Anchor rod coordinated deformation relation testing method based on distributed optical fiber sensor

Abstract

The invention discloses an anchor rod coordinated deformation relation testing method based on a distributed optical fiber sensor, and the method comprises the steps: predicting an optical fiber model and an optical fiber specification of which the current anchor rod strain test optical time domain reflection signal attenuation degree is slight according to the surveyed geological type, anchor rod type and anchor rod specification; carrying out on-off and reflection loss monitoring identification on the laid optical fiber, and determining an on-off result and a loss evaluation index of an optical fiber link; obtaining light reflection signal characteristic parameters through a detector, and determining the position of a strain point and the optical fiber strain of the strain point; determining an anchor rod axial force formula by adopting a deformation coordination equation and an elastic theory; and determining a load test value based on the optical fiber strain of the strain point and an anchor rod axial force formula, and judging an anchor rod strain test effect based on the deformation coordination coefficient. According to the invention, the application effect of the optical fiber sensor in the strain test of the anchor rod is obviously improved, an efficient and accurate monitoring solution is provided, and the optical fiber sensor can adapt to complex and variable engineering environments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical engineering monitoring, and particularly relates to a method for testing the coordinated deformation relationship of an anchor rod based on a distributed optical fiber sensor. BACKGROUND

[0002] In geotechnical engineering, anchor rod support is a widely used reinforcement technology for improving the stability of engineering structures such as slopes, foundation pits, and tunnels. In order to ensure the safety and reliability of the project, it is necessary to monitor the strain state of the anchor rod in real time so as to timely discover abnormal conditions and take corresponding measures. Traditional anchor rod strain testing methods mainly use electrical measurement sensors such as resistance strain gauges and vibrating wire strain gauges. Although these methods can meet the engineering requirements to some extent, they have some shortcomings. For example, electrical measurement sensors are susceptible to electromagnetic interference, have poor long-term stability, and are difficult to implement distributed measurement. In complex and harsh geological environments, the installation and maintenance costs of the sensors are high. For long anchor rods, wiring is difficult, and it is difficult to fully reflect the strain distribution of the anchor rod. With the development of optical fiber sensing technology, distributed optical fiber sensors have attracted more and more attention in the field of geotechnical engineering monitoring due to their unique advantages. Such sensors have the advantages of small size, light weight, good flexibility, strong anti-electromagnetic interference capability, and the ability to implement long-distance distributed measurement, which can effectively make up for the shortcomings of traditional electrical measurement sensors. The sensor realizes high-sensitivity measurement of strain and has good linearity and repeatability, which makes it possible to test the anchor rod strain with high precision. Through effective bonding of the distributed optical fiber and the anchor rod body, and by utilizing the good coordinated deformation relationship between them, a new way is opened up for the deformation testing method of the anchor rod. However, there are still some key problems to be solved when applying distributed optical fiber sensors to anchor rod strain testing. On the one hand, how to ensure the coordinated deformation between the optical fiber sensor and the anchor rod, i.e. to ensure that the two can deform synchronously during the stress process, is the key to accurate measurement. On the other hand, anchor rods are often in complex engineering environments, with narrow installation space and harsh conditions. In this case, how to accurately and firmly install the optical fiber sensor and avoid damage to it is also a key factor in ensuring accurate measurement of the distributed optical fiber sensor. SUMMARY

[0003] The present application provides a method for testing the coordinated deformation relationship of an anchor rod based on a distributed optical fiber sensor, which mainly includes:

[0004] According to the geological type, anchor rod type and anchor rod specification of the survey, the optical fiber model and optical fiber specification with a slight light time domain reflection signal attenuation degree for the current anchor rod strain testing light are predicted;

[0005] The on-off and reflection loss monitoring and identification of the laid optical fiber are performed through a red light pen and an OSI device to determine the on-off result and loss evaluation index of the optical fiber link.

[0006] The narrow linewidth pulse is emitted to the optical fiber by the semiconductor laser, and the optical reflection signal characteristic parameter is obtained by the detector to determine the strain point position and the optical fiber strain of the strain point;

[0007] According to the elastic modulus of the anchor rod, the cross-sectional area of the anchor rod, the elastic modulus of the optical fiber and the cross-sectional area of the optical fiber, the deformation compatibility equation and the elastic theory are used to determine the anchor rod axial force formula;

[0008] Based on the optical fiber strain of the strain point and the anchor rod axial force formula, the load test value is determined, and the deformation compatibility coefficient is used to judge the anchor rod strain test effect.

