Method for installing drainage pipes in the ground

Abstract

Even when a lubricant is used to insert drainage pipes into the ground, the reduction in the groundwater collection function caused by the drainage pipes is suppressed. [Solution] A method for installing a drainage pipe in the ground for draining groundwater in the ground, comprising a drainage pipe insertion step in which a lubricant is used when inserting a drainage pipe into the ground to allow groundwater to permeate and collect in the pipe, wherein the lubricant has a predetermined viscosity when the drainage pipe is inserted into the ground, and after the drainage pipe has been inserted into the ground, the predetermined viscosity is reduced by the decomposition performance of organic matter.

Description

Technical Field

[0006]

[0001] The present invention relates to a method for installing a drain pipe in the ground.

Background Art

[0002] In Patent Document 1, for example, a method of installing a drain pipe made of a cylindrical woven fabric in the ground and collecting and draining groundwater through this drain pipe has been proposed when draining groundwater for the purpose of preventing liquefaction of the ground.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When collecting and draining groundwater using a drain pipe installed in the ground, when inserting this drain pipe into the ground, it has also been proposed to use a lubricant to reduce the friction between the surface of the drain pipe and the ground. However, when using a lubricant simply for the purpose of reducing friction, after installing the drain pipe in the ground, the groundwater collection function of the drain pipe may be reduced due to the presence of the lubricant, and sufficient drainage may not be possible in some cases.

[0005] An object of the present invention is to suppress a decrease in the groundwater collection function of a drain pipe even when the drain pipe is inserted into the ground using a lubricant.

Means for Solving the Problems

[0006] The invention according to claim 1 is a method for installing a drain pipe in the ground for draining groundwater in the ground, having a drain pipe insertion step of using a lubricant when inserting a drain pipe that allows groundwater to permeate and collect water inside the pipe into the ground, and the lubricant is when inserting the drain pipe into the groundHaving a first viscosity The drainage pipe is inserted into the ground. A predetermined period has elapsed. Later, due to its ability to decompose organic matter The viscosity changes to a second viscosity which is lower than the first viscosity. The drain pipe insertion step involves excavating the ground by advancing a rod toward a receiving shaft provided in the ground, forming a bore in the ground, attaching the drain pipe to one end of the rod, and pulling the drain pipe from the receiving shaft into the bore while spraying the lubricant from one end of the rod, thereby inserting the drain pipe into the ground. Furthermore, the first viscosity is 200 mPa·s or more and 700 mPa·s or less, the second viscosity is 0 mPa·s or more and 100 mPa·s or less, and the predetermined period is 1 day or more and 10 days or less. This is a method for installing drainage pipes underground, characterized by the following features. The invention described in claim 2 is a method for installing a drain pipe in the ground according to claim 1, characterized in that the drain pipe insertion step involves drawing the drain pipe into the bore while spraying the lubricant from a guiding member provided at one end of the rod to guide the drain pipe into the bore. The invention described in claim 3 is that the drain pipe is a cylindrical woven fabric, and the lubricant, after being inserted into the ground, has the ability to decompose organic matter. The viscosity is changed from the first viscosity to the second viscosity. The method for installing a drainage pipe in the ground according to claim 1 is characterized by lowering the height so as not to obstruct the collection of groundwater into the drainage pipe via the woven fabric. The invention described in claim 4 is that the lubricant contains a polysaccharide, and the polysaccharide is broken down into low molecular weight. The viscosity is changed from the first viscosity to the second viscosity. This is a method for installing a drainage pipe in the ground according to claim 1, characterized by lowering the temperature. [Effects of the Invention]

