Intelligent piezoelectric film hollow grouting anchor rod dynamic strain monitoring device and application thereof in underground engineering

Abstract

The invention discloses an intelligent piezoelectric film hollow grouting anchor rod dynamic strain monitoring device and application thereof in underground engineering, and relates to the technical field of geotechnical engineering anchor rod monitoring. The main anchor rod system comprises a hollow inner steel pipe, a hollow anchor rod body arranged on the hollow inner steel pipe in a sleeving mode, a cavity formed between the hollow inner steel pipe and the hollow anchor rod body, a rubber ring and an external steel ring, and the rubber ring and the external steel ring are located at the two ends of the hollow anchor rod body and located in the cavity. According to the intelligent piezoelectric film hollow grouting anchor rod strain monitoring device provided by the invention, the distributed piezoelectric film is pasted in the hollow anchor rod body along the axial direction of the anchor rod, and the hollow steel pipe is arranged in the hollow anchor rod body, so that the basic performance of the hollow grouting anchor rod is reserved; and comprehensive real-time monitoring of dynamic strain generated by the anchor rod under high and low frequency vibration, instantaneous impact and cyclic loading is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of anchor monitoring in geotechnical engineering, and in particular relates to an intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device and its application in underground engineering. Background Art

[0002] As an important support method, anchor rods are widely used in geotechnical engineering fields such as underground engineering, coal mines, and road slopes. Common anchor rods include solid anchor rods and hollow grouting anchor rods. Although the solid anchor rod has a simple structure, there is a problem of mortar loss during construction, which affects the grouting effect. In contrast, the hollow grouting anchor rod has the function of a grouting pipe through its unique hollow design. It not only realizes pressure grouting, can better fill cracks and consolidate rock and soil, but also the hollow structure inside the anchor rod reduces the weight of the anchor rod body. In addition, the stiffness and shear strength of the hollow anchor rod body have also been significantly improved. However, in underground engineering, due to the strong dynamic effects caused by drilling and blasting construction and large-scale mechanical excavation, the anchor rod is often subjected to strong vibration, fault dislocation, explosion impact and cyclic loading and other multi-mode dynamic loads. These effects will cause significant dynamic strains in the anchor rod, including high and low frequency vibrations, transient impact and cyclic loading, which will have a serious impact on the mechanical properties of the anchor rod. Long-term strong dynamic action may cause fatigue accumulation damage, plastic deformation or even fracture failure of anchor rods, posing a major threat to the overall structural stability and safety of underground projects. Therefore, real-time monitoring of the stress state of anchor rods under dynamic strain is crucial for safety assessment and early warning of underground projects.

[0003] In underground engineering, traditional anchor strain monitoring methods mainly use resistance strain gauges and fiber Bragg grating sensors, but these technologies have limited effect on dynamic strain monitoring under strong dynamic forces. Resistance strain gauges have low sensitivity to high-frequency dynamic loads and transient impact responses, and are easily damaged in humid and high-vibration underground engineering environments; although fiber Bragg grating sensors can monitor dynamic strain, they are complex to install and costly, and signal acquisition requires high environmental stability.

[0004] In summary, a new type of anchor monitoring technology is needed to solve the above problems. It can accurately, in real time and continuously monitor the dynamic strain on the anchor section while reducing costs and environmental interference, so as to timely grasp the changes in anchor force and evaluate the stability of the support structure and engineering safety. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide an intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device and its application in underground engineering, and solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0007] An intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device, comprising:

[0008] The main anchor system includes a hollow inner steel pipe, a hollow anchor body sleeved on the hollow inner steel pipe, a cavity arranged between the hollow inner steel pipe and the hollow anchor body, and rubber rings and an external steel ring located at both ends of the hollow anchor body and in the cavity;

[0009] Piezoelectric film system, the piezoelectric film system includes a distributed piezoelectric film sensor, a charge amplifier and a storage oscilloscope coordinated with the main anchor system, the distributed piezoelectric film sensor includes a piezoelectric film, electrodes located on both sides of the piezoelectric film, a crimping terminal arranged on one side of the electrode, an electrode lead arranged at one end of the crimping terminal, and a piezoelectric film protective layer sleeved on the piezoelectric film and the two electrodes;

