Steel pipe pile cutting device and steel pipe pile cutting method

Abstract

To provide a steel pipe pile cutting device and a steel pipe pile cutting method which can cut a steel pipe pile with a variable inner diameter at a predetermined depth position.SOLUTION: A pile 2 is cut by a steel pipe pile cutting device 3 which has a main shaft 4 inserted inside a pile 2, an arm 5 for fixation which is provided at the lower part of the main shaft 4 and is stretchable in a radial direction of the pile 2, an arm 6 for a cutting machine which is provided at a lower part of the main shaft 4, and a cutting machine 7 provided at the tip of the arm 6 for the cutting machine. The arm 6 for the cutting machine is stretchable in the radial direction of the pile 2, and is rotatable around the main shaft 4. The cutting machine 7 can jet high pressure water toward the inner surface of the pile 2.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a steel pipe pile cutting device and a steel pipe pile cutting method for removing a steel pipe pile installed in a water bottom ground. [Background technology]

[0002] Demand for renewable energy is increasing with the aim of reducing greenhouse gas emissions. Renewable energy sources include, for example, solar power generation, wind power generation, hydroelectric power generation, geothermal power generation, and biomass power generation. Wind power generation facilities are often installed in mountainous areas far from residential areas because noise and vibrations from wind turbines can affect the living environment and the impact on living space, etc. must be fully considered. However, it is difficult to secure land for installing large wind turbines in mountainous areas, and it is also difficult to secure a traffic route to the wind power generation facility and install a power transmission line, etc. For this reason, installation of wind power generation facilities on the sea (on the water) is being considered. As a fixed-bottom foundation structure for a floating wind power generation facility, for example, there is one that is supported by a single steel pipe pile driven into the bottom of the water. The steel pipe pile for a floating wind power generation facility is generally a large-diameter steel pipe, and the diameter of the upper end of the steel pipe pile is approximately the same as the base of the tower that supports the wind turbine.

[0003] Offshore wind power generation facilities must be removed after a certain period of time (for example, 20 years after installation). When removing the fixed-bottom foundations of an offshore wind power generation facility, the steel pipe piles must be cut and removed at a depth of 1.0m below the water bottom ground surface ("Guidelines for the Operation of the Public Bidding System for Occupancy in General Sea Areas," June 2019, Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry, Ports and Harbors Bureau, Ministry of Land, Infrastructure, Transport and Tourism). Patent Document 1 discloses a method for removing a pile foundation installed on the bottom of the water, in which a casing is inserted into a steel pipe pile, and a holding means provided on the outer periphery of the casing is pressed against the inner surface of the surrounding wall of the steel pipe pile, and the steel pipe is cut with a plasma torch on a turntable provided on the casing. Furthermore, Patent Document 2 discloses a method for removing steel pipe piles from an above-water structure, in which multiple small holes connecting the inside and outside of the steel pipe pile are formed, a blocking cap is attached to the head of the steel pipe pile, and compressed air is supplied into the inside of the steel pipe pile, causing the compressed air to spray out of the small holes while the steel pipe pile is pulled out. The steel pipe pile removal method of Patent Document 1 requires inserting a casing into the steel pipe pile whose diameter has been reduced at the pile head, which results in a large gap between the inner wall surface of the steel pipe pile and the casing at the cut point, making it impossible to fix the casing in a desired position. As a result, the steel pipe pile cannot be cut stably. Furthermore, the method of removing steel pipe piles in Patent Document 2 involves pulling out the steel pipe piles, which requires the long steel pipe piles to be pulled up to a specified length and then cut multiple times, making the work time-consuming. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 03-228917 [Patent Document 2] JP 2016-199874 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a steel pipe pile cutting device and a steel pipe pile cutting method that are capable of cutting steel pipe piles whose inner diameters vary at a predetermined depth position. [Means for solving the problem]

