JP7288412B2 - Installation method of drain material - Google Patents

Description

The present invention relates to a method of placing a drain material using an auger.

Conventionally, in hard ground or ground mixed with hard soil masses and obstacles, pre-drilling is performed with an auger or the like, and a drain material is placed. In addition, there is a method of crushing the ground with a rock drill or the like provided at the tip of the breaker, driving the breaker and casing into the ground together with a board drain, and pulling out the breaker and casing from the ground leaving the drain (for example, , see Patent Document 1).

Patent Publication No. 3700160

However, the method of pre-drilling using an auger or the like has the problem that the construction cost is high and the construction period is long. The method described in Patent Document 1 can shorten the construction period, but requires complicated processing of the tip of the breaker. In order to solve these problems, it is desirable to drive the drain material at the same time as drilling with the auger. would rotate, causing twisting in the drain material and collapsing the flow path, possibly rendering it ineffective.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and its object is to provide a method of placing a drain material by using an auger to place the drain material without twisting. That is.

In order to achieve the above object, the present invention provides a method of placing a drain material using an auger, comprising a hollow rod of the auger containing a belt-like drain material and a suction pipe having one end connected to the drain material. A step a of inserting a hose and connecting the drain material to an anchor arranged at the lower end of the hollow rod; a step b of rotating the hollow rod to excavate the ground; in the ground and pulling out the hollow rod, and in the step a, a swivel mechanism is positioned between the other end of the suction hose extending from the upper end of the hollow rod and the anchor. and rotating the hollow rod while pulling the other end of the suction hose upward in the step b.

In the present invention, by providing a swivel mechanism between the anchor and the other end of the suction hose extending from the upper end of the hollow rod, the auger is inserted into the hollow rod when the auger is rotated to excavate the ground. Twisting of the drain material can be prevented. Therefore, the twisting does not collapse the flow path of the drain material and impair the suction function. Further, by connecting the drain material to the anchor, the hollow rod can be pulled out while the drain material is reliably left in the ground.

The swivel mechanism is provided, for example, at a connecting portion between the anchor and the drain member.
The swivel mechanism may be provided at a portion of the suction hose protruding from the upper end of the hollow rod.
When the swivel mechanism is provided at the connecting portion between the anchor and the drain material, the rotation of the anchor is not transmitted to the drain material, so that twisting of the drain material can be more reliably prevented.
When the swivel mechanism is provided at the portion protruding from the upper end of the hollow rod of the suction hose, the drain material rotates together with the anchor, but the rotation of the drain material is not transmitted to the part above the swivel mechanism. can be prevented. In addition, it is possible to prevent dirt from being caught in the swivel mechanism, and it is possible to visually recognize that the swivel is moving. After placing the drain material, the swivel mechanism can be removed and reused.
When the swivel mechanisms are provided at the two locations described above, the lower swivel mechanism provided at the connecting portion between the anchor and the drain material mainly functions, so that the rotation of the anchor is not transmitted to the drain material. When the function of the lower swivel mechanism deteriorates for some reason and the drain material rotates, the rotation of the drain material is prevented by the function of the upper swivel mechanism provided at the part protruding from the upper end of the hollow rod of the suction hose. It is not transmitted to the part above the upper swivel mechanism. Therefore, if swivel mechanisms are provided at two locations, twisting of the drain material can be more reliably prevented.

The drain member may be provided with a reinforcing member for increasing rigidity.
Moreover, the cross section of the width direction of the said drain material may be curved.
By providing a reinforcing member for increasing rigidity or curving the cross section in the width direction, the shape of the drain member can be easily maintained, and twisting can be prevented more reliably.

The hollow rod is provided with a protrusion on the outer peripheral surface near the lower end, the anchor is provided with an arc-shaped locking portion in a plan view on the upper surface, and one end of the arc of the locking portion is positioned on the upper surface of the anchor. When the hollow rod is rotated in the step b, the projection is pressed against the other end of the locking portion, so that the anchor rotates together with the hollow rod. Then, when the auger is rotated in the step c in the direction opposite to the step b, the projection rides on the locking portion from one end of the locking portion and moves toward the other end, thereby moving from the anchor. It is desirable that the hollow rods are separated.
As a result, the hollow rod can be easily separated from the anchor when the auger is pulled out from the ground, and the drain material connected to the anchor can be prevented from rising together with the hollow rod.

