An anchor rod deformation monitoring structure based on cable sensing and a use method thereof

Abstract

The application provides an anchor rod deformation monitoring structure based on cable sensing and a use method, and relates to the technical field of underground engineering monitoring.The anchor rod structure comprises an anchor rod body, a coaxial cable, a joint presser, a connector and a terminal load, the coaxial cable is provided with a distributed Fabry-Perot strain sensor, the coaxial cable and the anchor rod body are mutually bonded, one end of the coaxial cable is connected with the terminal load through an SMA joint connector, the other end of the coaxial cable is connected with a vector network analyzer through an SMA joint connector after being led out from an anchor rod tray, and the joint presser is arranged on the bonding section of the coaxial cable and the anchor rod and generates a characteristic impedance discontinuity.The anchor rod can be used for monitoring and analyzing the axial deformation, bending deformation and breakage of the anchor rod, realizes real-time monitoring of the axial deformation and bending deformation of the anchor rod without affecting the reinforcement effect of the anchor rod, and has the advantages of wide application range, resistance to high-temperature and high-pressure liquid environment, small transmission loss, high spatial resolution and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underground engineering monitoring, and particularly relates to an anchor rod deformation monitoring structure based on cable sensing and a use method. BACKGROUND

[0002] Anchor rod support refers to a reinforcing support method used in surface engineering such as slope, rock-soil deep foundation pit and underground chamber construction such as tunnel and stope. The anchor rod support has been widely used in the field of support engineering due to the advantages of low cost, good support effect, simple operation and flexible use. The anchor rod support plays an important role in reinforcing rock mass, limiting rock mass deformation and enhancing rock mass stability in rock-soil engineering, and is widely used in engineering fields such as mining, metallurgy, water conservancy and hydropower, railway and highway, and military industry. For mine engineering, with the increase of mining depth, it is necessary to monitor the stress and strain of the anchor rod itself to judge the support capacity of the anchor rod itself and to give early warning of underground disasters.

[0003] The traditional anchor rod stress and strain monitoring method mainly realizes the monitoring by pasting resistance strain gauges on the anchor rod body. However, the resistance strain gauges cannot maintain long-term stable monitoring effect due to high humidity in the underground engineering environment, and the resistance strain gauges have small range, which makes it difficult to realize the whole process monitoring of anchor rod deformation and damage. In recent years, optical fiber sensing technology has been gradually applied to anchor rod deformation measurement. Although the optical fiber sensing technology has the advantages of corrosion resistance, small size and high sensitivity, there are still a series of key problems, especially the small long-term allowable strain, which makes it difficult to be used for local large deformation monitoring, and the bending, overheating or mechanical action easily causes damage to the optical fiber. In addition, the existing anchor rod deformation monitoring technology usually only monitors the axial strain of the anchor rod, ignoring the bending deformation monitoring of the anchor rod. When the anchor rod is in the state of intersecting with the sliding surface, the sliding surface can exert shear stress on the anchor rod to cause bending deformation of the anchor rod. Therefore, the monitoring of the bending deformation degree of the anchor rod is of great significance to reflect the working state of the anchor rod. SUMMARY

[0004] In order to solve the problems existing in the existing anchor rod monitoring method, realize continuous, stable and real-time monitoring of the anchor rod without affecting the reinforcing effect of the anchor rod, the present application provides an anchor rod deformation monitoring structure based on cable sensing and a use method, and the specific technical solutions are as follows.

[0005] An anchor rod deformation monitoring structure based on cable sensing, comprising an anchor rod body, a coaxial cable, a joint presser and a terminal load, the coaxial cable is bonded with the anchor rod body, the joint presser is arranged on the bonding section of the coaxial cable and the anchor rod body; the coaxial cable is provided with a Fabry-Perot (F-P) strain sensor; one end of the coaxial cable is connected with the terminal load through an SMA joint connector, and the other end is connected with a vector network analyzer (VNA) through an SMA joint connector after passing out from an anchor rod tray; the joint presser is arranged on the bonding section of the coaxial cable and the anchor rod body and generates a characteristic impedance discontinuity; the coaxial cable F-P strain sensor monitors the strain of the anchor rod body in real time.

