JP7732778B2 - Hollow steel pipe and method for extracting existing structure using the same - Google Patents

Description

The present invention relates to a hollow steel pipe and a method for extracting an existing structure using the pipe.

For example, when an existing structure standing on foundation piles is to be removed and a new structure constructed in its place, the disposal of the existing piles can be broadly classified into three categories: "direct use," "retention," and "removal." Of these, "removal" involves pulling out the existing piles and driving in new ones (see, for example, Patent Document 1).

As mentioned above, one method for uprooting and removing existing piles involves inserting a hollow steel pipe around the existing pile and then pulling it out. This separates the existing pile from the surrounding ground by separating it with a hollow steel pipe, essentially isolating the connection. This prevents the surrounding ground from collapsing when the existing pile is pulled out, and allows the removal work to be carried out more smoothly.

JP 2017-66721 A

However, if soil adheres to the inside of the hollow steel pipe, it may not be possible to fully achieve the intended effect of separating the edges.

The present invention aims to provide a hollow steel pipe that prevents soil from adhering to the inside of the hollow steel pipe, thereby fully maximizing the effectiveness of isolating existing structures buried in the ground, such as existing piles, from the surrounding ground, and a method for extracting existing structures using the hollow steel pipe.

One aspect of the present invention is a hollow steel pipe used to extract an existing structure buried in the ground, such as an existing pile, while it is contained within the hollow steel pipe, and to fill a backfill material into the hollow steel pipe after the existing structure has been extracted.
This hollow steel pipe has an adhesion prevention mechanism that scrapes off soil and backfill material that has adhered to the inner wall of the hollow steel pipe.

A hollow steel pipe with such an adhesion prevention mechanism can fully perform the following functions: (1) When the pile is pulled out, the soil between the hollow steel pipe and the pile is sufficiently loosened; (2) When backfill material is poured in, the soil is sufficiently loosened so that the soil remaining inside the hollow steel pipe does not act as a lid, preventing the backfill material from being inserted; and (3) When the hollow steel pipe is pulled out of the ground, the filled backfill material is sufficiently loosened so that it does not clog the casing, preventing the backfill material from being discharged along with the hollow steel pipe.

The adhesion prevention mechanism in the hollow steel pipe described above may also include a co-rotation prevention mechanism.

The co-rotation suppression mechanism for the hollow steel pipe described above may include an opening provided along the outer wall of the hollow steel pipe and a protrusion that passes through the opening from the inside to the outside of the hollow steel pipe.

The adhesion prevention mechanism for the hollow steel pipe described above may comprise an annular body provided inside the hollow steel pipe and a protruding body provided on the annular body and extending in the central axis direction of the hollow steel pipe, the opening being an elongated hole, and the annular body and the protruding body being rotatable relative to the hollow steel pipe along the elongated hole.

The adhesion prevention mechanism in the hollow steel pipe described above may include a protrusion provided on the inner wall of the hollow steel pipe.

The protrusions of the hollow steel pipes described above may be hemispherical.

In the hollow steel pipe described above, an adhesion prevention mechanism may be provided below the hollow steel pipe.

The hollow steel pipe described above may have multiple casings connected along the central axis of the hollow steel pipe, and at least the lowest casing among these multiple casings may be provided with an adhesion prevention mechanism.

Another aspect of the present invention is a method for extracting an existing structure buried in the ground using a hollow steel pipe as described above.

This invention prevents soil from adhering to the inside of hollow steel pipes, thereby achieving the full effect of isolating existing structures from the surrounding ground using hollow steel pipes.