In the step b, the presence or absence of twisting of the drain material may be confirmed by a camera arranged in the hollow rod.
Thereby, when the twist of the drain material is confirmed, it is possible to take measures to eliminate the twist.

Advantageous Effects of Invention According to the present invention, it is possible to provide a method of placing a drain material that can place the drain material using an auger without twisting the drain material.

FIG. 1 shows an auger 1; FIG. 4 is a diagram showing a method of placing a drain material 8 using the auger 1; A view showing the vicinity of the lower end of the auger 1. FIG. FIG. 4 shows an anchor 6; The figure which shows the vicinity of the lower end part of the auger 1 during excavation. The figure which shows the vicinity of the lower end part of the auger 1 during extraction. FIG. 1 shows an auger 1; The figure which shows the example which provided the swivel mechanism 12 in two places. The figure which shows the drain material 8. FIG. A view showing the vicinity of the lower end of the auger 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

[First embodiment]
FIG. 1 shows an auger 1 used in a first embodiment of the invention. FIG. 1(a) is a vertical sectional view of the auger 1 on a plane perpendicular to the width direction of the drain material 8, and FIG. 1(b) is a vertical cross section of the auger 1 on a plane parallel to the width direction of the drain material 8. It is a diagram.

As shown in FIG. 1, the auger 1 consists of a hollow rod 2, an anchor 6 and the like. The hollow rod 2 is a cylindrical member whose diameter is reduced in the vicinity of the lower end portion 26, and a screw 20 is provided on the outer peripheral surface 4 from the lower end portion 26 to a predetermined height. An anchor 6 is arranged at the lower end 26 of the hollow rod 2 . The anchor 6 is a circular plate having a larger diameter than the lower end 26 of the hollow rod 2, and is provided with an excavating edge (not shown).

A strip-shaped drain member 8 and a suction hose 11 having one end connected to the drain member 8 are inserted into the interior 3 of the hollow rod 2 . The other end of the suction hose 11 protrudes from the upper end of the hollow rod 2 and is connected via a swivel mechanism 12 to a rope 13 for traction. A camera 19 is arranged in the interior 3 of the hollow rod 2 . The camera 19 is arranged, for example, suspended from above the hollow rod 2 .

The drain material 8 is composed of a plate-shaped core material and a non-woven fabric covering the surface of the core material. The drain material 8 is based on the material of the non-woven fabric portion, which can be expected to have a relatively water repellent effect due to its high lipophilicity, but it is also possible to use a plastic board drain or paper drain with further improved water repellency. . The cross section of the drain material 8 in the width direction is linear.

A cap 10 is attached to the upper end of the drain member 8 , and the lower end of a suction hose 11 is connected to the cap 10 . A connecting portion between the drain member 8 and the cap 10 is provided with a sealing member 9b for preventing inflow of air or the like from the gap. A seal member 9a is provided at the lower end of the drain member 8 to prevent inflow of air or the like. A lower end of the drain material 8 is fixed to the anchor 6 . The entire length of the drain material 8 functions as a suction portion. The length of the suction portion is set according to the thickness of the oil layer 22 (FIG. 2) to be suctioned.

The swivel mechanism 12 is a bearing swivel that connects the rope 13 and the suction hose 11 so that they can rotate freely relative to each other under load. By connecting with the swivel mechanism 12, the edge between the rope 13 and the suction hose 11 is cut in a state where the suction hose 11 is pulled upward by the rope 13, and the rotational force is not transmitted. In addition, since tension can be applied by the rope 13, it is possible to prevent the drain material 8, which is not self-sustaining, from collapsing inside the hollow rod.

FIG. 2 is a diagram showing a method of placing the drain material 8 using the auger 1. As shown in FIG. To drive the drain material 8 into the ground 21, first, as shown in FIG. Also, the drain material 8 is connected to the anchor 6 arranged at the lower end portion 26 of the hollow rod 2 . Then, as shown in FIG. 2(a), the upper end of the suction hose 11 is connected to the rope 13 via the swivel mechanism 12, and the auger 1 is arranged at a predetermined position on the ground 21. As shown in FIG.

