Drain pipe and method of burying drain pipe

Abstract

To prevent a drain pipe from being rotated interlockingly with the rotation of a drilling pipe and twisted to close a water channel.SOLUTION: The drain pipe (1) includes a drain pipe main body (2), and a stopper portion (3) which is provided in the vicinity of a distal end of the drain pipe main body (2) or at a connection portion of the drain pipe main body (2) so as to protrude outward in a radial direction of the drain pipe main body (2) and which includes a ground locking portion (7) rotatable around an axis of the drain pipe main body (2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a drainage pipe and a method for burying the drainage pipe. [Background technology]

[0002] Due to the recent frequent occurrence of abnormal rainfall and earthquakes, many embankments and other earthwork structures have collapsed, and countermeasures are required. As a countermeasure, a technology is known that improves rainfall resistance and earthquake resistance by inserting drainage pipes into the soil of embankments and other structures to drain groundwater in embankments during heavy rainfall and dissipate excess pore water pressure during earthquakes (see, for example, Patent Document 1).

[0003] The outer diameter of the pipe used as a drainage pipe is usually 40 to 60 mm, and the pipe has multiple water collection holes to allow water to be collected. Each pipe is generally 1 to 4 m long, and the drainage pipe is buried in the ground by connecting these pipes and inserting them into the excavated holes.

[0004] A drilling pipe is generally used for excavation. After excavation, a drainage pipe is inserted into the drilling pipe, and then the drilling pipe alone is rotated and pulled out to bury the drainage pipe in the ground. In this case, if the drilled hole faces upward, the drainage pipe inserted into the hole may fall out downward due to its own weight. Patent Document 1 describes a structure that prevents the drainage pipe from falling out.

[0005] Patent Document 1 describes a drainage pipe installation method that includes a drilling step in which a drilling pipe is used to drill a hole in the ground, a drainage pipe insertion step in which a drainage pipe is inserted into the drilling pipe, and a drilling pipe withdrawal step in which the drilling pipe is rotated and withdrawn. The drilling pipe withdrawal step of this method is characterized by providing a stopper member at the tip of the drainage pipe, connecting a linear member to the tip of the drainage pipe, fixing the tip of the linear member, applying tension to the linear member, and then withdrawing the drilling pipe. Furthermore, Figures 2 and 3 of Patent Document 1 disclose a stopper member structure in which six blades extending radially outward and toward the tuyere are attached near the front of a tubular section with a conical head, and the radially outer ends of the blades are bent radially inward. Furthermore, the drainage pipe and the tubular section with the blades are fastened with bolts. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-283484 Summary of the Invention [Problem to be solved by the invention]

[0007] In the drain pipe installation method of Patent Document 1, when the drilling pipe is rotated and pulled out, soil and sand flow between the drilling pipe and the drain pipe located inside it, causing the drain pipe to rotate in conjunction with the rotation of the drilling pipe. In this case, the blades attached to the drain pipe are fixed to the ground, preventing the drain pipe from rotating. This can result in the drain pipe twisting and blocking the waterway. Alternatively, the fixing portion between the drain pipe and the tubular portion or the attachment portion between the tubular portion and the blades can be damaged, causing the stopper member to detach from the drain pipe, resulting in the drain pipe becoming dislodged. Furthermore, because the radially outer ends of the blades are bent radially inward, the radially outer ends of the blades do not penetrate the ground, making the drain pipe prone to becoming dislodged.

[0008] Therefore, the present invention aims to provide a drainage pipe that is installed in the ground by pulling out the drilling pipe while rotating it, and a method for burying the drainage pipe, in which even if soil and sand flows between the drilling pipe and the drainage pipe, the drainage pipe will rotate in conjunction with the rotation of the drilling pipe, preventing the drainage pipe from twisting and closing the waterway, and preventing damage to the fixing part between the drainage pipe and the stopper part, which will affect the drainage pipe's mechanism for preventing it from coming out. [Means for solving the problem]

