Analysis model and diagnosis method for detecting influence of foreign matters in hole on inverted vertical line of concrete dam

Abstract

The invention discloses an analysis model and a diagnosis method for detecting influence of in-hole foreign matters on a concrete dam inverted vertical line. In order to solve the problems that an existing method highly depends on artificial experience, foreign matter touch judgment is inaccurate, foreign matter touch positioning is difficult to achieve and the like, the efficient inverted plumb line state non-contact diagnosis method is constructed on the basis of a correction model of a string vibration theory in combination with inverted plumb line system natural vibration frequency detection. According to the method, the length of a free swing section of a vertical line is calculated through known inverted line tension, linear density and actually measured natural vibration frequency in combination with information such as in-hole water depth and floater parameters, and the actual length of the vertical line is compared, so that whether the inverted line is in abnormal touch or not is judged. The method has the advantages of non-invasiveness, high sensitivity, high positioning precision and the like, the distortion risk of monitoring data can be effectively reduced, and reliable technical support is provided for stable operation and precise maintenance of a concrete dam safety monitoring system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete dam safety monitoring, in particular to an analysis model and a diagnosis method for detecting the influence of siltation or foreign matter in a hole on a reverse plumb line of a concrete dam. BACKGROUND

[0002] In the safety monitoring system of large and medium-sized concrete dam projects, horizontal displacement observation based on the plumb line method is a basic and reliable monitoring method. The plumb line method includes two layout forms of normal plumb line and reverse plumb line, which can be used for high-precision measurement of the horizontal displacement between the internal structure of the concrete dam or different parts of the dam body, and is widely used in dam stability and displacement monitoring. It has important significance in ensuring the safety of concrete dam structures and building risk early warning systems. The core principle of the plumb line method is to set a stainless steel wire (usually about 1mm in diameter) with one end fixed and the other end applying a plumb direction tension in the vertical line hole of the dam body, forming a relatively stable plumb reference line in space. When the dam body deforms, the reference line remains vertical, and by measuring the horizontal offset of the different elevation measuring points relative to the plumb reference line, the relative displacement between the elevation measuring points can be determined. The reverse plumb line method is to set an anchor point at the bottom of the drill hole in the dam foundation rock mass, and fix one end of the reverse plumb line wire to the anchor point and connect the other end to the float device in the observation room of the dam body. The float is placed in a damping float tank filled with damping liquid, and the steel wire is tensioned and straightened by using the buoyancy, forming a plumb reference line with an absolute position that does not change.

[0003] The aperture of the reverse plumb line monitoring system is usually 100-150mm, and the maximum depth of the reverse plumb hole can reach 50-100m, and most of the hole section is in the bedrock and is immersed in water for a long time. During the long-term operation of the concrete dam, there is a high risk of foreign matter intrusion into the vertical line hole, such as calcium scale attached to the hole wall, accidental falling of debris, accidental entry of small animals, and sediment accumulation, etc. Once the foreign matter in the hole comes into contact with the plumb line, it will directly cause the displacement monitoring data to deviate, and if this kind of interference cannot be identified and excluded in time, it may lead to misjudgment of the displacement state of the dam body.

[0004] In current actual engineering practice, there is still a lack of technical means that are convenient, efficient and have intelligent identification capability to determine whether there is foreign matter in the inverted hole that interferes with the monitoring data of the inverted line, and it is even more difficult to effectively identify the specific position of the foreign matter. At present, the method of manually disturbing the float to determine the touch is commonly used in engineering, that is, the float is manually moved a certain distance and then released, and after the plumb line system stabilizes, whether the plumb line returns to the initial position is observed to speculate whether the inverted plumb line is in contact. However, this method has significant limitations: on the one hand, when the contact force between the plumb line and the hole wall is weak (the original contact position is restored after recovery), the contact force is strong (the touch position cannot be changed by moving the float), or the plumb line is completely blocked by foreign matter, it is difficult to effectively identify the touch state; on the other hand, this method highly depends on manual operation, which is not only inefficient, but also greatly affected by the operation method and subjective judgment of personnel, and has a high risk of misjudgment; in addition, this method cannot accurately locate the touch position, and it is also difficult to quantify the influence of the touch on the monitoring data, which cannot meet the demand of high precision and intelligentization of concrete dam safety monitoring. SUMMARY