[0009] Further, the optical fiber model and the optical fiber specification with slight optical time domain reflection signal attenuation degree in the current anchor rod strain test are predicted according to the geological type, the anchor rod type and the anchor rod specification of the survey, comprising:

[0010] Through the anchor rod strain test database, the historical data of the survey ground type, the anchor rod type, the anchor rod specification, the optical fiber model and the optical fiber specification are obtained, the survey ground type includes high slope, foundation pit, mining area and tunnel; according to the geological type, the anchor rod type, the anchor rod specification, the optical fiber model and the optical fiber specification of the survey, the signal attenuation degree of the optical time domain reflection signal is marked, the recurrent neural network is used for model training, the optical fiber model prediction model is constructed, and the signal attenuation degree includes severe, moderate and slight; according to the geological type, the anchor rod type and the anchor rod specification obtained in the current anchor rod strain test, the optical fiber model prediction model is used to predict the optical fiber model and the optical fiber specification with slight optical time domain reflection signal attenuation degree in the current anchor rod strain test.

[0011] Further, the continuity and reflection loss monitoring and identification of the laid optical fiber are performed by the red light pen and the OSI device, and the continuity result and the loss evaluation index of the optical fiber link are determined, comprising:

[0012] According to the predicted optical fiber model and the optical fiber specification with slight optical time domain reflection signal attenuation degree in the current anchor rod strain test, the optical fiber for the current anchor rod strain test is determined, and the distributed optical fiber sensor is laid in the groove pre-set in the anchor rod steel bar; the red light pen is used to inject light at the tail end of the optical fiber, and whether there is a light leakage point along the path is identified to judge the continuity of the optical fiber; the reflection loss value of each port is recorded by connecting the OSI device, and the loss distribution curve of the transmission link is recorded to judge whether there is a serious attenuation section with reflection loss greater than the preset loss threshold, and the loss evaluation index of the serious attenuation section of the optical fiber link is output; if the optical fiber has a light leakage point and a serious attenuation section, the optical fiber is re-laid according to the original process according to the light leakage point position and the serious attenuation section position of the optical fiber link until there is no light leakage point and serious attenuation section in the continuity and reflection loss re-inspection.

[0013] Furthermore, the step of using a semiconductor laser to emit narrow-linewidth pulses into the optical fiber and obtaining characteristic parameters of the light reflection signal through a detector to determine the location of the strain point and the fiber strain at the strain point includes:

[0014] Using a semiconductor laser as the light source, the power of the semiconductor laser is adjusted according to the preset measurement distance and preset accuracy requirements of the current anchor bolt strain test. Narrow linewidth pulses are emitted into the optical fiber, and the emission timestamp is recorded. An indium gallium arsenide detector is used as the detector to obtain the characteristic parameters of the light reflection signal and the reflection timestamp. The strain point distance formula is then used to... Calculate the distance L of strain point i in the optical fiber. i The location of the strain point is determined, and the characteristic parameters of the light reflection signal, the reflection timestamp, and the strain point location are saved to the anchor bolt strain test database. The characteristic parameters of the light reflection signal include the reflection wavelength, reflectivity contrast, and light intensity, where n is the refractive index of the optical fiber, and Δt is the optical fiber refractive index. i Let be the time delay at strain point i, and c be the speed of light. Using the anchor bolt strain test database, the characteristic parameters of the light reflection signal at historical strain points are obtained, and the fiber strain at the corresponding strain points is labeled. A recurrent neural network is used to train the model, constructing a fiber strain prediction model. Based on the characteristic parameters of the light reflection signal at the strain point obtained in real time from the anchor bolt strain test, the fiber strain at the strain point is determined using the fiber strain prediction model.

[0015] Furthermore, based on the elastic modulus of the anchor bolt, the cross-sectional area of ​​the anchor bolt, the elastic modulus of the optical fiber, and the cross-sectional area of ​​the optical fiber, the deformation compatibility equation and elasticity theory are used to determine the anchor bolt axial force formula, including:

[0016] Based on indoor experiments and literature review, the elastic modulus and cross-sectional area of ​​the anchor bolt, as well as the elastic modulus and cross-sectional area of ​​the optical fiber, were obtained. By applying different tensile forces, the formulas were used to... Determine the adhesion coefficient k b Define anchor strain and fiber strain Let A be a linear function, where A m Let A be the cross-sectional area of ​​the anchor bolt. f Let be the cross-sectional area of ​​the optical fiber, F be the applied tensile force, and x be the position. Based on the deformation compatibility equation and the bonding coefficient, a deformation compatibility model between the optical fiber and the anchor is established, and the strain relationship is derived as follows: Based on the elastic modulus and elasticity theory of materials, Hooke's law is used to obtain the anchor bolt stress as σ. m (x)=E m ·ε m (x) and fiber stress σ f (x)=E f ·ε f (x), and determine the strain compatibility formula. wherein, E m is the elastic modulus of the anchor rod, E f is the elastic modulus of the optical fiber; based on the strain compatibility relationship formula and the anchor rod stress, the anchor rod axial force formula is determined as F m (x) = A m ·σ m (x) = A m ·k b E f ·ε f (x).