[0009] [1] A drainage pipe that is inserted into a boring pipe after excavating the ground with the boring pipe and then installed in the ground by rotating and pulling out the boring pipe, the drainage pipe having a drainage pipe body and a stopper portion that is arranged near the tip or at the connection portion of the drainage pipe body so as to protrude radially outward from the drainage pipe body and has a ground engagement portion that can rotate around the axis of the drainage pipe body. [2] A drainage pipe as described in [1], in which a reduced diameter section having a diameter smaller than the outer diameter of the drainage pipe body is provided near the tip or at the connection section of the drainage pipe body, the stopper section has a ring-shaped section rotatably arranged around the reduced diameter section, and the ground engagement section is connected to the outer surface of the ring-shaped section. [3] A drainage pipe as described in [1] or [2], wherein the ground engaging portion is elongated and the tip thereof is approximately triangular in shape. [4] The drain pipe described in [2], wherein the ground engagement portion has a first ground engagement portion extending from the annular portion radially outward of the drain pipe body and toward the base end of the drain pipe body, and a second ground engagement portion formed by further bending from the end of the first ground engagement portion radially outward of the drain pipe body. [5] A drainage pipe as described in [2] or [4], in which the annular portion and the ground engaging portion are formed integrally by cutting a plate material.

[0010] [6] A method for burying a drainage pipe, comprising: a drainage pipe having a drainage pipe body and a stopper portion provided near the tip or at the connection portion of the drainage pipe body so as to protrude radially outward from the drainage pipe body and having a ground engagement portion that can rotate around the axis of the drainage pipe body; a drilling step for excavating the ground with a drilling pipe; a drainage pipe insertion step for inserting the drainage pipe into the drilling pipe while pressing the ground engagement portion against the inner surface of the drilling pipe; and a drilling pipe withdrawal step for withdrawing the drilling pipe while rotating the pipe; wherein in the drilling pipe withdrawal step, after the drilling pipe is withdrawn, the ground engagement portion expands, thereby fixing the ground engagement portion to the ground. [7] A method for burying a drainage pipe described in [6], in the drilling pipe pulling-out process, the drilling pipe is pulled out toward the base end of the drainage pipe body beyond the ground engagement portion, and the ground engagement portion is widened.After that, the drilling pipe is pushed toward the tip end of the drainage pipe body and the tip of the drilling pipe is pressed against the ground engagement portion, thereby causing the tip end of the ground engagement portion to dig into the ground. [8] A method for burying a drainage pipe described in [6] or [7], in which, in the drilling pipe pulling-out process, the drilling pipe is pulled out toward the base end of the drainage pipe body beyond the ground engagement portion, the ground engagement portion is widened, and then the drainage pipe is pulled toward the base end, causing the tip of the ground engagement portion to dig into the ground. [Effects of the Invention]

[0011] With the above-mentioned configuration, since the stopper part can rotate around the axis of the drain pipe body, even if earth and sand flow between the drilling pipe and the drain pipe, the drain pipe will rotate in conjunction with the rotation of the drilling pipe, causing the drain pipe to twist and close the waterway. In addition, the fixing part between the drain pipe and the stopper part will not be damaged, which will affect the drain pipe's slip-out prevention mechanism. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a side view of the drain pipe according to the embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged side view of the drain pipe body according to the embodiment of the present invention. [Figure 3] FIG. 4 is a side view of a stopper portion according to the embodiment of the present invention. [Figure 4] FIG. 4 is a front view of a stopper portion according to the embodiment of the present invention. [Figure 5] 1 is a flowchart of a method for burying a drainage pipe according to an embodiment of the present invention. [Figure 6] 1 is an explanatory diagram of a method for burying a drainage pipe according to an embodiment of the present invention. FIG. [Figure 7] FIG. 10 is a side view showing another embodiment of the ground anchoring portion. [Figure 8] 10A and 10B are enlarged side views illustrating other configurations of the reduced diameter portion. [Figure 9] FIG. 10 is an explanatory diagram of another method for burying drainage pipes. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Drainage pipes (drainage pipes) are often inserted into earthwork structures such as embankments and cuts for railways, roads, and residential areas, or into uncovered soil slopes without cement coating, etc., in mountainous areas where slopes and landslides are a concern. Drainage pipes drain groundwater from embankments, cuts, and the ground, suppressing the rise of the groundwater level during rainfall and dissipating excess pore water pressure during earthquakes, thereby improving the rainfall resistance and earthquake resistance of the slope. After excavating the ground with a boring pipe, the drainage pipe is inserted into the boring pipe and installed in the ground by rotating and pulling out the boring pipe.

