Analysis model for judging influence of foreign matters in hole on concrete dam normal vertical line and positioning method

Abstract

The invention discloses an analysis model for judging influence of in-hole foreign matters on a concrete dam normal vertical line and a positioning method. Aiming at the technical defects that an existing manual displacement resetting method is high in omission factor and cannot accurately position a foreign matter touch position and the like, a normal vertical line natural vibration frequency analysis model is established based on a string vibration theory, and the equivalent length of a vertical line is calculated by exciting the vertical line and measuring the first-order natural vibration frequency in combination with steel wire tension, linear density and a comprehensive correction coefficient. And further judging a touch state and positioning the elevation of a touch point. The method can effectively identify and position the condition that the normal vertical line is touched by the foreign matter in the vertical line hole, remarkably improves the fault identification and diagnosis capability of a vertical line monitoring system, eliminates the hidden danger of monitoring data distortion caused by the foreign matter in the hole of the vertical line monitoring system, and improves the accuracy and reliability of concrete dam vertical line monitoring data.

Description

Technical Field

[0001] The invention relates to the field of safety monitoring of concrete dams in water conservancy projects, and particularly discloses an analysis model and a positioning method for judging whether a vertical line of a concrete dam is affected by foreign matter in a hole. Background Art

[0002] In the concrete dam safety monitoring system, deformation monitoring is a core component in assessing structural safety. Displacement observation methods based on both vertical and inverted plumb lines are widely used for long-term monitoring of concrete dams, offering high accuracy and long-term stability. The basic principle of the vertical plumb line method is to vertically route a highly elastic stainless steel wire (typically with a nominal diameter of approximately 1.0 mm) through a plumb line hole in the dam body. Under the weight of the weight, the wire remains taut, forming a plumb line. A high-precision coordinate measuring machine is used to measure the horizontal displacement of monitoring points at different elevations on the dam body relative to this line, thereby obtaining characteristic deformation parameters of the dam body under operating conditions. This displacement data can be used to assess the structural safety of concrete dams and provide a crucial basis for identifying and diagnosing potential safety hazards. To ensure measurement accuracy, the weight is typically immersed in a damping fluid to suppress plumb line swing caused by environmental vibrations or airflow disturbances, maintaining the plumb line's stability.

[0003] However, the measurement accuracy of the plumb line method is highly dependent on the smooth flow of the plumb line hole. To minimize its impact on the dam structure, plumb lines are typically designed with a small diameter (generally 100-150 mm, though some extra-high arch dams, due to the large displacement magnitude, have the diameter increased to 200-300 mm). The length of a single section can reach the maximum permitted by design specifications, 50 meters. This narrow and long hole channel is sensitive to interference from foreign objects and difficult to inspect. Over the long service life of a concrete dam, the risk of foreign matter intrusion into the hole is significant. Foreign matter in the hole can originate from calcareous scale deposited on the hole wall, debris dropped during construction or maintenance, small animals that stray into the hole, and debris from partially detached hole walls. If the plumb line wire contacts or even becomes stuck with foreign matter, the plumb line loses its ideal plumb position, directly distorting the displacement monitoring data. If this type of interference is not promptly identified and corrected, it can seriously mislead the assessment of the dam's actual displacement and safety status, posing a potential safety risk.

[0004] At present, in engineering practice, manual displacement observation is often used as the main means to determine whether the vertical line touches the hole wall or foreign objects. This method involves manually moving the weight horizontally for a certain distance and then releasing it. After it stabilizes, the vertical line is observed to see whether it returns to its original position accurately. If it cannot be reset, it is qualitatively inferred that there is a touch problem. However, this method has significant limitations: (1) For "soft touch" interference (such as slight contact between the steel wire and the pipe wall or foreign objects in the pipe), the steel wire may temporarily break away from the foreign object after the human disturbance and return to its original position, resulting in missed detection; and in the "hard jam" state (the steel wire is firmly stuck by a hard foreign object), the steel wire cannot move at this point and may be mistakenly judged as no abnormality; (2) This method has no ability to locate the touch point position and cannot provide location information for subsequent repair work such as maintenance and dredging. It relies only on experience for qualitative judgment, lacks quantitative basis, and has low reliability.