[0010] A connecting element, the connecting element comprising an adhesive applied to the inner surface of the hollow anchor body, a coating material 1 applied to the distributed piezoelectric film sensor, and a coating material 2 applied to the coating material 1;

[0011] The grouting stop system includes a grouting stop plug arranged at one end of the hollow anchor rod body, a pad arranged on the hollow anchor rod body, a nut threadedly engaged on the hollow anchor rod body, and a gasket ring 1 and a gasket ring 2 sleeved on the hollow anchor rod body, wherein the gasket ring 1 is located between the grouting stop plug and the pad, and the gasket ring 2 is located between the pad and the nut.

[0012] Optionally, the outer wall of the hollow anchor rod is provided with threads, and a notch is provided on one of the external steel rings.

[0013] Optionally, the diameter of the hollow anchor body is 25-32mm, the thickness is 3-7mm, the diameter of the hollow inner steel tube is 23-30mm, the thickness is 1-2mm, the length of the rubber ring is 18-22mm, the thickness is 1-3mm, the hollow inner steel tube is the same length as the hollow anchor body, and the outer ring diameter and inner ring diameter of the external steel ring are consistent with the hollow anchor body and the hollow inner steel tube respectively.

[0014] Optionally, the piezoelectric film is a PVDF piezoelectric film, the thickness of the PVDF piezoelectric film is 30 μm-240 μm, the piezoelectric film protective layer is a polyvinyl fluoride protective layer, the electrode lead is a 28AWG wire, and the two electrodes are a positive electrode and a negative electrode respectively.

[0015] Optionally, the adhesive is KH502 adhesive with a fast curing speed, and the coating thickness of the adhesive is 25-35 μm.

[0016] Optionally, the coating material 1 is J133 material with a thickness of 1-5 mm.

[0017] Optionally, the second coating material is glass glue.

[0018] Optionally, an exhaust hole is provided on the slurry stopper.

[0019] An application of an intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device in underground engineering includes the following steps:

[0020] Step 1: pre-assemble the piezoelectric film hollow grouting anchor rod;

[0021] Step 2: Drill holes on the rock mass to be supported, insert the assembled piezoelectric film hollow grouting anchor into the hole, and inject grout; the injection pressure is in the range of 0.3-1.0 MPa, and the injection starts from the bottom of the hole and proceeds upward layer by layer to prevent the formation of voids;

[0022] Step 3: After the grouting is completed and solidified, the lead wire of the piezoelectric film sensor in the piezoelectric film hollow grouting anchor is led out of the tail end of the anchor, connected to the charge amplifier and storage oscilloscope, and data analysis is performed.

[0023] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art. Of course, any product implementing the present invention does not necessarily need to achieve all the advantages described below at the same time:

[0024] 1. The intelligent piezoelectric film hollow grouting anchor strain monitoring device provided by the present invention not only retains the basic performance of the hollow grouting anchor, but also realizes comprehensive real-time monitoring of the dynamic strain generated by the anchor due to high and low frequency vibrations, instantaneous impact and cyclic loading, by pasting a distributed piezoelectric film in the hollow anchor body along the anchor axial direction and embedding a hollow steel pipe therein. Unlike traditional static monitoring methods, the piezoelectric film can quickly respond to changes in the anchor force, accurately capture the dynamic strain caused by vibration, impact and cyclic loads, and reflect the stress state of the anchor during the construction process in real time.

[0025] 2. Piezoelectric film has the characteristics of high sensitivity and rapid response, and can capture the tiny dynamic changes of anchor rods when subjected to strong dynamic forces such as drilling and blasting or mechanical extrusion, thereby significantly improving the accuracy and real-time performance of monitoring data; at the same time, piezoelectric film sensors are easy to install and low in cost, which is conducive to their promotion and application in large-scale underground projects; the monitoring device can help engineers evaluate the force changes of anchor rods in complex dynamic environments in real time, accurately understand the deformation and stress state of anchor rods, and timely optimize support plans to ensure the safety and stability of underground projects.

