Foundation pit underwater excavation pit bottom flatness detection device and detection method thereof

Abstract

In order to solve the problem that the flatness of the bottom of an existing foundation pit excavated underwater is difficult to detect, the invention provides a device for detecting the flatness of the bottom of the foundation pit excavated underwater, which comprises a foundation pit excavated on a stratum, a datum point power supply array and an inspection instrument submerged into a muddy water layer to detect the flatness, and the bottom mark array is distributed at the bottom of the underwater pit. According to the method, a reference point power source array, an inspection instrument and a bottom mark array are effectively combined, a reference coordinate system is constructed through the reference point power source array, the inspection instrument automatically calculates absolute coordinates under the reference coordinate system where the inspection instrument is located, and coordinates under the inspection instrument relative coordinate system where a bottom mark is located are automatically calculated by activating the bottom mark point power source inspection instrument; and obtaining the absolute position of each bottom mark in the reference coordinate system one by one through multiple coordinate conversion calculations. The multi-action interactive control among the reference point power supply, the inspection instrument and the bottom mark is realized by setting the specific electric field frequency, the floating recovery and data acquisition of the device are finally completed, the three-dimensional configuration of the pit bottom surface is obtained through 3D data processing, and the flatness of the pit bottom of the whole underwater excavation foundation pit is accurately reflected.

Description

Technical Field

[0001] This invention belongs to the field of underwater excavation technology for foundation pits, and specifically relates to a device and method for detecting the flatness of the bottom of an underwater excavation foundation pit. Background Technology

[0002] The development of ultra-deep underground spaces in soft soil and water-rich areas faces safety risks caused by confined water. Conventional dry excavation methods are prone to adverse situations such as seepage in the retaining walls and sudden water inrush at the bottom of the pit. In recent years, a foundation pit construction method using underwater excavation has been gradually developed. This method first constructs the retaining walls, then effectively reduces or even balances the water and soil pressure difference between the inside and outside of the pit by filling the pit with water. Underwater soil is then extracted using specialized equipment such as grab buckets or cutter suction hoppers, thus effectively protecting the foundation pit from the impact of sudden water inrush during the excavation stage. Subsequently, the bottom is sealed by underwater concrete pouring, and finally the water in the pit is pumped out for structural construction.

[0003] During underwater excavation of the foundation pit, the visibility of the water inside the pit is very low, making it impossible to directly judge the actual situation of the pit bottom. Over-excavation and under-excavation of the excavation surface are difficult to avoid, which can easily have an adverse impact on subsequent construction. Therefore, it is necessary to test the flatness of the excavation surface. At the same time, during the underwater pouring of concrete to seal the bottom, the flatness of the concrete surface directly affects the quality of the bottom sealing construction. Therefore, it is also necessary to test the flatness of the bottom sealing concrete surface. Furthermore, during the subsequent bottom slab pouring process, there are also construction control requirements for the flatness of the underwater poured concrete.

[0004] Currently, when inspecting the flatness of the bottom of underwater excavation pits, construction workers generally use sonar detection, depth sounding rod or water-weight array methods, underwater mechanical flatness meters, and gradual inspection by divers. However, the methods for inspecting the flatness of the bottom of underwater excavation pits are indeed different from those for reservoirs and seabed topography inspections. The muddy environment of underwater excavation results in large errors in sonar detection and extremely low visibility, making multibeam echo sounders, side-scan sonar, and underwater 3D lasers unsuitable. Using depth sounding rods or water-weight array methods is extremely inefficient and labor-intensive. Underwater mechanical flatness meters are also inefficient and unsuitable for soft soil foundations. Gradual inspection by divers is also an option, but underwater divers are engaged in specialized work with relatively complex safety management. The presence of a muddy layer at the bottom of the pit results in extremely low or even zero visibility, severely limiting the divers' operational capabilities and easily leading to misjudgments and omissions.