This is a diagram showing an example of a construction procedure for inserting and burying a hollow steel pipe without peripheral holes and having a spiral 10S around it into the ground. 10A and 10B are diagrams showing an example of a construction procedure for extracting an embedded hollow steel pipe. FIG. 10 is a diagram illustrating a pin-type joint as an example of a joint between casings. FIG. 10 is a plan view illustrating a flange type joint as an example of a joint between casings. 10A and 10B are front and side views illustrating a flange type joint as an example of a joint between casings. This figure shows an example of a construction procedure in which a hollow steel pipe with a spiral around it and no peripheral holes is inserted into the ground, up to the extraction of an existing pile. This is a diagram showing an example of a construction procedure in which a hollow steel pipe with a spiral around it and a peripheral hole is inserted into the ground, and then an existing pile is pulled out. This is a diagram showing an example of a construction procedure in which a hollow steel pipe without a spiral around it and without peripheral holes is inserted into the ground and an existing pile is pulled out. This is a diagram showing an example of a construction procedure in which a hollow steel pipe with a peripheral hole and no spiral around it is inserted into the ground and an existing pile is pulled out. 1A to 1C are diagrams showing an example of a cover member that opens and closes a peripheral hole, as viewed from three different directions. 10A to 10C are diagrams showing another example of a cover member for opening and closing a peripheral hole, as viewed from three different directions. FIG. 10 is a diagram showing an example of an adhesion suppression mechanism formed by a protrusion provided on the inner peripheral wall of a hollow steel pipe. 1 is a perspective view showing an example of an adhesion suppression mechanism composed of a protrusion, an annular body, and a protruding body that can rotate relative to a hollow steel pipe. FIG. 1 is a plan view showing an example of an adhesion suppression mechanism composed of a protrusion, an annular body, and a protruding body that can rotate relative to a hollow steel pipe. FIG. FIG. 1 is a perspective view showing an example of a fastening tool that can be used when removing a buried hollow steel pipe. FIG. 10 is a perspective view showing another example of a fastening tool that can be used when removing a buried hollow steel pipe. FIG. 10 is a diagram showing a schematic example of a configuration for sending air or water into the casing pipe to remove soil clogs downward. FIG. 10 is a plan view schematically showing an example of a configuration for spraying air, water, etc. using a jet pipe for edge cutting provided on the peripheral surface of a casing. 10 is a cross-sectional view showing an example of a configuration for spraying air, water, etc. using a jet pipe for edge cutting provided on the peripheral surface of a casing. FIG. FIG. 10 is a diagram showing an example of the configuration of an introduction member that maintains verticality when pouring a hollow steel pipe.

The configuration of the present invention will be described in detail below based on an example of an embodiment shown in the drawings (see Figure 1, etc.).

The hollow steel pipe 10 of the present invention is used to penetrate around an existing pile P buried in the ground G when it is pulled out and removed, thereby separating the existing pile P from the surrounding ground G. Below, we will first explain the construction procedure for penetrating and burying the hollow steel pipe 10 into the ground G, and then the construction procedure for pulling out the existing pile P (see Figures 1 to 6), and then explain the structural features of the hollow steel pipe 10 (see Figure 7, etc.).

[Construction procedure for inserting and burying the hollow steel pipe 10 into the ground G]
An example of a construction procedure for inserting and burying a hollow steel pipe 10 without peripheral holes and having a spiral 10S around its periphery into the ground G will be described below (see FIG. 1). Note that the soil around an existing pile P in the ground G is indicated by the symbol D in FIG. 1.

A mouth pipe 81 is installed around the existing pile P (see Figure 1(A)). The lower casing 11 is erected in a hole J separate from the pile hole H where the existing pile P is located, and a jig 82 is connected to connect the casing to the drive unit of the construction machine. A wire 83 is also attached to the head of the existing pile P (see Figure 1(A)).

The lower casing 11 is driven around the existing pile P and the jig 82 is removed. The middle casing 12 is erected in a separate hole J and the jig 82 is connected (see Figure 1 (B)).

Connect the middle casing 12 to the lower casing 11 (see Figure 1 (C)).

The middle casing 12 is cast and the jig 82 is removed. The upper casing 13 is erected in a separate hole J and the jig 82 is connected (see Figure 1 (D)).

Connect the upper casing 13 to the middle casing 12 (see Figure 1 (E)).

The hollow steel pipe 10, consisting of the upper casing 13, middle casing 12, and lower casing 11, is cast to the planned depth (see Figure 1 (F)).

Make the jig 82 removable by, for example, removing the nuts connecting the jig 82 to the upper casing 13 (see Figure 1 (G)).

The hollow steel pipe 10 is again driven to the planned depth using only the pushing force, and the jig 82 is removed (see Figure 1 (H)).

[Procedure for pulling out the hollow steel pipe 10]
An example of a construction procedure for extracting the hollow steel pipe 10 buried as described above (after removing the existing pile) will be described (see FIG. 2).

The mouth pipe 81 is first pulled out, and the area around the pile hole H is excavated. A worker descends into the enlarged pile hole, connects the jig 82 to the hollow steel pipe 10 (and its upper casing 13), and pours in soil as backfill material (indicated by the symbol B in the figure) (see Figure 2 (A)).

When compacting, after adding backfill material B, pull up the casing and then compact it by pushing it in again one or more times (see Figure 2 (B)).

Add soil (see Figure 2 (C)).

The hollow steel pipe 10 is pulled up and tamped (see Figure 2 (D)).

Remove the upper casing 13 and add soil (see Figure 2 (E)).

The middle casing 12 and lower casing 11 are pulled up and tamped down (see Figure 2 (F)).

Remove the inner casing 12 (see Figure 2 (G)).

Pull out and remove the lower casing 11 (see Figure 2 (H)).

Pull out the mouth pipe 81 and backfill the pile hole H (see Figure 2 (I)).