[0014] First, we will explain the configuration of the water drainage pipe 1. In the following explanation, unless otherwise specified, "axial direction" means the direction in which the axis A of the water drainage pipe 1 (water drainage pipe main body 2) extends, "radial direction" means the radial direction with the axis A as the central axis, and "circumferential direction" means the circumferential direction with the axis A as the central axis. Furthermore, "tip side" means the side of the tip of the water drainage pipe 1 in the axial direction, and "base end side" means the base side of the water drainage pipe 1 in the axial direction, opposite the tip side.

[0015] As shown in Figure 1, the drain pipe 1 has a drain pipe body 2 and a stopper portion 3 provided near the tip of the drain pipe body 2. The stopper portion 3 is a mechanism for preventing the drain pipe 1 from coming out. The drain pipe body 2 has a plurality of pipes 4 connected to each other and a tip cap 5 fitted onto the tip. Each pipe 4 is formed so that its outer diameter is, for example, 40 mm or more and 60 mm or less, and the pipe wall thickness is, for example, 2.3 mm. The pipe 4 has multiple water collection holes 41 with a diameter of approximately 5 mm formed therein, through which groundwater and excess pore water permeate. The length of each of the pipes 4 that are connected to each other is, for example, 1 m or more and 4 m or less.

[0016] Next, the connection structure between the pipes 4 will be described, with the pipe 4 arranged upstream of the water flowing through the drain pipe 1 being referred to as the first pipe 4A, and the pipe 4 arranged downstream being referred to as the second pipe 4B. A tube-reduced portion 42 is formed near the end of the first pipe 4A. The tube-reduced portion 42 is a portion that is reduced in diameter from the outer diameter of the pipe 4A. The outer diameter of the tube-reduced portion 42 is formed to be slightly smaller than the inner diameter of the pipe 4A. An end of a second pipe 4B that is not contracted is inserted into the contracted portion 42 of the first pipe 4A, and the two pipes are joined by a rivet.

[0017] The tip cap 5 is a member for reducing earth pressure resistance during penetration. As shown in FIG. 2, the tip cap 5 has a conical cap body 51 and a cap connection part 52 for connecting the cap body 51 to the pipe. The cap connection part 52 is inserted into the inside of the pipe 4 while being pressed, and is fixed in place by the frictional force between the cap connection part 52 and the pipe 4. In this embodiment, the cap connection part 52 consists of two protrusions, and the tip cap 5 is fixed to the pipe 4 by inserting the protrusions into the pipe 4 while slightly deforming them. The method for fixing the tip cap 5 is not limited to this, and it may be fixed using a fastening member such as a bolt.

[0018] The tip cap 5 is attached to the pipe 4 so that a predetermined gap G is provided between the cap body 51 and the pipe 4 to attach the stopper portion 3 rotatably around the axis A. In the water drain pipe body 2, the portion between the cap body 51 and the pipe 4 forms a reduced diameter section C whose diameter is smaller than the outer diameter of the water drain pipe body 2. In other words, in this embodiment, a reduced diameter section C whose outer diameter is smaller than the outer diameter of the water drain pipe body 2 (pipe 4) is provided near the tip of the water drain pipe body 2.

[0019] As shown in Figures 3 and 4, the stopper portion 3 has an annular portion 31 and a plurality of ground engaging portions 7 that are arranged to protrude radially outward from the annular portion 31 and are connected to the outer surface of the annular portion 31. The annular portion 31 is an annular part that is attached to the reduced diameter portion C of the drain pipe main body 2 so as to be rotatable around the axis A. The annular portion 31 is formed so as to rotate smoothly in the circumferential direction when the stopper portion 3 is attached to the reduced diameter portion C of the drain pipe main body 2. Specifically, the annular portion 31 in this embodiment has an octagonal cylindrical shape, and is formed so that the distance F between the opposing parallel portions is approximately the same as the outer diameter of the pipe 4 and is slightly larger than the maximum outer diameter of the reduced diameter portion C. The annular portion 31 in this embodiment is formed by welding two pieces of flat steel together.

[0020] Considering that the annular portion 31 rotates in the circumferential direction, it is preferable that the cross section of the annular portion 31 is circular. The octagonal cylindrical annular portion 31 of this embodiment is preferable in that it is easy to connect the ground anchoring portion 7 formed of flat steel on the outer surface.

