JP2024040720A - Condition measuring device and method - Google Patents

Abstract

To improve measurement accuracy of state measurement of a measurement object by an optical fiber cable.SOLUTION: A state measurement device 100 comprises: an optical fiber cable 50 which is embedded in a folded manner in a borehole 2; and a cover member 60 which covers a folded-back part 50a of the optical fiber cable 50. The optical fiber cable 50 comprises: a first optical fiber cable 51 which is embedded in a forward path; and a second optical fiber cable 52 which is embedded in a return path and is connected to the first optical fiber cable 51 in the cover member 60.SELECTED DRAWING: Figure 1

Description

The present invention relates to a condition measuring device and a condition measuring method.

Patent Document 1 discloses a condition measuring device that measures the condition of the ground using an optical fiber cable buried in the ground.

Japanese Patent Application Publication No. 2002-156215

In the condition measuring device disclosed in Patent Document 1, an optical fiber cable for strain measurement is provided as an optical fiber cable buried in the ground, and a measurement value measured by the optical fiber cable for strain measurement is corrected. For this reason, a temperature-compensated fiber optic cable is provided. Since these optical fiber cables are separately connected to the scattered light measuring device, measurements are performed at different timings. If the timing at which measurements are performed differs in this way, for example, if the temperature changes between the time when measurement is performed using an optical fiber cable for strain measurement and the time when measurement using an optical fiber cable for temperature compensation is completed, In this case, the amount of strain is corrected at a temperature different from the temperature at which the measurement using the optical fiber cable for strain measurement is performed. For this reason, there is a possibility that the measurement accuracy of the amount of distortion may be reduced.

An object of the present invention is to improve the accuracy of measuring the state of an object to be measured using an optical fiber cable.

The present invention is a condition measuring device that measures the state of an object to be measured using an optical fiber cable, the optical fiber cable being folded back and buried inside the object to be measured so as to reciprocate within the object. a cover member that covers a folded part of the optical fiber cable; the optical fiber cable includes a first optical fiber cable buried in the outward route; and a first optical fiber cable buried in the return route and connected to the first optical fiber cable within the cover member. 2 optical fiber cable.

According to the present invention, it is possible to improve the accuracy of measuring the state of an object to be measured using an optical fiber cable.

FIG. 1 is a diagram showing a state measuring device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view for explaining the configuration of a first optical fiber cable. FIG. 3 is a cross-sectional view for explaining the configuration of a second optical fiber cable. It is a figure showing the cover member of the condition measuring device concerning an embodiment of the present invention. It is a figure which shows the modification of the cover member of the condition measuring device based on embodiment of this invention. It is a figure which shows the modification of the condition measuring device based on embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A condition measuring device according to an embodiment of the present invention will be described below with reference to the drawings.

First, the configuration of a condition measuring device 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 4. The condition measuring device 100 is a device that measures the condition of the ground 1, which is an object to be measured, using an optical fiber cable 50 buried in the ground 1. Note that the object to be measured is not limited to the ground 1, and may be any object as long as it is possible to bury the optical fiber cable 50, for example, a concrete structure such as a dam. It's okay.

When constructing civil engineering structures, it is important to understand the ground conditions such as landslides, and it is also important to understand the progress of loosened areas that occur in the ground due to the excavation of underground cavities such as tunnels. For example, as shown in Figure 1, a borehole 2 is drilled vertically upward in the ground 1 to detect distortions and loosened areas in the ground. An optical fiber cable 50 is buried in the (insertion hole). The borehole 2 is a bottomed hole with one end closed inside the ground or structure that is the object to be measured, and the other end open to the ground or structure that is the object to be measured.

The optical fiber cable 50 buried in the borehole 2 is distorted in accordance with the distortion in the ground and the loosening of the ground 1. Therefore, as will be described later, by measuring the distortion of the optical fiber cable 50, It is possible to measure the distortion of the ground 1 and the loosening of the ground 1.

The condition measuring device 100 shown in FIG. a cover member 60 attached to the tip end side of the optical fiber cable 50 to cover the folded part 50a of the optical fiber cable 50; It mainly includes a filling hose 30 provided along the line.

The pipe material 10 is a hollow elongated member made of resin such as polyvinyl chloride and has an outer diameter sufficiently smaller than the inner diameter of the borehole 2, and has an internal passage 11 formed to penetrate in the axial direction. , a communication hole 12 that is open at one end on the inner circumferential surface of the internal passage 11 and communicates between the inside and outside of the pipe material 10.

