WO2022109938A1

WO2022109938A1 - Method for measuring size of power transmission tower foundation

Info

Publication number: WO2022109938A1
Application number: PCT/CN2020/131834
Authority: WO
Inventors: 张兴森; 梁庆国; 梁世容; 李君华; 边美华; 卢展强; 刘桂婵; 彭家宁
Original assignee: 广西电网有限责任公司电力科学研究院
Priority date: 2020-11-26
Filing date: 2020-11-26
Publication date: 2022-06-02

Abstract

A method for measuring the size of a power transmission tower foundation. In the method, taking the fact that a Rayleigh-wave phase velocity has different propagation speeds in different media as a theoretical basis, when there is a difference between the properties of soil of a power transmission tower foundation and that around the power transmission tower foundation, resulting in different Rayleigh-wave phase velocities, the three-dimensional size measurement of a power transmission tower foundation is implemented by means of Rayleigh-wave detection technology. The method has the advantages of a fast measurement speed and not damaging a target structure. Especially when a foundation is buried relatively deep, the size of the foundation can be easily obtained by means of the method; and when the sizes of a large number of power transmission tower foundations need to be measured, the method can reflect the high efficiency thereof.

Description

A method for measuring the foundation size of a transmission tower

technical field

The invention relates to the technical field of measurement of the base size of a power transmission tower, in particular to a method for measuring the base size of a power transmission tower.

Background technique

The importance of the foundation to the structure is self-evident. The transmission tower foundation is the key structure of the support tower, and its safety is one of the key factors affecting the safe operation of the power system. However, due to the influence of factors such as on-site objective conditions and human subjectivity, some transmission tower foundations have defects at the beginning of their construction. Through the investigation, it is found that the deviation of the foundation size and design of the transmission tower is a common defect, and some foundations even appear partially spherical at the bottom, which will greatly reduce the bearing capacity of the foundation and bury hidden dangers for the occurrence of accidents. Therefore, it is very necessary and urgent to carry out special inspections for such defects. Since most of the foundations are located underground, the detection of such defects can only be carried out by manual excavation at present. However, this detection method has obvious shortcomings. It will not only cause secondary damage to the foundation, but also have problems such as high cost and low efficiency. At the same time, it is difficult to operate some foundations with large buried depths, making this method unable to meet large-scale requirements. Therefore, an efficient and practical detection method is urgently needed to make up for the shortcomings of the existing basic detection technology of transmission towers.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides a method for measuring the foundation size of a transmission tower. Based on the different propagation speeds of Rayleigh waves in different media, there is a difference in the properties of the soil around the foundation of the transmission tower and the foundation of the transmission tower. , resulting in different Rayleigh wave phase velocities, through the existing Rayleigh wave detection technology to achieve the three-dimensional size measurement of the transmission tower foundation. The specific technical solutions are as follows:

A method for measuring the foundation size of a transmission tower, comprising the following steps:

S1: Determine the detection range according to the design data of the transmission tower foundation, establish an xy plane coordinate system within the detection range, and arrange several measurement points and acquisition systems;

S2: Select an excitation point outside the detection range, generate an excitation signal at the excitation point, and collect Rayleigh wave signals of each measurement point through the acquisition system;

S3: According to the collected Rayleigh wave signals of each measuring point, obtain the Rayleigh wave phase velocity of each measuring point at different depths;

S4: Based on the Rayleigh wave phase velocities of each measuring point, a spatially continuous Rayleigh wave phase velocity distribution cloud map is obtained by means of interpolation fitting;

S5: Determine the Rayleigh wave phase velocity of the transmission tower foundation according to the Rayleigh wave phase velocity distribution cloud diagram, and then find the size range that matches the Rayleigh wave phase velocity of the transmission tower foundation in the Rayleigh wave phase velocity distribution cloud diagram. This size range obtains the outline of the transmission tower foundation, and then determines the size of the transmission tower foundation.

Preferably, the acquisition system includes a vibration exciter, several detectors, a collector, a wireless transmission module, and a data processor; the vibration exciter is arranged at the excitation point, and the detector is arranged at each measuring point where the vibration exciter and several detectors are connected to the collector through data lines; the collector, the wireless transmission module and the data processor are connected in sequence; the vibration exciter is used to generate excitation signals; It is used to collect Rayleigh wave signals of each measuring point; the collector is used to collect the data of the vibration exciter and the detector, and transmit the collected data to the data processor through the wireless transmission module for storage and processing.