[0006] Preferably, the coaxial cable comprises an inner conductor, an outer conductor, an insulation layer and a protective layer, the outer layer of the inner conductor is wrapped with the insulation layer, the outer layer of the insulation layer is wrapped with the outer conductor, and the outer layer of the outer conductor is wrapped with the protective layer.

[0007] Preferably, the coaxial cable F-P strain sensor monitors the axial deformation of the anchor rod in real time, and the coaxial cable is arranged along the axial direction of the anchor rod body.

[0008] Further preferably, the coaxial cable is pasted to the surface of the anchor rod body along the axial direction of the anchor rod body.

[0009] Further preferably, the coaxial cable is pasted in a shallow groove opened along the axial direction of the anchor rod body, and the opening depth of the shallow groove is 2-4 mm.

[0010] Further preferably, the coaxial cable F-P sensor monitors the bending deformation of the anchor rod, and the coaxial cable is wound and pasted on the surface of the anchor rod body according to the direction of the wrap angle of 30°.

[0011] Further preferably, the F-P strain sensor is arranged on the coaxial cable, which is composed of a pair of structural reflectors arranged in the cable, when the radio frequency electromagnetic wave is transmitted into the coaxial cable from one end and transmitted in the coaxial cable, the electromagnetic wave will produce reflected electromagnetic wave at the two structural reflectors, the two reflected electromagnetic waves produce resonance, and form an interference spectrum in the frequency domain.

[0012] Further preferably, the VNA monitors the frequency shift of the interference spectrum formed by the F-P sensor, and the frequency shift rate is the strain generated by the anchor rod segment between the two structural reflectors of the F-P sensor; the signal source in the VNA excites to generate an input signal, the input signal passes through a signal separation device and is transmitted along the line to each sensing element, the reflected signal is reflected back to the VNA at each sensing element, passes through the signal separation device and is transmitted to a receiver, the receiver tests, compares and analyzes the reflected, transmitted and input signals of the measured device, so as to complete the measurement of the change amount.

[0013] A kind of cable sensing-based anchor rod deformation real-time monitoring method, using the cable sensing-based anchor rod deformation monitoring structure described above, for the deformation monitoring of anchor rod in indoor simulation test, or the deformation monitoring of anchor rod in engineering surrounding rock support, comprising:

[0014] Making anchor rod: selecting anchor rod and using it to bear coaxial cable, configuring joint presser (structure reflector) and terminal load on coaxial cable; bonding coaxial cable and one end of anchor rod body, applying pre-tightening force to the other end of coaxial cable, so that coaxial cable maintains 0.05%-0.1% normal strain, then bonding coaxial cable and anchor rod body along full length;

[0015] Installing anchor rod: drilling hole in coal rock mass, drilling hole diameter is divided into two sections, drilling hole diameter near drilling hole opening is slightly larger than that of the other side, which facilitates coaxial cable to be led out of drilling hole, and at the same time avoids coaxial cable leading-out section from being extruded by hole wall and tray during anchor rod installation process; then putting anchor rod into drilling hole, full-length anchoring is carried out through anchoring agent, anchor rod tray is arranged at hole opening, nut is tightened to apply pre-stress, lead-out hole is drilled in anchor rod tray, coaxial cable is led out from lead-out hole;

[0016] Monitoring anchor rod deformation: VNA monitors frequency shift of interference spectrum formed by F-P sensor, frequency shift rate is strain generated by anchor rod section between two structure reflectors of F-P sensor, according to strain variation law of sensor under different deformation conditions of anchor rod, deformation condition and deformation degree of anchor rod are judged.

[0017] It is further preferred that when anchor rod is used for deformation monitoring of anchor rod in indoor simulation test, adhesive between coaxial cable and anchor rod body is epoxy resin, phenolic resin or neoprene adhesive; when anchor rod is used for deformation monitoring of anchor rod in engineering surrounding rock support, adhesive between coaxial cable and anchor rod body is polyphosphoric acid compound or epoxy resin glue.