[0007] According to the present invention, even when a drainage pipe is inserted into the ground using a lubricant, the reduction in the groundwater collection function of the drainage pipe can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of the configuration of a drainage system to which this embodiment is applied. [Figure 2] This diagram shows the configuration of a drain pipe to which this embodiment is applied, and is a view of the drain pipe from the outer circumference. [Figure 3]This diagram shows an example of the configuration of a drilling propulsion device used in the borehole drilling process and the drain pipe insertion process. [Figure 4] This diagram shows an example of a method for installing drainage pipes, and is a cross-sectional view along the vertical direction of the ground where the drainage pipes will be installed. [Figure 5] This diagram shows an example of a method for installing drainage pipes, and is a cross-sectional view along the vertical direction of the ground where the drainage pipes will be installed. [Figure 6] This diagram shows an example of a method for installing drainage pipes, and is a cross-sectional view along the vertical direction of the ground where the drainage pipes will be installed. [Figure 7] This diagram illustrates an example of attaching a drain pipe to a flexible rod, and is a magnified view of the tip of the flexible rod. [Figure 8] This figure shows the change in the viscosity of the lubricant over time. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the attached drawings. Figure 1 shows an example of the configuration of the drainage system 1 to which this embodiment is applied. Figure 1 corresponds to a cross-sectional view obtained by cutting the ground 9 in the vertical direction in which the drainage system 1 is used. The drainage system 1 of this embodiment is used to drain groundwater present in the ground 9 to the outside of the ground 9 and to lower the groundwater level in the ground 9. More specifically, the drainage system 1 is used to lower the groundwater level in the ground 9 from the initial water level P1 to the target water level P2.

[0010] The drainage system 1 has a drainage section 100 that collects and drains groundwater from the ground 9. The drainage system 1 also has a first shaft 510 that is excavated vertically from the surface 91 of the ground 9 and is used for maintenance of the drainage section 100. The drainage system 1 also has a second shaft 520 that is excavated vertically from the surface 91 and into which the groundwater collected by the drainage section 100 is drained. The first vertical shaft 510 and the second vertical shaft 520 are provided at positions separated horizontally. The distance between the first vertical shaft 510 and the second vertical shaft 520 can be, for example, 30 m or more and 100 m or less.

[0011] The drainage section 100 is installed in the ground 9 and has a drain pipe 120 that collects groundwater in the ground 9. One end 121 of the drain pipe 120 is connected to the first vertical shaft 510, and the other end 122 is connected to the second vertical shaft 520. Further, the drainage section 100 has a drainage mechanism 150 that is attached to the other end 122 of the drain pipe 120 and drains the groundwater collected by the drain pipe 120 into the second vertical shaft 520. The drainage mechanism 150 is installed inside the second vertical shaft 520. The drainage mechanism 150 is configured in a U-shape by, for example, an inlet pipe, a connecting pipe, and an outlet pipe connected to the other end 122 of the drain pipe 120, and includes a U-shaped pipe that drains groundwater into the second vertical shaft 520.

[0012] The drain pipe 120 is a tubular member having flexibility and formed with a space through which groundwater can pass inside. The drain pipe 120 has an inclined portion 123 that extends in a direction inclined horizontally downward from the ground 9 from one end 121 connected to the first vertical shaft 510. Further, the drain pipe 120 has an extension portion 124 that extends horizontally from the end of the inclined portion 123 toward the other end 122 connected to the second vertical shaft 520. Note that the extension portion 124 does not necessarily have to extend horizontally as long as the inclination angle with respect to the horizontal direction is smaller than that of the inclined portion 123. In the present embodiment, the extension portion 124 of the drain pipe 120 is installed below the target water level P2 of the groundwater. Details of the drain pipe 120 will be described later.

[0013] The first vertical shaft 510 is a vertical shaft derived from a starting vertical shaft 530 (see FIG. 4 described later) formed in the ground 9 when installing the drain pipe 120 described later. In this example, one end 121 of the drain pipe 120 is connected to the bottom of the first vertical shaft 510. The depth of the first vertical shaft 510 is shallower than that of the second vertical shaft 520. Also, the depth of the first vertical shaft 510 is shallower than the target water level P2. The depth of the first vertical shaft 510 can be, for example, 0.7 m.

[0014] The second vertical shaft 520 is a vertical shaft derived from the access vertical shaft 540 (see FIG. 4 described later) formed in the ground 9 when installing the drain pipe 120 described later. The second vertical shaft 520 has, for example, a cylindrical shape. In this example, the other end 122 of the drain pipe 120 is connected to the side surface of the second vertical shaft 520. The depth of the second vertical shaft 520 is deeper than the target water level P2. The depth of the second vertical shaft 520 can be, for example, 3.5 m. Note that the depths of the first vertical shaft 510 and the second vertical shaft 520 may be changed according to the topography and geology of the ground 9 where the drain pipe 120 is provided, the flow of groundwater, the initial water level P1 of groundwater, etc.