The acquisition system wirelessly transmits the data collected at the inspection site to the data processor for storage. The inspection and management personnel can view the inspection data in real time through the data processor and make judgments on the inspection results. The system can solve the problems that the current transmission tower foundation size detection data is difficult to collect, transmit and use electricity, thereby improving the detection efficiency.

Preferably, the collector needs to set a collection working frequency band, and the working frequency band is calculated according to the buried depth of the transmission tower foundation.

Preferably, the calculation method of the working frequency band is as follows:

S1: The relationship between the Rayleigh wave effective detection depth H and the wavelength λ _R is expressed by the improved equivalent half-space method, that is, the relationship between the effective detection depth H, the wavelength-depth conversion coefficient β and the wavelength λ _R is:

H=βλ _R ;

S2: The wavelength-depth conversion coefficient β is related to the Poisson’s ratio μ of the measured object, as shown in Table 1 below:

Table 1 The relationship between the wavelength-depth conversion coefficient β and the Poisson's ratio μ of the measured object

μμ	0.10.1	0.150.15	0.20.2	0.250.25	0.30.3	0.350.35	0.40.4	0.450.45	0.50.5
βbeta	0.550.55	0.5750.575	0.6250.625	0.650.65	0.70.7	0.750.75	0.790.79	0.840.84	0.8750.875

According to Table 1, the relationship between the wavelength-depth conversion coefficient β and the Poisson's ratio μ of the measured object is obtained by fitting the index as follows:

β=0.486e ^1.2μ ;

S3: According to the dispersion characteristics of Rayleigh waves, the relationship between the wavelength λ _R , frequency f and wave speed λ _R of Rayleigh waves is:

Then the Rayleigh wave frequency f is calculated as:

Preferably, the determination of the detection range in the described step S1 is as follows: determine the outer contour of the transmission tower foundation according to the design data, and expand the outer outline of the transmission tower foundation by 2m to form the detection range.

Preferably, the method for arranging the measuring points in the step S1 is as follows: according to the xy plane coordinate system established by the detection range, several measuring lines are arranged parallel to the x-axis according to a certain distance and at equal intervals, and each measuring line is numbered; Several measuring points are arranged at equal intervals on each survey line, and the distance between two adjacent survey points on the same survey line is equal to the distance between two adjacent survey lines, and each survey point is numbered according to survey line-measuring point. For example, 2-1 represents the first hit of the second line.

Preferably, the excitation point in the step S2 is set at a distance of 5 meters from the nearest measuring point. According to the characteristics of Rayleigh waves, the excitation point should be as far away from the observation point as possible, and the maximum buried depth of the transmission tower foundation is small, generally less than 10 meters, so the excitation point should be selected 5 meters away from the nearest observation point.

Preferably, the step S4 specifically includes the following steps:

S41: Obtain the Rayleigh wave phase velocity-depth curve of each measuring point based on the Rayleigh wave phase velocity of each measuring point, and obtain the coordinate value of each measuring point according to the xy plane coordinate system established by the detection range, and find the phase on the same survey line. For the velocity values of two adjacent measuring points at the same depth, the velocity distribution along the x-axis between two adjacent measuring points on the same measuring line is obtained by means of linear interpolation;

Suppose the coordinates of two adjacent measuring points on the same survey line are (x ₁ , y ₁ , z), (x ₂ , y ₁ , z), respectively, and the corresponding Rayleigh wave phase velocities are v ₁ , v ₂ , then The wave velocity v(x, y ₁ , z) at any point (x, y ₁ , z) between these two measuring points on the survey line is:

S42: According to step S41, the Rayleigh wave phase velocity distribution cloud map of any point on the survey line along the depth direction can be obtained, that is, the Rayleigh wave phase velocity x-z two-dimensional distribution cloud map of the Rayleigh wave phase speed along each survey line direction can be obtained;

S43: According to the x-z two-dimensional distribution cloud map of Rayleigh wave phase velocity of adjacent survey lines, find the Rayleigh wave phase velocity at each survey line position at the same x and z, and obtain the y-axis between the two survey lines through linear interpolation Rayleigh wave phase velocity distribution in the direction;

Assuming that the y coordinates of the two survey lines are y ₁ and y ₂ respectively, the wave velocity v(x, y, z) at any point (x, y, z) between the two survey lines is:

S44: Through step S43, the Rayleigh wave phase velocity distribution at any point along the y-axis direction can be obtained, and by combining the Rayleigh wave phase velocity x-z two-dimensional distribution cloud map in step S42, the three-dimensional Rayleigh wave phase velocity in the entire detection range can be obtained Velocity distribution cloud map.