[0021] The ground engaging portion 7 is a long member provided so as to protrude radially outward from the drainage pipe main body 2. The ground engaging portion 7 is connected to the outer surface of the annular portion 31 and is therefore rotatable around the axis A. In this embodiment, four ground engaging portions 7 are provided at equal intervals around the circumference. The ground engaging portion 7 has a first ground engaging portion 71 that extends radially outward from the annular portion 31 and toward the base end side A2 of the drainage pipe main body 2, and a second ground engaging portion 72 that is formed by bending further from the end of the first ground engaging portion 71 radially outward from the drainage pipe main body 2.

[0022] The angle a1 of the first ground engaging portion 71 (the angle between the main surface of the first ground engaging portion 71 and the axis A of the drainage pipe main body 2) is preferably 5° or more and 30° or less, and more preferably 10° or more and 20° or less, relative to the axis A of the drainage pipe main body 2. In this embodiment, the angle a1 of the first ground engaging portion 71 is 14°. The angle a2 of the second ground engaging portion 72 (the angle between the main surface of the first ground engaging portion 71 and the main surface of the second ground engaging portion 72) is preferably 10° or more and 20° or less with respect to the main surface of the first ground engaging portion 71. In this embodiment, the angle a2 of the second ground engaging portion 72 is 15°.

[0023] The angle a3 formed between the main surface of the second ground engaging portion 72 and the axis A is preferably 15° or more and 50° or less, and more preferably 25° or more and 35° or less. In this embodiment, the angle a3 formed between the main surface of the second ground engaging portion 72 and the axis A is 29° (14° + 15°). According to the study of the inventors, it was found that the second ground anchoring portion 72 can be easily anchored to the ground by setting the angle a3 between the main surface of the second ground anchoring portion 72 and the axis A to be 15° or more and 50° or less.

[0024] As described above, the drainage pipe 1 is installed in the ground after the ground has been excavated with the drilling pipe, and the length of the ground engagement part 7 is determined based on the diameter of the borehole formed in the ground after excavation. The ground engagement part 7 of this embodiment is formed so that the maximum outer diameter D of the stopper part 3 shown in Figure 4 is larger than the diameter of the borehole.

[0025] The ground anchoring portion 7 is preferably formed from an elastically deformable material, specifically flat steel. In environments where corrosion resistance is required, stainless steel is more preferable. The width of the ground anchoring portion 7 is preferably 10 mm to 20 mm. The width of the ground anchoring portion 7 in this embodiment is 12 mm. The thickness of the ground anchoring portion 7 is preferably 1.0 mm to 3.2 mm. The thickness of the ground anchoring portion 7 in this embodiment is 1.5 mm.

[0026] The tip P of the elongated ground engaging portion 7 is substantially triangular. That is, the ground engaging portion 7 has a sharpened shape that gradually becomes thinner toward the tip. In this embodiment, the tip P is formed so that the angle of the triangle is approximately 60°. The shape of the tip P of the ground engaging portion 7 may be any shape that easily bites into the ground, and may be an isosceles triangle with an angle of less than 60°, or a right triangle. Furthermore, the shape of the tip P of the ground engaging portion 7 does not necessarily have to be triangular, and may be a trapezoid or a sawtooth shape with multiple approximately triangular portions.

[0027] [How to install drainage pipes] Next, a method for burying the drainage pipe 1 will be described. As shown in Figure 5, the method of burying a drainage pipe includes a drilling process S1 in which the ground is excavated with a drilling pipe, a drainage pipe insertion process S2 in which the drainage pipe is inserted into the drilling pipe, a drilling pipe removal process S3 in which the drilling pipe is removed while rotating, and a drilling pipe removal process S4 in which the drilling pipe is removed.

[0028] In the drilling step S1, a machine having a drilling function is used to excavate the ground using a double pipe consisting of a cylindrical drill pipe and a drilling pipe placed on the outside. The diameter of the drilling pipe can be appropriately selected based on the specifications of the drainage pipe to be buried, and is preferably 1.5 to 1.8 times the diameter of the drainage pipe, for example. 6(a) is a cross-sectional view showing the state of the ground after drilling and with the drill pipe removed. A predetermined gap is formed between the drill pipe 10 and the drill hole H.

