JPH11351983A - Landslide detecting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect landslide without being affected by installation condition of an optical fiber or temperature change by calculation for correcting the distortion value of a temperature change component for the distortion value of a distortion-detecting optical fiber, thus calculating a true distortion value. SOLUTION: A distortion-detecting optical fiber 10 and a temperature-detecting optical fiber 11 are installed on a slope 1 and a slope upper part 2 where the landslide may occur. An optical switch 3 switches between the distortion-detecting optical fiber 10 and the temperature-detecting optical fiber 11, alternately, according to the control signal outputted from a signal processor 5. A distortion distribution measuring device 4 measures distortion-distribution of the corresponding optical fiber 10 or 11, and transmits a measuring result to the signal processor 5. At a correcting/calculating part 52, the distortion value indicated by a distortion-distribution measuring result 50 is offset by the distortion value which changes under the effect of the temperature indicated by a distortion-distribution measuring result 51 to calculate a direct distortion value at the distortion-detecting optical fiber 10, which is outputted to a comparison circuit 53 and a data recording part 57. The comparison circuit 53 ignores presence of distortion, and when a distortion which exceeds a specified value is detected, an alert 56 is outputted from an alarm 55.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a landslide detection system for detecting landslides on slopes such as mountains and cliffs.

[0002]

2. Description of the Related Art In steep hills and cliffs, landslides (hereinafter referred to as landslides) occur frequently due to heavy rain, earthquakes, and the like. In order to minimize the damage caused by these landslides, it is necessary to establish a forecasting method that accurately monitors the signs of landslides.

Conventional methods of this kind include a method of monitoring changes in pore pressure inside the ground and an AE (Acoustic) that detects ultrasonic waves generated inside the ground at the time of landslide collapse.
Although the Emission method is known, the effects of topography and trees are not quantified, and the reliability and durability of the measuring instrument are also regarded as problems.

As a method of directly monitoring the ground deformation, a distance measuring device or a displacement meter is used, or the ground deformation is converted into an optical fiber bend, and the amount of transmitted light is reduced by bending the optical fiber. There is a method that utilizes attenuation (microbending method).

FIGS. 9A to 9E are diagrams showing a ground collapse detection system by the micro-bending method. 9A and 9B are diagrams illustrating an example of laying an optical fiber, where FIG. 9A is a perspective view and FIG. 9B is a side view. Conventionally, as shown in FIGS. 9A and 9B, a plurality of troughs 22 are arranged on a ground surface 21 or in a groove (not shown) provided on the ground surface 21. At this time, a gap 23 is provided for each of one or a plurality of troughs 22 (every two in FIG. 9) and arranged in the longitudinal direction, and a bar 24 is erected on the ground of each gap 23.

After one optical fiber 25 is routed along the groove of each trough 22 so as to form a loop 27 intersecting with the rod 24 at each gap 23, each of the troughs 2 is formed.
2 is covered with a lid 26. In addition, it is desirable to pack a filler (pebble or the like) so that small animals do not enter each trough 22.

FIGS. 9C to 9E are views showing a case where the ground 21 has collapsed. When a part of the ground 21 collapses, the trough installed on the ground collapses as shown in FIG. 9C. Then, the optical fiber crossing the adjacent rod-like body 24 is pulled by the trough, so that the loop 27 changes from the state before collapse shown in FIG. 9D to the diameter shown in FIG. Deform to be smaller.

In this method, since the sensing light is incident from one end of the optical fiber 25 and the received light intensity is detected at the other end, when the diameter of the loop 27 is reduced, the attenuation of the transmitted light of the optical fiber 25 is increased, and the received light intensity is reduced. It is possible to detect that the trough has collapsed because the value has fallen below the prescribed value.

