Displacement measuring device and ground displacement measuring method

Abstract

To provide a displacement measuring device capable of recovering an optical fiber cable sensor from a measurement hole after measuring a ground displacement.SOLUTION: A displacement measuring device 10 comprises: a pipe 20 inserted into a measuring hole 90; a packer 30 capable of being expanded and contracted in the pipe 20; upper and lower flat plates 40, 40 disposed between an external surface of the packer 30 and an internal surface of the pipe 20; an optical fiber cable sensor 50 fitted to the flat plate 40; and a positioning member 60 disposed in the pipe 20. The optical fiber cable sensor 50 can be connected to a measuring device 80. An insertion port 63 in which a connection part 35 between the packers 30, 30 adjacent to each other is inserted and an engaged part 64 with which an engaging part 48 formed on the flat plate 40 is engaged are formed on the positioning member 60.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a displacement measurement device for measuring ground displacement in front of a tunnel face during tunnel construction and a ground displacement measurement method using the displacement measurement device.

Background Art

[0002] For example, in tunnel construction, it is necessary to manage the ground displacement in front of the tunnel face in order to adopt an appropriate construction method according to the ground conditions in front of the tunnel face. As a method for measuring ground displacement, there is a method of inserting an optical fiber cable sensor into a measurement hole formed toward the front of the tunnel face and analyzing the time until scattered light returns after irradiating the optical fiber cable sensor with light from a measurement device or the frequency distribution of the scattered light to grasp the ground displacement. Patent Document 1 discloses that an optical fiber cable sensor is attached to the outer peripheral surface of a pipe, the pipe is inserted into a measurement hole, and grout material is filled into the measurement hole to fix the optical fiber cable sensor in the measurement hole.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described conventional ground displacement measurement method, since the optical fiber cable sensor is embedded in the grout material filled in the measurement hole, there is a problem that the optical fiber cable sensor cannot be recovered after measuring the ground displacement. For example, if an optical fiber cable sensor capable of measuring ground displacement with high resolution and high accuracy over the entire length is applied to the above-described conventional ground displacement measurement method, the construction cost will increase.

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

[0006] To solve the aforementioned problems, the first invention provides a displacement measuring device comprising: a pipe inserted into a measuring hole; a bag-shaped packer that can expand and contract within the pipe; upper and lower flat plates positioned between the outer surface of the packer and the inner surface of the pipe; an optical fiber cable sensor attached to the flat plates; and a positioning member positioned within the pipe. In this displacement measuring device, a plurality of the packers are connected in the direction of extension of the pipe. The optical fiber cable sensor can be connected to a measuring device that measures the strain of the optical fiber cable sensor. When the packer is expanded, the flat plates are configured to be sandwiched and fixed between the outer surface of the packer and the inner surface of the pipe. The positioning member has an insertion opening through which the connecting portions of adjacent packers are inserted, and upper and lower engaged portions into which the engaging portions formed on the two flat plates are engaged, respectively.

[0007] To solve the aforementioned problems, the second invention is a ground displacement measurement method for measuring ground displacement. This ground displacement measurement method comprises the steps of: inserting the displacement measurement device into a measurement hole provided in the ground; filling a filler between the inner surface of the measurement hole and the outer surface of the pipe to position the pipe; pressurizing the inside of the packer to expand the packer, sandwiching the flat plate between the outer surface of the packer and the inner surface of the pipe to fix the optical fiber cable sensor to the pipe; measuring the strain of the optical fiber cable sensor; depressurizing the inside of the packer to contract the packer; and removing the packer, the flat plate and the optical fiber cable sensor from the pipe.

[0008] In this invention, a packer is expanded inside a pipe inserted into a measurement hole in the ground, and a flat plate is sandwiched between the outer surface of the packer and the inner surface of the pipe, thereby fixing the optical fiber cable sensor to the pipe. After measuring the ground displacement using the optical fiber cable sensor, the packer is deflated to release the optical fiber cable sensor from the pipe, allowing the optical fiber cable sensor to be retrieved from inside the pipe. Thus, in this invention, since the optical fiber cable sensor can be recovered from the ground after measuring the ground displacement, the cost required for measuring ground displacement can be reduced even when using expensive optical fiber cable sensors and packing devices that are expected to provide high-precision displacement. In other words, by applying this invention to a displacement measurement method using expensive optical fiber cable sensors and packing devices, ground displacement can be determined with high accuracy. Furthermore, in this invention, the upper and lower plates are engaged with a positioning member, thereby positioning both plates within the pipe. This allows the horizontal positions of the upper and lower optical fiber cable sensors attached to both plates to be aligned, making it possible to accurately determine the vertical ground displacement.

[0009] In the displacement measuring device described above, if the engaged portion is a hole formed in the alignment member, and the engaged portion protruding from the flat plate is inserted into the engaged portion, the engaged portion of the flat plate can be easily engaged with the engaged portion of the alignment member.

