Axial force synchronous monitoring system and monitoring method for composite anchor cable

Abstract

The invention discloses an axial force synchronous monitoring system and monitoring method for a composite anchor cable, and the system can synchronously monitor the change of the axial force of an anchor cable center wire and a steel edge wire through two measurement modes in a manner that a fiber grating sensor is arranged in the anchor cable CFRP center wire and a resistance strain gauge is arranged on the steel edge wire, thereby achieving the synchronous monitoring of the axial force of the anchor cable center wire and the steel edge wire. The problem that data of a single axial force measurement mode is not accurate enough is solved, the two measurement modes are carried out independently and do not affect each other, if a single measurement mode breaks down, the other measurement mode is not affected, and the more stable and long-acting anchor cable axial force monitoring requirement can be met; the bridge box and the strain gauges form a temperature compensation circuit through the strain connecting lines, the influence that the resistance of the strain connecting lines changes along with the temperature when the strain gauges are used for monitoring for a long time is effectively eliminated, the bridge box and the ground are connected through the ground wire, the influence of an interference electric field in the strain gauge measurement process is eliminated, and the accuracy of anchor cable axial force measurement data is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of support cable monitoring, and particularly to an axial force synchronous monitoring system and monitoring method for a composite material cable. Background Art

[0002] In foundation pit engineering, as a common support form, cables are often combined with other structures for support, such as: bored cast-in-place piles, Larssen steel sheet piles, PC method piles, slope engineering, etc., to jointly carry out support. The basic stress principle of the cable is that the cable body and the surrounding soil jointly bear the lateral earth pressure through cement bonding, so as to ensure the safety of the foundation pit side wall.

[0003] There are many factors affecting the support effect of the cable, such as: physical and mechanical properties of the soil, foundation pit excavation depth, lengths of the free section and the anchorage section of the cable rod, vertical and horizontal spacings of the cables, ultimate bearing capacity of the cables, construction quality of the cables, etc. To effectively ensure the safety of the underground main structure construction during the foundation pit stage and prevent the failure of the support structure caused by the relaxation of the axial force of the cable rod, it is necessary to regularly monitor the axial force of the cable.

[0004] In recent years, a new type of cable with carbon fiber reinforced plastics (CFRP) as the central wire of the cable has emerged. An optical fiber grating sensor is built into the central wire of the cable. Based on the basic assumption of the coordinated deformation of the central wire and the side wires of the cable, the axial force of the CFRP cable is measured by measuring the wavelength difference of the grating.

[0005] Although this method can accurately measure the axial force at the center of the cable, there are still the following two deficiencies:

[0006] First, the thermal expansion coefficients of different materials are different. When the temperature changes, the deformation of the CFRP central wire and the side wires of the cable will be inconsistent. It is not accurate enough to calculate the stress and strain of the whole cable solely relying on the stress and strain components of the CFRP central wire.

[0007] Second, there are certain deficiencies in the optical fiber grating sensor itself. Especially when measuring the axial force of a single cable for a long time, it is sensitive to both stress and temperature changes, and the changes in temperature and stress will affect the measurement of the axial force of the cable at the same time. Summary of the Invention

[0008] The present invention provides an axial force synchronous monitoring system and monitoring method for a composite material cable, which are used to solve the technical problems that when the temperature changes, the deformation of the CFRP central wire and the side wires of the cable will be inconsistent, resulting in inaccurate calculation of the stress and strain of the whole cable, and the optical fiber grating sensor is sensitive to both stress and temperature changes, and the changes in temperature and stress will affect the measurement of the axial force of the cable at the same time.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] The present invention provides an axial force synchronous monitoring system for a composite material anchor cable, including a foundation pit. Support piles are arranged at intervals on the side wall of the foundation pit, and a capping beam is arranged at the top of the support piles, which is flush with the ground. Drills are arranged at the upper part of the side wall of the foundation pit and at the intervals between the support piles. The drills are inclined downward and extend into the formation.

[0011] A composite stranded wire, a positioning bracket, a strain gauge, and a grouting pipe are arranged in the drill. There are two strands of the composite stranded wire, which are laid along the length direction of the drill. The positioning brackets are arranged at intervals along the length direction of the composite stranded wire for positioning the composite stranded wire. The end of the grouting pipe is arranged at the bottom of the drill and is arranged throughout the length of the drill.