On the other hand, recently, the following method for measuring the amount of strain applied to an optical fiber by analyzing the scattered light of the optical fiber has been developed. In this method, the frequency shift of the backward Brillouin scattered light, that is, the value obtained by subtracting the center frequency of the Brillouin scattered light spectrum from the optical frequency of the incident light is the tensile stress applied to the optical fiber, that is, the relative elongation due to the equivalent tensile stress. Focusing on the fact that it increases with the elongation strain of the optical fiber, the abnormal point of the optical fiber (or optical cable) is searched for from the increase of the Brillouin frequency shift.

In this method, pulse light is incident from one end of an optical fiber, and backscattered light of Brillouin scattered light generated in the optical fiber is detected with high sensitivity by a coherent detection method. At this time, the strain distribution of the optical fiber is measured from the frequency shift distribution of the Brillouin scattered light by utilizing the fact that the Brillouin scattered light is induced by the interaction between the light wave and the sound wave in the optical fiber to shift the optical frequency.

The relationship between the frequency shift of Brillouin scattered light and the amount of distortion is given by the following equation (1).

Fb (ε) = fb (0) (1 + Cε) (1) Here, fb (0) is a Brillouin frequency shift when the strain amount ε (%) is zero (the Brillouin scattering (The value obtained by subtracting the center frequency of the spectrum), and the value when the wavelength of the incident light is 1500 nm is 11 GHz. C is a proportional coefficient, which is about 4.5. When the above equation (1) is solved for ε, ε = {fb (ε) −fb (0)} / {Cfb (0)} (2) Therefore, by measuring the Brillouin frequency shift, the distortion of the optical fiber can be obtained.

In order to measure the Brillouin frequency shift, it is necessary to efficiently receive weak Brillouin scattered light. As this method, BOTDA (Brillouin Op
tical Fiber Domain Analysis) and BOTDR (Brillo)
uin Optical Time Domain Reflectometry).

BOTDA is an application of Brillouin gain spectroscopy, and the optical power of backward Brillouin scattered light generated by pump pulse light can be increased by probe light. On the other hand, BOTDR receives weak Brillouin scattered light by high-sensitivity reception using means such as coherent reception. Thus, BO
TDA and BOTDR can measure with high sensitivity,
Since the relative optical frequency can be measured with high accuracy, the distribution of the Brillouin frequency shift of the optical fiber can be measured by either method. These methods are described in the literature (IEEJ, BI Vol. J73-BI, No. 2, pp. 144-152, 1990; Technical
Digest of International Quantum Electronics Confe
rence (IQEC '92), paper no. MoL. 4, pp. 42-43, 1992).

In these methods, the peak frequency of Brillouin scattered light is obtained by scanning the input light or the frequency of the light receiving unit in order to obtain the Brillouin frequency shift. Also, by measuring the time required for the scattered light to return to the incident end by making the incident light into a pulse shape, the distribution of strain in each part of the optical fiber can be obtained. , Measurement of one frequency depends on the condition
¹² to 220 The average calculation is performed about ²⁰ times.

The BOTDR (hereinafter, referred to as a strain distribution measuring device) has an optical fiber length of 2 m and is about 0.2 mm (0.01%).
Although it has the ability to detect the above amount of elongation, since the Brillouin frequency shifts depending on the temperature of the optical fiber, the strain amount changes by about 10% at about 10 ° C. Requires a temperature correction operation.

[0017]

The above-mentioned micro-bending method is mainly for detecting the disintegration of the soil surface.
If this method is used for detecting the deformation of the soil surface before the soil surface collapses, the following sensitivity is obtained.

FIG. 10 is a graph showing the relationship between the optical fiber loop diameter and the amount of transmitted light attenuation, with the horizontal axis representing the loop diameter of the optical fiber and the vertical axis representing the transmitted light attenuation. As can be seen from FIG. 10, the optical fiber does not show attenuation of transmitted light when the loop diameter is 20 mmφ or more, but the loop diameter is 10 mmφ.
Below this, the attenuation increases, which in our test is 5 mm
When it was less than φ, disconnection occurred.

