Intelligent roof strata monitoring system and method based on CCFPI cable strain sensor

Abstract

The application provides a roof stratum intelligent monitoring system and method based on a CCFPI cable strain sensor, and relates to the technical field of mine safety monitoring. The system comprises a strain sensor, a temperature sensor, a water pressure sensor, a fixing sleeve, a terminal load, a vector network analyzer, a server and a remote monitoring device. The strain sensor uses a coaxial cable strain sensor. The end of the strain sensor is connected with the terminal load and the vector network analyzer. The server receives the characteristic frequency monitoring displacement data of the strain sensor, and analyzes and determines the strain condition of the stratum and the change condition of the aquifer. Arranging the monitoring system can realize large-range surrounding rock displacement monitoring. The boreholes are arranged along different directions respectively. The server integrates the stratum strain information of different directions, the water temperature and water pressure changes of the aquifer, and realizes real-time monitoring. The monitoring system and method can realize comprehensive monitoring of large-range stratum displacement and the water temperature and water pressure of the aquifer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mine safety monitoring, and in particular to a roof strata intelligent monitoring system and method based on a CCFPI cable strain sensor. BACKGROUND

[0002] Coal mine roof disaster is a disaster caused by the instability of roof rock in underground mining. Due to its high frequency of occurrence and large proportion of total accidents, it seriously restricts the safety production of coal mines, so it is necessary to prevent and control roof disasters. Real-time monitoring of roof strata movement is one of the key means to prevent and control roof instability. Through analysis of monitoring data of roof strata movement, early warning of possible disasters can be carried out, which is of great significance to the safe and efficient production of coal mines.

[0003] There are many monitoring methods for the movement of roadway roof strata in the prior art, such as using an automatic total station combined with a computer to form a roadway surrounding rock deformation measurement and analysis system, which makes non-contact monitoring of surrounding rock deformation more reliable and accurate; three-dimensional laser scanning deformation monitoring has the characteristics of rapidity, dynamics and digitization, but the above methods can only monitor the deformation of the roadway surrounding rock and cannot monitor the internal movement of the roof strata; with the development of optical fiber sensing technology, distributed optical fiber deformation monitoring system has become the research focus of roadway surrounding rock stability monitoring due to its advantages of distributed, long distance and real-time, but due to the material properties of fiber Bragg grating, when the roadway surrounding rock or roof produces large displacement, it is easy to break. In addition, the existing monitoring methods cannot realize comprehensive monitoring of strata displacement and water temperature and pressure changes in aquifer. In order to realize comprehensive monitoring of large-scale strata displacement and aquifer, further improvement of the existing monitoring system and monitoring method is needed. SUMMARY

[0004] In order to realize real-time intelligent monitoring of large-scale roof strata displacement and aquifer, the present application uses a distributed coaxial cable Fabry-Perot interferometer (CCFPI) sensor, which is essentially N (N≥2) impedance discontinuities distributed at a certain interval, which serve as electromagnetic wave reflection points. Any two reflection points form a coaxial cable Fabry-Perot (F-P) unit, and when the distance between the two reflection points changes, it causes the frequency shift of the wave trough. According to the relationship between frequency shift and strain, the strain value between the reflection points is calculated, and the displacement value between the reflection points is obtained according to the distance between the reflection points, so as to determine the distribution of strain and axial displacement of the roof strata along the borehole axis. The present application provides a roof strata intelligent monitoring system and method based on a CCFPI cable strain sensor. The specific technical solutions are as follows.

[0005] The application discloses a roof stratum intelligent monitoring system based on a CCFPI cable strain sensor, which comprises a strain sensor, a temperature sensor, a water pressure sensor, a fixed sleeve, a terminal load, a vector network analyzer, a server and a remote monitoring device; the strain sensor is a coaxial cable strain sensor; the strain sensor is connected with the terminal load and the vector network analyzer at the end; the server receives the characteristic frequency of the strain sensor and determines displacement data; the remote monitoring device determines the strain condition of the stratum according to the monitored displacement data; a plurality of strain sensors are arranged at different positions respectively; each strain sensor is connected with the vector network analyzer; each vector network analyzer is connected with the server; the server integrates the stratum strain information at different positions; the temperature sensor and the water pressure sensor are arranged on the strain sensor; the strain sensor is arranged in the fixed sleeve; and the fixed sleeve is fixed in the drilling hole by pouring.

