Method for installing underground displacement meter and underground displacement meter installation unit

Abstract

To suppress twisting of an underground displacement meter.SOLUTION: An underground displacement meter installation method that installs a linear underground displacement meter 10 in an underground hole 5 in the ground 1 comprises a holder installation step of inserting the underground displacement meter 10 into an insertion hole 31 of a holder 30 holding the underground displacement meter 10 along its longitudinal direction and attaching the holder 30 to the underground displacement meter, and an insertion step of inserting the underground displacement meter 10 into the underground hole together with the holder 30 and supporting the underground displacement meter 10 with respect to the underground hole 5 by the holder 30. The center of gravity G of the holder 30 is shifted from the cross-sectional center O of the underground displacement meter 10 on a cross section perpendicular to the longitudinal direction of the underground displacement meter 10 when the holder 30 is attached to the underground displacement meter 10.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for installing a ground displacement meter and a holder.

Background Art

[0002] Patent Document 1 discloses a technique for measuring ground displacement by installing a linear displacement meter in a linear space provided in the ground.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When measuring ground displacement with a linear displacement meter as disclosed in Patent Document 1, if torsional deflection occurs around the longitudinal direction of the displacement meter, a deviation will occur between the direction of the displacement measured by the displacement meter and the actual direction of ground displacement. Therefore, in the measurement of ground displacement using a linear displacement meter, it is required to suppress the torsional deflection of the displacement meter.

[0005] An object of the present invention is to suppress the torsional deflection of a ground displacement meter.

Means for Solving the Problems

[0006] The present invention is a method for installing a linear ground displacement meter in a ground hole in the ground, including: A support process involves supporting the underground displacement meter on a linear support section so as to be aligned with the underground displacement meter, a holder attachment step of inserting the ground displacement meter along the longitudinal direction into an insertion hole of a holder for holding the ground displacement meter and attaching the holder to the ground displacement meter; and support part and Ground displacement meter an insertion step of inserting the ground displacement meter together with the holder into the ground hole and supporting the ground displacement meter against the ground hole by the holder. and support part The method includes a holder attachment step of inserting the ground displacement meter along the longitudinal direction into an insertion hole of a holder for holding the ground displacement meter and attaching the holder to the ground displacement meter, and an insertion step of inserting the ground displacement meter together with the holder into the ground hole and supporting the ground displacement meter against the ground hole by the holder. In the holder mounting process, The center of gravity of the holder On a cross-section perpendicular to the longitudinal directionGround displacement meter So that it is located below the center of the cross-section The holder It holds an underground displacement meter. In this state, The support part is supported by a holder. Ground displacement meter Hold upwards , In the insertion process, the support part is positioned above the underground displacement meter, and the support part is grasped and pushed towards the back of the underground hole, thereby inserting the underground displacement meter into the underground hole together with the holder. ru. Furthermore, the present invention relates to a ground displacement meter installation unit for installing a linear ground displacement meter in a ground bore in the ground, comprising: a linear support part provided along the ground displacement meter and supporting the ground displacement meter; and a holder that holds the ground displacement meter and the support part, wherein the holder holds the ground displacement meter such that the center of gravity of the holder is located below the center of the cross-sectional area of ​​the ground displacement meter on a cross-section perpendicular to the longitudinal direction of the ground displacement meter, and the holder holds the support part above the ground displacement meter. [Effects of the Invention]

[0007] According to the present invention, twisting of the underground displacement meter is suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing a subterranean displacement meter installed in a borehole in the ground according to an embodiment of the present invention. [Figure 2] This is an enlarged view showing a ground displacement meter installed underground by the ground displacement meter installation method according to an embodiment of the present invention. [Figure 3] This is a cross-sectional view along the line III-III in Figure 2. [Figure 4] This figure shows the steps of the underground displacement meter installation method according to an embodiment of the present invention in chronological order. [Figure 5] This is a cross-sectional view showing the operation of a holder according to an embodiment of the present invention. [Figure 6] This is a cross-sectional view showing a modified example of a holder according to an embodiment of the present invention. [Modes for carrying out the invention]

[0009] The following describes, with reference to the drawings, the underground displacement meter installation method and the holder 30 according to an embodiment of the present invention.