From the above, it can be seen that the smaller the loop diameter intersecting with the rod-shaped body 24, the better the sensitivity to the minute deformation. However, it is desirable to set the loop diameter to about 20 mmφ so that light attenuation does not normally occur. Also, in order to detect disintegration over a long distance, it is necessary to make a large number of loops. Considering the effects of loop diameter variation and temperature change when laying an optical fiber, the loop diameter for disintegration detection is considered. The detection limit is about 10 mmφ or less.

The circumference with a loop diameter of 20 mmφ is 20π, approximately 62.8 mm, and the circumference with a loop diameter of 10 mmφ is 1π.
0π, which is approximately 31.4 mm, and becomes detectable when the length between the rods 24 shown in FIG. 9D extends about 31.4 mm or more. If the length between the rods 24 is 2 m, 31.4 / 2000 = 0.016,
In the case of 20 m, 31.4 / 20000 = 0.016, and the sensitivity to change in shape is poor. Moreover, the length between the rods 24, 24 is set to an optical fiber loop diameter of 20 mm.
It is also difficult to lay as long as 20 m without sagging.

An object of the present invention is to provide a sediment collapse detection system that can easily lay an optical fiber and detect a landslide without being affected by the laid state of the optical fiber or a change in temperature.

[0022]

Means for Solving the Problems In order to solve the above problems and achieve the object, the earth and sand collapse detection system of the present invention is configured as follows.

(1) The earth and sand collapse detection system of the present invention comprises:
An optical fiber for strain detection laid on the target soil,
A temperature detection optical fiber laid so as to have slack at predetermined intervals on the earth and sand, and a strain distribution measuring means for measuring each strain distribution by switching the strain detection optical fiber and the temperature detection optical fiber, An arithmetic unit that performs an operation of correcting a distortion value of a temperature change in the temperature detection optical fiber with respect to a distortion value of the distortion detection optical fiber, and calculates a true distortion value of the distortion detection optical fiber, Detecting means for detecting the collapse of the earth and sand when the strain value calculated by the calculating means is equal to or more than a specified value.

(2) The earth and sand collapse detection system of the present invention is the system described in the above (1), and the optical fiber for strain detection is wound at least once every predetermined length and laid on the earth and sand.

(3) The earth and sand collapse detection system of the present invention is the system as described in (2) above, and the strain detecting optical fiber is laid on the earth and sand so as to have slack at predetermined intervals.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a diagram showing a configuration of a landslide detection system according to a first embodiment of the present invention. In FIG. 1, a slope (slope) 1 and a slope upper (slope upper) 2 at which there is a risk of earth and sand collapse occurring.
The optical fiber 10 for detecting strain and the optical fiber 1 for detecting temperature
1 is laid.

The optical switch 3 alternately switches between the strain detecting optical fiber 10 and the temperature detecting optical fiber 11 in accordance with a control signal output from the signal processor 5, and connects to the strain distribution measuring device 4. The strain distribution measuring device 4 measures the strain distribution of the corresponding optical fiber 10 or 11, and transmits the measurement result to the signal processor 5 via the communication line 6.

The signal processor 5 performs a correction operation based on the strain distribution measurement result 50 of the strain detecting optical fiber 10 and the strain distribution measurement result 51 of the temperature detecting optical fiber 11 transmitted via the communication line 6. The unit 52 cancels the strain value that changes due to the influence of the temperature indicated by the strain distribution measurement result 51 from the strain value indicated by the strain distribution measurement result 50 to calculate the true strain value in the optical fiber 10 for strain detection. The data is output to the comparison circuit 53 and the data recording unit 57.

The comparison circuit 53 monitors the presence or absence of a distortion exceeding a prescribed value, and when a distortion exceeding the prescribed value is detected, the alarm 5
5 outputs an alarm 56 and an abnormal position (not shown). The data recording unit 57 sequentially records the data 571 to 57n of the strain distribution measurement result. When a change in the distortion that is equal to or greater than a specified value occurs during a predetermined period from the data recording unit 57, the temporal change monitoring unit 54 outputs an alarm 56 and an abnormal position (not shown) from the alarm 55.