[0018] The cable sensing-based anchor rod deformation monitoring structure and use method provided by the application have the beneficial effects that coaxial cable sensor can withstand larger deformation, can play a supporting role in combination with anchor rod to support surrounding rock, can withstand larger tensile stress or shear stress, has a larger sensing range and a wider application range; the anchor rod deformation monitoring structure can effectively monitor deformation and damage of anchor rod itself, has small coaxial cable transmission loss, facilitates long-distance transmission, and is conducive to realizing intelligent monitoring; the monitoring method has high spatial resolution, can realize online real-time monitoring of anchor rod deformation through interconnection of VNA and computer; in addition, the anchor rod deformation monitoring structure has the advantages of resisting high-temperature and high-pressure liquid environment, strong long-term monitoring stability, long service life and the like. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is an installation schematic diagram of cable sensing-based anchor rod deformation monitoring structure.

[0020] Figure 2 is the anchor rod tray structure schematic diagram with cable leading hole;

[0021] Figure 3 is the coaxial cable layered structure schematic diagram;

[0022] Figure 4 is the coaxial cable structure schematic diagram with F-P strain sensor arranged;

[0023] Figure 5 is the anchor rod axial deformation monitoring structure schematic diagram;

[0024] Figure 6 is the anchor rod bending deformation monitoring structure schematic diagram;

[0025] Figure 7 is the anchor rod bending deformation monitoring principle diagram;

[0026] Figure 8 is the coaxial cable strain law curve during anchor rod deformation;

[0027] Figure 9 is the coaxial cable variation law curve with winding angle;

[0028] Figure 10 is the monitoring system principle schematic diagram;

[0029] Figure 11 is the anchor rod laying structure schematic diagram;

[0030] Figure 12 is the cable sensor measured strain statistical diagram during anchor rod axial deformation;

[0031] Figure 13 is the cable sensor measured strain statistical diagram during anchor rod bending deformation;

[0032] Figure 14 is the coaxial cable leading mode schematic diagram from borehole and tray;

[0033] In the figure: 1-anchor rod body, 2-coaxial cable, 3-joint presser, 4-terminal load, 5-joint connector, 6-anchor rod tray, 7-VNA, 8-rock mass, 9-adhesive, 10-anchoring agent, 11-anchor rod hole, 12-cable leading hole, 13-inner conductor, 14-outer conductor, 15-insulating layer, 16-protection layer, 17-structure reflection point, 18-circuit, 19-signal source, 20-receiver, 21-signal separation device, 22-coaxial cable F-P strain sensor, 23-sprayed concrete; 24-roadway; 25-nut; 26-borehole. DETAILED DESCRIPTION

[0034] In combinationFigures 1 to 14 The specific embodiments of the anchor rod deformation monitoring structure based on cable sensing and the use method provided by the application are illustrated.

[0035] In order to be applicable to the monitoring and analysis of the stress and strain of the anchor rod, the damage degree and the like in civil engineering, tunnel engineering, mineral engineering and the like, the axial deformation and bending deformation of the anchor rod are monitored in real time without affecting the reinforcement effect of the anchor rod.

[0036] An anchor rod deformation monitoring structure based on cable sensing, comprising an anchor rod body, a coaxial cable, a joint presser, a joint connector and a terminal load, the coaxial cable is bonded with the anchor rod body, the joint connector is arranged at both ends of the coaxial cable, the joint presser is arranged at the bonding section of the coaxial cable and the anchor rod, forming two structural reflection points, and a pair of structural reflection points constitute a coaxial cable F-P strain sensor. One end of the coaxial cable is connected with the terminal load through an SMA joint connector, and the other end is connected with a VNA through an SMA joint connector after being pulled out from the anchor rod tray. The joint presser is arranged at the bonding section of the coaxial cable and the anchor rod, and generates a characteristic impedance discontinuity, and the coaxial cable F-P strain sensor monitors the deformation of the anchor rod in real time.