[0010] The following describes a case in which the underground displacement gauge 10 is used as a displacement measuring instrument to measure the displacement of the ground 1 directly above the underground space, in connection with construction work to construct an underground space such as a tunnel within the ground.

[0011] For example, when constructing an underground space such as a tunnel in the ground using a shield tunneling machine, it is important to grasp the displacement of the ground directly above the shield tunneling machine in order to prevent ground settlement and heave. For this reason, as shown in FIG. 1, a linear in-situ displacement meter 10 capable of detecting ground displacement may be installed directly above the planned route 3 of a shield tunneling machine 4 that constructs a tunnel T in the ground 1.

[0012] The in-situ hole 5 into which the in-situ displacement meter 10 is inserted is pre-drilled substantially parallel to the planned route 3 of the shield tunneling machine 4 so as to have a curved portion that bends in the same direction as the planned route 3 in the horizontal and vertical directions from the shaft 2 where the shield tunneling machine 4 starts.

[0013] As the in-situ displacement meter 10 inserted into the in-situ hole 5, for example, one using an optical fiber cable is used. Since the in-situ displacement meter 10 using an optical fiber cable has a known configuration, detailed illustration and description are omitted. For example, it is configured by spirally winding one or more optical fiber cables in the axial direction (longitudinal direction) inside a sheath material. When using a plurality of optical fiber cables, they are spirally wound with their phases shifted from each other.

[0014] Since the optical fiber cable generates strain in response to the strain in the ground and the loosening of the ground 1, it is possible to measure the strain in the ground and the loosening of the ground 1 by measuring the strain of the optical fiber cable.

[0015] Specifically, the optical fiber cable has the property of slightly backscattering the incident pulsed light, and by utilizing this property, it is possible to measure the strain at multiple positions in the optical fiber cable. Since the frequency of the scattered light depends on the strain of the optical fiber cable, the strain of the optical fiber cable can be measured by irradiating the optical fiber cable with pulsed light and measuring the frequency of the scattered light. Also, by measuring the time from when pulsed light is incident on the optical fiber cable until the scattered light generated in the optical fiber cable returns to the incident position, it is possible to measure the position where the scattered light is generated, that is, the position where the optical fiber cable is strained.

[0016] Therefore, by inserting the in-situ displacement meter 10 including an optical fiber cable into the in-situ hole 5 drilled directly above the planned path 3 of the shield tunneling machine 4, the displacement of the ground 1 caused by the tunneling of the shield tunneling machine 4 can be grasped by measuring the strain generated in the optical fiber cable.

[0017] Note that the in-situ displacement meter 10 is not limited to an optical fiber cable, and any type of displacement meter may be used as long as it can measure the displacement of the ground 1. For example, it may be formed linearly by connecting a plurality of detection units with acceleration sensors, pressure sensors, strain sensors, or tilt sensors attached thereto in the longitudinal direction.

[0018] In order to smoothly insert the in-situ displacement meter 10 into the in-situ hole 5, a pipe member 6 (tubular member) into which the in-situ displacement meter 10 is inserted is installed in the in-situ hole 5 as shown in FIG. 2. Note that the pipe member 6 is not an essential component. The in-situ displacement meter 10 may be directly inserted into the in-situ hole 5 without any other member intervening therebetween.

[0019] The in-situ displacement meter 10 is supported by a linear wire passing wire 20 (supporting portion) provided along the in-situ displacement meter 10. The passing wire 20 is formed of, for example, a resin having higher strength and flexibility than the in-situ displacement meter 10.

[0020] The in-situ displacement meter 10 and the passing wire 20 are integrated by being held by a plurality of holders 30 provided at intervals in their longitudinal directions. As shown in FIGS. 2 and 3, the in-situ displacement meter 10 and the passing wire 20 are integrated by the holder 30 in a state of being arranged side by side along the vertical direction. The holder 30 is inserted into the pipe member 6 together with the in-situ displacement meter 10 and the passing wire 20. That is, the in-situ displacement meter 10 and the passing wire 20 are supported by the inner peripheral surface of the pipe member 6 (and thus the in-situ hole 5) via the holder 30.