[Casing joint example (pin type)]
As an example of a joint between casings, a pin type will be described (see Figure 3). Note that although an example of joining (connecting) the lower casing 11 and the upper casing 13 is shown here, it goes without saying that a similar structure can also be applied when an intermediate casing 12 is interposed between them.

In this example, the protrusion 13b of the upper casing 13 is inserted into the L-shaped groove 11d on the inner surface of the lower casing 11 and rotated circumferentially (in the example shown in Figure 3, the upper casing 13 is rotated clockwise when viewed from above) until the protrusion 13b is locked into the groove 11d (see Figures 3(A) and (B)). Then, the bridge 17a is inserted into the groove 11d of the lower casing 11, and the pin 17b is inserted into the pin hole 11e of the lower casing 11 to secure the bridge 17a (see Figure 3(C)). In this way, the bridge 17a prevents the movement of the protrusion 13b, and the lower casing 11 and upper casing 13 are joined (connected). A bolt or the like may be used instead of the pin 17b.

[Example of joining casings (flange type)]
As another example of a joint between casings, a flange type will be described (see FIGS. 4A and 4B). When joining (connecting) the lower casing 11 and the upper casing 13 in the same manner as in the above example, flanges 11f and 13f are provided at the upper end of the lower casing 11 and the lower end of the upper casing 13, respectively, and the lower casing 11 and the upper casing 13 can be joined (connected) by aligning the bolt holes of the flanges 11f and 13f and fastening them with bolts 18a and nuts 18b (see FIGS. 4A and 4B).

[Example of construction procedure from penetrating the hollow steel pipe 10 into the ground G to pulling out the existing pile P]
Next, an example of a construction procedure will be described (see FIG. 5 ) in which a hollow steel pipe 10 with no peripheral holes and a spiral 10S around its periphery is inserted into the ground G and an existing pile P is pulled out. Note that some of the construction procedures shown below differ from the construction procedure shown in FIG. 1 , but any of the procedures can be selected as appropriate for actual construction, and the construction procedures are not limited to any one of them.

In this example, first, the lower casing 11 and the upper casing 13 are connected in advance (see Figure 5 (A)).

In addition, a reinforcing steel rod 84 for edge separation confirmation is attached to the head of the existing pile P in the pile hole H to confirm that the edge between the casing and the existing pile P has been severed (see Figure 5(B)). When attaching the reinforcing steel rod 84, if the hollow portion of the head of the existing pile P is concrete or the like, a simple method such as directly inserting the reinforcing steel rod 84 with a hammer may be employed. Here, edge separation as used herein refers to the fact that when the hollow steel pipe 10 (or the casing constituting it) is inserted while rotating around the existing pile P, the edge between the existing pile P and the ground G is severed, causing the existing pile P to rotate along with the rotation of the hollow steel pipe 10 (or the casing constituting it). The state in which the existing pile P can be pulled out is when the edge between the existing pile P and the ground G has been completely severed, and this state is confirmed by the phenomenon of the reinforcing steel rod 84 for edge separation confirmation rotating along with the existing pile P. This allows the periphery of the existing pile P to be sufficiently severed (separated).

Next, the lower casing 11 and upper casing 13 are driven around the existing pile P and penetrated (see Figure 5(C)). The upper casing 13 is then temporarily removed, and the middle casing 12 and upper casing 13 are connected and assembled in a hole (casing installation hole) J separate from the pile hole H. Once assembled, the middle casing 12 and upper casing 13 are connected to the lower casing 11 (see Figure 5(D)). The hollow steel pipe 10 (the lower casing 11, middle casing 12, and upper casing 13) is then driven and penetrated to an appropriate depth (see Figure 5(E)). The upper casing 13 is then removed, and the existing pile P is pulled out of the pile hole H (see Figure 5(F)). After the existing pile P is pulled out, soil is backfilled, leaving the hollow steel pipe 10 (the lower casing 11 and middle casing 12) in the ground G to prevent loosening of the surrounding ground (not shown).

[Another example of construction procedure from penetrating the hollow steel pipe 10 into the ground G to pulling out the existing pile P]
In the above example, a hollow steel pipe 10 having a spiral 10S around its periphery and no peripheral holes is used. However, similar procedures can also be used when other hollow steel pipes 10 are used. As other examples, FIG. 6 shows an example of the construction procedure when a hollow steel pipe 10 having a spiral 10S around its periphery and a peripheral hole (indicated by the reference symbol 20) is used. FIG. 7 shows an example of the construction procedure when a hollow steel pipe 10 having no spiral around its periphery and no peripheral holes is used. FIG. 8 shows an example of the construction procedure when a hollow steel pipe 10 having no spiral around its periphery and a peripheral hole 20 is used. The construction procedures shown in FIGS. 6 to 8 are the same as those shown in FIG. 5, and therefore, the explanations for FIGS. 6 to 8 will be omitted. Needless to say, the above explanation is merely an example, and a casing without a peripheral hole and having a spiral 10S around it (see Figure 5) may be used in combination with a casing with a peripheral hole 20 and having a spiral 10S around it, or a casing without a peripheral hole and having no spiral around it (see Figure 7) may be used in combination with a casing with a peripheral hole 20 and having no spiral around it (see Figure 8).