Next, as shown in FIG. 2( b ), the hollow rod 2 is rotated while being tensioned by the rope 13 , that is, while the suction hose 11 and the drain material 8 are pulled upward by the rope 13 . Then, the anchor 6 rotates together with the hollow rod 2, the excavating blade excavates the ground 21, the screw 20 loosens the soil around the hollow rod 2, and the auger 1 penetrates into the ground 21. - 特許庁

While the auger 1 is excavating, the anchor 6, the drain material 8, and the suction hose 11 rotate together with the auger 1, but the rotation of the upper end of the suction hose 11 is not transmitted to the rope 13 because the edge is cut off by the swivel mechanism 12. Since the drain material 8 and the suction hose 11 rotate freely with respect to the rope 13, the drain material 8 rotates but is not twisted.

During excavation, the state of the inside 3 of the hollow rod 2 is confirmed by the camera 19 . Since the camera 19 is suspended from above the hollow rod 2, it does not rotate even when the auger 1 is rotated. If it is found by checking with the camera 19 that the drain material 8 is twisted, it may be possible to take measures to eliminate the twist. For example, the rotation of the auger 1 may be temporarily stopped and the drain material 8 may be rotated in a direction to eliminate the twist. Also, the swivel mechanism 12 may be inspected and, if a problem is found, the swivel mechanism 12 may be replaced.

As shown in FIG. 2(c), when the drain material 8 reaches the groundwater level fluctuation range 23, excavation by the auger 1 is stopped. The groundwater level fluctuation range 23 is grasped by, for example, a preliminary survey using an observation well. By excavating with the rope 13 pulling the suction hose 11 and the drain material 8 upward, the drain material 8 can be accurately installed in the groundwater level fluctuation range 23 .

Next, as shown in FIG. 2(d), the hollow rod 2 of the auger 1 is pulled out leaving the anchor 6, the drain material 8 and part of the suction hose 11 in the ground 21. Then, as shown in FIG. As a result, the drain material 8 is driven into the ground 21 at a predetermined depth. After that, the connection between the suction hose 11 and the rope 13 via the swivel mechanism 12 is released. Rope 13 and swivel mechanism 12 can be used to drive drain material 8 at other locations.

The ground-side end of the suction hose 11 is connected to a vacuum suction section (not shown) when necessary. Oils and the like in the oil layer 22 of the ground 21 are recovered from the drain material 8 to the ground by suctioning using the vacuum suction part.

FIG. 3 is a diagram showing the vicinity of the lower end of the auger 1. As shown in FIG. 3(a) is a perspective view of the lower end of the auger 1, and FIG. 3(b) is a view of the lower end of the auger 1 viewed from below. FIG. 4 is a diagram showing the anchor 6. FIG. FIG. 4(a) is a perspective view of the anchor 6, and FIG. 4(b) is a view of the anchor 6 viewed from above.

As shown in FIG. 3, the auger 1 is provided with projections 5 on the outer peripheral surface 4 near the lower end 26 of the hollow rod 2 . The lower end of projection 5 is level with the lower end 26 of hollow rod 2 . The thickness of the projection 5 is assumed to be smaller than the width of a gap 15 (FIG. 4), which will be described later. The projection 5 is provided in at least one location.

As shown in FIG. 4, the anchor 6 is provided with an arcuate locking portion 7 on the upper surface 14 in plan view. One end 7a of the arc of the locking portion 7 is located on the upper surface 14 of the anchor 6, and the height continuously increases toward the other end 7b. Each locking portion 7 has, for example, a substantially half arc shape in plan view, and a gap 15 is formed between the two locking portions 7 .

FIG. 5 shows the vicinity of the lower end of the auger 1 during excavation. FIG. 5(a) is a perspective view of the vicinity of the lower end of the auger 1 during excavation, and FIG. 5(b) is a sectional view along line BB shown in FIG. 5(a). FIG. 6 is a view showing the vicinity of the lower end of the hollow rod 2 during extraction. 6(a) and 6(b) are diagrams showing the vicinity of the lower end of the hollow rod 2 after starting to pull out.

