Displacement measuring device and ground displacement measuring method

Abstract

To provide a displacement measurement device that can collect optical fiber cable sensors from a measurement hole after measuring ground displacement.SOLUTION: A displacement measurement device 10 includes: a guide pipe 20 to be inserted into a measurement hole 90; a bag-shaped packer 30 capable of expanding and contracting in the guide pipe 20; and optical fiber cable sensors 50 arranged between an outer surface of the packer 30 and an inner surface of the guide pipe 20. The optical fiber cable sensor 50 can be connected to a measuring device for measuring the displacement of the optical fiber cable sensor 50. In a state where the packer 30 is expanded, the optical fiber cable sensor 50 is sandwiched and fixed between the outer surface of the packer 30 and the inner surface of the guide pipe 20.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a displacement measuring device for measuring ground displacement ahead of a tunnel face during tunnel construction, and a ground displacement measuring method using the displacement measuring device. [Background technology]

[0002] For example, in tunnel construction, in order to adopt an appropriate construction method depending on the ground conditions ahead of the tunnel face, it is necessary to manage ground displacement ahead of the tunnel face. One method of measuring ground displacement is to insert a fiber optic cable sensor into a measurement hole formed in front of the tunnel face, and then analyze the time it takes for the scattered light to return from the measuring device to the fiber optic cable sensor, as well as the frequency distribution of the scattered light, to determine ground displacement. Patent document 1 discloses that an optical fiber cable sensor is attached to the outer surface of a guide tube, the guide tube is inserted into a measurement hole, and grout material is filled into the measurement hole, thereby fixing the optical fiber cable sensor within the measurement hole. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-156215 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional ground displacement measurement method described above, the optical fiber cable sensor is embedded in the grout material filled in the measurement hole, so there is a problem in that the optical fiber cable sensor cannot be retrieved after measuring the ground displacement. For example, the displacement measurement method using the OFDR (Optical Frequency Domain Reflectometry) method requires the use of an expensive optical fiber cable sensor, but applying such an optical fiber cable sensor to the conventional ground displacement measurement method described above increases the construction cost. Furthermore, when optical fiber cable sensors are attached to the top, bottom, left, and right positions on the outer surface of a guide tube with a circular cross section and this guide tube is inserted into a measurement hole with a circular cross section, the guide tube may twist circumferentially, causing the optical fiber cable sensors to be positioned in a manner that is not vertically aligned and horizontally aligned.

[0005] The present invention aims to solve the above-mentioned problems and to provide a displacement measurement device and a ground displacement measurement method that can recover an optical fiber cable sensor from inside a measurement hole after measuring ground displacement. [Means for solving the problem]

[0006] To solve the above problems, a first invention is a displacement measurement device comprising a guide tube inserted into a measurement hole, a bag-shaped packer that can expand and contract within the guide tube, and an optical fiber cable sensor disposed between the outer surface of the packer and the inner surface of the guide tube. The optical fiber cable sensor is connectable to a measurement device that measures the displacement of the optical fiber cable sensor. A flat plate is disposed between the outer surface of the packer and the inner surface of the guide tube, with the inner surface of the flat plate facing the outer surface of the packer and the outer surface of the flat plate facing the inner surface of the guide tube, and a recess extending in the longitudinal direction of the guide tube is formed on the inner or outer surface of the flat plate, and the optical fiber cable sensor is fitted into the recess. When the packer is inflated, the fiber optic cable sensor is sandwiched and fixed between the outer surface of the packer and the inner surface of the guide tube. To solve the above problems, a second invention provides a ground displacement measurement method for measuring ground displacement. The displacement measurement device is inserted into a measurement hole formed in the ground, and a filler is filled between the inner wall of the measurement hole and the guide tube to position the guide tube. Next, pressure is applied inside the packer to expand the packer, and the optical fiber cable sensor is sandwiched and fixed between the outer surface of the packer and the inner surface of the guide tube. Then, after measuring the displacement of the optical fiber cable sensor, pressure is reduced inside the packer to contract the packer, and the packer and the optical fiber cable sensor are removed from the guide tube.