[0005] In summary, the existing technology has defects such as insufficient detection reliability, no touch point positioning capability, and lack of quantitative judgment basis. Summary of the Invention

[0006] The purpose of the present invention is to provide an analysis model and a positioning method for judging whether the vertical line of a concrete dam is affected by foreign matter in a hole.

[0007] To achieve the above objectives, the technical solution provided by the present invention includes the following contents:

[0008] An analytical model and location method for evaluating the impact of foreign objects in a concrete dam's vertical line on a hole is proposed. The model, based on string vibration theory, constructs a quantitative mapping relationship between the first-order natural frequency of the vertical line and its equivalent length. The equivalent length of the vertical line is calculated by inversely measuring the natural frequency to determine whether there is a collision. The specific steps are as follows:

[0009] S1: Determine the vertical tension of the vertical wire based on the design data and vertical line density The lower end of the vertical line above the weight is clamped in the horizontal direction with a clamp to keep the vertical line tension unchanged. The lower end of the vertical line is fixed in the horizontal direction. Then the upper and lower ends of the vertical line system are in a tight state, which is consistent with the string vibration model with both ends fixed. Based on the string vibration theory, the measured vertical line is Order natural frequency Calculate the length of the vertical line from the upper fixed point to the lower fixture fixed end , the calculation formula is:

[0010]

[0011] Where, is the estimated length of the vertical line, The measured value is collected by exciting the vertical line with the fixture at the lower end of the vertical line tightened. The natural frequency of the order, is the vertical tension, is the vertical line density;

[0012] S2: Vertical line density calibration of vertical line wire,

[0013] If the first inspection is carried out at the beginning of plumb line installation, the estimated length of the plumb line Actual length of perpendicular line The error between them comes from the fundamental frequency measurement error. The relative errors of the two are comparable. The estimated length is used to check whether there are defects in the installation of the vertical line and to judge whether the vertical line touches the pipe wall.

[0014] If the first test is carried out after a certain period of time after the installation of the vertical line, the vertical line density will increase slightly due to the influence of the attachments. Order natural frequency Calculated length of vertical line according to initial line density There will be a slight increase, so the vertical line can be used to calculate the length Equal to the actual length , based on which the linear density of the vertical line is calibrated, and the calculation formula is:

[0015]

[0016] Where, is the vertical equivalent linear density after calibration in this test, is the vertical tension, The measured value is collected by exciting the vertical line with the fixture at the lower end of the vertical line tightened. The natural frequency of the order, is the actual length of the vertical line;

[0017] S3: Remove the fixture that fixes the lower end of the vertical line and revise the formula for calculating the length of the vertical line based on string vibration theory. The revised formula is as follows:

[0018]

[0019] Where, The estimated length of the vertical line without clamp fastening is: is the comprehensive correction coefficient, is the vertical tension, To detect the calibrated vertical equivalent linear density, The measured value is picked up by stimulating the vertical line without clamp fastening. order natural frequency;

[0020] S4: The vertical lengths calculated based on the presence and absence of fixtures in the same period should be equal, and the comprehensive correction coefficient can be determined accordingly. , the calculation formula is as follows:

[0021]

[0022] Where, is the comprehensive correction coefficient, and They are the measured values ​​collected by exciting the vertical line with and without the clamp fastening at the lower end of the vertical line. order natural frequency;

[0023] S5: Within 2 years after the first test or parameter calibration, with a test period of half a year, there is no need to clamp the lower end of the vertical line. By stimulating the vertical line and measuring the Order natural frequency , based on this, calculate the length of the vertical line from the upper fixed point to the lower hammer :

[0024]

[0025] Where, This is the estimated length of the vertical line without clamp fastening in this test. This is the first actual measurement collected by the excitation vertical line without fixture fastening in this test. The natural frequency of the order, is the vertical tension, is the comprehensive correction coefficient, is the vertical equivalent linear density;

[0026] S6: Compare the estimated length of the vertical line of this test and actual length , judge the contact between the vertical line and the hole wall or foreign matter in the hole, if and If the relative difference is less than 5%, it is judged that no touch occurs. Otherwise, Significantly smaller than , it indicates that there is contact between the vertical line and the hole wall or the object in the hole.