[0017] Further, based on the strain point optical fiber strain and the anchor rod axial force formula, the load test value is determined, and the anchor rod strain test effect is judged based on the deformation compatibility coefficient, including:

[0018] According to the cross-sectional area of the anchor rod, the bond coefficient, the elastic modulus of the optical fiber and the strain point optical fiber strain, the anchor rod axial force formula is used to determine the anchor rod axial force of the strain point as the load test value; according to the load loading value and the load test value, the load displacement curve of the anchor rod and the load axial force along the depth distribution curve are drawn; if the deformation compatibility coefficient of the distributed optical fiber and the anchor rod is greater than the preset coefficient threshold, it is judged that the current optical fiber strain measurement data is reliable, the distributed optical fiber sensor responds normally, and the bond state is good, wherein the deformation compatibility coefficient is the ratio of the optical fiber strain and the anchor rod strain; if the deformation compatibility coefficient of the distributed optical fiber and the anchor rod is less than the preset coefficient threshold, it is judged that the current anchor rod strain test effect is poor, and the installation state of the distributed optical fiber sensor, the parameter configuration of the data acquisition system are comprehensively investigated and corrected, and the anchor rod strain test is carried out again and the load test value is calculated until the deformation compatibility coefficient of the distributed optical fiber and the anchor rod is greater than the preset coefficient threshold.

[0019] The technical scheme provided by the embodiment of the application can include the following beneficial effects:

[0020] This invention provides a method for testing the coordinated deformation relationship of anchor bolts based on distributed optical fiber sensors. By accurately predicting the optical fiber model and specifications, this invention selects fibers suitable for current geological conditions and anchor bolt types, effectively reducing fiber signal attenuation and ensuring high measurement accuracy and stability. Real-time monitoring of fiber reflection signal loss and continuity allows for dynamic evaluation of the fiber's operating status and timely adjustment of system configuration, thus ensuring the accuracy and stability of measurement results. Furthermore, by combining a semiconductor laser and a detector, this invention can accurately measure light reflection signals, locate strain points, and calculate fiber strain data. By combining elasticity theory and deformation coordination equations, this invention can accurately calculate the anchor bolt axial force and determine the load test value based on the fiber strain value at the strain point and the anchor bolt axial force formula. This invention uses a deformation coordination coefficient to judge the anchor bolt strain test effect, thereby ensuring the long-term stability and reliability of the optical fiber sensor in complex geological environments. This invention significantly improves the application effect of optical fiber sensors in anchor bolt strain testing, providing a highly efficient and accurate monitoring solution that can adapt to complex and changing engineering environments. Attached Figure Description

[0021] Fig. 1 This is a flowchart of a method for testing the coordinated deformation relationship of anchor bolts based on distributed optical fiber sensors according to the present invention.

[0022] Fig. 2 This is a schematic diagram of a method for testing the coordinated deformation relationship of anchor bolts based on distributed optical fiber sensors according to the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] like Figs. 1-2 This embodiment of the method for testing the coordinated deformation relationship of anchor bolts based on distributed optical fiber sensors may specifically include:

[0025] Step S101: Based on the surveyed geological type, anchor type, and anchor specifications, predict the fiber type and specifications for the current anchor strain test optical time domain reflection signal attenuation level as slight.

[0026] Historical data on surveyed geological types, anchor types, anchor specifications, fiber optic cable types, and fiber optic cable specifications were obtained from an anchor strain test database. Surveyed geological types included high slopes, foundation pits, mining areas, and tunnels. Based on the surveyed geological type, anchor type, anchor specifications, fiber optic cable type, and fiber optic cable specifications, the signal attenuation level of the optical time-domain reflectometry (OTDR) signal was labeled. A recurrent neural network was used to train a model to construct a fiber optic cable type prediction model, categorizing signal attenuation levels as severe, moderate, and slight. Based on the geological type, anchor type, and anchor specifications obtained from the current anchor strain test, the fiber optic cable type prediction model was used to predict the fiber optic cable type and specification with a slight attenuation level in the current anchor strain test's ODR signal.

