedom.

[0020] Furthermore, when a pile is extracted using a vibro hammer, the pile can be gripped securely using the vibro hammer, thereby enabling extraction work to be carried out efficiently. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is an overall view of a spar-type offshore wind power generation facility 1. [Figure 2] FIG. 2 is a diagram showing how to drive a pile anchor 7 using a vibro hammer 8. [Figure 3] This is an exploded view of the Vibro Hammer 8 (when hammering). [Figure 4] 1A and 1B show a vibro hammer 8 (during driving), in which (A) is a front view and (B) is a side view. [Figure 5] 10A and 10B are diagrams for explaining the degree of freedom of rotational attitude control and position control. [Figure 6] 4 is a control explanatory diagram according to a first embodiment of the vibro hammer 8. FIG. [Figure 7] 10 is a control explanatory diagram according to a second embodiment of the vibro hammer 8. FIG. [Figure 8] 10 is a control explanatory diagram according to a third embodiment of the vibro hammer 8. FIG. [Figure 9] FIG. 1 is a diagram showing a gyro thruster 16 that can rotate 360°. [Figure 10] 1A and 1B show a pile anchor 7, in which (A) is a side view and (B) is a view taken along the line BB. [Figure 11] 1A to 1C are diagrams showing how to lift a pile anchor 7 using a vibro hammer 8. [Figure 12] 1A to 1D are diagrams showing the procedure for driving a pile anchor 7 using a vibro hammer 8. [Figure 13] 1 is an exploded view of the vibro hammer 8 (when being pulled out). [Figure 14] 1A and 1B show a vibro hammer 8 (when being pulled out), in which (A) is a front view and (B) is a side view. [Figure 15] 1A to 1D are diagrams showing how a pile anchor 7 is gripped by a vibro hammer 8. [Figure 16]1 is a diagram showing how to extract a pile anchor 7 using a vibro hammer 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0023] [Spar-type offshore wind power generation facility 1] First, the spar-type offshore wind power generation facility 1 to be moored will be described in detail with reference to FIG.

[0024] The spar-type offshore wind power generation facility 1 comprises a spar-type float 2, a tower 3 connected to the top of the spar-type float 2, a nacelle 4 installed on the top of the tower 3, multiple blades extending from the nacelle 4, and a mooring rope 6, one end of which is connected to the spar-type float 2 and the other end of which is connected to a pile anchor 7 installed on the seabed, in order to hold the spar-type offshore wind power generation facility 1 in a fixed position on the sea.

[0025] The spar-type float 2 is a float that floats in an upright position like a fishing float, and a suitable float structure is that disclosed by one of the present applicants in Patent Publication No. 5274329, which comprises a lower concrete floating structure in which concrete precast cylindrical bodies are stacked vertically in multiple tiers and fastened together with PC steel to form a single unit, and an upper steel floating structure connected to the upper side of this lower concrete floating structure.

[0026] The tower 3 is made of steel, concrete or PRC (prestressed reinforced concrete), but it is preferable to use one made of steel so that the total weight is small.

[0027] As shown in Figure 1, it is desirable that the mooring point P of the mooring line 5 to the float 4 be set below the sea surface and higher than the center of gravity G of the float 4. This makes it possible to prevent the ship from coming into contact with the mooring line 5. Also, since a resistance moment is generated around the center of gravity G of the float 4 at the mooring point P to prevent the float 2 from tipping over too much, the tilting posture of the tower 3 can be maintained appropriately.

[0028] The nacelle 4 is a device equipped with a generator that converts the rotation of the blades 5, 5 . . . into electricity, a controller that can automatically change the angle of the blades 7, and the like.

[0029] The pile anchor 7 is a type of anchor in which a connecting part for a mooring rope 6 is provided on the side of a steel pile, and as shown in Figure 2, the pile anchor 7 is vibrated in the up and down direction by a vibro hammer 8 suspended by a crane work barge 30, which causes the pile anchor 7 to sink under its own weight while destroying and fluidizing the seabed sediment, and the pile is installed by driving it into the seabed while the vibration reduces the friction between the pile and the seabed sediment, which increases as the pile is driven in.