[0021] As shown in Figure 3, the holder 30 has a split structure comprising a first holder body 40 and a second holder body 50 that is detachably attached to the first holder body 40. The holder 30 is provided with an insertion hole 31 that penetrates in the thickness direction (perpendicular to the plane of the paper in Figure 3) through which the underground displacement meter 10 and the wire puller 20 are inserted along the longitudinal direction. The holder 30 is formed so that it can be inserted into the pipe member 6, with its maximum width in the direction perpendicular to the thickness direction (maximum dimension on the plane shown in Figure 3) being slightly smaller than the inner diameter of the pipe member 6. The first holder body 40 and the second holder body 50 are made of, for example, steel. The first holder body 40 and the second holder body 50 are provided side by side in the vertical direction.

[0022] The first holder body 40 is a substantially semicircular member in a cross-sectional view perpendicular to the longitudinal direction of the underground displacement meter 10 shown in Figure 3 (a cross-sectional view perpendicular to the axial direction of the insertion hole 31). A semicircular first recess 42 is formed on the flat surface 41 of the first holder body 40 to which the second holder body 50 is attached. The inner diameter of the first recess 42 is formed to correspond to the outer diameter of the underground displacement meter 10. Furthermore, the part of the semicircular first holder body 40 corresponding to the arc (hereinafter referred to as the "arc portion 43") is not an arc shape corresponding to the inner circumferential surface of the pipe member 6, but is formed in a wave shape (gear-like) with repeated undulations in the circumferential direction. As a result, when inserted into the pipe member 6, the contact area (ground contact area) between the first holder body 40 and the pipe member 6 can be reduced, thereby suppressing friction, making it easier to insert the holder 30 and the underground displacement meter 10 into the pipe member 6 when installing the underground displacement meter 10, which will be described later.

[0023] The second holder body 50 has a pair of flat plate portions 51 that are provided on substantially the same plane, and a bent portion 52 that connects one end of the opposing pair of flat plate portions 51, and is formed in a substantially Ω shape in the cross-sectional view shown in Figure 3. The pair of flat plate portions 51 of the second holder body 50 are parallel to the flat surface 41 of the first holder body 40 and are attached by bolts 60. In addition, a second recess 53 is formed by the bent shape of the bent portion 52. When the first holder body 40 and the second holder body 50 are connected to each other, an insertion hole 31 through which the underground displacement meter 10 and the wire pulling 20 are inserted is formed between the first holder body 40 and the second holder body 50 by the first recess 42 of the first holder body 40 and the second recess 53 of the second holder body 50.

[0024] The first holder body 40 and the second holder body 50 are made of the same material (steel in this embodiment), and the first holder body 40 has a larger volume. Therefore, the first holder body 40 is heavier than the second holder body 50. From another perspective, the center of gravity G of the holder 30 is displaced (shifted) vertically downward with respect to the center O of the cross-section of the underground displacement meter 10 in the cross-section shown in Figure 3.

[0025] Next, the method for installing the underground displacement meter in this embodiment will be described.

[0026] The following describes the case where the underground hole 5 formed in the ground is a bottomed hole. Note that the underground displacement meter installation method according to this embodiment is not limited to bottomed holes, but may also be applied to through holes that open to the ground at both ends.

[0027] First, we will explain the drilling of the underground hole 5 for installing the underground displacement gauge 10 and the installation of the pipe member 6 to be inserted into the underground hole 5.

[0028] As shown in Figure 1, the underground borehole 5 is formed by drilling from the shaft 2 toward the ground 1 using a drilling rod extending from a drilling machine (not shown) installed inside the shaft 2. A drilling machine capable of performing curved drilling is used.

[0029] Once the underground hole 5 is drilled, a pipe member 6 is inserted into the drilling rod. The pipe member 6 is a hollow tubular member made of biodegradable plastic that is decomposed into water and carbon dioxide by microorganisms in the soil over time, and the end that is inserted into the drilling rod is a closed end. The pipe member 6 may also be made of a resin such as polyvinyl chloride.

[0030] Then, by withdrawing the drilling rod from the underground hole 5, the pipe member 6 inserted into the drilling rod remains in the underground hole 5 and is positioned within the underground hole 5.

[0031] The gap between the outer surface of the pipe member 6 remaining in the underground hole 5 and the inner wall surface of the underground hole 5 is filled by injecting grout (filling material), such as cement bentonite (not shown). In this way, the underground displacement meter 10 is inserted into the pipe member 6 installed in the underground hole 5.

[0032] Next, I will explain the installation of the underground displacement meter 10.