[Cover member 30 for opening and closing peripheral hole 20]
When a hollow steel pipe 10 having a peripheral hole 20 is used (see Figs. 6 and 8), a cover member 30 can be used in combination, which functions as a soil flow-in/outflow prevention member for preventing soil from flowing in or out through the peripheral hole 20. This cover member 30 will be described below (see Figs. 9 and 10).

The cover member 30 is a cover that opens and closes the circumferential hole (hole portion) 20 provided in the hollow steel pipe 10 (or the casing that constitutes it), and when closed, at least a portion of the circumferential hole 20 is blocked. The advantages of providing a circumferential hole 20 in the hollow steel pipe 10 include: (1) reducing resistance and preventing soil clogging inside the pipe by allowing mud and water to pass through the pipe during construction; (2) allowing the pipe to be placed above ground by passing an iron rod through the circumferential hole 20 during construction; and (3) improving construction work efficiency by allowing the interior of the steel pipe to be observed. However, a potential issue that can arise when providing a circumferential hole 20 in the hollow steel pipe 10 is that after an existing pile P is pulled out of the ground G, soil from the collapsed surrounding ground may flow into the hollow steel pipe 10 through the circumferential hole 20. If soil flows into the hollow steel pipe 10 through the peripheral holes 20 in this way, it may not be possible to fill all of the intended amount of backfill soil, which could result in variations in the strength of the backfill material B after backfilling or the creation of hollow spaces. In this regard, providing a cover member 30 that can freely open and close the peripheral holes 20 can solve this problem. Furthermore, by leaving the peripheral holes 20 open when necessary, the intended function of the peripheral holes 20 can be achieved. The cover member (or blocking member) 30 does not have to completely cover the entire peripheral hole 20. Furthermore, it does not have to cover all of the multiple peripheral holes 20 provided in the hollow steel pipe 10.

An example of the specific structure of the lid member 30 is shown in the figure and explained below. The lid member 30 shown in Figure 9 is connected to the hollow steel pipe 10 (the casing that constitutes it) with a connecting pin 31, allowing it to be opened and closed freely, and is designed so that when it is closed, it cannot be opened when it is locked with a locking pin 33 (see Figures 9(A) to (C)).

The specific shape of the connecting pin 31 is not particularly limited, but in this embodiment, the connecting pin 31 is provided directly above the peripheral hole 20, along the direction of a tangent extending circumferentially on the peripheral surface (surface of the outer wall 10o) of the hollow steel pipe 10 (or casing). The cover member 30 connected by a hinge structure including such a connecting pin 31 opens and closes with the connecting pin 31 as the rotation center in a direction (approximately the vertical direction during installation) parallel to the central axis 10C of the hollow steel pipe 10 or the central axis of the casing (indicated by symbol C in Figures 4B and 11) (see Figure 9(C), etc.).

The locking pin 33 is a pin consisting of a shaft portion and a head portion with a larger diameter that can be inserted and removed into both the cylindrical portion 36 provided at the end of the cover member 30 and the cylindrical portion 16 provided on the outer wall 10o of the hollow steel pipe 10. When the locking pin 33 is inserted when the cylindrical portion 36 and the cylindrical portion 16 are aligned in a straight line, the cover member 30 is locked and held in a closed state (see Figure 9(A), etc.).

Another example of the specific structure of the cover member 30 is illustrated and described below. The cover member 30 shown in Figure 10 is composed of a member that slides along a guide member 32 attached to the hollow steel pipe 10 (or casing). In this embodiment, the guide member 32 includes, for example, a pair of parallel members (stepped to prevent the cover member 30 from falling outward in the radial direction of the hollow steel pipe 10) and a member positioned below them during installation to function as a stopper. The guide members 32 are arranged on three sides to form a channel shape (U-shaped) with only the upper side open during installation (see Figure 10(A) and other figures). The cover member 30 is inserted into the guide member 32 from the upper side during installation and positioned in a predetermined position. Furthermore, a locking pin (locking member) 33 can be inserted into a pin hole 32a provided near the upper end of the guide member 32 to lock the cover member 30 to prevent it from moving upward or falling off the guide member 32 (see Figure 10(C) and other figures).