[0027] If the first inspection is carried out at the beginning of plumb line installation, there will be very little attachment on the plumb line wire surface, and there will be only a very slight difference between the actual line density and the initial line density. and actual length The error between the two is primarily due to fundamental frequency measurement errors. When fundamental frequency measurement accuracy is at least 97%, the accuracy of the estimated plumb line length can reach over 95%. Based on this, the estimated length can be used to assess whether the plumb line installation is flawed and further determine whether the plumb line touches the pipe wall. If the initial inspection is performed some time after plumb line installation, the plumb line density may have increased slightly compared to the initial density due to attachments such as dust and scale. In this case, the plumb line density needs to be calibrated.

[0028] In step S6, if and If the relative difference is less than 5%, it is judged as no touch. Otherwise, if Significantly smaller than , it indicates that there is contact between the vertical line and the hole wall or foreign matter in the hole. The elevation of the contact point can be calculated using the following difference method:

[0029]

[0030] Where, is the elevation of the touch point, is the vertical line hanging height, is the actual length of the vertical line, Calculate the length of the vertical line for this test.

[0031] In order to reduce the adverse effects caused by the cumulative increase in vertical line density within the same calibration cycle and the failure to recalibrate, the change in the estimated length obtained from two consecutive tests can be used for judgment. Calculated length of vertical line compared with the last test If the relative difference is less than 5%, it is judged as no touch; if Significantly smaller than , indicating that there is contact between the vertical line and the hole wall or the object in the hole, which can be calculated based on the ratio of the length of the current vertical line to the length of the previous vertical line. , use the proportional method to locate the elevation of the touch point:

[0032]

[0033]

[0034] Where, is the elevation of the touch point, is the vertical line hanging height, is the actual length of the vertical line, is the estimated length for this time, is the last estimated length, The estimated length for this time Compared with the last estimated length ratio.

[0035] Of the two methods for evaluating and locating touch points mentioned above, the first method has the advantages of intuitive formulas and easy implementation, making it suitable for quick judgment; the second method utilizes the results of the previous test and performs better in terms of positioning accuracy, making it suitable for high-precision quantitative analysis and positioning of touch status.

[0036] Considering the differences in project environmental conditions, the growth rate of plumb line attachments varies. Monitoring data indicates that under adverse conditions, the annual growth rate of plumb line density can reach 2-5%. Since the estimated plumb line length is inversely proportional to the square root of the line density, a biennial calibration frequency can keep the relative error of the estimated plumb line length within 5%, ensuring the accuracy of plumb line contact detection. The calibration interval for line density and comprehensive correction coefficient can be adjusted appropriately based on changes in calibration parameters over time to keep calibration parameter changes within 5%.

[0037] In the test method of the vertical line of the concrete dam affected by foreign matter in the hole, since the proportion of the total weight of the steel wire to the tension is less than 1%, the tension of the entire vertical wire is It is uniformly taken as a constant value and approximately calculated based on the net gravity of the weight in the damping fluid, which is in line with engineering practice and is reasonable.

[0038] The slender structure of the vertical line typically causes its fundamental frequency to fall within a low-frequency range of 1 to 20 Hz. Within this frequency range, the influence of air resistance on its natural vibration characteristics is negligible. To quantify the actual effect of air resistance, a dynamic model incorporating air-structure coupling was established based on finite element simulation technology. By comparing the simulation results for two operating conditions, considering air resistance and ignoring it, it was found that when air resistance was accounted for, the first-order natural frequency of the vertical line system was slightly lower than when air resistance was ignored. The absolute value of the frequency calculation error between the two conditions was less than 0.01%. This result fully confirms the engineering judgment that air resistance has a negligible effect on the natural vibration characteristics of the vertical line under low-frequency conditions.