[0006] Preferably, the strain sensor comprises a male connector, a joint crimping machine and a coaxial cable; the joint crimping machine is connected with the coaxial cable through a wire crimper.

[0007] Preferably, the coaxial cable forms an impedance discontinuous point at the joint crimping machine, and electromagnetic wave reflection occurs at the discontinuous point.

[0008] Preferably, the fixed sleeve comprises a straight sleeve and an extendable sleeve, the straight sleeve and the extendable sleeve are connected in sequence, and the coaxial cable is pasted in the protective sleeve.

[0009] Preferably, the fixed sleeve is further provided with movable anchor nails, springs, limiters, traction ropes, pull rings and lifting rings; the tail ends of the movable anchor nails are connected with the springs; the movable anchor nails pass through the movable holes on the straight sleeve respectively; and the tail ends of the movable anchor nails are connected in series through the traction ropes.

[0010] Preferably, the pull ring is arranged at the end of the fixed sleeve, the lifting ring is arranged in the other end of the fixed sleeve, the traction rope passes through the lifting ring and is connected with the limiter, and the length of the traction rope in the fixed sleeve is adjusted through the pull ring.

[0011] Preferably, the axial strain ε a The calculation formula is:

[0012] ε a = αε f = α(ε f - ε t )

[0013] Wherein, ε f is the strain on the coaxial cable, ε′ f is the strain generated by the comprehensive action of force and temperature on the cable, ε t is the strain value measured by the temperature compensation sensor, and α is a strain transmission coefficient.

[0014] A rock formation monitoring method based on a CCFPI cable strain sensor, using the above-mentioned roof rock formation intelligent monitoring system based on a CCFPI cable strain sensor, comprises the following steps:

[0015] S1. Determine the length and spacing of the boreholes based on geological and mining conditions;

[0016] S2. Assemble the strain sensor, temperature sensor, water pressure sensor, and fixed sleeve, and determine the position of the temperature sensor and water pressure sensor;

[0017] S3. Arrange a borehole above the coal mining face, install the fixed casing into the borehole, adjust the movable anchor and insert it into the surrounding rock of the borehole, and inject cement slurry into the space between the fixed casing and the borehole. In a borehole with an aquifer, secure the end stopper of the fixed casing to the ground or the mining face, and there is no need to inject cement slurry into the space between the fixed casing and the borehole.

[0018] S4. Connect the coaxial cable to the vector network analyzer and set the parameters of the vector network analyzer;

[0019] S5. Repeat steps S3-4 to monitor multiple boreholes respectively, monitoring the displacement of rock formations in multiple directions and the water temperature and water pressure of the aquifer.

[0020] S6. Install the fixed casing into the borehole according to the location of the aquifer, and adjust the movable anchor to insert it into the surrounding rock of the borehole to monitor the rock displacement in multiple directions and the water temperature and pressure of the aquifer.

[0021] It is further preferred that the diameter of the borehole is larger than the diameter of the fixed sleeve, the vector network is 200MHz, and the termination frequency is 6.0GHz; the rock formation is displaced, the distance between the two reflection points of the strain sensor changes accordingly, and the trough frequency shifts at the same time, and the vector network analyzer obtains the strain between the reflection points.

[0022] It is further preferred that holes are drilled in the rock formation in different directions, and the remote monitoring device monitors the displacement of the rock formation in multiple directions; the temperature sensor and the water pressure sensor monitor the area where the aquifer is located.