[0015] Subsequently, the configuration of the drain pipe 120 will be described in detail. FIG. 2 is a diagram showing the configuration of the drain pipe 120 to which the present embodiment is applied, and is a view of the drain pipe 120 seen from the outside. The drain pipe 120 is a flexible cylindrical member in which a space for groundwater to flow is formed inside.

[0016] The diameter of the drain pipe 120 is not particularly limited, but it is preferably smaller than the diameter of a conventional drain pipe used for draining groundwater, which is 200 mm to 300 mm. The diameter of the drain pipe 120 can be exemplified, for example, in the range of 40 mm or more and 70 mm or less. Hereinafter, the case where the diameter of the drain pipe 120 is 53 mm will be described as an example. In the present embodiment, by using the small-diameter drain pipe 120, it is possible to install the drain pipe 120 in the ground 9 without using a large-scale propulsion method or the like.

[0017] The drain pipe 120 of this embodiment is made of a tubular woven fabric having warp threads 131 arranged in a ring in the cross-sectional direction of the drain pipe 120 and weft threads 132 woven spirally with respect to the warp threads 131. The warp threads 131 are composed of flexible synthetic fibers. Examples of warp threads 131 include synthetic fibers made of long polyester or nylon fibers.

[0018] The weft thread 132 has rigidity greater than or equal to a predetermined size. The weft thread 132 is composed of at least one of a metal wire made of stainless steel or the like, or a rigid resin wire made of a rigid monofilament material.

[0019] As shown in Figure 2, the drain pipe 120 of this embodiment has fray-preventing portions 135 at both ends 133 and 134 to prevent the warp threads 131 from unraveling from the weft threads 132. The fray-preventing portions 135 can be formed, for example, by a heat treatment that melts and integrates the warp threads 131 and the weft threads 132, or by applying an adhesive.

[0020] The drain pipe 120 of this embodiment, having the above configuration, possesses flexibility and self-shape retention. Specifically, the drain pipe 120 can be easily bent in the bending direction due to the warp threads 131 made of flexible synthetic fibers in the longitudinal direction. Furthermore, the drain pipe 120 ensures self-shape retention in the radial direction, allowing the cross-sectional shape to be maintained in a cylindrical shape due to the rigid weft threads 132.

[0021] Furthermore, the drain pipe 120 is constructed from a tubular woven fabric in which warp threads 131 and weft threads 132 are woven together, and has fine pores formed by the mesh size of the warp threads 131 and weft threads 132. The drain pipe 120 is designed so that groundwater from the ground 9 enters the inside of the drain pipe 120 through these pores, thereby ensuring good drainage. The density of holes in the drain pipe 120 can be exemplified by a range of, for example, 30,000 holes / m or more and 60,000 holes / m or less. Furthermore, it is preferable that the diameter of the holes formed in the drain pipe 120 be 100 μm or less. By having a hole diameter of 100 μm or less, soil and sediment from the ground 9 are prevented from entering the inside of the drain pipe 120, thereby preventing soil runoff and clogging of the drain pipe 120 by soil and sediment. An example of a hole diameter formed in the drain pipe 120 is a range of 25 μm to 80 μm.

[0022] Next, we will explain how to install the drainage pipe 120 within the ground 9. In the following, the method for installing the drainage pipe 120 within the ground 9 may be referred to as the method for installing the drainage pipe 120. The method for installing the drain pipe 120 in this embodiment includes a shaft formation step, a drilling and excavation step, and a drain pipe insertion step. Figure 3 shows an example of the configuration of the drilling propulsion device 110 used in the drilling and drainage pipe insertion processes. Figures 4 to 6 show an example of a method for installing a drain pipe 120, and are cross-sectional views along the vertical direction of the ground 9 where the drain pipe 120 is installed. Figure 4 shows the shaft formation process, Figure 5 shows the drilling and excavation process, and Figure 6 shows the drain pipe installation process.

[0023] First, let me explain the drilling and jacking device 110. The drilling jacking device 110 includes a bit 111 for drilling the ground 9 and a hollow flexible rod 112 that is flexible and has the bit 111 attached to its tip. The drilling jacking device 110 also includes a drive unit 114 for driving the flexible rod 112. The drilling jacking device 110 also includes a guide unit 115 for guiding the direction of travel of the flexible rod 112 and an angle adjustment unit 116 for adjusting the angle of the guide unit 115.