[0026] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described below are only some embodiments. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0028] In the figure:

[0029] Figure 1 It is a schematic diagram of the anchor rod device in the present invention;

[0030] Figure 2 It is a schematic diagram of the grouting stopping system of the anchor device in the present invention;

[0031] Figure 3 is a cross-sectional view of the anchor device in the present invention;

[0032] Figure 4 for Figure 3 A schematic diagram of the enlarged structure at A in the middle;

[0033] Figure 5 for Figure 3 Section 1-1;

[0034] Figure 6 This is a schematic diagram of the external steel ring and rubber ring of the anchor device in the present invention;

[0035] Figure 7 A top view of the package of the distributed piezoelectric film in the present invention;

[0036] Figure 8 It is a side view of the package of the distributed piezoelectric film in the present invention;

[0037] Fig. 9 This is a schematic diagram of the piezoelectric effect principle of the piezoelectric film sensor in the present invention;

[0038] Fig.10 It is a schematic diagram of a specific embodiment of the present invention.

[0039] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0040] In the figure: 1-main anchor system, 2-piezoelectric film system, 3-connecting element, 4-grouting system, 11-hollow anchor body, 12-hollow inner steel pipe, 13-rubber ring, 14-external steel ring, 21-distributed piezoelectric film sensor, 22-charge amplifier, 23-storage oscilloscope, 211-piezoelectric film, 212-piezoelectric film protective layer, 213-electrode, 214-crimping terminal, 215-electrode lead, 31-adhesive, 32-coating material one, 33-coating material two, 41-grouting plug, 42-gasket, 43-nut, 44-gasket one, 45-gasket two.

[0041] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0042] The present invention will now be described in further detail with reference to the accompanying drawings.

[0043] Example 1: Please refer to Figure 1-10 As shown, in this embodiment, an intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device is provided, comprising:

[0044] The main anchor system 1 comprises a hollow inner steel tube 12, a hollow anchor body 11 sleeved on the hollow inner steel tube 12, a cavity arranged between the hollow inner steel tube 12 and the hollow anchor body 11, a rubber ring 13 and an external steel ring 14 located at both ends of the hollow anchor body 11 and in the cavity;

[0045] The piezoelectric film system 2 includes a distributed piezoelectric film sensor 21, a charge amplifier 22 and a storage oscilloscope 23 that cooperate with the main anchor system 1, and the distributed piezoelectric film sensor 21 includes a piezoelectric film 211, electrodes 213 located on both sides of the piezoelectric film 211, a crimping terminal 214 arranged on one side of the electrode 213, an electrode lead 215 arranged at one end of the crimping terminal 214, and a piezoelectric film protective layer 212 sleeved on the piezoelectric film 211 and the two electrodes 213;

[0046] The assembly element 3 includes an adhesive 31 applied to the inner surface of the hollow anchor body 11, a coating material 1 32 applied to the distributed piezoelectric film sensor 21, and a coating material 2 33 applied to the coating material 1 32;

[0047] The grouting stop system 4 includes a grouting stop plug 41 arranged at one end of the hollow anchor body 11, a pad 42 arranged on the hollow anchor body 11, a nut 43 threadedly engaged on the hollow anchor body 11, and a gasket 1 44 and a gasket 2 45 sleeved on the hollow anchor body 11, the gasket 1 44 is located between the grouting stop plug 41 and the pad 42, and the gasket 2 45 is located between the pad 42 and the nut 43.

[0048] The outer wall of the hollow anchor body 11 of this embodiment is provided with threads, and one of the outer steel rings 14 is provided with a notch.

[0049] The hollow anchor body 11 of this embodiment has a diameter of 25-32mm and a thickness of 3-7mm, the hollow inner steel tube 12 has a diameter of 23-30mm and a thickness of 1-2mm, the length of the rubber ring 13 is 18-22mm and the thickness is 1-3mm, the hollow inner steel tube 12 is the same length as the hollow anchor body 11, and the outer ring diameter and inner ring diameter of the external steel ring 14 are respectively consistent with the hollow anchor body 11 and the hollow inner steel tube 12.