[0023] The roof stratum intelligent monitoring system and method based on the CCFPI cable strain sensor have the beneficial effects that: the coaxial cable is utilized, and the terminal load and the adapter are respectively arranged, so that the independent monitoring lines are ensured, the coaxial port not connected is not existed, and the problems of signal leakage and signal interference of adjacent equipment are not occurred; the fixed sleeve is arranged and grouting is fixed, so that the strain sensor and the stratum form a deformation coordination system, the good ductility of the strain sensor is utilized to effectively monitor the stratum deformation in a large range; in addition, the impedance matching between the terminal load and the transmission line is realized, so that all electromagnetic energy is absorbed without reflection, the impedance matching of the signal is ensured, and the signal leakage of the idle port is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a stratum displacement monitoring method flow chart based on the CCFPI cable strain sensor;

[0025] Figure 2 is a structure schematic diagram of the cable strain sensor;

[0026] Figure 3 is a fixed sleeve internal structure schematic diagram;

[0027] Figure 4 is an enlarged view of the movable anchor nail structure;

[0028] Figure 5 is a principle schematic diagram of the movable anchor nail adjustment;

[0029] Figure 6 is a structure schematic diagram of the strain cable and the fixed sleeve;

[0030] Figure 7 is an upward drilling arrangement mode schematic diagram of the cable strain sensor;

[0031] Figure 8 is a plane view of the upward drilling arrangement mode of the cable strain sensor;

[0032] Figure 9 is a downward drilling arrangement mode schematic diagram of the cable strain sensor;

[0033] Figure 10 is a plane view of the downward drilling arrangement mode of the cable strain sensor;

[0034] Figure 11 is a stratum displacement measurement curve schematic diagram of the cable strain sensor.

[0035] In the figure: 1-male connector, 2-connector press fitter, 3-strain sensor, 4-temperature sensor, 5-sealing plug, 6-terminal load, 7-coaxial cable, 8-adhesive, 9-straight casing, 10-telescopic casing, 11-coaxial cable displacement monitoring device, 12-vector network analyzer, 13-server, 14-remote monitoring center, 15-cement mortar, 16-drilling hole, 17-ground, 18-mining working face, 19-tunnel, 20-goaf, 21-water pressure sensor, 101-pull ring, 102-limiter, 103-traction rope, 104-movable anchor, 105-sealing hole, 106-spring structure, 107-lifting ring, 201-actual displacement curve of rock formation, 202-displacement curve monitored by inclined sensor. DETAILED DESCRIPTION

[0036] Combine Figures 1 to 11 As shown, the specific implementation of the roof rock formation intelligent monitoring system and method based on CCFPI cable strain sensor provided by the present invention is described.

[0037] An intelligent roof strata monitoring system based on CCFPI cable strain sensors includes a strain sensor, temperature sensor, water pressure sensor, fixed casing, terminal load, vector network analyzer, server, and remote monitoring device. The strain sensor and temperature sensor work together to monitor the roof strata. The terminal load and vector network analyzer independently work with the strain sensor to prevent signal leakage and interference. The server and remote monitoring device can process a wide range of roof monitoring data to determine the roof strata condition.

[0038] The strain sensor is a coaxial cable strain sensor, the end of which is connected to a terminal load and a vector network analyzer. A server receives the characteristic frequency displacement data from the strain sensor, and the remote monitoring device determines the strain of the rock formation based on this displacement data. Multiple strain sensors are arranged horizontally, each connected to a vector network analyzer. Each vector network analyzer is connected to the server, which integrates rock formation strain information from different locations. The remote monitoring device reads the server's monitoring data in real time via the internet and obtains and processes roof monitoring information. A temperature compensation sensor is connected in series with the strain sensor, and a protective sleeve is installed outside the strain sensor. When the roof rock formation shifts along the borehole axis, the distance between the two reflection points of the CCPFI cable strain sensor changes, causing a frequency shift in the trough. Based on the relationship between frequency shift and strain, the strain value between the reflection points is calculated using the vector network analyzer. The displacement value between the reflection points is calculated based on the distance between the basic reflection points. The displacement values ​​between the reflection points are then used to determine the distribution of strain and axial displacement of the roof rock formation along the borehole axis.

