Distributed optical fiber system for shallow-buried tunnel deformation monitoring

Abstract

The utility model relates to a distributed optical fiber system used for shallow-buried tunnel deformation monitoring. The distributed optical fiber system comprises an optical fiber demodulation host and an OTDR device which are respectively connected with an MEMS optical switch. A C port and a D port of the MEMS optical switch are used for being connected with the two ends of an optical fiber loop arranged along the tunnel. The MEMS optical switch is used for adjusting a port C and a port D of the MEMS optical switch to be respectively connected with a port A and a port B of the optical fiber demodulation host, or any port of the MEMS optical switch is connected with a port E of the OTDR equipment; when the optical fiber loop is an access, the optical fiber demodulation host works in a BOTDA mode; when the optical fiber loop is in an open circuit state, the optical fiber demodulation host works in a BOTDR mode; the OTDR equipment is used for accurately judging whether the pre-tensioned optical fiber is broken or not, and after the cable is broken, the monitoring mode is switched from the BOTDA mode to the BOTDR mode through the computer, so that the deformation monitoring of the tunnel can be always in a full-range monitoring state, and the method has very high practicability and wide applicability.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of distributed optical fiber systems, specifically related to a kind of distributed optical fiber system for shallow tunnel deformation monitoring belongs to structural health monitoring field. BACKGROUND

[0002] In the process of shallow tunnel excavation, due to stress release, vault convergence deformation in tunnel, groundwater and other reasons, collapse and other risks will occur, affecting construction safety and use safety after delivery, so safety monitoring is of great significance in tunnel construction and operation management.

[0003] Optical measurement technology represented by total station is widely used in tunnel deformation monitoring, but it has the disadvantages of being affected by line of sight obstruction, low measurement accuracy, limited coverage range and the like. The optical fiber monitoring module has a series of advantages such as distributed, high resolution and accuracy, real-time monitoring, strong anti-interference capability, long-distance monitoring and the like.

[0004] To ensure the safety of the tunnel during construction and operation, long-term and real-time monitoring of the deformation of the tunnel is needed to understand the deformation state of the tunnel under actual working conditions and provide basis and technical support for tunnel integrity evaluation and tunnel operation management.

[0005] Therefore, it is necessary to provide a distributed optical fiber monitoring module to obtain real-time tunnel deformation data and provide collapse early warning. One way is to bury the optical fiber in the concrete during tunnel construction, and the second way is to fix the optical fiber on the tunnel wall at intervals. When monitoring with the second way, pre-strain is needed because optical fiber without pre-strain cannot withstand compressive strain, so the convergence deformation of the tunnel cannot be monitored. The existing dual-mode optical fiber demodulation host integrated with BOTDA and BOTDR functions can use the BOTDA mode to measure the optical fiber from both ends, analyze the measured strain data with software, determine whether the cable is broken, and switch to the BOTDR mode for single-end measurement after the cable is broken. However, the convergence deformation monitoring of the tunnel requires pre-strain, making the strain data measured by the optical fiber demodulation host more complex, and it is difficult for the software to determine whether the optical fiber strain measured at a certain position is the real strain or the false strain caused by cable breakage, thereby affecting the switching of the optical fiber demodulation host from the BOTDA mode to the BOTDR mode. SUMMARY

[0006] To solve the problems of the prior art, the utility model aims to provide a distributed optical fiber system for shallow tunnel deformation monitoring.

[0007] To achieve the above-mentioned objectives, the utility model adopts the following technical solutions:

[0008] A distributed optical fiber system for shallow tunnel deformation monitoring, comprising an optical fiber demodulation host and an OTDR device connected with a MEMS optical switch respectively;

[0009] The C port and the D port of the MEMS optical switch are used for connecting two ends of an optical fiber loop arranged along a tunnel;

[0010] The MEMS optical switch is used for adjusting the C port and the D port to be connected with the A port and the B port of the optical fiber demodulation host respectively, or any port to be connected with the E port of the OTDR device;

[0011] When the optical fiber loop is in a pass-through state, the optical fiber demodulation host is used for emitting monitoring laser in a BOTDA mode;

[0012] When the optical fiber loop is in a broken state, the optical fiber demodulation host is used for emitting monitoring laser in a BOTDR mode;

[0013] The OTDR device is used for detecting whether the optical fiber loop is in a pass-through state.

