Hydropower station diversion tunnel longitudinal crack depth detection method

Abstract

The invention discloses a hydropower station diversion tunnel longitudinal crack depth detection method, which comprises the following steps: arranging ultrasonic measuring points above and below a diversion tunnel longitudinal crack to obtain a reinforced concrete sound velocity representative value; arranging ultrasonic measuring points within the length range of the crack; performing ultrasonic detection, and judging the depth of the crack through ultrasonic waves; adjusting the position of the ultrasonic measuring point according to the depth of the fracture until the ultrasonic shape is in a suitable state; and calculating the depth of each detection point of the longitudinal crack. According to the technical scheme, by means of the method for detecting the longitudinal crack depth of the reinforced concrete in the diversion tunnel of the hydropower station through the ultrasonic waves, crack depth detection and calculation of the circular tunnel are completed, and in order to judge the development condition and the stability state of the crack, the crack depth can be regularly detected in the overhaul period of a hydropower station generator set; therefore, monitoring of longitudinal crack expansion and extension is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of water conservancy and hydropower project detection, and particularly relates to a method for detecting the depth of longitudinal cracks in the diversion tunnel of a hydropower station. Background Art

[0002] As an important part of a hydropower station, the diversion tunnel plays an irreplaceable role in diverting water and generating electricity in the hydropower station. The diversion tunnel is generally located in a mountain body or a dam and is constantly under the pressure of water flow for a long time. With the increasing operation time of the hydropower station and the influence of the external environment, cracks often appear in the lining reinforced concrete structure of the diversion tunnel. Lining cracks are one of the common diseases in the diversion tunnel and will affect the bearing capacity and safety of its structure to varying degrees. Therefore, detecting the cracks in the lining concrete of the diversion tunnel and timely discovering the development of the cracks are of great significance for ensuring the safe operation of the tunnel.

[0003] Currently, the conventional non-destructive method for detecting the depth of cracks is the ultrasonic method, which applies the principle of the best path and the minimum time in acoustic wave propagation (Fermat's principle). When cracks occur in the reinforced concrete structure, the crack is filled with an air layer, and the two sides are reinforced concrete layers. The transmitter and receiver of the ultrasonic transducer are respectively arranged on both sides of the crack. Since the propagation speed of ultrasonic waves in concrete and air is quite different, the propagation time of ultrasonic waves bypassing the crack end is less than the time of ultrasonic waves transmitting through the crack. However, in the reinforced concrete structure (the spacing between the concrete and steel bars in the diversion tunnel is generally 20 cm), when the steel bar passes through the crack and is close to the transducer, the acoustic signal propagating in the steel bar will reach the receiving transducer earlier than the acoustic signal of the ultrasonic wave bypassing the crack end. At this time, the measured acoustic time does not reflect the crack depth. By using the ultrasonic first-wave phase reversal method, that is, when the distance between the transducer and the crack is greater than or equal to a certain distance, the amplitude phase of the first wave of the ultrasonic wave bypassing the crack end will undergo a 180° reversal change. Thus, the acoustic signal of the ultrasonic wave bypassing the crack end can be obtained and the influence of the steel bar on acoustic wave detection can be reduced. According to the measured values of parameters such as the propagation time of acoustic waves in the reinforced concrete and their relative changes, comprehensive calculations are carried out, and finally the depth of the crack is obtained.

[0004] Currently, the methods and detection systems for detecting cracks in the reinforced concrete of the diversion tunnel are not yet perfect. The ultrasonic detection of the depth of concrete cracks mainly focuses on the detection on the horizontal plane. The longitudinal crack is parallel to the axis direction of the diversion tunnel, and its test surface is a circular curved surface. Therefore, it is not applicable to the detection of the depth of longitudinal concrete cracks, and the influence of steel bars is not considered in the current crack detection of the diversion tunnel. For some diversion tunnels with a large diameter, still using the method on the horizontal plane to detect the depth of longitudinal cracks will cause a large deviation in the detection results of the crack depth of the lining structure of the diversion tunnel and the evaluation of the trend and speed of the subsequent crack propagation and extension.