[0030] In the example shown in Figure 3, the vibro hammer 8 used to drive the pile anchor 7 is a device composed of, from the top down, a load cell 9, a shock absorber 10, a weight device 11, and a vibro hammer main body 12. Ordinary vibro hammers are mainly constructed by combining a shock absorber to prevent the transmission of vibrations with the vibro hammer main body, but because the driving work will be done underwater, it is preferable to use one that is combined with a weight device 11 to apply a downward load to the pile anchor 7. It should be noted that the load cell 9 and weight device 11 can be omitted as desired.

[0031] The vibro hammer body 12 is equipped with a pair of eccentric weights, one on the left and one on the right, and a vibration exciter 13 that generates a force (excitation force) in the vertical direction by rotating these weights in the same phase in opposite directions, as well as a gripping device 14 (having a pair of chucks 14a, 14b on the left and right) that grips the pile on the lower side. By sealing high-pressure inert gas in the space where the eccentric weights of the vibro hammer body 12 are arranged, it is possible to drive and pull out the pile without buckling failure even in a high-pressure environment with a water depth of more than 100m.

[0032] The vibro hammer body 12 is connected to the weight device 11 so that it can rotate at least 90° from the hanging state, and as will be described later, by lifting the vibro hammer body 12 with a lifting tool 22 and turning it sideways at an angle of 90°, it is possible to face the gripping device 14 (having a pair of chucks 14a, 14b on the left and right) of the vibro hammer body 12 sideways.

[0033] Figure 4 shows the vibro hammer 8 in an assembled state. The vibro hammer 8 according to the present invention is provided with a pair of left and right thrusters 15, 15 on its sides in order to control at least the rotational attitude (yaw) around the Z axis. Thrusters are essentially propulsion devices that enable ship maneuvering, such as turning and moving laterally when approaching or leaving a berth, azimuth control, and maintaining a fixed position. Structurally, it is a device with a rotating propeller inside a cylindrical body (pod).

[0034] In the vibro hammer 8 according to the present invention, the thrusters 15 are used for controlling the rotational attitude and position of the vibro hammer 8. The arrangement of the thrusters 15 and their control will be described in detail below.

[0035] First, rotational attitude control and position control involve movement control with up to six degrees of freedom, as shown in Figure 5. Specifically, the six degrees of freedom to be controlled are rotational attitude around the Z axis (yaw), movement in the Z axis direction (heave), rotational attitude around the Y axis (roll), movement in the Y axis direction (surge), rotational attitude around the X axis (pitch), and movement in the X axis direction (sway).

[0036] The first embodiment shown in Fig. 6 is an embodiment in which only the rotational attitude (yaw) around the Z axis is controlled. As shown in the figure, thrusters 15 (A, B) are arranged on both sides of the vibro hammer 8. By rotating these left and right pair of thrusters AB in opposite directions, it becomes possible to control the rotational attitude (yaw) of the vibro hammer 8 around the Z axis.

[0037] The second embodiment shown in Fig. 7 is designed to control all six degrees of freedom. Thrusters 15A, 15B are arranged in two upper and lower stages on each of the four sides of the vibro hammer 8. The upper stage thrusters 15A (reference symbols: A to D) are arranged so that the thrust is in the vertical direction, and the lower stage thrusters 15B (reference symbols: E to H) are arranged so that the thrust is in the horizontal direction. Note that these directions may be reversed.

[0038] As shown in the front view, heave control is possible by rotating the upper stage thrusters ABCD in the same direction. Yaw control is possible by rotating thrusters EFGH in the same direction. Also, as shown in the side view, roll control is possible by rotating thruster AC in the opposite direction, and pitch control is possible by rotating thruster BD in the opposite direction. Furthermore, as shown in the plan view, surge control is possible by rotating thrusters EG in the same direction, and sway control is possible by rotating thrusters HF in the same direction.

[0039] The third embodiment shown in Fig. 8 is an example using a slewing thruster 16 (also called an azimuth thruster 16) that can rotate 360°. As shown in Fig. 9, this azimuth thruster 16 is equipped with a propeller 16B on a cylindrical body (pod) 16A that rotates 360°, and by using this, it is possible to reduce the number of thrusters to be installed while enabling control with many degrees of freedom.