The beneficial effects of the present invention are: in view of the shortcomings of the existing electric tower foundation size detection technology, based on the Rayleigh wave detection technology, a non-destructive detection method for the transmission tower foundation size is proposed, which has the advantages of fast detection speed and accurate detection of target structures. There is no damage and other advantages, especially when the depth of the foundation is large, the method can easily obtain the size of the foundation. This method is especially efficient when it is necessary to perform dimension inspection on a large number of transmission tower foundations.

Description of drawings

Fig. 1 is the structural representation of the acquisition system;

Fig. 2 is the structural schematic diagram of the vibration exciter;

Fig. 3 is the relation curve of the wavelength depth conversion coefficient and the Poisson's ratio of the measured object;

Fig. 4 is the schematic diagram of detection range;

Fig. 5 is the measuring point distribution diagram in the embodiment;

Figure 6 is the wave velocity distribution along the depth of the measuring points 1-1, 3-2, 3-3 and 5-3;

Figure 7 is the nephogram of the x-z two-dimensional Rayleigh wave phase velocity distribution of Line 3.

Detailed ways

In order to better understand the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

S1: Determine the detection range according to the design data of the transmission tower foundation, establish an xy plane coordinate system within the detection range, and arrange several measurement points and acquisition systems. Since the top section of the transmission tower foundation is a rectangle, the xy plane coordinate system can be the origin of the intersection of the diagonal lines of the transmission tower foundation.

As shown in Figure 1, the acquisition system includes an exciter, several detectors, a collector, a wireless transmission module, and a data processor; the exciter is arranged at the excitation point, the detector is arranged at each measurement point, and the excitation The vibrator and several detectors are connected with the collector through the data line; the collector, the wireless transmission module and the data processor are connected in sequence; the vibrator is used to generate the excitation signal; the detector is used to collect the Rayleigh wave signal of each measuring point; The collector is used to collect the data of the exciter and the detector, and transmit the collected data to the data processor through the wireless transmission module for storage and processing.

The acquisition system can also include mobile terminals such as mobile phones and tablets, as well as monitoring terminals such as computers. These terminals are connected to the wireless transmission module and can view the collected data at any time and find problems in time. Concentrate on the test itself, and view the detection data in real time through the mobile terminal; at the same time, the commander at the far end can conveniently retrieve the detection data and results through the mobile terminal or monitoring terminal and make corresponding decisions to guide the on-site detection personnel.

As shown in Figure 2, the exciter includes a Chengtai 20LB hammer, a force sensor located in the handle of the hammer, and an impact pad. The hammer weighs 20 pounds, and the impact pad is 20cm, 20cm, and 5cm in length, width, and height, respectively. The impact load is formed by hitting the impact pad with a force hammer, which causes the ground to vibrate. When the hammer hits the impact pad, the force sensor converts the acceleration change of the hammer into a force signal, and the force signal is transmitted to the collector through the data line.

The wireless transmission module includes the wireless signal transmission DTU, the wireless signal transmission DTU includes a 3G or 4G mobile card, the wireless signal transmission DTU is installed near the collector, and is connected with the collector through a signal line. The wireless signal transmission DTU adopts USR-G780 4G LTE DTU, and the collected data is wirelessly transmitted to the data processor for storage through the 3G or 4G network.

Among them, the detector adopts CDJ-Z100 all-digital detector, and the collector adopts DZQ6-2A engineering seismic wave velocity meter.

The collector needs to set the working frequency band for collection, and the working frequency band is calculated according to the buried depth of the transmission tower foundation. The calculation method of the working frequency band is as follows:

(1) The relationship between the effective detection depth H of Rayleigh wave and the wavelength λ _R is expressed by the improved equivalent half-space method, that is, the relationship between the effective detection depth H, the wavelength-depth conversion coefficient β and the wavelength λ _R is:

H = βλ _R (1).

