JP3773772B2 - Strain distribution measurement method for ground and rock - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ground / rock mass strain distribution measuring method for measuring ground / rock mass strain distribution using an optical fiber.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a ground / rock strain distribution measuring method for measuring the ground / rock strain distribution using an optical fiber is already well known. It is known that the Brillouin frequency shift amount, which is the measurement principle of a strain sensor using this optical fiber, has temperature dependency as well as strain dependency.
[0003]
[Problems to be solved by the invention]
By the way, conventionally known methods for measuring strain distribution of ground and rock using optical fibers do not take into account the above-described temperature dependence. Accordingly, the temperature coefficient of Brillouin frequency shift νB is dνB / dT = 1.0 [MHZ / ℃], there is a problem that distorted measurement error of 1 × 10 ^-4 at a temperature fluctuations 5 ° C. An accurate measurement result was not obtained.
[0004]
The present invention has been made to solve the above-mentioned problems, and its purpose is to capture the object to be measured as a line and to measure up to several tens of kilometers. Another object of the present invention is to provide a strain distribution measurement method for the ground and rock mass that can be measured in real time.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the ground / rock mass strain distribution measuring method according to claim 1 of the present invention includes a plurality of laying rods on both sides of the ground / rock mass on both sides of the object to be measured, such as a plurality of cracks with appropriate intervals. A single optical fiber that was inserted into the tube of a predetermined length while applying a certain tension to the upper part of each laying rod was laid with an adhesive, and the temperature in the tube was set in advance. In a state where the temperature is maintained, and the optical fibers not measured are slack-free, and a strain / loss integrated optical pulse tester is connected to one end of the optical fiber. by measuring the longitudinal strain occurring in the optical fiber based on Brillouin scattered light in the strain-loss integrated optical pulse tester strain of soil-bedrock for measuring the strain distribution of the ground-rock In the distribution measurement method, in order to maintain the temperature in the pipe at a preset temperature, a heating wire heater is wound around the outside of the pipe, covered with a heat insulating material, a reflective material is wound around the outside, and a temperature sensor is provided in the pipe. It is characterized by.
[0006]
Accordingly, the laying rods are driven on both sides of the ground and the rock on both sides of the measurement target such as a plurality of cracks at appropriate intervals. Then, an optical fiber that is inserted while applying a certain tension into a pipe having a predetermined length is laid with an adhesive on the upper part of each laying rod. Next, the temperature in the tube is maintained at a preset temperature. Further, in the length direction generated in the optical fiber based on the Brillouin scattered light in the optical fiber in a strain / loss integrated optical pulse tester in a state where the optical fibers not to be measured are saglessly tensioned. By measuring the strain , the temperature distribution of the installed optical fiber is suppressed, and the strain distribution of the ground and rock is measured accurately and in real time. Moreover, it is possible to measure several tens of kilometers by capturing the measurement object as a line. Further, a heating wire heater is wound around the outside of the tube, covered with a heat insulating material, a reflecting material is wound around the outside, and a temperature sensor is provided inside the tube, so that the temperature in the tube is maintained at a preset temperature. In addition, the temperature distribution of the laid optical fiber is suppressed and the strain distribution of the ground / rock mass is measured accurately and in real time without being affected by the ambient temperature.
[0007]
The ground / rock rock strain distribution measuring method according to claim 2 of the present invention is the ground / rock rock strain distribution measuring method according to claim 1 , wherein one optical fiber is laid with an adhesive on the laying rod. At the time of caulking, it is laid by wire bonding and the upper surface of the wire bonding is protected by a cover.
[0008]
Therefore, one optical fiber is laid by wire bonding, and the upper surface of the wire bonding is protected by the cover, thereby further improving the laying.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0010]
Referring to FIG. 1, for example, in rock 1 more crack 3A, 3 B, 3C, 3D has occurred. A plurality of crack 3A that this occurs, 3 B, 3C, a portion of 3D, the measuring points of the optical fiber 5, which will be described in detail later, for example, (1), and (2), (3), (4), An optical fiber 5 is laid at this position, and one end of the optical fiber 5 is connected to an integrated strain / loss optical pulse tester 7. One end of a cord 9 is connected to the strain / loss integrated optical pulse tester 7 and the other end of the cord 9 is connected to a plug 11. One end of a cord 13 is connected to the plug 11 and the other end of the cord 13 is connected to a power source 15. As an example of the power supply 15, since the optical fiber 5 is not affected by electromagnetic induction or noise, a simple generator (with a gasoline engine) can be used. One end of a cord 17 is connected to the strain / loss integrated optical pulse tester 7 and the other end of the cord 17 is connected to a monitor 19 as an output means. Further, one end of a cord 21 is connected to the monitor 19 and the other end of the cord 21 is connected to the plug 11. The plug 11 is connected to the power source 15 through the cord 13.