The communication hole 12 is formed on the tip side of the pipe material 10 when the condition measuring device 100 is inserted into the borehole 2, and is used to fill the borehole 2 with grout 40 (filling material) through the filling hose 30. When doing so, it functions as a discharge port for discharging the air inside the borehole 2 to the outside of the borehole 2.

The expanded diameter body 20 includes an expansion part 22 that expands radially outward in accordance with the pressure of the supplied fluid, a support part 21 that supports the expansion part 22 inside in the radial direction, and a support part 21 that supplies pressurized fluid. and a supply pipe 24. FIG. 1 shows a state in which the expansion portion 22 expands toward the outside in the radial direction of the borehole 2 and presses the inner wall surface of the borehole 2.

The expansion part 22 is a rubber or metal member having a barrel-shaped or cylindrical outer shape, and is a member made of rubber or metal and is used to supply fluid to a space (not shown) formed between the support part 21 and the expansion part 22. The support portion 21 supports the support portion 21 so as to expand radially outward in response to pressure.

The support portion 21 is fixed to the outer surface of the cover member 60 via a fixture (not shown).

The supply pipe 24 is attached to the pipe material 10 along the axial direction, and one end 24a thereof opens into a space formed between the support part 21 and the expansion part 22. The other end 24b of the supply pipe 24 is connected to a fluid supply source such as a pump (not shown) outside the borehole 2 before the pressurized fluid is supplied to the expansion section 22 through the supply pipe 24. When the supply of fluid to the expansion part 22 is completed, the expansion part 22 is accommodated in the borehole 2, as shown in FIG. In addition, in order to maintain the expanded state of the once-inflated expansion part 22, a check valve for preventing backflow of the supplied fluid may be provided on the supply pipe 24.

The fluid supplied to the expanded diameter body 20 through the supply pipe 24 is, for example, pressurized water, and the expansion part 22 presses the inner wall surface of the borehole 2 with a load corresponding to the water pressure. Note that the fluid supplied to the expanded diameter body 20 is not limited to water, and may be compressed air or pressurized hydraulic oil.

The filling hose 30 is a hose through which the grout 40 filled into the borehole 2 flows, and is attached along the pipe material 10 so that a discharge port 30a for discharging the grout 40 opens in the borehole 2. There is. As shown in FIG. 1, the position of the discharge port 30a is set vertically lower than the communication hole 12 formed in the pipe material 10. Note that the discharge port 30a may be disposed vertically lower than the communication hole 12, and may be disposed near the open end 2b of the borehole 2, for example. The other end of the filling hose 30 is connected to a grout delivery pump (not shown) outside the borehole 2.

As shown in FIG. 1, the optical fiber cable 50 is folded back at a folding portion 50a near the bottom surface 2a of the borehole 2, and is provided in the ground 1 so as to reciprocate within the borehole 2.

The distal end 50b of the optical fiber cable 50 is arranged near the open end 2b of the borehole 2, and is sealed with a sealing material such as oil or silicone to prevent reflection from occurring at the distal end surface. On the other hand, the base end 50c of the optical fiber cable 50 is connected to the measuring device 70 outside the borehole 2.

The optical fiber cable 50 includes a first optical fiber cable 51 buried in the outward path from the open end 2b side of the borehole 2 to the bottom surface 2a, and a second optical fiber cable buried in the return path from the bottom surface 2a side to the open end 2b. The cable 52 is mainly composed of two different optical fiber cables. Note that the expressions "outward route" and "return route" are used to distinguish the routes on which optical fiber cables are laid, and those buried on the outward route are referred to as second optical fiber cables, and those buried on the return route are referred to as first optical fiber cables. It may also be a fiber cable.

The first optical fiber cable 51 is an optical fiber sensor used to measure strain occurring in the ground 1, and as shown in FIG. It has a member 51e and a resin coating 51d that covers these members. The first optical fiber strand 51a is composed of a core 51b, a cladding 51c surrounding the outer periphery of the core 51b, and an ultraviolet curing resin (not shown) covering the periphery of the cladding 51c. Note that FIG. 2 is a cross-sectional view of the first optical fiber cable 51.

The surface of the covering 51d is embossed to improve adhesion to the grout 40 filled in the borehole 2. Thereby, the strain generated in the ground 1 via the grout 40 is easily transmitted to the first optical fiber strand 51a.

The second optical fiber cable 52 is an optical fiber sensor used to measure the temperature inside the ground 1, and as shown in FIG. 3, has a second optical fiber strand 52a and a metal tube 52d (coating) arranged to cover the second optical fiber strand 52a.