[0050] The piezoelectric film 211 of this embodiment is a PVDF piezoelectric film 211 , the thickness of the PVDF piezoelectric film 211 is 30 μm-240 μm, the piezoelectric film protection layer 212 is a polyvinyl fluoride protection layer, the electrode lead 215 is a 28AWG wire, and the two electrodes 213 are a positive electrode 213 and a negative electrode 213 .

[0051] The adhesive 31 of this embodiment is KH502 adhesive with a fast curing speed, and the coating thickness of the adhesive 31 is 25-35 μm.

[0052] The coating material 32 of this embodiment is J133 material with a thickness of 1-5 mm.

[0053] The second coating material 33 of this embodiment is glass glue.

[0054] The slurry stopping plug 41 of this embodiment is provided with an exhaust hole.

[0055] The intelligent piezoelectric film hollow grouting anchor strain monitoring device provided by the present invention not only retains the basic performance of the hollow grouting anchor, but also realizes comprehensive real-time monitoring of the dynamic strain generated by the anchor due to high and low frequency vibrations, instantaneous impact and cyclic loading, by pasting a distributed piezoelectric film in the hollow anchor body along the anchor axial direction and embedding a hollow steel pipe therein. Unlike traditional static monitoring methods, the piezoelectric film can quickly respond to changes in the anchor force, accurately capture the dynamic strain caused by vibration, impact and cyclic loads, and reflect the stress state of the anchor during the construction process in real time.

[0056] Piezoelectric film has the characteristics of high sensitivity and rapid response, and can capture tiny dynamic changes in anchor rods when subjected to strong dynamic forces such as drilling and blasting or mechanical extrusion, thereby significantly improving the accuracy and real-time nature of monitoring data; at the same time, piezoelectric film sensors are easy to install and low in cost, which is conducive to their promotion and application in large-scale underground projects; the monitoring device can help engineers evaluate the force changes of anchor rods in complex dynamic environments in real time, accurately understand the deformation and stress state of anchor rods, and timely optimize support plans to ensure the safety and stability of underground projects.

[0057] Embodiment 2: Application of an intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device in underground engineering, comprising the following steps:

[0058] Step 1: pre-assemble the piezoelectric film hollow grouting anchor rod;

[0059] Step 2: Drill holes on the rock mass to be supported, insert the assembled piezoelectric film hollow grouting anchor into the hole, and inject grout; the injection pressure is in the range of 0.3-1.0 MPa, and the injection starts from the bottom of the hole and proceeds upward layer by layer to prevent the formation of voids;

[0060] Step 3: After the grouting is completed and solidified, the lead wire of the piezoelectric film sensor 21 in the piezoelectric film hollow grouting anchor is led out of the tail end of the anchor, connected to the charge amplifier 22 and the storage oscilloscope 23, and data analysis is performed.

[0061] Embodiment 3: In view of the special requirements for monitoring the stress state of anchor rods and the advantages of monitoring with piezoelectric film 211, the present invention designs an intelligent piezoelectric film hollow grouting anchor rod dynamic strain monitoring device, including a main anchor rod system 1, a piezoelectric film system 2, a connecting element 3, and a grouting stop system 4. This embodiment is suitable for underground projects, and integrates the functions of the hollow grouting anchor rod and the piezoelectric film 211, which not only retains the original grouting anchor rod's support function for underground projects, but also can realize real-time monitoring of the stress and strain state of the anchor rod, so as to timely evaluate the anchoring effect and optimize the support plan to ensure project safety.

