Method for determining karst cave critical area in foundation where tower foundation in lightning high-incidence area is located

Abstract

A method for determining a karst cave critical area in a foundation where a tower foundation in a thunder and lightning high-incidence area is located comprises the following steps that the foundation containing a karst cave, a tower and a tower foundation are manufactured in an equal-proportion reduction mode and placed in a model box, and a monitoring system and lightning stroke simulation equipment are placed in the model box; a plurality of model boxes are established, the karst cave in each model box is located under the center point of the tower foundation and has different vertical distances from the ground surface, lightning stroke simulation equipment is started to perform lightning stroke simulation on the foundation in each model box, and a critical vertical distance is obtained; a plurality of model boxes are established, the vertical distance between the karst cave in each model box and the ground surface is the critical vertical distance, the horizontal distances between the karst cave and the center point of the tower foundation are different, lightning stroke simulation equipment is started to conduct lightning stroke simulation on the foundation in each model box, and the critical horizontal distance is obtained; and determining a critical area according to the critical vertical distance and the critical horizontal distance. The method is high in test accuracy, low in test cost and high in reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of transmission tower foundations, and particularly relates to a method for determining the critical area of karst caves in the foundation of transmission towers in lightning-prone areas. Background Technique

[0002] As an important part of a transmission project, the stability of a transmission tower foundation is directly related to the safe operation of a transmission line. When a transmission tower foundation is set in a lightning-prone area, since lightning often occurs in a lightning-prone area, the generated lightning will not only damage the tower body, but also cause certain damage to the foundation soil around the transmission tower foundation through direct lightning strikes. For a karst geological area with more karst caves in the foundation, lightning strikes will induce the instability and collapse of the karst caves in the foundation where the tower foundation is located, thereby causing the overturning instability of the transmission tower foundation.

[0003] In the prior art, generally, the lightning strikes suffered by a transmission line and a transmission tower are analyzed and studied, and less research is conducted on the influence of lightning strikes on karst caves distributed in the foundation, and it is impossible to accurately evaluate the influence degree of lightning strikes on karst caves and the influence on the safe service of the tower foundation. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects and problems in the prior art that it is impossible to accurately evaluate the influence of lightning strikes on karst caves, and to provide a method for determining the critical area of karst caves in the foundation of transmission towers in lightning-prone areas that can accurately evaluate the influence of lightning strikes on karst caves.

[0005] To achieve the above purpose, the technical solution of the present invention is: a method for determining the critical area of karst caves in the foundation of transmission towers in lightning-prone areas, the method comprising the following steps:

[0006] Step 1: According to the actual engineering situation, prepare a foundation containing karst caves, a tower and a tower foundation in equal proportion and place them in a model box; place a monitoring system and a simulated lightning strike device in the model box;

[0007] Step 2: Establish a plurality of model boxes according to Step 1, with the karst caves in each model box being directly below the center point of the tower foundation and having different vertical distances from the ground surface; start the simulated lightning strike device to conduct simulated lightning strikes on the foundation containing karst caves in each model box, and monitor the deformation degree of the karst caves and the inclination degree of the tower foundation under different vertical distance conditions from the ground surface after the lightning strike through the monitoring system;

[0008] Calculate the first vertical distance from the ground surface when the deformation degree of the karst cave reaches the threshold value and the second vertical distance from the ground surface when the inclination degree of the tower foundation reaches the threshold value, and calculate the critical vertical distance according to the maximum value of the first vertical distance and the second vertical distance;

[0009] Step 3: Establish multiple model boxes according to Step 1. In each model box, the vertical distance from the karst cave to the ground surface is the critical vertical distance, and the horizontal distances from the karst cave to the center point of the tower foundation are different. Start the simulated lightning strike equipment to conduct simulated lightning strikes on the foundation containing the karst cave in each model box, and monitor the deformation degree of the karst cave and the inclination degree of the tower foundation under different horizontal distance conditions from the karst cave to the center point of the tower foundation after the lightning strike through the monitoring system;

[0010] Calculate the first horizontal distance from the karst cave to the center point of the tower foundation when the deformation degree of the karst cave reaches the threshold value, and the second horizontal distance from the karst cave to the center point of the tower foundation when the inclination degree of the tower foundation reaches the threshold value, and calculate the critical horizontal distance according to the maximum value of the first horizontal distance and the second horizontal distance;

[0011] Step 4: Determine the critical area of the karst cave according to the critical vertical distance and the critical horizontal distance.