[0024] The bit 111 is rotated by the drive unit 114 via the flexible rod 112 to excavate the ground 9. The bit 111 contains a transmitter (not shown) that emits electromagnetic waves. The drilling propulsion device 110 installs a receiver 119 (see Figure 5) on the ground surface 91 to receive the electromagnetic waves emitted from the bit 111. Based on the intensity of the electromagnetic waves received by the receiver 119, the position, depth, orientation, etc. of the bit 111 in the ground 9 are detected, and the ground 9 is drilled based on the detection results. Furthermore, the bit 111 is provided with a nozzle (not shown) for ejecting liquid supplied through a supply channel (not shown) located inside the flexible rod 112 to the outside. Excavation of the ground 9 by the drilling jacking device 110 may be carried out while ejecting a liquid such as a lubricant from the nozzle.

[0025] The flexible rod 112 has flexibility that allows it to be bent in a predetermined direction relative to its length. The flexible rod 112 is constructed by connecting multiple rods. Specifically, the flexible rod 112 has a bit 111 attached to its tip, and other rods are connected to the rear end of one rod. Furthermore, when the drilling propulsion device 110 excavates the ground 9, as the bit 111 advances while excavating within the ground 9, other rods are sequentially connected to the rear end of the rod, thereby forming a flexible rod 112 of the desired length. A drive unit 114 is connected to the rear end of the flexible rod 112, which is made up of multiple connected rods. In this embodiment, the tip of the flexible rod 112 is the downstream end in the direction of propulsion during the drilling process, and the end furthest from the drive unit 114. The rear end of the flexible rod 112 is the upstream end in the direction of propulsion during the drilling process, and the end to which the drive unit 114 is connected.

[0026] The flexible rod 112 has a cylindrical shape. Inside the flexible rod 112, there is a supply channel for supplying liquids such as lubricants used in drilling and drainage pipe installation processes from the rear end to the front end of the flexible rod 112. The flexible rod 112 and the bit 111 attached to the end of the flexible rod 112 have a diameter slightly smaller than the diameter of the drain pipe 120. For example, if the diameter of the drain pipe 120 is 53 mm, the diameters of the flexible rod 112 and the bit 111 can be 50 mm.

[0027] The drive unit 114 drives the flexible rod 112 to rotate it and also applies vibration to the flexible rod 112. The drive unit 114 drives the flexible rod 112, applying a predetermined torque, rotational force, and vibration to the bit 111 connected to the tip of the flexible rod 112. This allows the bit 111 to advance through the ground 9 while cutting it.

[0028] The guide section 115 supports the flexible rod 112 and guides the direction in which the flexible rod 112 moves. The guide section 115 supports the flexible rod 112 such that it inclins downward as the flexible rod 112 moves from the rear end to the front end. The angle adjustment unit 116 adjusts the approach angle, which is the angle at which the flexible rod 112 supported by the guide unit 115 is inserted into the ground 9, by adjusting the inclination angle of the guide unit 115. For example, the angle adjustment unit 116 adjusts the inclination angle of the guide unit 115 so that the approach angle is between 15 degrees and 45 degrees.

[0029] Next, each step in the installation method of the drain pipe 120 in this embodiment will be described in order. In the shaft formation process, a launch shaft 530 is provided in the ground 9 where the drainage pipe 120 will be installed, for inserting the bit 111 and flexible rod 112 of the drilling jacking device 110. In addition, in the shaft formation process, a receiving shaft 540 is provided in the ground 9 at a predetermined distance from the launch shaft 530, for the bit 111 that has been inserted from the launch shaft 530 to reach. The launch shaft 530 is formed in a sloping shape, having a vertically extending wall surface 531 and an inclined surface 532 extending from the wall surface 531 toward the ground surface 91. The launch shaft 530 can be, for example, about 1 m wide, 3 m long, and 0.7 m deep. The receiving shaft 540 can have a cylindrical shape extending vertically. The depth of the receiving shaft 540 is greater than the depth of the launching shaft 530 and the target water level P2 (see Figure 1). The depth of the receiving shaft 540 can be, for example, about 5m to 6m.