[0005] The purpose of the present application is to provide an analysis model and a diagnostic method for detecting the influence of foreign matter in the hole on the inverted plumb line of a concrete dam. The model is based on the theory of string vibration, and simplifies the inverted plumb line system into a string vibration model and modifies the calculation formula of the first-order natural frequency. In combination with the finite element simulation analysis to obtain the value list of the correction coefficient, the flexible constraint of the float end, the water resistance, the change of the linear density and other engineering factors are comprehensively considered, so as to build a diagnostic analysis framework suitable for actual operation conditions. The length of the free swing section of the plumb line, the touch point and its elevation are accurately located by inversely calculating the first-order natural frequency. This effectively fills the technical gap of existing foreign matter detection and positioning methods for inverted holes, and can avoid distortion of monitoring data, providing strong technical support for stable operation and maintenance of the safety monitoring system of the concrete dam.

[0006] To achieve the above-mentioned purpose, the technical solution provided by the present application includes the following contents:

[0007] The test object of the method for detecting the influence of foreign matter in the hole on the inverted plumb line of a concrete dam is the existing inverted plumb line monitoring system in the concrete dam, which includes the lower end fixed inverted plumb line steel wire, float, damping liquid, float box and water in the hole, and the upper end of the string vibration model of the float tension.

[0008] An analysis model and a diagnostic method for detecting the influence of foreign matter in the hole on the inverted plumb line of a concrete dam, characterized in that the method simplifies the inverted plumb line vibration into a string vibration model and modifies the first-order natural frequency formula, and the equivalent length of the plumb line is calculated by measuring the frequency, and the actual length is compared to determine the touch and positioning, which specifically includes the following steps:

[0009] S1: Determine the actual length of the inverted plumb line steel wire according to the design data , the upward tension of the float and vertical line density ;

[0010] S2: The inverted plumb line system is simplified to a string vibration model with both ends fixed, and its theoretical value is calculated based on the classical string vibration theory. The natural frequency is calculated as follows:

[0011]

[0012] Where, The ideal string vibration model The natural frequency of the order, is the actual length of the vertical line, is the upward tension of the float, is the vertical line density;

[0013] S3: Considering the flexible constraint characteristics of the inverted float end and the damping effect of the water in the hole, the calculation formula of the first-order natural frequency is modified. The modified calculation formula is:

[0014]

[0015] Where, is the first-order natural frequency of the vertical system, is the actual length of the vertical line, is the upward tension of the float, is the vertical line density, is the vertical float end constraint correction coefficient, is the water resistance correction coefficient;

[0016] S4: Excite the inverted plumb line to generate vibration, and use the vibration sensor to collect the first order natural frequency of the inverted plumb line , and calculate the length of the free swing section of the vertical line according to the correction formula, the formula is:

[0017]

[0018] Where, The estimated length of the vertical free swing section is: The first measured value of the vertical system The natural frequency of the order, is the upward tension of the float, is the vertical line density, is the vertical float end constraint correction coefficient, is the water resistance correction coefficient;

[0019] S5: Compare the length of the vertical free swing section Actual length of perpendicular line , judge the contact between the vertical line and the hole wall or foreign matter in the hole; specifically: calculate the length of the free swing section of the inverted vertical line Actual length of perpendicular line The threshold of the difference is taken as 5% of the actual length;

[0020] when , and when the dam displacement monitoring value of the vertical system has no abnormality, it is determined that the vertical system has no contact;

[0021] when , the vertical lines touch.

[0022] If the length of the free swing section of the inverted vertical line is calculated Significantly smaller than actual length , it indicates that there is a contact problem between the vertical line and the hole wall or the object in the hole. The elevation of the contact point is calculated based on the length difference or change ratio, specifically:

[0023]

[0024] Where, is the elevation of the touch point, is the bottom elevation of the inverted plumb line, is the actual length of the vertical line, Calculate the length of the free swing section of the vertical line.