The second optical fiber strand 52a, like the first optical fiber strand 51a, is composed of a core 52b, a clad 52c surrounding the outer periphery of the core 52b, and an ultraviolet curing resin (not shown) covering the periphery of the clad 52c. .

The metal tube 52d is a steel tube made of highly corrosion-resistant stainless steel or nickel alloy, and has an inner diameter larger than the outer diameter of the second optical fiber strand 52a. In other words, a slight gap is formed between the second optical fiber 52a and the metal tube 52d, so that the second optical fiber 52a can freely expand and contract without being restricted by the metal tube 52d. It has become. Note that FIG. 3 is a cross-sectional view of the second optical fiber cable 52.

Followability of the cladding 51c (first optical fiber wire 51a) to the coating 51d of the first optical fiber cable 51 for strain measurement, and cladding 52c to the metal tube 52d (coating) of the second optical fiber cable 52 for temperature measurement Comparing the followability of (the second optical fiber strand 52a), the former is higher and the latter is lower. In other words, when comparing the coefficient of friction between the coating 51d of the first optical fiber cable 51 and the cladding 51c and the coefficient of friction between the coating (metal tube 52d) and the cladding 52c of the second optical fiber cable 52, the former is larger than the latter. In other words, when comparing the followability of the first optical fiber 51a (cladding 51c) and the followability of the second optical fiber 52a (cladding 52c) to the grout 40 (filling material) in which each coating is buried, The former is higher and the latter is lower.

In particular, the surface of the coating 51d of the first optical fiber cable 51 is embossed as described above, so that the coating 51d easily adheres to the grout 40. It can be said that the followability of the wire 51a (cladding 51c) is further improved. Furthermore, a slight gap is provided between the second optical fiber strand 52a of the second optical fiber cable 52 and the metal tube 52d (sheathing), as described above, and the second optical fiber strand 52a is connected to the metal tube 52d. Since it is difficult to follow the grout 52d (covering), it can be said that the followability of the second optical fiber strand 52a (cladding 52c) to the grout 40 is lowered.

That is, when a strain occurs in the ground 1, the strain is easily transmitted to the first optical fiber strand 51a via the coating 51d in the first optical fiber cable 51, while the second optical fiber cable 52 This makes it difficult for the strain to be transmitted to the second optical fiber strand 52a via the metal tube 52d.

In addition, in the second optical fiber cable 52 for temperature measurement, the metal tube 52d with high thermal conductivity serves as a coating that covers the second optical fiber wire 52a, so that the temperature of the ground 1 is lower than that of the second optical fiber wire. 52a.

The first optical fiber cable 51 and the second optical fiber cable 52 are arranged so that the first optical fiber strand 51a and the second optical fiber strand 52a are inside the cover member 60 that covers the folded part 50a of the optical fiber cable 50. The connection is made by being fused. Specifically, the first optical fiber strand 51a and the second optical fiber strand 52a are connected by fusion bonding the cores 51b and 52b and fusion bonding the claddings 51c and 52c. What are the sheathing 51d of the first optical fiber cable 51 and the metal tube 52d (coating) of the second optical fiber cable 52, which are obstacles when fusing the first optical fiber strand 51a and the second optical fiber strand 52a? , are each previously removed over a predetermined length from the end. A portion where the first optical fiber strand 51a and the second optical fiber strand 52a are fused together is protected by a protective sleeve 54, which will be described later. Note that the method of connecting the first optical fiber cable 51 and the second optical fiber cable 52 is not limited to fusion splicing, and may be mechanical splice connection or connector connection. However, in order to reduce splicing loss at the spliced portion, it is preferable to use fusion splicing.

In addition, the first optical fiber cable 51 and the second optical fiber cable 52, which are provided along the axial direction on the outer circumferential surface of the pipe material 10, are laid on the pipe material 10 with the fixing tape 14 together with the supply pipe 24 and the filling hose 30, and are integrated into the pipe material 10. It is fixed so that it becomes . Note that the pipe material 10, the first optical fiber cable, and the second optical fiber cable are not integrated when the pipe material 10, the first optical fiber cable, and the second optical fiber cable are inserted into the borehole 2. That's fine. A plurality of fixing tapes 14 are provided at predetermined intervals in the axial direction.

The cover member 60 is a resin casing formed by injection molding, and as shown in FIG. It has a cover member (not shown) that is attached to the housing part 61 so that the optical fiber cable 50 routed inside the part 61 is not exposed to the outside. Note that FIG. 4 shows the internal shape of the accommodating part 61 in a state where the lid member is removed from the accommodating part 61.