[0011]
The laying state of the optical fiber 5 will be described in more detail. Referring to FIG. 2, the optical fiber 5 is inserted on the bedrock at the measurement target positions (1), (2), (3), and (4). For example, a PVC pipe 23 having good durability as a pipe is provided. Laying rods 25 are driven into the rock mass 1 on both sides of the PVC pipe 23. A plate 27 is provided above each laying rod 25. Then, the single optical fiber 5 inserted into the PVC pipe 23 having a predetermined length while applying a certain tension is laid on the plate 27 not by point bonding but by line bonding with the adhesive 29. As this adhesive 29, for example, it is preferable to use an instantaneous adhesive and a resin adhesive in combination. Then, the optical fiber 5 between the measurement objects, that is, between the position (1) and the position (2) , between the position (2) and the position (3) , and between the position (3) and the position (4) is slack without tension. To the state.
[0012]
Therefore, the optical fiber 5 can be laid more easily and easily and firmly with the adhesive 29. Moreover, since the optical fiber 5 is inserted into the polyvinyl chloride tube 23, the optical fiber 5 can be protected from being disconnected.
[0013]
In order to maintain the temperature in the PVC pipe 23 at a preset temperature, as shown in FIG. 3, a heating wire heater 31 is wound around the outside of the PVC pipe 23 in a spiral shape, for example. And the heat insulating material 33, such as a foaming polystyrene, is covered by the outer side of the heating wire heater 31, for example. Further, a reflective material 35 made of, for example, aluminum is wound around the heat insulating material 33. A temperature sensor 37 is provided in the left side of the PVC pipe 23 in FIG. 3, and this temperature sensor 37 is connected to a temperature regulator 39. The heating wire heater 31 is connected to the temperature regulator 39 and the voltage regulator 41, and the temperature regulator 39 and the voltage regulator 41 are connected to each other. Further, the PVC pipe 23 around which the reflecting material 35 is wound is fixed to the rock mass 1 by a PVC pipe fixing rod 25A as shown in FIG.
[0014]
Therefore, the temperature in the PVC pipe 23 is detected by the temperature sensor 37 and is ON / OFF controlled by the temperature regulator 39 and the voltage regulator 41 to control the temperature in the PVC pipe 23 to a predetermined constant temperature. Therefore, the temperature error can be corrected when measuring the strain.
[0015]
The distortion / loss integrated optical pulse tester 7 is also called OTDR (Brillouin Optical Time Domain Reflectometer), and its principle will be described. Both the distortion distribution and the optical loss distribution in the length direction of the optical fiber 5 are measured. However, in this embodiment, since the strain distribution in the length direction of the former optical fiber 5 is related, measurement of the strain distribution will be described.
[0016]
That is, since the Brillouin scattered light in the optical fiber 5 is very weak, in order to measure the strain distribution, coherent detection (which interferes with the signal light and the reference light) can be detected with high sensitivity. And a detection method for converting into an electrical signal in the intermediate frequency band). The Brillouin scattered light is scattered light caused by periodic fluctuations in the density of the optical fiber glass caused when light incident on the optical fiber 5 propagates through the optical fiber 5, and this fluctuation in density is also a light. In the optical fiber 5 used for optical communication to propagate through the fiber 5, the frequency of the Brillouin scattered light is shifted by about 10 GHz to the low frequency side when the wavelength of the light source is 1.55 μm due to the Doppler effect. is there.
[0017]
In FIG. 4, the detection unit 43 of the distortion / loss integrated optical pulse tester 7 includes a light source unit 45, an optical multiplexer / demultiplexer 47, and a coherent optical receiver 49, and outputs from the laser oscillator 51 in the light source unit 45. The light is demultiplexed into two by an optical multiplexer / demultiplexer 53, one of which is used as a light source for producing pulsed light through an optical frequency converter 55 and an optical pulse modulator 57, and the other is used for coherent detection. Let it be light.
[0018]
The pulsed light is incident on the optical fiber 5 via the optical multiplexer / demultiplexer 47, and the backward Brillouin scattered light generated in the optical fiber 5 is received by the coherent optical receiver 49 via the optical multiplexer / demultiplexer 47. Since the frequency of the Brillouin scattered light is approximately 10 GHz lower than the frequency of the incident pulsed light as described above, the optical frequency converter 55 makes the difference between the frequency of the Brillouin scattered light and the incident pulsed light substantially equal. Pulse light that has been shifted about 10 GHz in advance to the high frequency side is made incident on the optical fiber 5 . Thereby, the frequencies of the Brillouin scattered light and the reference light are substantially equal, and the Brillouin scattered light can be detected with high sensitivity by coherent detection. The Brillouin scattered light is measured every time the frequency of the incident pulse light is changed using the optical frequency converter 55, and the frequency at which the intensity of the Brillouin scattered light is maximized at each measurement position in the length direction of the optical fiber 5 is measured. The strain in the length direction of the optical fiber 5 can be measured.