[0062] The main anchor system 1 includes a hollow anchor body 11, a hollow inner steel tube 12, a rubber ring 13, and an external steel ring 14. The hollow anchor body 11 is threaded, which is convenient for cutting and lengthening operations on the one hand, and enhances the anchoring effect of the anchor on the other hand. The hollow inner steel tube 12 is sleeved inside the hollow anchor body 11, and the axes of the two coincide, so that a cavity is formed between the hollow anchor body 11 and the hollow inner steel tube 12. The rubber ring 13 is distributed at both ends of the hollow anchor body 11, and is located in the cavity formed by the hollow anchor body 11 and the hollow inner steel tube 12. After the rubber ring 13 is placed at both ends of the hollow anchor body 11, the hollow anchor body 11 and the hollow inner steel tube 12 are welded and closed by the external steel ring 14. The external steel ring 14 located at the exposed end of the anchor tail reserves a notch to facilitate the connection of the piezoelectric film 211 lead wire with the collector. In this embodiment, the hollow anchor body 11 has a diameter of 25 mm and a thickness of 5 mm; the diameter of the hollow inner steel tube 12 is 2 mm smaller than that of the hollow anchor body 11 and has a thickness of 1.5 mm; the length of the rubber ring 13 is 20 mm and the thickness is 2 mm. The hollow steel tube is the same length as the hollow anchor body 11, and the outer ring diameter and inner ring diameter of the external steel ring 14 are respectively consistent with the hollow anchor body 11 and the hollow inner steel tube 12.

[0063] The main anchor system 1 adopts the method of built-in hollow inner steel tube 12, the purpose of which is to protect the piezoelectric film system 2 and prevent the pressure slurry from impacting and damaging the piezoelectric film system 2 during anchor grouting. The addition of the rubber ring 13 forms a 2mm cavity between the hollow anchor body 11 and the hollow inner steel tube 12, avoiding the extrusion and damage of the piezoelectric film system 2 by the direct contact between the hollow inner steel tube 12 and the pressure film.

[0064] The piezoelectric film system 2 includes a distributed piezoelectric film sensor 21, a charge amplifier 22 and a storage oscilloscope 23. The distributed piezoelectric film sensor 21 includes a piezoelectric film 211, a piezoelectric film protective layer 212, an electrode 213, a crimping terminal 214, and an electrode lead 215. The piezoelectric film 211 is made of PVDF piezoelectric film 211, the piezoelectric film protective layer 212 is made of polyvinyl fluoride material, and the lead is made of 28AWG wire. The electrodes 213 are distributed on both sides of the piezoelectric film 211, wherein one side electrode 213 is a positive electrode 213, and the other side electrode 213 is a negative electrode 213. The positive electrode 213 and the negative electrode 213 are each led out through the crimping terminal 214 by an electrode lead 215, and the piezoelectric film 211 and the electrodes 213 on both sides are encapsulated by the piezoelectric film protective layer 212. The electrode lead 215 is protected by an acrylic hollow tube, and a sufficient length needs to be reserved to pass through the notch reserved by the external steel ring 14 in the main anchor system 1, and is used to connect the charge amplifier 22 and the storage oscilloscope 23. Among them, the thickness of the PVDF piezoelectric film 211 is 30μm to 240μm, the outer diameter of the acrylic hollow tube is 2mm, the same diameter as the hole reserved by the external steel ring 14, and the connection between the two is sealed with silicone.

[0065] The dynamic strain monitoring capability of the distributed piezoelectric film sensor 21 is based on the unique characteristics of the piezoelectric effect. When the PVDF piezoelectric film 211 is subjected to periodic or transient stretching and compression, its internal crystal structure undergoes rapid and continuous deformation with the change of external dynamic stress, generating a dynamic potential difference proportional to the stress change. This potential difference will induce dynamic induction of charge at both ends of the positive and negative electrodes 213, and generate corresponding electrical signals through an external circuit. Since the piezoelectric effect can reflect the frequency, amplitude and time characteristics of stress changes in real time, the piezoelectric film 211 exhibits high sensitivity and wide frequency response characteristics when monitoring dynamic strains such as vibration, impact and cyclic loads, making it particularly suitable for capturing stress change signals under complex dynamic conditions. In this embodiment, the present invention is applied to the monitoring of underground engineering, and its advantage is that after the piezoelectric film system 2 is integrated into the anchor rod, it not only realizes the basic functions such as anchor rod anchoring and grouting reinforcement, but also utilizes the characteristics of the distributed piezoelectric film sensor 21 to monitor the high sensitivity of dynamic strain in real time. Multiple sensor units are evenly distributed at different positions in the anchor measurement area. Each unit is an independent dynamic observation point, which can capture high-frequency dynamic strain signals caused by vibration, impact and cyclic loads at different positions, thereby fully reflecting the stress state of the anchor under complex working conditions.