The housing part 61 has a plate-shaped bottom wall 61a and a side wall 61b formed along the outer edge of the bottom wall 61a. A curvature holding part 63 capable of holding the curvature is provided, a first holding part 64 capable of holding the first optical fiber cable 51, a second holding part 65 capable of holding the second optical fiber cable 52, and a first holding part 63 capable of holding the first optical fiber cable 51. A sleeve holding part 66 capable of holding the protective sleeve 54 that protects the fused portion between the optical fiber strand 51a and the second optical fiber strand 52a, and an extra length holding part 67 capable of holding the extra length part are provided. It will be done.

The curvature retaining portion 63 includes a bulging portion 63a that bulges out in a circular shape from the bottom wall 61a, and a groove portion 63b formed between the bulging portion 63a and the side wall 61b. The outer peripheral surface of the bulging portion 63a is an arcuate surface 63c with a predetermined curvature, and the optical fiber cable 50 inserted into the groove portion 63b is held along the arcuate surface 63c. By being held by the curvature holding portion 63 in this manner, the direction in which the optical fiber cable 50 extends is changed. In other words, the portion held by the curvature holding portion 63 becomes the folded portion 50a of the optical fiber cable 50.

The magnitude of the curvature of the arcuate surface 63c is set according to the minimum bending radius of the optical fiber cable 50 in order to avoid an increase in the bending loss of the optical fiber cable 50. For example, as shown in FIG. 4, when the second optical fiber strand 52a is provided in the folded part 50a, the magnitude of the curvature of the circular arc surface 63c is determined according to the minimum bending radius of the second optical fiber strand 52a. It is set so that bending loss does not increase.

Note that in order to reduce the bending loss at the folded portion 50a, it is better to reduce the curvature of the arcuate surface 63c, but if the curvature of the arcuate surface 63c is reduced, the width of the cover member 60 increases. The inner diameter of the borehole 2 into which the is inserted must be increased. On the other hand, since the cost and time required for drilling the borehole 2 increase as the inner diameter of the borehole 2 becomes larger, it is preferable to make the inner diameter of the borehole 2 as small as possible.

In addition, in general, cables such as the first optical fiber cable 51 and the second optical fiber cable 52 are compared with bare wires such as the first bare optical fiber 51a and the second bare optical fiber 52a. In this case, the optical fiber wire is easier to bend and its minimum bending radius is smaller.

Therefore, in this embodiment, by arranging a strand such as the second optical fiber strand 52a in the folded portion 50a, the curvature of the circular arc surface 63c is increased and the width of the cover member 60 is made as large as possible. I'm keeping it small. This makes it possible to insert the cover member 60 even if the inner diameter of the borehole 2 is small.

The shape of the bulging portion 63a provided with the arcuate surface 63c is not limited to a circular shape, and the shape of the bulging portion 63a is not limited to a circular shape, and the shape extends toward the distal end side of the cover member 60 that comes into contact with the bottom surface 2a of the borehole 2 when inserted into the borehole 2. Any shape may be used as long as it has a convex arcuate surface 63c, for example, a semicircular shape or a crescent shape.

The first holding part 64 is a groove part 64a formed in a shape capable of holding the first optical fiber cable 51 by fitting the first optical fiber cable 51 into which the coating 51d has not been removed, and the second holding part 65 is a groove 65a formed into a shape capable of holding the second optical fiber cable 52 by fitting the second optical fiber cable 52 into which the metal tube 52d has not been removed. Each groove portion 64a, 65a is formed by cutting out a portion of the side wall 61b so as to communicate the inside and outside of the housing portion 61.

The sleeve holding portion 66 is a groove portion 66b formed between a side wall 61b extending linearly and an inner wall 66a extending parallel thereto, and the width of the groove portion 66b is larger than the outer diameter of the protective sleeve 54. is also set slightly smaller. By fitting the protective sleeve 54 into the groove 66b, the fused portion of the first optical fiber strand 51a and the second optical fiber strand 52a is fixed to the cover member 60 via the protective sleeve 54.

The protective sleeve 54 is a tubular member provided to protect the fragile portion of the fused portion between the first optical fiber strand 51a and the second optical fiber strand 52a. A rod-shaped hard member is provided spanning the fiber strand 51a and the second optical fiber strand 52a.

The extra length holding part 67 is used to hold the extra length of the first optical fiber 51a from which the coating 51d has been removed with a margin when connecting the first optical fiber cable 51 and the second optical fiber cable 52. The remaining length of the second optical fiber 52a from which the metal tube 52d has been removed is the part to be routed, and has a bulging portion 67a that bulges out in a semicircular shape from the bottom wall 61a. A part of the outer peripheral surface of the bulging portion 67a is an arcuate surface 67b having a predetermined curvature, and the optical fiber cable 50 is held along the arcuate surface 67b.