[0037] The coaxial cable has the characteristics of low price, low transmission loss, strong stability, resistance to high temperature and high pressure liquid working environment and the like, which comprises an inner conductor, an outer conductor, an insulating layer and a protective layer, the outer layer of the inner conductor is wrapped with the insulating layer, the outer layer of the insulating layer is wrapped with the outer conductor, and the outer layer of the outer conductor is wrapped with the protective layer; the insulating material is usually made of flexible material with relatively high dielectric constant, the protective layer is usually plastic, and usually extends to cover the cable length of the outer conductor. The coaxial cable with F-P strain sensor mainly implants two structural reflectors in the coaxial cable to construct a single coaxial cable F-P strain sensor. Two joint pressers are firmly pressed on the cable with a minimum interval of 2 cm, so that the coaxial cable generates a characteristic impedance discontinuity; the joint presser is a copper crimp ring. The joint connector is an SMA straight male connector, which can be used in relatively harsh working conditions. The SMA straight male connector is connected at both ends of the cable, and then connected with the VNA and the terminal load at both ends respectively. When the radio frequency electromagnetic wave signal excited by the VNA is transmitted into the coaxial cable from one end and transmitted in the coaxial cable, the electromagnetic wave will produce reflected electromagnetic wave at the two reflectors, and the two reflected electromagnetic waves will produce resonance, forming an interference spectrum in the frequency domain.

[0038] According to practical experience, the coaxial cable mainly used is RG58 and RG400. The diameter of RG58 coaxial cable is 4.95 mm, the characteristic impedance is 53 Ω, the insulating medium is PEP, the maximum working frequency is 1000 MHz, and the working temperature range is -70℃ to +200℃; the diameter of RG400 coaxial cable is 5 mm, the characteristic impedance is 50 Ω, the insulating medium is PTFE, the maximum working frequency is 12.4 GHz, and the working temperature range is -55℃ to +200℃. The length of SMA straight male connector is 24 mm, and the width is 7.9 mm. The length of terminal load is 10.92 mm, the width is 4.57 mm, the characteristic impedance is 50 Ω, the maximum working frequency is 6 GHz, and the working temperature range is -55℃ to 125℃.

[0039] The diameter of the anchor rod body is 16-32 mm, the length is 150-260 cm, the cross section is circular, and the material is 45# carbon structural steel. The coaxial cable F-P strain sensor monitors the axial deformation of the anchor rod, and the coaxial cable is arranged along the axial direction of the anchor rod body and is pasted on the surface of the anchor rod body along the axial direction of the anchor rod body.

[0040] In addition, the coaxial cable part with the coaxial cable F-P strain sensor unit and the temperature compensation sensor unit is bonded on the anchor rod body, wherein the coaxial cable F-P strain sensor unit is pasted on the anchor rod body, and the temperature compensation sensor unit exceeds the anchor rod and is a free section. By drilling treatment on the anchor rod tray, the coaxial cable with the coaxial cable F-P strain sensor unit and the temperature compensation sensor unit can be led out of the drill hole. In order to realize temperature compensation, first, drill a hole in the coal rock mass, install a claw hook at the bottom of the hole, then put the single-point temperature compensation deformation monitoring anchor rod into the drill hole, and let the claw hook at the bottom of the drill hole hook the iron ring on the anchor rod body, to complete the fixation of the tail of the anchor rod. The anchor rod tray is arranged at the hole mouth, and the nut is tightened to apply a prestress to fix it. The anchor rod tray is drilled to lead out the coaxial cable with the coaxial cable F-P strain sensor and the temperature compensation sensor from the lead-out hole.

[0041] In this embodiment, the shallow groove in which the coaxial cable arranged along the axial direction of the anchor rod body is pasted has a groove depth of 2-4 mm, so as to ensure further adhesion of the coaxial cable and the anchor rod body, so that the coaxial cable will not relatively displace with the anchor rod body even in a complex engineering environment, thereby ensuring the monitoring accuracy. In addition, the groove depth is determined through multiple tests, and the groove depth in this range has negligible effect on the strength of the anchor rod body, and the coaxial cable can be well arranged.

[0042] In combination with Figures 7 to 9The coaxial cable F-P strain sensor monitors the bending deformation of the anchor rod. The coaxial cable is wound on the surface of the anchor rod body at a wrapping angle of 30°. Theoretical analysis obtains the relationship between the cable strain and the wrapping angle under axial and bending deformation conditions. For example, the axial strain reaches its absolute maximum at 90°, and the wrapping angle of 27° is not sensitive to axial deformation and bending deformation. Therefore, the monitoring sensitivity of the cable strain sensor can be adjusted by adjusting the wrapping angle of the coaxial cable.