[0014] The above-mentioned MEMS optical switch, optical fiber demodulation host and OTDR device are connected with a computer respectively,

[0015] The computer is used for switching and making the MEMS optical switch connect with the OTDR device according to a first monitoring result fed back by the optical fiber demodulation host in a BOTDA mode;

[0016] The computer is used for driving the OTDR device and switching and making the MEMS optical switch connect with the optical fiber demodulation host according to a second monitoring result fed back by the OTDR device.

[0017] Further, when the second monitoring result is in a pass-through state, the computer is used for switching the optical fiber demodulation host in a BOTDA mode;

[0018] When the second monitoring result is in a broken state, the computer is used for switching the optical fiber demodulation host in a BOTDR mode.

[0019] The above-mentioned optical fiber loop is laid along a length direction of a tunnel in a serpentine mode respectively.

[0020] The above-mentioned optical fiber loop is pre-strained.

[0021] Further, the above-mentioned pre-strain is interval strain.

[0022] Further, the interval distance of the above-mentioned interval strain is 1 m, and the interval strain is 4000 micro-strain and 6000 micro-strain alternately.

[0023] The utility model discloses the beneficial effect lies in:

[0024] The utility model discloses a kind of distributed optical fiber systems for shallow-buried tunnel deformation monitoring, accurate judgement whether the optical fiber of pre-tension strain appears cable break by using OTDR equipment, and after cable break appears, by computer, monitoring mode is switched from BOTDA mode to BOTDR mode, so that the deformation monitoring of tunnel can be always in full-range monitoring state;By setting optical fiber pre-tension strain, optical fiber can not only measure tension strain, but also can measure compression strain, with strong practicality and extensive applicability. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the structural diagram of monitoring module of distributed optical fiber system.

[0026] Figure 2 It is the schematic diagram of connection of monitoring module and optical fiber loop in tunnel.

[0027] Figure 3 It is Figure 2 top view.

[0028] Figure 4 It is the strain distribution diagram of optical fiber of pre-tension strain.

[0029] Meaning of mark in drawing is as follows: 1, monitoring module, 2, optical fiber demodulation host computer, 3, OTDR equipment, 4, MEMS optical switch, 5, computer, 6, A port, 7, connecting optical fiber, 8, C port, 9, D port, 10, B port, 11, network cable, 12, USB line, 13, RS232 line, 14, E port, 15, tunnel, 16, optical fiber of pre-tension strain, 17, fixed point. DETAILED DESCRIPTION

[0030] The utility model is specifically introduced in connection with drawing and specific embodiment.

[0031] A kind of distributed optical fiber system for shallow-buried tunnel deformation monitoring is composed of monitoring module 1 and optical fiber loop.

[0032] Figure 1 It is the monitoring module 1 composed of optical fiber demodulation host computer 2, OTDR equipment 3, (array) MEMS optical switch 4 and computer 5.

[0033] Optical fiber demodulation host computer 2 is connected with the two ends of optical fiber loop by C port 8 and D port 9.

[0034] Computer 5 is connected with optical fiber demodulation host computer 2 by network cable 11, is connected with OTDR equipment 3 by USB line, is connected with MEMS optical switch 4 by RS232 line.

[0035] MEMS optical switch 4 has the function of adjusting and switching channel:

[0036] Channel 1: A port 6 and B port 10 of the fiber demodulation host 2 are connected with C port 8 and D port 9 of the MEMS optical switch 4 respectively.

[0037] Channel 2: E port 14 of the OTDR device 3 is connected with C port 8 of the MEMS optical switch 4, and D port 9 is not used.

[0038] The working state of the fiber demodulation host 2 has a BOTDA mode and a BOTDR mode.