[0030] Next, in the drilling process, the flexible rod 112 is moved along the inclined surface 532 of the launching shaft 530, while the bit 111 and the flexible rod 112 are driven in from the wall surface 531 of the launching shaft 530. Then, the flexible rod 112 is rotated by the drive unit 114, while the bit 111 is advanced toward the receiving shaft 540. In this way, the ground 9 is excavated so that the bit 111 passes through an area below the target water level P2, thereby forming a borehole 550. In addition, in the drilling process, the rods constituting the flexible rod 112 are sequentially connected to the rear end of the flexible rod 112 while excavating the ground 9. Furthermore, in the drilling process, the ground 9 may be excavated while a liquid such as lubricant is ejected from the nozzle of the bit 111.

[0031] In this embodiment, as shown in Figure 5, a receiver 119 that receives electromagnetic waves from the bit 111 is used to detect the position, depth, and orientation of the bit 111 while performing so-called guided boring, which involves drilling the ground 9. The drilling propulsion device 110 can guide the propulsion direction of the bit 111 in a three-dimensional direction by guided boring. This makes it possible to form a borehole 550 that corresponds to the groundwater level in the ground 9 and the topography of the ground 9.

[0032] Once the tip of the flexible rod 112 and the bit 111 attached to the tip of the flexible rod 112 reach the receiving shaft 540 and the drilling of the borehole 550 is completed, the drainage pipe installation process is then carried out. In the drain pipe installation process, first, the bit 111 is removed from the tip of the flexible rod 112. Then, the drain pipe 120 is attached to the tip of the flexible rod 112.

[0033] Figure 7 illustrates an example of attaching a drain pipe 120 to a flexible rod 112, and is an enlarged view of the tip of the flexible rod 112. In the drain pipe installation process, after removing the bit 111 (see Figure 5) from the tip of the flexible rod 112, the diameter-expanding reamer 145 is first attached to the flexible rod 112. The diameter-expanding reamer 145 is a component that enlarges the diameter of the borehole 550 (see Figure 6) by advancing it along the borehole 550 (see Figure 6) through the ground 9 (see Figure 6). The diameter-expanding reamer 145 is an example of a guide component. The diameter-expanding reamer 145 has an outlet 145a formed therein for ejecting liquid supplied through a supply passage provided in the flexible rod 112 to the outside.

[0034] Next, a connecting member 140 is attached to the tip of the diameter-expanding reamer 145 to connect the flexible rod 112 and the drain pipe 120. The connecting member 140 is a so-called towing head. The connecting member 140 has a cylindrical main body portion 141 to which the drain pipe 120 is attached. The connecting member 140 also has a diameter-reducing portion 142 that decreases in diameter from the main body portion 141 towards the end. The connecting member 140 also has a joint 143 attached to the end of the diameter-reducing portion 142 and connected to the diameter-expanding reamer 145. In the drain pipe installation process, the drain pipe 120 is attached to the main body 141 of the connecting member 140, and then the connecting member 140 is connected to the diameter-expanding reamer 145 via the joint 143. As a result, the drain pipe 120 is attached to the flexible rod 112 with the connecting member 140 and the diameter-expanding reamer 145 in between.

[0035] Although not shown in the diagram, the connecting member 140 has multiple protrusions on the outer circumferential surface of the main body 141. The connecting member 140 has the function of expanding the diameter of the main body 141 outward by rotating the diameter-reducing portion 142 and tightening it onto the main body 141. As a result, the drain pipe 120 is attached to the outer circumference of the main body 141, and by expanding the diameter of the main body 141, the drain pipe 120 is pressed from the inner circumference by the protrusions of the main body 141, and the drain pipe 120 is fixed to the connecting member 140.

[0036] In the drain pipe insertion process, the flexible rod 112 is rotated by the drive unit 114 (see Figure 3) while the drain pipe 120 attached to the flexible rod 112 is pulled into the borehole 550. In addition, in the drain pipe insertion process, the rods constituting the flexible rod 112 are sequentially removed from the rear end of the flexible rod 112 while the drain pipe 120 is pulled in. As a result, the drain pipe 120 is drawn into the borehole 550 and inserted into the ground 9.