[0010] In the displacement measuring device described above, if a plurality of the flat plates are connected in the direction of extension of the pipe, and adjacent flat plates are connected by connecting members superimposed on the inner surfaces of adjacent flat plates, and a screw member inserted from the outer side into a mounting hole formed in the flat plate is screwed into a screw hole formed in the connecting member, the number of parts can be reduced by forming the engagement portion with the tip of the screw member protruding to the inner surface side of the connecting member.

[0011] In the displacement measuring device described above, when the packer is expanded, the flat plate may move in the extension direction. However, by forming the engaged portion as an elongated hole extending in the extension direction of the flat plate, it is possible to prevent the alignment member from obstructing the movement of the flat plate. [Effects of the Invention]

[0012] The displacement measuring device and ground displacement measuring method of the present invention allow for the retrieval of the optical fiber cable sensor from within the ground after measuring the ground displacement, thereby reducing the cost required for high-precision measurement of ground displacement. Furthermore, the displacement measuring device and ground displacement measuring method of the present invention allow for the alignment of the horizontal positions of the upper and lower optical fiber cable sensors, enabling accurate determination of the vertical ground displacement. [Brief explanation of the drawing]

[0013] [Figure 1] This is a perspective view showing a tunnel according to an embodiment of the present invention. [Figure 2] This is a side cross-sectional view showing a tunnel according to an embodiment of the present invention. [Figure 3] This figure shows a tunnel according to an embodiment of the present invention, and is a cross-sectional view taken along line III-III in Figure 2. [Figure 4] This is a side cross-sectional view showing an embodiment of the present invention in which a measurement hole is formed. [Figure 5] This is an axial cross-sectional view showing the packer in a contracted state in a displacement measuring device according to an embodiment of the present invention. [Figure 6] This is a perspective view showing a pipe, a flat plate, and a packer in a displacement measuring device according to an embodiment of the present invention. [Figure 7] This is an axial cross-sectional view showing the packer in an expanded state in a displacement measuring device according to an embodiment of the present invention. [Figure 8] This is an axial cross-sectional view showing a portion of the displacement measuring device according to an embodiment of the present invention, where an insertion spacer is provided. [Figure 9]In the displacement measurement device according to an embodiment of the present invention, it is a side view showing a part where an insertion spacer is provided. [Figure 10] In the displacement measurement device according to an embodiment of the present invention, it is an axial cross-sectional view showing a part where an alignment member is provided. [Figure 11] In the displacement measurement device according to an embodiment of the present invention, it is a view showing a part where an alignment member is provided, and is a cross-sectional view taken along the line XI-XI in FIG. 10. [Figure 12] In the displacement measurement device according to an embodiment of the present invention, it is a perspective view showing an alignment member. [Figure 13] In the displacement measurement device according to another embodiment of the present invention, it is an axial cross-sectional view showing a state where a packer is expanded.

Mode for Carrying Out the Invention

[0014] Embodiments of the present invention will be described in detail with appropriate reference to the drawings. FIG. 1 is a perspective view showing a tunnel 1 according to an embodiment of the present invention. FIG. 2 is a side cross-sectional view showing the tunnel 1 according to an embodiment of the present invention. FIG. 3 is a view showing the tunnel 1 according to an embodiment of the present invention, and is a cross-sectional view taken along the line III-III in FIG. 2. The displacement measurement device 10 and the ground displacement measurement method of the present embodiment are for grasping the ground displacement in front of the face 2 of the tunnel 1 shown in FIG. 1. The tunnel 1 of the present embodiment is formed by a mountain tunnel construction method and has a horseshoe-shaped cross-sectional shape. Note that 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. 2, widened portions 3 are formed at predetermined intervals (for example, 12 m) in the longitudinal direction on the wall portion of the tunnel 1. The widened portion 3 is a part where the wall portion of the tunnel 1 is widened outward from the standard cross-section. In the tunnel 1 of the present embodiment, as shown in FIG. 3, three widened portions 3 are formed at predetermined intervals in the longitudinal direction. In the present embodiment, widened portions 3 are formed at the left and right ends and the top of the tunnel 1, respectively. As shown in Figure 2, measurement holes 90 are formed in the ground surrounding tunnel 1, extending diagonally upward from the widened section 3 toward the front of the tunnel face 2.

