JPH07167685A - Ground deformation sensing apparatus - Google Patents

Abstract

PURPOSE:To estimate a ground deformation distribution due to a land subsidence, etc. CONSTITUTION:A sensor cable 2 has a flexible tube 21 and an optical fiber deformation sensor 1 for sensing a bent of the tube 21 assembled in an entire length in the tube 21. A sensor cable 2 embedded in the ground 3 is bent by following a movement of the ground 3, and deformed, when the ground 3 is deformed, by following the ground 3. Light quantity changes of the cable 2 reflected from positions in the sensor 1 are received, a curvature distribution is obtained along a longitudinal direction of the cable 2 by a ground deformation calculating processor 5, a liner shape of the cable 2 is estimated from the distribution, and the ground deformation is estimated from this value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground deformation sensing device using an optical fiber used for grasping a wide range of ground deformation such as earthquake, landslide, and ground subsidence.

[0002]

2. Description of the Related Art Conventionally, the following techniques are known as techniques for measuring ground deformation such as ground subsidence. That is, as shown in FIG. 6, subsidence bars 102 are attached to predetermined road surface measurement points 101a to 101c on the ground 3, respectively, and ground deformation is obtained by periodically measuring the subsidence amount of these subsidence bars 102. ing. FIG. 7 shows a subsidence amount measuring mechanism installed at road surface measurement points 101a to 101c, and the like.
Reference numeral 02 is a sinking rod, and 104 is a plate buried in the soil.

[0003]

However, the following problems have been pointed out in the above-mentioned means for measuring the ground deformation by using the settlement amount measuring mechanism or the like.

(1) In order to grasp the deformation state of the ground over a wide area, it is necessary to provide a considerably large number of subsidence amount measuring mechanisms, which causes a cost increase and the installation work becomes very complicated.

(2) Currently, with this means, the measurement is to be made once a year on a regular basis, but it is not possible to cope with sudden ground deformation.

(3) Further, since the subsidence measurement work is performed off-line, it takes a considerably long time to complete the work.

Therefore, an object of the present invention is to make it possible to measure the ground deformation distribution online by creating a large number of measurement points, and to install a large number of subsidence amount measuring mechanisms as in the prior art. It is to provide a ground deformation sensing device that does not require surveying.

[0008]

The ground deformation sensing device of the present invention is a flexible tube and an optical fiber deformation for sensing bending of the tube which is incorporated into the tube over its entire length. Consisting of sensors,
A sensor cable that is embedded in the ground and can be bent following the movement of the ground, and an optical signal is incident on the optical fiber deformation sensor and is reflected from each position in the optical fiber deformation sensor. An optical TDR device for receiving a light amount change due to the curvature of the sensor cable;
The curvature distribution along the longitudinal direction of the sensor cable is obtained from the output from the optical TDR device, the linearity of the sensor cable is estimated from the curvature distribution of the sensor cable, and the ground deformation is estimated from this value. It is characterized in that it comprises a state calculation processor.

[0009]

According to the ground deformation sensing device of the present invention,
When a sensor cable with an optical fiber deformation sensor is installed in the ground and an optical pulse is incident from the incident end of this optical fiber deformation sensor, the rear that changes depending on the curvature in the optical fiber deformation sensor due to ground deformation The intensity of scattered light can be detected, and the distribution of ground deformation can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described based on the embodiments shown in the drawings. FIG. 1 is a perspective view showing an embodiment of the present invention, showing a situation in which a sensor cable is installed in the ground. A sensor cable 2 with a diameter of 14 mm, which incorporates an optical fiber deformation sensor 1 with a diameter of 6 mm over the entire length, is embedded in the ground 3 at a depth of 1.5 m. When the ground 3 is deformed as shown in FIG. Deforms following the ground, and the optical fiber deformation sensor 1 uses optical TDR.
An optical signal is input from the device (optical pulse tester) 4, and a light amount change of the sensor cable 2 reflected from each position in the optical fiber deformation sensor 1 is received. The curvature distribution is obtained along the longitudinal direction of 2, and the linear shape of the sensor cable 2 is estimated from this curvature distribution, and the ground deformation is estimated from this value.