[0037] Furthermore, during the drain pipe installation process, the drain pipe 120 is installed while lubricant is ejected from a nozzle 145a formed in the diameter-expanding reamer 145. The lubricant is supplied to the diameter-expanding reamer 145 from, for example, a lubricant supply device (not shown) installed on the ground surface 91 via a supply channel provided in the flexible rod 112. During the drain pipe installation process, by injecting a lubricant while pulling the drain pipe 120 into the borehole 550, friction between the ground 9 exposed on the surface of the borehole 550 and the drain pipe 120 and the diameter-enlarging reamer 145 can be reduced. This allows for smooth installation of the drain pipe 120. The lubricant used in the drainage pipe installation process will be explained in detail later.

[0038] In the drain pipe insertion process, once the end of the drain pipe 120 reaches the launch shaft 530 by being pulled into the borehole 550, the connecting member 140, the diameter expanding reamer 145, and the flexible rod 112 are removed from the drain pipe 120. Through the above steps, the installation of the drainage pipe 120 into the ground 9 is completed. In this example, the end of the drain pipe 120 on the launch shaft 530 side is in contact with one end 121 of the drain pipe 120 (see Figure 1), and the end on the receiving shaft 540 side is in contact with the other end 122 of the drain pipe 120 (see Figure 1).

[0039] Subsequently, the launch shaft 530 is modified to form the first shaft 510 (see Figure 1), which will be used for maintenance of the drainage section 100 (see Figure 1). In addition, the arrival shaft 540 is modified to form the second shaft 520 (see Figure 1), which will be used for draining groundwater collected by the drainage section 100. Furthermore, a drainage mechanism 150 (see Figure 1) is installed in the second shaft 520, and the drainage mechanism 150 is connected to the other end 122 of the drain pipe 120 that is exposed in the second shaft 520. This results in the drainage system 1 shown in Figure 1.

[0040] The drainage system 1 collects and drains groundwater so that the groundwater level in the ground 9 drops from the initial water level P1 to the target water level P2. As described above, the drain pipe 120 is installed within the ground 9 at an initial water level P1 and below the target water level P2. As a result, groundwater in the ground 9 permeates through holes formed in the drain pipe 120 and is collected in the internal space of the drain pipe 120. The groundwater then flows through the internal space of the drain pipe 120 from one end 121 to the other end 122 and is drained to the outside of the ground 9 via the drainage mechanism 150. This lowers the groundwater level within the ground 9.

[0041] The drainage system 1 of this embodiment can be used to suppress liquefaction of the ground 9 caused by earthquakes by lowering the groundwater level within the ground 9. Furthermore, the drainage system 1 can be used to stabilize the ground 9 in large-scale embankment areas by draining excess groundwater. Additionally, the drainage system 1 can be used to provide stable drainage during rainfall on slopes, road embankments, etc. In other words, the drainage system 1 can be used regardless of whether the ground 9 is natural ground or artificial ground. Furthermore, in this embodiment, the target water level P2 is set to 3.0 m, and the drainage pipe 120 is installed in the ground 9 so that the depth of the extension 124 from the ground surface 91 is 3.0 m or less. However, the depth from the ground surface 91 to which the drainage pipe 120 is installed may be changed depending on the purpose of using the drainage system 1, and the behavior of groundwater flow and water level which differ depending on the topography and geology of the ground 9.

[0042] Next, we will explain the lubricants used in the drain pipe installation process. If a lubricant is used when installing the drainage pipe 120 in the ground 9 during the drainage pipe installation process, the presence of the lubricant may reduce the water collection function of the drainage pipe 120 when collecting groundwater afterward, which may result in insufficient drainage. In contrast, in this embodiment, during the drain pipe installation process, a lubricant is used that has a predetermined viscosity when the drain pipe 120 is inserted into the ground 9, while its viscosity decreases after insertion into the ground 9 due to its organic matter decomposition performance.

[0043] Figure 8 shows the change in viscosity of lubricants over time. The horizontal axis of Figure 8 represents the number of days elapsed, and the vertical axis represents viscosity. Figure 8 shows the changes in viscosity of five types of lubricants A to E and water. Of the lubricants A to E shown in Figure 8, lubricants A and B decrease in viscosity over time and are suitable for use in the drain pipe installation process of this embodiment. Of the lubricants A to E shown in Figure 8, lubricants C to E are conventional lubricants that show little change in viscosity over time.