[0043] The coaxial cable F-P strain sensor is wound on the anchor rod body at a wrapping angle θ. The wrapping angle θ can be selected according to the deformation range that the anchor rod may encounter or is designed to measure. The coaxial cable and the anchor rod body are bonded using an adhesive to produce synchronous deformation. One end of the coaxial cable sensor is connected to a terminal load, and the other end is connected to a VNA.

[0044] According to theoretical analysis, under the condition of axial deformation of the anchor rod, the relationship between the strain generated by the cable and the axial strain of the anchor rod when the wrapping angle is θ is:

[0045]

[0046] Under the condition of bending deformation of the anchor rod, the relationship between the strain generated by the cable and the axial strain of the anchor rod is:

[0047]

[0048] where ε f is the strain generated by the cable, ε a is the axial strain of the anchor rod (positive for stretching), θ is the wrapping angle, is the azimuth angle, v is the Poisson's ratio of the anchor rod, R is the radius of curvature of the bending deformation of the anchor rod, and r is the radius of the anchor rod.

[0049] In principle, ε f is calculated by the following formula:

[0050] Δλ = λ (1 - P e ) Kε f (3)

[0051] where Δλ is the wavelength shift generated under the action of strain, λ is the Bragg wavelength, P e is the strain effect of the refractive index, and K is the adhesion coefficient of the cable and the anchor rod.

[0052] In fact, the cable strain ε f can be directly calculated from the above formula and the wavelength shift Δλ monitored by the VNA. Given the cable strain ε f , the wrapping angle θ, and the Poisson's ratio v of the anchor rod, the anchor rod axial strain ε aFor pure bending deformation, the axial strain of the anchor ε a is 0, the cable strain ε f , the wrap angle θ, the anchor Poisson's ratio v and the azimuth angle are known, the curvature radius R of the anchor bending deformation can be solved by substituting them into equation (2).

[0053] Because the coaxial cable is spirally wound on the anchor rod body at a fixed angle, the variation curve of the coaxial cable strain along the azimuth angle under each deformation condition shows unique characteristics. The distribution law of the cable sensor strain under two different deformation conditions is given, which reflects the law of the cable strain under different azimuth angles. The axial deformation condition is a constant displacement, so the strain generated on the cable is independent of the azimuth angle position of the sensor; under the bending deformation condition, the data monitored by the cable sensor is approximately a sinusoidal curve, and the period of the data variation of the bending deformation cable sensor is equivalent to a period of winding on the anchor, i.e. 360°.

[0054] The F-P strain sensor is arranged on the coaxial cable, which is composed of a pair of structural reflectors arranged in the cable. When the radio frequency electromagnetic wave is transmitted into the coaxial cable from one end and transmitted in the coaxial cable, the electromagnetic wave will produce reflected electromagnetic wave at the two structural reflectors, and the two reflected electromagnetic waves will produce resonance and form an interference spectrum in the frequency domain. The VNA monitors the frequency shift of the interference spectrum formed by the F-P sensor, and the frequency shift rate is the strain generated by the anchor segment between the two structural reflectors of the F-P sensor; the signal source in the VNA excites the input signal, the input signal passes through the signal separation device, is transmitted along the line to each sensing element, the reflected signal is reflected back to the VNA at each sensing element, passes through the signal separation device, and is transmitted to the receiver. The receiver tests, compares and analyzes the reflection, transmission and input signals of the measured device, so as to complete the measurement of the variation.

[0055] A kind of anchor deformation monitoring method based on cable sensing, using the above-mentioned anchor deformation monitoring structure based on cable sensing, for the deformation monitoring of anchor in indoor simulation test, or the deformation monitoring of anchor in engineering surrounding rock support, comprising:

[0056] Making anchor rod: selecting anchor rod and loading coaxial cable with it, cutting appropriate length of cable, calibrating reflection point position according to actual needs and making structural reflection point, installing joint connector at both ends of coaxial cable, one end of which is connected to terminal load; bonding coaxial cable and one end of anchor rod body, applying pre-tightening force to the other end, which is generally about 0.1KN, so that the coaxial cable maintains a normal strain of 0.05%-0.1%, and then bonding the coaxial cable and the anchor rod along the full length.