[0066] This distributed arrangement significantly expands the monitoring coverage, enabling sensors to capture the temporal and spatial variation characteristics of anchor stress and monitor dynamic strain distribution in real time, providing reliable data for anchoring effect evaluation and support scheme optimization, and ensuring the safety of underground projects.

[0067] The piezoelectric film system 2 and the main anchor system 1 are assembled and bonded through the assembly element 3 to achieve the dual functions of anchor grouting and monitoring. The assembly element 3 includes an adhesive 31, a coating material 1 32, and a coating material 2 33. The adhesive 31 is used for the preliminary fixation of the distributed piezoelectric film 211 and the hollow anchor body 11. The adhesive 31 used is a KH502 adhesive with a fast curing speed. It is applied on the inner surface of the hollow anchor body 11 where the distributed PVDF piezoelectric film 211 is to be arranged. It is applied multiple times and the total coating thickness is maintained at 25-35μm, so as to achieve good insulation between the distributed PVDF piezoelectric film 211 and the hollow anchor body 11, and reduce the influence of the adhesive layer on the sensor element. In addition, the adhesive layer can also realize the strain transfer between the hollow anchor body 11 and the distributed PVDF piezoelectric film 211. The coating material 132 is coated on the surface of the distributed piezoelectric film sensor 21 and the surrounding area. The coating material 132 used is J133 material with a thickness of 1-5mm. The purpose is to ensure that the distributed PVDF piezoelectric film 211 is in full contact with the inner surface of the hollow anchor body 11 to achieve the effect of coordinated deformation. The coating material 233 is coated on the cured J133 surface and the outer surface of the acrylic hollow tube and the surrounding area. The coating material 233 used is glass glue. The purpose is to avoid impact damage caused by vibration of the anchor in the rock body. The adhesive and coating material 132 together constitute the secondary protective layer of the distributed PVDF piezoelectric film sensor 21.

[0068] The grouting system 4 includes a grouting plug 41, a pad 42, a nut 43, a washer 1 44, and a washer 2 45. After the anchor rod is inserted, the grouting plug 41 is installed to fix the anchor rod. The grouting plug 41 is installed at the end of the hollow anchor rod body 11 and abuts against the end face of the borehole. The purpose is to maintain the grouting pressure during the grouting process so that the slurry can fully fill the gaps in the surrounding rock and seal the anchor hole to prevent the slurry from overflowing. The grouting plug 41 is provided with an exhaust hole to discharge the air in the anchor hole during the grouting process; after the slurry is finally set, the pad 42 is installed and the nut 43 is tightened; the pad 42 is installed at the exposed end of the hollow anchor rod body 11, located between the nut 43 and the grouting plug 41, close to the anchoring surface, and perpendicular to the axis of the anchor rod to expand the anchoring range of the anchor rod; the washer 1 44 and the washer 2 45 are arranged between the grouting plug 41 and the pad 42 and between the pad 42 and the nut 43, respectively, to improve the anti-slip property of the anchor rod and the sealing effect of the borehole.

[0069] Embodiment 4: Application of an intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device of the present invention in underground engineering, the specific application steps are as follows:

[0070] S1, pre-assembly of piezoelectric film anchor system;

[0071] According to the technical requirements of the present invention, in the factory, the various components of the processed piezoelectric film system 2, including the hollow anchor body 11, hollow steel pipe, anchor head, slurry stopper 41, pad 42, nut 43, rubber ring 13, external steel ring 14, etc., are assembled in the following order: bonding the hollow anchor body 11 and the distributed piezoelectric film sensor 21 with an adhesive element → installing the hollow inner steel pipe 12 and the rubber ring 13 → welding the external steel ring 14 and passing the acrylic hollow tube containing the piezoelectric film 211 through the reserved hole of the external steel ring 14 → welding the anchor head.