[0005] The patent application document with the publication number CN113607823A discloses a method for detecting the depth of longitudinal cracks in cylindrical concrete using ultrasonic waves. However, the cylindrical concrete is different from the reinforced concrete lining of the diversion tunnel in this application, and the structures of the cylinder and the lining of the diversion tunnels with different diameters in this application are different. This document does not disclose the relevant technical methods for detecting the depth of cracks in reinforced concrete. Although both this document and this application calculate the depth of concrete cracks based on a circular surface, their detection positions and detection surfaces are different, and the core calculation methods are also different. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for detecting the depth of longitudinal cracks in the diversion tunnel of a hydropower station.

[0007] The present invention is achieved through the following technical solutions.

[0008] A method for detecting the depth of longitudinal cracks in the diversion tunnel of a hydropower station provided by the present invention includes the following steps:

[0009] Arrange ultrasonic measurement points above and below the longitudinal crack of the diversion tunnel to obtain the representative value of the sound velocity of the reinforced concrete.

[0010] Arrange ultrasonic measurement points within the length range of the crack.

[0011] Conduct ultrasonic testing and judge the crack depth through the ultrasonic waveform.

[0012] Adjust the positions of the ultrasonic measurement points according to the depth of the fracture crack until the ultrasonic waveform reaches a suitable state.

[0013] Calculate the depth of each detection point of the longitudinal crack.

[0014] Preferably, in step 1, ultrasonic measurement points are arranged above and below the longitudinal crack length range by a non-crack-crossing detection method. The connection line between the ultrasonic transmitting transducer and the receiving transducer is located at the center position of two adjacent vertical support members. The measured acoustic time value is t for the transmitting transducer and the receiving transducer. Use the regression analysis method to obtain the linear equation l = a + bt, and replace the sound velocity value v of the concrete for this group of ultrasonic detections with the regression coefficient b. A total of three groups of ultrasonic measurement points are arranged, namely v1, v2, and v3, and calculate the representative value v of the sound velocity of the reinforced concrete according to the following formula d :

[0015]

[0016] In step 2, arrange 3 ultrasonic measurement points within the length range of the crack, namely the middle detection point O, the detection points P and Q on both sides;

[0017] Step 3: Denote the tip at the bottom of the crack as B, and denote the linear distances from the detection points O, P, and Q to point B as L OB , L PB and L QB , L OB , L PB and L QB are the crack depths to be determined;

[0018] Step 4: Arrange the ultrasonic transmitting transducer at position A1 and the receiving transducer at position C1. The transmitting and receiving transducers are located on both sides of the crack, and the arc lengths between positions A1, C1 and the detection point O are equal;

[0019] Step 4.1: Adjust the ultrasonic measurement point position. When reaching the position of the phase inversion critical point, the position of the transmitting transducer is point A, and the position of the receiving transducer is point C at this time. Read the first arrival time t of the received wave of the concrete crack phase inversion;

[0020] Step 5: Define the linear distance between position A and position B as L AB , and define the linear distance between position B and position C as L BC , then L AB and L BC can be obtained:

[0021]

[0022] Step 6: Denote the center of the circular cross-section of the water conveyance tunnel as S, the radius of the water conveyance tunnel as R, and denote the arc length between the detection point O and position A measured as: arc length AO. Denote ∠ASO as α. The central angle ∠ASO corresponding to the arc length AO can be expressed as the following formula:

[0023]

[0024] Step 7: According to the central angle ∠ASO and triangle ASO, L DS , L OD and L AD can be obtained respectively:

[0025] L DS = Rcosα (4)

[0026] L OD = L OS - L DS = R - Rcosα (5)

[0027] L AD = Rsinα (6)

[0028] Step 8: According to triangle ABD and the calculated L AB and LAD , the Pythagorean theorem can be used to determine L BD :

[0029]

[0030] Step 9, from L OB = L BD - L OD , the crack depth L at the detection point O is obtained OB :

[0031]

[0032] Step 10, repeat Steps 4 to 9 to respectively detect and calculate the crack depth values L PB and L QB at the detection point P and the detection point Q, that is, the depths of each detection point of the longitudinal crack are obtained.

[0033] Preferably, in Step 4.1, if the continuous waveform received by the ultrasonic receiving transducer is a waveform with the first wave amplitude upward, it indicates that the crack depth is less than 30 cm at this time. In order to obtain the acoustic signal of the ultrasonic wave bypassing the crack end, that is, the concrete crack phase inversion received wave, the transmitting transducer and the receiving transducer are symmetrically moved outward with point O as the center until the continuous waveform received by the receiving transducer is the concrete crack phase inversion received wave, that is, a waveform with the first wave amplitude downward, and the position of the change critical point is the concrete received wave phase inversion position.