[0012] Each strand of the composite stranded wire includes a CFRP center wire and steel side wires twisted on the outer side of the CFRP center wire. A strain gauge is arranged in the middle or at the end of the steel side wire. The strain gauges are connected through strain connecting wires, and the strain connecting wires are fixedly connected to the composite stranded wire. The strain connecting wires extend towards the drill outlet and are connected to a strain gauge, which is used to measure the stress of the steel side wire in a single composite stranded wire. The CFRP center wire is provided with a fiber Bragg grating sensor, which is connected to a fiber optic sensing data line. The fiber optic sensing data line is connected to a demodulator, which is used to measure the stress of the CFRP center wire in a single composite stranded wire. An anchoring device is arranged at the mouth of the drill, and the strain connecting wire, the demodulation connecting wire, and the grouting pipe pass through the anchoring device.

[0013] Preferably, the positioning bracket includes a cylinder body and wedge-shaped dividing wings arranged at intervals on the outer side of the cylinder body. The center line of the cylinder body coincides with the center line of the drill. The composite stranded wire and the strain connecting wire are arranged between two adjacent wedge-shaped dividing wings, and the grouting pipe is inserted into the cylinder body.

[0014] Preferably, it further includes a data processing center. The data processing center uses two interfaces. One interface is electrically connected to the demodulator through a demodulation signal line, and the other interface is electrically connected to the strain gauge through a strain signal line.

[0015] Preferably, it further includes a bridge box. The bridge box uses three interfaces. One interface is electrically connected to the strain connecting wire, one interface is connected to the strain gauge through a bridge box signal line, and the remaining interface is provided with a grounding wire connected to the ground.

[0016] Preferably, the inside of the bridge box is a resistance circuit, and the outside is a terminal structure. The strain gauge and the bridge box form a temperature compensation circuit through the strain connecting wire.

[0017] Preferably, the strain gauge is fixedly bonded to the steel side wire through epoxy resin, and the strain connecting wire is fixedly tied to the composite stranded wire through lead wires. The lead wires are arranged at intervals in the length direction of the strain connecting wire or the composite stranded wire.

[0018] Preferably, the strain gauge internally includes a strain main control module, a strain data storage module, a strain acquisition module, a strain data transmission module, and a strain warning module; the strain main control module is electrically connected to the strain data transmission module, the strain warning module, the strain data storage module, and the strain acquisition module respectively, and the strain data transmission module is electrically connected to the data processing center.

[0019] Preferably, the demodulator internally includes an optical fiber main control module, an optical fiber data storage module, an optical fiber acquisition module, an optical fiber data transmission module, and an optical fiber warning module; the optical fiber main control module is electrically connected to the optical fiber data transmission module, the optical fiber warning module, the optical fiber data storage module, and the optical fiber acquisition module respectively; the optical fiber data transmission module of the demodulator is electrically connected to the data processing center.

[0020] The present invention also provides a method for synchronously monitoring the axial force of a composite material anchor cable, including the following steps:

[0021] Step 1, arranging the devices in the borehole: Drilling a borehole, terminating the hole formation when reaching the predetermined position of the formation, installing the strain gauge on the surface of the steel side wire of the composite stranded wire, firmly binding the strain connecting wire and the composite stranded wire and placing them together on the positioning bracket, arranging the spacing of the positioning brackets so that the composite stranded wire and the strain connecting wire are flat in the borehole;

[0022] Step 2, grouting: Aligning the center of the grouting pipe with the center of the positioning bracket and inserting it so that the bottom of the grouting pipe is flush with the bottom of the borehole, using the grouting equipment to grout the borehole with cement slurry from the inlet of the grouting pipe until the slurry reaches the designed length of the composite stranded wire;

[0023] Step 3, anchor cable tensioning: When the strength of the consolidated body reaches 75% of the designed strength, use a hydraulic jack to tension all the composite stranded wires in a single borehole according to the designed prestress value, and use an anchoring device to lock the composite stranded wires at the mouth of the borehole, passing the strain connecting wire and the composite stranded wire through the anchoring device and leaving a certain length;