[0039] Based on model string vibration theory, this invention constructs a quantitative mapping relationship between the first-order natural frequency of a positive vertical line and its equivalent length (when the vertical line does not touch the entire pipe wall, the equivalent length is the original total length of the vertical line; when the vertical line touches the pipe wall, the equivalent length is the length below the touch point). By inferring the vertical line's equivalent length from the measured natural frequency, the contact status and the elevation of the contact point can be accurately determined. To ensure the accuracy of the estimated equivalent length of the vertical line, the invention regularly measures the vertical line's fundamental frequency under two operating conditions: with and without a clamp tightening the lower end of the vertical line. The vertical line's line density and comprehensive correction factor are then calibrated to dynamically update the parameters, ensuring the accuracy of the estimated equivalent length of the vertical line. In most testing conditions where parameter calibration is not required, the lower end of the vertical line does not need to be clamped; simply exciting the vertical line and acquiring the fundamental frequency allows for rapid and simple testing. This invention overcomes the shortcomings of existing methods, such as high missed detection rates and inability to locate foreign objects, providing a quantitative analysis-based method for detecting foreign object contact within the vertical line hole, significantly improving the monitoring reliability of the concrete dam vertical line system.

[0040] The test model for detecting the influence of foreign matter in the hole on the vertical line of a concrete dam described in the present invention is constructed based on the existing vertical line monitoring system. The existing vertical line monitoring system includes, from top to bottom, a fixed point at the top of the vertical line, a vertical line steel wire, and a weight connected to the lower end of the vertical line, and the weight is immersed in the damping fluid contained in the damping box. The weights from the top to the bottom of the vertical line system must not touch the hole wall or other objects, otherwise the vertical line displacement monitoring data will be distorted, affecting the accuracy of the monitoring results. On the basis of the original vertical line system, the present invention needs to add the following test devices: The fixture is used to temporarily clamp the lower end of the vertical line during model parameter calibration (it can be set above the damping box) to prevent the lower end of the vertical line from generating horizontal displacement, so that the boundary conditions of the vertical line system are highly consistent with the fixed end constraints in the classical string vibration model; The excitation and fundamental frequency acquisition device is used to apply vibration excitation to the vertical line and collect the fundamental frequency response signal of the vertical line system in real time, providing key data support for subsequent equivalent length calculation and touch judgment.

[0041] The present invention breaks through the qualitative analysis mode that relies on experience judgment in the traditional detection of foreign body touch of the vertical line, and establishes a quantitative identification model based on string vibration theory. By simplifying the vertical line system into a string vibration system with fixed ends at both ends, the quantitative relationship between the natural frequency and the estimated vertical line length is used to accurately distinguish the touch state and locate the touch position. Different from the subjective method in the prior art that mainly judges by heavy hammer disturbance and observation reset, the present invention innovatively introduces a method of estimating the length of the vertical line by measuring the natural frequency, and combines finite element simulation to verify the rationality of model assumptions such as air resistance and boundary constraints. It effectively solves the technical difficulties of traditional methods in identifying and locating foreign body touch in the vertical line hole, avoids the risk of misjudgment of concrete dam deformation caused by long-term distortion of monitoring data due to vertical line touch, and provides technical support for improving the data reliability, diagnostic accuracy and operational safety of the concrete dam vertical line monitoring system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a simplified schematic diagram of the perpendicular chord vibration model, in which:

[0043] Positive plumb line hole 1, shelf 2, damping box 3, plumb line fixing block 4, positive plumb line 5, heavy hammer 6, damping fluid 7.

[0044] Figure 2 Flow chart for calculation of touch point positioning; DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below through specific embodiments. However, this should not be understood as limiting the scope of the present invention to the following embodiments, and all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0046] Example 1: A concrete dam is equipped with a vertical line system, the main parameters of which are as follows: diameter of the vertical line stainless steel wire , actual length , effective weight of hammer (The buoyancy of the damping fluid has been deducted). After the plumb line is installed, use a clamp to clamp the lower end of the plumb line (above the weight) in the horizontal direction to maintain the plumb line tension and achieve a fixed constraint in the horizontal direction of the lower end of the plumb line. At this point, the upper and lower ends of the plumb line system are in a tightened state, which can be equivalent to a string vibration model with both ends fixed. Based on the string vibration theory, the measured Order natural frequency , the length of the vertical line from the upper fixed point to the lower fixture fixed end can be calculated , the calculation formula is:

[0047]

[0048] Where, is the estimated length of the vertical line, The measured value is collected by exciting the vertical line under the condition that the fixture at the lower end of the vertical line is tightened. The natural frequency of the order, is the vertical tension, is the vertical line density.