When excavating the ground with the auger 1, the hollow rod 2 is moved in the direction indicated by the arrow A with the projection 5 of the hollow rod 2 arranged in the gap 15 between the engaging portions 7 of the anchor 6 as shown in FIG. rotate. Then, the protrusion 5 is pressed against the end 7b of the locking portion 7, and the anchor 6 rotates together with the hollow rod 2. As shown in FIG. The auger 1 excavates the ground 21 while pushing the anchor 6 in the direction indicated by the arrow A with the hollow rod 2 .

When pulling out the hollow rod 2 from the ground, the hollow rod 2 is rotated in the direction opposite to the arrow A shown in FIG. That is, the hollow rod 2 is rotated in the direction indicated by the arrow C as shown in FIG. Then, immediately after the start of rotation in the direction of arrow C, the projection 5 of the hollow rod 2 rides on the upper surface 27 from the end 7a of the locking portion 7 as shown in FIG. 6(a). When the rotation in the direction of arrow C is further advanced, the projection 5 moves on the upper surface 27 toward the end portion 7b as shown in FIG. 6(b). As a result, the hollow rod 2 is gradually separated from the upper surface 14 of the anchor 6, leaving the anchor 6 and the drain material 8 on the ground.

Thus, in the first embodiment, since the swivel mechanism 12 is provided at the upper end of the suction hose 11, the rotation of the drain material 8 and the suction hose 11 is transmitted to the rope 13 when the auger 1 is rotated to excavate the ground 21. not. Therefore, twisting can be prevented even if the drain material 8 rotates, and the suction function of the drain material 8 is not impaired by twisting. Since the swivel mechanism 12 is always on the ground, it is possible to prevent soil from being caught in it and to visually recognize its operation. Also, the swivel mechanism 12 can be easily removed after the drain material 8 is placed.

In the first embodiment, by connecting the drain material 8 to the anchor 6, the hollow rod 2 can be pulled out while the drain material 8 is reliably left in the ground 21. FIG. Also, by providing the projection 5 on the hollow rod 2 and providing the locking portion 7 on the anchor 6 . The hollow rod 2 can be easily separated from the anchor 6.

In the first embodiment, the projection 5 is arranged only in one gap 15 of the locking portion 7, but the projection 5 indicated by the dotted line in FIG. The projections 5 may be arranged in the two gaps 15 of 7 . Further, if the hollow rod 2 can be easily pulled out with the anchor 6 left even without the projection 5 and the locking portion 7, the projection 5 and the locking portion 7 may be omitted.

Installation of the camera 19 is not essential. Also, the camera 19 may be taken in and out from the interior 3 of the hollow rod 2 as required.

Other examples of the present invention will be described below as second to fourth embodiments. In each embodiment, points different from the embodiments described so far will be described, and descriptions of similar configurations will be omitted by attaching the same reference numerals in the drawings and the like. In addition, the configurations described in each embodiment, including the first embodiment, can be combined as necessary.

[Second embodiment]
FIG. 7 shows an auger 1 according to a second embodiment of the invention. In the second embodiment, the installation position of the swivel mechanism 12 is different from that in the first embodiment. As shown in FIG. 7, in the second embodiment, the upper end of the suction hose 11 is directly connected to the rope 13, and the swivel mechanism 12 is provided at the connecting portion between the anchor 6 and the drain material 8. As shown in FIG.

The swivel mechanism 12 is a bearing swivel that connects the anchor 6 and the drain member 8 so that they can rotate freely relative to each other under load. By connecting with the swivel mechanism 12, the edge between the anchor 6 and the drain member 8 is cut off while the suction hose 11 is pulled upward by the rope 13, and the torque is not transmitted.

In order to drive the drain material 8 into the ground, as shown in FIG. to connect the drain material 8 to the anchor 6. Then, the upper end of the suction hose 11 is connected to the rope 13 and the auger 1 is arranged at a predetermined position on the ground.

The auger 1 is then rotated to excavate the ground under tension by the rope 13 , that is, with the suction hose 11 and the drain material 8 pulled upward by the rope 13 . During excavation by the auger 1, the anchor 6 rotates with the auger 1, but the rotation of the anchor 6 is not transmitted to the drain material 8 because the edge is cut by the swivel mechanism 12. - 特許庁Since the drain material 8 does not rotate, it is not twisted.