[0057] The protective layer, outer conductor and insulating layer of one end of the cable are peeled off to expose the inner conductor, the tip of the SMA straight male connector is welded on the inner conductor by an electric soldering iron, the SMA straight male connector is connected to the cable through the tip, and finally the joint compression device is placed at the connection between the SMA straight male connector and the cable, and the joint compression device is squeezed by using the wire crimping pliers, so that the SMA connector of the coaxial cable is made, and the above operation is repeated at the other end. Start the VNA and set the relevant parameters, connect the one end of the cable to the vector network analyzer, and connect the other end to a 50Ω terminal load; adjust the VNA to the time domain mode, start to squeeze the joint compression device by using the wire crimping pliers at the position of the calibrated reflection point, and observe the reflection peak height to make the reflection peak heights of the two reflection points basically consistent. In addition, it should be noted that the joint compression device is preferably squeezed by the wire crimping pliers for multiple times, because the deformation of the joint compression device may rebound in the case of less squeezing times, thereby reducing the reflection amplitude of the reflection point and affecting the use effect of the sensor.

[0058] Installing anchor rod: drilling in coal and rock mass, the drilling diameter is divided into two sections, the drilling diameter near the drilling opening is slightly larger than the drilling diameter on the other side, which facilitates the coaxial cable to be drawn out of the drilling, and avoids the coaxial cable drawing section from being squeezed by the hole wall and the tray during the installation of the anchor rod; then the anchor rod is put into the drilling, anchored by anchor agent, the anchor rod tray is arranged at the hole opening, the nut is tightened to apply pre-stress, and the anchor rod tray is drilled to draw out the coaxial cable.

[0059] The arrangement of the anchor rod in the roadway is as shown in Figure 11 In this embodiment, the anchor rod row spacing is 0.8 m, and there are 9 anchor rods in each row with a spacing of 0.8 m. In the elastic deformation stage of the anchor rod, the formula for converting the strain of the anchor rod into stress is: σ=aEε; wherein σ is the anchor rod axial force, a is the strain conversion coefficient measured by indoor test, E is the elastic modulus of the anchor rod, and ε is the measured strain of the cable sensor.

[0060] The coaxial cable with multiple cable sensors is directly pasted on the surface of the anchor rod in the axial direction to measure the axial strain. The anchor rod body is first axially slotted, and then the coaxial cable with multiple cable sensors is bonded to the slotted part of the anchor rod by an adhesive to measure the axial strain. Then the strain values at each sensor position of the anchor rod can be obtained by monitoring the frequency shift of each sensor according to the following formula.

[0061]

[0062] wherein ε a is the axial strain of the anchor rod, ε f is the strain generated by the cable, f N is the Nth order resonance frequency, Δf N is the Nth order frequency shift, and P effα is the effective elastic coefficient of the coaxial cable insulation layer, and α is the strain transfer coefficient, which is related to the type and properties of the adhesive and is determined experimentally.

[0063] This embodiment takes a winding angle of 30° and an anchor rod Poisson's ratio of 0.29 as an example to determine the relationship between the strain on the cable and the axial strain of the anchor rod:

[0064]

[0065] In fact, the VNA can directly calculate the cable strain ε using the above formula and the monitored frequency offset. f Under the condition of axial deformation of the anchor bolt, the cable strain ε is known. f The anchor bolt's axial strain ε can be directly calculated by substituting the wrap angle θ and the anchor bolt's Poisson's ratio ν into formula (1). a Under the condition of pure bending deformation of the anchor bolt, the axial strain ε of the anchor bolt is... a The cable strain ε is 0. f The wrap angle θ, the anchor bolt Poisson's ratio ν, and the azimuth angle Given that the radius of curvature R of the anchor rod bending deformation can be solved by substituting it into formula (2).

[0066] In addition, the relationship between the axial strain of the single-point temperature-compensated sensing anchor and the cable strain is as follows:

[0067] ε a =αε f =α(ε') f -ε t (6)

[0068] Where, ε f ε is the strain generated in the cable due to the force applied. a It is the axial strain of the anchor bolt, ε' f ε is the strain generated by the combined effects of stress and temperature on the cable. t This refers to the strain produced by the cable under temperature, i.e., the strain measured by the temperature compensation sensor.