[0005] In addition, underwater equipment positioning mainly relies on a combination of technologies such as acoustic detection, inertial navigation (INS), and SLAM. However, in muddy water environments with "near-zero visibility," SLAM technologies such as vision, lidar, and millimeter-wave radar are difficult to apply. Acoustic signals attenuate significantly in muddy water environments, resulting in limited applicability. Relying solely on inertial navigation (INS), which calculates position, velocity, and attitude by measuring acceleration and angular velocity, leads to rapid growth of accumulated errors due to integral drift, which cannot be eliminated. Summary of the Invention

[0006] In order to accurately and effectively detect the flatness of the bottom of an excavation pit, this invention provides a device and method for detecting the flatness of the bottom of an underwater excavation pit.

[0007] The technical solution of the underwater excavation pit bottom flatness detection device of the present invention is as follows:

[0008] A device for detecting the flatness of the bottom of an underwater excavation pit, characterized in that it includes:

[0009] A foundation pit is excavated on the ground. A retaining wall is provided around the foundation pit. A mud-water layer and a mud slurry layer are arranged from top to bottom inside the foundation pit. The mud slurry layer is located on the upper side of the bottom of the foundation pit.

[0010] A reference point power supply array, comprising three or more reference point power supplies respectively set at positions around the perimeter of the underwater excavation pit above the water surface, to construct a reference coordinate system, and capable of transmitting point power supply electric field signals of different electric field frequencies into the pit one by one.

[0011] An inspection instrument that dives into the mud and water layer to detect the flatness of the surface. The inspection instrument can dive to a certain depth and start autonomous cruise detection at the boundary between the mud and water layer and the mud layer. The absolute coordinate position of the inspection instrument in the reference coordinate system is further determined by calculating the electric field strength between the inspection instrument and the reference point power array and the distance between each power point. The inspection instrument can import the CAD data of the foundation pit plan and combine its own absolute coordinates with the foundation pit plan map to complete autonomous full-coverage cruise.

[0012] An array of bottom markers distributed at the bottom of an underwater pit, the array of bottom markers including multiple bottom markers set at the bottom of the pit, the bottom markers and the inspection instrument are interactively controlled by the electric field frequency, and the local coordinate relative position of the bottom markers and the inspection instrument is determined by the electric field strength.

[0013] Furthermore, the base marker includes a triangular cone-shaped shell, with a base marker power transmitter and a base marker electric field strength detector respectively located at the four apex corners of the triangular cone shell. Inside the triangular cone shell, there is a power supply and control compartment, and a base marker controller is located in the control compartment. A folded buoyancy bag is located in the middle of the surface of the triangular cone shell, and a gas generator is located inside the folded buoyancy bag. The base marker power transmitter, the base marker electric field strength detector, and the gas generator are all communicatively connected to the base marker controller.

[0014] Furthermore, the inspection device includes a head cover, a central rod, and a base with an overall cross-shaped structure, with the central rod positioned between the head cover and the base.

[0015] Furthermore, the helmet is equipped with a top electric field strength detector, a hydraulic detector, a buoyancy control module, a ballast water tank, a thruster, a control processing host, a motion and attitude control module, a power supply module, and an electric field signal control module. The ballast water tank is located at the upper end of the helmet. The hydraulic detector and the buoyancy control module are located inside the ballast water tank. The top electric field strength detector is located at the top of the ballast water tank. The thrusters are symmetrically located on both sides of the helmet. The control processing host, the motion and attitude control module, the power supply module, and the electric field signal control module are all located inside the helmet. The control processing host is communicatively connected to the top electric field strength detector, the hydraulic detector, the buoyancy control module, the ballast water tank, the thruster, the motion and attitude control module, and the electric field signal control module. The power supply module is electrically connected to the top electric field strength detector, the hydraulic detector, the buoyancy control module, the thruster, the control processing host, the motion and attitude control module, and the electric field signal control module.

[0016] Furthermore, a power supply array is provided at three of the vertices of the base, and a bottom electric field strength detector is provided at the center of the base.