[0040] As shown in FIG. 8, simply placing one azimuth thruster 16 (reference numerals A to D) on each of the four sides of the vibrohammer 8 enables six-degree-of-freedom control. Specifically, as shown in the front view, yaw control is enabled by rotating azimuth thrusters A, B, C, and D in the same direction while the azimuth thrusters 16 are oriented vertically to exert thrust in the horizontal direction. As shown in the side view (1), surge control is enabled by rotating azimuth thrusters A, B, and C in the same direction, and sway control is enabled by rotating azimuth thrusters B, B, and C in the same direction. As shown in the side view (2), roll control is enabled by rotating azimuth thrusters A, B, and C in the opposite direction while the azimuth thrusters 16 are oriented horizontally to exert thrust in the vertical direction, and pitch control is enabled by rotating azimuth thrusters B, B, and C in the opposite direction. Heave control is also enabled by rotating azimuth thrusters A, B, C, and C in the same direction.

[0041] In the second and third embodiments described above, all six degrees of freedom can be controlled, but it is also possible to control any number of the six degrees of freedom, including at least the rotational attitude (yaw) around the Z axis.

[0042] [How to install pile anchor 7] Next, a method for driving the pile anchor 7 using the vibro hammer 8 will be described.

[0043] As shown in Figure 10, the pile anchor 7 has a chucking plate 18 at the center of the top end of the pile 17 for clamping with a pair of left and right chucks 14a, 14b of the vibro hammer 8, and a funnel-shaped guide cone 19 that widens upward around the top edge of the pile 17. In the illustrated example, a pair of fan-shaped guide cones 19A, 19B are provided on the left and right. The funnel-shaped guide cone 19 may also have an inverted cone shape that extends around the entire circumference. A pad eye 21 for connecting the mooring rope 6 is provided on the side of the pile 17. Since a greater holding force can be expected mathematically when the connection point of the mooring rope 6 is located underground rather than at the pile head, the pad eye 21 is located below the seabed.

[0044] In addition, an auxiliary lifting piece 20 is provided on the side of the upper end of the pile 17 to allow it to be lifted up with a crane in case it becomes impossible to remove it with the vibro hammer 8.

[0045] The procedure for lifting the pile anchor 7 with the vibro hammer 8 is as follows: first, the pile anchor 7 is placed horizontally, as shown in Figure 11. With the vibro hammer 8 suspended by a crane, a lifting tool 22 such as a lever block (registered trademark) is provided between the weight device 11 and the vibro hammer main body 12, and the vibro hammer main body 12 is lifted up to a 90° horizontal position. With the gripping device 14 (having a pair of left and right chucks 14a, 14b) of the vibro hammer main body 12 in the horizontal position, it is brought close to the pile anchor 7 and the chucking plate 18 of the pile anchor 7 is gripped by the gripping device 14, and the vibro hammer 8 is then moved upward to hold the pile anchor 7 in a suspended state.

[0046] Then, as shown in Figure 12, once the vibro hammer 8 holding the pile anchor 7 is lowered into the water (Figure 12(A)), the rotational attitude and position of the vibro hammer 8 are controlled to guide it to the correct installation location and make it land on the seabed (Figure 12(B)). Once the pile anchor 7 has landed on the seabed, the vibro hammer 8 is operated to gradually drive it into the seabed (Figures 12(C)(D)).

[0047] It is desirable that the mooring rope 6 be connected to the pile anchor 7 in advance on the deck of the work boat or in shallow water, and that the mooring rope 6 be held in a suspended state by a winch or auxiliary crane on the work boat so that no unnecessary load is placed on the pile anchor 7. Also, a hydraulic pump unit (not shown) for driving the vibro hammer 8 can be installed on the work boat and hydraulic oil can be supplied from there, or a hydraulic pump unit (not shown) can be installed in advance on the seabed and hydraulic oil can be supplied from there.

[0048] [Pile anchor 7 removal procedure] Next, a method for extracting the pile anchor 7 using the vibro hammer 8 will be described.

[0049] First, the configuration of the vibro hammer 8 for extracting the pile anchor 7 will be described. As shown in Figures 13 and 14, the configuration of the vibro hammer 8 during extraction is a device comprising, from top to bottom, a load cell 9, a shock absorber 10, and a vibro hammer main body 12. That is, since there is no need to apply a load in the direction of gravity during extraction, the weight device 11 is removed. Also, as shown in Figure 14, in order to guide the pair of left and right chucks 14a, 14b of the gripping device 14 to a position where they can grip the chucking plate 18 of the pile anchor 7, a relatively long guide bar 23a extending vertically is provided on one side 14a of the chuck, and a relatively short guide bar 23b extending vertically is provided on the other side 14b of the chuck.

[0050] The pile anchor 7 is extracted by the vibrohammer 8 in the following procedure of first to fourth steps, as shown in FIGS.