[0049] diameter 1mm, length The total weight of a 50m stainless steel wire is only 3.02N, and the actual tension of the plumb line ranges from 500N to 503N. Therefore, the effective weight of the weight of 500N can be roughly regarded as the constant tension of the entire wire, with an error of less than 1%, which is feasible in engineering.

[0050] (1) The measured value of the vertical line is Order natural frequency is 2.84Hz, then

[0051] m

[0052] Where, is the estimated length of the vertical line, The measured value is collected by exciting the vertical line under the condition that the fixture at the lower end of the vertical line is tightened. The natural frequency of the order, is the vertical tension, is the vertical line density.

[0053] At this time, the calculated length of the vertical line is slightly longer than the actual length of the vertical line by 50m, indicating that the installed vertical line has no contact. The calculated length error can be regarded as a normal deviation within the range of system error, which is mainly caused by three factors: First, the tension value used in the calculated model is 500N at the lower end of the vertical line, while the actual tension of the vertical line is slightly greater than 500N due to the weight of the vertical line. The tension value in the formula is slightly low; second, the measured natural frequency (compared with the ideal state without damping in vacuum) is slightly lower due to the influence of air resistance; third, the fundamental frequency measurement error.

[0054] If the tension error of the vertical line vibration, air resistance and measurement system error are equivalently combined into the linear density effect for calibration, the equivalent linear density after calibration is:

[0055] kg / m

[0056] Where, is the vertical line density after calibration in this test, is the vertical tension, The measured value is collected by exciting the vertical line under the condition that the fixture at the lower end of the vertical line is tightened. The natural frequency of the order, is the actual length of the vertical line.

[0057] The calibrated equivalent linear density is slightly greater than the original linear density of the steel wire ( =0.00616 kg / m);

[0058] (2) Release the fixture and measure the vertical line system in its natural state. Order natural frequency The comprehensive correction coefficient can be calibrated based on the natural frequency under two working conditions: with and without a fixture. The calibrated comprehensive correction coefficient is for:

[0059]

[0060] Where, is the comprehensive correction coefficient, and They are the measured values ​​collected by stimulating the vertical line with and without the clamp fastening at the lower end of the vertical line during this test. order natural frequency.

[0061] (3) Use the calibrated linear density and comprehensive correction factor, and the natural frequency measured this time , the estimated length of the vertical line is:

[0062]

[0063] Where, is the estimated length of the vertical line for the condition without fixture fastening, is the comprehensive correction coefficient, is the vertical tension, is the vertical line density after calibration in this test, The measured data collected by the excitation vertical line for the clamp-free fastening condition order natural frequency.

[0064] (4) In the following two years, a total of four tests were conducted at a cycle of once every six months. Order natural frequency They are 2.78 Hz, 2.76 Hz, 2.74 Hz and 2.72 Hz respectively. . Substituting the above frequency values ​​into the formula for calculating the length of the vertical line, the calculated lengths of the vertical lines are 50.36m, 50.72m, 51.09m and 51.47m respectively. The calculated lengths show a trend of slightly increasing gradually, and are all greater than the original actual length of the vertical line of 50 m. It is judged that the vertical line is non-contact during this period. The main reason for the increase in the calculated length is that the accumulation of attachments on the vertical line leads to a slow increase in the line density, which causes the natural frequency to decrease and the calculated length to increase relatively. This change trend is in line with the physical law of the accumulation and growth of attachments on the vertical line, and also verifies the sensitivity and rationality of the method of the present invention to parameter changes in the non-contact state.