[0019]
As shown in FIG. 5, the controller 59 of the distortion / loss integrated optical pulse tester 7 includes a CPU 61. The CPU 61 inputs various data such as a keyboard. The means 63 is connected and the monitor 19 such as a CRT for displaying various data and graphs is connected. The CPU 61 is connected to a coherent light receiver 49 of the detection unit 43.
[0020]
Further, as shown in FIG. 6, the CPU 61 is connected with a frequency / distortion relationship file 65 in which data having a proportional relationship between the frequency and distortion of the Brillouin scattered light is obtained in advance. Yes. The CPU 61 is connected to a strain data file 67 that is filed by obtaining the strain in the length direction of the optical fiber 5 and the initial strain data filed in the strain data file 67 and the strain data after a lapse of a predetermined time. The calculation means 69 for calculating the distortion difference based on the above is connected.
[0021]
With the above configuration, for example, as shown in FIGS. 7 (A) and 7 (B), the temperature change in time series was experimentally performed with Samples 1 and 2, and the result as shown in FIG. 8 was obtained. Got. As can be seen from the temperature change, sample 1 has no time-dependent temperature change, whereas sample 2 has a time-series temperature change. Therefore, it is understood that the structure as shown in FIG. 3 is not affected by the temperature change. In FIG. 8, the outside air temperature is shown for reference.
[0022]
Further, in the state shown in FIG. 1, the frequency of the Brillouin scattered light is measured by the coherent light receiver 49 through the detection unit 43 , and the measured frequency of the Brillouin scattered light is calculated with the frequency and distortion of the control unit 59. In this case, the distortion in the length direction of the optical fiber 5 is obtained by the proportional relationship between the frequency and the distortion of the Brillouin scattered light obtained in advance. When the obtained strain in the length direction of the optical fiber 5 is filed in the strain data file 67 and displayed on the monitor 19 , for example, the curve (A) (initial value) is obtained as shown in FIG. It is drawn.
[0023]
Similarly, when the distortion / loss integrated optical pulse tester 7 measures again at a later date, the frequency of the Brillouin scattered light is measured by the coherent light receiver 49 via the detection unit 43 , and the measured Brillouin scattered light is measured. By incorporating the frequency into the relationship file 65 between the frequency and distortion of the control unit 59, the distortion in the length direction of the optical fiber 5 is obtained in a proportional relationship between the frequency and distortion of the Brillouin scattered light obtained in advance. When the obtained strain in the length direction of the optical fiber 5 is filed in the strain data file 67 and displayed on the monitor 19 , for example, a curve (B) (measured value) is obtained as shown in FIG. It is drawn.
[0024]
By calculating the difference between the value of the drawn curve (B) and the value of the curve (A) by the calculation means 69, without being affected by the temperature change at the time of measurement, without correcting the temperature, The distortion difference at the measurement locations (1), (2), (3), and (4) can be measured continuously and accurately in real time.
[0025]
FIG. 10 shows an alternative embodiment to FIG. 10, parts that are the same as the parts in FIG. 3 are given the same reference numerals, and detailed descriptions thereof will be omitted. In FIG. 10, the laying rod 25 is driven into the rock mass 1 on both sides of the PVC pipe 23. A plate 27 is provided above each laying rod 25. Then, one optical fiber (measuring optical fiber) 5 inserted into the polyvinyl chloride tube 23 having a predetermined length while applying a certain tension, and another one inserted in a slack state without tension. The dummy optical fiber 71 is laid by the adhesive 29 not by point bonding but by line bonding. As this adhesive 29, for example, it is preferable to use an instantaneous adhesive and a resin adhesive in combination. The strain / loss integrated optical pulse tester 7 is connected to one end of the one optical fiber 5 and the other one dummy optical fiber 71, and this strain / loss integrated optical pulse tester 7 is connected. The monitor 19 and the power source 15 are connected to the device 7 as shown in FIG. Moreover, the configuration of the distortion / loss integrated optical pulse tester 7 is the same as that shown in FIGS.
[0026]
With the above configuration, measurement is performed as in the above embodiment. At that time, a single optical fiber 5 detects mixed data of actual strain and strain due to the effect of temperature, and the dummy optical fiber 71 detects only data of strain due to the effect of temperature. By calculating the difference, the actual strain that is not affected by temperature is measured. FIG. 11 shows an example of actual measurement. In FIG. 11, the curve (A) is the initial value, and the curve (B) is data with distortion and temperature change. Therefore, the actual distortion can be measured continuously and accurately in real time from the data in the measurement section.