[0051] (1st step) As shown in Figure 15(A), the vibro hammer 8 suspended by a crane is moved to the position of the pile anchor 7 by performing rotational attitude control and position control using the thrusters 15, 16 described above. Next, as shown in Figure 15(B), the tip of the long guide bar 23a of the vibro hammer 8 is brought into contact with the guide cone 19A of the pile anchor 7.

[0052] (Second step) As shown in Figure 15(C), with the tip of the long guide bar 23a abutting against the guide cone 19A, the long guide bar 23a is guided by the guide cone 19A to the center of the pile 17, thereby positioning the vibro hammer 8 at the upper position of the pile anchor 7.

[0053] (Third Step) From this state, as shown in Figure 15 (D), by moving the vibro hammer 8 downward, the long guide bar 23a and the short guide bar 23b are inserted into the inside of the pile 17 while straddling the chucking plate 18, thereby guiding the pair of left and right chucks 14a, 14b to a position where they can clamp the chucking plate 18.

[0054] (Step 4) As shown in Figure 16, the chucking plate 18 is clamped between a pair of left and right chucks 14a, 14b of the vibro hammer 8, and then the pile anchor 7 is pulled out by moving it upward while applying vibration.

[0055] [Other examples] (1) In the above embodiment, an offshore wind power generation facility 1 is shown as an example of an offshore structure, but the vibro hammer 8 according to the present invention can also be suitably used for driving and pulling out pile anchors for mooring other offshore structures, such as buoys and floating water bases.

[0056] (2) In the above embodiment, pile anchors for mooring the offshore wind power generation facility 1 have been used as an example for explanation. However, the vibro hammer of the present invention can also be used to drive steel sheet piles, underwater foundation piles for supporting superstructures, and the like, in addition to pile anchors. [Explanation of symbols]

[0057] 1...Spar-type offshore wind power generation facility, 2...Spar-type floating body, 3...Tower, 4...Nacelle, 5...Blade, 6...Mooring line, 7...Pile anchor, 8...Vibro hammer, 9...Load cell, 10...Shock absorber, 11...Weight device, 12...Vibro hammer body, 13...Vibrator, 14...Gripping device (chucks 14a, 14b), 15...Thruster, 16...Azimuth thruster (swivel-type thruster capable of 360° rotation), 17...Pile, 18...Chucking plate, 19A, 19B...Guide cone, 20...Auxiliary lifting piece, 21...Pad eye, 22...Lifting tool, 23a...Long guide bar, 23b...Short guide bar

Claims

1. A vibro hammer for use underwater, The vibro hammer is characterized in that the vibro hammer is provided with a thruster for controlling the rotational attitude (yaw) around at least the Z axis.

2. 2. A vibrohammer according to claim 1, further comprising thrusters for controlling a plurality of degrees of freedom including at least the rotational attitude about the Z axis (yaw) out of six degrees of freedom: rotational attitude about the Z axis (yaw), movement in the Z axis direction (heave), rotational attitude about the Y axis (roll), movement in the Y axis direction (surge), rotational attitude about the X axis (pitch), and movement in the X axis direction (sway).

3. 3. The vibro hammer according to claim 2, wherein the thruster is a rotary thruster that can rotate 360 ​​degrees.

4. A method for extracting a pile driven into the bottom of a body of water using the vibro hammer according to any one of claims 1 to 3, The pile is provided with a chucking plate at the center of the upper end of the pile to be clamped by a pair of left and right chucks of the vibro hammer, and a funnel-shaped guide cone that widens upward is provided on the periphery of the upper end of the pile, a relatively long guide bar extending in the vertical direction is provided on one side of a pair of left and right chucks of the vibro hammer, and a relatively short guide bar extending in the vertical direction is provided on the other side of the chucks, a first step of bringing a tip of the long guide bar of the vibro hammer into contact with a guide cone of a pile; a second step of positioning the vibro hammer at an upper position of the pile by guiding the long guide bar to the center of the pile using the guide cone while the tip of the long guide bar is in contact with the guide cone; a third step of moving the vibro hammer downward from that state to insert the long guide bar and the short guide bar into the inside of the pile while straddling the chucking plate, thereby guiding the pair of left and right chucks to a position where they can clamp the chucking plate; and a fourth step of clamping the chucking plate with a pair of left and right chucks of the vibro hammer and then moving it upward while applying vibration to extract the pile.

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