[0029] In the drain pipe insertion step S2, the drain pipe 1 having the stopper portion 3 is inserted into the drilling pipe 10. As shown in FIG. 6( b ), by inserting the drainage pipe 1 into the drilling pipe 10 , the ground engaging portion 7 of the stopper portion 3 is elastically deformed and pressed against the inner peripheral surface of the drilling pipe 10 .

[0030] In the drilling pipe withdrawal step S3, as shown in Figure 6(c), the drilling pipe 10 is rotated and pulled out toward the base end side A2 of the drainage pipe main body 2 beyond the ground engagement part 7 until the ground engagement part 7 is released from the tip of the drilling pipe 10. This opens the ground engagement part 7, and the stopper part 3 functions as a mechanism to prevent the drainage pipe 1 from coming out. Furthermore, even if earth and sand has flowed between the drilling pipe 10 and the drainage pipe 1, the rotatable stopper part 3 prevents damage from occurring between the drainage pipe 1 and the stopper part 3 even if the drainage pipe 1 rotates as the drilling pipe 10 rotates.

[0031] Next, as shown in Figure 6(d), the drilling pipe 10 is pushed into the tip side A1 of the drainage pipe main body 2. In other words, the drilling pipe 10 is pushed toward the bottom of the borehole H. This causes the tip of the drilling pipe 10 to abut against the inner surface of the ground engagement part 7, causing the ground engagement part 7 to deform and expand, coming into close contact with the ground (the inner surface of the borehole H). This causes the tip part P of the ground engagement part 7 to dig into the ground, thereby better demonstrating its function as a mechanism to prevent the drainage pipe 1 from slipping out.

[0032] In this method, it is preferable to bend the tip of the ground anchoring portion 7 as shown in Fig. 7, as this makes it easier for the tip to pierce the ground. Setting the tip angle a4 to 45° or more (preferably 60° to 95°) makes it easier for the tip to dig into the ground.

[0033] In the drilling pipe removal step S4, the drilling pipe 10 is removed by being pulled out while being rotated, as shown in FIG. 6(e).

[0034] According to the above embodiment, when the drilling pipe 10 is pulled out while being rotated, earth and sand flows between the drilling pipe 10 and the drainage pipe 1, and even if the drainage pipe 1 rotates in conjunction with the rotation of the drilling pipe 10, the ground locking portion 7, which functions as a mechanism to prevent the drainage pipe 1 from coming out, is fixed to the rotatable annular portion 31, so no twisting occurs in the drainage pipe 1. This prevents the water channel inside the drainage pipe 1 from being closed, prevents damage from occurring between the drainage pipe 1 and the stopper portion 3, and does not affect the mechanism to prevent the drainage pipe 1 from coming out.

[0035] Furthermore, by making the ground engaging portion 7 a two-stage structure consisting of a first ground engaging portion 71 and a second ground engaging portion 72, the angle a1 can be reduced to reduce the resistance when inserting the drainage pipe into the drilling pipe, while the angle a3 can be increased to make it easier to engage the tip side of the ground engaging portion 7 with the ground.

[0036] In the above embodiment, the reduced diameter section C is formed by the cap connecting section 52 of the tip cap 5, and the stopper section 3 is located near the tip of the drain pipe main body 2, but the configuration of the reduced diameter section C is not limited to this as long as it has an outer diameter smaller than the outer diameter of the drain pipe main body 2 (pipe 4). For example, the diameter of the pipe 4 may be reduced by press molding using hydraulic pressure or the like. Alternatively, as shown in Figure 8, the connection section between pipes 4 may serve as the reduced diameter section C.

[0037] In the above embodiment, the annular portion 31 is formed by welding two pieces of flat steel together, and the ground engaging portion 7 is joined to the outer surface of the annular portion 31 to form the stopper portion 3, but the annular portion 31 and the ground engaging portion 7 may be formed integrally by cutting a plate material. In this way, by forming the stopper portion into an integral portion, it is possible to reduce manufacturing costs.

[0038] Furthermore, as long as the annular portion 31 can rotate in the circumferential direction of the drain pipe body 2, it is not limited to a closed cross section, and may be an open cross section with an opening in part. Furthermore, the number, shape and material of the ground anchoring portion 7 are not limited as long as it can be fixed to the ground, such as a plate material or a rod material.