[0015] Figure 5 is an axial cross-sectional view showing the state in which the packer 30 is contracted in the displacement measuring device 10 according to an embodiment of the present invention. As shown in Figure 5, the measurement hole 90 is composed of a borehole 92 and a pipe 91 inserted into the borehole 92. In this embodiment, the pipe 91 is a cylindrical steel pipe. As shown in Figure 3, measurement holes 90 are formed from each widened section 3 toward the front of the tunnel face 2 (see Figure 1). Figure 8 is an axial cross-sectional view showing the portion of the displacement measuring device 10 according to an embodiment of the present invention in which the insertion spacer 70 is provided. As shown in Figure 8, multiple communication holes 91a are formed in the circumferential wall of the pipe body 91 at intervals in the circumferential and axial directions. Specifically, two communication holes 91a, 91a facing each other in the radial direction of the pipe body 91 are arranged at intervals in the longitudinal direction. In addition, two adjacent communication holes 91a, 91a in the longitudinal direction of the pipe body 91 are arranged alternately with a 90-degree phase difference in the circumferential direction of the pipe body 91. Furthermore, the pipe body 91 is not limited to a steel pipe; for example, a pipe body made of resin may also be used. Figure 4 is a side cross-sectional view showing an embodiment of the present invention in which a measurement hole 90 is formed. In this embodiment, as shown in Figure 4, a measurement hole 90 is formed in the ground using the AGF method with a tunnel drilling machine. The drilling blade 93 for excavating the ground is attached to the tip of the pipe 91. A rod 94 is inserted through the pipe 91, and the tip of the rod 94 is connected to the drilling blade 93. The outer diameter of the drilling blade 93 is formed to be slightly larger than the outer diameter of the pipe 91. When the rod 94 is rotated forward around its axis, the rod 94 and the drilling blade 93 remain connected, and when the rod 94 is rotated backward around its axis, the connection between the rod 94 and the drilling blade 93 is released.

[0016] When forming a measurement hole 90 in the ground, the drive mechanism of the tunnel drilling machine rotates the rod 94 forward around its axis, and while excavating the ground with the drilling blade 93 to form a borehole 92, the pipe body 91 is inserted into the borehole 92 together with the drilling blade 93. After excavating the borehole 92 to a predetermined depth, the rod 94 is rotated backward around its axis, separating the rod 94 from the drilling blade 93, and the rod 94 is withdrawn from the pipe body 91. As a result, a measurement hole 90 consisting of the borehole 92 and the pipe body 91 is formed in the ground. The drilling blade 93 and the pipe body 91 are left in the ground. Since the outer diameter of the drilling blade 93 is larger than the outer diameter of the pipe body 91, a gap is formed between the inner surface of the borehole 92 and the outer surface of the pipe body 91. For example, the outer diameter of the drilling blade 93 is 121 mm, while the outer diameter of the pipe body 91 is set to 114.3 mm. As shown in Figure 8, the pipe body 91 is filled with a filler material 4 such as silica resin or cement grout. This filler material 4 is also filled into the gap between the inner surface of the excavation hole 92 and the outer surface of the pipe body 91 through each of the communication holes 91a of the pipe body 91. As a result, the filler material 4 positions the pipe body 91 within the excavation hole 92.

[0017] As shown in Figure 5, the displacement measuring device 10 includes a pipe 20 inserted into the tube 91 of the measuring hole 90, a packer 30 placed inside the pipe 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 pipe 20. Figure 11 is a cross-sectional view taken along line XI-XI in Figure 10, showing the portion of the displacement measuring device 10 according to an embodiment of the present invention where the alignment member 60 is provided. Furthermore, as shown in Figure 11, the displacement measuring device 10 includes a positioning member 60 arranged inside the pipe 20. Furthermore, as shown in Figure 8, the displacement measuring device 10 is equipped with an insertion spacer 70 attached to the outer surface of the pipe 20.

[0018] Figure 6 is a perspective view showing the pipe 20, flat plate 40, and packer 30 in the displacement measuring device 10 according to an embodiment of the present invention. As shown in Figure 6, pipe 20 is a rectangular tube made of PVC (polyvinyl chloride) that extends in the front-to-back direction. In this embodiment, four rectangular pipes 20, each with an axial length of 3m and a width of 50cm, are connected to form a pipe with a total length of 12m. Note that the material of pipe 20 is not limited to resin; for example, steel pipes may be used. Also, the length of pipe 20 and the number of pipes 20 connected together are not limited. Four planes 21 are formed on the outer surface of the pipe 20, in the upper, lower, left, and right directions. When the pipe 20 is placed on a horizontal plane, the upper and lower planes 21, 21 are positioned horizontally, and the left and right planes 21, 21 are positioned vertically. As shown in Figure 5, the pipe 20 in this embodiment is formed with a square cross-sectional shape, but it may also have a rectangular cross-sectional shape. Furthermore, an inclined surface may be formed between two adjacent planes 21, 21 to form a polygonal cross-sectional shape such as a hexagon or octagon. The pipe 20 is positioned at the bottom of the pipe body 91. A filler material 4 is filled between the outer surface of the pipe 20 and the inner surface of the pipe body 91, and this filler material 4 positions the pipe 20 within the pipe body 91.