[0034] Preferably, in Step 4.1, if the continuous waveform received by the ultrasonic receiving transducer is a waveform with the first wave amplitude downward, the transmitting transducer and the receiving transducer are symmetrically moved towards the crack detection point O. If the waveform does not change, it indicates that the crack depth is greater than 30 cm at this time, and the received wave signal is the steel bar penetration wave; in order to obtain the concrete crack phase inversion received wave and reduce the influence of the steel bar on ultrasonic detection, the transmitting transducer and the receiving transducer are symmetrically moved outward with point O as the center until the continuous waveform received by the ultrasonic receiving transducer is a superimposed wave of the steel bar penetration wave and the concrete crack phase inversion received wave superimposed together. At this time, the concrete received wave phase inversion phenomenon under the front edge of the steel bar penetration wave is observed, and the position of the change critical point is the concrete received wave phase inversion position.

[0035] Preferably, in Step 1, the acoustic time values measured point by point in a group are t, and the arc length distances between the transmitting transducer and the receiving transducer are 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, and 500 mm for a group of point-by-point measurement distances.

[0036] Preferably, the connection line between the ultrasonic transmitting transducer and the receiving transducer in step 1 is located at the central position between two adjacent vertical support members.

[0037] Preferably, in step 2, the midpoint of the distance between the two vertical support members closest to the center of the crack is used as the intermediate detection point O, and the midpoints of the distances between the two vertical support members closest to the two ends of the crack are used as the detection points P and Q on both sides.

[0038] The beneficial effects of the present invention are as follows:

[0039] By adopting the technical solution of the present invention, a method for detecting the depth of longitudinal cracks in reinforced concrete by using ultrasonic waves in the diversion tunnel of a hydropower station improves the detection and calculation of the crack depth in a circular tunnel. In order to judge the development status and stability of the cracks, the crack depth can be regularly detected during the overhaul period of the hydropower generator set to achieve the monitoring of the extension of longitudinal cracks. Description of the Drawings

[0040] Figure 1 is the layout diagram of the transducers for detecting the representative value of the sound velocity of reinforced concrete;

[0041] Figure 2 is the side view of the longitudinal crack and the detection points of the lining concrete of the diversion tunnel;

[0042] Figure 3 is the layout diagram of the crack depth detection points located at the center of the distance between the vertical support members;

[0043] Figure 4 is the waveform with the first wave amplitude upward (positive phase);

[0044] Figure 5 is the received wave with phase reversal of the reinforced concrete crack when the crack depth is small (negative phase);

[0045] Figure 6 is the waveform diagram of the superposition of the steel bar transmitted wave and the received wave with phase reversal of the concrete crack;

[0046] Figure 7 is the schematic diagram of the principle for calculating the depth of the longitudinal crack in the diversion tunnel; Figure 8 is the schematic layout diagram of the vertical support members and the crack depth detection points;

[0047] In the figure: 101 - transmitting transducer, 102 - receiving transducer, 103 - vertical support member, 104 - longitudinal crack, 105 - crack depth detection point, 106 - diversion tunnel, 107 - lining reinforced concrete of the diversion tunnel, 108 - steel bar transmitted wave, 109 - received wave with phase reversal of the concrete crack. Detailed Embodiment

[0048] The technical solution of the present invention will be further described below, but the scope of protection is not limited thereto.

[0049] Embodiment:

[0050] As Figures 1 to 8 shown, a method for detecting the depth of longitudinal cracks in a diversion tunnel of a hydropower station includes the following steps:

[0051] Step 1, arrange ultrasonic measuring points above and below the length range of the longitudinal crack 104 by the non-crossing crack detection method. The specific arrangement of the non-crossing crack detection method is as follows: the crack is not between the transmitting transducer 101 and the receiving transducer 102, and the space between the transmitting transducer 101 and the receiving transducer 102 is all concrete wall, so as to detect the velocity of ultrasonic waves in this concrete wall, that is, the lining reinforced concrete 107 of the diversion tunnel. The connection line of the ultrasonic transmitting transducer 101 and the receiving transducer 102 is located at the central position between two adjacent vertical support members 103. The vertical support member 103 can be a vertical steel bar. The measured sound travel time of the transmitting transducer 101 and the receiving transducer 102 is t, and the linear equation l = a + bt is obtained by the regression analysis method. The regression coefficient b is used to replace the sound velocity value v of the concrete detected by this group of ultrasonic tests. A total of three groups of ultrasonic measuring points are arranged, that is, v1, v2, and v3 are obtained, and the representative value v of the sound velocity of the reinforced concrete is calculated according to the following formula d :