[0007] In the present invention, a packer is expanded inside a guide pipe inserted into a measurement hole provided in the ground, and the optical fiber cable sensor is sandwiched between the outer surface of the packer and the inner surface of the guide pipe, thereby fixing the optical fiber cable sensor inside the guide pipe. After measuring ground displacement using the optical fiber cable sensor, the packer is deflated to release the optical fiber cable sensor from its fixation to the guide pipe, allowing the optical fiber cable sensor to be retrieved from inside the guide pipe. As described above, with the present invention, the optical fiber cable sensor can be retrieved from within the ground after measuring ground displacement, so the cost required for measuring ground displacement can be reduced even when using an expensive optical fiber cable sensor and packer device that are expected to provide high-precision displacement meters.In other words, by applying the present invention to displacement measurement methods that use expensive optical fiber cable sensors and packer devices, such as OFDR displacement measurement methods, ground displacement can be measured with high precision. In the displacement measuring device described above, if the guide tube is extended in the front-to-back direction and at least four planes (top, bottom, left, and right) are formed on the outer surface of the guide tube, the guide tube is less likely to rotate around its axis when inserted into the measurement hole, so the optical fiber cable sensor can be correctly inserted into the specified position in the measurement hole. In the displacement measuring device described above, by extending the guide pipe in the front-to-rear direction and forming at least two upper and lower planes or two left and right planes on the inner surface of the guide pipe, it is possible to measure ground displacement in the vertical or horizontal direction.

[0008] In the displacement measuring device, a flat plate is placed between the outer surface of the packer and the inner surface of the guide pipe, with the inner surface of the flat plate facing the outer surface of the packer and the outer surface of the flat plate facing the inner surface of the guide pipe. A recess extending in the front-rear direction is formed on the inner or outer surface of the flat plate, and the optical fiber cable sensor is fitted into the recess. This allows The fiber optic cable can stabilize the sensor. Furthermore, if the recessed portion is formed on the inner surface of the flat plate and the optical fiber cable sensor is configured to contact the outer surface of the packer when the packer is inflated, the accuracy of measuring ground displacement can be improved. In the displacement measuring device described above, by placing the flat plates on the top, bottom, left, and right sides of the packer and providing the optical fiber cable sensor on each of the flat plates, it is possible to measure horizontal and vertical ground displacement. [Effects of the Invention]

[0009] The displacement measuring device and ground displacement measuring method of the present invention can reduce the cost required for measuring ground displacement with high accuracy because the optical fiber cable sensor can be retrieved from inside the ground after measuring the ground displacement. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a side cross-sectional view showing a tunnel according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the tunnel according to the embodiment of the present invention taken along line II-II of FIG. 1. FIG. [Figure 3] FIG. 2 is an axial cross-sectional view showing a state in which a packer is contracted in the displacement measuring device according to the embodiment of the present invention. [Figure 4] FIG. 2 is a perspective view showing a guide tube, a flat plate, and a packer in the displacement measuring device according to the embodiment of the present invention. [Figure 5] FIG. 2 is an axial cross-sectional view showing a state in which a packer is expanded in the displacement measuring device according to the embodiment of the present invention. [Figure 6] FIG. 10 is an axial cross-sectional view showing a state in which a packer is expanded in a displacement measuring device according to another embodiment of the present invention. [Figure 7] FIG. 10 is an axial cross-sectional view of a displacement measuring device according to another embodiment of the present invention, in which the axial cross-section of a guide tube is rectangular. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional side view showing a tunnel 1 according to an embodiment of the present invention. The displacement measuring device 10 and the ground displacement measuring method of this embodiment are used to grasp the ground displacement ahead of the face 2 of the tunnel 1 shown in FIG. FIG. 2 is a cross-sectional view of the tunnel 1 according to the embodiment of the present invention taken along line II-II of FIG. The tunnel 1 of this embodiment is formed by a mountain tunneling method and has a horseshoe-shaped cross section, as shown in Fig. 2. However, the construction method and cross-sectional shape of the tunnel 1 are not limited, and for example, the tunnel may have a circular cross section. As shown in Fig. 1, widened sections 3 are formed in the wall of tunnel 1 at predetermined intervals (for example, 12 m) in the extension direction. The widened sections 3 are areas where the wall of tunnel 1 is widened outward from the standard cross section. In tunnel 1 of this embodiment, five widened sections 3 are formed at predetermined intervals in the extension direction, as shown in Fig. 2. The widened portions 3 are formed at the left and right ends and top of the tunnel 1, and also between the left and right ends and the top. As shown in Figure 1, measurement holes 90 are formed in the ground surrounding the tunnel 1, pointing diagonally upward from the widening section 3 toward the front of the tunnel face 2. The measurement holes 90 are formed from cylindrical steel pipes 91 (see Figure 3). As shown in Figure 2, a measurement hole 90 is formed from each widening section 3 toward the front of the tunnel face 2. The pipe for forming the measurement hole 90 shown in FIG. 1 is not limited to the steel pipe 91, and may be made of, for example, a resin pipe. In this embodiment, the steel pipe 91 is buried in the ground by the AGF method using a tunnel drill. Specifically, a drilling blade (not shown) is attached to the tip of the steel pipe 91, the steel pipe 91 is rotated around its axis using the tunnel drill, and the steel pipe 91 is inserted into the ground while the ground is excavated by the drilling blade.