The shape of the bulging portion 67a provided with the circular arc surface 67b is not limited to a semicircular shape, and may be any shape as long as it has the circular arc surface 67b. It may be circular like the portion 63a. In addition, when the extra length part is short, the optical fiber cable 50 may be held along the groove part 67c formed between the bulge part 67a and the side wall 61b, as shown by the broken line. Further, when the extra length is long, the optical fiber cable 50 may be held by going around the bulge 63a of the curvature holding part 63.

Further, the extra length holding section 67 is not limited to holding the extra length of the second optical fiber strand 52a, as shown in FIG. It may be formed at a position where the extra length of one optical fiber strand 51a can be held.

The cover member 60, in which the optical fiber cable 50 is routed inside, is constructed of a pipe material 10 such that the side of the part where the curvature retaining portion 63 for retaining the folded portion 50a is provided faces the bottom surface 2a of the borehole 2. Attached to the tip. That is, when inserting the pipe material 10 etc. into the borehole 2, the cover member 60 is first inserted into the borehole 2, and is inserted until the tip of the cover member 60 comes into contact with the bottom surface 2a of the borehole 2. .

The condition measuring device 100 further includes a flange 16 at the open end 2b of the borehole 2 for fixing the base end of the pipe material 10 to the borehole 2.

The flange 16 is a plate-like member provided to support the base end of the pipe material 10 that protrudes outside the borehole 2, and supports the pipe material 10 and the optical fiber cable 50 provided around the pipe material 10. It has an insertion hole 16a through which the filling hose 30 can be inserted, and a plurality of bolt holes 16b through which the anchor bolts 4 embedded in the ground 1 surround the opening of the borehole 2. The flange 16 is fixed to the borehole 2 by tightening the nut 5 screwed onto the anchor bolt 4.

Further, the flange 16 is formed with a sealant injection hole (not shown) whose one end opens in the borehole 2, and a sealant such as urethane material is applied to the vicinity of the flange 16 in the borehole 2 through this sealant injection hole. By injecting the stopper 18, the open end 2b of the borehole 2 is closed, and the space within the borehole 2 is closed off from the outside.

The optical fiber cable 50 is filled with grout 40 (filling material) such as cement bentonite through the filling hose 30 into the space in the borehole 2 that is blocked by injecting the sealing material 18 into the open end 2b. is buried in the borehole 2 together with the pipe material 10, and becomes almost integrated with the ground 1. Note that when the grout 40 is filled, the air in the borehole 2 is discharged to the outside of the borehole 2 through the communication hole 12 and the internal passage 11 of the pipe material 10.

Next, we will explain how to measure the condition of the ground 1, which is the object to be measured, using the condition measurement device 100 configured as described above.

Generally, optical fiber cables have the property of slightly scattering the incident pulsed light backwards, and by utilizing this property, it is possible to measure strain at multiple positions in the optical fiber cable. . Since the frequency of the scattered light depends on the distortion of the optical fiber cable, the distortion of the optical fiber cable can be measured by injecting pulsed light into the optical fiber cable and measuring the frequency of the scattered light. In addition, by measuring the time it takes for the scattered light generated within the optical fiber cable to return to the incident position after pulsed light is input into the optical fiber cable, it is possible to determine the position where the scattered light occurs, that is, the distortion in the optical fiber cable. The resulting position can be measured.

On the other hand, the frequency of scattered light changes not only due to distortion but also due to changes in ambient temperature, so if the strain is simply calculated from the frequency of scattered light, the calculated strain will include the frequency change due to temperature change. will also be included. In other words, in order to accurately measure distortion, it is necessary to compensate for the amount of change in frequency that corresponds to temperature change.

In order to compensate for changes in frequency depending on temperature, it may be possible to provide a separate optical fiber cable for temperature compensation, but it is difficult to measure by using an optical fiber cable for measuring strain and an optical fiber cable for temperature compensation. For example, if the temperature changes between the time when the measurement using the optical fiber cable for strain measurement is performed and the measurement using the optical fiber cable for temperature compensation is completed, the timing for measuring the strain may be different. The amount of distortion will be corrected at a temperature different from the temperature at which the measurement using the optical fiber cable was performed.

For this reason, simply providing an optical fiber cable for temperature compensation cannot reliably eliminate the influence of temperature changes, and as a result, there is a risk that the measurement accuracy of the amount of strain will decrease.