[0017] The present invention also provides a detection method for a device for detecting the flatness of the bottom of an underwater excavation pit, characterized by comprising the following steps:

[0018] First step: Evenly throw multiple bottom markers onto the bottom surface of the foundation pit, and then place the inspection instrument at the junction of the mud-water layer and the mud slurry layer;

[0019] The second step: During the inspection process, the power supply of one of the reference points is turned on. At this time, the electric field frequency is the target activation frequency, and the electric field strength is higher than the target activation field strength. When the inspection device approaches a target, the target electric field strength detector on the target senses an electric field with a frequency of the target activation frequency, which exceeds a certain threshold, and no electric field with a frequency of the target emission frequency is sensed. Then the target is "wake up and activated". After the target is "activated", it turns on its own point power supply and generates an electric field with the target emission frequency.

[0020] The third step: When the bottom electric field strength detector of the inspection instrument detects the presence of an electric field with the emission frequency of the base target in the current electric field environment, it then adjusts to a horizontal hovering posture. Based on the right-angled arrangement of point power sources, it measures the electric field strength of the base target's own point power source, calculates the straight-line distances, and finally converts them into the coordinate matrix of the base target with the inspection instrument as the local coordinate. After completing the calculation, it saves the local coordinate matrix, the direction parameters of the inspection instrument, and the time series.

[0021] Fourth step: After saving the local data, the inspection instrument will turn off the point power array. The current base electric field detection is lower than the base activation field strength, that is, it is "hypnotized" and turns off its own point power electric field to enter the "complete" state, that is, it will no longer respond to the base activation frequency.

[0022] Fifth step: The inspection instrument remains stationary. Based on the electric field strength detector at its top, the overall coordinate matrix in the coordinate system determined by the reference point power supply in the previous step is measured. Based on the size of the inspection instrument itself, the actual conversion relationship between the local coordinates and the reference coordinates is obtained from the electric field strength detector at its top and the point power supply array arranged in the rectangular coordinate system at its bottom. Thus, the actual coordinate position of the bottom mark in the reference coordinate system is obtained.

[0023] Step 6: The inspection instrument reactivates the power supply array, replans the inspection route based on its own coordinates calculated above, adjusts its direction and attitude, and completes the measurement of the overall coordinate position of each bottom marker at the bottom of the pit through full coverage inspection.

[0024] Step 7: After completing the survey, turn off the power to the activation point on the survey instrument. The power to the reference point is activated at the "flying" frequency. After the electric field strength detectors on the survey instrument and each bottom marker identify that the current frequency is "flying", the buoyancy control module of the survey instrument performs the ascent operation, while each bottom marker starts the gas generator, opens the folded buoyancy bag, and the survey instrument and each bottom marker float to the upper side of the water surface in the pit, thus completing the recovery operation.

[0025] Step 8: After the inspection device is retrieved, it is imported into the computer via the wireless transmission module or by removing its memory card. Finally, all coordinate data is read through 3D graphics processing software, which can complete the interpolation and smoothing of the pit bottom plane, thereby completing the surface detection of the entire pit bottom plane and intuitively displaying the flatness of the pit bottom plane.

[0026] Furthermore, the algorithm for calculating the distance between the inspection instrument and the reference point power array through the electric field strength between them, and determining the current coordinate position of the inspection instrument includes:

[0027] First step: Taking the minimum number of three point power sources as an example, the electrical signal frequencies emitted by the three point power sources O, A, and B are freq1, freq2, and freq3, respectively. Assume that they are directly arranged to form a rectangular coordinate system, with the origin at O ​​and the three orthogonal coordinate axes OX, OY, and OZ, where point O is at coordinates (0, 0, 0), point A is at coordinates (a, 0, 0), and point B is at coordinates (0, b, 0).

[0028] The second step: The underwater inspection device is equipped with an electric field frequency detector and an electric field strength detector. The frequency of the electric signal, freq1, freq2, and freq3, is measured by the electric field frequency detector to identify which point power source, O, A, or B, the signal originates from. The electric field strength detector can measure the electric field strength E(r) at this point. For a point power source in a uniform medium, its electric field strength distribution is directly proportional to the resistivity ρ and the current I, and inversely proportional to the square of the distance, d^2.