[0019] As shown in Figure 6, the packer 30 is a synthetic rubber bag that extends in the front-to-back direction. The packer 30 can be expanded by pressurizing its interior with gas or liquid. After expanding the packer 30, it can be contracted by depressurizing its interior. In this way, the packer 30 can be repeatedly expanded and contracted. Furthermore, the material of the packer 30 is not limited to synthetic rubber; various materials can be used as long as they are expandable and contractible. Before expansion, the packer 30 is formed in a circular cross-section, as shown in Figure 5. The outer surface 31 of the packer 30 faces the inner surfaces 22 of the pipe 20 on all sides, with a gap between them.

[0020] As shown in Figure 6, the flat plate 40 is a plate-shaped member made of PVC (polyvinyl chloride) that extends in the front-to-back direction. The material of the flat plate 40 is not limited to PVC; various materials can be used. For example, four flat plates 40 with an axial length of 3m are connected to form a length of 12m. The length of the flat plate 40 and the number of flat plates 40 connected together are not limited. As shown in Figure 5, the flat plates 40 are positioned between the outer surface 31 of the packer 30 and the inner surface 22 of the pipe 20. Four flat plates 40 are positioned on the sides of the packer 30, one above the other and one to the left and one to the 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 pipe 20.

[0021] A recessed portion 43 extending in the front-to-back direction is formed on the inner surface 42 of the flat plate 40 (see Figure 6). The recessed portion 43 is formed in the center of the width direction of the flat plate 40. Furthermore, the recessed portion 43 is formed in a triangular cross-sectional shape such that its width decreases as it moves outward from the inner surface 42 of the flat plate 40. Note that the position and cross-sectional shape of the recessed portion 43 are not limited. In the displacement measuring device 10 of this embodiment, the recessed portions 43, 43 of the upper and lower flat plates 40, 40 are positioned at the same location in the left-right direction, and the recessed portions 43, 43 of the left and right flat plates 40, 40 are positioned at the same location in the up-down direction.

[0022] As shown in Figure 6, the optical fiber cable sensors 50 extend in the front-to-back direction. The four optical fiber cable sensors 50 are fitted into recesses 43 on the top, bottom, left, and right sides of the flat plate 40. After fitting the optical fiber cable sensors 50 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 fiber optic cable sensors 50, 50 are positioned at the same location in the left-right direction, and the left and right fiber optic cable sensors 50, 50 are positioned at the same location in the up-down direction. As shown in Figure 1, the optical fiber cable sensor 50 can be connected to a measuring device 80 that determines ground displacement based on the strain of the optical fiber cable sensor 50. The measuring device 80 is a computer that analyzes the time it takes for 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, to determine the strain in the extension direction of the optical fiber cable sensor 50. In this embodiment, the measuring device 80 calculates the strain of the optical fiber cable sensor 50 using the OFDR displacement measurement method, but the strain of the optical fiber cable sensor 50 may also be calculated using various analysis methods such as the BOTDR method or the PPP-BOTDA method.

[0023] Figure 7 is an axial cross-sectional view showing the state in which the packer 30 is inflated in the displacement measuring device 10 according to an embodiment of the present invention. As shown in Figure 7, when the packer 30 is expanded inside the pipe 20, the packer 30 pushes the flat plate 40 towards the inner surface 22 of the pipe 20, and the outer surface 41 of the flat plate 40 is pressed against the inner surface 22 of the pipe 20. Furthermore, as the outer surface 31 of the packer 30 is pressed against the inner surfaces 42 of the top, bottom, left, and right flat plates 40, four planes are formed on the outer surface 31 of the packer 30, and the packer 30 deforms into a rectangular cross-sectional shape. The optical fiber cable sensor 50 is then sandwiched and fixed between the outer surface 31 of the packer 30 and the inner surface 22 of the pipe 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 to the left and one to the right, are fixed inside the pipe 20.

[0024] In the displacement measuring device 10 of this embodiment, as shown in Figure 11, a plurality of packers 30 are connected in the direction of extension of the pipe 20. At the connecting portion 35 of adjacent packers 30, 30, the adjacent packers 30, 30 are connected by inserting a plug provided on one packer 30 into a socket on the other packer 30. Within the pipe 20, a positioning member 60 is placed in the area where the connecting portion 35 is located. Figure 12 is a perspective view showing the alignment member 60 in a displacement measuring device 10 according to an embodiment of the present invention. As shown in Figure 12, the alignment member 60 comprises a rectangular flat plate portion 61 whose normal direction is in the front-to-back direction (the direction in which the pipe 20 extends), and four side plates 62 that protrude forward from the top, bottom, left, and right edges of the flat plate portion 61. Figure 10 is an axial cross-sectional view showing the portion of the displacement measuring device according to an embodiment of the present invention where the alignment member is provided. As shown in Figure 10, a circular insertion opening 63 is provided in the center of the flat plate portion 61. The insertion opening 63 is the part through which the connecting portion 35 is inserted. As shown in Figure 12, the side plate 62 has two engaging portions 64, 64 formed thereon. On the upper and lower side plates 62, 62, the two engaging portions 64, 64 are spaced apart in the left-right direction, while on the left and right side plates 62, 62, the two engaging portions 64, 64 are spaced apart in the up-down direction. The engaging portions 64 are elongated holes extending in the front-rear direction.