[0024] Step 4, installing the devices outside the borehole: Connecting the strain gauge and the bridge box with the strain connecting wire, connecting the bridge box and the strain gauge with the bridge box signal wire, grounding the bridge box, connecting the strain gauge and the data processing center with the strain signal wire, peeling the CFRP center wire of the composite stranded wire at the mouth of the borehole to expose the fiber Bragg grating sensor, connecting the fiber Bragg grating sensor with the demodulator, and connecting the demodulator and the data processing center with the demodulation signal wire;

[0025] Step 5, axial force monitoring: including the following two monitoring methods,

[0026] 1) When the stress of the composite stranded wire changes, the resistance value in the strain gauge of the steel side wire changes. At this time, according to the formula Calculate the stress change data of the steel edge wire of the composite stranded wire; where ΔR is the change in the resistance value of the strain gauge, R is the resistance value of the strain gauge, K1 is the fixed proportional constant of the strain gauge, ΔF is the stress change of the steel edge wire of the composite stranded wire, E is the elastic modulus of the steel edge wire, and A is the cross-sectional area of ​​the steel edge wire;

[0027] 2) When the stress of the composite strand changes, the refractive index of the fiber Bragg grating sensor in the CFRP center wire changes. At this time, according to the formula Calculate the stress change data of the CFRP center wire of the composite stranded wire; where Δλ is the change in the central wavelength of the grating, λ is the central wavelength of the grating, K2 is the grating strain sensitivity coefficient, ΔF is the stress change in the central wire of the composite stranded wire, E is the elastic modulus of the central wire of the CFRP, and A is the cross-sectional area of ​​the central wire of the CFRP.

[0028] Preferably, when the stress change of the steel edge wire exceeds 20% of the prestressed design value, the strain gauge activates the strain warning module; when the stress change of the CFRP center wire exceeds 20% of the prestressed design value, the demodulator activates the optical fiber warning module; when the strain gauge and the demodulator both issue warnings at the same time, the data processing center sends a warning signal to the staff, and the staff quickly performs emergency processing on the warning position and the warning device and cancels the equipment warning signal; when only one of the strain gauge and the demodulator issues a warning, the data processing center sends a notification signal to the staff, and the staff inspects and maintains the warning position and the warning device and cancels the warning signal; when neither the strain gauge nor the demodulator issues a warning, the staff regularly monitors the axial force of the composite anchor cable through the data processing center to ensure the safety of the construction site.

[0029] The beneficial effects of the present invention are embodied in:

[0030] 1) The present invention provides a synchronous axial force monitoring system and method for composite anchor cables. By setting a fiber grating sensor in the CFRP center wire of the anchor cable and setting a resistance strain gauge in the steel side wire, the two measurement methods can synchronously monitor the changes in the axial force of the center wire and the steel side wire of the anchor cable, solving the problem that the data of a single axial force measurement method is not accurate enough. The two measurement methods are performed separately without affecting each other. If a single measurement method fails, the other measurement method is not affected, which can meet the needs of more stable and long-term anchor cable axial force monitoring. At the same time, the monitoring system uses two measurement methods to simultaneously obtain the axial force data of different side wires of the anchor cable, so as to analyze the force mechanism of the anchor cable from multiple angles and more comprehensively.

[0031] 2) The present invention provides an axial force synchronous monitoring system and monitoring method for a composite material anchor cable. A temperature compensation circuit is formed by connecting a bridge box and strain gauges with strain connecting wires, effectively eliminating the influence of the resistance value of the strain connecting wires changing with temperature during long-term monitoring using strain gauges. The bridge box is connected to the ground with a ground wire, eliminating the influence of the interfering electric field during the measurement of the strain gauges, and ensuring the accuracy of the measured data of the anchor cable axial force;

[0032] 3) The present invention provides an axial force synchronous monitoring system and monitoring method for a composite material anchor cable. A strain warning module is built into the strain gauge, and an optical fiber warning module is built into the demodulator. When the axial force of the composite stranded wire exceeds the warning value, the strain gauge and the demodulator can give warnings separately, complementing each other and not affecting each other, realizing synchronous warning of the two monitoring methods, and effectively ensuring the safety and stability of the foundation pit project.