[0006] The steel pipe pile cutting device of the present invention for solving the above problem includes a main shaft inserted into the steel pipe pile, a fixing arm provided at the bottom of the main shaft and capable of expanding and contracting in the diametrical direction of the steel pipe pile, a cutter arm provided at the bottom of the main shaft, and a cutter provided at the tip of the cutter arm. The cutter arm is capable of expanding and contracting in the diametrical direction of the steel pipe pile and is rotatable around the main shaft,At the tip of the fixing arm, a vertical movement guide roller that rolls vertically along the inner surface of the steel pipe pile and an outrigger that can be advanced from the tip of the fixing arm are provided, The cutting machine is capable of spraying high-pressure water toward the inner surface of the steel pipe pile. In addition, the steel pipe pile cutting method of the present invention, which uses the steel pipe pile cutting device to cut a steel pipe pile installed in a water bottom ground, includes an excavation process of excavating inside the steel pipe pile and excavating the outer periphery of the head of the steel pipe pile from the water bottom ground surface, a cutting machine insertion process of lowering the main shaft from the upper end of the steel pipe pile to insert the cutting machine into the steel pipe pile and extending the fixing arm to abut the fixing arm against the inner surface of the steel pipe pile, a cutting process of cutting the steel pipe pile by spraying high-pressure water from the cutting machine while rotating the cutting machine inside the steel pipe pile, and a backfilling process of backfilling the outer periphery of the steel pipe pile.

[0007] According to the steel pipe pile cutting device and method, by extending and retracting the fixing arm, the main shaft can be stabilized even in the steel pipe pile whose inside diameter changes, and the cutter arm can be rotated stably at a desired position. Therefore, the steel pipe pile can be cut stably and efficiently by the cutter.

[0008] Also A vertical movement guide roller that rolls vertically along the inner surface of the steel pipe pile is provided at the tip of the fixing arm. To When the cutting machine is lowered together with the main shaft into the steel pipe pile, the vibration of the main shaft is suppressed and the main shaft can be positioned at the center of the steel pipe pile. In addition, If a rotation guide roller that rolls circumferentially around the steel pipe pile along the inner surface of the steel pipe pile is provided at the tip of the cutting machine arm, the rotation of the cutting machine arm is stabilized and shaking is suppressed, allowing the steel pipe pile to be cut efficiently by the cutting machine. It is also preferable that the pile pile further includes a pile periphery fixing means fixed to the outer surface of the head of the steel pipe pile, and a plurality of support members that secure a bearing force from the bottom ground, support the pile periphery fixing means, and are extendable and contractible by a jack. In this case, the cutting status of the steel pipe pile can be confirmed by the jack pressure of the jack in the cutting step. That is, the cutting progress status can be confirmed by detecting the change in the jack pressure of each of the plurality of support members arranged around the steel pipe pile. Effect of the Invention

[0009] According to the steel pipe pile cutting device and steel pipe pile cutting method of the present invention, it is possible to cut a steel pipe pile whose inside diameter changes at a predetermined depth position. [Brief description of the drawings]