In the diagrams shown in the above explanation, the outer wall 10o of the hollow steel pipe 10 (or casing) is shown as if it were flat (see Figures 9 and 10), but please note that this is merely for the sake of convenience in the illustration. It goes without saying that if the hollow steel pipe 10 (or casing) is cylindrical, the outer wall 10o will actually be curved in the circumferential direction.

The cover member 30 may also be a mesh-like member made of reinforcing bars or the like.

The cover members 30 described above using examples may be placed over all of the circumferential holes 20 of the hollow steel pipe 10, or they may be placed over only some of the multiple circumferential holes 20. In short, when preventing soil from the collapsed surrounding ground from flowing into the inside of the hollow steel pipe 10 through the circumferential holes 20, depending on the desired level, it may not be necessary to cover all of the circumferential holes 20. In such cases, it may be sufficient to place cover members 30 over only some of the multiple circumferential holes 20.

Furthermore, when covering only some of the multiple circumferential holes 20 in this manner, the covering members 30 may be arranged to block the circumferential holes 20 provided in at least the lowest casing of the multiple casings (in the above embodiment, the lower casing 11). Generally, it is the underlying ground that is most problematic if it loosens during a series of construction works, and if the underlying ground loosens, it is expected that stable backfilling will become relatively difficult. If this point is taken into consideration when covering only some of the multiple circumferential holes 20, for example, by blocking the circumferential hole 20 of the lowest casing with the covering member 30 as described above, it will be possible to prevent the ground in the lower layers from loosening.

The cover member 30 described above is merely one suitable example of a member that functions as a soil flow prevention member for preventing soil from flowing in or out through the peripheral holes 20. In addition to the cover member 30 described above, the soil flow prevention member may have the following configurations and aspects.
- The outside, including the peripheral hole 20, is sealed by wrapping it around with tape or by using a ring-shaped plate that covers the outer periphery of the casing. - A plate with a diameter larger than the peripheral hole 20 is fastened to the outer wall and the plate with bolts or the like so as to seal the peripheral hole 20. - The peripheral hole 20 is sealed with a plug.

[Adhesion suppression mechanism]
The hollow steel pipe 10 may be provided with an adhesion prevention mechanism 40 as a mechanism for preventing the adhesion of soil, etc. If soil adheres or sticks to the inside of the hollow steel pipe 10, there is a risk that the intended edge-cutting effect cannot be fully achieved. However, by providing the adhesion prevention mechanism 40, it is possible to achieve the desired edge-cutting effect.

One specific example of the adhesion prevention mechanism 40 is configured with protrusions 41 provided on the inner peripheral wall 10i of the hollow steel pipe 10 (see Figure 11). In this case, a smooth shape for the protrusions 41 is preferable in that it makes it difficult for soil to adhere to the surface and thus helps prevent adhesion. As an example, in this embodiment, multiple protrusions 41 with an approximately hemispherical shape are provided on the inner peripheral wall 10i of the hollow steel pipe 10 (see Figure 11). Note that the shape of the protrusions 41 is not limited to hemispherical.

Another specific example of the adhesion prevention mechanism 40 will be described (see Figures 12A and 12B). The adhesion prevention mechanism 40 shown in the figures includes a co-rotation prevention mechanism 42. Co-rotation, as used in this specification, refers to the phenomenon in which, when a hollow steel pipe 10 (or the casing that makes it up) is inserted into an existing pile P while rotating around it, the soil between the hollow steel pipe 10 and the existing pile P rotates around the existing pile P along with the hollow steel pipe 10. The co-rotation prevention mechanism 42 is configured to effectively suppress this phenomenon of co-rotation.

A specific example of the co-rotation suppression mechanism 42 is shown. In this embodiment, the co-rotation suppression mechanism 42 includes an aperture 43, a protrusion 44, an annular body 45, and a protruding body 46 (see Figures 12A and 12B).

The apertures 43 consist of holes formed in the outer wall 10o of the hollow steel pipe 10. In this embodiment, two apertures 43 are provided at the same height and in opposing positions. This pair of holes consists of elongated holes formed along the circumferential direction by a circumferential angle A, for example, approximately 90° (see Figure 12B). Note that such apertures 43 may also function and be used as the circumferential holes (hole portions) 20 in the above-described embodiment.

The protrusion 44, annular body 45, and protruding body 46 are integrally formed. The annular body 45 is a circular member, and in this embodiment, its cross-sectional shape is rectangular, but it may also be circular or other shapes. The annular body 45 is formed with an outer diameter slightly smaller than the inner diameter (of the inner peripheral wall 10i) of the hollow steel pipe 10, and is placed inside the hollow steel pipe 10.