[0027]
From the above, the object to be measured can be captured as a line, and measurement up to several tens of kilometers can be made possible, and the behavior of the ground and rock can be grasped. And it can be applied to measurement and monitoring of slope failure (such as crack displacement measurement) and measurement and monitoring for preventing secondary disasters (such as ensuring safety during slope construction).
[0028]
In addition, this invention is not limited to embodiment mentioned above, It can implement in another aspect by making an appropriate change.
[0029]
【The invention's effect】
As can be understood from the description of the embodiment of the invention as described above, according to the invention of claim 1, for laying on both sides of the ground / rock mass on both sides of the measurement object such as a plurality of cracks with appropriate intervals. The rod is driven. Then, an optical fiber that is inserted while applying a certain tension into a pipe having a predetermined length is laid with an adhesive on the upper part of each laying rod. Next, the temperature in the tube is maintained at a preset temperature. In addition, the optical fiber between each measurement object is in a state where it is sagless, and is a strain / loss integrated optical pulse tester, in the length direction generated in the optical fiber based on Brillouin scattered light in the optical fiber By measuring the strain , the temperature distribution of the installed optical fiber can be suppressed and the strain distribution of the ground and rock can be measured accurately and in real time. In addition, the measurement object can be captured as a line and measurement of several tens of kilometers can be made possible. Moreover, a heating wire heater is wound around the outside of the tube, covered with a heat insulating material, a reflecting material is wrapped around the outside, and a temperature sensor is provided inside the tube, so that the temperature inside the tube is maintained at a preset temperature. As a result, the temperature distribution of the installed optical fiber can be suppressed and the strain distribution of the ground and rock can be measured accurately and in real time without being affected by the ambient temperature.
[0030]
According to the invention of claim 2 , one optical fiber is laid by wire bonding, and the upper surface of the wire bonding is protected by the cover, so that the laying can be further improved.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram illustrating a method for distributing strain of a rock mass that measures the strain distribution of a rock mass, for example, according to the present invention.
FIG. 2 is a perspective view of an example showing a state in which an optical fiber is laid at each measurement location.
FIG. 3 is an explanatory diagram of an example of correcting the temperature of distortion at each measurement location.
FIG. 4 is a circuit explanatory diagram of a detection unit of a distortion / loss integrated optical pulse tester;
FIG. 5 is a configuration block diagram of a control unit of the distortion / loss integrated optical pulse tester.
FIG. 6 is a diagram showing the relationship between the frequency and distortion of Brillouin scattered light.
FIGS. 7A and 7B are cross-sectional views showing samples with and without a heater wound around a PVC pipe into which an optical fiber is inserted, respectively.
8 is a graph showing data obtained by measuring distortion using the samples of FIGS. 7A and 7B. FIG.
FIG. 9 is a graph showing data obtained by measuring strain with a plurality of optical fibers.
FIG. 10 is an explanatory diagram of an example of temperature correction of distortion at each measurement point according to another embodiment.
FIG. 11 is a graph showing data obtained by measuring strain with a plurality of optical fibers according to another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rock bed 3A-3D Crack 5 Optical fiber 7 Strain / loss integrated optical pulse tester 9 Code 19 Monitor (output means)
23 PVC pipe (pipe)
25 Laying Rod 27 Plate 29 Adhesive 31 Electric Heater 33 Heat Insulating Material 35 Reflective Material 37 Temperature Sensor 39 Temperature Controller 41 Voltage Regulator 43 Detection Unit 59 Control Unit

Claims (2)

Drive laying rods on both sides of the ground / rock mass on both sides of the object to be measured, such as multiple cracks with appropriate spacing, and apply a certain tension to the upper part of each laying rod in a pipe of a preset length. One optical fiber inserted while being laid was laid with an adhesive, and the temperature inside the tube was maintained at a preset temperature, and the optical fibers that were not measured were slacked without tension. In this state, a strain / loss integrated type optical pulse tester is connected to one end of the optical fiber, and the strain in the length direction generated in the optical fiber based on the Brillouin scattered light in the optical fiber is converted into the strain / loss integrated type optical pulse. By measuring the strain distribution of the ground and rock mass by measuring with a tester ,
In order to maintain the temperature in the tube at a preset temperature, a heating wire heater is wound around the outside of the tube, covered with a heat insulating material, a reflective material is wound around the outside, and a temperature sensor is further provided in the tube. To measure strain distribution of ground and rock. Wherein the top of each laying rod, when allowed to lay one optical fiber with an adhesive, with allowed to lay a line bonding, according to claim 1, characterized by being made to protect the cover a top of the line adhesive Strain distribution measurement method for ground and bedrock.

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