[0010] [Figure 1] 1 is a front view showing an embodiment of the water facility of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a steel pipe pile cutting device. [Diagram 3] 1A and 1B are diagrams showing the lower part of a steel pipe pile cutting device, in which (a) is a cross-sectional view and (b) is a plan view. [Figure 4] 1A and 1B are diagrams showing the fixing arm, in which (a) shows the outrigger retracted and (b) shows the outrigger extended. [Diagram 5] 4 is a flowchart showing a method for cutting a steel pipe pile according to the present embodiment. [Figure 6] FIG. 1 is a front view showing each step of a method for cutting a steel pipe pile, where (a) is a preparation step, (b) is an excavation step, (c) is an excavation step following (b), (d) is a support step, a cutting machine insertion step and a cutting step, (e) is a removal step, and (f) is a backfilling step. [Figure 7] 1A and 1B are diagrams showing a support means, in which (a) is a front view and (b) is a plan view. [Figure 8] FIG. 4 is a cross-sectional view showing an installation state of a cutting machine. [Figure 9] 10A and 10B are diagrams showing a method for checking the cutting state according to another embodiment, in which (a) is an overall view and (b) is an enlarged sectional view. [Figure 10] 13A and 13B are side views showing a method for checking the cutting state according to another embodiment. [Figure 11] 11A and 11B are cross-sectional views showing a method for checking the cutting state according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In this embodiment, a case will be described where a foundation structure 13 (pile 2) of an offshore wind power generation facility (floating facility) 1 is removed. FIG. 1 is a front view of the offshore wind power generation facility 1. As shown in FIG. 1, the offshore wind power generation facility 1 has a wind turbine 11, a pillar 12 supporting the wind turbine 11, and a foundation structure 13 supporting the pillar 12. The wind turbine 11 and the pillar 12 are provided at a position higher than the water surface WL by the foundation structure 13. The wind turbine 11 is provided rotatably on the upper end of the pillar 12. The pillar 12 is erected on the foundation structure 13. The foundation structure 13 is a so-called monopile foundation consisting of one steel pipe pile (pile 2) erected from the waterbed ground G. The pile 2 is installed vertically directly below the support pillar 12 of the offshore wind power generation facility 1. The pile 2 is erected in the waterbed ground G with sufficient embedment. The pile 2 in this embodiment is made of a steel pipe. The central axis of the pile 2 coincides with an extension of the central axis of the support pillar 12 of the offshore wind power generation facility 1. The pile 2 has a larger diameter than the support pillar 12, and the upper end of the pile 2 is tapered to match the diameter of the lower end of the support pillar 12. In other words, the inner diameter of the upper end of the pile 2 changes so that it becomes smaller as it goes up.

[0012] The foundation structure 13 (piles 2) is removed by cutting the piles 2 at a depth 1.0 m below the water bottom ground surface after removing the wind turbine 11 and the support columns 12. A steel pipe pile cutting device 3 is used to cut the piles 2. The steel pipe pile cutting device 3 is shown in Figure 2. As shown in FIG. 2, the steel pipe pile cutting device 3 includes a main shaft 4, a fixing arm 5, a cutting machine arm 6, and a cutting machine 7. The main shaft 4 is a rod-shaped member that is inserted inside the pile 2. The main shaft 4 is inserted inside the pile 2 while being suspended by a lifting machine such as a crane ship. The main shaft 4 is inserted into the center of the pedestal 41 and is supported by the pedestal 41, thereby suppressing lateral shaking.

[0013] 3(a) and (b) show the lower end of the steel pipe pile cutting device 3. As shown in Fig. 3(a), the fixing arm 5 is provided at the lower end (lower part) of the main shaft 4. In this embodiment, as shown in Fig. 3(b), three fixing arms 5, 5, 5 are provided at equal intervals in the circumferential direction. The fixing arms 5 are extendable in the diameter direction of the pile 2 in response to changes in the inner diameter of the pile 2. The fixing arms 5 in this embodiment extend and retract by approximately 1.5 m. The fixing arms 5 extend and retract in synchronization. In other words, the three fixing arms 5, 5, 5 are configured to always have the same length.

[0014] As shown in Figures 3(a) and (b), the tip of the fixing arm 5 is provided with a vertical movement guide roller 51 that rolls vertically along the inner surface of the pile 2, and an outrigger 52 that is arranged to be able to advance from the tip of the fixing arm 5. 4(a) and (b) show the tip of the fixing arm 5. As shown in FIG. 4(a) and (b), a pair of vertical movement guide rollers 51, 51 are provided on both side surfaces of the tip of each fixing arm 5 so as to be rotatable about a horizontal axis. That is, the vertical movement guide rollers 51 are provided so as to run on the inner surface of the pile 2 when the main shaft 4 is moved up and down inside the pile 2. By running each vertical movement guide roller 51 on the inner surface of the pile 2, the position of the main shaft 4 is prevented from deviating from the center of the pile 2. The outrigger 52 is provided at the tip of the fixing arm 5 so as to protrude from between the pair of vertical movement guide rollers 51, 51 toward the inner surface of the pile 2. When the main shaft 4 is moved, the outrigger 52 is stored in the fixing arm 5, and when the main shaft 4 is placed at a predetermined position, the outrigger 52 advances from the tip of the fixing arm 5 toward the inner surface of the pile 2 and abuts against the inner surface of the pile 2, thereby fixing the fixing arm 5 (main shaft 4). The outriggers 52 provided on each fixing arm 5 are configured to extend and retract synchronously and extend by the same length.