[0039] As shown in Figure 2 and Figure 3 , the pre-tensioned fiber 16 is laid in a serpentine manner in the tunnel arch part, compared with the longitudinal and transverse straight laying manner, the length of the fiber to be laid is greatly reduced and the construction is more convenient. Preferably, the angle between the direction of the serpentine fixed laying fiber and the length direction of the tunnel is between 30° and 60°.

[0040] In use,

[0041] Running state (S1):

[0042] In normal operation, the fiber demodulation host 2 works in the BOTDA mode, the laser is emitted from the A port 6 of the fiber demodulation host 2, passes through the connecting fiber 7, enters the fiber in the tunnel from the C port 8 of the MEMS optical switch 4, and the returned laser passes through the B port 10 of the fiber demodulation host 2 again through the connecting fiber 7, and returns to the fiber demodulation host 2, forming a loop.

[0043] The fiber demodulation host 2 is connected with the computer 5 through the network cable 11 to transmit data and control signals.

[0044] After the fiber demodulation host 2 completes a strain demodulation in the BOTDA mode, the first monitoring result is fed back to the computer 5, the computer 5 issues an instruction to suspend the operation of the fiber demodulation host 2, and starts the OTDR device 3 through the USB line 12, and controls the C port 8 of the array MEMS optical switch 4 and the E port 14 of the OTDR device 3 to be connected through the RS232 line 13, and the D port 9 is not used; that is, the instruction to start checking the optical cable breakage is issued.

[0045] When the OTDR device 3 works, the laser is emitted from the E port 14 of the OTDR device 3, passes through the connecting fiber 7, and enters the fiber in the tunnel from the C port 8 of the MEMS optical switch 4 to check whether the fiber in the tunnel has a cable breakage.

[0046] Running state (S2):

[0047] When the OTDR device 3 feeds back the second monitoring result to the computer, the computer judges whether the fiber in the tunnel has a cable breakage through the second monitoring result.

[0048] If the optical fiber in the tunnel is not broken, the computer 5 restores the optical fiber demodulation host 2 to operate in the BOTDA mode through the network cable 11, and controls the C port 8 and the D port 9 of the array MEMS optical switch 4 to be connected to the A port 6 and the B port 10 of the optical fiber demodulation host 2 respectively through the RS232 cable 13. Then, the system returns to the running state (S1).

[0049] Running state (S3):

[0050] If the optical fiber in the tunnel is broken, the computer 5 analyzes the broken position of the optical fiber in the tunnel according to the second monitoring result. At the same time, the computer 5 switches the optical fiber demodulation host 2 from the BOTDA mode to the BOTDR mode through the network cable 11, and sets the broken position; and controls the C port 8 and the D port 9 of the array MEMS optical switch 4 to be connected to the A port 6 and the B port 10 of the optical fiber demodulation host 2 respectively through the RS232 cable 13.

[0051] Then, the laser is emitted from the A port 6 and the B port 10 respectively, enters the optical fiber in the tunnel from two directions, and performs single-end measurement; that is, according to the set broken position, the strain data of the optical fiber in the tunnel until the broken position is obtained from two directions, and the deformation of the entire optical fiber in the tunnel can also be monitored.

[0052] Thereafter, the BOTDR mode is maintained, and the OTDR device 3 is no longer operated until the broken cable is repaired and the entire system is reset.

[0053] Figure 2 Fig. 1 is a schematic diagram of the connection between the monitoring module and the optical fiber in the tunnel, Figure 3 Fig. 2 is a schematic diagram of the connection between the monitoring module and the optical fiber in the tunnel, Figure 2 Fig. 3 is a top view of the monitoring module.

[0054] The monitoring module 1 is placed in or beside the tunnel 15.

[0055] In normal operation, the optical fiber demodulation host 2 in the monitoring module 1 operates in the BOTDA mode, the laser is emitted from the C port 8, returns to the D port 9 through the connecting optical fiber 7 and the pre-tensioned optical fiber 16, and the strain value in the pre-tensioned optical fiber 16 is measured.