[0029]

[0030] Where ρ is the resistivity of the liquid, I is the total current flowing from the point source, r is the distance to the point source, and E(d) is the magnitude of the electric field intensity; the formula can be used to calculate:

[0031]

[0032] The third step: Based on the above method for calculating distance r and the method for distributing the electric field source, the distances from the underwater inspection instrument P to points O, A, and B are d_op, d_ap, and d_bp, respectively. Then, based on geometric knowledge, the coordinates of point P in a given coordinate system can be calculated as follows:

[0033]

[0034] At this point, the method for locating the inspection instrument in the relatively homogeneous upper mud and water layer (approximately tens of meters high) can be determined.

[0035] Furthermore, the base marker and the inspection instrument are interactively controlled by the electric field frequency, and the relative position of the local coordinates of the base marker and the inspection instrument is determined by the electric field strength.

[0036] This invention discloses a device and method for detecting the flatness of the bottom of an underwater excavation pit. The device features a reasonable overall design, simple structure, and convenient operation. It effectively combines a reference point power array, a survey instrument, and a bottom marker array. A reference coordinate system is constructed through the reference point power array, and the survey instrument automatically calculates its absolute coordinates within this system. By activating the bottom marker power supply, the survey instrument automatically calculates the coordinates of the bottom marker relative to the survey instrument's coordinate system. Through multiple coordinate transformations, the absolute position of each bottom marker in the reference coordinate system is obtained. Multiple interactive controls among the reference point power supply, survey instrument, and bottom markers are achieved by setting a specific electric field frequency. Finally, the device is retrieved and data is collected. 3D data processing yields the three-dimensional configuration of the pit bottom, accurately reflecting the flatness of the entire underwater excavation pit bottom. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the foundation pit structure of a foundation pit bottom flatness detection device and detection method according to the present invention.

[0038] Figure 2 This is a schematic diagram of the structure of a bottom marker array distributed inside the foundation pit, which is a device and method for detecting the flatness of the bottom of an underwater excavation pit according to the present invention.

[0039] Figure 3 This is a schematic diagram of the structure of a device and method for detecting the flatness of the bottom of an underwater excavation pit, as described in this invention, in which the inspection instrument is placed inside the pit.

[0040] Figure 4 This is a schematic diagram of the structure of a device and marker floating on the upper side of the mud and water layer for detecting the flatness of the bottom of an underwater excavation pit according to the present invention.

[0041] Figure 5 This is a schematic diagram of the structure of an inspection instrument for a device and method for detecting the flatness of the bottom of an underwater excavation pit, as described in this invention.

[0042] Figure 6 This is a schematic diagram of the bottom marker of a device and method for detecting the flatness of the bottom of an underwater excavation pit according to the present invention.

[0043] Figure 7 The present invention relates to a coordinate system between the inspection instrument and the reference point power array of an underwater excavation pit bottom flatness detection device and detection method. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0045] Example 1

[0046] refer to Figures 1 to 7 This embodiment of a device for detecting the flatness of the bottom of an underwater excavation pit includes a pit 100, a reference point power array 200, an inspection instrument 300, and a bottom marker array 400.

[0047] The foundation pit 100 is excavated on the stratum 500. A retaining wall 600 is provided around the foundation pit 100. Inside the foundation pit 100, a mud-water layer 110 and a mud slurry layer 120 are arranged from top to bottom. The mud slurry layer 110 is located on the upper side of the bottom of the foundation pit 100.

[0048] The reference point power supply array 200 includes three or more reference point power supplies respectively set at positions around the underwater excavation pit 100 above the water surface, to construct a reference coordinate system, and can transmit point power supply electric field signals of different electric field frequencies into the pit one by one.

[0049] The inspection instrument 300 dives into the mud-water layer to detect the flatness. The inspection instrument 300 does not have an umbilical cable and can dive to a certain depth on its own. It starts autonomous cruise detection at the boundary between the mud-water layer 110 and the mud layer 120. The inspection instrument 300 and the reference point power array 200 are connected by calculating the electric field strength between them and the distance between the power sources at each point. This further determines the absolute coordinate position of the inspection instrument 300 in the reference coordinate system. The inspection instrument 300 can import the CAD data of the foundation pit plan and combine it with its own absolute coordinates and the foundation pit plan map to complete autonomous full-coverage cruise.