[0025] During the long-term service life of the plumb wire, its linear density gradually increases due to the accumulation of attachments such as dust and scale. If the initial linear density and the currently measured wire vibration frequency are still used to estimate the length of the plumb line's free swinging section according to the formula, and under ideal operating conditions where the wire is not in contact with the hole wall or objects within the hole, statistical analysis of measured data shows that the estimated length of the plumb line's free swinging section exhibits an average annual increase of 0-2%. This phenomenon is due to the increase in linear density caused by the accumulation of attachments on the plumb wire, while the initial linear density is still used in the estimated length calculation. To eliminate the estimated value errors caused by time-varying linear density, historical data from regular inspections can be used to locate the touch point based on the ratio of the estimated lengths from the two most recent inspections.

[0026] If the vertical wire is not cleaned and maintained regularly, and the estimated length in a certain test is significantly reduced compared with the previous test, it means that the vertical wire is in contact with the hole wall or the components inside the hole. The ratio of the estimated length of the free swing section of the vertical line to the estimated length of the previous vertical line is used. , quantitatively locate the elevation position of the touch point:

[0027]

[0028] Where, is the elevation of the touch point, is the ratio of the current calculated length of the free swing section of the plumb line to the last calculated length, is the elevation of the bottom of the inverted plumb line, is the actual length of the plumb line.

[0029] To balance the calculation accuracy and work efficiency, the calculated length of the free swing section of the plumb line needs to be optimized. Since the ratio of the total weight of the steel wire to the upward tension is less than 1%, the tension of the plumb line is simplified as the upward tension, i.e. the buoyancy of the float, which can meet the accuracy requirements of engineering calculation. The linear density of the plumb line When calculating, the slight mass increment caused by the oxidation film and a small amount of adhering substances on the stainless steel wire has little effect on the linear density, which can be generally ignored. When the linear density growth caused by the adhering substances may exceed 5%, based on the change of the fundamental frequency obtained from the initial and current detection, the plumb line is judged to be not touched, and the current linear density is corrected by making the twice calculated lengths equal:

[0030]

[0031]

[0032] In the formula, are the current and initial linear densities, respectively, are the current and initial water resistance correction coefficients, respectively, and if the water level in the inverted plumb hole changes little, the two take the same value, are the current and initial plumb float end constraint correction coefficients, respectively, and if the float parameters remain unchanged, the two take the same value, and are the current and initial measured natural frequencies of the first and second orders, respectively.

[0033] If the current calculated length of the plumb line has a significant change, it is judged that the plumb line has touched, and the touch positioning is performed according to the above method.

[0034] The invention approximates the flexible constraint of the float end in the plumb line system to the fixed end constraint in the string vibration system, i.e. the inverted plumb line is equivalent to the string vibration model with both ends fixed. In order to correct the calculation error caused by the fixed end constraint assumption, a correction coefficient ​​​The fundamental frequency calculation formula is corrected. For this purpose, a fluid-solid coupling dynamic model including a float-damping liquid-cable structure is established. By comparing the simulation analysis and analytical calculation results of the two working conditions of the float end flexible constraint and the solid end constraint, the results show that the first-order natural frequency of the inverted line taking into account the float end flexible constraint is lower than that of the solid end constraint condition. The relative error between the two frequencies is about 10%, and the calculation error needs to be eliminated through the correction coefficient. Based on the simulation analysis results, a systematic correction coefficient value scheme is formed for the influence of the float flexible constraint under different working conditions. The float end constraint correction coefficient The specific values ​​are shown in the following table:

[0035] Table 1 Correction coefficients The value of

[0036]

[0037] The results of finite element simulation analysis show that the inverted float has a large influence on the correction coefficient when the outer diameter is 40~50cm, the height is 35~55cm and the deadweight is 100~200N. The effect of the float size and deadweight is very small, so the float size and deadweight are not listed as factors affecting the correction coefficient in Table 1; the vertical length has little effect on the correction coefficient. The impact is relatively obvious.

[0038] The slender structure of the inverted plumb line causes its fundamental frequency to fall within the 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 using finite element simulation technology. By comparing simulation results for operating conditions with and without air resistance, it was found that, after accounting for air resistance, the first-order natural frequency of the inverted plumb line was slightly lower than that of the condition without air resistance. The relative difference between the two frequencies was less than 0.01%, confirming the engineering judgment that the influence of air resistance is very minimal.