[0025] In the displacement measuring device 10 of this embodiment, as shown in Figure 11, a plurality of flat plates 40 are connected in the front-rear direction (the direction of extension of the pipe 20). Adjacent flat plates 40, 40 are connected by a connecting member 45. The connecting member 45 is a steel plate-shaped member that is superimposed on the inner surfaces of the adjacent flat plates 40, 40. Multiple mounting holes 44 are formed in the flat plate 40. In this embodiment, four mounting holes 44 arranged in the front-to-back direction are arranged in two rows, left and right (see Figure 10). The connecting member 45 has multiple screw holes 46 formed therein. Each screw hole 46 communicates with each mounting hole 44 of the flat plate 40. Then, the screw member 47, which is inserted into the mounting hole 44 from the outer surface of the flat plate 40, is screwed into the screw hole 46 of the connecting member 45, thereby fixing the connecting member 45 to the inner surface of the flat plate 40. In this embodiment, of the four screw members 47 arranged in the front-to-back direction, the tip of the last screw member 47 protrudes toward the inner surface of the connecting member 45. The tip of the screw member 47 constitutes an engaging portion 48 that is inserted into the engaged portion 64 of the alignment member 60.

[0026] In the displacement measuring device 10 of this embodiment, as shown in Figure 8, insertion spacers 70 are attached to the outer surface of the pipe 20. In this embodiment, multiple insertion spacers 70 are provided at intervals (for example, 1.5 m intervals) in the extension direction of the pipe 20. The insertion spacer 70 comprises a frame member 71 attached to the outer surface of the pipe 20, left and right support members 72, 72 attached to the frame member 71, and a roller 73 provided on the support member 72. The frame member 71 is an annular member that surrounds the pipe 20. In this embodiment, the frame member 71 is formed by bending a strip-shaped member into a rectangular shape along the outer circumference of the pipe 20, and one end of the strip-shaped member and the other end are connected on the upper surface of the pipe 20 using bolts.

[0027] The left and right support members 72, 72 are attached to the lower part of the left and right sides of the frame member 71, respectively. The upper part of the support member 72 is fixed to the outer surface of the pipe 20 by joining means such as welding. The lower part of the support member 72 is inclined outward from the pipe 20. The roller 73 is rotatably connected to the lower end of the support member 72. The roller 73 is rotatable on the inner surface of the pipe body 91 of the measuring hole 90 in the direction of extension of the measuring hole 90. This allows the pipe 20 to move within the pipe body 91 while being supported by the multiple insertion spacers 70. Figure 9 is a side view showing the portion of the displacement measuring device 10 according to an embodiment of the present invention in which the insertion spacer 70 is provided. As shown in Figure 9, the outer diameter of the roller 73 is larger than the inner diameter of the communication hole 91a formed in the pipe body 91. In the insertion spacer 70 of this embodiment, the two rollers 73, 73 are attached to the lower end of the support member 72 in a state where they are aligned in the extension direction of the pipe 20.

[0028] Next, a method for measuring ground displacement using the displacement measuring device 10 of this embodiment will be described. The ground displacement measurement method of this embodiment includes the steps of forming a measurement hole 90 (hole formation step), inserting a displacement measurement device 10 into the measurement hole 90 (device insertion step), positioning the pipe 20 (positioning step), fixing the optical fiber cable sensor 50 to the pipe 20 (measurement preparation step), measuring the displacement of the optical fiber cable sensor 50 (measurement step), shrinking the packer 30 (recovery preparation step), and removing the optical fiber cable sensor 50, etc., from the pipe 20 (sensor recovery step).