[0065] (5) In the test at the end of the second year, i.e., year t=2.0, in addition to the first Order natural frequency In addition to 2.72Hz, the lower end of the vertical line was locked with a fixture to form a fixed end constraint condition. Order natural frequency The value is 2.76Hz. Based on the frequency measurement under two working conditions, with and without the fixture, and combined with the actual total length of the vertical line , after recalibrating the equivalent linear density, the equivalent linear density is obtained as follows:

[0066] kg / m

[0067] After recalibrating the comprehensive correction coefficient, the comprehensive correction coefficient is obtained for:

[0068] 5

[0069] (4) In the test at t=2.5 years, the vertical system was measured to be Order natural frequency =2.70Hz. Based on the previously calibrated equivalent linear density and other parameters, the estimated length of the vertical line is:

[0070]

[0071] It is judged that the vertical lines are not touching.

[0072] (5) In the test at t=3.0, the vertical system was measured to be Order natural frequency is 3.92Hz. Substituting it into the newly calibrated formula, the estimated length of the vertical line is:

[0073]

[0074] It is determined that the vertical line touches, and the elevation of the touch point is:

[0075] =

[0076] That is, the vertical line touch point is 15.3m below the hanging height of the vertical line.

[0077] (6) Identification and location analysis of soft touch problems

[0078] The above-mentioned identification and positioning method assumes that there is a "hard contact" between the vertical line and the hole wall (or the object in the hole), that is, it is assumed that the touch point is regarded as the rigid constraint end of the steel wire. For the "soft touch" scenario, in the above example, it is further assumed that the newly installed vertical wire has no attachments, and 15 m below the hanging point of the vertical line, the steel wire and the object in the hole are in "soft contact". The "soft contact" is simplified to a horizontal spring with a spring stiffness coefficient of k=0.3 N / mm. Based on finite element simulation technology, a refined mechanical model including the coupling of spring-wire-weight-damping fluid is established, and the dynamic characteristics of the vertical system are numerically simulated. The simulation results show that under this specific working condition, the first-order natural frequency of the vertical line is The formula for calculating the length of the vertical line is: The touch point is 36.3m below the top of the vertical line, 13.7m below the top of the vertical line, 1.3m away from the preset soft touch point. This positioning accuracy is sufficient to guide actual maintenance operations, demonstrating the effectiveness and adaptability of the method of the present invention in identifying and locating soft touches.

[0079] This patented technical solution can accurately determine whether a concrete dam's vertical line contacts the wall of a vertical hole or foreign objects within the hole, and precisely locate the contact point. This model method boasts excellent engineering adaptability and detection sensitivity, effectively identifying abnormal conditions caused by contact within the vertical line system. This prevents long-term distortion or misjudgment of monitoring data due to undetected contact issues, thereby providing a strong guarantee for the accuracy and reliability of concrete dam structural deformation monitoring.