[0039] The influence of water resistance in the inverted hole is also studied by finite element simulation technology, which builds a refined model including fluid-chord interaction. The results of multi-operating numerical simulation analysis show that the added mass and damping effect of water will slightly change the natural vibration characteristics of the inverted chord. Based on the simulation results, a systematic correction coefficient value scheme is formed for the influence of added mass and damping of water under different operating conditions. The water resistance correction coefficient is The specific values ​​are shown in the following table:

[0040] Table 2 Correction coefficients The value of

[0041]

[0042] The measurement accuracy of the first order natural frequency of the present application reaches 98% and above to meet the needs of judging whether the inverted plumb line touches the hole wall or the object in the hole. In the measurement tool and method, mature and simple test instruments suitable for the frequency band near 1-20 Hz can be selected, for example, the magnetic armature is clamped on the stainless steel wire, the frequency sweeping is performed by using the non-contact electromagnetic exciter, the vibration signal of the plumb line is picked up in a non-contact manner by using the laser Doppler vibration meter, and the vibration fundamental frequency is obtained by combining the spectrum analyzer.

[0043] Under the erosion of a humid environment, the surface of the stainless steel plumb line will generate an oxide film with a thickness of 10-100 nm. The oxide film causes the mass per unit length of the plumb line wire to increase by 0.1-1 mg / m, which accounts for less than 0.005% of the initial mass of the wire, far below the allowable range of engineering measurement error (±0.3%). Therefore, in actual engineering calculation and analysis, this part of the mass increment can be ignored. In contrast, the influence of attachments such as dust and scale on the vibration performance of the plumb line cannot be ignored. Without regular maintenance measures, the annual mass growth rate of the plumb line wire due to the deposition of attachments is about 2%-5%. If the water and gas flowing in the pipe are clean, the mass growth rate is smaller. When the detection cycle is half a year, the change in linear density caused by the attachments will cause the natural frequency of the plumb line to decay by about 1% between two adjacent detection times. If the linear density value is constant when calculating the length, the calculated length of the free swing section of the plumb line will increase by no more than 1% every half year. Therefore, the natural frequency of the inverted plumb line is detected every half year, and the linear density of the plumb line is corrected under the premise of no touch.

[0044] The detection model and evaluation method proposed by the present application equivalent simplify the inverted plumb line into an ideal string vibration model with both ends fixed based on the classical string vibration theory, and realize efficient detection and positioning of the blockage or foreign matter touching in the inverted hole by modifying the natural frequency calculation formula (considering factors such as flexible constraint of the float end, water resistance, and linear density error). The advantages are:

[0045] (1) The string vibration theory is applied to detect and identify the plumb line and the pipe wall touching problem. The modified natural frequency calculation formula is closer to the actual working condition, solving the problem of inaccurate touch judgment and inability to locate foreign matter by the traditional float moving method;

[0046] (2) On the premise of detecting and comparing the linear density change rule every half year, the length of the free swing section of the plumb line is calculated by the measured frequency, which can accurately locate the elevation of the touch point, and the detection accuracy reaches 95% without complex equipment;

[0047] (3) Provide a standardized and non-contact solution for the maintenance of the concrete dam inverted vertical line system monitoring facilities, avoiding the long-term misjudgment of monitoring data and causing dam safety risks;

[0048] (4) The entire detection method can be standardized and deployed, suitable for engineering application and promotion. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 Simplified schematic diagram of inverted vertical line chord vibration model;

[0050] Wherein, 1 is a shelf, 2 is a float, 3 is a dam body, 4 is a float box, 5 is an inverted vertical line, 6 is an observation pier, 7 is a bedrock, and 8 is an anchoring point.

[0051] Figure 2 Flowchart of technical solution. DETAILED DESCRIPTION

[0052] The present application will be further described below in conjunction with examples. The present embodiment is implemented on the basis of the technical solution of the present application, and gives a detailed implementation manner and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0053] Example 1: A concrete dam of a certain hydropower project is provided with an inverted vertical line system, and the main parameters are as follows: stainless steel wire diameter , actual length of vertical line , water depth in inverted vertical hole 40m, upward tension of float above vertical line , float diameter 45cm, float self weight 100N, and float height 50cm (completely immersed in damping liquid).