The protrusions 44 are formed as a pair of protrusions, for example two protrusions, formed to extend radially outward from the annular body 45. Each of the pair of protrusions 44 is arranged so that it protrudes from the inside to the outside of the hollow steel pipe 10 through an opening 43. The opening 43, which is an elongated hole, functions as a guide to guide each protrusion 44 circumferentially. The protrusions 44 guided by the opening 43 can rotate circumferentially relative to the hollow steel pipe 10 together with the annular body 45 by an amount corresponding to the circumferential angle A (slightly less than 90° in this embodiment) (see Figure 12B).

The protrusions 46 are arranged to protrude from the annular body 45 and are configured to move circumferentially along the inner wall 10i of the hollow steel pipe 10, acting like a scraper to scrape off soil adhering to the inner wall 10i. Based on this, the protrusions 46 of this embodiment are configured to extend vertically along the axial direction of the central axis 10C of the hollow steel pipe 10, and are capable of scraping off soil adhering to the inner wall 10i by an area equivalent to the product of their vertical length and the circumferential movement length corresponding to the circumferential angle A. The number of such protrusions 46 is not particularly limited. In this embodiment, four protrusions 46 are arranged at equal intervals (every 90°) on the annular body 45 (see Figures 12A and 12B).

The adhesion suppression mechanism 40, including the co-rotation suppression mechanism 42 configured in this manner, prevents soil from adhering or sticking to the interior of the hollow steel pipe 10 when the hollow steel pipe 10 is inserted into ground G, thereby enabling the edge-cutting effect to be fully realized. Furthermore, in the co-rotation suppression mechanism 42 of this embodiment, the integrally formed member consisting of the protrusion 44, annular body 45, and protruding body 46 can rotate circumferentially relative to the hollow steel pipe 10 along the elongated opening 43 by an amount corresponding to the circumferential angle A. Therefore, when the hollow steel pipe 10 rotates forward or backward, the protrusion 44 protruding outward remains stuck in the soil, thereby loosening the soil and backfill material B inside the pipe. Furthermore, the protrusion 46, which moves relatively along the inner peripheral wall 10i of the hollow steel pipe 10, also functions to scrape off soil adhering to the inner peripheral wall 10i. A hollow steel pipe 10 equipped with such an adhesion suppression mechanism 40 can fully perform the following functions: (1) When the existing pile P is pulled out, the soil between the hollow steel pipe 10 and the existing pile P is sufficiently loosened; (2) When the backfill material B is introduced, the soil is sufficiently loosened so that the soil remaining inside the hollow steel pipe 10 does not act as a lid, preventing the backfill material B from being filled; and (3) When the hollow steel pipe 10 is pulled out of the ground G, the filled backfill material B is sufficiently loosened so that it does not clog the casing, preventing the backfill material B from being discharged along with the hollow steel pipe.

When the hollow steel pipe 10 is made up of multiple casings, as in this embodiment, providing the adhesion prevention mechanism 40 in at least the lowest casing (in this embodiment, the lower casing 11) makes it possible to prevent clogging at the tip end of the hollow steel pipe 10, where soil is particularly likely to clog. The adhesion prevention mechanism 40 needs to be located at least below the hollow steel pipe 10. In the case of a casing, the adhesion prevention mechanism 40 needs to be located in the lowest casing. The hollow steel pipe 10 (or the casing that constitutes it) may be provided with both the protrusion 41 and the co-rotation prevention mechanism 42.

[Method for removing hollow steel pipes after filling with backfill material]
As described above, after the existing pile P is pulled out of the ground G, the hollow steel pipe 10 is left in the ground G, and backfilling material B is used to prevent loosening of the surrounding ground. However, when the hollow steel pipe 10 is pulled out and removed after backfilling, the soil inside the hollow steel pipe 10 may rise up and not fall down. If this phenomenon occurs, there is a possibility that the excavated hole will not be filled with enough soil, resulting in a hollow space. In view of the above, in this embodiment, the following means are adopted to prevent this possibility (see FIG. 13, etc.).

That is, a so-called "kanzashi" (iron rod) 51 is inserted through the peripheral hole 20 of the casing 11 (12, 13) that constitutes the hollow steel pipe 10, and both ends of the kanzashi 51 are placed directly on the ground G or on a boat (foundation) 52, using a fastening device 50 to hang (rest) the casing 11 (12, 13) (see Figure 13). Alternatively, instead of using the kanzashi 51, a wire 53 attached to the boat 52 can be passed through the peripheral hole 20 to hang the casing 11 (12, 13) (see Figure 14).

By using such a means as a pin 51 or wire 53 to temporarily hold the casing 11 (12, 13), and repeating the steps of gradually (for example, at the level of several tens of centimeters) pouring backfill material B into the hollow steel pipe 10 and then pulling up the casing 11 (12, 13), soil clogging inside the hollow steel pipe 10 is prevented.