The sensor cable 2 includes a tube 21 made of flexible polyethylene, an optical fiber deformation sensor 1 installed inside the tube 21, and a space between the tube 21 and the optical fiber deformation sensor 1 (about 3 mm)
And a jelly (filler) 6 filled in.
The sensor cable 2 having such a structure does not transmit the expansion and contraction of the tube 21 to the optical fiber deformation sensor 1, but transmits only the bending, and protects the optical fiber deformation sensor 1 from earth pressure, groundwater, and the like.

FIG. 2 is a transverse sectional view showing the structure of the optical fiber deformation sensor, and FIG. 3 is a longitudinal sectional view. Cylindrical outer diameter 5 mm
Two optical fiber vinyl core wires 12 are installed along the longitudinal direction of the coil spring 11 at positions (upper and lower) shifted by 180 ° in the circumferential direction, and the optical fiber vinyl core wires 12 are attached by a heat-shrinkable coating tube 13. When fixed to the coil spring 11 and bent entirely in the direction 14 shown in FIG. 3, the pitch of the coil spring 11 becomes narrower. (Optical fiber) 15 is distorted
The local bending of the optical fiber 15 detects the change in the amount of light when the light incident from one end of the optical fiber 15 returns to the incident end, estimates the curvature from the change in the amount of light, and widens the pitch between the coil springs 11. Since the optical fiber 15 installed on the pulling side (upper side) has no change in the amount of light, by discriminating the optical fiber 15 on the compression side and the pulling side,
The direction of bending can also be estimated.

In this optical fiber deformation sensor 1, the optical fiber 15 covered by the optical fiber vinyl core wire 12 is displaced by "360 ° / the above-mentioned offset angle" at each position offset by an equal angle in the circumferential direction of the coil spring 11. "If you arrange this, for example, every 90 °, 4 (360 ° / 90 °)
If arranged, the bending direction can be estimated in the vertical and horizontal directions in FIG. Optical fiber 15
If the number of is increased, the direction in which the bending direction can be estimated increases.

FIG. 4 is a block diagram showing in detail the optical TDR device and the ground deformation calculation processor. In the optical TDR device 4, the pulse semiconductor laser 41, the optical directional coupler 42, the spectroscope 43, the photodetector 44, and the O / E converter 45.
And a waveform observing means 46 of an oscilloscope for observing the waveform of an electric phenomenon that changes rapidly, and an optical pulse is generated from the pulse semiconductor laser 41 and is incident on the optical fiber deformation sensor 1. By the incidence of this light pulse, the reflected light including the backscattered light that changes according to the amount of deformation in the optical fiber deformation sensor 1 is reflected by the optical directional coupler 4.
The light is guided to the spectroscope 43 via 2, where the backscattered light is separated from the reflected light, and the photodetector 44 detects the intensity of the backscattered light and supplies it to the waveform observing means 46. Therefore, the waveform observing means 46 can observe the light intensity having a function of time based on the output of the O / E converter 45. Thereafter, the observation output from the waveform observing means 46 is introduced into the ground deformation calculation processor 5, where the distribution of ground deformation is estimated.

FIG. 5 shows a landslide surface detection method. The multi-core optical fiber cable 200 is extended to the landslide area, the plurality of transmission optical fiber core wires 201 and the plurality of sensor cables 2 in the multi-core optical fiber cable 200 are connected, and the sensor cable 2 is inserted into the boring hole 203. The gap between the sensor cable 2 and the boring hole 203 is filled with grout material 204. On the other hand, at the end of the multi-core optical fiber cable 200, the optical channel selector 2
05, and the optical channel selector 205 and optical TD
The R device 4 and the ground deformation calculation processor (personal computer) 5 are connected. The personal computer 5 performs control and calculation such as channel switching of each sensor cable 2 and loss change measurement by the optical TDR device 4. Each sensor cable 2 can detect the distance from the ground surface to the slip surface due to occurrence of a landslide, and a large number of sensor cables 2 can estimate the slip surface. Also, the amount of landslide movement can be estimated from the change in loss of 2 for each sensor cable.

