Non-contact monitoring method for axial force of end anchoring anchor rod

Abstract

The invention discloses a non-contact monitoring method for the axial force of an end anchoring anchor rod, and relates to the technical field of anchor rod axial force measurement. The monitoring method comprises the steps that firstly, relevant parameters of surrounding rock, relevant parameters of an anchor rod in the anchoring process and relevant parameters of an anchoring agent are obtained; acquiring strain data of an anchor rod tray in the anchoring system by adopting a full-field strain measurement system, transmitting the strain data to a data processing module of the full-field strain measurement system, and acquiring anchor supporting force by virtue of a stress-strain relationship of the anchor rod tray; finally, a calculation analysis formula of the mechanical relation between the anchor supporting force Ft generated by the anchor rod tray and the anchor rod axial force F is constructed in a computer; and inputting the values of the related parameters obtained in the step 1 and the step 2 into a calculation analysis formula, and calculating to obtain the axial force of the end anchoring anchor rod. By means of the method, non-contact measurement of the anchor supporting force of the anchor rod can be achieved, and the integrity of an anchoring system is further protected.

Description

Technical Field

[0001] The present invention relates to the technical field of anchor rod axial force measurement, and in particular to a non-contact monitoring method for the axial force of an end-anchored anchor rod. Background Art

[0002] End-anchored anchor rods provide anchoring force through anchoring agents, allowing the anchor rods to withstand a certain amount of tension and enhance the tensile strength of the surrounding rock. At present, although end-anchored anchor rods have certain defects and shortcomings compared to full-length anchored anchor rods, they are still widely used in mine tunnel support due to their economical nature and good support effect for most surrounding rock conditions, especially for less complex tunnels. With the continuous increase in coal mining depth in recent years, the surrounding rock conditions of tunnels have become increasingly complex, which has also put higher requirements on end-anchored anchor rods. Therefore, in order to improve the support performance of end-anchored anchor rods in actual engineering and extend their service life, it is very necessary to monitor the axial force of end-anchored anchor rods.

[0003] Currently, monitoring the axial force of anchor bolts in coal mines primarily relies on tools such as torque pullers, force anchors, pull gauges, steel string gauges, and hydraulic pillow dynamometers. While these tools do facilitate monitoring of anchor bolt axial force, they still present numerous challenges. Some measurement methods alter the support state of the anchor support system, often leading to significant discrepancies between test results and actual stress conditions. Other methods require the deployment of a certain number of measurement points for fixed-point monitoring, hindering large-scale, continuous monitoring of anchor bolt stress conditions. Furthermore, most methods still rely on contact measurement, which cannot adequately guarantee the integrity of the support system and can disrupt the anchor bolt's effectiveness. Therefore, developing real-time, continuous, and non-contact monitoring technologies and methods for anchor bolt axial force is crucial for ensuring the quality of anchor support.

[0004] This shows that the prior art needs to be further improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a non-contact monitoring method for the axial force of an end-anchored anchor rod, which can obtain continuous axial force distribution of the anchor rod body in a non-contact manner without destroying the integrity of the anchor rod and the tunnel surrounding rock anchoring structure, thereby providing a new technical means for non-contact monitoring of the axial force of the end-anchored anchor rod.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A non-contact monitoring method for the axial force of an end anchor bolt comprises the following steps in sequence:

[0008] Step 1: Obtain relevant parameters of the surrounding rock, relevant parameters of the anchor rod during the anchoring process, and relevant parameters of the anchoring agent;

[0009] Step 2: Using a full-field strain measurement system to obtain strain data of the anchor tray in the anchoring system, transmitting the strain data to a data processing module of the full-field strain measurement system, and obtaining the anchoring force by means of the stress-strain relationship of the anchor tray;

[0010] Step 3: Construct the anchor force F generated by the anchor tray in the computer t The calculation formula of the mechanical relationship with the anchor rod axial force F; inputting the values ​​of the relevant parameters obtained in steps 1 and 2 into the calculation formula to calculate the end anchor rod axial force;

[0011] The specific steps of calculating the analytical formula are as follows: first, obtain the analytical formula for calculating shear stress, as shown in formula (1) (2):

[0012] When l≤x≤L,

[0013] When 0≤x≤l, τ(x)=0 (2);

[0014] Anchor force F t The magnitude of is equal to the force exerted by the tray on the anchor rod or nut, as shown in formula (3):