[0015] The cutter arm 6 is a member that supports the cutter 7, and is provided on the fixing arm 5 below the main shaft 4, as shown in FIG. 3(a). The cutter arm 6 is extendable in the diametric direction of the pile 2 in response to changes in the inner diameter of the pile 2, and is rotatable about the main shaft 4. The cutter arm 6 of this embodiment extends and retracts by approximately 1.5 m. As shown in FIG. 3(b), in this embodiment, a pair of cutter arms 6, 6 are provided so as to be aligned in a straight line with the main shaft 4 in between. The pair of cutter arms 6, 6 extend and retract in synchronization. That is, the lengths of both cutter arms 6, 6 are configured to always be the same. As shown in FIG. 3(a), the cutting machine arm 6 of this embodiment is provided so as to protrude laterally from the lower end of a cylindrical body 61 fitted on the main shaft 4. The cylindrical body 61 has an inner diameter larger than the outer diameter of the main shaft 4. The upper end of the cylindrical body 61 is supported by a rotary motor 62 fixed to the main shaft 4. When the rotary motor 62 is operated, the cylindrical body 61 rotates around the main shaft 4, and the cutting machine arm 6 rotates in conjunction with the rotation of the cylindrical body 61. In this embodiment, a reinforcing member (diagonal member) 63 is disposed at the corner between the cutting machine arm 6 and the cylindrical body 61, thereby increasing the rigidity of the joint between the cutting machine arm 6 and the cylindrical body 61.

[0016] As shown in Fig. 3(a), in this embodiment, a sliding plate 64 is interposed between the fixing arm 5 and the cutting machine arm 6. The sliding plate 64 is made of a low-friction plate material and reduces the frictional force with the cutting machine arm 6. By interposing the sliding plate 64 between the fixing arm 5 and the cutting machine arm 6, the resistance during rotation of the cutting machine arm 34 is reduced. As shown in Fig. 3(b), a rotation guide roller 65 that rolls in the circumferential direction of the pile 2 along the inner surface of the pile 2 is provided at the tip of the cutting machine arm 6. The rotation guide roller 65 runs along the inner surface of the pile 2 when the cutting machine arm 6 is rotated, thereby suppressing vibration of the cutting machine arm 6 (cutting machine 7).

[0017] 3(a) and (b), the cutting machine 7 is provided (mounted) at the tip of the cutting machine arm 6. The cutting machine 7 has a nozzle 71 that sprays high-pressure water containing an abrasive toward the inner surface of the pile 2. The steel pipe pile cutting device 3 cuts the pile 2 by spraying high-pressure water from the cutting machine 7 (nozzle 71) as the cutting machine arm 6 rotates.

[0018] The following describes a method for cutting a steel pipe pile using the steel pipe pile cutting device 3. Figure 5 shows the steps of the method for cutting a steel pipe pile of this embodiment. Figures 6(a) to (f) show the working status of each process. As shown in Figure 5, the pile cutting method of this embodiment comprises a preparation process S1, an excavation process S2, a support process S3, a cutting machine insertion process S4, a cutting process S5, a removal process S6, and a backfilling process S7. In the preparation process S1, the offshore wind power facility 1 (wind turbines 11 and pillars 12) is removed, leaving behind the foundation structure 13 (piles 2). Figure 6(a) shows the foundation structure 13 (piles 2) after the wind turbines 11 and pillars 12 have been removed. The upper ends of the piles 2 are left protruding above the water surface WL.