[0039] The strain sensor consists of a male connector, a connector presser, and a coaxial cable. The connector presser is connected to the coaxial cable via a crimping pliers. The coaxial cable forms an impedance discontinuity at the connector presser, where electromagnetic waves reflect, forming a Fabry-Perot interferometer cavity and a coaxial cable CCFPI strain sensing unit.

[0040] The protective sleeve includes a straight sleeve and a telescopic sleeve, which are connected in sequence, and the coaxial cable is adhered to the protective sleeve. A sealing plug is provided at the end of the protective sleeve, and the protective sleeve and the coaxial cable are installed in the drilled hole. The telescopic sleeve can be made of rubber materials, or a pleated corrugated telescopic sleeve to connect and fix the straight sleeve. Other structures that are convenient for telescopic connection can also be used. The fixed sleeve is also provided with a movable anchor, a spring, a limiter, a traction rope, a pull ring and a lifting ring. The tail end of the movable anchor is connected to the spring, and multiple movable anchors pass through the movable holes on the straight sleeve respectively. The tail ends of the movable anchors are also connected in series through the traction rope. The pull ring is provided at the end of the fixed sleeve, and the lifting ring is provided inside the other end of the fixed sleeve. The traction rope passes through the lifting ring and is connected to the limiter. The length of the traction rope in the fixed sleeve is adjusted by the pull ring. When the cable strain sensor is attached to the fixed sleeve, a preload of approximately 0.1 kN should be applied to keep the initial state of the cable at a positive strain of approximately 0.05%-0.1%.

[0041] A rock formation intelligent monitoring method based on a CCFPI cable strain sensor, using the above-mentioned roof rock formation intelligent monitoring system based on a CCFPI cable strain sensor, comprises the following steps:

[0042] S1. Determine the length and spacing of boreholes based on geological and mining conditions; geological and mining conditions include working face parameters and borehole histograms. Estimate the extent of overburden deformation caused by mining based on the working face, burial depth, mining height, strike and dip length, and overburden characteristics. Approximately determine the location of the aquifer based on the borehole histogram.

[0043] S2. Assemble the strain sensor, temperature sensor, water pressure sensor, and fixed sleeve, and determine the positions of the temperature sensor and water pressure sensor.

[0044] S3. Arrange a borehole above the coal mining face, install the fixed casing into the borehole, adjust the movable anchor and insert it into the surrounding rock of the borehole, and inject cement slurry into the space between the fixed casing and the borehole. In a borehole with an aquifer, secure the end stopper of the fixed casing to the ground or the mining face, and there is no need to inject cement slurry into the space between the fixed casing and the borehole.

[0045] S4. Connect the coaxial cable to the vector network analyzer and set the parameters of the vector network analyzer.

[0046] S5. Repeat steps S3-4 to monitor multiple boreholes respectively, monitoring the rock formation displacement in multiple directions and the water temperature and water pressure of the aquifer.

[0047] ① Rock displacement monitoring

[0048] The coaxial cable displacement monitoring device is connected to the vector network analyzer via an SMA connector. The vector network analyzer connects the monitored roof displacement monitoring data to the server via a bus. By analyzing the monitoring data from different monitoring positions, the roof rock displacement monitoring status of a large area is obtained. The remote monitoring center reads the monitoring data from the cloud server in real time through the Internet and publishes the monitoring information in real time.

[0049] Axial strain ε a The calculation formula is:

[0050] ε a =αε f =α(ε f -ε t )

[0051] Among them, ε f is the strain on the coaxial cable, ε′ f is the strain caused by the combined effect of cable stress and temperature, ε t The strain value measured by the temperature compensation sensor, α is the strain transfer coefficient.

[0052] During measurement, the relative strain under the influence of temperature is taken into account to achieve temperature compensation function.