[0015] When l≤x≤L,

[0016] The anchor force F is derived t The analytical formula for the mechanical relationship between the anchor axial force F and the anchor bolt axial force F is shown in equations (4) and (5):

[0017] When l≤x≤L,

[0018] When 0≤x≤l, F=F t (5);

[0019] In formulas (1), (2), (3), (4), and (5), D is the borehole diameter; d is the anchor rod diameter; x is the distance between any point on the anchor rod and the roadway surface; 1 is the length of the anchor rod free section; L is the total length of the anchor rod; I is the gap width between the anchor rod body and the borehole, that is, I = (Dd) / 2W is the shear stiffness coefficient of the anchoring agent and the surrounding rock; E is the elastic modulus of the anchor rod body; Q is a constant, C is the intermediate quantity replaced for the convenience of calculation, e is a mathematical constant, the base of the natural logarithm function, and its value is approximately 2.71828.

[0020] In the above-mentioned non-contact monitoring method for the axial force of an end-anchored anchor rod, in step one, the relevant parameters of the surrounding rock refer to the shear stiffness of the surrounding rock; the relevant parameters of the anchor rod during the anchoring process include the borehole diameter, the anchor rod diameter, the total length of the anchor rod, the length of the free section of the anchor rod, and the width of the gap between the anchor rod body and the borehole; the relevant parameters of the anchor agent include the shear stiffness of the anchor agent.

[0021] In the above-mentioned non-contact monitoring method for the axial force of an end-anchored anchor rod, in step 2, the full-field strain measurement system includes an image acquisition module, a liftable rotatable bracket, a high-resolution camera, a laser ranging device and an illumination device. The image acquisition module is located on the upgradeable rotatable bracket, and the liftable rotatable bracket is used to realize all-round monitoring of the changes in the anchor rod tray; the laser ranging device is used to measure and determine the spatial position of the tray; and the illumination device is used to provide light source to the system.

[0022] The above-mentioned non-contact monitoring method of the axial force of the end-anchored anchor rod is to arrange a full-field strain measurement system at a suitable position in the tunnel where the target anchor rod is located, aim a high-resolution camera at the anchor rod tray, use an image acquisition module to perform image acquisition, and import the acquired image into the full-field strain measurement system. Combined with the digital image correlation method, by tracking the speckle image on the surface of the anchor rod tray, the dynamic measurement of the surface displacement and strain of the anchor rod tray during the deformation process is achieved, and the acquired data is combined with the relevant mechanical parameters of the anchor rod tray, and the stress-strain relationship is used to infer the anchoring force of the anchor rod tray during the deformation process.

[0023] In the above-mentioned non-contact monitoring method for the axial force of an end-anchored anchor rod, in step three, W=W1W2 / (W1+W2), wherein W1 is the shear stiffness of the anchoring agent, and W2 is the shear stiffness of the surrounding rock.

[0024] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0025] (1) The present invention obtains the mechanical relationship between the axial force of the anchor rod and the anchor support force by analyzing the stress conditions of the end anchor rod. Through analysis, it can be seen that the axial force of each node of the end anchor rod in the free section is equal and evenly distributed, while the axial force in the anchor section changes in an exponential relationship with the anchor rod's anchor support force. The analytical calculation makes the calculation of the anchor rod axial force more accurate and intuitive. The present invention obtains the strain data of the anchor rod tray in the tunnel through a full-field strain measurement system. Under the premise of not contacting the anchor system, the full-field deformation of the tray is observed. There is no need to attach strain gauges or pull the anchor rod. It only needs to combine the collected images with the digital image correlation method to obtain the full-field strain distribution and stress-strain curve of the tray, thereby realizing non-contact measurement of the anchor rod's anchor support force and further protecting the integrity of the anchor system.

[0026] (2) In the present invention, the image acquisition module in the full-field strain measurement system is fixed on a bracket that can be freely moved, lifted and rotated, breaking the limitations of the anchor rod axial force inspection range in previous technologies. The device is flexible in configuration and easy to carry, which expands the monitoring range of the anchor rod axial force and can realize multi-angle and all-round monitoring of the top plate and the anchor rods on both sides of the tunnel. It only needs to adjust the position angle and direction to obtain comprehensive, complete and accurate stress and strain data of the tray, monitor the blind areas that cannot be monitored by previous technologies, provide more data support for the detection of the anchor rod axial force, and make the detection area of ​​the anchor rod axial force freer and more complete.