[0033] In the installation of the underground displacement meter 10, first, a holder attachment process is performed in which the holder 30 is attached to the underground displacement meter 10. Specifically, as shown in Figure 4(a), the wire 20 is positioned so that it is relatively vertically upward, and the wire 20 is placed along the underground displacement meter 10, thereby supporting the underground displacement meter 10 (support process). Then, the first holder body 40 and the second holder body 50 of the separated holder 30 clamp the underground displacement meter 10 and the wire 20 from above and below. At this time, the first holder body 40 is relatively on the lower vertical side. Then, the first holder body 40 and the second holder body 50 are connected to each other by bolts 60. As a result, the underground displacement meter 10 is clamped by the holder 30 and integrated with the wire 20, with the insertion hole 31 formed by the first holder body 40 and the second holder body 50 inserted along its longitudinal direction. Note that, for the sake of clarity, the illustration of bolt 60 is omitted in Figure 4.

[0034] Next, an insertion process is performed in which the underground displacement meter 10, along with the wire guide 20 integrated by the holder 30, is inserted into the pipe member 6 in the underground hole 5. In the insertion process, as shown in Figure 4(b), the underground displacement meter 10 is positioned in a normal position without twisting, and the wire guide 20, which is provided along the underground displacement meter 10 and supports the holder 30, is grasped, and the underground displacement meter 10 is inserted into the pipe member 6 through the opening of the pipe member 6. Then, the wire guide 20 is pushed towards the back of the underground hole 5. This allows the underground displacement meter 10 to be inserted into the pipe member 6 in the underground hole 5 without putting any load on the underground displacement meter 10. The normal position is a position in which the wire guide 20 and the underground displacement meter 10 are aligned vertically, and the cross-sectional center O of the underground displacement meter 10 and the center of gravity G of the holder 30 are aligned vertically (aligned on the vertical axis) (see Figure 3). However, the insertion process does not exclude the step of gripping the underground displacement gauge 10 and inserting it into the pipe member 6 of the underground hole 5.

[0035] Furthermore, as shown in Figure 3, when the underground displacement meter 10 is inserted into the pipe member 6 together with the holder 30, the underground displacement meter 10 and the wire pulling 20 inserted into the pipe member 6 are supported by the inner surface of the pipe member 6 via the holder 30. The holder 30 contacts the inner surface of the pipe member 6 at the corrugated arc portion 43 of the first holder body 40. In this way, by contacting the inner surface of the pipe member 6 with the corrugated arc portion 43, the holder 30 can reduce the contact area and, consequently, the frictional force between itself and the inner surface of the pipe member 6 compared to when it contacts the inner surface of the pipe member 6 with a corresponding arc surface. As a result, when pushing the underground displacement meter 10 deeper into the underground hole 5 together with the holder 30, the resistance from the inner surface of the pipe member 6 is reduced, making it easier to insert the underground displacement meter 10.

[0036] When the underground displacement meter 10 is inserted into the underground hole 5 by a predetermined amount, a new holder 30 is attached to the underground displacement meter 10 and the wire 20, as shown in Figure 4(c), and the underground displacement meter 10 is further inserted into the underground hole 5 together with the holder 30. In this way, the holder attachment process, in which the holder 30 is attached to the underground displacement meter 10 and the wire 20, and the insertion process, in which the underground displacement meter 10 is inserted into the pipe member 6 together with the holder 30 and the wire 20, and the holder 30 supports the underground displacement meter 10 on the inner surface of the pipe member 6, are repeated, and the underground displacement meter 10 is inserted to the deepest part of the underground hole 5. Note that the method of installing the underground displacement meter is not limited to the holder attachment process and the insertion process being performed repeatedly, but each may be performed only once. Also, multiple holders 30 may be attached to the underground displacement meter 10 in a single holder attachment process.

[0037] Even when attempting to insert the wire puller and the underground displacement meter into the underground hole in a normal position, with the wire puller and the underground displacement meter aligned vertically, twisting can occur in the longitudinal direction of the underground displacement meter during the process of pushing (pushing) the meter into the hole. When the underground displacement meter twists in the longitudinal direction, a discrepancy occurs between the direction of the displacement being measured and the direction of the actual ground displacement. To accurately measure the ground displacement, it is necessary to understand the amount of this twisting, but accurately determining the amount of twisting is difficult. Therefore, it is necessary to suppress the twisting that occurs in the underground displacement meter.