[0053] Among them, the drilling methods can be divided into the following two types according to the needs of the monitoring range: one is to drill from top to bottom from the ground to the roof of the mining face, and a borehole is arranged every 20 to 50 meters along the mining direction of the working face. Each borehole is arranged in the rock layer at a different depth to monitor the displacement of the rock layer at different depths, so as to realize real-time monitoring of the sinking displacement of the rock layer at different positions on the ground; the other is to drill from bottom to top from the tunnel section, and a borehole is arranged every 20 to 50 meters. The drilling direction is parallel to the vertical or at an angle of β. The drilling depth is the theoretical calculated height from the broken rock layer area to the stable rock layer area above the tunnel. When the borehole is parallel to the vertical direction, the rock layer displacement area is determined according to the strain value sensed by the cable strain sensor. When the borehole is at an angle of β to the vertical direction, the rock layer displacement area is determined according to S=L×cosβ, where L is the rock layer displacement in the borehole.

[0054] ②Aquifer temperature monitoring

[0055] The temperature of different depth rock stratum and aquifer is different, the cable strain sensor with temperature sensor can determine the position of aquifer according to the temperature change of different depth. Because the aquifer is separated by thick rock stratum, the water temperature is relatively stable in four seasons, so the water temperature of initial monitoring is taken as the constant value C of the water level of monitoring point. When the aquifer is damaged and the water source is lost, the temperature sensor monitors the temperature of rock stratum or the middle separation layer. Therefore, when the water temperature monitored by the temperature sensor in the cable changes compared with the constant value C, it indicates that the aquifer has displacement and may be damaged. In the monitoring process, multi-point drilling is used for real-time large-scale monitoring, and the temperature change value monitored by multiple sensors is used to accurately invert the temperature change range of the aquifer.

[0056] ③Aquifer pressure monitoring

[0057] When the water pressure changes, the elastic diaphragm at the bottom of the cable strain sensor is subjected to pressure change, and different pressure changes cause different deformation of the elastic diaphragm. Through the transmission mechanism, the deformation of the elastic diaphragm is converted into the deformation of the cable, and finally into the frequency shift of the wave trough. As long as the relationship between the frequency shift and the change of water pressure is measured, the water pressure value can be measured in real time through the change of electromagnetic wave characteristic parameters. When the water pressure value exceeds the specified range, the early warning information is immediately sent to the monitoring center.

[0058] When any measured dynamic measurement parameter exceeds the specified threshold value, the server receives the dynamic parameter signal of the monitoring, and immediately transmits it to the remote control center through the Internet. The remote control center obtains the degree and influence range of the aquifer damage according to the dynamic parameters of the aquifer measured by multiple directional drilling, so as to reduce the risk of serious disasters such as water inrush.

[0059] The strain sensor with fixed sleeve is installed in the drilling hole at different depths, and a vector network analyzer is connected to the end of each drilling hole. The vector network analyzer analyzes the data monitored by the coaxial cable to obtain the corresponding displacement of the displacement sensor at different depths, so as to realize real-time observation of the subsidence amount of the roadway roof at different positions underground from the ground. Then, the subsidence amount of the rock stratum at different positions monitored is taken as the standard for judging whether the roadway roof rock stratum is separated.

[0060] The diameter of the drilling hole is greater than the diameter of the protective sleeve, the vector network is 200MHz, and the terminal frequency is 6.0GHz. When the rock stratum of the roof is displaced, the distance between the two reflection points of the strain sensor changes, and the wave trough also changes in frequency. The vector network analyzer obtains the strain between the reflection points. The frequency value corresponding to the characteristic wave trough in the initial state is saved on the vector network analyzer. In each subsequent measurement, the vector network analyzer is directly connected, the above parameters are set, and the frequency value corresponding to the characteristic wave trough at this time is saved.

[0061] The remote monitoring device monitors the roof displacement in multiple directions when drilling holes in the roof in different directions. The cable strain sensor can monitor each rock layer of the roof, and can utilize the ductility and not be broken. The coaxial cable can bear larger strain and not be failed due to a larger displacement of the rock layer.

[0062] The system utilizes the coaxial cable, and sets the terminal load and the adapter respectively, so that the monitoring lines are independent, there is no coaxial port not connected, and there is no signal leakage and adjacent equipment signal interference problem. The impedance between the terminal load and the transmission line is matched, so that all electromagnetic energy is absorbed without reflection, which ensures the impedance matching of the signal and greatly reduces the signal leakage of the idle port.