When using such means to prevent soil from clogging the hollow steel pipe 10, the following devices or means may be used in combination to more effectively prevent clogging.
The rod 54 is pushed into the casing 11 (12, 13) from above (see FIG. 14).
- Protrusions inside the casing 11 (12, 13) are eliminated to prevent resistance. In other words, while nails or iron bars (rectangular pieces of iron) are sometimes attached to the casing 11 (12, 13) to loosen the soil during excavation, these can actually create resistance when backfilling, causing the soil to clog, so these are eliminated.
- Use a material that is less likely to clog as backfill material B.
- Air or water is pumped into the pipes of the casing 11 (12, 13) from above ground to apply pressure and drop the soil clog downward (see Figure 15).
Air or water outlets 19 are provided on the peripheral surface of the casing 11 (12, 13), and air or water is ejected from the air outlets 19 using an air or water ejection pipe 59 for edge cutting (see FIGS. 16A and 16B). Although not shown, an ejection pipe (ejection passage) may be formed so as to pass through the thicker portion of the casing 11 (12, 13).

In addition, if the casing 11 (12, 13) is temporarily suspended using the hairpin 51 or wire 53 as described above, the peripheral hole 20 may be provided in the upper (vertically upward) part of the casing 11 (12, 13).

[Ensuring verticality, checking the pile head (inlet pipe)]
Conventionally, when driving steel pipe piles, a construction machine equipped with a vibration damper is used to keep the steel pipe pile vertical. However, when the hollow steel pipe 10 (the casings 11, 12, 13 that constitute it) is the target, it can be difficult to damp the casing, especially when the pipe has a large diameter.

Furthermore, when removing the existing pile P, there are several issues: (1) it is unknown whether the existing pile P is in a vertical position in the ground; (2) after the hollow steel pipe (and its casing) has been driven in, it is not possible to confirm whether the existing pile and the hollow steel pipe (and its casing) are vertical; and (3) if the hollow steel pipe is driven in without maintaining a vertical position, it will interfere with the existing pile and, in some cases, twist off the existing pile.

In this regard, in this embodiment, when driving and penetrating the hollow steel pipe 10 around the existing pile P, an introduction member 60 is used to maintain the verticality of the hollow steel pipe 10 during installation, thereby solving the above-mentioned problem (see Figure 17). By using such an introduction member 60, the hollow steel pipe 10 can be installed evenly relative to the pile center (the central axis Pc of the existing pile P).

The introduction member 60 of this embodiment is composed of a tubular body that is smaller than the inner diameter of the hollow steel pipe 10 and larger than the outer diameter of the existing pile P, and is arranged along the inner wall 10i of the hollow steel pipe 10 (see Figure 17). The introduction member 60 may also be composed of a rebar cage that is arranged along the inner circumference of the hollow steel pipe 10 and is smaller than the inner diameter of the hollow steel pipe 10 and larger than the outer diameter of the existing pile. Such an introduction member 60 allows the hollow steel pipe 10 to maintain its verticality. However, introduction members with different configurations, such as an introduction member 60 in which the inner diameter of at least a portion (or all) of the upper side is larger than the outer diameter of the casing 11 (12, 13), can also be used.

There are no particular restrictions on the material of the introduction member 60. In this embodiment, a steel tubular introduction member 60 is used. The introduction member 60 is more likely to maintain its verticality if it is made of a highly rigid material.

In addition, the introduction member 60 of this embodiment is hollow and has a holding member 61 formed, for example, in the shape of a sleeve or a dish, on the inner periphery of the introduction member 60, which is held by the head of the existing pile P. By holding a portion of the tip of the introduction member 60 in the head of the existing pile P, it is possible to maintain verticality.

In addition, the introduction member 60 of this embodiment has an insertion portion 62 that is inserted into the excavated soil after excavating the soil around the existing pile P. By using this insertion portion 62 to insert the introduction member 60 into the ground G, the hollow steel pipe 10 can be guided so that it is parallel to the existing pile P, even if the existing pile P is at an angle.

The introduction member 60 may be configured so that its upper portion extends above ground when it is positioned between the existing pile P and the hollow steel pipe 10 when the hollow steel pipe 10 is driven into place. When the excavated soil is backfilled after the pile head has been confirmed, the reinforcing rod 84 inserted into the pile head may become unclear, making it impossible to reconfirm the pile head and making it impossible to reliably continue to confirm the pile head underground. However, with this type of introduction member 60, the location of the existing pile P can be easily confirmed.