[0072] S2. Specific operation of the piezoelectric film anchor system embodiment;

[0073] During the initial support of underground engineering, according to the design requirements of underground engineering, the drilling positions are arranged on the rock mass to be supported. Use drilling equipment to perform drilling construction at the designated location to ensure that the drilling depth and diameter meet the design standards. Clean the remaining rock debris and impurities inside the borehole to ensure that the hole wall is clean; then check the integrity of the piezoelectric film 211 anchor rod assembled in step S1 to ensure that the piezoelectric film 211 and the lead are not damaged. Carefully insert the piezoelectric film 211 anchor rod into the borehole to ensure that the anchor rod is vertical and located in the center of the borehole. Install the grouting plug 41, pad 42 and nut 43 of the anchor rod, tighten the nut 43 to fix the anchor rod, and ensure that it is in close contact with the hole wall. Use a quick grouting joint to connect the tail end of the anchor rod to the grouting equipment. Check the grouting machine and connecting parts to ensure that there is no leakage. Start the grouting equipment and inject grouting materials such as cement mortar into the borehole through the hollow part of the anchor rod. Keep the grouting pressure within the range of 0.3-1.0MPa, start grouting from the bottom of the borehole, and proceed upward layer by layer to prevent the formation of voids. And ensure continuity during the grouting process, avoid long interruptions, and prevent the slurry from solidifying in the middle. After the grouting is completed, wait for the slurry to fully solidify and reach the design strength requirements. After the grouting is completed and solidified, the lead of the piezoelectric film sensor 21 is led out of the tail end of the anchor rod and connected to the charge amplifier 22 and the storage oscilloscope 23.

[0074] S3, data analysis of piezoelectric film anchor system;

[0075] In underground engineering, due to the strong dynamic effects caused by drilling and blasting construction, large-scale mechanical excavation, etc., anchor rods are often subjected to multi-mode dynamic loads such as strong vibration, fault dislocation, explosion impact and cyclic loading. These effects will cause the anchor rod to produce significant dynamic strain, and the distributed piezoelectric film sensor 21 will also produce dynamic stretching or compression under the synergistic effect of the dynamic load of the anchor rod. Under dynamic strain conditions, the crystal structure of the PVDF piezoelectric film 211 deforms rapidly, and a dynamic charge signal proportional to the strain change is generated on the surface. These signals can reflect the frequency, amplitude and change law of the anchor rod force in real time, and the dynamic strain information of the anchor rod surface can be quantitatively obtained by measuring the charge signal.

[0076] Since the piezoelectric film sensor 21 has a high internal impedance and a low output energy, its dynamic signal needs to be amplified by a dedicated charge amplifier 22 to ensure that the weak signal still has sufficient strength and resolution in a high-frequency dynamic environment. The amplified signal is then connected to a high-speed storage oscilloscope 23 for collection and recording, which can fully capture the strain change trajectory of the anchor rod under complex dynamic conditions.

[0077] This real-time dynamic monitoring capability enables the piezoelectric film sensor 21 to accurately evaluate the stress state and deformation law of the anchor rod, especially under the conditions of high-frequency vibration and transient impact caused by drilling and blasting construction or mechanical disturbance, the piezoelectric film 211 exhibits excellent dynamic response characteristics and reliability. This not only helps to judge the stress safety of the anchor rod, but also provides an accurate basis for optimizing underground engineering support, which is of great significance to ensuring the overall stability and construction safety of underground engineering.

[0078] The present invention is not limited to the above-mentioned embodiments. Anyone should be aware that any structural changes made under the enlightenment of the present invention, and any technical solutions that are the same or similar to the present invention, fall within the protection scope of the present invention. The technology, shape, and structural parts not described in detail in the present invention are all well-known technologies.