FIG. 2 is a view showing the laid state of the strain detecting optical fiber 10 and the temperature detecting optical fiber 11 shown in FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals.

The optical fibers 10 and 11 are fixed to the slope 1 or the like at predetermined intervals by a mounting jig 20. Mounting jig 20
When the slope 1 is made of concrete, the optical fibers 10 and 11 are fixed by using an adhesive when the slope 1 is ground, or by driving a pile when the slope 1 is ground. The configuration of the mounting jig 20 is not particularly limited as long as it has a function of expanding and contracting the optical fiber according to the deformation of the slope 1. The optical fibers 10 and 11 are fixed near the end of the slope 1 by a connecting portion 31 in the same manner as the mounting jig 20, and further connected to the optical switch 3 via a multi-optical cable 32.

In FIG. 2, when the slope 1 is stretched and deformed in the t direction, the strain detecting optical fiber 10 between the mounting jigs 20 and 20 is similarly stretched, so that the strain value increases. However,
The temperature detecting optical fiber 11 is provided with a slack 111 between the mounting jigs 20, 20, and the optical fiber 11 does not expand and the strain value does not increase. Appear as change.

It is desirable that these optical fibers 10 and 11 are used by inserting them into an extensible steel pipe or the like (not shown) for protection. In addition, portions of the optical fibers 10 and 11 that are not related to the strain detection can be used by being welded to a general optical transmission cable or connected by an optical connector.

FIGS. 3A to 3C are diagrams showing characteristics of the optical fibers 10 and 11 according to the first embodiment of the present invention. FIG. 3A shows the strain distribution measuring device 4 using the amount of elongation of the slope 1 in the t direction when the length between the two optical fiber fixing jigs 20 shown in FIG. Strain measurements are shown on the y-axis in percentages.

The strain detecting optical fiber 10 extends in the same manner as the slope 1 extends in the t direction. Therefore, when the slope 1 extends in the t direction by 0.2 mm or more (measurement less than 0.2 mm is impossible), strain can be measured.
When elongated by mm, the measured strain value is 0.03%, which means that the strain amount can be measured correctly. On the other hand, since the temperature detecting optical fiber 11 has slack as described above, the slope 1
Has no relation to the elongation in the t direction.

FIG. 3B shows the strain distribution measured by the strain distribution measuring device 4 with the temperature of the slope 1 when the length between the two optical fiber fixing jigs 20 shown in FIG. The measured values are shown on the y-axis in percentages. As can be seen from FIG. 3 (b), when the temperature of the slope 1 increases from 10 ° C. to 20 ° C., the measured strain values of both the strain detecting optical fiber 10 and the temperature detecting optical fiber 11 increase by 0.05%. I do. As described above, since the measured strain value changes depending on the temperature, it is necessary to correct the strain amount due to the temperature. In particular, when an optical fiber is laid in a wide area, a temperature variation locally occurs in a sunshine, a shade, or the like. Therefore, it is necessary to measure the temperature of each part.

FIG. 3C shows an optical fiber 10 for strain detection.
5 shows an example of strain distribution measurement over the entire length of the optical fiber 11 for temperature detection, where the x-axis shows the position of the optical fiber and the y-axis shows the measured strain value. In the figure, since the strain measurement values of the strain detecting optical fiber 10 and the temperature detecting optical fiber 11 coincide in the Q1 section (shown slightly shifted for explanation), the strain due to the temperature change is measured in this section. You can see that it is done.

In the figure, only the strain measurement value of the strain detecting optical fiber 10 changes in the section Q2, and there is no change in the strain measurement value of the temperature detecting optical fiber 11, so that the actual strain is measured in this section. You can see that it is. In the section Q3 in the figure, since both the strain measurement values of the strain detecting optical fiber 10 and the temperature detecting optical fiber 11 change, it can be seen that both the actual strain and the temperature change. Therefore, from the strain measurement value of the strain detecting optical fiber 10, the temperature detecting optical fiber 1
By subtracting the distortion measurement value of 1, the true distortion value can be obtained.