[0033] Other features and advantages of the present invention will be described in the following specification, and will be partly obvious from the specification, or will be understood by implementing the present invention; the main purpose and other advantages of the present invention can be achieved and obtained through the solutions specifically pointed out in the specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of the monitoring system of the present invention.

[0035] Figure 2 is Figure 1 the sectional view taken along A - A' in

[0036] Figure 3 is Figure 1 the partial enlarged view at B in

[0037] Figure 4 is a schematic diagram of the pasting positions of the resistance strain gauges of the present invention.

[0038] Figure 5 is a schematic cross-sectional view of the composite stranded wire of the present invention.

[0039] Figure 6 is a schematic diagram of the module connection relationship of the strain gauge of the present invention.

[0040] Figure 7 is a schematic diagram of the module connection relationship of the demodulator of the present invention.

[0041] Reference numerals: 1 - drilling hole, 2 - composite stranded wire, 21 - CFRP center wire, 22 - steel side wire, 23 - fiber Bragg grating sensor, 3 - grouting pipe, 4 - anchoring device, 5 - positioning bracket, 51 - cylinder, 52 - wedge-shaped dividing wing, 6 - strain gauge, 7 - strain connecting wire, 8 - lead wire, 9 - bridge box, 10 - bridge box signal wire, 11 - ground wire, 12 - strain gauge, 13 - strain signal wire, 14 - fiber optic sensing data wire, 15 - demodulator, 16 - demodulation signal wire, 17 - data processing center, 18 - capping beam, 19 - retaining pile. Specific implementation mode

[0042] The technical solution of the present invention will be described in detail below through embodiments. The following embodiments are merely exemplary and can only be used to explain and illustrate the technical solution of the present invention, rather than being construed as a limitation to the technical solution of the present invention.

[0043] Embodiment. In this embodiment, a certain foundation pit support project is taken as an example. The plot belongs to the alluvial-proluvial plain landform, with a flat terrain. The proposed site was originally farmland and forest land, and is now an empty land after site leveling. The foundation pit adopts the support form of retaining piles + anchor cables. In this embodiment, the traditional steel anchor cables are successfully and effectively replaced by the new composite material self-sensing anchor cable system. Not only the anchoring effect of the anchor fittings reaches the expectation and the connectors are firmly connected, but also the foundation pit deformation is well controlled by using the composite material anchor cable synchronous monitoring system and monitoring method. According to the information obtained from the composite stranded wire, in the first and second stages, this set of connection and anchoring system functions stably and successfully reaches the required tension, meeting the engineering expectations. On this basis, since the composite material anchor cable is lighter in weight than the traditional anchor cable, the transportation cost is reduced to a certain extent, and the labor intensity of workers is reduced. At the same time, the use of the composite stranded wire makes the tensile force visible, greatly improving the construction accuracy, reducing the cost of foundation pit monitoring and effectively ensuring the safety of the foundation pit project.

[0044] Referring to Figures 1-5 , the present invention provides an axial force synchronous monitoring system for a composite material anchor cable, including a foundation pit. Retaining piles 19 are arranged at intervals on the side wall of the foundation pit. A capping beam 18 is arranged at the top of the retaining piles 19, and the capping beam 18 is flush with the ground; a drilling hole 1 is arranged at the upper part of the side wall of the foundation pit and at the interval of the retaining piles 19, and the drilling hole 1 slopes downward and extends into the formation;

[0045] A composite stranded wire 2, a positioning bracket 5, a strain gauge 6, and a grouting pipe 3 are arranged in the drilling hole 1; there are two strands of the composite stranded wire 2, which are laid along the length direction of the drilling hole 1. The positioning brackets 5 are arranged at intervals along the length direction of the composite stranded wire 2 for positioning the composite stranded wire 2; the end of the grouting pipe 3 is arranged at the bottom of the drilling hole 1 and is arranged throughout the drilling hole 1;