[0019] In the excavation process S2, the periphery of the pile 2 is excavated 1 m or more from the water bottom ground surface GL. First, as shown in Fig. 6(b), the scouring prevention works 14 installed on the water bottom ground surface GL around the periphery of the pile 2 are removed. Next, as shown in Fig. 6(c), the periphery of the pile 2 is excavated 1 m or more to form a recess 21 around the pile 2 and excavate the soil and sand accumulated inside the pile 2.

[0020] In the supporting step S3, as shown in Fig. 6(d), the head of the pile 2 is supported by a supporting means 8. The supporting means 8 includes a plurality of supporting members (pillars) 81, 81 that secure a bearing capacity from the water bottom ground G, and a pile periphery fixing means 82 fixed to the outer surface of the head of the pile 2. The supporting means 8 is shown in Figs. 7(a) and (b). A plurality of support members 81, 81 are arranged around the pile 2 as shown in Figs. 7(a) and (b). The upper end of the support member 81 is connected to the pile periphery fixing means 82 via a jack 83. The support member 81 can be extended and retracted by the jack 83. The jack 83 is configured to be able to measure the jack pressure. In this embodiment, six support members 81, 81, ... (jacks 83, 83, ...) are arranged at equal intervals. The pile periphery fixing means 82 is made of steel and is fixed to the head of the pile 2, and is supported from below by the support member 81. In addition, at the lower end of the support member 81, as shown in Fig. 6(d), a foundation body (spread foundation) 84 having an area capable of securing sufficient bearing capacity from the water bottom ground surface GL is formed. The support means 8 applies a load to the support member 81 by applying pressure to the jack 83, and secures bearing capacity from the water bottom ground G in advance (absorbs ground subsidence in advance).

[0021] In the cutting machine insertion step S4, the cutting machine 7 is inserted into the pile 2. FIG. 8 shows the state of insertion of the cutting machine 7. The cutting machine 7 is inserted into the pile 2 by lowering the main shaft 4 suspended by the lifting machine from the upper end of the pile 2. When the main shaft 4 (fixing arm 5) is inserted into the pile 2, the fixing arm 5 and the cutting machine arm 6 are contracted as shown in FIG. 8. The main shaft 4 is lowered, and when the fixing arm 5 and the cutting machine arm 6 pass through the head of the pile 2 and reach the general part of the pile 2 (the part with an expanded inner diameter), the fixing arm 5 is extended according to the inner diameter of the pile 2. Then, the main shaft 4 is further lowered while the vertical movement guide roller 51 provided at the tip of the fixing arm 5 is rotated along the inner surface of the pile 2. In this way, the main shaft 4 can be maintained in a state of being disposed at the center of the pile 2. The lower end of the main shaft 4 is disposed at the center of the pile 2 by the fixing arm 5. Moreover, by supporting the main shaft 4 by a pedestal 41 at the upper end of the pile 2, the main shaft 4 is arranged along the central axis of the pile 2. Note that the pedestal 41 is installed at the upper end of the pile 2 after the cutting machine arm 6 and the cutting machine 7 are stored inside the pile 2. After the cutting machine 7 (main shaft 4) is lowered to a predetermined position (the nozzle 71 is 1 m lower than the water bottom ground surface GL), the outrigger 52 of the fixing arm 5 is extended and brought into contact with the inner surface of the pile 2.

[0022] In the cutting process S5, the pile 2 is cut at a position -1 m below the water bottom ground surface. Specifically, first, the cutting machine arm 6 is extended until the rotation guide roller 65 abuts against the inner surface of the pile 2, and the cutting machine 7 is brought close to the inner surface of the pile 2. Next, the cutting machine 7 (cutting machine arm 6) is rotated 180 degrees while spraying high-pressure water containing an abrasive from the nozzle 71 of the cutting machine 7, thereby cutting the pile 2 over its entire circumference. In this embodiment, the cutting status of the pile 2 is confirmed by the jack pressure of the jacks 83 of the support member 81. That is, by confirming that the jack pressure of all the jacks 83 has become smaller than before the cutting started, it can be confirmed that the pile 2 has been cut over its entire circumference. If there is a variation in the jack pressure of the multiple jacks 83, it is determined that the cutting of the pile 2 is incomplete, and the cutting machine 7 is directed toward the jack 83 with the larger jack pressure, and high-pressure water is sprayed.