[0027] (3) The present invention adopts a full-field strain measurement system, which can monitor the anchoring force of the anchor tray in real time, and then obtain the real-time distribution of the axial force of the anchor rod body. The data obtained by the existing technology often has a delay and cannot monitor the stress state of the anchor rod axial force in a timely manner. The strain measurement system adopted by the present invention solves this problem better. It not only analyzes the changes in the anchoring state in real time, but also improves the problem of untimely data collection and processing caused by technical reasons, making the acquisition of relevant data more timely and efficient.

[0028] (4) The mechanical relationship between the anchor support force and the anchor rod axial force used in the present invention is relatively simple, and the required parameters are all basic parameters in the anchor rod anchoring process, and basically no additional complex technical means are required to measure them. This greatly simplifies the workflow of parameter acquisition in the method, significantly reduces the workload, and further improves work efficiency.

[0029] In summary, the method of the present invention can realize non-contact monitoring of the axial force of the end anchoring anchor rod, the method is simple to operate, and can be promoted and applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the process of the non-contact monitoring method of the present invention;

[0031] Figure 2 Schematic diagram of the full-field strain measurement system of the present invention in use;

[0032] Figure 3 This is a force model diagram of the end anchoring anchor rod of the present invention;

[0033] Figure 4 This is a structural diagram of the image acquisition module of the present invention;

[0034] In the picture:

[0035] 1. Anchor rod body, 2. Nut, 3. Anchor tray, 4. Anchoring agent, 5. Surrounding rock, 6. Image acquisition module, 7. Liftable and rotating bracket, 8. High-resolution camera, 9. Laser ranging device, 10. Lighting device. DETAILED DESCRIPTION

[0036] The present invention proposes a non-contact monitoring method for the axial force of an end-anchored anchor rod. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0037] The full-field strain measurement system described in this invention includes an image acquisition module 6, a high-resolution camera 8, a laser rangefinder 9, and an illumination device 10. Its structure and operating principle are identical to those of existing strain measurement systems. However, the present invention incorporates a retractable and rotatable support 7, which supports the image acquisition module 6, enabling multi-angle and multi-directional monitoring of the tunnel roof and anchor bolts on both sides. The full-field strain measurement system is connected to a computer, allowing the collected image data to be directly transferred to the computer.

[0038] Research background of this invention: In the existing technology, the detection of anchor rod axial force mostly relies on pull-off gauges, steel chord stress boxes or strain gauges arranged on the rod itself. These measurement methods are complex to arrange and have a large workload. They are more susceptible to external environmental disturbances and require certain changes to the anchoring structure to obtain the required data. There are certain difficulties and errors in the collection and processing of data.

[0039] The main technical concept of the present invention is: in view of the fact that the existing technology cannot achieve non-contact monitoring of the axial force of the anchor rod, and most of the contact monitoring in the existing technology can only monitor the force conditions at the measuring point, therefore, the present invention provides a non-contact monitoring method of the axial force of the end-anchored anchor rod, which obtains the strain data of the anchor rod tray in the anchoring system through a full-field strain measurement system, transmits the data to the data processing module, obtains the anchoring force according to the stress-strain relationship of the anchor rod tray, and constructs a calculation formula for the mechanical relationship between the anchoring force generated by the anchor rod tray and the axial force of the anchor rod in the computer, and inputs the obtained relevant parameter values ​​into the constructed calculation formula to obtain the axial force value of the end-anchored anchor rod at any position of the rod body.

[0040] The technical solution of the present application is further described in detail below with reference to the accompanying drawings.

[0041] like Figure 1 As shown, a non-contact monitoring method for the axial force of an end anchor bolt comprises the following steps:

[0042] Step 1: Obtain relevant parameters of the surrounding rock 5, relevant parameters of the anchor rod during the anchoring process, and relevant parameters of the anchoring agent 4 respectively.

[0043] The above-mentioned parameters related to the surrounding rock are the shear stiffness of the surrounding rock, which can be obtained by coring the surrounding rock of the tunnel and conducting mechanical tests on the cores. Figure 3As shown, the relevant parameters of the anchor rod during the anchoring process include the anchoring force and the relevant parameters of the anchor rod body 1, among which the relevant parameters of the anchor rod body 1 during the anchoring process include the borehole diameter, the anchor rod diameter, the total length of the anchor rod, the length of the free section of the anchor rod, and the width of the gap between the anchor rod body and the borehole; the relevant parameters of the anchoring agent include the shear stiffness of the anchoring agent, and the specific method of obtaining the parameters is: according to the type and material of the selected anchoring agent, and corresponding experiments are performed to obtain the parameters.