[0046] Each composite strand 2 includes a CFRP central wire 21 and steel edge wires 22 twisted and arranged on the outer side of the CFRP central wire 21; a strain gauge 6 is arranged in the middle or at the end of the steel edge wire 22, and the strain gauge 6 is adhesively fixed to the steel edge wire 22 through epoxy resin. The strain gauge 6 is connected through a strain connecting wire 7, and the strain connecting wire 7 is fixedly bound to the composite strand 2 through a lead wire 8. The lead wires 8 are arranged at intervals in the length direction of the strain connecting wire 7 or the composite strand 2. The strain connecting wire 7 extends towards the outlet of the drilling hole 1 and is connected with a strain gauge 12 arranged thereon. The strain gauge 12 is used to measure the stress of the steel edge wire 22 in a single composite strand 2; the CFRP central wire 21 is provided with a fiber Bragg grating sensor 23, the fiber Bragg grating sensor 23 is connected with a fiber optic sensing data line 14, and the fiber optic sensing data line 14 is connected with a demodulator 15. The demodulator 15 is used to measure the stress of the CFRP central wire 21 in a single composite strand 2; an anchoring device 4 is arranged at the opening of the drilling hole 1. The strain connecting wire 7, a demodulation connecting wire and a grouting pipe 3 pass through the anchoring device 4, and the grouting pipe 3 is a PVC pipe.

[0047] It further includes a data processing center 17. The data processing center 17 uses two interfaces. One interface is electrically connected with the demodulator 15 through a demodulation signal wire 16, and the other interface is electrically connected with the strain gauge 12 through a strain signal wire 13. It further includes a bridge box 9. The bridge box 9 uses three interfaces. One interface is electrically connected with the strain connecting wire 7, one interface is connected with the strain gauge 12 through a bridge box signal wire 10, and the remaining one interface is provided with a grounding wire 11 connected to the ground. The inside of the bridge box 9 is a resistance circuit, and the outside is a terminal structure. The strain gauge 6 and the bridge box 9 form a temperature compensation circuit through the strain connecting wire 7.

[0048] Refer to Figure 2 , the positioning bracket 5 includes a cylinder body 51 and wedge-shaped dividing wings 52 arranged at intervals on the outer side of the cylinder body 51. The center line of the cylinder body 51 coincides with the center line of the drilling hole 1; the composite strand 2 and the strain connecting wire 7 are arranged between two adjacent wedge-shaped dividing wings 52, so that the composite strand 2 reaches a predetermined position in the drilling hole 1 and is better stressed, and the grouting pipe 3 is inserted into the cylinder body 51.

[0049] Refer to Figure 6 , the strain gauge 12 internally includes a strain main control module, a strain data storage module, a strain acquisition module, a strain data transmission module, and a strain warning module; the strain main control module is electrically connected to the strain data transmission module, the strain warning module, the strain data storage module, and the strain acquisition module respectively, and the strain data transmission module is electrically connected to the data processing center 17.

[0050] Refer to Figure 7, inside the demodulator 15, there are a fiber optic main control module, a fiber optic data storage module, a fiber optic acquisition module, a fiber optic data transmission module, and a fiber optic warning module; the fiber optic main control module is electrically connected to the fiber optic data transmission module, the fiber optic warning module, the fiber optic data storage module, and the fiber optic acquisition module respectively; the fiber optic data transmission module of the demodulator 15 is electrically connected to the data processing center 17.

[0051] The present invention also provides a method for synchronously monitoring the axial force of a composite material anchor cable, which includes the following steps:

[0052] Step 1, arranging the devices in the borehole 1: Drill the borehole 1. The borehole 1 starts to drill between the retaining piles 19 at a certain inclination angle and terminates when reaching the predetermined position of the formation. On the ground, grind the steel side wire 22 at the stress measurement position in the middle or at the bottom of the composite strand 2 to be flat, paste it on the surface of the steel side wire 22, and fix the other side firmly with epoxy resin. Tie the strain connection wire 7 and the composite strand 2 firmly with wire 8 and place them on the positioning bracket 5 together. Arrange the positioning brackets 5 at a certain interval so that the composite strand 2 and the strain connection wire 7 are flat in the borehole 1;