[0052]

[0053] Step 2, in the longitudinal crack of the diversion tunnel 106, one of the parameters for judging the crack extension is the crack depth. In order to judge the development status and stability status of the crack, the crack depth is regularly detected to realize the monitoring of the crack extension trend and speed. Therefore, the detection points located in the middle of the crack, the left end of the crack, and the right end of the crack are respectively selected. The measuring points can be appropriately densified according to the crack length and the detection purpose. Three ultrasonic measuring points are arranged within the crack length range, namely the middle detection point O, the detection points P and Q on both sides;

[0054] Step 3, represent the tip of the crack bottom as B, and the straight-line distances from the detection points O, P, and Q to point B are respectively represented as L OB 、L PB and L QB , L OB 、L PB and L QB are the crack depths to be determined;

[0055] Step 4, arrange the ultrasonic transmitting transducer 101 at the A1 position and the receiving transducer 102 at the C1 position. The transmitting transducer 101 and the receiving transducer 102 are respectively located on both sides of the crack, and the starting positions are close to the crack. The arc lengths between the positions A1, C1 and the detection point O are equal;

[0056] Step 4.1: Adjust the position of the ultrasonic measurement point. When the position of the phase inversion critical point occurs, the position of the transmitting transducer 101 is point A, and the position of the receiving transducer 102 is point C at this time. Read the initial arrival time t of the concrete crack phase inversion received wave 109.

[0057] Step 5: Define the straight-line distance between position A and position B as L AB , and define the straight-line distance between position B and position C as L BC , as Figure 7 shown, then L AB and L BC can be obtained:

[0058]

[0059] Step 6: Represent the center of the circular cross-section of the diversion tunnel as S. According to the design data of the hydropower station diversion tunnel, the known radius of the diversion tunnel can be obtained as R. The arc length between the measured detection point O and position A is expressed as: arc length AO. Represent ∠ASO as α. The central angle ∠ASO corresponding to the arc length AO can be expressed by the following formula:

[0060]

[0061] Step 7: According to the central angle ∠ASO and triangle ASO, L DS , L OD and L AD can be obtained respectively:

[0062] L DS = Rcosα (4)

[0063] L OD = L OS - L DS = R - Rcosα (5)

[0064] L AD = Rsinα (6)

[0065] Step 8: According to triangle ABD and the calculated L AB and L AD , the Pythagorean theorem can be used to determine L BD :

[0066]

[0067] Step 9: From L OB = L BD - L OD , the crack depth L OB at the detection point O can be obtained:

[0068]

[0069] Step 10: Repeat Steps 4 to 9 to respectively detect and calculate the crack depth values L PB and L QB at the detection point P and the detection point Q, that is, obtain the depths of each detection point of the longitudinal crack.

[0070] In Step 4.1, the sound velocity of the steel bar is 5500 m / s, the sound velocity of the reinforced concrete is 4000 m / s, the spacing between the steel bars is 20 cm, concrete protective layers are provided above and below the steel bars, and the thickness of the concrete protective layer is 20 cm. If the continuous waveform received by the ultrasonic receiving transducer 101 is a waveform with the first wave amplitude upward (defined as the positive phase), as Figure 4 shown, it indicates that the crack depth is less than 30 cm at this time. In order to obtain the sound signal of the ultrasonic wave bypassing the crack end, that is, the concrete crack phase inversion received wave 109, symmetrically move the transmitting transducer 101 and the receiving transducer 102 outward with point O as the center until the continuous waveform received by the receiving transducer 101 is the concrete crack phase inversion received wave 109, that is, a waveform with the first wave amplitude downward (defined as the negative phase), as Figure 5 shown, and the position of its change critical point is the concrete received wave phase inversion position.