[0029] As shown in Figure 4, in the hole-forming process, first, a drilling blade 93 is attached to the tip of the pipe 91, and a rod 94 is inserted into the pipe 91, and the tip of the rod 94 is connected to the drilling blade 93. Then, the drive mechanism of the tunnel drill (not shown) rotates the rod 94 in the forward direction around its axis, and the drilling blade 93 excavates the ground to form a borehole 92, while the pipe body 91 is inserted into the borehole 92 together with the drilling blade 93. After excavating the borehole 92 to a predetermined depth, the rod 94 is rotated in the reverse direction around its axis to separate it from the drilling blade 93, and then the rod 94 is withdrawn from inside the pipe 91. As a result, a measurement hole 90 consisting of the borehole 92 and the pipe 91 is formed in the ground. In the device insertion process, as shown in Figure 6, the packer 30 and the upper, lower, left, and right flat plates 40 are inserted into the measurement hole 90 from the base end of the pipe 91 along with the pipe 20. A fiber optic cable sensor 50 is fixed to each of the flat plates 40. At this time, as shown in Figure 8, the pipe 20 is inserted into the pipe body 91 while the rollers 73 of the insertion spacer 70 attached to the pipe 20 are rolled on the inner surface of the pipe body 91. After inserting the pipe 20 into the pipe body 91, a positioning process is performed. In the positioning process, a filler material 4 is filled between the outer surface of the pipe 20 and the inner surface of the pipe body 91 to position the pipe 20 inside the pipe body 91. Furthermore, the filler material 4 filled inside the pipe 91 also fills the gap between the inner surface of the excavated hole 92 and the outer surface of the pipe 91 through each of the communication holes 91a in the pipe 91. As a result, the filler material 4 positions the pipe 20 within the excavated hole 92.

[0030] In the measurement preparation step, as shown in Figure 7, the packer 30 is pressurized to expand it. When the packer 30 is expanded, each flat plate 40 is pressed against the inner surface 22 of the pipe 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 pipe 20. In this way, the optical fiber cable sensors 50 on the top, bottom, left, and right are fixed inside the pipe 20. When displacement occurs in the ground while the displacement measuring device 10 is installed, at least a portion of the pipe 91 bends in accordance with the ground displacement, and furthermore, the pipe 20 and each optical fiber cable sensor 50 experience strain in the extension direction in accordance with the displacement of the pipe 91. In the measurement process, the strain in the extension direction of each optical fiber cable sensor 50 is measured by analyzing the time it takes for the scattered light to return after light is incident on the optical fiber cable sensor 50 from the measuring device 80 shown in Figure 1, and the frequency distribution of the scattered light. The measuring device 80 determines the ground displacement in front of the tunnel face 2 based on the strain of the optical fiber cable sensor 50.

[0031] The recovery preparation process is carried out after extending the tunnel 1 to the tip of the measurement hole 90 while measuring the ground displacement in front of the tunnel face 2. In the recovery preparation process, as shown in Figure 5, the pressure inside the packer 30 is reduced to cause the packer 30 to contract. When the packer 30 is contracted, the pressure on each flat plate 40 and each optical fiber cable sensor 50 against the inner surface of the pipe 20 is released. In the recovery process, the packer 30 and each flat plate 40 are extracted and recovered from the base end of the pipe 20. This allows each optical fiber cable sensor 50, along with each flat plate 40, to be retrieved from inside the pipe 20. As tunnel 1 shown in Figure 1 is excavated, a measurement hole 90 is similarly formed in the ground in front of the tunnel face 2, and as shown in Figure 5, a displacement measuring device 10 is inserted into the measurement hole 90 to repeatedly measure ground displacement.

[0032] In the displacement measuring device 10 and ground displacement measuring method described above, as shown in Figure 7, the packer 30 is expanded inside the pipe 20 inserted into the measuring 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 pipe 20, thereby easily fixing the optical fiber cable sensor 50 inside the pipe 20. After measuring ground displacement using the optical fiber cable sensor 50, as shown in Figure 5, the packer 30 is contracted to release the optical fiber cable sensor 50 from being fixed to the pipe 20, allowing the optical fiber cable sensor 50 to be recovered from inside the pipe 20. Thus, in the displacement measuring device 10 and ground displacement measuring method of this embodiment, the optical fiber cable sensor 50 can be recovered from the ground after measuring the ground displacement. Therefore, even when using an expensive optical fiber cable sensor 50 and packer device that can be expected to provide high-precision displacement, the cost required for measuring ground displacement can be reduced. In other words, it can be applied to displacement measuring methods that use an expensive optical fiber cable sensor 50 and packer device, such as the OFDR type displacement measuring method, to accurately determine ground displacement.

[0033] In the displacement measuring device 10 of this embodiment, the pipe 20 has upper, lower, left, and right flat surfaces 21 formed on its outer surface. With this configuration, when the pipe 20 is inserted into the measuring hole 90, the pipe 20 is less likely to rotate around its axis, so that each optical fiber cable sensor 50 can be correctly inserted into the predetermined position in the measuring hole 90. Furthermore, as shown in Figure 8, when inserting the pipe 20 into the tube 91 of the measurement hole 90, the roller 73 of the insertion spacer 70 attached to the pipe 20 is rolled on the inner surface of the tube 91 while the pipe 20 is inserted into the tube 91. This allows the pipe 20 and the optical fiber cable sensor 50 to be smoothly inserted into the measurement hole 90. Furthermore, as shown in Figure 9, since the outer diameter of the roller 73 is formed to be larger than the inner diameter of the communication hole 91a of the pipe body 91, it is possible to prevent the roller 73 from getting stuck in the communication hole 91a of the pipe body 91. Furthermore, since the insertion spacer 70 has two rollers 73, 73 arranged in the front-to-back direction, the stability of the insertion spacer 70 can be increased. Also, when the roller 73 passes over the communication hole 91a of the pipe body 91, it is supported by the other roller 73 positioned on the inner surface of the pipe body 91, thus preventing the roller 73 from getting caught in the communication hole 91a.