Therefore, in this embodiment, as described above, the first optical fiber cable 51 used to measure the strain occurring in the ground 1, and the second optical fiber cable 52 used to measure the temperature inside the ground 1. A single optical fiber cable 50 formed by connecting the Reliably eliminates the effects of temperature changes on quantity measurements.

Specifically, first, a predetermined pulsed light is inputted into the optical fiber cable 50 from a light source (not shown) in the measuring device 70 (light input step).

Subsequently, the strain in the ground 1 is measured along the borehole 2 based on the scattered light (reflected light) returning from the first optical fiber cable 51 of the optical fiber cables 50 (distortion measurement step). The distortion is measured, for example, by a known BOTDR (Brillouin Optical Time Domain Reflectometry) method that uses Brillouin scattering.

Almost simultaneously, the temperature of the ground 1 is measured along the borehole 2 based on the scattered light (reflected light) returning from the second optical fiber cable 52 of the optical fiber cable 50 (temperature measurement step). Temperature measurement, like strain measurement, is performed by the well-known BOTDR method.

When the strain distribution and temperature distribution in the axial direction inside the borehole 2 are measured simultaneously in this way, the strain measured in the first optical fiber cable 51 is calculated using the temperature measured in the second optical fiber cable 52. Corrected (correction process).

Here, the frequency difference (frequency shift) acquired by the first optical fiber cable 51 to calculate the strain also includes a difference corresponding to temperature, as described above. On the other hand, the frequency difference (frequency shift) acquired by the second optical fiber cable 52 includes only a difference corresponding to temperature, and does not include a difference corresponding to strain.

Therefore, by subtracting the frequency difference acquired by the second optical fiber cable 52 from the frequency difference acquired by the first optical fiber cable 51, the frequency difference caused only by distortion can be determined. Based on the frequency difference caused only by the strain determined in this way, the strain occurring at a predetermined position in the borehole 2 can be measured with high accuracy.

Note that the measurement of strain and temperature is not limited to the above method, and may be performed using other methods as long as they can be measured based on the backscattered light of the optical fiber cable 50. For example, the measurement of strain and temperature may be performed using the well-known optical frequency Reflectometry) method, or a combination of the above method and the OFDR method.

According to the above embodiment, the following effects are achieved.

According to the condition measuring device 100 according to the present embodiment, the optical fiber cable 50 buried in the borehole 2 includes a first optical fiber cable 51 buried in the outward path and a second optical fiber cable 52 buried in the backward path. are integrated by being connected.

Therefore, the measurement with the first optical fiber cable 51 and the measurement with the second optical fiber cable 52 are performed at the same timing. This makes it possible to correct the measured value measured by the first optical fiber cable 51 with the measured value measured by the second optical fiber cable 52 at the same timing, and as a result, the distortion of the ground 1 (object to be measured) It is possible to improve the accuracy of measuring the state of objects. Moreover, since the measurement with the first optical fiber cable 51 and the measurement with the second optical fiber cable 52 are performed simultaneously, the time required to measure the strain in the ground 1 can be shortened.

Furthermore, the optical fiber cable 50 is held at a predetermined curvature by the cover member 60 at the folded portion 50a. Therefore, occurrence of bending loss at the folded portion 50a is suppressed, and as a result, it is possible to maintain measurement accuracy over the entire area of the optical fiber cable 50 even when the folded portion 50a is included.

Further, a connecting portion between the first optical fiber cable 51 and the second optical fiber cable 52 is arranged within the cover member 60. Therefore, the connecting portion, which is a vulnerable portion, can be protected from the outside.

Note that the following modifications are also within the scope of the present invention, and the configuration shown in the modification may be combined with the configuration described in the above embodiment, or the configurations described in the following different modifications may be combined. is also possible.

In the above embodiment, the second optical fiber strand 52a is arranged in the folded portion 50a. Instead, as in a modification shown in FIG. 5, a third optical fiber 53 (third optical fiber cable) different from the first optical fiber 51a and the second optical fiber 52a is folded back. The third optical fiber strand 53 may be held by a curvature holding part 63. Note that FIG. 5 is a diagram corresponding to FIG. 4.

In the modification shown in FIG. 5, the first optical fiber cable 51 and the second optical fiber cable 52 are connected via a third optical fiber wire 53. Specifically, one end 53a of the third optical fiber 53 is fused to the first optical fiber 51a, and the other end 53b of the third optical fiber 53 is fused to the second optical fiber 52a. Each fused portion is protected by a first protective sleeve 154 and a second protective sleeve 155, respectively.