[0071] In Step 4.1, the sound velocity of the steel bar is 5500 m / s, the sound velocity of the reinforced concrete is 4000 m / s, the spacing between the steel bars is 20 cm, concrete protective layers are provided above and below the steel bars, and the thickness of the concrete protective layer is 20 cm. If the continuous waveform received by the ultrasonic receiving transducer is a waveform with the first wave amplitude downward, symmetrically move the transmitting transducer 101 and the receiving transducer 102 to the crack detection point O. If the waveform does not change (excluding the phase inversion wave when it has reached the phase inversion position), it indicates that the crack depth is greater than 30 cm at this time, and the received wave signal is the steel bar penetration wave 108; in order to obtain the concrete crack phase inversion received wave 109 and reduce the influence of the steel bar on the ultrasonic detection, symmetrically move the transmitting transducer 101 and the receiving transducer 102 outward with point O as the center until the continuous waveform received by the ultrasonic receiving transducer is the superimposed wave of the steel bar penetration wave 108 and the concrete crack phase inversion received wave 109 superimposed together, as Figure 6 shown. At this time, observe the concrete received wave phase inversion phenomenon under the front edge of the steel bar penetration wave 108, and the position of its change critical point is the concrete received wave phase inversion position.

[0072] When the spacing between the steel bars and the thickness of the concrete protective layer are the same, as the sound velocity of the steel bar increases, the crack depth demarcation line value will gradually decrease, and as the spacing between the steel bars and the thickness of the protective layer increase, the crack depth demarcation line value will also increase.

[0073] In step 1, the acoustic time value of a group of point-by-point measurements is t. The arc length distances between the transmitting transducer 101 and the receiving transducer 102 are 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, and 500 mm respectively, which are a group of point-by-point measurement distances. Among them, 1 transmitting transducer 101 is set, and 7 receiving transducers 102 are set according to 7 arc length distance points.

[0074] As Figure 2 As shown, in step 1, the connection line between the ultrasonic transmitting transducer 101 and the receiving transducer 102 is located at the center position of two adjacent vertical support members 103, and all crack depth detection points 105 should be located at the center of the spacing between the vertical support members 103 to avoid the influence of steel bars on the acoustic wave detection. If it is too close to the steel bars, the acoustic wave will directly propagate through the steel bars, and the received acoustic wave is not the wave propagating from the tip of the crack bottom. The closer to the steel bars, the greater the influence of the steel bar penetration wave 108, which may cause the reverse wave to be not obvious and the reverse wave acoustic velocity value cannot be read.

[0075] As Figure 8 As shown, in step 2, the center point of the spacing between the two vertical support members 103 closest to the center of the crack 104 is used as the middle detection point O, and the center points of the spacing between the two vertical support members 103 closest to the two ends of the crack are used as the detection points P and Q on both sides.

Claims

1. A method for detecting the depth of longitudinal cracks in the diversion tunnel of a hydropower station, characterized in that, It includes the following steps: Arrange ultrasonic measurement points above and below the longitudinal crack of the water diversion tunnel to obtain the representative value of the ultrasonic velocity of reinforced concrete; Arrange ultrasonic measurement points within the crack length range; Conduct ultrasonic testing and judge the crack depth through the ultrasonic waveform; Adjust the positions of the ultrasonic measurement points according to the crack depth until the ultrasonic waveform reaches a suitable state; Calculate the depths of each detection point of the longitudinal crack.