[0056] When the optical fiber is broken at one position, the optical fiber demodulation host 2 in the monitoring module 1 is switched to the BOTDR mode, the laser is emitted from the C port 8 and the D port 9 respectively, and returns to the broken position through the connecting optical fiber 7 and the pre-tensioned optical fiber 16, and the strain of the optical fiber of all lengths can also be measured.

[0057] After the optical fiber is broken at one position, although the monitoring module is switched to the BOTDR mode and can still operate, in order to prevent more optical fiber breaks and to improve the measurement accuracy, the broken optical fiber should be repaired as soon as possible, and after the repair, the monitoring module is manually switched back to the BOTDA mode.

[0058] Figure 4 The pre-tensioned optical fiber is locally magnified. The pre-tensioned optical fiber 16 is fixed on the tunnel surface by fixing points 17, and is pre-tensioned by 4000 micro-strain or 6000 micro-strain per 1m interval. The pre-tensioned optical fiber 16 is alternately pre-tensioned by different strain values, and is fixed on the tunnel surface by fixing points 17. By the method of alternately pre-tensioning different strain values, the pre-tensioned optical fiber 16 can increase the measuring range of strain.

[0059] Supposing that the optical fiber can accurately measure 8000 micro-strain tension, the optical fiber pre-tensioned by 4000 micro-strain can measure strain from -4000 micro-strain to 4000 micro-strain, and the optical fiber pre-tensioned by 6000 micro-strain can measure strain from -6000 micro-strain to 2000 micro-strain.

[0060] Therefore, Figure 4 The method of alternately pre-tensioning can measure tunnel deformation from -6000 micro-strain to 4000 micro-strain, the method of uniformly pre-tensioning by 4000 micro-strain can measure tunnel deformation from -4000 to 4000 micro-strain, the method of uniformly pre-tensioning by 6000 micro-strain can measure tunnel deformation from -6000 to 2000 micro-strain, and the method of not pre-tensioning can only measure tension and cannot measure compression.

[0061] The basic principle, main features and advantages of the present application are shown and described above. The skilled in the art should understand that the above examples do not limit the present application in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present application.

Claims

1. A distributed optical fiber system for deformation monitoring of shallow tunnels, characterized by, The fiber demodulation host and the OTDR device are connected with the MEMS optical switch respectively; The C port and the D port of the MEMS optical switch are used to connect two ends of the fiber loop arranged along the tunnel; The MEMS optical switch is used to adjust the C port and the D port to be connected with the A port and the B port of the fiber demodulation host respectively, or any port to be connected with the E port of the OTDR device; When the fiber loop is in circuit, the fiber demodulation host is used to emit monitoring laser in the BOTDA mode; When the fiber loop is in disconnection, the fiber demodulation host is used to emit monitoring laser in the BOTDR mode; The OTDR device is used to detect whether the fiber loop is in circuit.

2. The distributed fiber optic system of claim 1, wherein, The MEMS optical switch, the fiber demodulation host and the OTDR device are connected with a computer respectively, The computer is used to switch and make the MEMS optical switch connect with the OTDR device according to the first monitoring result fed back by the fiber demodulation host in the BOTDA mode; The computer is used to drive the OTDR device and switch and make the MEMS optical switch connect with the fiber demodulation host according to the second monitoring result fed back by the OTDR device.

3. The distributed fiber optic system of claim 2, wherein, When the second monitoring result is in circuit, the computer is used to switch the fiber demodulation host in the BOTDA mode; When the second monitoring result is in disconnection, the computer is used to switch the fiber demodulation host in the BOTDR mode.

4. The distributed fiber optic system of claim 1, wherein, The fiber loop is laid in a serpentine way along the length direction of the tunnel.

5. The distributed fiber optic system of claim 1, wherein, The fiber loop is pre-strained.

6. The distributed fiber optic system of claim 5, wherein, The pre-strain is interval strain.

7. The distributed fiber optic system of claim 6, wherein, The interval distance of the interval strain is 1m, and the interval strain is 4000 micro-strain and 6000 micro-strain alternately.

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