[0038] In this embodiment, since the underground displacement meter 10 is integrated with the wire guide 20 by the holder 30, when twisting occurs, the underground displacement meter 10, the wire guide 20, and the holder 30 twist together as a single unit. The center of gravity G of the holder 30 attached to the underground displacement meter 10 is displaced vertically downward from the center of the cross-section O of the underground displacement meter 10 on a cross-section perpendicular to the longitudinal direction of the underground displacement meter 10. In other words, the center of gravity G of the holder 30 is offset (away from) the center of the cross-section O of the underground displacement meter 10. From another perspective, the lower part of the holder 30 (first holder body 40), which is vertically below the center of the cross-section O of the underground displacement meter 10, is configured to be heavier than the upper part of the holder 30 (second holder body 50), which is vertically above the center of the cross-section O of the underground displacement meter 10.

[0039] In this embodiment, as shown in Figure 5, if the underground displacement meter 10, together with the holder 30, attempts to twist (temporarily twists) around its longitudinal direction, the imaginary line L connecting the cross-sectional center O of the underground displacement meter 10 and the center of gravity G of the holder 30 tilts with respect to the vertical axis. When this state occurs, the component force F1 of the gravity Fg of the holder 30 acts as a moment on the underground displacement meter 10 to restore the twist to its original position. Therefore, in this embodiment, the underground displacement meter 10 is less prone to twisting around its longitudinal direction, and even if temporary twisting occurs, the twist is resolved by the gravity (weight) of the holder 30.

[0040] According to the above embodiments, the following effects are achieved.

[0041] In this embodiment, since the underground displacement meter 10 is held by the holder 30, if the underground displacement meter 10 twists in the longitudinal direction, the holder 30 also rotates along with the twist. Since the center of gravity G of the holder 30 is offset from the cross-sectional center O of the underground displacement meter 10, when the holder 30 rotates together with the underground displacement meter 10, a force is generated in the holder 30 that tries to return it to its original position due to its own weight. Therefore, even if the underground displacement meter 10 is temporarily twisted during the process of inserting it into the underground hole 5, the twist of the underground displacement meter 10 can be eliminated by the holder 30 trying to return to its original position due to its own weight. Thus, in this embodiment, the twisting of the underground displacement meter 10 can be suppressed and the accuracy of displacement measurement can be improved.

[0042] Furthermore, in this embodiment, the arc portion 43 of the first holder body 40 that contacts the inner circumferential surface of the pipe member 6 is formed in a corrugated shape. This reduces friction between the holder 30 and the pipe member 6, allowing the underground displacement meter 10 to be easily inserted into the pipe member 6.

[0043] Although this embodiment has been described above, the following modifications are also within the scope of the present invention. Furthermore, it is possible to combine the configurations shown in the modifications with the configurations described in the above embodiment, or to combine the configurations described in the following different modifications.

[0044] In the above embodiment, the underground displacement gauge 10 and the wire guide 20 are inserted into the underground hole 5 in a position where they are aligned vertically, one above the other. In order to prevent twisting of the underground displacement gauge 10, it is desirable to position the wire guide 20 either vertically above or below the underground displacement gauge 10, but it is not limited to this.

[0045] For example, as shown in Figure 6, the underground displacement gauge 10 and the wire guide 20 may be inserted into the pipe member 6 of the underground hole 5 in a position where they are aligned vertically and horizontally perpendicular to the longitudinal direction of the underground displacement gauge 10. In the modified example shown in Figure 6, the holder 30 is made of, for example, resin or metal, and its outer shape is formed to be substantially circular, corresponding to the inner circumferential surface of the pipe member 6, and has a pair of circular insertion holes 31a, 31b into which the underground displacement gauge 10 and the wire guide 20 are inserted, respectively. The holder 30 is formed in a half-split structure, divided vertically into upper and lower sections so as to divide the pair of insertion holes 31a, 31b into two parts each. In the holder 30, the first holder body 40 on the vertically lower side is configured as a solid structure with no voids inside, and the second holder body 50 on the vertically upper side is configured as a hollow structure having a cavity 50a filled with gas inside. Furthermore, the first holder body 40 may be constructed as a structure filled with a heavy material such as metal, which has a specific gravity greater than that of the first holder body 40. Also, the second holder body 50 may be constructed as a structure filled with an object other than gas, which has a specific gravity less than that of the second holder body 50. As a result, the weight of the first holder body 40 will be greater than the weight of the second holder body 50. Therefore, even with such modifications, the same effects and advantages as in the above embodiment can be achieved.