2. The longitudinal crack depth detection method for the diversion tunnel of a hydropower station according to claim 1, characterized in that It includes the following steps: Step 1, arrange ultrasonic measuring points above and below the longitudinal crack length range by non-crack-crossing detection method. The connection line of the ultrasonic transmitting transducer (101) and the receiving transducer (102) is located at the central position of two adjacent vertical support members (103). The measured acoustic time value is t for the transmitting transducer (101) and the receiving transducer (102). Use the regression analysis method to obtain the linear equation l = a + bt, and replace the sound velocity value v of the concrete in this group of ultrasonic detections with the regression coefficient b. A total of three groups of ultrasonic measuring points are arranged, namely v1, v2, and v3 are obtained, and the representative value v of the sound velocity of reinforced concrete is calculated according to the following formula d : Step 2: Arrange 3 ultrasonic measurement points within the crack length range, namely the middle detection point O, the detection points P and Q on both sides; Step 3: Denote the tip at the bottom of the crack as B, and denote the straight-line distances from the detection points O, P, and Q to point B as L OB , L PB and L QB , L OB , L PB and L QB are the crack depths to be determined; Step 4: Arrange the ultrasonic transmitting transducer (101) at position A1 and the receiving transducer (102) at position C1. The transmitting transducer (101) and the receiving transducer (102) are located on both sides of the crack respectively, and the arc lengths between positions A1, C1 and the detection point O are equal; Step 4.1: Adjust the positions of the ultrasonic measurement points. When the position of the phase reversal critical point occurs, the position of the transmitting transducer (101) is point A, and the position of the receiving transducer (102) is point C at this time. Read the initial arrival time t of the concrete crack phase reversal received wave; Step 5, define the straight-line distance between position A and position B as L AB , define the straight-line distance between position B and position C as L BC , then L AB and L BC can be obtained: Step 6: Represent the center of the circular cross-section of the water diversion tunnel as S, the radius of the water diversion tunnel as R, and the measured arc length between the detection point O and position A as: arc length AO. Represent ∠ASO as α. The central angle ∠ASO corresponding to the arc length AO can be expressed by the following formula: Step 7, according to the central angle ∠ASO and triangle ASO, L DS , L OD and L AD can be obtained respectively: L DS = R cos α (4) L OD = L OS - L DS = R - R cosα (5) L AD = Rsinα (6) Step 8, based on triangle ABD and the calculated L AB and L AD , the Pythagorean theorem can be used to determine L BD : Step 9, from L OB = L BD - L OD , the crack depth L at the detection point O is obtained OB : Step 10: Repeat Steps 4 to 9 to respectively detect and calculate the crack depth values L at detection point P and detection point Q, that is, obtain the depths of each detection point of the longitudinal crack. PB and L QB , namely, obtain the depths of each detection point of the longitudinal crack.

3. The longitudinal crack depth detection method for the water diversion tunnel of a hydropower station according to claim 2, wherein: In the above step 4.1, if the continuous waveform received by the ultrasonic receiving transducer (101) is a waveform with the first wave amplitude upward, it indicates that the crack depth is less than 30 cm at this time. In order to obtain the sound signal of the ultrasonic wave bypassing the crack end, that is, the concrete crack phase reversal received wave, symmetrically move the transmitting transducer (101) and the receiving transducer (102) outward with point O as the center until the continuous waveform received by the receiving transducer (101) is the concrete crack phase reversal received wave, that is, a waveform with the first wave amplitude downward. The position of its change critical point is the concrete received wave phase reversal position.

4. The longitudinal crack depth detection method for a diversion tunnel of a hydropower station according to claim 2, wherein: In the above step 4.1, if the continuous waveform received by the ultrasonic receiving transducer is a waveform with the first wave amplitude downward, symmetrically move the transmitting transducer (101) and the receiving transducer (102) towards the crack detection point O. If the waveform does not change, it indicates that the crack depth is greater than 30 cm at this time, and the received wave signal is the steel bar penetration wave; in order to obtain the concrete crack phase reversal received wave and reduce the influence of the steel bar on ultrasonic testing, symmetrically move the transmitting transducer (101) and the receiving transducer (102) outward with point O as the center until the continuous waveform received by the ultrasonic receiving transducer is a superimposed wave of the steel bar penetration wave and the concrete crack phase reversal received wave superimposed together. At this time, observe the concrete received wave phase reversal phenomenon under the front edge of the steel bar penetration wave, and the position of its change critical point is the concrete received wave phase reversal position.

5. The longitudinal crack depth detection method for the water diversion tunnel of a hydropower station according to claim 2, wherein: In step 1, the acoustic time value measured point by point in a group is t, and the arc length distances between the transmitting transducer (101) and the receiving transducer (102) are 200mm, 250mm, 300mm, 350mm, 400mm, 450mm, and 500mm respectively, which are a group of distances measured point by point.

6. The longitudinal crack depth detection method for a diversion tunnel of a hydropower station according to claim 2, characterized in that: In step 1, the connection line between the ultrasonic transmitting transducer (101) and the receiving transducer (102) is located at the central position between two adjacent vertical support members (103).

7. The method for detecting the depth of longitudinal cracks in the diversion tunnel of a hydropower station according to claim 2, characterized in that: In step 2, the midpoint of the distance between the two vertical support members (103) closest to the center of the crack is used as the intermediate detection point O, and the midpoints of the distances between the two vertical support members (103) closest to the two ends of the crack are used as the detection points P and Q on both sides.

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