[0069] Monitoring anchor bolt deformation: The VNA monitors the frequency shift of the interferogram formed by the FP sensor. The rate of change of frequency shift is the strain generated in the anchor bolt section between the two structural reflectors of the FP sensor. The signal source in the VNA generates an input signal, which is transmitted to each sensing element along the line through a signal separation device. The reflected signal is reflected back to the VNA at each sensing element, and after passing through the signal separation device, it is transmitted to the receiver. The receiver tests, compares, and analyzes the reflected, transmitted, and input signals of the device under test, thereby completing the determination of the change.

[0070] In the embodiment, the actual observation is also made on the strain value of the cable sensor under the condition of the axial deformation of the anchor rod, wherein the axial deformation of the anchor rod is segmented deformation, the axial strain of the monitoring segment of the No. 1 and No. 2 sensors is ε f1 , the axial strain of the monitoring segment of the No. 3 and No. 4 sensors is ε f2 , the axial strain of the monitoring segment of the No. 5 and No. 6 sensors is ε f3 , and ε f2 > ε f1 > ε f3 . The strain value of the cable sensor under the condition of the bending deformation of the anchor rod is observed, wherein the curvature radius of the anchor rod is R, and the curvature radius R of the anchor rod can be calculated according to the winding angle θ, the azimuth angle of each sensor and the corresponding measured strain value ε f . Since the cable sensor and the anchor rod are bonded together by the adhesive in the embodiment, the strain monitored by the cable sensor cannot directly replace the strain of the anchor rod itself, and the strain conversion coefficient α under different adhesives can be calculated through experiments.

[0071] In the deformation monitoring of the anchor rod in the indoor simulation test, the adhesive between the coaxial cable and the anchor rod body is epoxy resin, phenolic resin or neoprene adhesive, and in the deformation monitoring of the anchor rod in the engineering surrounding rock support, the adhesive between the coaxial cable and the anchor rod body is polyphosphoric acid aluminum compound or epoxy resin adhesive.

[0072] The anchor rod deformation monitoring structure and the use method, the coaxial cable sensor can withstand larger deformation, and can jointly support the surrounding rock with the anchor rod, can withstand larger tensile stress or shear stress, has a larger sensing range and a wider application range. The anchor rod deformation monitoring structure can effectively monitor the deformation and damage of the anchor rod, the coaxial cable has small transmission loss, and the long-distance transmission can be conveniently realized, which is beneficial to realize intelligent monitoring. The monitoring method has high spatial resolution, the VNA and the computer are interconnected, the online real-time monitoring of the deformation of the anchor rod can be realized, and the anchor rod deformation monitoring structure has the advantages of resisting high-temperature and high-pressure liquid environment, high long-term monitoring stability, long service life and the like.

[0073] 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 person skilled in the art within the essential scope of the present application should also belong to the protection scope of the present application.

Claims

1. A cable sensing based real-time monitoring method for deformation of an anchor rod, using a cable sensing based anchor rod deformation monitoring structure, characterized by, The anchor rod body, the coaxial cable, the joint presser and the terminal load are included, the coaxial cable is bonded with the anchor rod body, the joint presser is arranged in the coaxial cable and the anchor rod bonding section, the coaxial cable has the Fabry-Perot strain sensor, one end of the coaxial cable is connected with the terminal load through the SMA joint connector, the other end is connected with the vector network analyzer through the SMA joint connector after being led out from the anchor rod tray, the joint presser is pressed in the coaxial cable and the anchor rod bonding section, and the characteristic impedance is discontinuous, the Fabry-Perot strain sensor on the coaxial cable monitors the strain of the anchor rod body in real time. The method is used for deformation monitoring of the anchor rod in indoor simulation test or engineering surrounding rock support, and comprises the following steps: Manufacturing the anchor rod: selecting the anchor rod and loading the coaxial cable, arranging the joint presser and the terminal load on the coaxial cable, bonding the coaxial cable and the anchor rod body at one end, applying the pre-tightening force to the other end of the coaxial cable, so that the coaxial cable maintains the positive strain of 0.05%-0.1%, and then bonding the coaxial cable and the anchor rod body along the full length; Installing the anchor rod: drilling the hole in the coal rock mass, the drilling diameter is divided into two sections, the drilling diameter near the drilling hole is slightly larger than that of the other side, which facilitates the coaxial cable to be led out from the drilling hole and avoids the coaxial cable leading-out section from being extruded by the hole wall and the tray during the installation of the anchor rod, then the anchor rod is put into the drilling hole, the full-length anchoring is carried out through the anchoring agent, the anchor rod tray is arranged at the hole mouth, the nut is tightened to apply the pre-stress, the leading-out hole is drilled in the anchor rod tray, and the coaxial cable is led out from the leading-out hole; Monitoring the deformation of the anchor rod: the vector network analyzer monitors the frequency shift of the interference spectrum formed by the Fabry-Perot strain sensor, the frequency shift change rate is the strain generated by the anchor rod section between the two structure reflectors of the Fabry-Perot strain sensor, and the deformation condition and deformation degree of the anchor rod are judged according to the sensor monitoring strain change rule with the azimuth angle under different deformation conditions of the anchor rod.