[0012] The simulated lightning strike equipment includes an impulse current generator, and the output end of the impulse current generator is connected to the foundation containing the karst cave.

[0013] The specific calculation steps of the first vertical distance z 1 in Step 2 are as follows:

[0014] Record the displacement value of the top of the karst cave under different vertical distance conditions from the karst cave to the ground surface after the lightning strike through the monitoring system, calculate the deformation degree of the karst cave according to the displacement value of the top of the karst cave, and draw a curve of the change of the deformation degree of the karst cave with the vertical distance from the karst cave to the ground surface. When the deformation degree of the karst cave reaches the threshold value, obtain the corresponding first vertical distance z 1 of the karst cave from the ground surface.

[0015] The specific calculation steps of the second vertical distance z 2 in Step 2 are as follows:

[0016] Record the inclination degree of the tower foundation under different vertical distance conditions from the karst cave to the ground surface after the lightning strike through the monitoring system, record and draw a curve of the change of the inclination degree of the tower foundation and the deformation degree of the karst cave. When the inclination degree of the tower foundation reaches the threshold value, obtain the corresponding deformation degree of the karst cave, and determine the second vertical distance z 2 of the karst cave from the ground surface according to the corresponding deformation degree of the karst cave.

[0017] The specific calculation steps of the first horizontal distance x 1 in Step 3 are as follows:

[0018] Record the displacement values of the top of the karst cave under different horizontal distance conditions from the center point of the tower foundation after lightning strikes through the monitoring system, calculate the deformation degree of the karst cave according to the displacement values of the top of the karst cave, and draw the change curve of the deformation degree of the karst cave with the horizontal distance from the center point of the tower foundation. When the deformation degree of the karst cave reaches the threshold, obtain the first horizontal distance x of the karst cave from the center point of the tower foundation 1 。

[0019] The specific calculation steps of the second horizontal distance x in step three 2 are as follows:

[0020] Record the inclination of the tower foundation under different horizontal distance conditions from the center point of the tower foundation after lightning strikes through the monitoring system, record and draw the change curve of the inclination of the tower foundation and the deformation degree of the karst cave. When the inclination of the tower foundation reaches the threshold, obtain the corresponding deformation degree of the karst cave, and determine the second horizontal distance x of the karst cave from the center point of the tower foundation according to the corresponding deformation degree of the karst cave 2 。

[0021] The deformation degree of the karst cave is the ratio of the displacement value of the top of the karst cave to the diameter of the karst cave. The determination steps of the deformation degree threshold of the karst cave are as follows:

[0022] Draw the change curve of the deformation degree of the karst cave with time within the set time after lightning strikes when the karst cave is located directly below the center point of the tower foundation at a distance of times the foundation width. Record the deformation degree of the karst cave corresponding to the maximum slope of the change curve as the deformation degree threshold of the karst cave

[0023] The critical area V of the karst cave 0 The calculation formula is:

[0024] V 0 =z u ×x u ×x u ;

[0025] x u ={x 1 ,x 2} max ;

[0026] z u ={z 1 ,z 2} max ;

[0027] Among them, z u is the critical vertical distance, x u is the critical horizontal distance, x 1 is the first horizontal distance, x 2 is the second horizontal distance, z 1 is the first vertical distance, z2 is the second vertical distance.