[0027] For example, an anchor bolt strain test is being conducted in a foundation pit project. Different types of anchor bolts and fiber optic devices are used in the test to monitor changes in anchor bolt stress. Historical data on the survey site type, anchor bolt type, anchor bolt specifications, and fiber optic type and specifications are obtained from an anchor bolt strain test database. For example, the survey site type is a foundation pit, the anchor bolt type is a rebar anchor, the anchor bolt specifications are 28mm diameter and 10 meters long, and the fiber optic type is SMF-28, the fiber optic specification is standard single-mode fiber, and the operating wavelength is 1550nm. Survey site types include high slopes, foundation pits, mining areas, and tunnels. Based on the historical data on the survey site type, anchor bolt type, anchor bolt specifications, and fiber optic type and specifications, and by labeling the signal attenuation degree of the optical time-domain reflectometry (OTDR) signal, a recurrent neural network is used to train a model to construct a fiber optic type prediction model. This model predicts the attenuation degree of the ODR signal, categorized as severe, moderate, and slight. In the current test, new data was obtained including the survey site being a foundation pit, the anchor type being a rebar anchor, the anchor specifications being 20mm in diameter and 15 meters in length, and the use of a pre-existing fiber optic model to predict the fiber type and specifications for which the time-domain reflectometry (TDR) signal attenuation in the current anchor strain test was slight. The model predicted the fiber signal to be G657.B3, a standard single-mode fiber, with an operating wavelength of 1.3μm, indicating slight signal attenuation.

[0028] Step S102: Using a red light pen and OSI equipment, the continuity and reflection loss of the deployed optical fiber are monitored and identified to determine the continuity results and loss evaluation indicators of the optical fiber link.

[0029] Based on the predicted slight attenuation of the time-domain reflective signal in the current anchor bolt strain test, the fiber type and specifications are determined for the current anchor bolt strain test. Distributed fiber optic sensors are then deployed within pre-defined grooves in the anchor bolt reinforcement. A red light pen is used to illuminate the fiber optic tail, and optical leakage points are identified along the path to determine the fiber's continuity. The reflection loss values ​​at each port are recorded using an OSI device, and the loss distribution curve of the transmission link is also recorded. This helps determine if there are severely attenuated sections where the reflection loss exceeds a preset loss threshold, and outputs the loss assessment index for the severely attenuated fiber link. If optical leakage points and severely attenuated sections exist, the fiber is re-laid according to the original process, based on the locations of the leakage points and severely attenuated sections, until continuity and reflection loss re-checks show no optical leakage points or severely attenuated sections.

[0030] For example, based on the previously predicted slight attenuation of the optical time-domain reflectometry signal, fiber type G657.B3 was selected, with standard single-mode fiber and an operating wavelength of 1.3μm. Following this selection, the distributed fiber optic sensors were deployed according to the predetermined plan. The anchor rods were polished to remove surface rust and impurities, improving the adhesion between the fiber and the anchor rod. Grooves, 2-3mm deep, were etched into the surface of the anchor rods to provide space for fiber placement. The grooves were wiped clean and dry with alcohol to ensure optimal conditions for fiber bonding. The distributed fiber optic sensors were embedded in the grooves of the anchor rods. Initial fixation was achieved by applying 502 glue every 5-8cm to prevent fiber movement during deployment. Then, epoxy resin was used to bond the entire fiber optic section, ensuring a tight bond between the fiber and the anchor rod and improving strain transfer efficiency. After installation, a red light pen was used to illuminate the fiber's tail end, and the fiber path was carefully inspected for any light leakage points. By observation, if light leakage is observed along the fiber optic path illuminated by a red light pen, a problem can be confirmed at that location, indicating that the fiber optic cable is not completely sealed or is damaged. If, during inspection, a light leakage point is found at the end of the fiber optic cable at a depth of 4 meters from the anchor bolt, this indicates significant damage or poor connection at that location. Connect an OSI device to record the reflection loss value at each port and further record the loss distribution curve of the entire fiber optic link. The preset loss threshold is 0.5 dB. If the loss value of a segment of the fiber optic link exceeds this threshold, it indicates severe attenuation in that segment, affecting the accuracy of the test. Suppose that the OSI device measurement reveals a section of fiber optic cable at 10 meters with a reflection loss of 1.2 dB, far exceeding the preset loss threshold, indicating severe attenuation in that segment. Based on the above test results, record the location of the light leakage point at 4 meters and the location of the severely attenuated section at 10 meters, and re-lay the fiber optic cable according to the original process. First, repair the leakage point at the end of the fiber optic cable to ensure a good fiber optic connection. Then, re-lay the fiber optic cable, ensuring that the reflection loss of that segment is within the normal range and there are no light leakage points. After redeployment, the fiber optic path was checked again using a red light pen and OSI equipment to confirm that there were no light leakage points and that the reflection loss values ​​were all below the preset loss threshold. All measurement results showed that the fiber optic connection was good and the loss distribution met the requirements.