[0053] Step 2, grouting: Align the center of the grouting pipe 3 with the center of the positioning bracket 5 and insert it so that the bottom of the grouting pipe 3 is flush with the bottom of the borehole 1. Use the grouting equipment to grout the borehole 1 with cement slurry from the inlet of the grouting pipe 3 until the slurry reaches the designed length of the composite strand 2;

[0054] Step 3, anchor cable tensioning: When the strength of the consolidation body reaches 75% of the designed strength, use a hydraulic jack to tension all the composite strands 2 in a single borehole 1 according to the designed prestress value, and use the anchoring device 4 to lock the composite strands 2 at the mouth of the borehole 1. Pass the strain connection wire 7 and the composite strand 2 through the anchoring device 4 and reserve a certain length;

[0055] Step 4, installing the devices outside the borehole 1: Connect the strain gauge 6 and the bridge box 9 with the strain connection wire 7, connect the bridge box 9 and the strain gauge 12 with the bridge box signal wire 10, ground the bridge box 9, connect the strain gauge 12 and the data processing center 17 with the strain signal wire 13, strip the CFRP center wire 21 of the composite strand 2 at the mouth of the borehole 1 to expose the fiber Bragg grating sensor 23, connect the fiber Bragg grating sensor 23 with the demodulator 15, and connect the demodulator 15 and the data processing center 17 with the demodulation signal wire 16;

[0056] Step 5, axial force monitoring: It includes the following two monitoring methods,

[0057] 1) When the stress of the composite strand 2 changes, the resistance value in the strain gauge 6 of the steel side wire 22 changes. At this time, according to the formula Calculate the stress variation data of the steel edge wire 22 of the composite stranded wire 2; wherein ΔR is the variation of the resistance value of the strain gauge 6, R is the resistance value of the strain gauge 6, K1 is the fixed proportional constant of the strain gauge 6, ΔF is the stress variation of the steel edge wire 22 of the composite stranded wire 2, E is the elastic modulus of the steel edge wire 22, and A is the cross-sectional area of ​​the steel edge wire 22;

[0058] 2) When the stress of the composite strand 2 changes, the refractive index of the fiber grating sensor 23 in the CFRP center wire 21 changes. At this time, according to the formula Calculate the stress change data of the CFRP center wire 21 of the composite strand 2; wherein, Δλ is the change in the grating center wavelength, λ is the grating center wavelength, K2 is the grating strain sensitivity coefficient, ΔF is the stress change in the CFRP center wire 21 of the composite strand 2, E is the elastic modulus of the CFRP center wire 21, and A is the cross-sectional area of ​​the CFRP center wire 21.

[0059] Furthermore, when the stress change of the steel edge wire 22 exceeds 20% of the prestressed design value, the strain gauge 12 activates the strain warning module; when the stress change of the CFRP center wire 21 exceeds 20% of the prestressed design value, the demodulator 15 activates the optical fiber warning module; when the strain gauge 12 and the demodulator 15 both issue warnings at the same time, the data processing center 17 sends a warning signal to the staff, and the staff quickly performs emergency processing on the warning position and the warning equipment and cancels the equipment warning signal; when only one of the strain gauge 12 and the demodulator 15 issues a warning, the data processing center 17 sends a notification signal to the staff, and the staff inspects and maintains the warning position and the warning equipment and cancels the warning signal; when neither the strain gauge 12 nor the demodulator 15 issues a warning, the staff regularly monitors the axial force of the composite anchor cable through the data processing center 17 to ensure the safety of the construction site.

[0060] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that a technician familiar with the technical field can think of within the technical scope disclosed in the present invention should be covered within the protection scope of the present invention.