[0028] Determine the critical karst cave area V 0 After that, use the monitoring system to detect the total volume V of the cracks derived from the karst cave when the karst cave is at the boundary position of the critical area under the action of lightning strike 3 and the average crack length l, and correct the critical karst cave area V according to the following formula 0 as follows:

[0029] V 0 ′ = {V 1 , V 2} max ;

[0030] V 1 = (1 + α)V 0 ;

[0031] V 2 = (z u + l) × (x u + l) × (x u + l);

[0032]

[0033] Among them, V 0 ′ is the corrected critical karst cave area, V is the original volume of the karst cave cavity, z u is the critical vertical distance, and x u is the critical horizontal distance.

[0034] The monitoring system includes an inclination sensor, a laser displacement sensor, and a ground penetrating radar. The inclination sensor is arranged at the corner of the tower foundation, and the laser displacement sensor is arranged at the bottom of the karst cave cavity;

[0035] The inclination sensor is used to detect the inclination of the tower foundation;

[0036] The laser displacement sensor is used to detect the displacement value of the top of the karst cave;

[0037] The ground penetrating radar is used to detect the total volume of the cracks derived from the karst cave and the average crack length when the karst cave is at the boundary position of the critical area under the action of lightning strike.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. In the method for determining the critical area of karst caves in the foundation of tower bases in lightning-prone areas of the present invention, a reduced-scale model test is used for research. Since the karst caves will deform and the tower bases will tilt after lightning strikes, by introducing two parameters, namely the deformation degree of the karst cave and the tilt degree of the tower base, the critical vertical distance and critical horizontal distance of the karst cave are comprehensively calculated and obtained. The critical area is comprehensively determined by the critical vertical distance and critical horizontal distance. Through the critical area, it can be judged whether the tower base will be unstable due to lightning strikes, so that the critical area of the karst cave is more in line with the actual situation and has a higher accuracy. Therefore, the test of the present invention has high accuracy, good visualization effect and low test cost.

[0040] 2. In the method for determining the critical area of karst caves in the foundation of tower bases in lightning-prone areas of the present invention, the karst cave deformation degree index is used to normalize karst caves of different specifications and sizes, making the results more credible. Considering that the karst cave will deform to a certain extent after lightning strikes, when the deformation degree reaches the threshold, even if it is not damaged at present, the karst cave will continue to deform until it collapses during the later service process, causing the tower base to be unstable. By introducing the karst cave deformation degree threshold, the value when the slope of the karst cave deformation degree change curve is the largest after lightning strikes, that is, when the karst cave turns into an unstable deformation stage, is taken as the threshold. Using this threshold to determine the critical distance of the karst cave makes it more in line with the actual situation and has a higher accuracy. When determining the critical distance of the karst cave, comprehensively according to the karst cave deformation degree threshold and the tower base inclination degree, considering that when the tower base inclination degree reaches the threshold, the karst cave has not reached the deformation degree threshold, or when the karst cave deformation reaches the karst cave deformation degree threshold, the tower base inclination degree has not reached the threshold, comprehensively comparing the two values and taking the larger value as the critical distance makes the determined result on the safe side. Therefore, the present invention has a higher accuracy and credibility.

[0041] 3. In the method for determining the critical area of karst caves in the foundation of tower bases in lightning-prone areas of the present invention, since lightning strikes will cause fissures to occur in the karst caves in the foundation, by obtaining the total volume and average length of the fissures derived from the karst caves, the critical area is corrected, so that the calculation accuracy and safety reserve can be further improved. Therefore, the present invention has a higher accuracy and credibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is the flow schematic diagram of the present invention.

[0043] Figure 2 is the structural schematic diagram of the model box in the present invention.

[0044] Figure 3 is the control schematic diagram of the model box in the present invention.

[0045] In the figure: model box 1, foundation 2, karst cave 3, pole tower 4, pole tower foundation 5, monitoring system 6, inclination sensor 61, laser displacement sensor 62, ground penetrating radar 63, simulated lightning strike device 7, control system 8. Specific implementation mode

[0046] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation modes.