[0031] Step S103: A narrow linewidth pulse is emitted into the optical fiber using a semiconductor laser, and the characteristic parameters of the light reflection signal are obtained through a detector to determine the location of the strain point and the fiber strain at the strain point.

[0032] Using a semiconductor laser as the light source, the power of the laser is adjusted according to the preset measurement distance and accuracy requirements for anchor bolt strain testing. Narrow-linewidth pulses are emitted into the optical fiber, and the emission timestamp is recorded. An indium gallium arsenide detector is used as the detector to obtain the characteristic parameters of the light reflection signal and the reflection timestamp. The results are then analyzed using the strain point distance formula. Calculate the distance L of strain point i in the optical fiber. i The location of the strain point is determined, and the characteristic parameters of the light reflection signal, the reflection timestamp, and the strain point location are saved to the anchor bolt strain test database. The characteristic parameters of the light reflection signal include the reflection wavelength, reflectivity contrast, and light intensity, where n is the refractive index of the optical fiber, and Δt is the optical fiber refractive index. i Let be the time delay at strain point i, and c be the speed of light. Using the anchor bolt strain test database, the characteristic parameters of the light reflection signals at historical strain points are obtained, and the fiber strain at the corresponding strain points is labeled. A recurrent neural network is used to train the model, constructing a fiber strain prediction model. Based on the characteristic parameters of the light reflection signals at strain points obtained in real time from anchor bolt strain tests, the fiber strain at the strain point is determined using the fiber strain prediction model.

[0033] For example, a semiconductor laser is used as the light source to emit narrow-linewidth pulsed signals into an optical fiber, and the timestamp of each signal emission is recorded. Based on the project's preset measurement distance requirement of 100 meters and accuracy standard of 1 centimeter, the power of the semiconductor laser is adjusted and pulsed signals are emitted to ensure accurate measurement of the light reflection signal at the strain point. The light signal is transmitted through the optical fiber and received by an indium gallium arsenide detector installed in the system. The detector records the characteristic parameters of the reflected signal, including the reflection wavelength, reflectivity contrast, and light intensity, and records the timestamp of the reflected signal. The time delay Δt at a specific strain point i is obtained through measurement. i Given that the optical fiber has a refractive index n of 1.46 and the speed of light c is 3 × 10⁻⁵ microseconds, and the wavelength of light is 0.5 microseconds, the optical fiber has a refractive index n of 1.46, and the speed of light c is 3 × 10⁻⁵ microseconds, the wavelength of light is 0.5 microseconds. 8 meters per second. According to the strain point distance formula... Calculate the distance L of strain point i in the optical fiber. i The distance is 51.37 meters, therefore the location of strain point i in the optical fiber is approximately 51.37 meters. The characteristic parameters of the light reflection signal, the reflection timestamp, and the strain point location calculated using the above formula are saved to the anchor bolt strain test database. As the test progresses, the characteristic parameters of the light reflection signal at historical strain points are obtained from the anchor bolt strain test database, and the corresponding optical fiber strain is labeled. Using this historical data, a recurrent neural network is used to train the model and construct an optical fiber strain prediction model. In subsequent strain tests, the real-time acquired characteristic parameters of the light reflection signal at strain points are input into the optical fiber strain prediction model. The model predicts based on the training data and ultimately determines the optical fiber strain at the current strain point.

[0034] Step S104: Based on the elastic modulus of the anchor bolt, the cross-sectional area of ​​the anchor bolt, the elastic modulus of the optical fiber, and the cross-sectional area of ​​the optical fiber, the deformation compatibility equation and elasticity theory are used to determine the formula for the axial force of the anchor bolt.

[0035] Based on indoor experiments and literature review, the elastic modulus and cross-sectional area of ​​the anchor bolt, as well as the elastic modulus and cross-sectional area of ​​the optical fiber, were obtained. By applying different tensile forces, the formula was used... Determine the adhesion coefficient k b Define anchor strain. and fiber strain Let A be a linear function, where A m Let A be the cross-sectional area of ​​the anchor bolt. f Let be the cross-sectional area of ​​the optical fiber, F be the applied tensile force, and x be the position. Based on the deformation compatibility equation and the bonding coefficient, a deformation compatibility model between the optical fiber and the anchor is established, yielding the strain relationship as follows: Based on the elastic modulus and elasticity theory of materials, Hooke's law is used to obtain the anchor bolt stress as σ. m (x)=E m ·ε m (x) and fiber stress σ f (x)=E f ·ε f (x), and determine the strain compatibility formula. , of which E m E represents the elastic modulus of the anchor bolt. f Let F be the elastic modulus of the optical fiber. Based on the strain compatibility formula and the anchor bolt stress, the anchor bolt axial force formula is determined to be F. m (x)=A m ·σ m (x)=A m ·k b E f ·ε f (x).