When the auger 1 is penetrated to a predetermined depth in the ground, the hollow rod 2 is pulled out leaving the anchor 6, the swivel mechanism 12, the drain member 8 and part of the suction hose 11 in the ground. As a result, the drain material 8 is driven into the ground at a predetermined depth. After that, the connection between the suction hose 11 and the rope 13 is released.

In the second embodiment, since the swivel mechanism 12 is provided at the connecting portion between the anchor 6 and the drain material 8 , the rotation of the anchor 6 is not transmitted to the drain material 8 when the auger 1 is rotated to excavate the ground 21 . Therefore, twisting of the drain material 8 can be prevented, and the suction function of the drain material 8 is not impaired by twisting.

In the first and second embodiments, the swivel mechanism 12 is provided at one position between the upper end of the suction hose 11 extending from the upper end of the hollow rod 2 and the anchor 6, but the swivel mechanism 12 is provided at two positions. may FIG. 8 is a diagram showing an example in which swivel mechanisms 12 are provided at two locations. In the example shown in FIG. 8, a swivel mechanism 12 is provided at the connecting portion between the upper end of the suction hose 11 and the rope 13 as in the first embodiment, and the anchor 6 and the drain material 8 are connected as in the second embodiment. A swivel mechanism 12 is provided at the joint.

If the swivel mechanisms 12 are provided at the two locations, the upper swivel mechanism 12-1 can be used as collateral for the lower swivel mechanism 12-2. During excavation by the auger 1, the rotation of the anchor 6 is not transmitted to the drain material 8 due to the main function of the lower swivel mechanism 12-2, thereby preventing the drain material 8 from rotating and twisting. If the function of the lower swivel mechanism 12-2 deteriorates for some reason and the rotation of the anchor 6 is transmitted to the drain material 8, the upper swivel mechanism 12-2 functions to cause the drain material 8 and the suction material to be sucked. Rotation of the hose 11 is not transmitted to the rope 13, and twisting does not occur even if the drain material 8 rotates.

[Third embodiment]
FIG. 9 is a diagram showing a drain member 8 according to a third embodiment of the invention. 9(a) is an elevational view of the drain member 8, and FIG. 9(b) is a cross-sectional view along line DD shown in FIG. 9(a). The third embodiment differs from the first embodiment in that the drain material 8 is reinforced.

As shown in FIG. 9 , in the third embodiment, reinforcing members 16 are provided on both sides of the drain member 8 . The reinforcing member 16 is a member having a U-shaped cross section, and is installed by fitting the U-shaped groove portion into the drain member 8 .

According to the third embodiment, the rigidity of the drain material 8 can be increased by reinforcing the drain material 8 with the reinforcing material 16 . If the rigidity of the drain member 8 is increased, it becomes easier to retain its shape, and it is possible to more reliably prevent the occurrence of twisting when a rotational force is applied.

[Fourth embodiment]
FIG. 10 is a diagram showing the vicinity of the lower end of the auger 1 according to the fourth embodiment of the invention. FIG. 10(a) is a vertical cross-sectional view in a direction perpendicular to the width direction of the drain member 8a, and FIG. 10(b) is a cross-sectional view along line EE shown in FIG. 10(a). The fourth embodiment is different from the first embodiment mainly in that the cross section of the drain member 8a in the width direction is curved, and in that the auger 1 is provided with the sensor 18 .

As shown in FIG. 10(b), the cross section of the drain member 8a in the width direction is curved. As shown in FIG. 10(a), the lower end of the drain member 8a is connected to the anchor 6a. The anchor 6a is provided with a sensor inserting portion 17 in the center, and a sensor 18 is installed in the sensor inserting portion 17. As shown in FIG. A window portion 28 is provided in the sensor insertion portion 17 . Sensor 18 is connected to rope 25 . A swivel mechanism 24 may be provided between the sensor 18 and the rope 25 .

During the excavation of the ground by the auger 1, the drain member 8a and the suction hose 11 rotate with the rotation of the anchor 6a as in the first embodiment. Twisting of the material 8a is prevented.

When the auger 1 is rotated, the sensor insertion portion 17 rotates together with the anchor 6a without moving its position in a plan view, and penetrates into the ground. Since there is a gap between the sensor 18 and the sensor inserting portion 17 , the sensor 18 does not rotate together with the sensor inserting portion 17 . If the sensor 18 rotates together with the sensor insertion portion 17 due to clogging of the gap due to the inflow of earth and sand from the window 28, the rotation transmission between the sensor 18 and the rope 25 is cut off by the swivel mechanism 24. , twisting of the sensor 18 is prevented.