[0047] Example 1:

[0048] See Figures 1 to 3 , a method for determining the critical area of a karst cave in the foundation where the pole tower foundation is located in a lightning-prone area, the method comprising the following steps:

[0049] Step 1: Referring to the actual engineering situation of a certain high-voltage transmission line in the western Hubei region, according to the similarity ratio principle, the foundation 2, pole tower 4 and pole tower foundation 5 containing the karst cave 3 are prepared in equal proportion and placed in the model box 1. The inclination sensor 61 is arranged at the corner of the pole tower foundation 5, and the laser displacement sensor 62 is arranged at the bottom of the cavity of the karst cave 3.

[0050] Step 2: Multiple model boxes 1 are established according to Step 1. The size of the model box 1 is 3m×3m×3m. The karst cave 3 in each model box 1 is located directly below the center point of the pole tower foundation 5 and has different vertical distances from the ground surface. The simulated lightning strike device 7 is started to conduct simulated lightning strikes on the foundation 2 containing the karst cave 3 in each model box 1. The deformation degree of the karst cave 3 and the inclination degree of the pole tower foundation 5 under different vertical distance conditions from the ground surface after the lightning strike are monitored respectively by the laser displacement sensor 62 and the inclination sensor 61.

[0051] Calculate the first vertical distance of the karst cave 3 from the ground surface when the deformation degree of the karst cave reaches the threshold value and the second vertical distance of the karst cave 3 from the ground surface when the inclination degree of the pole tower foundation 5 reaches the threshold value, and calculate the critical vertical distance according to the maximum value of the first vertical distance and the second vertical distance.

[0052] Step 3: Multiple model boxes 1 are established according to Step 1. The size of the model box 1 is 3m×3m×3m. The karst cave 3 in each model box 1 has a vertical distance from the ground surface equal to the critical vertical distance and different horizontal distances from the center point of the pole tower foundation 5. The simulated lightning strike device 7 is started to conduct simulated lightning strikes on the foundation 2 containing the karst cave 3 in each model box 1. The deformation degree of the karst cave 3 and the inclination degree of the pole tower foundation 5 under different horizontal distance conditions from the center point of the pole tower foundation 5 after the lightning strike are monitored respectively by the laser displacement sensor 62 and the inclination sensor 61.

[0053] Calculate the first horizontal distance between the karst cave 3 and the center point of the tower foundation 5 when the deformation degree of the karst cave reaches the threshold, and the second horizontal distance between the karst cave 3 and the center point of the tower foundation 5 when the inclination degree of the tower foundation 5 reaches the threshold, and calculate the critical horizontal distance based on the maximum value of the first horizontal distance and the second horizontal distance;

[0054] Step 4: Determine the critical area of the karst cave according to the critical vertical distance and the critical horizontal distance.

[0055] The simulated lightning strike device 7 includes an impulse current generator, and the output end of the impulse current generator is connected to the foundation 2 containing the karst cave 3.

[0056] In this embodiment, the inclination threshold of the tower foundation 5 is 0.5%, the input end of the impulse current generator is connected to the control system 8, the control system 8 is respectively connected to the inclination sensor 61 and the laser displacement sensor 62. After detecting the inclination degree of the tower foundation 5, the inclination sensor 61 sends the data to the control system 8, and after detecting the displacement value of the top of the karst cave 3, the laser displacement sensor 62 sends the data to the control system 8.

[0057] Embodiment 2:

[0058] The basic content is the same as that of Embodiment 1, the difference is:

[0059] The specific calculation steps of the first vertical distance z in Step 2 1 are as follows:

[0060] Record the displacement values of the top of the karst cave 3 under different vertical distance conditions between the karst cave 3 and the ground surface after the lightning strike through the monitoring system 6, calculate the deformation degree of the karst cave according to the displacement values of the top of the karst cave 3, and draw a change curve of the deformation degree of the karst cave with the vertical distance between the karst cave 3 and the ground surface. When the deformation degree of the karst cave reaches the threshold, obtain the corresponding first vertical distance z between the karst cave 3 and the ground surface 1 = 1.2m.