[0012] FIG. 3 is an axial cross-sectional view showing a state in which the packer 30 is contracted in the displacement measuring device 10 according to the embodiment of the present invention. As shown in Figure 3, the displacement measurement device 10 comprises a guide tube 20 inserted into the measurement hole 90, a packer 30 placed inside the guide tube 20, and four flat plates 40 and four optical fiber cable sensors 50 placed between the outer surface of the packer 30 and the inner surface of the guide tube 20.

[0013] FIG. 4 is a perspective view showing a guide pipe, a flat plate, and a packer in the displacement measuring device according to the embodiment of the present invention. The guide tube 20 is a tubular body made of PVC (polyvinyl chloride) and extending in the front-rear direction, as shown in Fig. 4. The material of the guide tube 20 is not limited to resin, and for example, a steel pipe may also be used. Four flat surfaces 21, ie, top, bottom, left and right surfaces, are formed on the outer surface of the guide tube 20. The top and bottom flat surfaces 21, 21 are arranged horizontally, and the left and right flat surfaces 21, 21 are arranged vertically. 3, the guide tube 20 of this embodiment is formed to have a square cross section, but may also have a rectangular cross section. Note that an inclined surface may be formed between two adjacent flat surfaces 21, 21 to form a polygonal cross section such as a hexagon or octagon. Guide tube 20 is placed below measurement hole 90. Filler 4 such as silica resin or cement milk is filled between the outer surface of guide tube 20 and the inner surface of measurement hole 90, and guide tube 20 is positioned within measurement hole 90 by this filler 4.

[0014] As shown in FIG. 4, the packer 30 is a bag made of synthetic rubber and extends in the front-to-rear direction. The packer 30 can be expanded by pressurizing the inside with gas or liquid. After the packer 30 is expanded, the packer 30 can be contracted by decompressing the inside of the packer 30. In this way, the packer 30 can be repeatedly expanded and contracted. The material of the packer 30 is not limited to synthetic rubber, and various materials can be used as long as they are expandable and contractible. Before expansion, the packer 30 has a circular cross section as shown in Figure 3. The outer surfaces 31 of the packer 30 face the upper, lower, left, and right inner surfaces 22 of the guide pipe 20 with a gap therebetween.

[0015] The flat plate 40 is a plate-shaped member made of PVC (polyvinyl chloride) and extending in the front-rear direction, as shown in Fig. 4. The material of the flat plate 40 is not limited to PVC, and various materials can be used. 3, the flat plates 40 are arranged between the outer surface 31 of the packer 30 and the inner surface 22 of the guide pipe 20. Four flat plates 40 are arranged on the sides of the packer 30, above, below, left and right. The inner surface 42 of the flat plate 40 faces the outer surface 31 of the packer 30 , and the outer surface 41 of the flat plate 40 faces the inner surface 22 of the guide pipe 20 .

[0016] A recessed portion 43 extending in the front-rear direction is formed on the inner surface 42 of the flat plate 40 (see FIG. 4). The recessed portion 43 is formed in the center portion in the width direction of the flat plate 40. The recessed portion 43 is formed in a triangular cross-sectional shape so that the width decreases from the inner surface 42 of the flat plate 40 toward the outside. The position and cross-sectional shape of the recessed portion 43 are not limited. In the displacement measuring device 10 of this embodiment, the recesses 43, 43 of the upper and lower flat plates 40, 40 are arranged at the same position in the left-right direction, and the recesses 43, 43 of the left and right flat plates 40, 40 are arranged at the same position in the up-down direction.