[0044] As shown in Figure 8, lubricants A and B have a viscosity in the range of 400 mPa·s to 600 mPa·s during the initial period, more specifically from day 0 to day 2. Then, the viscosity of lubricants A and B gradually decreases over time, and after day 6, the viscosity is 100 mPa·s or less. In addition, after day 6, the viscosity of lubricants A and B decreases to about the same level as water. On the other hand, conventional lubricants C to E show almost no decrease in viscosity over time. In this embodiment, the viscosity of the lubricant is the viscosity of the lubricant measured by a B-type viscometer.

[0045] The lubricant of this embodiment has a first viscosity when the drain pipe 120 is installed in the ground 9 during the drain pipe installation process. The first viscosity can be, for example, in the range of 200 mPa·s to 700 mPa·s, and preferably in the range of 300 mPa·s to 600 mPa·s. With the first viscosity in this range, the friction between the ground 9 exposed on the surface of the borehole 550 and the drain pipe 120, etc., can be reduced by the lubricant during the drain pipe installation process. This makes it possible to smoothly install the drain pipe 120 into the borehole 550. If the first viscosity is 200 mPa·s or less, the lubricant's effect in reducing friction between the ground 9 and the drain pipe 120, etc., during the drain pipe installation process tends to be insufficient. Also, if the first viscosity exceeds 700 mPa·s, it may become difficult to eject the lubricant from the enlargement reamer 145, etc., during the drain pipe installation process.

[0046] Furthermore, after adjusting the viscosity of the lubricant to a first viscosity, the viscosity decreases to a second viscosity, which is lower than the first viscosity, after a predetermined period of time has elapsed. The second viscosity can be, for example, between 0 mPa·s and 100 mPa·s. By having the second viscosity within this range, when the drainage pipe 120 is installed in the ground 9 and groundwater is collected by the drainage pipe 120, the lubricant is prevented from hindering the water collection function of the drainage pipe 120. In this embodiment, the first viscosity of the lubricant is an example of a predetermined viscosity. Reducing the viscosity of the lubricant from the first viscosity to the second viscosity corresponds to reducing the predetermined viscosity.

[0047] The time required for the viscosity of the lubricant to decrease from the first viscosity to the second viscosity varies depending on factors such as the time required to install the drain pipe 120 and the time between the installation of the drain pipe 120 and the start of drainage by the drainage system 1. However, it can be exemplified as being in the range of 1 to 10 days, and preferably in the range of 3 to 7 days. If the time required for the viscosity of the lubricant to decrease is excessively short, the viscosity of the lubricant may decrease during the drainage pipe installation process, and the effect of reducing friction between the ground 9 and the drainage pipe 120 may not be sufficiently obtained. Conversely, if the time required for the viscosity of the lubricant to decrease is excessively long, the viscosity of the lubricant may not decrease after the drainage pipe 120 is installed in the ground 9 until drainage by the drainage system 1 begins, and the water collection function of the drainage pipe 120 may be hindered by the lubricant.

[0048] The lubricant of this embodiment contains a high molecular weight organic substance. Furthermore, the lubricant is obtained by dissolving the high molecular weight organic substance in water, seawater, or the like. The first viscosity of the lubricant can be adjusted by controlling the molecular weight and concentration of the organic substance.

[0049] Furthermore, lubricants work by dissolving high molecular weight organic matter in water or seawater, and then, over time, the high molecular weight organic matter decomposes into lower molecular weight molecules, resulting in a decrease in viscosity. In other words, lubricants contain high molecular weight organic matter that can be decomposed over time. In the drainage pipe installation process, after the drainage pipe 120 is installed in the ground 9, the high molecular weight organic matter contained in the lubricant decomposes. Along with the decomposition of the organic matter, the solid matter in the mud wall formed on the inner surface of the borehole 550 is dispersed. As a result, the seepage area from which groundwater emerges is exposed on the inner surface of the borehole 550, making it easier for groundwater to be collected in the drainage pipe 120.