[0039] [Other methods of burying drainage pipes] In the above-described method for burying a drainage pipe, in the drilling pipe withdrawal step S3, the drilling pipe 10 is pushed toward the bottom of the borehole H to deform the ground engagement portion 7 so that it widens, but as shown in Fig. 9, the drainage pipe 1 may be withdrawn toward the base end side A2 to cause the tip of the ground engagement portion 7 to dig into the ground. This method also allows the drainage pipe 1 to better function as a mechanism for preventing it from slipping out. Furthermore, by combining the method of pushing the drilling pipe 10 toward the bottom of the excavation hole H (the method shown in Figure 6(d)) with the method of pulling the drainage pipe 1 toward the base end side A2 (the method shown in Figure 9), the tip of the ground engagement portion 7 digs more deeply into the ground, further improving its function as a slip-out prevention mechanism. [Explanation of symbols]

[0040] 1...Drain pipe, 2...Drain body, 3...Stopper part, 4...Pipe, 5...Tip cap, 7...Ground retaining part, 10...Drilling pipe, 41...Water collection hole, 42...Contracted pipe part, 51...Cap body, 52...Cap connection part, 31...Annular part, 32...Ground retaining part, 71...First ground retaining part, 72...Second ground retaining part, A...Axis, A1...Tip side, A2...Base side, C...Contracted diameter part, D...Maximum outer diameter, G...Gap, P...Tip part.

Claims

1. After excavating the ground with a boring pipe, a drainage pipe is inserted into the boring pipe and installed in the ground by rotating and pulling out the boring pipe. A water drain pipe body, A drainage pipe having a stopper portion that is arranged near the tip or connection portion of the drainage pipe body so as to protrude radially outward from the drainage pipe body, and that has a ground engagement portion that can rotate around the axis of the drainage pipe body.

2. A reduced diameter portion having a diameter smaller than the outer diameter of the drain pipe body is provided near the tip or at the connection portion of the drain pipe body, the stopper portion has an annular portion rotatably disposed around the reduced diameter portion, The drain pipe according to claim 1 , wherein the ground anchoring portion is connected to an outer surface of the annular portion.

3. 3. The drainage pipe according to claim 1, wherein the ground anchoring portion is elongated and has a tip end that is substantially triangular.

4. A drain pipe as described in claim 2, wherein the ground engagement portion has a first ground engagement portion extending from the annular portion radially outward of the drain pipe body and toward the base end of the drain pipe body, and a second ground engagement portion formed by further bending from the end of the first ground engagement portion radially outward of the drain pipe body.

5. The drain pipe according to claim 2 or 4, wherein the annular portion and the ground anchoring portion are integrally formed by cutting a plate material.

6. A drainage pipe having a drainage pipe body and a stopper portion provided near the tip or at the connection portion of the drainage pipe body so as to protrude radially outward from the drainage pipe body and having a ground engaging portion that can rotate around the axis of the drainage pipe body, a drilling process of excavating the ground with a drilling pipe; A drainage pipe insertion process in which the drainage pipe is inserted into the drilling pipe while pressing the ground engaging portion against the inner peripheral surface of the drilling pipe; and a drilling pipe drawing step of drawing out the drilling pipe while rotating it, In the drilling pipe extraction step, after the drilling pipe is extracted, the ground engagement portion expands, thereby fixing the ground engagement portion to the ground.

7. In the drilled pipe drawing process, A method for burying a drainage pipe as described in claim 6, wherein the drilling pipe is pulled out toward the base end of the drainage pipe body beyond the ground engagement portion, the ground engagement portion is widened, and then the drilling pipe is pushed toward the tip end of the drainage pipe body and the tip of the drilling pipe is pressed against the ground engagement portion, thereby causing the tip end of the ground engagement portion to dig into the ground.

8. In the drilled pipe drawing process, A method for burying a drainage pipe as described in claim 6 or claim 7, wherein the drilling pipe is pulled out toward the base end of the drainage pipe body beyond the ground engagement portion, the ground engagement portion is widened, and then the drainage pipe is pulled toward the base end so that the tip of the ground engagement portion is embedded in the ground.

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