In the present method, the elongation amount of the optical fiber is 2 m long and 0.2 mm (0.2 / 2000 = 10 ^-4 or more).
Can be detected, the conventional method (31.4 / 20000 =
(More than 0.0016) can be detected. Then, when a distortion equal to or more than the specified value occurs, an alarm 56 is generated.

FIGS. 4A to 4C are side views of the slope shown in FIG. As a precursor to the debris collapse, cracks appear at the upper part of the slope as shown in FIGS. FIG. 4A shows a state in which a crack 8 has been generated in the upper slope 2 by a tensile force 7 from below, FIG. 4B shows a state in which the crack 8 has progressed, and FIG. Shows a state in which accumulates at an accelerating rate, and in the case of FIG. 4C, the collapse is imminent. Also, on the slope 1, "Harami"
Although a convex shape change called 9 appears, the upper slope 2
The occurrence of cracks 8 and “scissors” 9 indicates a sign of collapse.

At this time, the temporal change monitoring unit 5 in FIG.
4 monitors the strain displacement state based on the data of the data recording unit 57, and issues an alarm 56 from the alarm 55 when the strain state which is a precursor of the collapse is indicated. Therefore, collapse is detected early.

(Second Embodiment) FIG. 5 is a diagram showing a configuration of a landslide detection system according to a second embodiment of the present invention. 5, the same parts as those in FIG. 2 are denoted by the same reference numerals. As shown in FIGS. 4 (a) to 4 (c), landslides occur after a relatively long-term change in the shape of the slope, and in a short time due to heavy rain. It has been reported in a watering test simulating that the shape change before landslide collapse was small. In the second embodiment, a local minute change is detected with high sensitivity.

In FIG. 5, the strain detecting optical fiber 13 is composed of one optical fiber and is wound a plurality of times in order to increase the strain detecting sensitivity. Assuming that the length of l in FIG.
Assuming that the optical fiber 13 is wound 2.5 times in the meantime, the length of the strain detecting optical fiber 13 in this section 1 is 40 cm.
It is about 2m which is 5 times cm.

Therefore, as described with reference to FIG. 3A, while the elongation detection performance of the optical fiber 2m was 0.2 mm or more, the elongation of this section 1 was 0.02 mm / 5. It can be seen that can be detected. This indicates that if the entire length of the strain detecting optical fiber 13 is similarly wound by 2.5 turns, the strain detection sensitivity can detect a change in ground shape of 0.02 mm / 5 at 40 cm over the entire length.

FIG. 6 shows the strain detecting optical fiber 10 and a 40 cm unit length on the slope of the strain detecting optical fiber 13 wound 2.5 times about every 40 cm in order to detect local minute changes with high sensitivity. It is a figure which showed the amount of elongation and the strain detection characteristic, and it turns out that the optical fiber 13 has 5 times the detection sensitivity. The unit length l and the number of windings for detecting a local minute change with high sensitivity are not limited. For example, if the unit length l is 20 cm and the number of windings is 4.5, 2
It is assumed that a local strain change of 0 cm is detected at 0.02 m / 9, and can be changed in accordance with the ground deformation detection sensitivity requirement.

(Third Embodiment) FIG. 7 is a diagram showing a configuration of a landslide detection system according to a third embodiment of the present invention. 7, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals.

As described above, landslides may be caused by accumulation of ground deformation, or may be caused suddenly by heavy rain. In the former case, the change in the strain shape of the optical fiber is relatively large, and it is necessary to detect the strain over a wide range by improving the strain detection sensitivity. Effective for detection. The third embodiment is designed to meet these requirements.

In FIG. 7, the optical fiber 13 for strain detection is provided with slacks 15 at predetermined intervals. The signal processor 5 includes the temperature detecting optical fiber 1 as in the first embodiment.
Based on 0 and the distortion measurement value of the optical fiber 13 for distortion detection, the correction operation unit 52 performs temperature correction. Optical fiber disconnection detector 5
8 detects a disconnection prevention alarm 59 when detecting that the strain detecting optical fiber 13 has been pulled to the disconnection limit.