[0017] 3, the optical fiber cable sensors 50 extend in the front-to-rear direction. The four optical fiber cable sensors 50 are fitted into the recesses 43 on the top, bottom, left, and right of the flat plate 40. After the optical fiber cable sensors 50 are fitted into the recesses 43, the recesses 43 are coated with epoxy resin, thereby fixing the optical fiber cable sensors 50 to the inner surface 42 of the flat plate 40. The upper and lower optical fiber cable sensors 50, 50 are arranged at the same position in the left-right direction, and the left and right optical fiber cable sensors 50, 50 are arranged at the same position in the up-down direction. The fiber optic cable sensor 50 can be connected to a measurement device 80 that measures the displacement of the fiber optic cable sensor 50, as shown in FIG. The measuring device 80 is a computer, and can grasp the radial displacement of the optical fiber cable sensor 50 by analyzing the time it takes for the scattered light to return after light is incident on the optical fiber cable sensor 50, as well as the frequency distribution of the scattered light. In the measuring device 80 of this embodiment, the displacement of the optical fiber cable sensor 50 is calculated using an OFDR displacement measurement method, but the displacement of the optical fiber cable sensor 50 may also be calculated using various analysis methods such as the BOTDR method or the PPP-BOTA method.

[0018] FIG. 5 is an axial cross-sectional view showing a state in which the packer 30 is expanded in the displacement measuring device 10 according to the embodiment of the present invention. As shown in Figure 5, when the packer 30 is expanded inside the guide pipe 20, the packer 30 pushes the flat plate 40 toward the inner surface 22 of the guide pipe 20, and the outer surface 41 of the flat plate 40 is pressed against the inner surface 22 of the guide pipe 20. In addition, as the outer surface 31 of the packer 30 is pressed against the inner surfaces 42 of the flat plates 40 on the top, bottom, left, and right, four flat surfaces are formed on the outer surface 31 of the packer 30, and the packer 30 is deformed into a rectangular cross-sectional shape. Then, the optical fiber cable sensor 50 is sandwiched and fixed between the outer surface 31 of the packer 30 and the inner surface 22 of the guide tube 20. The optical fiber cable sensor 50 is in contact with the outer surface 31 of the packer 30. In this way, four optical fiber cable sensors 50, one above, one below, one left, and one right, are fixed inside the guide tube 20.

[0019] Next, a ground displacement measuring method using the displacement measuring device 10 of this embodiment will be described. First, a drilling blade (not shown) is attached to the tip of the steel pipe 91 shown in Figure 1, and a tunnel rock drill (not shown) is used to insert the steel pipe 91 from the widening section 3 of the tunnel 1 into the ground in front of the face 2. This forms a measurement hole 90 in the ground using the steel pipe 91. 4, a packer 30 is inserted into the guide pipe 20, and flat plates 40 are inserted between the outer surface of the packer 30 and the inner surface of the guide pipe 20 on the top, bottom, left, and right sides. An optical fiber cable sensor 50 is fixed to the flat plates 40. Then, as shown in FIG. 3, the packer 30, the flat plates 40, and the optical fiber cable sensors 50, together with the guide pipe 20, are inserted into the measurement hole 90 from the base end of the steel pipe 91. After the guide tube 20 is inserted into the measurement hole 90 , the filler 4 is filled between the outer surface of the guide tube 20 and the inner surface of the measurement hole 90 , and the guide tube 20 is positioned within the measurement hole 90 .

[0020] 5, when the inside of the packer 30 is pressurized and the packer 30 is expanded, each flat plate 40 is pressed against the inner surface 22 of the guide tube 20. As a result, the optical fiber cable sensor 50 is sandwiched and fixed between the outer surface 31 of the packer 30 and the inner surface 22 of the guide tube 20. In this way, the optical fiber cable sensors 50 on the top, bottom, left, and right sides are fixed inside the guide tube 20. When a displacement occurs in the ground and a part of the steel pipe 91 is bent, displacement follows the displacement of the steel pipe 91 and occurs in the guide pipe 20 and each optical fiber cable sensor 50 . 1 to the optical fiber cable sensors 50 and analyzing the time it takes for the scattered light to return and the frequency distribution of the scattered light, it is possible to measure the displacement of each optical fiber cable sensor 50. Since the displacement of the optical fiber cable sensors 50 indicates the displacement of the ground, the measuring device 80 can be used to grasp the ground displacement ahead of the tunnel face 2.