[0034] In the displacement measuring device 10 of this embodiment, as shown in Figure 6, the optical fiber cable sensor 50 is fitted into a recess 43 formed in the flat plate 40, so that the optical fiber cable sensor 50 can be stabilized inside the pipe 20. Also, as shown in Figure 7, when the packer 30 is expanded, the optical fiber cable sensor 50 comes into contact with the outer surface of the packer 30, so that the accuracy of measuring ground displacement can be improved. In the displacement measuring device 10 of this embodiment, flat plates 40 are arranged on the top, bottom, left, and right sides of the packer 30, and each flat plate 40 is provided with an optical fiber cable sensor 50. Furthermore, the upper and lower optical fiber cable sensors 50, 50 are positioned at the same location in the left-right direction, and the left and right optical fiber cable sensors 50, 50 are positioned at the same location in the up-down direction. In Figure 7, when the left-right direction is the X direction, the axial direction of the pipe 20 is the Y direction, and the up-down direction is the Z direction, for example, if bending deformation occurs in the pipe 20 due to the vertical displacement (deformation) of the ground, the amount of vertical displacement of the pipe 20 is measured based on the strain in the extension direction of the optical fiber cable sensor 50 measured by each of the upper and lower optical fiber cable sensors 50, 50. If the measurement is performed with one of the upper and lower optical fiber cable sensors 50, 50 shifted in the left-right direction (X direction) relative to the other, there is a risk of large errors. In this embodiment, since the upper and lower optical fiber cable sensors 50, 50 are positioned at the same location in the left-right direction, the ground displacement in the vertical direction (Z direction) can be measured with high accuracy. Furthermore, in the displacement measuring device 10 of this embodiment, since the left and right flat plates 40, 40 are positioned by the bottom plate of the pipe 20, the vertical positions of the left and right optical fiber cable sensors 50, 50 can be precisely aligned, and consequently, the horizontal (X-direction) ground displacement can be precisely determined. In the displacement measuring device 10 of this embodiment, as shown in Figure 10, the upper and lower plates 40, 40 are engaged with the alignment member 60, thereby positioning both plates 40, 40 within the pipe 20. This allows for precise alignment of the horizontal positions of the upper and lower optical fiber cable sensors 50, 50 attached to both plates 40, 40, enabling accurate determination of vertical ground displacement. In the displacement measuring device 10 of this embodiment, the engaging portion 48 protruding from the flat plate 40 can be easily engaged with the engaged portion 64, which is a hole in the alignment member 60, by inserting the engaging portion 48 protruding from the flat plate 40 into the engaged portion 64. In the displacement measuring device 10 of this embodiment, the engagement portion 48 is formed by the tip of the screw member 47 for fixing the flat plate 40 to the connecting member 45, thus reducing the number of parts. As shown in Figure 7, when the packer 30 is expanded, the flat plate 40 may move in the extension direction. However, as shown in Figure 11, the engaged portion 64 of the alignment member 60 in this embodiment is an elongated hole that extends in the extension direction of the flat plate 40, thus preventing the alignment member 60 from obstructing the movement of the flat plate 40.

[0035] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from its spirit. In this embodiment, as shown in Figure 1, the measurement hole 90 is formed diagonally upward from the widened section 3 of the tunnel 1 toward the front of the tunnel face 2. However, the measurement hole 90 may be formed from the inner wall surface of the tunnel 1 without forming the widened section 3 in the tunnel 1. Figure 13 is an axial cross-sectional view showing the packer 30 in an expanded state in the displacement measuring device 10 according to another embodiment of the present invention. In the displacement measuring device 10 of this embodiment, as shown in Figure 5, the optical fiber cable sensor 50 is fixed to the inner surface 42 of the flat plate 40. However, as shown in Figure 13, a recess 43 may be formed on 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 Figure 5, four optical fiber cable sensors 50 are provided inside the pipe 20, one above, one below, one to the left, and one to the right. However, the number and arrangement of the optical fiber cable sensors 50 are not limited. In the ground displacement measurement method of this embodiment, the measurement hole 90 is constructed by inserting the pipe body 91 into the excavated hole 92, but the measurement hole 90 may also be constructed using only the excavated hole 92. The shape and material of the pipe body 91, pipe 20, packer 30, and flat plate 40 are not limited and can be set appropriately according to the construction conditions. Furthermore, as in the displacement measuring device 10 of this embodiment, if the pipe 20 is made of a softer material than the pipe body 91, the pipe 20 is more likely to displace in accordance with the displacement of the pipe body 91, thus allowing for accurate determination of ground displacement.