Claims

1. An analytical model and positioning method for judging the influence of foreign matter in the hole on the vertical line of a concrete dam, characterized in that: Based on string vibration theory, this model constructs a quantitative mapping relationship between the first-order natural frequency of the vertical line and its equivalent length. The equivalent length of the vertical line is calculated by inversely measuring the natural frequency, thereby determining whether there is a touch. The specific steps are as follows: S1: Determine the vertical tension of the vertical wire based on the design data and vertical line density The lower end of the vertical line above the weight is clamped in the horizontal direction with a clamp to keep the vertical line tension unchanged. The lower end of the vertical line is fixed in the horizontal direction. Then the upper and lower ends of the vertical line system are in a tight state, which is consistent with the string vibration model with both ends fixed. Based on the string vibration theory, the measured vertical line is Order natural frequency Calculate the length of the vertical line from the upper fixed point to the lower fixture fixed end , the calculation formula is: ， Where, is the estimated length of the vertical line, The measured value is collected by exciting the vertical line with the fixture at the lower end of the vertical line tightened. The natural frequency of the order, is the vertical tension, is the vertical line density; S2: Vertical line density calibration of vertical line wire, If the first inspection is carried out at the beginning of plumb line installation, the estimated length of the plumb line Actual length of perpendicular line The error between them comes from the fundamental frequency measurement error. The relative errors of the two are comparable. The estimated length is used to check whether there are defects in the installation of the vertical line and to judge whether the vertical line touches the pipe wall. If the first test is carried out after a certain period of time after the installation of the vertical line, the vertical line density will increase slightly due to the influence of the attachments. Order natural frequency Calculated length of vertical line according to initial line density There will be a slight increase, so the vertical line can be used to calculate the length Equal to the actual length , based on which the linear density of the vertical line is calibrated, and the calculation formula is: ， Where, is the vertical equivalent linear density after calibration in this test, is the vertical tension, The measured value is collected by exciting the vertical line with the fixture at the lower end of the vertical line tightened. The natural frequency of the order, is the actual length of the vertical line; S3: Remove the fixture that fixes the lower end of the vertical line and revise the formula for calculating the length of the vertical line based on string vibration theory. The revised formula is as follows: ， Where, The estimated length of the vertical line without clamp fastening is: is the comprehensive correction coefficient, is the vertical tension, To detect the calibrated vertical equivalent linear density, The measured value is picked up by stimulating the vertical line without clamp fastening. order natural frequency; S4: The vertical lengths calculated based on the presence and absence of fixtures in the same period should be equal, and the comprehensive correction coefficient can be determined accordingly. , the calculation formula is as follows: ， Where, is the comprehensive correction coefficient, and They are the measured values ​​collected by exciting the vertical line with and without the clamp fastening at the lower end of the vertical line. order natural frequency; S5: Within 2 years after the first test or parameter calibration, with a test period of half a year, there is no need to clamp the lower end of the vertical line. By stimulating the vertical line and measuring the Order natural frequency , based on this, calculate the length of the vertical line from the upper fixed point to the lower hammer : ， Where, This is the estimated length of the vertical line without clamp fastening in this test. This is the first actual measurement collected by the excitation vertical line without fixture fastening in this test. The natural frequency of the order, is the vertical tension, is the comprehensive correction coefficient, is the vertical equivalent linear density; S6: Compare the estimated length of the vertical line of this test and actual length , judge the contact between the vertical line and the hole wall or foreign matter in the hole, if and If the relative difference is less than 5%, it is judged that no touch occurs. Otherwise, Significantly smaller than , it indicates that there is contact between the vertical line and the hole wall or the object in the hole.

2. The analytical model and positioning method for judging the influence of foreign matter in the hole on the vertical line of a concrete dam as claimed in claim 1, characterized in that: If it is determined in step S6 that the vertical line touches the hole wall or a foreign object in the hole, the elevation of the touching point is calculated according to the length difference method or the change ratio method; The difference method is specifically: ， Where, is the elevation of the touch point, is the vertical line hanging height, is the actual length of the vertical line, Calculate the length of the vertical line for this test; The specific proportion method is: like Significantly smaller than , then according to the ratio of the current estimated length to the last estimated length , locate the elevation of the touch point: ， Where, is the elevation of the touch point, is the vertical line hanging height, is the actual length of the vertical line, The estimated length for this time Compared with the last estimated length ratio.

3. The analytical model and positioning method for judging the influence of foreign matter in the hole on the vertical line of a concrete dam as claimed in claim 1, characterized in that: If the time between the last parameter calibration and the current test is 2 years, and the test determines that the vertical line does not touch the hole wall, the vertical line density and comprehensive correction factor must be calibrated again: ， ， Where, is the vertical line density after calibration for this test, is the comprehensive correction coefficient after calibration for this test, is the vertical tension, and They are the measured values ​​obtained by exciting the positive vertical line vibration under the conditions of with and without clamping the lower end of the vertical line. The natural frequency of the order, is the actual length of the vertical line.

4. The analytical model and positioning method for judging the influence of foreign matter in a hole on the vertical line of a concrete dam as claimed in claim 1, characterized in that: The measurement of the first-order natural frequency is suitable for test instruments in the 1-20 Hz frequency range, and the detection cycle is once every six months, or immediately when an abnormal vertical line measurement value is found during the monitoring process.

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