[0050] The bottom marker array 400 is distributed at the bottom of the underwater pit. The bottom marker array 400 includes multiple bottom markers 410 set at the bottom of the pit. The bottom markers 410 and the inspection instrument 300 are interactively controlled by the electric field frequency. The relative position of the local coordinates of the bottom markers and the inspection instrument is determined by the electric field strength.

[0051] The base marker 410 includes a triangular cone shell 411 that is generally triangular in shape. A base marker power transmitter 412 and a base marker electric field strength detector 414 are respectively provided at the four apex corners of the triangular cone shell 411. A power supply and control compartment is provided inside the triangular cone shell 411. A base marker controller is provided in the control compartment. A folded buoyancy bag 413 is provided in the middle of the surface of the triangular cone shell 411. A gas generator is provided inside the folded buoyancy bag 413. The base marker power transmitter, the base marker electric field strength detector and the gas generator are respectively connected to the base marker controller for communication.

[0052] The inspection device 300 includes a head cover 310, a central rod 320, and a base 330 with an overall cross-shaped structure. The central rod 320 is located between the head cover 310 and the base 330. This structure allows the inspection device to float relatively stably at the interface between the mud-water layer and the mud layer.

[0053] The helmet 310 is equipped with a top electric field strength detector 311, a hydraulic detector 319, a buoyancy control module 312, a ballast water tank 313, a thruster 315, a control processing host 314, a motion and attitude control module 316, a power supply module 317, and an electric field signal control module 318.

[0054] Ballast water tank 313 is located at the upper end of head cover 310. Hydraulic detector 319 and buoyancy control module 312 are located inside ballast water tank 313. Top electric field strength detector 311 is located at the top of ballast water tank 313. Thrusters 315 are symmetrically arranged on both sides of head cover 310. Control processing host 314, motion and attitude control module 316, power supply module 317 and electric field signal control module 31 are all located inside head cover 310.

[0055] The control processing host 314 is communicatively connected to the top electric field strength detector 311, the hydraulic detector 319, the buoyancy control module 312, the ballast water tank 313, the thruster 315, the motion and attitude control module 316, and the electric field signal control module 318, respectively. The power supply module 317 is electrically connected to the top electric field strength detector 311, the hydraulic detector 319, the buoyancy control module 312, the thruster 315, the control processing host 314, the motion and attitude control module 316, and the electric field signal control module 318, respectively.

[0056] A power supply array 331 is provided at three of the vertices of the base 330, and a bottom electric field strength detector 332 is provided at the center of the base 330.

[0057] Example 2

[0058] The present invention also provides a detection method for a device for detecting the flatness of the bottom of an underwater excavation pit, comprising the following steps:

[0059] First step: Evenly throw multiple bottom markers onto the bottom surface of the foundation pit, and then place the inspection instrument at the junction of the mud-water layer and the mud slurry layer;

[0060] The second step: During the inspection process, the power supply of one of the reference points is turned on. At this time, the electric field frequency is the target activation frequency, and the electric field strength is higher than the target activation field strength. When the inspection device approaches a target, the target electric field strength detector on the target senses an electric field with a frequency of the target activation frequency, which exceeds a certain threshold, and no electric field with a frequency of the target emission frequency is sensed. Then the target is "wake up and activated". After the target is "activated", it turns on its own point power supply and generates an electric field with the target emission frequency.

[0061] The third step: When the bottom electric field strength detector of the inspection instrument detects the presence of an electric field with the emission frequency of the base target in the current electric field environment, it then adjusts to a horizontal hovering posture. Based on the right-angled arrangement of point power sources, it measures the electric field strength of the base target's own point power source, calculates the straight-line distances, and finally converts them into the coordinate matrix of the base target with the inspection instrument as the local coordinate. After completing the calculation, it saves the local coordinate matrix, the direction parameters of the inspection instrument, and the time series.

[0062] Fourth step: After saving the local data, the inspection instrument will turn off the point power array. The current base electric field detection is lower than the base activation field strength, that is, it is "hypnotized" and turns off its own point power electric field to enter the "complete" state, that is, it will no longer respond to the base activation frequency.