[0061] The specific calculation steps of the second vertical distance z in Step 2 2 are as follows:

[0062] Record the inclination degree of the tower foundation 5 under different vertical distance conditions between the karst cave 3 and the ground surface after the lightning strike through the monitoring system 6, record and draw a change curve of the inclination degree of the tower foundation 5 and the deformation degree of the karst cave. When the inclination degree of the tower foundation 5 reaches 0.5%, obtain the corresponding deformation degree of the karst cave, and determine the second vertical distance z between the karst cave 3 and the ground surface according to the corresponding deformation degree of the karst cave 2 = 1.0m.

[0063] The specific calculation steps of the first horizontal distance x in Step 3 1 are as follows:

[0064] Record the displacement values of the top of the karst cave 3 at different horizontal distances from the center point of the tower foundation 5 after the lightning strike through the monitoring system 6, calculate the deformation degree of the karst cave based on the displacement values of the top of the karst cave 3, and draw a curve of the change of the deformation degree of the karst cave with the horizontal distance from the center point of the karst cave 3 to the tower foundation 5. When the deformation degree of the karst cave reaches the threshold, obtain the first horizontal distance x of the karst cave 3 from the center point of the tower foundation 5 1 = 1.5 m.

[0065] In the third step, the specific calculation steps of the second horizontal distance x 2 are as follows:

[0066] Record the inclination of the tower foundation 5 under different horizontal distance conditions of the karst cave 3 from the center point of the tower foundation 5 after the lightning strike through the monitoring system 6, record and draw a curve of the change of the inclination of the tower foundation 5 and the deformation degree of the karst cave. When the inclination of the tower foundation 5 reaches 0.5%, obtain the corresponding deformation degree of the karst cave, and determine the second horizontal distance x of the karst cave 3 from the center point of the tower foundation 5 according to the corresponding deformation degree of the karst cave 2 = 1.6 m.

[0067] The calculation formula for the critical area V of the karst cave 0 is:

[0068] V 0 = z u × x u × x u ;

[0069] x u = {x 1 , x 2} max ;

[0070] z u = {z 1 , z 2} max ;

[0071] Among them, z u is the critical vertical distance, x u is the critical horizontal distance, x 1 is the first horizontal distance, x 2 is the second horizontal distance, z 1 is the first vertical distance, z 2 is the second vertical distance.

[0072] In this embodiment, since z 1 is greater than z 2 , so the critical vertical distance z u selects the value of z 1 , that is, 1.2 m. Since x 1 is less than x2 , so the critical vertical distance x u Select x 2 with a value of 1.6 m, then V 0 = 1.2 m × 1.6 m × 1.6 m ≈ 3.1 m 3 .

[0073] Example 3:

[0074] The basic content is the same as that of Example 2, the difference is that:

[0075] The karst cave deformation degree is the ratio of the displacement value at the top of Karst cave 3 to the diameter of Karst cave 3. The steps for determining the karst cave deformation degree threshold are as follows:

[0076] Draw the variation curve of the karst cave deformation degree with time within a set time after lightning strike when Karst cave 3 is located directly below the center point of the tower foundation 5 at a position 2 times the foundation width. Record the karst cave deformation degree corresponding to the maximum slope of the variation curve as the karst cave deformation degree threshold.

[0077] In this embodiment, the foundation width refers to the short side length of the tower foundation 5, the set time is 24 hours, and the karst cave deformation degree threshold is 12%.