[0023] In the removal process S6, as shown in Fig. 6(e), the cut portion of the pile 2, the support means 8, and the cutting machine 7 are collected. That is, when it is confirmed that the entire circumference of the pile 2 has been cut, the spraying of high-pressure water is stopped, the support means 8 is removed from the pile 2, and the cut portion of the pile 2 is pulled up from the water using a lifting machine or the like. The cutting machine 7 is collected by retracting the outrigger 52 and then pulling up the spindle 4. In the backfilling step S7, as shown in FIG. 6(f), the outer periphery (recess 21) of the pile 2 is backfilled.

[0024] According to the steel pipe pile cutting device 3 and the steel pipe pile cutting method of this embodiment, the fixing arm 5 can be extended and retracted to stabilize the spindle 4 inside the pile 2 whose inside diameter changes, and the cutter arm 6 can be rotated stably at a desired position. This makes it possible to cut the pile 2 by the cutter 7 stably and efficiently. In addition, a vertical movement guide roller 51 that rolls vertically along the inner surface of the pile 2 is provided at the tip of the fixing arm 5, so that when the cutting machine 7 is lowered together with the main shaft 4, the vibration of the main shaft 4 is suppressed and the main shaft 4 can be positioned at the center of the pile 2. In addition, since a rotation guide roller 65 is provided at the tip of the cutting machine arm 6, the rotation of the cutting machine arm 6 is stabilized and shaking is suppressed. Therefore, shaking of the rotation of the cutting machine 7 is also suppressed, and cutting of the pile 2 can be performed efficiently. In addition, since the progress of cutting of the pile 2 can be checked by the jack pressure of the jack 83, the efficiency of the work can be improved.

[0025] 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. For example, the floating facility supported by the piles 2 is not limited to an offshore wind power generation facility. Furthermore, the vertical movement guide roller 51 and the rotation guide roller 65 may be provided as necessary. Moreover, the base provided at the upper end of the pile 2 may be provided as necessary, and may be omitted. The configuration of the support means 8 of the pile 2 is not limited. In the above embodiment, the cutting arm 6 is provided above the fixing arm 5. However, the cutting arm 6 may be provided below the fixing arm 5. Further, the location where the rotation motor 62 is installed is not limited, and it may be installed above the pile 2, for example. By rotating the main shaft 4, the cutter arm 6 may be rotated.

[0026] Furthermore, the method of checking the cutting status of the pile 2 is not limited to that shown in the above embodiment. For example, as shown in Figures 9(a) and (b), while the pile 2 is suspended by a crane, the inside of the pile 2 may be illuminated with a light 91, and the uncut portion may be found by checking for light leakage from the periphery of the pile 2. As a method of checking for light leakage from the periphery of the pile 2, for example, an underwater camera 92 may be used. As another method of confirming the cutting status, as shown in Figure 10, strip-shaped electrical conductivity sensors 93, 93, ... are installed around the cut portion of the pile 2, and after the pile 2 is cut, the portion where electrical conductivity is confirmed by the electrical conductivity sensors 93 is treated as an uncut portion of the pile 2 and is cut again, and the cutting is determined to be complete in the portion where electrical conductivity is not confirmed by the electrical conductivity sensors 93. Furthermore, as another method for checking the cutting status, as shown in FIG. 11, a laser sensor 94 or an ultrasonic sensor may be placed adjacent to the cutting machine 7, and the injection position of the nozzle 71 may be measured by the laser sensor 94 to check the completion of cutting at that position. [Explanation of symbols]