[0063] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or replacements made by the skilled in the art within the essential scope of the present application should also be within the protection scope of the present application.

Claims

1. An intelligent roof rock layer monitoring system based on CCFPI cable strain sensor, characterized in that: The system includes a strain sensor, a temperature sensor, a water pressure sensor, a fixed casing, a terminal load, a vector network analyzer, a server, and a remote monitoring device. The strain sensor uses a coaxial cable strain sensor, the end of which is connected to the terminal load and the vector network analyzer. The server receives the characteristic frequency of the strain sensor and determines displacement data. The remote monitoring device determines the strain of the rock formation based on the monitored displacement data. Multiple strain sensors are arranged in different orientations, each strain sensor is connected to a vector network analyzer, and each vector network analyzer is connected to the server. The server integrates the strain information of the rock formation in different orientations. The temperature sensor and water pressure sensor are configured on the strain sensor, and the strain sensor is configured in the fixed casing. The fixed casing is fixed in the borehole by casting. The strain sensor includes a male connector, a connector presser and a coaxial cable, wherein the connector presser is connected to the coaxial cable through a crimping pliers; The coaxial cable forms an impedance discontinuity point at the connector press, and electromagnetic wave reflection occurs at the discontinuity point; The fixed sleeve includes a straight sleeve and a telescopic sleeve, the straight sleeve and the telescopic sleeve are connected in sequence, and the coaxial cable is adhered to the protective sleeve; The fixed sleeve is also provided with a movable anchor, a spring, a limiter, a traction rope, a pull ring and a lifting ring. The tail end of the movable anchor is connected to the spring. The plurality of movable anchors pass through the movable holes on the straight sleeve respectively. The tail ends of the movable anchors are also connected in series through the traction rope. The pull ring is arranged at the end of the fixed sleeve, the lifting ring is arranged inside the other end of the fixed sleeve, the traction rope passes through the lifting ring and is connected to the limiter, and the length of the traction rope in the fixed sleeve is adjusted by the pull ring; The axial strain is ε a , the calculation formula is: e a =ae f =α(ε′ f -e t ) Among them, ε f is the strain on the coaxial cable, ε' f is the strain caused by the combined effect of cable stress and temperature, ε t is the strain value measured by the temperature compensation sensor, and α is the strain transfer coefficient.

2. A rock formation monitoring method based on a CCFPI cable strain sensor, using the roof rock formation intelligent monitoring system based on a CCFPI cable strain sensor according to claim 1, characterized in that the steps include: S1. Determine the length and spacing of the boreholes based on geological and mining conditions; S2. Assemble the strain sensor, temperature sensor, water pressure sensor, and fixed sleeve, and determine the position of the temperature sensor and water pressure sensor; S3. Drill holes are arranged above the coal mining face, fixed casings are installed into the holes, and movable anchors are inserted into the surrounding rock of the holes. Cement slurry is injected into the gap between the fixed casing and the holes. S4. Connect the coaxial cable to the vector network analyzer and set the parameters of the vector network analyzer; S5. Repeat steps S3-4 to monitor multiple boreholes respectively, monitoring the rock formation displacement in multiple directions and the water temperature and water pressure of the aquifer.

3. The rock formation monitoring method based on CCFPI cable strain sensor according to claim 2 is characterized in that: The diameter of the borehole is larger than the diameter of the fixed sleeve. The vector network is 200 MHz and the termination frequency is 6.0 GHz. When the rock formation shifts, the distance between the two reflection points of the strain sensor changes accordingly, and the trough frequency shifts simultaneously. The vector network analyzer obtains the strain between the reflection points.

4. The intelligent roof displacement monitoring method based on CCFPI cable strain sensor according to claim 2 is characterized in that: Holes are drilled in different directions in the rock formation, and the remote monitoring device monitors the rock formation displacement in multiple directions; temperature sensors and water pressure sensors monitor the area where the aquifer is located.

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