[0044] Step 2: Use the full-field strain measurement system to obtain the strain data of the anchor tray 3 in the anchoring system, transmit the strain data to the data processing module of the full-field strain measurement system, and obtain the anchoring force with the help of the stress-strain relationship of the anchor tray 3.

[0045] The specific steps are: Figure 2 As shown, a full-field strain measurement system is arranged at a suitable location in the tunnel, the spatial position of the anchor tray 3 is determined by the laser ranging device 9, and the target anchor tray 3 is sprayed with speckle paint. Then, a high-resolution camera 8 and an illumination device 10 are aimed at the anchor tray 3 to track the speckle image on the surface of the anchor tray 3. The collected tray image data is imported into the full-field strain measurement system. Combined with the digital image correlation method, the dynamic measurement of the displacement and strain of the anchor tray surface during the deformation process is realized. The acquired data is combined with the relevant mechanical parameters of the anchor tray, and the stress-strain relationship is used to infer the anchoring force exerted on the tray during the deformation process.

[0046] In this step, the contact measurement method used in the existing technology to obtain the axial force of the anchor rod is avoided. This step uses the full-field strain measurement system to collect the speckle image of the anchor rod tray through a high-resolution camera to obtain the strain of the tray. There is no need to contact the anchor rod at all, which protects the anchoring system to the greatest extent. The data obtained is more random, continuous and reliable.

[0047] Step 3: Construct the anchor force F generated by the anchor tray in the computer t The calculation formula of the mechanical relationship with the anchor rod axial force F; inputting the values ​​of the relevant parameters obtained in steps 1 and 2 into the calculation formula to calculate the end anchor rod axial force;

[0048] The specific steps of calculating the analytical formula are as follows: first, obtain the analytical formula for calculating shear stress, as shown in formula (1) (2):

[0049] When l≤x≤L,

[0050] When 0≤x≤l, τ(x)=0 (2);

[0051] Anchor force F tThe magnitude of is equal to the force exerted by the tray on the anchor rod or nut 2, as shown in formula (3):

[0052] When l≤x≤L,

[0053] The anchor force F is derived t The analytical formula for the mechanical relationship between the anchor axial force F and the anchor bolt axial force F is shown in equations (4) and (5):

[0054] When l≤x≤L,

[0055] When 0≤x≤l, F=F t (5);

[0056] In formulas (1), (2), (3), (4), and (5), D is the borehole diameter; d is the anchor rod diameter; x is the distance from any point on the anchor rod to the roadway surface; l is the length of the anchor rod free section; L is the total length of the anchor rod; I is the gap width between the anchor rod body and the borehole, that is, I = (Dd) / 2; W is the shear stiffness coefficient between the anchor and the surrounding rock, W = W1W2 / (W1+W2), where W1 is the shear stiffness of the anchor and W2 is the shear stiffness of the surrounding rock; E is the elastic modulus of the anchor rod body; Q is a constant, C is the intermediate quantity replaced for the convenience of calculation, e is a mathematical constant that is the base of the natural logarithm function and has a value of approximately 2.71828.

[0057] In the above steps, since the anchor force of the anchor tray is constantly changing during the support process, the measured strain data of the tray needs to be transmitted to the computer in real time. The full-field strain measurement system itself is connected to the computer, so the collected image data can be directly transmitted to the computer.

[0058] In the above steps, the shear stiffness W2 of the surrounding rock, the shear stiffness W1 of the anchoring agent, and the relevant parameters of the anchor rod body during the anchoring process, including: borehole diameter D, anchor rod diameter d, total anchor rod length L, anchor rod free section length l, and gap width I between the anchor rod and the borehole, can all be input into the computer through the keyboard.

[0059] By following the above steps as a whole, you can obtain the real-time and continuous axial force of the target anchor on your computer. Because the axial force is obtained through non-contact measurement of the anchor system, it is completely unaffected by external conditions, allowing for a more realistic and accurate assessment of the anchor's support status.