[0036] For example, based on the characteristics of fiber optic sensors, the distributed fiber optic sensing principle is used to analyze the deformation response of the fiber under different stress conditions, and obtain the strain distribution formula of the fiber, defined as... , where ε f (x) represents the strain of the optical fiber at position x, ε m (x) represents the strain at the corresponding position of the anchor bolt, and L represents the total length of the optical fiber. Based on the bonding properties between the optical fiber and the anchor bolt, a deformation compatibility equation is established between the anchor bolt and the optical fiber. If the bonding coefficient is k... b Then the strain compatibility relationship between the anchor and the optical fiber is obtained as ε. m (x)=k b ε f(x). A standard tensile test was conducted, and the stress and strain of the sample were recorded during the test. The elastic modulus E of the anchor bolt was calculated using the formula σ=Eε. m Based on experiments or literature review, the elastic modulus E of the optical fiber was obtained. f The cross-sectional area A of the optical fiber f and the cross-sectional area A of the anchor rod m Based on experimental data, the bonding performance between the optical fiber and the anchor rod was determined. A tensile test was used to determine the bonding coefficient between the optical fiber and the anchor rod. In the experiment, different tensile forces were applied, and the deformation of the optical fiber and the anchor rod was recorded. The formula was then used to determine the bonding coefficient. Determine the adhesion coefficient k b Based on the obtained mechanical equilibrium equations and considering the stress distribution of the anchor bolt and optical fiber, the strain relationship between them is derived using the integral method, and the anchor bolt strain is defined. and fiber strain Let F be a linear function, where F is the applied tensile force and x is the position. Based on the deformation compatibility equation, combined with the adhesion coefficient k... b A deformation coordination model between the optical fiber and the anchor was established, and the strain relationship was derived. Based on the elastic modulus of the material, the strain function between the anchor rod and the optical fiber is derived using elasticity theory. If the relationship between stress and strain is linear, the strain relationship related to force and position is derived as follows: and And thus, the final strain compatibility formula is obtained. Based on the strain compatibility formula and the anchor bolt stress, the anchor bolt axial force formula is determined to be F. m (x)=A m ·σ m (x)=A m ·k b E f ·ε f (x).

[0037] Step S105: Based on the fiber strain and anchor bolt axial force formulas at the strain points, determine the load test value, and judge the anchor bolt strain test effect based on the deformation compatibility coefficient.

[0038] Based on the cross-sectional area of ​​the anchor bolt, the bonding coefficient, the elastic modulus of the optical fiber, and the fiber strain at the strain point, the anchor bolt axial force at the strain point is determined using the anchor bolt axial force formula, and this is used as the load test value. Based on the load applied and the load test values, the load-displacement curve and the load axial force distribution curve along the depth of the anchor bolt are plotted. If the deformation compatibility coefficient between the distributed optical fiber and the anchor bolt is greater than a preset threshold, the current optical fiber strain measurement data is considered reliable, the distributed optical fiber sensor response is normal, and the bonding state is good. The deformation compatibility coefficient is the ratio of optical fiber strain to anchor bolt strain. If the deformation compatibility coefficient between the distributed optical fiber and the anchor bolt is less than the preset threshold, the current anchor bolt strain test effect is considered poor. A comprehensive investigation and correction of the installation status of the distributed optical fiber sensor and the parameter configuration of the data acquisition system are conducted, and the anchor bolt strain test is repeated and the load test value is calculated again until the deformation compatibility coefficient between the distributed optical fiber and the anchor bolt is greater than the preset threshold.