The sensor 18 is, for example, a probe that emits UV light and captures the fluorescence emission of the oil with a camera. In this case, when the auger 1 excavates the ground, the camera of the sensor 18 analyzes the fluorescence image obtained through the window 28 to evaluate the distribution of the oil layer in the ground. Sensor 18 may be a probe that heats the ground with a heater to volatilize volatile organic compounds (VOCs). In this case, when the ground is excavated by the auger 1, volatilized VOCs are recovered from the window 28 and the concentration is measured by gas chromatography to evaluate the distribution of the oil layer in the ground.

In the fourth embodiment, the ground is excavated by the auger 1 while the sensor 18 evaluates the distribution of the oil layer in the ground. Then, when the drain material 8a is arranged at the position of the oil layer, the excavation by the auger 1 is stopped.

According to the fourth embodiment, by curving the cross section of the drain member 8a in the width direction, the rigidity of the drain member 8a can be increased, the shape can be easily maintained, and twisting can be prevented. Moreover, by using the curved drain member 8a, the hole 17 can be provided in the center of the anchor 6a and the sensor 18 can be installed.

According to the fourth embodiment, by installing the sensor 18, the distribution of the oil layer can be evaluated while the auger 1 is drilling the ground. Therefore, preliminary survey of oil reservoirs using observation wells becomes unnecessary.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope of the technical ideas disclosed in the present application, and these naturally belong to the technical scope of the present invention. Understood.

Reference Signs List 1 Auger 2 Hollow rod 3 Inside 4 Outer peripheral surface 5 Protrusions 6, 6a Anchors 7 Engaging parts 7a, 7b Ends 8 , 8a Drain material 9a, 9b Seal material 10 Cap 11 Suction hose 12, 12-1, 12-2, 24 Swivel mechanism 13, 25 Rope 14 , 27 …… Upper surface 15 …… Gap 16 …… Reinforcing material 17 …… Hole 18 …… Sensor 19 …… Camera 20 …… Screw 21 …… Ground 22 …… Oil layer 23 …… …Groundwater level fluctuation range ２６……Lower end

Claims (7)

A method of placing a drain material using an auger,
A step a of inserting a strip-shaped drain material and a suction hose having one end connected to the drain material into a hollow rod of an auger, and connecting the drain material to an anchor arranged at the lower end of the hollow rod. and,
a step b of rotating the hollow rod to excavate the ground;
leaving the anchor and the drain material in the ground and withdrawing the hollow rod;
and
In the step a, a swivel mechanism is provided between the other end of the suction hose extending from the upper end of the hollow rod and the anchor;
A method of placing a drain material, wherein in the step b, the hollow rod is rotated while pulling the other end of the suction hose upward. 2. The method of placing a drain material according to claim 1, wherein the swivel mechanism is provided at a connecting portion between the anchor and the drain material. 3. The method of placing a drain material according to claim 1, wherein the swivel mechanism is provided at a portion of the suction hose protruding from the upper end of the hollow rod. 4. The method of placing a drain material according to claim 1, wherein the drain material is provided with a reinforcing material for increasing rigidity. 5. The method of placing a drain material according to claim 1, wherein the cross section of the drain material in the width direction is curved. The hollow rod is provided with a protrusion on the outer peripheral surface near the lower end,
The anchor is provided with an arc-shaped engaging portion in plan view on the upper surface, and the engaging portion has one end of the arc positioned on the upper surface of the anchor and continuously increasing in height toward the other end,
When the hollow rod is rotated in step b, the projection is pressed against the other end of the engaging portion, thereby rotating the anchor together with the hollow rod,
When the auger is rotated in the step c in the direction opposite to the step b, the projection rides on the locking portion from one end of the locking portion and moves toward the other end, thereby moving from the anchor to the hollow. 6. The method of placing a drain material according to any one of claims 1 to 5, wherein the rod is separated. 7. The method of placing a drain material according to any one of claims 1 to 6, wherein, in said step b, presence or absence of twisting of said drain material is confirmed by a camera arranged in said hollow rod. .

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