When an alarm is generated, the optical fiber fixing jig 20 at the corresponding location of the optical fiber 13 for strain detection is released, and the slack 15 of the optical fiber 13 is extended by a predetermined length.
After returning the strain amount of the strain detecting optical fiber 13 to the initial value,
The fixing jig 20 is set again. Thereafter, the data recorded in the data recording unit 57 by the control line (not shown) is set so as to add the distortion of the disconnection limit value.

FIG. 8 (a) is a diagram showing a distortion change situation when a ground change at a certain monitoring point progresses for a long period of time in the month, and at each point of 1n, 2n,..., 9n, 10n. This indicates that the strain detecting optical fiber 13 has reached the disconnection limit (0.1% in the figure) and the optical fiber has been reset. Therefore, in this example, the ground deformation at time 10n from time 0 is 0.1 × 10 = 1%, and if the distortion value of the comparison circuit 53 shown in FIG. Generate 56.

FIG. 8 (b) is a diagram showing a state of strain change when sudden ground deformation occurs due to heavy rain, and point P indicates that 0.05% ground deformation occurred per unit time Δt. If a unit time Δt and a strain increment of 0.05% are set in the temporal change monitoring unit 54 shown in FIG. 7, an alarm 56 is generated at this time.

It should be noted that the present invention is not limited to only the above embodiments, and can be carried out with appropriate modifications without departing from the scope of the invention.

(Summary of Embodiment) The configuration, operation and effect shown in the embodiment are summarized as follows.

[1] The earth and sand collapse detection system described in the embodiment includes a strain detection optical fiber 10 laid on the target earth and sand (1, 2) and a slack at predetermined intervals on the earth and sand. An optical fiber for temperature detection 11 laid so as to have the optical fiber 111; a strain distribution measuring means (4) for switching between the optical fiber for strain detection 10 and the optical fiber for temperature detection 11 to measure each strain distribution; An operation unit for performing an operation for correcting the distortion value of the temperature change in the temperature detection optical fiber 11 with respect to the distortion value of the detection optical fiber 10 to calculate a true distortion value of the distortion detection optical fiber 10 ( 52),
If the strain value calculated by the calculating means (52) is equal to or more than a specified value, the detecting means (5
4).

As described above, according to the above-described sediment collapse detection system, the strain detecting optical fiber 10 and the temperature detecting optical fiber 11 are laid on slopes or the like for early detection of sediment collapse, and are switched by the optical switch 3. The strain distribution of each of the optical fibers 10 and 11 is measured using a strain distribution measuring device (strain distribution measuring means) 4.

The strain detecting optical fiber 10 expands and contracts with the change in the shape of the slope. However, the temperature detecting optical fiber 11 is laid with a slack 111 on the slope, so that the temperature detecting optical fiber 11 has Regardless of the shape change, only the strain value due to the temperature change of the slope ground is measured.

Accordingly, the signal processor (arithmetic means) 5 corrects the distortion distribution of the optical fiber 10 for distortion detection to the distortion value corresponding to the temperature change in the optical fiber 11 for temperature detection, thereby obtaining the true distortion value. Calculate, and if a strain value equal to or greater than the specified value is detected, an alarm for ground collapse is output. In addition, the state of the strain change is constantly monitored, and when a strain change exceeding a specified value is detected within a predetermined time, an alarm signal for ground collapse is output. Therefore, the optical fibers 10 and 11 are easily laid and the
It is possible to detect the collapse of earth and sand without being affected by the laying state of 0, 11 or a change in temperature.

[2] The earth and sand collapse detection system described in the embodiment is the system according to the above [1], and the distortion detecting optical fiber 13 is wound at least once for every predetermined length and the above soil and sand is detected. Laying in (1, 2).

Therefore, according to the above-described sediment collapse detection system, since the distortion detection optical fiber 13 is wound at least once every predetermined length to detect the sediment collapse, the local shape change of the sloped land can be detected with high sensitivity. And early detection of earth and sand collapse.