[0039] For example, an anchor strain test is being conducted on a high slope project, and the cross-sectional area of ​​the anchor has been obtained as 5 × 10⁻⁶. -4 m 2 The bonding coefficient between the optical fiber and the anchor rod is 0.95, and the elastic modulus of the optical fiber is 70 N / m. 2 The fiber strain at a certain strain point i was measured to be 4 × 10 using a distributed fiber optic sensor. -4Based on the strain test data of the anchor bolt, the axial force of the anchor bolt at the strain point was determined to be 13300N using the anchor bolt axial force formula, which was taken as the load test value. Based on the load applied and the load test values, the load-displacement curve and the load axial force distribution curve along the depth of the anchor bolt were plotted. It was assumed that the load at the loading point during the test was 12kN. Based on the difference between the load test value and the applied value, these two curves were plotted. The load-displacement curve shows the displacement change caused by the anchor bolt under stress, while the load axial force distribution curve along the depth of the depth reveals the axial force change inside the anchor bolt. During this process, the deformation compatibility coefficient between the distributed optical fiber and the anchor bolt was calculated. Based on the known data, it was assumed that the calculated ratio of the optical fiber strain to the anchor bolt strain, i.e., the deformation compatibility coefficient, was 0.95. If the preset coefficient threshold is 0.9, since the calculated deformation compatibility coefficient of 0.95 is greater than the preset coefficient threshold of 0.9, it was determined that the current optical fiber strain measurement data was reliable, the response of the distributed optical fiber sensor was normal, the bonding state was good, and the test results were valid. However, if the deformation compatibility coefficient is 0.8, which is less than the preset threshold of 0.9, it indicates that the strain of the distributed optical fiber and the anchor bolt is not well matched. This may mean that there is a problem with the installation of the optical fiber sensor or that the data acquisition system is improperly configured. In this case, a comprehensive investigation and correction of the installation status of the distributed optical fiber sensor and the configuration of the data acquisition system is required. After the investigation is completed, the anchor bolt strain test should be carried out again, the load test value should be calculated, and the deformation compatibility coefficient should be re-evaluated. Only when the deformation compatibility coefficient recovers to a value greater than the preset threshold can the data be confirmed to be accurate and reliable, and the test process can be terminated.

[0040] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the concept of this application. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for testing the coordinated deformation relationship of anchor bolts based on distributed optical fiber sensors, characterized in that, The method includes: Based on the geological type, anchor type, and anchor specifications surveyed, the fiber optic type and specifications are predicted to have a slight attenuation of the time-domain reflectance signal in the current anchor strain test. Using a red light pen and OSI equipment, the continuity and reflection loss of the deployed optical fiber are monitored and identified to determine the continuity and loss assessment indicators of the optical fiber link. A semiconductor laser is used to emit narrow linewidth pulses into an optical fiber, and the characteristic parameters of the light reflection signal are obtained through a detector to determine the location of the strain point and the fiber strain at the strain point. Based on the elastic modulus of the anchor bolt, the cross-sectional area of ​​the anchor bolt, the elastic modulus of the optical fiber, and the cross-sectional area of ​​the optical fiber, the formula for the axial force of the anchor bolt is determined using the deformation compatibility equation and elasticity theory. Based on the fiber strain and anchor bolt axial force formulas at strain points, the load test values ​​are determined, and the anchor bolt strain test effect is judged based on the deformation compatibility coefficient.

2. The method according to claim 1, wherein, The fiber optic type and specification used to predict the slight attenuation of the current anchor strain test optical time-domain reflectance signal based on the surveyed geological type, anchor type, and anchor specifications include: Historical data on surveyed geological types, anchor types, anchor specifications, fiber optic models, and fiber optic specifications were obtained from the anchor strain test database. Surveyed geological types included high slopes, foundation pits, mining areas, and tunnels. Based on the surveyed geological types, anchor types, anchor specifications, fiber optic models, and fiber optic specifications, the signal attenuation degree of the optical time-domain reflectometry (OTDR) signal was labeled. A recurrent neural network was used to train the model, constructing a fiber optic model prediction model. The signal attenuation degree was categorized as severe, moderate, and slight. Based on the geological types, anchor types, and anchor specifications obtained from the current anchor strain test, the fiber optic model prediction model was used to predict the fiber optic model and specification with a slight attenuation degree in the current anchor strain test's ODR signal.

3. The method according to claim 1, wherein, The process involves using a red light pen and OSI equipment to monitor and identify the continuity and reflection loss of the deployed optical fibers, determining the continuity results and loss assessment indicators of the optical fiber link, including: Based on the predicted fiber type and specifications indicating slight attenuation of the current anchor bolt strain test optical time-domain reflection signal, the fiber for the current anchor bolt strain test is determined, and distributed fiber optic sensors are deployed in the pre-set grooves in the anchor bolt reinforcement. A red light pen is used to inject light at the end of the fiber, and the presence of light leakage points is identified along the path to determine the continuity of the fiber. By connecting to an OSI device, the reflection loss value of each port is recorded, and the loss distribution curve of the transmission link is recorded to determine whether there is a severely attenuated section where the reflection loss exceeds the preset loss threshold. The loss evaluation index of the severely attenuated fiber link is then output. If there are optical leakage points and severely attenuated sections in the optical fiber, the optical fiber should be re-laid according to the original process based on the location of the optical leakage points and the location of the severely attenuated sections in the optical fiber link, until the continuity and reflection loss are re-checked and there are no optical leakage points or severely attenuated sections.