[0021] After extending the tunnel 1 to the tip of the measurement hole 90 while measuring the ground displacement ahead of the tunnel face 2, the pressure inside the packer 30 is reduced to contract the packer 30, as shown in Figure 3. This releases the flat plates 40 and optical fiber cable sensors 50 from the guide pipe 20. The packer 30 and each flat plate 40 are removed and recovered from the base end of the guide tube 20. This allows the optical fiber cable sensor 50 to be recovered from inside the guide tube 20 together with the flat plates 40. Similarly, a measurement hole 90 is formed in the ground ahead of the tunnel face 2 of the tunnel 1 shown in FIG. 1, and a displacement measuring device 10 is inserted into the measurement hole 90 as shown in FIG. 3 to repeatedly measure ground displacement.

[0022] In the displacement measuring device 10 and ground displacement measuring method described above, as shown in Figure 5, the packer 30 is expanded inside the guide tube 20 inserted into the measurement hole 90 provided in the ground, and the optical fiber cable sensor 50 is sandwiched between the outer surface of the packer 30 and the inner surface of the guide tube 20, thereby making it possible to easily fix the optical fiber cable sensor 50 inside the guide tube 20. After measuring ground displacement using the optical fiber cable sensor 50, the packer 30 is contracted as shown in Figure 3 to release the optical fiber cable sensor 50 from its attachment to the guide tube 20, thereby allowing the optical fiber cable sensor 50 to be retrieved from inside the guide tube 20. As described above, with the displacement measurement device 10 and ground displacement measurement method of this embodiment, the optical fiber cable sensor 50 can be retrieved from within the ground after measuring ground displacement. Therefore, even when using an expensive optical fiber cable sensor 50 and packer device that are expected to provide high-precision displacement meters, the cost required for measuring ground displacement can be reduced. In other words, the present invention can be applied to a displacement measurement method that uses an expensive optical fiber cable sensor 50 and packer device, such as an OFDR displacement measurement method, to measure ground displacement with high precision.

[0023] In the displacement measurement device 10 of this embodiment, four flat surfaces 21, one above, one below, one left, and one right, are formed on the outer surface of the guide tube 20. With this configuration, when the guide tube 20 is inserted into the measurement hole 90, the guide tube 20 is unlikely to rotate around its axis, so that each optical fiber cable sensor 50 can be inserted correctly into the predetermined position in the measurement hole 90.

[0024] In the displacement measuring device 10 of this embodiment, the optical fiber cable sensor 50 is fitted into the recess 43 formed in the flat plate 40, so that the optical fiber cable sensor 50 can be stabilized within the guide tube 20. Furthermore, as shown in Fig. 5, if the optical fiber cable sensor 50 comes into contact with the outer surface of the packer 30 when the packer 30 is expanded, the measurement accuracy of ground displacement can be improved. In the displacement measurement device 10 of this embodiment, flat plates 40 are placed on the top, bottom, left, and right sides of the packer 30, and an optical fiber cable sensor 50 is provided on each flat plate 40. Furthermore, the upper and lower optical fiber cable sensors 50, 50 are placed at the same position in the left-right direction, and the left and right optical fiber cable sensors 50, 50 are placed at the same position in the up-down direction. In this way, ground displacement in the horizontal and vertical directions can be measured with high accuracy.