[0054] The inverted vertical line system is now simplified as a fixed-end chord vibration model, and the flexible constraint of the inverted float end and the water damping effect in the hole are considered. The base frequency calculation formula based on the classical chord vibration theory is modified, and the calculation formula is:

[0055]

[0056] In the formula, is the first-order natural frequency of the vertical line system, is the actual length of the vertical line, is the upward tension of the float, is the linear density of the vertical line, is the constraint correction coefficient of the float end of the vertical line, is the water resistance correction coefficient.

[0057] In conjunction with the present embodiment, the model of the present application is used for diagnosis:

[0058] (1) Simplified calculation of steel wire tension

[0059] The total mass of the 50m long steel wire is 0.302kg, and its actual tension range is between 497N (lower end of the steel wire) and 500N (upper end of the steel wire). Compared with the standard upward tension of the float of 500N, the maximum relative error value is less than 1%. Therefore, in the process of engineering calculation and analysis, the tension of the whole steel wire is approximately treated as 500N.

[0060] (2) Analysis of the influence of the upper end constraint condition of the inverted vertical line

[0061] Using finite element simulation technology, the upper end of the inverted vertical line is simulated and analyzed under the conditions of fixed end constraint and actual connection of the submerged float in the damping liquid. The results show that the first-order natural frequency calculated under the condition of fixed end constraint is slightly higher than that under the actual connection of the float, and the difference between the two frequency values is about 0.1%. According to Table 1, the vertical line float end constraint correction coefficient ξ = 0.998.

[0062] (3) Influence of fluid resistance on natural vibration characteristics

[0063] Due to the slender structure of the inverted vertical line, its fundamental frequency is in the low frequency vibration range of 1~20Hz, and the influence of air resistance on its natural vibration characteristics is relatively weak. The finite element simulation analysis results show that after considering the influence of air resistance, the first-order natural frequency of the vertical line is slightly lower than that when air resistance is ignored, and the frequency calculation error is less than 0.5%.

[0064] Through finite element simulation analysis verification, the fundamental frequency of the inverted vertical line needs to be corrected considering the damping effect of water, and the correction coefficient is shown in Table 2.

[0065] According to Table 2, the water resistance correction coefficient of the water depth of 40m in the hole of the length of 50m is .

[0066] (4) Influence of long-term use of inverted vertical line steel wire on line density change

[0067] In humid environment, a thickness of about 10nm~100nm of oxide film will be formed on the surface of stainless steel wire. Theoretically calculated, the mass increase of the vertical line steel wire per unit length caused by this is in the extremely small range of 0.1mg / m~1mg / m, and the influence of this mass increment on the natural vibration characteristics of the structure can be ignored.

[0068] The measured data shows that without maintenance, the vertical line steel wire will increase in mass by about 2%~5% per year due to dust and scale attachment. If the monitoring period is half a year, the reduction in natural frequency caused by this is about 1%.

[0069] Based on the above analysis, the first order natural frequency of the inverted vertical line can be detected to determine whether the vertical line is in contact with the hole wall or the object in the hole. Based on the above engineering parameters, the first order natural frequency of the inverted vertical line is calculated by using the modified formula of string vibration theory:

[0070]

[0071] wherein, is the first order natural frequency of the vertical line system, is the actual length of the vertical line, is the upward tension of the float, is the linear density of the vertical line, is the constraint correction coefficient of the float end of the vertical line, is the water resistance correction coefficient.

[0072] If the first order natural frequency of the inverted vertical line is , the length of the inverted vertical line is calculated as:

[0073]

[0074] wherein, is the calculated length of the free swing section of the vertical line, is the measured first order natural frequency of the vertical line, is the upward tension of the float, is the linear density of the vertical line, is the constraint correction coefficient of the float end of the vertical line, is the water resistance correction coefficient. The calculated length

[0075] =49.3m is less than 5% of the actual length , which can be considered as a normal deviation caused by the linear density of the inverted vertical line, the assumption of fixed end constraint condition and the measurement error of the fundamental frequency.

[0076] (5) Length difference based vertical line contact with hole wall or object in hole discrimination and positioning

[0077] If the first order natural frequency of the inverted vertical line is , the length of the free swing section of the inverted vertical line is calculated as:

[0078]

[0079] which is significantly smaller than the actual length , indicating that the vertical line is in contact with the hole wall or the object in the hole; if the elevation of the bottom of the inverted vertical line is =200m, the contact point elevation is:

[0080] ​

[0081] wherein, is the height of the touch point, is the height of the bottom of the inverted plumb line, is the actual length of the plumb line, is the calculated length of the free swing section of the plumb line.