Claims

1. An intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device, characterized in that: include: A main anchor rod system (1), the main anchor rod system (1) comprising a hollow inner steel pipe (12), a hollow anchor rod body (11) sleeved on the hollow inner steel pipe (12), a cavity arranged between the hollow inner steel pipe (12) and the hollow anchor rod body (11), rubber rings (13) located at both ends of the hollow anchor rod body (11) and located in the cavity, and an external steel ring (14); A piezoelectric film system (2), the piezoelectric film system (2) comprising a distributed piezoelectric film sensor (21), a charge amplifier (22) and a storage oscilloscope (23) coordinated with the main anchor system (1), the distributed piezoelectric film sensor (21) comprising a piezoelectric film (211), electrodes (213) located on both sides of the piezoelectric film (211), a crimping terminal (214) arranged on one side of the electrode (213), an electrode lead (215) arranged at one end of the crimping terminal (214), and a piezoelectric film protective layer (212) sleeved on the piezoelectric film (211) and the two electrodes (213); A connecting element (3), the connecting element (3) comprising an adhesive (31) applied to the inner surface of the hollow anchor rod body (11), a coating material 1 (32) applied to the distributed piezoelectric film sensor (21), and a coating material 2 (33) applied to the coating material 1 (32); A grout stopping system (4) comprises a grout stopping plug (41) arranged at one end of a hollow anchor rod body (11), a backing plate (42) arranged on the hollow anchor rod body (11), a nut (43) threadedly engaged with the hollow anchor rod body (11), and a first backing ring (44) and a second backing ring (45) sleeved on the hollow anchor rod body (11), wherein the first backing ring (44) is located between the grout stopping plug (41) and the backing plate (42), and the second backing ring (45) is located between the backing plate (42) and the nut (43).

2. The intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device according to claim 1 is characterized in that: The outer wall of the hollow anchor rod body (11) is provided with threads, and a notch is provided on one of the outer steel rings (14).

3. The intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device according to claim 1 is characterized in that: The hollow anchor body (11) has a diameter of 25-32 mm and a thickness of 3-7 mm, the hollow inner steel tube (12) has a diameter of 23-30 mm and a thickness of 1-2 mm, the rubber ring (13) has a length of 18-22 mm and a thickness of 1-3 mm, the hollow inner steel tube (12) has the same length as the hollow anchor body (11), and the outer ring diameter and inner ring diameter of the external steel ring (14) are respectively consistent with those of the hollow anchor body (11) and the hollow inner steel tube (12).

4. The intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device according to claim 1, characterized in that: The piezoelectric film (211) is a PVDF piezoelectric film (211), the thickness of the PVDF piezoelectric film (211) is 30 μm-240 μm, the piezoelectric film protective layer (212) is a polyvinyl fluoride protective layer, the electrode lead (215) is a 28AWG wire, and the two electrodes (213) are respectively a positive electrode (213) and a negative electrode (213).

5. The intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device according to claim 1, characterized in that: The adhesive (31) is KH502 adhesive with a fast curing speed, and the coating thickness of the adhesive (31) is 25-35 μm.

6. The intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device according to claim 1, characterized in that: The coating material 1 (32) is J133 material with a thickness of 1-5 mm.

7. The intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device according to claim 1, characterized in that: The second coating material (33) is glass glue.

8. The intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device according to claim 1, characterized in that: The slurry stopping plug (41) is provided with an exhaust hole.

9. Application of an intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device in underground engineering, characterized in that: The steps include: Step 1: pre-assemble the piezoelectric film hollow grouting anchor rod; Step 2: Drill holes on the rock mass to be supported, insert the assembled piezoelectric film hollow grouting anchor rod into the drill hole, and inject grout; Step 3: After the grouting is completed and solidified, the lead wire of the piezoelectric film sensor (21) in the piezoelectric film hollow grouting anchor is led out of the tail end of the anchor, connected to the charge amplifier (22) and the storage oscilloscope (23), and data analysis is performed.

10. Application of the intelligent piezoelectric film hollow grouting anchor dynamic strain monitoring device in underground engineering according to claim 9, characterized in that: In step 2, the grouting pressure is in the range of 0.3-1.0 MPa, starting from the bottom of the borehole and proceeding upward layer by layer to prevent the formation of voids.

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