The third optical fiber strand 53 is an optical fiber specialized for bending resistance, such as a holey fiber, and has a minimum bending radius smaller than that of the first optical fiber strand 51a and the second optical fiber strand 52a. used.

In this modification, as shown in FIG. 5, the housing part 161 of the cover member 160 is provided with a curvature holding part 63 similar to that of the above embodiment, and a first protection sleeve 154 that can hold the first protection sleeve 154 is provided in the housing part 161 of the cover member 160. A sleeve holding portion 166 and a second sleeve holding portion 167 capable of holding the second protective sleeve 155 are provided.

The first sleeve holding portion 166 is a groove portion 166b formed between a side wall 61b extending linearly and an inner wall 166a extending parallel thereto, and the width of the groove portion 166b is equal to the width of the first protective sleeve 154. is set slightly smaller than the outer diameter of the By fitting the first protective sleeve 154 into the groove 166b, the fused portion of the first optical fiber strand 51a and the third optical fiber strand 53 is fixed to the cover member 160 via the first protective sleeve 154. .

Like the first sleeve holding part 166, the second sleeve holding part 167 is a groove part 167b formed between a side wall 61b extending linearly and an inner wall 167a extending parallel thereto, and the width of the groove part 167b is The size of the second protective sleeve 155 is set to be slightly smaller than the outer diameter of the second protective sleeve 155. By fitting the second protective sleeve 155 into the groove 167b, the fused portion of the second optical fiber strand 52a and the third optical fiber strand 53 is fixed to the cover member 160 via the second protective sleeve 155. .

Since the third optical fiber strand 53 arranged in the folded part 50a has a smaller minimum bending radius than the first optical fiber strand 51a and the second optical fiber strand 52a, in this modification, the bending radius is smaller than that of the first optical fiber strand 51a and the second optical fiber strand 52a. Also, it becomes possible to increase the curvature of the arcuate surface 63c of the curvature retaining portion 63 and further reduce the width of the cover member 160. This allows the optical fiber cable 50 to be buried in the borehole 2 whose inner diameter is even smaller.

Note that the portion of the third optical fiber strand 53 held by the curvature holding section 63 may be in the form of an optical fiber cable covered with a resin coating, similar to the first optical fiber cable 51. good. Further, the accommodation portion 161 of the cover member 160 may be provided with an extra length holding portion 67 capable of holding an extra length portion, similarly to the above embodiment.

Further, in the embodiment described above, the optical fiber cable 50 is buried in the bore hole 2 that is drilled vertically upward in the ground 1. Alternatively, the optical fiber cable 50 may be buried in a borehole 2 that is drilled horizontally, or, as in a modified example shown in FIG. 2 may be embedded.

In the modification shown in FIG. 6, the optical fiber cable 50 is inserted into the borehole 2 together with a steel rope 264 instead of the pipe material 10.

Specifically, the condition measuring device 200 shown in FIG. 6 covers the optical fiber cable 50 that is folded back and buried so as to reciprocate along the axial direction of the borehole 2, and the folded part 50a of the optical fiber cable 50. It has a cover member 260, a weight 262 attached to the cover member 260, and a rope 264 whose one end is connected to the cover member 260.

Similar to the cover member 60 of the above embodiment, the cover member 260 has a configuration capable of holding the folded portion 50a of the optical fiber cable 50 at a predetermined curvature, and also has a structure that allows the folded portion 50a of the optical fiber cable 50 to be held at a predetermined curvature. It has a structure that can hold the connection part with.

The weight 262 is a metal member attached to the side surface of the cover member 260, and functions as a heavy object that stabilizes the position of the cover member 260 when inserting the cover member 260 into the borehole 2. Note that the weight 262 may be a cylindrical metal member in which a space in which the cover member 260 can be accommodated is formed. Further, the weight 262 may be connected to the distal end side of the cover member 260 via a wire or the like, and may be inserted into the borehole 2 before the cover member 260.

The rope 264 is a steel wire rope that suspends and supports the cover member 260 and the weight 262 when they are inserted into the borehole 2, and the other end is attached to a winding device such as a winch (not shown). ing. Note that the rope 264 is not limited to a steel wire rope, but may be a resin rope made of polyethylene or the like. Moreover, it is preferable that the rope 264 is a non-rotating rope. Further, one end of the rope 264 may be connected to a weight 262 instead of the cover member 260.

The optical fiber cable 50 that is folded back and provided in the borehole 2 is fixed to the rope 264 by a plurality of fixing tapes 14 provided at predetermined intervals in the axial direction, and is inserted into the borehole 2 in this state. Ru.