Claims

1. An axial force synchronous monitoring system for a composite material anchor cable, characterized in that, It includes a foundation pit, with retaining piles (19) arranged at intervals on the side wall of the foundation pit. A capping beam (18) is provided at the top of the retaining piles (19), and the capping beam (18) is flush with the ground. Drilling holes (1) are provided at the upper part of the side wall of the foundation pit and at the intervals between the retaining piles (19). The drilling holes (1) are inclined downward and extend into the formation. A composite stranded wire (2), a positioning bracket (5), a strain gauge (6), and a grouting pipe (3) are arranged in the drilling hole (1). The composite stranded wire (2) has two strands and is laid along the length direction of the drilling hole (1). The positioning brackets (5) are arranged at intervals along the length direction of the composite stranded wire (2) for positioning the composite stranded wire (2). The end of the grouting pipe (3) is arranged at the bottom of the drilling hole (1) and is arranged throughout the length of the drilling hole (1). Each strand of the composite stranded wire (2) includes a CFRP center wire (21) and steel side wires (22) twisted on the outer side of the CFRP center wire (21). A strain gauge (6) is arranged at the middle or end of the steel side wire (22). The strain gauges (6) are connected by strain connecting wires (7). The strain connecting wires (7) are fixedly connected to the composite stranded wire (2). The strain connecting wires (7) extend towards the outlet of the drilling hole (1) and are connected to a strain gauge (12). The strain gauge (12) is used to measure the stress of the steel side wire (22) in a single composite stranded wire (2). The CFRP center wire (21) is provided with a fiber Bragg grating sensor (23). The fiber Bragg grating sensor (23) is connected to a fiber optic sensing data line (14). The fiber optic sensing data line (14) is connected to a demodulator (15). The demodulator (15) is used to measure the stress of the CFRP center wire (21) in a single composite stranded wire (2). An anchoring device (4) is provided at the mouth of the drilling hole (1). The strain connecting wire (7), the demodulation connecting wire, and the grouting pipe (3) pass through the anchoring device (4).

2. The axial force synchronous monitoring system of a composite material anchor cable according to claim 1, characterized in that, The positioning bracket (5) includes a cylinder body (51) and wedge-shaped dividing wings (52) arranged at intervals on the outer side of the cylinder body (51). The center line of the cylinder body (51) coincides with the center line of the drilling hole (1). The composite stranded wire (2) and the strain connecting wire (7) are arranged between two adjacent wedge-shaped dividing wings (52). The grouting pipe (3) is inserted into the cylinder body (51).

3. The axial force synchronous monitoring system for a composite material anchor cable according to claim 1, characterized in that It further includes a data processing center (17). The data processing center (17) uses two interfaces. One interface is electrically connected to the demodulator (15) through a demodulation signal line (16), and the other interface is electrically connected to the strain gauge (12) through a strain signal line (13).

4. The axial force synchronous monitoring system for a composite material anchor cable according to claim 3, characterized in that, It further includes a bridge box (9). The bridge box (9) uses three interfaces. One interface is electrically connected to the strain connecting wire (7), one interface is connected to the strain gauge (12) through a bridge box signal line (10), and the remaining interface is provided with a grounding wire (11) connected to the ground.

5. The axial force synchronous monitoring system of a composite material anchor cable according to claim 4, characterized in that The interior of the bridge box (9) is a resistance circuit, and the exterior is a terminal structure. The strain gauge (6) and the bridge box (9) form a temperature compensation circuit through the strain connecting wire (7).

6. The axial force synchronous monitoring system of a composite material anchor cable according to claim 1, characterized in that, The strain gauge (6) is fixedly bonded to the steel edge wire (22) with epoxy resin. The strain connection wire (7) is fixedly tied to the composite stranded wire (2) with a lead wire (8). The lead wires (8) are arranged at intervals in the length direction of the strain connection wire (7) or the composite stranded wire (2).

7. The axial force synchronous monitoring system for a composite material anchor cable according to claim 5, characterized in that, The strain gauge (12) internally includes a strain main control module, a strain data storage module, a strain acquisition module, a strain data transmission module, and a strain warning module. The strain main control module is electrically connected to the strain data transmission module, the strain warning module, the strain data storage module, and the strain acquisition module respectively. The strain data transmission module is electrically connected to the data processing center (17).

8. The axial force synchronous monitoring system of a composite material anchor cable according to claim 7, characterized in that The demodulator (15) internally includes an optical fiber main control module, an optical fiber data storage module, an optical fiber acquisition module, an optical fiber data transmission module, and an optical fiber warning module. The optical fiber main control module is electrically connected to the optical fiber data transmission module, the optical fiber warning module, the optical fiber data storage module, and the optical fiber acquisition module respectively. The optical fiber data transmission module of the demodulator (15) is electrically connected to the data processing center (17).