[0046] Furthermore, friction between the holder 30 and the pipe member 6 may prevent the holder 30 from moving (rotating) relative to the pipe member 6, potentially preventing the torsion-removing effect from being fully realized. To address this, the underground displacement meter installation method may further include a torsion removal step, which is performed after the insertion step, to remove the torsion of the underground displacement meter 10 inserted into the underground hole 5. In the torsion removal step, the torsion of the underground displacement meter 10 is removed by methods such as applying vibration to the pipe member 6 or pouring water into the pipe member 6. Applying vibration to the pipe member 6 reduces friction between the holder 30 and the pipe member 6, making it easier for the holder 30 to move relative to the pipe member 6, thus making it easier to remove the torsion caused by the weight of the holder 30. Also, pouring water into the pipe member 6 causes the holder 30 to float away from the pipe member 6, allowing its weight to adjust its posture to a normal posture. Such a torsion removal step may be performed once or multiple times at any time after the initial insertion step.

[0047] Furthermore, in the above embodiment, the underground displacement meter 10 is supported by a wire puller 20 and inserted into the underground hole 5. However, in the method of installing the underground displacement meter 10, the wire puller 20 is not essential.

[0048] Furthermore, in the above embodiment, the holder 30 has two divided members, a first holder body 40 and a second holder body 50, which clamp the underground displacement meter 10. In contrast, the holder 30 is not limited to the configuration of the above embodiment, and for example, the underground displacement meter 10 may be held or clamped by a single member.

[0049] Furthermore, in the above embodiment, the underground displacement gauge 10 and the wire puller 20 are integrated only by the holder 30. In contrast, in addition to being integrated by the holder 30, they may also be integrated by fastening members such as adhesive tape or cable ties.

[0050] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of Symbols]

[0051] 1 ground 5 underground hole 10. Underground displacement meter 20 Wire pulling wire (support part) 30 holders 31 Through hole 31a Through hole 31b Through hole 40 First holder body 50 Second holder

Claims

1. A method for installing underground displacement gauges, which involves installing a linear underground displacement gauge in an underground hole in the ground, A support step involves supporting the underground displacement meter on a linear support portion so as to be aligned with the underground displacement meter, A holder mounting step involves inserting the underground displacement meter and the support portion into the insertion hole of the holder that holds the underground displacement meter, along the longitudinal direction of the underground displacement meter, and attaching the holder to the underground displacement meter and the support portion. The process includes inserting the underground displacement meter into the underground hole together with the holder, and supporting the underground displacement meter with respect to the underground hole by the holder, In the holder mounting step, while the holder is holding the underground displacement meter such that the center of gravity of the holder is located below the center of the cross-section of the underground displacement meter on a cross-section perpendicular to the longitudinal direction, the support portion is held above the underground displacement meter using the holder. In the insertion step, the support portion is grasped and pushed toward the back of the underground hole with the support portion positioned above the underground displacement meter, thereby inserting the underground displacement meter into the underground hole together with the holder. Method for installing underground displacement gauges.

2. A method for installing an underground displacement meter according to claim 1, In the insertion step, the underground displacement meter and the support part are inserted into the underground hole in a position aligned vertically. Method for installing underground displacement gauges.

3. A ground displacement meter installation unit for installing a linear ground displacement meter in a borehole in the ground, A linear support portion is provided along the aforementioned underground displacement meter and supports the underground displacement meter, The underground displacement meter and the holder for holding the support part are provided, In a state in which the holder holds the underground displacement meter such that the center of gravity of the holder is located below the center of the cross-sectional area of ​​the underground displacement meter on a cross-section perpendicular to the longitudinal direction of the underground displacement meter, the holder holds the support portion above the underground displacement meter. Underground displacement meter installation unit.

4. The underground displacement meter installation unit according to Claim 3, The aforementioned holder is, The first holder body and The system comprises a second holder body which is detachably attached to the first holder body and holds the underground displacement meter together with the first holder body, sandwiching the underground displacement meter between them. The first holder body is heavier than the second holder body. Underground displacement meter installation unit.

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