[0082] According to the calculation, it is shown that the touch point is about 15 m above the bottom of the inverted plumb line.

[0083] (6) Touching discrimination and positioning of the plumb line and foreign matter in the hole based on the length ratio of two measurement times

[0084] In the long-term service of the plumb line steel wire, its linear density will gradually increase due to the deposition of dust, scale and other attachments. According to the measured data, the annual growth of the linear density of the steel wire is about 2-5%. If the steel wire does not touch in the inverted plumb hole, in addition to the linear density, other factors affecting the vibration characteristics of the plumb line system remain basically unchanged. For two measurement times with a short interval (such as half a year) and without cleaning and maintenance, the actual linear density increases by 1-2.5%, the measured fundamental frequency decreases by about 1%, and the calculated length of the free swing section of the plumb line increases by about 1%. It can be considered that the error of the calculated length caused by the change of the linear density is small (the increase of the inferred length is about 1%). Therefore, the comparison and analysis of the calculated length ratio obtained from two measurement times at similar times can not only be used to identify the frequency change trend, but also can eliminate the system error caused by the simplification of the calculation model to a certain extent, and improve the reliability of the touch judgment and positioning.

[0085] According to the calculation of the length of the free swing section of the plumb line with the same linear density, if the calculated length of the inverted plumb line in a certain detection is significantly smaller than the calculated length of the detection half a year ago, the change of the calculated length caused by the change of the linear density can be ignored due to the short interval of the detection time, and the change of the calculated length is mainly caused by the touching of the foreign matter in the inverted plumb hole. The touch point height can be positioned according to the ratio of the length calculated value of this time to the length calculated value of the last time .

[0086]

[0087] wherein, is the height of the touch point, is the height of the bottom of the inverted plumb line, is the actual length of the plumb line (50 m), is the ratio of the calculated length of the plumb line this time to the calculated length of the plumb line last time;

[0088] According to the calculation results, it is shown that the touch point is about 16.5 m above the bottom of the inverted plumb line.

[0089] Since the estimated length is inversely proportional to the frequency, if the linear density is corrected using the estimated length value detected six months ago, the calibrated equivalent linear density is:

[0090]

[0091] Since the estimated length is inversely proportional to the square root of the linear density, the linear density calibration value of the last measurement, which was half a year ago, is used. Calculation is performed, and the correction length of the vertical free swing section calculated in this test is:

[0092] m

[0093] Using a total length of 50m, the touch point is approximately 16.3m above the bottom of the inverted plumb line. This is very close to the positioning result obtained by using the ratio of the estimated lengths of two similarly timed measurements (approximately 16.5m above the bottom of the inverted plumb line). This shows that using the ratio of the estimated lengths of two similarly timed measurements, without linear density correction, for positioning can automatically eliminate calculation errors caused by linear density variations.

[0094] (7) Soft touch identification and positioning analysis

[0095] The above two identification methods are mainly aimed at the "hard touch" situation 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, there is no water in the hole, and 15m above the bottom of the inverted plumb line, the steel wire and the object in the hole are in "soft contact". The "soft touch" is simplified to a horizontal spring with a spring stiffness coefficient of k=0.1N / mm. Based on finite element simulation technology, a refined mechanical model including the coupling of spring-wire-float-water-damping liquid is established, and the dynamic characteristics of the vertical line are numerically simulated. The results show that under this specific working condition, the first-order natural frequency value of the inverted plumb line is Based on the calculation formula of the inverted plumb line length of this patent, the length of the free swing section of the inverted plumb line obtained from the frequency value is The touch point is 36.2m above the bottom of the inverted line, and the location of the touch point is 13.8m above the bottom of the inverted line, which is only 1.2m away from the preset soft touch point. The positioning accuracy is sufficient to meet the needs of guiding actual maintenance operations, indicating that this method is also effective and adaptable for the identification and positioning of soft touch.