9. The axial force synchronous monitoring method of a composite material anchor cable according to claim 8, characterized in that, It includes the following steps: Step 1: Install the devices in the borehole (1). Drill the borehole (1), stop drilling when reaching the predetermined formation position. Install the strain gauge (6) on the surface of the steel edge wire (22) of the composite stranded wire (2). Tie the strain connection wire (7) and the composite stranded wire (2) firmly and place them together on the positioning bracket (5). Arrange the positioning brackets (5) at intervals so that the composite stranded wire (2) and the strain connection wire (7) are flat in the borehole (1). Step 2: Grouting. Align the center of the grouting pipe (3) with the center of the positioning bracket (5) and insert it so that the bottom of the grouting pipe (3) is flush with the bottom of the borehole (1). Use the grouting equipment to grout the borehole (1) with cement slurry from the inlet of the grouting pipe (3) until the slurry reaches the designed length of the composite stranded wire (2). Step 3: Anchor cable tensioning. When the strength of the consolidated body reaches 75% of the designed strength, use a hydraulic jack to tension all the composite stranded wires (2) in a single borehole (1) according to the designed prestress value, and use the anchoring device (4) to lock the composite stranded wire (2) at the mouth of the borehole (1). Pass the strain connection wire (7) and the composite stranded wire (2) through the anchoring device (4) and leave a certain length. Step 4: Install the devices outside the borehole (1). Connect the strain gauge (6) and the bridge box (9) with the strain connection wire (7), connect the bridge box (9) and the strain gauge (12) with the bridge box signal wire (10), ground the bridge box (9), connect the strain gauge (12) and the data processing center (17) with the strain signal wire (13), strip the CFRP center wire (21) of the composite stranded wire (2) at the mouth of the borehole (1) to expose the fiber Bragg grating sensor (23), connect the fiber Bragg grating sensor (23) with the demodulator (15), and connect the demodulator (15) and the data processing center (17) with the demodulation signal wire (16). Step 5: Axial force monitoring. It includes the following two monitoring methods, 1) When the stress of the composite stranded wire (2) changes, the resistance value in the strain gauge (6) of the steel edge wire (22) changes. At this time, according to the formula Calculate the stress change data of the steel edge wire (22) of the composite stranded wire (2); where, ΔR is the change in the resistance value of the strain gauge (6), R is the resistance value of the strain gauge (6), K1 is the fixed proportionality constant of the strain gauge (6), ΔF is the stress change of the steel edge wire (22) of the composite stranded wire (2), E is the elastic modulus of the steel edge wire (22), and A is the cross-sectional area of the steel edge wire (22); 2) When the stress of the composite stranded wire (2) changes, the refractive index of the fiber Bragg grating sensor (23) in the CFRP central wire (21) changes. At this time, according to the formula Calculate the stress change data of the CFRP central wire (21) of the composite stranded wire (2); where, Δλ is the change in the grating center wavelength, λ is the grating center wavelength, K2 is the grating strain sensitivity coefficient, ΔF is the stress change of the CFRP central wire (21) of the composite stranded wire (2), E is the elastic modulus of the CFRP central wire (21), and A is the cross-sectional area of the CFRP central wire (21).

10. The axial force synchronous monitoring method of a composite material anchor cable according to claim 9, characterized in that, When the stress variation of the steel edge wire (22) exceeds 20% of the prestress design value, the strain gauge (12) activates the strain warning module; when the stress variation of the CFRP center wire (21) exceeds 20% of the prestress design value, the demodulator (15) activates the optical fiber warning module; When the strain gauge (12) and the demodulator (15) both give warnings at the same time, the data processing center (17) sends a warning signal to the staff, and the staff quickly performs emergency processing on the warning location and the warning device and cancels the device warning signal; When only one of the strain gauge (12) and the demodulator (15) generates an early warning, the data processing center (17) sends a notification signal to the staff, who then inspects and maintains the early warning location and the early warning device and cancels the early warning signal; When neither the strain gauge (12) nor the demodulator (15) issues an early warning, the staff regularly monitors the axial force of the composite anchor cable through the data processing center (17) to ensure the safety of the construction site.

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