[0036] In the alignment member 60 of this embodiment, as shown in Figure 12, side plates 62 are provided on the upper, lower, left, and right edges of the flat plate portion 61, but only the upper and lower side plates 62, 62 may be provided. Furthermore, in the alignment member 60 of this embodiment, as shown in Figure 11, the engaging portion 48 of the screw member 47 protruding from the flat plate 40 is inserted into the engaged portion 64, which is a hole in the alignment member 60. However, the configuration of the engaging portion 48 and the engaged portion 64 is not limited. For example, the engaging portion may be formed by a projection formed on the flat plate 40.

[0037] In the displacement measuring device 10 of this embodiment, as shown in Figure 8, multiple insertion spacers 70 are provided on both the left and right sides of the pipe 20 and at intervals in the extension direction, but the number and spacing of the insertion spacers 70 are not limited. Furthermore, although the insertion spacer 70 of this embodiment is provided with two rollers 73, 73 as shown in Figure 9, the number of rollers 73 is not limited, and for example, one roller 73 or three or more rollers 73 may be provided. Furthermore, in the insertion spacer 70 of this embodiment, the outer diameter of the roller 73 is formed to be larger than the inner diameter of the communication hole 91a of the pipe body 91, but the outer diameter of the roller 73 is not limited. For example, even if the outer diameter of the roller 73 is smaller than the inner diameter of the communication hole 91a of the pipe body 91, if multiple rollers 73 are provided, the roller 73 will be supported by the other rollers 73 positioned on the inner surface of the pipe body 91 as it passes over the communication hole 91a, thus preventing the roller 73 from getting stuck in the communication hole 91a. [Explanation of Symbols]

[0038] 1 Tunnel 2. Facing 3 Widening section 4 Filling material 10 Displacement measuring device 20 pipes 30 Packers 35 Connecting part 40 flat plate 43 Recessed area 44 mounting holes 45 Connecting member 46 screw holes 47 Screw member 48 Engaging part 50 Fiber Optic Cable Sensors 60 Alignment member 61 Flat plate part 62 Side panel 63 Through-hole 64 Engaged portion 70 Insertion spacers 71 Frame members 72 Support member 73 Rollers 80 Measuring device 90 measuring holes 91 Body 91a Communication hole 92 boreholes 93 drilling blades 94 rods

Claims

1. A pipe inserted into the measurement hole, A bag-shaped packer that can expand and contract within the aforementioned pipe, Upper and lower flat plates are positioned between the outer surface of the packer and the inner surface of the pipe, A fiber optic cable sensor attached to the aforementioned flat plate, The pipe comprises an alignment member disposed within the pipe, Multiple packers are connected in the direction of extension of the pipe, The optical fiber cable sensor can be connected to a measuring device that measures the strain of the optical fiber cable sensor. When the packer is inflated, the flat plate is configured to be sandwiched and fixed between the outer surface of the packer and the inner surface of the pipe. The aforementioned alignment member includes: An insertion opening through which the connecting portion of adjacent packers is inserted, A displacement measuring device characterized in that the engaging portions formed on both of the aforementioned flat plates are each formed with upper and lower engaged portions that engage with each other.

2. The engaged portion is a hole formed in the alignment member, The displacement measuring device according to claim 1, characterized in that the engaging portion protruding from the flat plate is inserted into the engaged portion.

3. Multiple of the aforementioned flat plates are connected in the direction of extension of the pipe, The adjacent flat plates are connected by connecting members that are superimposed on the inner surfaces of the adjacent flat plates. The screw member inserted from the outer side into the mounting hole formed in the flat plate is screwed into the screw hole formed in the connecting member. The displacement measuring device according to claim 2, characterized in that the engagement portion is formed by the tip of the screw member that protrudes on the inner surface side of the connecting member.

4. The displacement measuring device according to claim 2, characterized in that the engaged portion is an elongated hole extending in the direction of extension of the flat plate.

5. A method for measuring ground displacement, A step of inserting the displacement measuring device described in any one of claims 1 to 4 into a measuring hole made in the ground, A step of positioning the pipe by filling the space between the inner surface of the measurement hole and the outer surface of the pipe with a filler, The process involves pressurizing the packer to expand it, sandwiching the flat plate between the outer surface of the packer and the inner surface of the pipe, and fixing the optical fiber cable sensor to the pipe. A step of measuring the strain of the optical fiber cable sensor, A step of reducing the pressure inside the packer to shrink the packer, The process of removing the packer, the flat plate, and the optical fiber cable sensor from the pipe, A method for measuring ground displacement, characterized by having the following features.

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