(2) The wavelength-depth conversion coefficient β is related to the Poisson’s ratio μ of the measured object, as shown in Table 1 below:

β=0.486e ^1.2μ ; (2)

As shown in Figure 3, by exponential fitting, the sum of squares of the correlation coefficients reaches 0.996. Therefore, the above formula can be used to calculate the wavelength-depth conversion coefficient under any Poisson's ratio. At the same time, the relative error can be used to describe the fitting accuracy of formula (2). After calculation, the relative error of the fitting accuracy is within 0.014. It can be seen that the fitting accuracy of formula (2) is high.

(3) According to the dispersion characteristics of Rayleigh waves, the relationship between the wavelength λ _R , frequency f and wave speed λ _R of Rayleigh waves is:

Then the Rayleigh wave frequency f is calculated as:

Since the foundation of the transmission tower is generally buried at a depth of 3 to 8 meters, the detection depth range H can be taken as 0.5m to 10m, the Poisson's ratio of concrete is taken as 0.2, and the Poisson's ratio of soil needs to be determined according to the actual situation of the site. The upper limit is 0.4, the lower wave speed of soil is taken as 100m/s, and the upper limit of the wave speed of concrete is taken as 3000m/s. Therefore, it can be calculated through the above formula that the working frequency band of Rayleigh wave detection set by the collector should be 6-4700Hz.

The acquisition system wirelessly transmits the data collected at the inspection site to the data processor for storage. The inspection and management personnel can view the inspection data in real time through the data processor and make judgments on the inspection results. This system can solve the problems that the current transmission tower foundation size detection data is not easy to collect, transmit and use electricity, thereby improving the detection efficiency.

As shown in Figure 4, the detection range is determined as follows: determine the outer contour of the transmission tower foundation according to the design data, and expand the outer contour of the transmission tower foundation by 2m to form the detection range. The layout method of the measuring points is as follows: According to the xy plane coordinate system established by the detection range, several measuring lines are arranged parallel to the x-axis at a certain distance and at equal intervals, and each measuring line is numbered; For several measuring points, the distance between two adjacent measuring points on the same measuring line is equal to the distance between two adjacent measuring lines, and each measuring point is numbered according to measuring line-measuring point. For example, 2-1 represents the first hit of the second line. In order to improve the accuracy of linear interpolation, the distance between two adjacent survey lines is in the range of 0.1m to 0.3, and the distance between two adjacent survey points on the same survey line is in the range of 0.1m to 0.3. The smaller the distance between two adjacent survey lines and the distance between two adjacent survey points on the same survey line, the higher the accuracy of the linear interpolation fitting, and the more accurate, adaptive, and layout the obtained Rayleigh wave phase velocity distribution cloud map. The distance between the two measuring lines or two measuring points on the foundation of the transmission tower is smaller than the distance between the two measuring lines or two measuring points arranged outside the foundation of the transmission tower, which can improve the accuracy of linear fitting.

S2: Select an excitation point outside the detection range, generate excitation signals at the excitation point, and collect Rayleigh wave signals of each measurement point through the acquisition system. The excitation point is set at 5 meters from the nearest measurement point. According to the characteristics of Rayleigh waves, the excitation point should be as far away from the observation point as possible, and the maximum buried depth of the transmission tower foundation is small, generally less than 10 meters, so the excitation point should be selected 5 meters away from the nearest observation point. Due to the limitation of instrument channels, each measuring point can be tested in batches, so it is necessary to excite the same point many times, and multiple collectors and detectors matching the number of measuring points can also be set.

S3: According to the collected Rayleigh wave signals of each measuring point, the Rayleigh wave phase velocity of each measuring point at different depths is obtained.

S4: Based on the Rayleigh wave phase velocity of each measuring point, a spatially continuous Rayleigh wave phase velocity distribution cloud map is obtained by means of interpolation fitting. Specifically include the following steps:

The size of a reinforced concrete transmission tower foundation is: length and width are 0.4m, height is 1.75m, using C25 concrete prefabrication. The foundation is prefabricated with a formwork first, then hoisted into a hole, and then backfilled to form the final transmission tower foundation.