[0027] 1. Offshore wind power generation facilities (floating facilities) 2 piles (steel pipe piles) 3 Steel pipe pile cutting device 4 spindle 5 Fixing arm 51 Vertical guide roller 52 Outrigger 6 Cutting machine arm 65 Rotating guide roller 7 cutting machine 8 Support means 81 Support member 82 Pile outer circumference fixing means 83 Jack

Claims

1. A steel pipe pile cutting device for cutting steel pipe piles installed on the bottom of the water, A main shaft inserted into the steel pipe pile; A fixing arm provided at the lower part of the main shaft and capable of expanding and contracting in the diameter direction of the steel pipe pile; a cutting machine arm provided under the main shaft; A cutting machine provided at a tip of the cutting machine arm, The cutting machine arm is extendable in the diameter direction of the steel pipe pile and rotatable around the main shaft, At the tip of the fixing arm, a vertical movement guide roller that rolls vertically along the inner surface of the steel pipe pile and an outrigger that can be advanced from the tip of the fixing arm are provided, The steel pipe pile cutting device is characterized in that the cutting machine is capable of spraying high-pressure water toward the inner surface of the steel pipe pile.

2. A steel pipe pile cutting device as described in claim 1, characterized in that a rotating guide roller which rolls circumferentially around the steel pipe pile along the inner surface of the steel pipe pile is provided at the tip of the cutting machine arm.

3. A pile outer periphery fixing means fixed to the outer surface of the head of the steel pipe pile; and a plurality of support members for securing a bearing force from the bottom ground and supporting the pile outer periphery fixing means. The steel pipe pile cutting device according to claim 1 or 2, characterized in that the support member is extendable and retractable by a jack.

4. A steel pipe pile cutting method for cutting a steel pipe pile installed on a bottom ground using the steel pipe pile cutting device described in any one of claims 1 to 3, An excavation process of excavating the inside of the steel pipe pile and excavating the outer periphery of the steel pipe pile 1 m or more from the water bottom ground surface; A cutting machine insertion process in which the main shaft is lowered from the upper end of the steel pipe pile to insert the cutting machine into the steel pipe pile and the fixing arm is extended to bring the fixing arm into contact with the inner surface of the steel pipe pile; A cutting process of cutting the steel pipe pile by spraying high-pressure water from the cutting machine while rotating the cutting machine within the steel pipe pile; A backfilling process for backfilling the outer periphery of the steel pipe pile.

5. A method for cutting a steel pipe pile installed on a bottom of water using a steel pipe pile cutting device, The steel pipe pile cutting device is A main shaft inserted into the steel pipe pile; A fixing arm provided at the lower part of the main shaft and capable of expanding and contracting in the diameter direction of the steel pipe pile; a cutting machine arm provided under the main shaft; A cutting machine provided at a tip of the cutting machine arm, The cutting machine arm is extendable in the diameter direction of the steel pipe pile and rotatable around the main shaft, The cutting machine is capable of spraying high-pressure water toward the inner surface of the steel pipe pile, An excavation process of excavating the inside of the steel pipe pile and excavating the outer periphery of the steel pipe pile 1 m or more from the water bottom ground surface; A cutting machine insertion process in which the main shaft is lowered from the upper end of the steel pipe pile to insert the cutting machine into the steel pipe pile and the fixing arm is extended to bring the fixing arm into contact with the inner surface of the steel pipe pile; A supporting process in which a pile outer periphery fixing means is fixed to the outer surface of the head of the steel pipe pile, and a plurality of support members having a bearing capacity from the bottom ground are arranged around the steel pipe pile; A cutting process of cutting the steel pipe pile by spraying high-pressure water from the cutting machine while rotating the cutting machine within the steel pipe pile; A backfilling process for backfilling the outer periphery of the steel pipe pile, The support member is extendable and retractable by a jack. A steel pipe pile cutting method, characterized in that in the cutting step, a cutting status of the steel pipe pile is confirmed by a jack pressure of the jack.

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