[0050] Examples of high molecular weight organic substances included in the lubricant that can decompose over time include proteins and polysaccharides, and the use of polysaccharides is preferred. Furthermore, from the viewpoint of reducing the environmental burden on the ground, it is preferable to use naturally derived polysaccharides such as those from plants, seaweed, and microorganisms. Examples of such polysaccharides are not limited to xanthan gum, pectin, starch, mannan, guar gum, gum arabic, tragacanth gum, locust bean gum, tara gum, ramzan gum, gellan gum, and dextran. These polysaccharides may be used individually or in combination.

[0051] The weight-average molecular weight of polysaccharides contained in lubricants varies depending on the type of polysaccharide, but a range of 1 million to 50 million can be given as an example. Furthermore, the lubricant preferably has a pH of 5.0 to 8.0.

[0052] As described above, the method for installing the drain pipe 120 in this embodiment includes a drain pipe insertion step in which a lubricant is used when inserting the drain pipe 120, which allows groundwater to permeate and collect water inside the pipe, into the ground 9. The lubricant has a predetermined viscosity when the drain pipe 120 is inserted into the ground 9, but after the drain pipe 120 is inserted into the ground 9, its viscosity is reduced by the organic matter decomposition performance. As a result, when inserting the drain pipe 120 into the ground 9, friction between the drain pipe 120 and the ground 9 can be reduced by using a lubricant with a predetermined viscosity. Furthermore, when draining groundwater using the drain pipe 120, the reduction in the predetermined viscosity of the lubricant can suppress the decrease in the groundwater collection function of the drain pipe 120.

[0053] In the above-described method for installing the drainage pipe 120, a launching shaft 530 and a receiving shaft 540 are formed in the ground 9 during the shaft formation process. However, the launching shaft 530 and the receiving shaft 540 do not necessarily have to be formed. For example, cliffs or steps existing in the ground 9 may be used as the launching shaft 530 and the receiving shaft 540.

[0054] Although embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Various modifications and combinations are permitted as long as they do not contradict the spirit of the present invention. [Explanation of Symbols]

[0055] 1...Drainage system, 9...Ground, 91...Ground surface, 100...Drainage section, 110...Drilling jacking device, 111...Bit, 112...Flexible rod, 114...Drive unit, 115...Guide unit, 116...Angle adjustment unit, 120...Drainage pipe, 131...Warp thread, 132...Weft thread, 140...Connecting member, 145...Expanding reamer, 510...First shaft, 520...Second shaft, 530...Starting shaft, 540...Receiving shaft, 550...Drilling

Claims

1. A method for installing drainage pipes in the ground to drain groundwater from within the ground, The drainage pipe insertion process involves inserting a drainage pipe into the ground, which allows groundwater to permeate and collect inside the pipe, using a lubricant. The lubricant has a first viscosity when the drain pipe is inserted into the ground, and after the drain pipe has been inserted into the ground and a predetermined period of time has elapsed, it changes to a second viscosity which is lower than the first viscosity due to the decomposition performance of organic matter. The drain pipe insertion step involves advancing a rod toward a receiving shaft provided in the ground, excavating the ground to form a bore in the ground, attaching the drain pipe to one end of the rod, and pulling the drain pipe from the receiving shaft into the bore while spraying the lubricant from one end of the rod, thereby inserting the drain pipe into the ground. The first viscosity is 200 mPa·s or more and 700 mPa·s or less, the second viscosity is 0 mPa·s or more and 100 mPa·s or less, and the predetermined period is 1 day or more and 10 days or less. A method for installing drainage pipes underground, characterized by the following features.

2. The drain pipe insertion step involves drawing the drain pipe into the bore while spraying the lubricant from a guiding member provided at one end of the rod to guide the drain pipe into the bore. A method for installing a drainage pipe in the ground according to claim 1, characterized by the above.

3. The drain pipe is a cylindrical woven fabric, The lubricant, after being inserted into the ground, reduces its viscosity from the first viscosity to the second viscosity due to its organic matter decomposition properties, thereby not hindering the collection of groundwater into the drainage pipe via the woven fabric. A method for installing a drainage pipe in the ground according to claim 1, characterized by the above.

4. The method for installing a drainage pipe in the ground according to claim 1, characterized in that the lubricant contains polysaccharides, and the viscosity is reduced from the first viscosity to the second viscosity by the decomposition of the polysaccharides into low molecular weight molecules.

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