[0025] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified as appropriate within the scope of the invention. In this embodiment, as shown in Figure 1, a measurement hole 90 is formed diagonally upward from the widening section 3 of the tunnel 1 toward the front of the face 2, but the measurement hole 90 may also be formed from the inner wall surface of the tunnel 1 without forming the widening section 3 in the tunnel 1. FIG. 6 is an axial cross-sectional view showing a state in which the packer 30 is expanded in the displacement measuring device 10 according to another embodiment of the present invention. For example, in the displacement measuring device 10 of this embodiment, as shown in FIG. 3, the optical fiber cable sensor 50 is fixed to the inner surface 42 of the flat plate 40, but as shown in FIG. 6, a recess 43 may be formed in the outer surface 41 of the flat plate 40, and the optical fiber cable sensor 50 may be fitted into the recess 43. In the displacement measuring device 10 of this embodiment, as shown in FIG. 3, four optical fiber cable sensors 50 are provided in the guide tube 20 at the top, bottom, left and right, but the number and arrangement of the optical fiber cable sensors 50 are not limited. In the displacement measuring device 10 of this embodiment, the optical fiber cable sensor 50 is fixed to the flat plate 40. As a reference example of the present invention, It is also possible to dispose only the optical fiber cable sensor 50 between the outer surface of the guide tube 20 and the inner surface of the measurement hole 90 without providing the flat plate 40 . In the ground displacement measuring method of this embodiment, measurement hole 90 is formed by inserting steel pipe 91 into the ground, but measurement hole 90 may also be a hole excavated in the ground. The shapes and materials of the steel pipe 91, guide pipe 20, packer 30 and flat plate 40 are not limited, and can be set appropriately depending on the construction conditions. In addition, when the guide pipe 20 is made of a softer material than the steel pipe 91, as in the displacement measuring device 10 of this embodiment, the guide pipe 20 tends to displace in response to the displacement of the steel pipe 91, thereby enabling accurate measurement of ground displacement. FIG. 7 is an axial cross-sectional view of a displacement measuring device 10 according to another embodiment of the present invention, in which the axial cross-section of the guide tube 20 is rectangular. In the displacement measuring device 10 of this embodiment, the axial cross section of the guide tube 20 is formed as a square, but as shown in Fig. 7, the axial cross section of the guide tube 20 may also be formed as a rectangle in which the vertical sides are longer than the horizontal sides. In the displacement measuring device 10 shown in Fig. 7, the optical fiber cable sensors 50 and the flat plate 40 are arranged on both the left and right sides, which are the long sides of the guide tube 20. In this way, the flat plate 40 can be stabilized. In addition, the axial cross section of the guide tube 20 may be formed into a rectangle with the left and right sides longer than the top and bottom sides, and the optical fiber cable sensor 50 and flat plate 40 may be placed on both the top and bottom long sides of the guide tube 20. [Explanation of symbols]

[0026] 1. Tunnel 2 Cutting edge 3 Widening section 4 Filling material 10. Displacement measuring device 20 Guide tube 21 plane 22 Inner 30 Packer 31 Exterior 40 flat plate 41 Exterior 42 Inner 43 Recess 50 Fiber Optic Cable Sensor 80 Measuring Equipment 90 Measurement holes 91 Steel pipe

Claims

1. a guide tube inserted into the measurement hole; a bag-shaped packer that can expand and contract within the guide pipe; a fiber optic cable sensor disposed between an outer surface of the packer and an inner surface of the guide tube; the fiber optic cable sensor is connectable to a measurement device that measures displacement of the fiber optic cable sensor; a flat plate is disposed between the outer surface of the packer and the inner surface of the guide pipe; The inner surface of the flat plate faces the outer surface of the packer, The outer surface of the flat plate faces the inner surface of the guide pipe, a recess extending in the longitudinal direction of the guide pipe is formed on the inner or outer surface of the flat plate; The optical fiber cable sensor is fitted into the recessed portion, A displacement measuring device characterized in that, when the packer is inflated, the optical fiber cable sensor is sandwiched and fixed between the outer surface of the packer and the inner surface of the guide tube.

2. The displacement measuring device according to claim 1, The guide tube extends in the front-rear direction, A displacement measuring device characterized in that at least four flat surfaces, ie, top, bottom, left, and right, are formed on the outer surface of the guide tube.

3. The displacement measuring device according to claim 1, The guide tube extends in the front-rear direction, A displacement measuring device characterized in that at least two flat surfaces, one above and one below, or two flat surfaces, one to the left and one to the right, are formed on the inner surface of the guide tube.

4. A displacement measuring device according to claim 1, The recessed portion is formed on the inner surface of the flat plate, A displacement measuring device characterized in that, when the packer is inflated, the optical fiber cable sensor is in contact with the outer surface of the packer.

5. A displacement measuring device according to claim 1, The flat plates are arranged on the upper, lower, left, and right sides of the packer, a displacement measuring device, characterized in that the optical fiber cable sensor is provided on each of the flat plates;

6. A ground displacement measurement method for measuring ground displacement, comprising: a step of inserting the displacement measuring device according to any one of claims 1 to 5 into a measurement hole provided in the ground; a step of filling a gap between the inner wall of the measurement hole and the guide tube with a filler to position the guide tube; applying pressure to the inside of the packer to expand the packer, and sandwiching and fixing the optical fiber cable sensor between the outer surface of the packer and the inner surface of the guide tube; measuring the displacement of the fiber optic cable sensor; reducing pressure within the packer to shrink the packer; withdrawing the packer and the fiber optic cable sensor from the guide tube; A ground displacement measuring method comprising:

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