[0016]

As described above, according to the present invention, a sensor cable having an optical fiber deformation sensor can be embedded in the ground, and a wide range of ground deformation can be measured online. This brings about a useful effect.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the structure of an optical fiber deformation sensor for explaining one embodiment of the present invention.

FIG. 3 is a longitudinal sectional view showing the structure of an optical fiber deformation sensor for explaining one embodiment of the present invention.

FIG. 4 is a block diagram showing in detail an optical TDR device and a ground deformation calculation processor embodying a signal processing system for explaining an embodiment of the present invention.

FIG. 5 is a perspective view showing a ground deformation sensing situation for explaining an embodiment of the present invention.

FIG. 6 is a diagram illustrating a conventional ground deformation measuring method by surveying using a settlement measurement mechanism.

FIG. 7 is a cross-sectional view showing a subsidence amount measurement mechanism installed at a road surface measurement point used in a conventional method.

[Explanation of symbols]

 1 Optical Fiber Deformation Sensor 2 Sensor Cable 3 Ground 4 Optical TDR Device 5 Ground Deformation Calculation Processor (PC) 6 Jerry (Filling Material) 11 Coil Spring 12 Optical Fiber Vinyl Core 13 Coated Tube 14 Bending Direction 15 Optical Fiber Silicon Elementary wire (optical fiber) 21 Tube 41 Pulse semiconductor laser 42 Optical directional coupler 43 Spectrometer 44 Photodetector 45 O / E converter 46 Waveform observation means 101a, 101b, 101c Road surface measuring point 102 Sinking rod 103 Terminal box 104 Plate 200 Multi-core optical fiber cable 201 Optical fiber core wire for transmission 203 Boring hole 204 Grout material 205 Optical channel selector

Claims (4)

[Claims] 1. A flexible tube and an optical fiber deformation sensor for sensing bending of the tube, which is incorporated into the tube along its entire length.
A sensor cable that is embedded in the ground and can be bent according to the movement of the ground, and an optical signal is incident on the optical fiber deformation sensor and reflected from each position in the optical fiber deformation sensor. An optical TDR device that receives a change in the amount of light due to the curvature of the sensor cable, and a curvature distribution along the longitudinal direction of the sensor cable is obtained from the output from the optical TDR device, and the sensor cable is calculated from the curvature distribution of the sensor cable. A ground deformation sensing device, comprising: a ground deformation calculation processor that estimates the linearity of the ground deformation and estimates the ground deformation from this value. 2. The sensor cable comprises: the flexible tube; the optical fiber deformation sensor continuously arranged inside the tube; and a space between the tube and the optical fiber deformation sensor. And a jelly that protects the optical fiber deformation sensor from earth pressure, groundwater, etc., and transmits only bending of the tube without transmitting expansion and contraction of the tube to the optical fiber deformation sensor. The device of claim 1 having a cable structure that allows 3. The optical fiber deformation sensor comprises: a cylindrical coil spring arranged over the entire length of the sensor cable; and a longitudinal direction of the coil spring at a position shifted by 180 ° in the circumferential direction of the coil spring. Two optical fibers arranged along the optical fiber, coated with an optical fiber core wire, and for covering the outer peripheral surface of the coil spring and fixing the optical fiber core wire to the outer peripheral surface of the coil spring. 2. A device according to claim 1, characterized in that it comprises: 4. The optical fiber deformation sensor includes a cylindrical coil spring arranged over the entire length of the sensor cable, and a longitudinal direction of the coil spring for each position offset by an equal angle in the circumferential direction of the coil spring. An optical fiber covered with an optical fiber core wire, the number of which is 360 degrees divided by the offset angle, and the outer peripheral surface of the coil spring is covered, and the optical fiber core wire 2. A device according to claim 1, further comprising: a coating tube for fixing the outer peripheral surface of the coil spring.