2. The cable sensing based real-time monitoring method of rock bolt deformation according to claim 1, characterized in that, The coaxial cable comprises an inner conductor, an outer conductor, an insulating layer and a protective layer, the outer layer of the inner conductor is wrapped with the insulating layer, the outer layer of the insulating layer is wrapped with the outer conductor, and the outer layer of the outer conductor is wrapped with the protective layer.

3. The cable sensing based real-time monitoring method of rock bolt deformation according to claim 1, characterized in that, The anchor rod deformation monitoring structure monitors the axial deformation of the anchor rod, and the coaxial cable is arranged along the axial direction of the anchor rod body.

4. The real-time monitoring method of anchor rod deformation based on cable sensing according to claim 3, characterized in that, The coaxial cable is pasted on the surface of the anchor rod body along the axial direction of the anchor rod body.

5. The real-time monitoring method of anchor rod deformation based on cable sensing according to claim 3, characterized in that, The coaxial cable is pasted in the groove along the axial direction of the anchor rod.

6. The cable sensing based real-time monitoring method of rock bolt deformation according to claim 1, characterized in that, The anchor rod deformation monitoring structure monitors the bending deformation of the anchor rod, and the coaxial cable is wound and pasted on the surface of the anchor rod body according to the direction of the wrap angle of 30°.

7. The cable sensing based real-time monitoring method of rock bolt deformation according to claim 1, characterized in that, The Fabry-Perot strain sensor is arranged on the coaxial cable, the sensor is composed of a pair of structure reflectors arranged in the cable, when the radio frequency electromagnetic wave is transmitted into the coaxial cable from one end and transmitted in the coaxial cable, the electromagnetic wave will produce reflected electromagnetic wave at the two structure reflectors, the two reflected electromagnetic waves produce resonance, and the interference spectrum is formed in the frequency domain.

8. The cable sensing based real-time monitoring method of rock bolt deformation according to claim 1, characterized in that, The vector network analyzer monitors the frequency shift of the interference spectrum formed by the Fabry-Perot strain sensor, and the rate of change of the frequency shift is the strain generated by the anchor rod section between the two structure reflectors of the Fabry-Perot strain sensor; the signal source in the vector network analyzer excites to generate an input signal, the input signal passes through the signal separation device, is transmitted to each sensing element along the line, the reflected signal is reflected back to the vector network analyzer at each sensing element, passes through the signal separation device, is transmitted to the receiver, and the receiver tests, compares and analyzes the reflection, transmission and input signal of the measured device to complete the measurement of the change amount.

9. The cable sensing based real-time monitoring method of rock bolt deformation according to claim 1, characterized in that, When the anchor rod is used for deformation monitoring of the anchor rod in indoor simulation test, the adhesive between the coaxial cable and the anchor rod body is epoxy resin, phenolic resin or neoprene adhesive; when the anchor rod is used for deformation monitoring of the anchor rod in engineering surrounding rock support, the adhesive between the coaxial cable and the anchor rod body is polyphosphoric acid compound or epoxy resin glue.

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