That is, one aspect of the present invention is
(1) An introduction member that maintains the verticality of a hollow steel pipe when driving (penetrating) the hollow steel pipe around an existing structure buried in the ground, such as an existing pile.
(2) The introduction member described in (1) is composed of a tubular body that is smaller than the inner diameter of the hollow steel pipe and larger than the outer diameter of the existing structure, and is arranged along the inner circumference of the hollow steel pipe.
(3) The introduction member according to (2), wherein the tubular body is made of steel.
(4) The introduction member described in (1) is arranged along the inner circumference of the hollow steel pipe, and is composed of a reinforcing bar cage that is smaller than the inner diameter of the hollow steel pipe and larger than the outer diameter of the existing structure.
(5) An introduction member described in any one of (2) to (4), which is hollow and has a holding member on the inner periphery of the introduction member that is held on the head of the existing structure.
(6) An introduction member described in any one of (1) to (5), which excavates the soil around the existing structure and has an insertion portion that is inserted into the excavated soil.
(7) An introduction member as described in (6), in which the upper part of the introduction member extends to the ground when the introduction member is positioned between the existing structure and the hollow steel pipe when the hollow steel pipe is cast.
(8) A method for extracting an existing structure buried in the ground using the hollow steel pipe described in any one of (1) to (7).

The above-described embodiment is one preferred example of the present invention, but is not limited to this and various modifications are possible within the scope of the present invention. For example, the above-described embodiment describes the case where a hollow steel pipe 10 is inserted around an existing pile P, but the existing pile P is merely one example of an existing underground structure at the construction site. Naturally, the present invention can also be applied to cases where a hollow steel pipe 10 is inserted around various existing structures such as spread foundations, columnar improvement bodies, etc., in addition to existing piles; in other words, around objects that may become obstacles underground.

The present invention is suitable for use in methods for extracting hollow steel pipes and existing structures that use them.

10... Hollow steel pipe 10C... Center axis 10i... Inner peripheral wall 10o... Outer peripheral wall 10S... Spiral 11... Lower casing (casing)
11d...groove 11e...pin hole 12...intermediate casing (casing)
13...Upper casing (casing)
13b...protrusion portion 16...cylindrical portion 17a...piece 17b...pin 18a...bolt 18b...nut 19...air ejection hole 20...circumferential hole (hole portion)
30... Lid member (soil runoff prevention member)
31... connecting pin 32... guide member 32a... pin hole 33... locking pin (locking member)
36... Cylindrical portion 40... Adhesion prevention mechanism 41... Projection 42... Co-rotation prevention mechanism 43... Long hole (opening)
44... Projection body 45... Ring body 46... Projecting body 50... Locking tool 51... Hairpin (iron bar)
52... Ship 53... Wire 54... Rod 59... Air ejection pipe 60... Introduction member 60u... Upper part 61... Holding member 62... Insertion part 81... Mouth pipe 82... Jig 83... Wire 84... Reinforcement rod A... Circumferential angle of opening B... Backfill material C... Central axis of casing D... Soil G... Ground H... Pile hole J... Another hole P... Existing pile (existing structure)
Pc: central axis of the pile

Claims (6)

A hollow steel pipe used to extract an existing structure buried in the ground, such as an existing pile, while it is contained within the hollow steel pipe, and to fill the hollow steel pipe with backfill material after the existing structure has been extracted.
an adhesion suppression mechanism for scraping off soil and backfill material adhering to the inner peripheral wall of the hollow steel pipe;
The adhesion suppression mechanism includes a co-rotation suppression mechanism,
the co-rotation suppression mechanism comprises an opening provided along the outer peripheral wall of the hollow steel pipe, and a protrusion passing through the opening from the inside to the outside of the hollow steel pipe,
The adhesion prevention mechanism comprises a ring-shaped body provided inside the hollow steel pipe and a protrusion-shaped body provided on the ring-shaped body and extending in the central axis direction of the hollow steel pipe, the opening being a long hole, and the ring-shaped body and the protrusion-shaped body are capable of rotating relative to the hollow steel pipe along the long hole . The hollow steel pipe according to claim 1 , wherein the adhesion suppression mechanism comprises a protrusion provided on an inner peripheral wall of the hollow steel pipe. The hollow steel pipe according to claim 2 , wherein the protrusion is hemispherical. The hollow steel pipe according to claim 1 , wherein the adhesion suppression mechanism is provided below the hollow steel pipe. A hollow steel pipe as described in any one of claims 1 to 4 , wherein a plurality of casings are connected along the central axis direction of the hollow steel pipe, and at least the casing located at the lowest level among the plurality of casings is provided with the adhesion prevention mechanism. A method for extracting an existing structure, comprising extracting an existing structure buried in the ground using the hollow steel pipe according to any one of claims 1 to 5 .