4. The method according to claim 1, wherein, The method of using a semiconductor laser to emit narrow-linewidth pulses into an optical fiber and obtaining characteristic parameters of the light reflection signal through a detector to determine the location of the strain point and the fiber strain at the strain point includes: Using a semiconductor laser as a light source, the power of the semiconductor laser is adjusted according to the preset measurement distance and preset accuracy requirements of the current anchor bolt strain test, and a narrow linewidth pulse is emitted into the optical fiber, and the emission timestamp is recorded. An indium gallium arsenide (IGaAs) detector was used as the detector to obtain the characteristic parameters of the light reflection signal and the reflection timestamp, and the result was obtained using the strain point distance formula. Calculate the distance L of strain point i in the optical fiber. i The location of the strain point is determined, and the characteristic parameters of the light reflection signal, the reflection timestamp, and the strain point location are saved to the anchor bolt strain test database. The characteristic parameters of the light reflection signal include the reflection wavelength, reflectivity contrast, and light intensity, where n is the refractive index of the optical fiber, and Δt is the optical fiber refractive index. i Let be the time delay at strain point i, and c be the speed of light. Using the anchor bolt strain test database, the characteristic parameters of the light reflection signal at historical strain points are obtained, and the fiber strain at the corresponding strain points is labeled. A recurrent neural network is used to train the model, constructing a fiber strain prediction model. Based on the characteristic parameters of the light reflection signal at the strain point obtained in real time from the anchor bolt strain test, the fiber strain at the strain point is determined using the fiber strain prediction model.

5. The method according to claim 1, wherein, The formula for determining the axial force of the anchor bolt is derived by using the deformation compatibility equation and elasticity theory, based on the elastic modulus of the anchor bolt, the cross-sectional area of ​​the anchor bolt, the elastic modulus of the optical fiber, and the cross-sectional area of ​​the optical fiber. This includes: Based on indoor experiments and literature review, the elastic modulus and cross-sectional area of ​​the anchor bolt, as well as the elastic modulus and cross-sectional area of ​​the optical fiber, were obtained. By applying different tensile forces, the formulas were used to... Determine the bonding coefficient k b Define anchor strain and fiber strain Let A be a linear function, where A m Let A be the cross-sectional area of ​​the anchor bolt. f Let be the cross-sectional area of ​​the optical fiber, F be the applied tensile force, and x be the position. Based on the deformation compatibility equation and the bonding coefficient, a deformation compatibility model between the optical fiber and the anchor is established, and the strain relationship is derived as follows: Based on the elastic modulus and elasticity theory of materials, Hooke's law is used to obtain the anchor bolt stress σ. m (x)=E m ·ε m (x) and fiber stress σ f (x)=E f ·ε f (x), and determine the strain compatibility formula. Among them, E m E represents the elastic modulus of the anchor bolt. f The elastic modulus of the optical fiber is given; based on the strain compatibility formula and the anchor bolt stress, the anchor bolt axial force formula is determined to be F. m (x)=A m ·σ m (x)=A m ·k b E f ·ε f (x).

6. The method according to claim 1, wherein, The formulas for fiber optic strain and anchor bolt axial force based on strain points are used to determine the load test values, and the anchor bolt strain test results are judged based on the deformation compatibility coefficient, including: Based on the cross-sectional area of ​​the anchor bolt, the bonding coefficient, the elastic modulus of the optical fiber, and the fiber strain at the strain point, the anchor bolt axial force at the strain point is determined using the anchor bolt axial force formula and used as the load test value. Based on the load loading value and the load test value, the load-displacement curve of the anchor bolt and the load axial force distribution curve along the depth are plotted. If the deformation coordination coefficient between the distributed optical fiber and the anchor bolt is greater than the preset coefficient threshold, then the current optical fiber strain measurement data is considered reliable, the distributed optical fiber sensor response is normal, and the bonding state is good. The deformation coordination coefficient is the ratio of optical fiber strain to anchor bolt strain. If the deformation coordination coefficient between the distributed optical fiber and the anchor bolt is less than the preset coefficient threshold, it is determined that the current anchor bolt strain test effect is not good. A comprehensive investigation and correction of the installation status of the distributed optical fiber sensor and the parameter configuration of the data acquisition system are carried out, and the anchor bolt strain test is carried out again and the load test value is calculated until the deformation coordination coefficient between the distributed optical fiber and the anchor bolt is greater than the preset coefficient threshold.

Images