[0096] The present application can realize the rapid identification and positioning of the reverse plumb line touch anomaly, significantly reduce the risk of monitoring data distortion caused by hole touch, and has the characteristics of non-contact, high sensitivity and strong engineering applicability. The method can provide scientific and reliable technical basis for the operation and maintenance of the concrete dam displacement monitoring system, and ensure the accuracy and integrity of the plumb line monitoring data. At the same time, the technology helps maintenance personnel to quickly judge the source of the anomaly, implement accurate repair, and improve the response efficiency and disposal level of the dam structure safety risk.

Claims

1. An analytical model and diagnostic method for detecting the influence of foreign matter in the hole on the inverted line of a concrete dam, characterized in that: This method simplifies the inverted vertical line vibration into a string vibration model and modifies the first-order natural frequency formula. The equivalent length of the vertical line is deduced from the measured frequency, and compared with the actual length to determine the touch and locate the position. The method specifically includes the following steps: S1: Determine the actual length of the vertical line of the plumb line wire according to the design data , the upward tension of the float and vertical line density ; S2: The inverted plumb line system is simplified to a string vibration model with both ends fixed, and its theoretical value is calculated based on the classical string vibration theory. The natural frequency is calculated as follows: ， Where, The ideal string vibration model The natural frequency of the order, is the actual length of the vertical line, is the upward tension of the float, is the vertical line density; S3: Considering the flexible constraint characteristics of the inverted float end and the damping effect of the water in the hole, the calculation formula of the first-order natural frequency is modified. The modified calculation formula is: ， Where, is the first-order natural frequency of the vertical system, is the actual length of the vertical line, is the upward tension of the float, is the vertical line density, is the vertical float end constraint correction coefficient, is the water resistance correction coefficient; S4: Excite the inverted plumb line to generate vibration, and use the vibration sensor to collect the first order natural frequency of the inverted plumb line , and calculate the length of the free swing section of the vertical line according to the correction formula, the formula is: ， Where, The estimated length of the vertical free swing section is: The first measured value of the vertical system The natural frequency of the order, is the upward tension of the float, is the vertical line density, is the vertical float end constraint correction coefficient, is the water resistance correction coefficient; S5: Compare the length of the vertical free swing section Actual length of perpendicular line , judge the contact between the vertical line and the hole wall or foreign matter in the hole; specifically: calculate the length of the free swing section of the inverted vertical line Actual length of perpendicular line The threshold of the difference is taken as 5% of the actual length; when , and when the dam displacement monitoring value of the vertical system has no abnormality, it is determined that the vertical system has no contact; when , the vertical lines touch.

2. The analytical model and diagnostic method for detecting the influence of foreign matter in the hole on the inverted line of a concrete dam according to claim 1, characterized in that If it is determined to be a touch in step S5, the elevation of the touch point is calculated based on the length difference or the change ratio. The specific calculation formula based on the length difference is: ， Where, is the elevation of the touch point, is the bottom elevation of the inverted plumb line, is the actual length of the vertical line, Calculate the length of the free swing section of the vertical line; The touch point elevation calculation formula based on the change ratio is: ， Where, is the elevation of the touch point, is the ratio of the current estimated length of the vertical free swing segment to the last estimated length, is the bottom elevation of the inverted plumb line, is the actual length of the vertical line.

3. The analytical model and diagnostic method for detecting the influence of foreign matter in a hole on the inverted plumb line of a concrete dam as claimed in claim 1, characterized in that: In step S3, the vertical float end constraint correction coefficient is introduced and water resistance correction factor , according to different float parameters, vertical length and water depth in the hole, the finite element simulation analysis is used to determine and value.

4. The analytical model and diagnostic method for detecting the influence of foreign matter in a hole on the inverted plumb line of a concrete dam as claimed in claim 1, characterized in that: In step S4, the first-order natural frequency detection is performed using a test instrument in the 1-20 Hz frequency range; the detection cycle is once every six months.

5. The analytical model and diagnostic method for detecting the influence of foreign matter in the hole on the inverted line of a concrete dam as claimed in claim 1, characterized in that If the calculated length of the vertical free swing section is If there is no significant change, the initial and current detection lengths are equal to the vertical line density. Make corrections: Depend on , get , Where, are the current and initial vertical line densities, are the current and initial water resistance correction coefficients respectively. If the water level in the inverted hole does not change much, the two take the same value; are the current and initial vertical float end constraint correction coefficients respectively. If the float parameters remain unchanged, the two take the same value. and The current and initial measured order natural frequency.

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