Then, as shown in FIG. 6, in a state in which the distal end of the cover member 260 is in contact with the bottom surface 2a of the borehole 2 and the distal end 50b of the optical fiber cable 50 is located near the open end 2b of the borehole 2. , the borehole 2 is filled with grout 40.

Even when the optical fiber cable 50 is buried in the borehole 2 that is drilled vertically downward, the measurement accuracy of the strain in the ground 1 (the state of the object to be measured) is similar to the above embodiment. can be improved.

Further, in the embodiment described above, the second optical fiber strand 52a is arranged in the folded portion 50a. Alternatively, the first optical fiber cable 51 from which the sheath 51d is not removed or the second optical fiber cable 52 from which the metal tube 52d is not removed may be arranged in the folded portion 50a. However, as described above, in order to increase the curvature of the arcuate surface 63c of the curvature retaining section 63 that holds the folded part 50a, it is preferable to arrange the optical fibers 51a and 52a in the folded part 50a.

Further, in the above embodiment, the first optical fiber cable 51 is buried in the outward path from the open end 2b side of the borehole 2 to the bottom surface 2a, and the second optical fiber cable is buried in the return path from the bottom surface 2a side to the open end 2b. 52 are buried. Alternatively, the second optical fiber cable 52 may be buried in the outbound route, and the first optical fiber cable 51 may be buried in the return route.

Although the embodiments of the present invention have been described above, the above embodiments merely show 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. do not have.

100,200... Condition measuring device 1... Ground (object to be measured)
2...Boring hole (insertion hole)
40... Grout (filling material)
50... Optical fiber cable 50a... Folded part 51... First optical fiber cable 51a... First optical fiber bare wire 51b... Core 51c... Clad 51d... Covering 52...・Second optical fiber cable 52a... Second optical fiber wire 52b... Core 52c... Clad 52d... Metal tube (covering)
53...Third optical fiber wire (third optical fiber cable)
60, 160, 260...Cover member 63...Curvature holding part

Claims (8)

A condition measuring device that measures the condition of an object to be measured using an optical fiber cable,
The optical fiber cable is folded back and buried in the object to be measured so as to reciprocate within the object to be measured;
a cover member that covers the folded portion of the optical fiber cable;
The optical fiber cable includes a first optical fiber cable buried in the outward path, and a second optical fiber cable buried in the return path and connected to the first optical fiber cable within the cover member.
Condition measuring device. The first optical fiber cable and the second optical fiber cable each have a core, a cladding surrounding the outer periphery of the core, and a coating surrounding the outer periphery of the cladding,
The conformability of the cladding to the coating of the first optical fiber cable is higher than the conformability of the cladding to the coating of the second optical fiber cable.
The condition measuring device according to claim 1. The cover member has a curvature holding part that can hold the folded part of the optical fiber cable at a predetermined curvature.
The condition measuring device according to claim 1. The first optical fiber cable and the second optical fiber cable each have a core, a cladding surrounding the outer periphery of the core, and a coating surrounding the outer periphery of the cladding,
The curvature holding portion holds either the first optical fiber cable or the second optical fiber cable from which the sheathing has been removed in order to connect the first optical fiber cable and the second optical fiber cable. be done,
The condition measuring device according to claim 3. The first optical fiber cable and the second optical fiber cable are connected via a third optical fiber cable having a smaller allowable bending radius than the first optical fiber cable and the second optical fiber cable,
The third optical fiber cable is held in the curvature holding part,
The condition measuring device according to claim 3. The optical fiber cable is inserted into an insertion hole provided in the object to be measured,
A filler is filled in the gap between the optical fiber cable and the insertion hole.
A condition measuring device according to any one of claims 1 to 5. The first optical fiber cable and the second optical fiber cable each have a core, a cladding surrounding the outer periphery of the core, and a coating surrounding the outer periphery of the cladding,
The followability of the cladding of the first optical fiber cable with respect to the filler is higher than the followability of the cladding of the second optical fiber cable with respect to the filler.
The condition measuring device according to claim 6. A state measuring method for measuring the state of the object to be measured using the state measuring device according to any one of claims 1 to 5, comprising:
Injecting light into the optical fiber cable;
Measuring the distortion of the object to be measured based on scattered light returning from the first optical fiber cable among the optical fiber cables;
a step of measuring the temperature of the object to be measured based on scattered light returning from the second optical fiber cable of the optical fiber cable; and a step of correcting the measured distortion using the measured temperature. ,including,
Condition measurement method.

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