Set the square center of the transmission tower foundation as the coordinate origin, the x-axis is horizontal to the right, the y-axis is down, and the z-axis is along the depth direction of the foundation. Use lime and a tape measure to arrange survey lines 1 to 5 at equal intervals around the foundation, where survey line 3 coincides with the x-axis, the distance between two adjacent survey lines is 0.3m, and 5 survey lines are equally spaced on each survey line. The distance between two adjacent measuring points on the same survey line is 0.3m, marked with lime, and the measuring point number is: survey line number-measuring point number, such as 1-2 means No. 2 survey point on survey line 1 , the coordinates of the measuring point are (-0.3, 0.6, 0). The excitation point is arranged at a position 5m away from the 5-1 measuring point. As shown in Figure 5.

(1) Data collection

a. Connect the acquisition system, turn on the collector, and set the working frequency of Rayleigh wave detection to 6-4000Hz.

b. Place the 4 detectors at the measurement points 1-1 to 1-4 respectively, and use the vibration exciter to generate the excitation signal at the excitation point.

c. The collector performs data collection, and the collection time lasts for 10s.

d. After the collection of the batch is completed, move the detector to the next measurement point in sequence, and repeat steps b and c until all measurement points are collected.

(2) Data analysis

a. After the data collection is completed, the wave velocity distribution of each collection point along the z-axis can be obtained, as shown in Figure 6. The figure only lists the wave velocity distribution of the 1-1, 3-2, 3-3, and 5-3 measuring points. .

b. By formula (5), the x-z two-dimensional distribution cloud map of survey lines 1 to 5 can be obtained respectively. For example, the wave velocity distribution of survey line 3 is shown in Figure 7. Since the Rayleigh wave phase velocity is different in different media as the theoretical basis, there are differences in the properties of the soil around the transmission tower foundation and the transmission tower foundation, resulting in different Rayleigh wave phase velocities. There is a big difference between the speed of area 1 and the speed of area 1, and the speed distribution in area 1 is gradual from the center to both sides. Therefore, it can be determined that area 1 is the speed distribution of the foundation of the transmission tower, and area 2 is the soil on both sides of the foundation of the transmission tower. Therefore, it can be identified from area 1 that the length of the transmission tower foundation is 0.38m, and the buried depth (height) is 1.73m. By adopting the present invention, the size of the foundation of the transmission tower can be measured with high precision.

Similarly, the y-z two-dimensional distribution cloud map of Rayleigh wave phase velocity can be extracted from the cloud map, and then the width of the size of the transmission tower can be identified, which will not be repeated here.

The present invention is not limited to the specific embodiments described above, and the above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalents, etc. made within the spirit and principle of the present invention Substitutions and improvements, etc., should all be included within the protection scope of the present invention.

Claims

A method for measuring the foundation size of a power transmission tower, comprising the following steps:

S1: Determine the detection range according to the design data of the transmission tower foundation, establish an xy plane coordinate system within the detection range, and arrange several measurement points and acquisition systems;

S2: Select an excitation point outside the detection range, generate an excitation signal at the excitation point, and collect Rayleigh wave signals of each measurement point through the acquisition system;

S3: According to the collected Rayleigh wave signals of each measuring point, obtain the Rayleigh wave phase velocity of each measuring point at different depths;

S4: Based on the Rayleigh wave phase velocities of each measuring point, a spatially continuous Rayleigh wave phase velocity distribution cloud map is obtained by means of interpolation fitting;

S5: Determine the Rayleigh wave phase velocity of the transmission tower foundation according to the Rayleigh wave phase velocity distribution cloud diagram, and then find the size range that matches the Rayleigh wave phase velocity of the transmission tower foundation in the Rayleigh wave phase velocity distribution cloud diagram. This size range obtains the outline of the transmission tower foundation, and then determines the size of the transmission tower foundation.
The method for measuring the foundation size of a transmission tower according to claim 1, wherein the acquisition system comprises a vibration exciter, a plurality of detectors, a collector, a wireless transmission module, and a data processor; The vibration exciter is arranged at the excitation point, the detector is arranged at each measuring point, the vibration exciter and several detectors are connected to the collector through a data line; the collector, the wireless transmission module, the data processor connected in sequence; the vibration exciter is used to generate excitation signals; the detector is used to collect Rayleigh wave signals of each measuring point; the collector is used to collect the data of the vibration exciter and the wave detector and pass the collected data through The wireless transmission module transmits to the data processor for storage and processing.
The method for measuring the foundation size of a transmission tower according to claim 2, wherein the collector needs to set a working frequency band for collection, and the working frequency band is calculated according to the buried depth of the foundation of the transmission tower.
The method for measuring the basic size of a transmission tower according to claim 3, wherein the calculation method of the operating frequency band is as follows:

S1: The relationship between the Rayleigh wave effective detection depth H and the wavelength λ R is expressed by the improved equivalent half-space method, that is, the relationship between the effective detection depth H, the wavelength-depth conversion coefficient β and the wavelength λ R is:

H=βλ R ;

S2: The wavelength-depth conversion coefficient β is related to the Poisson’s ratio μ of the measured object, as shown in Table 1 below:

Table 1 The relationship between the wavelength-depth conversion coefficient β and the Poisson's ratio μ of the measured object

μ 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 beta 0.55 0.575 0.625 0.65 0.7 0.75 0.79 0.84 0.875

According to Table 1, the relationship between the wavelength-depth conversion coefficient β and the Poisson's ratio μ of the measured object is obtained by fitting with an index as follows:

β=0.486e 1.2μ ;

S3: According to the dispersion characteristics of Rayleigh waves, the relationship between the wavelength λ R , frequency f and wave speed λ R of Rayleigh waves is:

Then the Rayleigh wave frequency f is calculated as:
A method for measuring the foundation size of a transmission tower according to claim 1, wherein the detection range in the step S1 is determined as follows: the outer contour of the foundation of the transmission tower is determined according to the design data, and the outer contour of the foundation of the transmission tower is determined according to the design data. The outer contour is expanded by 2m to form the detection range.
The method for measuring the foundation size of a transmission tower according to claim 1, wherein the method for arranging the measuring points in the step S1 is as follows: the xy plane coordinate system established according to the detection range is parallel to the x axis according to a certain Arrange several survey lines at equal intervals, and number each survey line; arrange several survey points at equal intervals on each survey line, and the distance between two adjacent survey points on the same survey line is the same as that of two adjacent survey points. The distances of the lines are equal, and each measuring point is numbered according to the measuring line-measuring point.
The method for measuring the foundation size of a transmission tower according to claim 1, wherein the excitation point in the step S2 is set at a distance of 5 meters from the nearest measurement point.
The method for measuring the foundation size of a transmission tower according to claim 1, wherein the step S4 specifically includes the following steps:

S41: Obtain the Rayleigh wave phase velocity-depth curve of each measuring point based on the Rayleigh wave phase velocity of each measuring point, and obtain the coordinate value of each measuring point according to the xy plane coordinate system established by the detection range, and find the phase on the same survey line. For the velocity values of two adjacent measuring points at the same depth, the velocity distribution along the x-axis between two adjacent measuring points on the same measuring line is obtained by means of linear interpolation;

Suppose the coordinates of two adjacent measuring points on the same survey line are (x 1 , y 1 , z), (x 2 , y 1 , z), respectively, and the corresponding Rayleigh wave phase velocities are v 1 , v 2 , then The wave velocity v(x, y 1 , z) at any point (x, y 1 , z) between these two measuring points on the survey line is:

S42: According to step S41, the Rayleigh wave phase velocity distribution cloud map of any point on the survey line along the depth direction can be obtained, that is, the Rayleigh wave phase velocity x-z two-dimensional distribution cloud map of the Rayleigh wave phase speed along each survey line direction can be obtained;

S43: According to the x-z two-dimensional distribution cloud map of Rayleigh wave phase velocities of adjacent survey lines, find the Rayleigh wave phase velocities at the positions of each survey line at the same x and z, and obtain the y-axis between the two survey lines through linear interpolation Rayleigh wave phase velocity distribution in the direction;

Assuming that the y coordinates of the two survey lines are y 1 and y 2 respectively, the wave velocity v(x, y, z) at any point (x, y, z) between the two survey lines is:

S44: Through step S43, the Rayleigh wave phase velocity distribution at any point along the y-axis direction can be obtained, and by combining the Rayleigh wave phase velocity x-z two-dimensional distribution cloud map in step S42, the three-dimensional Rayleigh wave phase velocity in the entire detection range can be obtained Velocity distribution cloud map.