[0078] Example 4:

[0079] The basic content is the same as that of Example 2, the difference is that:

[0080] The monitoring system 6 further includes a ground penetrating radar 63. The ground penetrating radar 63 is connected to the control system 8. After detecting the fissures derived from the karst cave 3, the ground penetrating radar 63 sends the data to the control system 8, and the control system 8 calculates and processes the data detected by the ground penetrating radar 63 to obtain the images of the karst cave 3 and the fissures;

[0081] After determining the critical area V of the karst cave 0 , use the ground penetrating radar 63 to detect the total volume V of the fissures derived from the karst cave 3 when the karst cave 3 is located at the boundary position of the critical area after lightning strike 3 and the average length l of the fissures, and correct the critical area V of the karst cave according to the following formula 0 :

[0082] V 0 ′ = {V 1 , V 2} max ;

[0083] V 1 = (1 + α)V 0 ;

[0084] V 2 = (z u + l) × (xu (+l)×(x u +l);

[0085]

[0086] Among them, V 0 ' is the corrected critical area of the karst cave, V is the cavity volume of the original karst cave 3, z u is the critical vertical distance, x u is the critical horizontal distance.

[0087] In this embodiment, α is 0.17, l is 0.3m, and according to the calculation, V 1 is 3.6m 3 、V 2 is 5.4m 3 , the corrected critical area is V 0 ' = {V 1 , V 2} max = 5.4m 3 .

Claims

1. A method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-lightning-prone area, characterized in that: The method comprises the following steps: Step 1: According to the actual engineering situation, the foundation (2) containing the cave (3), the pole tower (4) and the pole tower foundation (5) are prepared in proportion and placed in the model box (1); the monitoring system (6) and the lightning simulation equipment (7) are placed in the model box (1); Step 2: Establish multiple model boxes (1) according to step 1, wherein the karst cave (3) in each model box (1) is located directly below the center point of the pole tower foundation (5) and at different vertical distances from the ground surface; start the simulated lightning strike device (7) to simulate the lightning strike on the foundation (2) containing the karst cave (3) in each model box (1), and monitor the deformation of the karst cave (3) and the inclination of the pole tower foundation (5) under different vertical distances from the ground surface after the lightning strike through the monitoring system (6); Calculating a first vertical distance between the cave (3) and the ground surface when the cave deformation reaches a threshold value and a second vertical distance between the cave (3) and the ground surface when the inclination of the tower foundation (5) reaches a threshold value, and calculating a critical vertical distance based on the maximum value of the first vertical distance and the second vertical distance; Step 3: Establish multiple model boxes (1) according to step 1, wherein the vertical distance between the karst cave (3) in each model box (1) and the ground surface is a critical vertical distance and the horizontal distance between the karst cave (3) and the center point of the pole tower foundation (5) is different; start the simulated lightning strike device (7) to simulate the lightning strike on the foundation (2) containing the karst cave (3) in each model box (1), and monitor the deformation of the karst cave and the inclination of the pole tower foundation (5) under different horizontal distances from the center point of the pole tower foundation (5) after the lightning strike through the monitoring system (6); Calculating a first horizontal distance between the cave (3) and the center point of the pole tower foundation (5) when the cave deformation reaches a threshold value and a second horizontal distance between the cave (3) and the center point of the pole tower foundation (5) when the inclination of the pole tower foundation (5) reaches a threshold value, and calculating the critical horizontal distance based on the maximum value of the first horizontal distance and the second horizontal distance; Step 4: Determine the critical area of ​​the cave based on the critical vertical distance and critical horizontal distance.

2. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in the lightning high-incidence area according to claim 1, characterized in that: The simulated lightning strike device (7) comprises an impulse current generator, the output end of which is connected to a foundation (2) containing a karst cave (3).

3. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in the lightning high-incidence area according to claim 1, characterized in that: The specific calculation steps of the first vertical distance z1 in step 2 are: The monitoring system (6) records the displacement value of the top of the cave (3) under different vertical distances from the ground surface after the lightning strike, calculates the deformation of the cave according to the displacement value of the top of the cave (3), and draws a curve of the change of the deformation of the cave with the vertical distance from the ground surface. When the deformation of the cave reaches a threshold, the first vertical distance z1 of the corresponding cave (3) from the ground surface is obtained.

4. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-prone area of ​​lightning according to claim 3, characterized in that: The specific calculation steps of the second vertical distance z2 in step 2 are: The monitoring system (6) records the inclination of the pole tower foundation (5) under different vertical distances between the cave (3) and the ground surface after the lightning strike, records and draws a curve of the change of the inclination of the pole tower foundation (5) and the cave deformation, obtains the corresponding cave deformation when the inclination of the pole tower foundation (5) reaches a threshold, and determines the second vertical distance z2 between the cave (3) and the ground surface based on the corresponding cave deformation.

5. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-prone area of ​​lightning according to claim 1, characterized in that: The specific calculation steps of the first horizontal distance x1 in step 3 are: The monitoring system (6) records the displacement value of the top of the cave (3) under different horizontal distance conditions from the center point of the pole tower foundation (5) after the lightning strike, calculates the deformation of the cave based on the displacement value of the top of the cave (3), and draws a curve of the change of the deformation of the cave with the horizontal distance from the center point of the pole tower foundation (5). When the deformation of the cave reaches a threshold, the corresponding first horizontal distance x1 of the cave (3) from the center point of the pole tower foundation (5) is obtained.

6. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-prone area of ​​lightning according to claim 5, characterized in that: The specific calculation steps of the second horizontal distance x2 in step 3 are: The monitoring system (6) records the inclination of the pole tower foundation (5) under different horizontal distance conditions between the cave (3) and the center point of the pole tower foundation (5) after the lightning strike, records and draws a curve of the change of the inclination of the pole tower foundation (5) and the cave deformation degree, obtains the corresponding cave deformation degree when the inclination of the pole tower foundation (5) reaches a threshold value, and determines the second horizontal distance x2 between the cave (3) and the center point of the pole tower foundation (5) based on the corresponding cave deformation degree.

7. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-prone area of ​​lightning according to claim 1, characterized in that: The cave deformation degree is the ratio of the displacement value of the top of the cave (3) to the diameter of the cave (3). The steps for determining the cave deformation degree threshold are as follows: A curve of the change of the deformation degree of the cave with time within a set time after the lightning strike is drawn when the cave (3) is located directly below the center point of the tower foundation (5) at a distance of 2 times the foundation width. The cave deformation degree corresponding to the maximum slope of the change curve is recorded as the cave deformation threshold.

8. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-prone area of ​​lightning according to claim 1, characterized in that: The calculation formula of the critical area V0 of the cave is: V0=z u ×x u ×x u ; x u ={x1,x2} max ; With u ={z1,z2} max ; Among them, z u is the critical vertical distance, x u is the critical horizontal distance, x1 is the first horizontal distance, x2 is the second horizontal distance, z1 is the first vertical distance, and z2 is the second vertical distance.

9. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-prone area of ​​lightning according to claim 1, characterized in that: After determining the critical area V0 of the cave, the monitoring system (6) is used to detect the total volume V3 and the average length l of the cracks derived from the cave (3) when the cave (3) is located at the boundary of the critical area after the lightning strike, and the critical area V0 of the cave is corrected according to the following formula: <h2 style=";text-align:left;direction:ltr">V0′={V1,V2}<h2 style=";text-align:left;direction:ltr"> max <h2 style=";text-align:left;direction:ltr"> ; V1=(1+α)V0; V2=(z u +l)×(x u +l)×(x u +l); Where V0′ is the modified critical area of ​​the cave, V is the volume of the original cave (3), z u is the critical vertical distance, x u is the critical horizontal distance.

10. The method for determining the critical area of ​​karst caves in the foundation where the tower foundation is located in a high-prone area of ​​lightning according to claim 9, characterized in that: The monitoring system (6) comprises a tilt sensor (61), a laser displacement sensor (62) and a geological radar (63), wherein the tilt sensor (61) is arranged at a corner of a tower foundation (5), and the laser displacement sensor (62) is arranged at the bottom of a cavity of a karst cave (3); The inclination sensor (61) is used to detect the inclination of the tower foundation (5); The laser displacement sensor (62) is used to detect the displacement value of the top of the cave (3); The geological radar (63) is used to detect the total volume and average length of cracks derived from the cave (3) after a lightning strike when the cave (3) is located at the boundary position of a critical area.

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