[0060] The amount of data obtained by the current existing technology depends entirely on the number of measurement devices arranged. Relevant data cannot be obtained at a location where no measurement device is arranged. The full-field strain measurement system adopted by the present invention can monitor the anchoring force of the anchor tray in real time, and then obtain the axial force distribution of the anchor rod body. What can be obtained is the data of all points within the field of view. The data obtained is continuous and accurate. With the help of the formula provided by the present invention, the axial force state of any point on the anchor rod body can be calculated, providing a reliable guarantee for the detection of the anchor rod axial force. Therefore, the present invention obtains the real-time stress state of the anchor rod by non-contact monitoring of the anchor tray strain, and performs real-time, non-contact, and non-disturbance detection of the anchor rod axial force based on the analytical formula of the mechanical relationship between the anchoring force and the anchor rod axial force. In this way, the support state of the end anchor anchor rod can be accurately and timely grasped, providing strong data support for the subsequent evaluation and optimization of the anchor rod support quality, which has a driving effect on ensuring the safety and efficient construction of coal mine projects.

[0061] The specific structure and working principle of the full-field strain measurement system of the present invention can be implemented by those skilled in the art with reference to existing technologies.

[0062] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present application and are not intended to limit the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection claimed in the present application.

Claims

1. A non-contact monitoring method for the axial force of an end anchor bolt, characterized in that: The following steps are included in sequence: Step 1, respectively obtaining relevant parameters of the surrounding rock, relevant parameters of the anchor rod during the anchoring process, and relevant parameters of the anchoring agent; Step 2: using a full-field strain measurement system to obtain strain data of the anchor tray in the anchoring system, transmitting the strain data to a data processing module of the full-field strain measurement system, and obtaining the anchor force by means of the stress-strain relationship of the anchor tray; Step 3: Construct the anchor force F generated by the anchor tray in the computer t The calculation formula of the mechanical relationship with the anchor rod axial force F; input the values ​​of the relevant parameters obtained in step 1 and step 2 into the calculation formula to calculate the end anchor rod axial force; The specific steps of calculating the analytical formula are as follows: first, the analytical formula for calculating shear stress is obtained, as shown in formula (1) (2): When 0≤x≤l, τ(x)=0 (2); Anchor force F t The magnitude of is equal to the force exerted by the tray on the anchor rod or nut, as shown in formula (3): The anchor force F is derived t The analytical formula for calculating the mechanical relationship with the anchor axial force F is shown in equations (4) and (5): When 0≤x≤l, F=F t (5); In formulas (1), (2), (3), (4), and (5), D is the borehole diameter; d is the bolt diameter; x is the distance from any point on the bolt to the tunnel surface; l is the length of the bolt free section; L is the total length of the bolt; I is the gap width between the bolt body and the borehole, that is, I = (Dd) / 2; W is the shear stiffness coefficient of the anchor and the surrounding rock; E is the elastic modulus of the bolt body; Q is a constant, C is the intermediate quantity replaced for the convenience of calculation, e is a mathematical constant, the base of the natural logarithm function, and its value is 2.71828.

2. A non-contact monitoring method for the axial force of an end anchor bolt according to claim 1, characterized in that: In step one, the relevant parameters of the surrounding rock refer to the shear stiffness of the surrounding rock; the relevant parameters of the anchor rod during the anchoring process include the borehole diameter, the anchor rod diameter, the total length of the anchor rod, the length of the free section of the anchor rod, and the width of the gap between the anchor rod body and the borehole; the relevant parameters of the anchor include the shear stiffness of the anchor agent.

3. The non-contact monitoring method of the axial force of an end anchor bolt according to claim 1 is characterized in that: In step two, the full-field strain measurement system includes an image acquisition module, a liftable and rotatable bracket, a high-resolution camera, a laser ranging device and a lighting device. The image acquisition module is located on the liftable and rotatable bracket, and the liftable and rotatable bracket is used to realize all-round monitoring of the changes of the anchor tray; the laser ranging device is used to measure and determine the spatial position of the tray; the lighting device is used to provide light source to the system.

4. A non-contact monitoring method for the axial force of an end anchor bolt according to claim 3, characterized in that: A full-field strain measurement system is arranged at a suitable position in the tunnel where the target anchor is located, a high-resolution camera is aimed at the anchor tray, and image acquisition module is used to acquire images. The acquired images are imported into the full-field strain measurement system. Combined with the digital image correlation method, the surface displacement and strain of the anchor tray during deformation are dynamically measured by tracking the speckle image on the surface of the anchor tray. The acquired data is combined with the relevant mechanical parameters of the anchor tray, and the stress-strain relationship is used to infer the anchor force of the anchor tray during deformation.

5. The non-contact monitoring method of the axial force of an end anchor bolt according to claim 1, characterized in that: In step three, W=W1W2 / (W1+W2), where W1 is the shear stiffness of the anchor and W2 is the shear stiffness of the surrounding rock.

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