[3] The earth and sand collapse detection system described in the embodiment is the system according to the above [2], and the earth and sand collapse optical fiber 13 has a slack 15 at predetermined intervals. It was laid on (1, 2) above.

Therefore, according to the above-mentioned sediment collapse detection system, the strain detection optical fiber 13 is wound at least once at a predetermined length and slacked at predetermined intervals to detect the sediment collapse. Ground deformation can be detected early with high sensitivity. That is, the change in the shape of the sloped land is monitored based on the strain measurement result of the optical fiber 13, and when the strain change value within a predetermined time exceeds a specified value, a warning of earth and sand collapse is output. Also, when the distortion change within a predetermined time is small, the amount of the change is monitored, and when the distortion at the cutting limit in the optical fiber 13 is detected, a disconnection prevention alarm is output. At this time, the slack 15 of the optical fiber 13 is extended by a predetermined length, and the distortion amount of the optical fiber is returned to the initial value. Then, these distortion changes are integrated,
If the distortion exceeds the specified value, a warning of earth and sand collapse is output.

[0062]

According to the landslide detection system of the present invention, it is possible to lay the optical fiber easily and detect the landslide without being affected by the laid state of the optical fibers or the temperature change.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a sediment collapse detection system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a laid state of a strain detecting optical fiber and a temperature detecting optical fiber according to the first embodiment of the present invention.

FIG. 3 is a diagram showing characteristics of the optical fiber according to the first embodiment of the present invention.

FIG. 4 is a side view of a slope according to the first embodiment of the present invention, showing an example of a change in slope shape of a precursor of earth and sand collapse.

FIG. 5 is a diagram illustrating a configuration of a landslide detection system according to a second embodiment of the present invention.

FIG. 6 is a diagram showing characteristics of an optical fiber according to a second embodiment of the present invention.

FIG. 7 is a view showing a configuration of a landslide detection system according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a distortion change state according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a ground collapse detection system using a micro-bending method according to a conventional example.

FIG. 10 is a diagram showing a relationship between an optical fiber loop diameter and a transmitted light attenuation amount according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Slope (slope) 2 ... Slope upper part (slope upper part) 3 ... Optical switch 4 ... Strain distribution measuring instrument 5 ... Signal processor 6 ... Communication line 7 ... Tensile force 8 ... Crack 9 ... Flame 10 ... Strain detection Optical fiber 11 ... Optical fiber for temperature detection 13 ... Optical fiber for strain detection 15 ... Looseness 20 ... Mounting jig 31 ... Connecting part 32 ... Multi optical cable 50 ... Strain distribution measurement result 51 ... Strain distribution measurement result 52 ... Correction calculation part 53 ... Comparison circuit 54 ... Aging monitoring unit 55 ... Alarm 56 ... Alarm 57 ... Data recording unit 58 ... Optical fiber disconnection detection unit 59 ... Disconnection prevention alarm

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masashi Miyasaka 12 Nishikicho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Inside Mitsubishi Heavy Industries, Ltd.

Claims (3)

[Claims] An optical fiber for strain detection laid on a target earth and sand, an optical fiber for temperature detection laid on the earth and sand so as to have slack at predetermined intervals, and an optical fiber for strain detection A strain distribution measuring unit that measures each strain distribution by switching the optical fiber for temperature detection, and an operation for correcting a distortion value of a temperature change in the optical fiber for temperature detection with respect to a distortion value of the optical fiber for distortion detection. Calculating means for calculating a true strain value of the optical fiber for strain detection, when the strain value calculated by the calculating means is a specified value or more, detection means for detecting collapse of the earth and sand, A landslide detection system characterized by comprising: 2. The earth and sand collapse detection system according to claim 1, wherein said strain detecting optical fiber is wrapped at least once every predetermined length and laid on said earth and sand. 3. The earth and sand collapse detection system according to claim 2, wherein the strain detecting optical fiber is laid on the earth and sand so as to have slack at predetermined intervals.