[0063] Fifth step: The inspection instrument remains stationary. Based on the electric field strength detector at its top, the overall coordinate matrix in the coordinate system determined by the reference point power supply in the previous step is measured. Based on the size of the inspection instrument itself, the actual conversion relationship between the local coordinates and the reference coordinates is obtained from the electric field strength detector at its top and the point power supply array arranged in the rectangular coordinate system at its bottom. Thus, the actual coordinate position of the bottom mark in the reference coordinate system is obtained.

[0064] Step 6: The inspection instrument reactivates the power supply array, replans the inspection route based on its own coordinates calculated above, adjusts its direction and attitude, and completes the measurement of the overall coordinate position of each bottom marker at the bottom of the pit through full coverage inspection.

[0065] Step 7: After completing the survey, turn off the power supply at the activation point on the survey instrument. The power supply at the reference point will be activated at the "flying" frequency. Once the electric field strength detectors on the survey instrument and each bottom marker identify that the current frequency is "flying", the buoyancy control module of the survey instrument will perform the ascent operation, while each bottom marker will start its gas generator, open the folded buoyancy bag, and the survey instrument and each bottom marker will float to the upper side of the water surface in the pit, thus completing the recovery operation.

[0066] Step 8: After the inspection device is retrieved, it is imported into the computer via the wireless transmission module or by removing its memory card. Finally, all coordinate data is read through 3D graphics processing software, which can complete the interpolation and smoothing of the pit bottom plane, thereby completing the surface detection of the entire pit bottom plane and intuitively displaying the flatness of the pit bottom plane.

[0067] The detection method includes an algorithm for calculating the distance between the inspection instrument 300 and the reference point power array through the electric field strength between them, and determining the current coordinate position of the inspection instrument.

[0068] First step: Taking the minimum number of three point power sources as an example, the electrical signal frequencies emitted by the three point power sources O, A, and B are freq1, freq2, and freq3, respectively. Assume that they are directly arranged to form a rectangular coordinate system, with the origin at O ​​and the three orthogonal coordinate axes OX, OY, and OZ, where point O is at coordinates (0, 0, 0), point A is at coordinates (a, 0, 0), and point B is at coordinates (0, b, 0).

[0069] The second step: The underwater inspection device is equipped with an electric field frequency detector and an electric field strength detector. The frequency of the electric signal, freq1, freq2, and freq3, is measured by the electric field frequency detector to identify which point power source, O, A, or B, the signal originates from. The electric field strength detector can measure the electric field strength E(r) at this point. For a point power source in a uniform medium, its electric field strength distribution is directly proportional to the resistivity ρ and the current I, and inversely proportional to the square of the distance, d^2.

[0070]

[0071] Where ρ is the resistivity of the liquid, I is the total current flowing from the point source, r is the distance to the point source, and E(d) is the magnitude of the electric field intensity; the formula can be used to calculate:

[0072]

[0073] The third step: Based on the above method for calculating distance r and the method for distributing the electric field source, the distances from the underwater inspection instrument P to points O, A, and B are d_op, d_ap, and d_bp, respectively. Then, based on geometric knowledge, the coordinates of point P in a given coordinate system can be calculated as follows:

[0074]

[0075] At this point, the method for locating the inspection instrument in the relatively homogeneous upper mud and water layer (approximately tens of meters high) can be determined.

[0076] The base marker 410 and the inspection instrument 300 are interactively controlled by the electric field frequency, and the relative position of the local coordinates of the base marker and the inspection instrument is determined by the electric field strength.

[0077] This embodiment discloses a device and method for detecting the flatness of the bottom of an underwater excavation pit. The device features a reasonable overall design, simple structure, and convenient operation. It effectively combines a reference point power array, a scanning instrument, and a bottom marker array. A reference coordinate system is constructed using the reference point power array, and the scanning instrument automatically calculates its absolute coordinates within this system. By activating the bottom marker power supply, the scanning instrument automatically calculates the coordinates of the bottom marker relative to the scanning instrument's coordinate system. Through multiple coordinate transformations, the absolute position of each bottom marker in the reference coordinate system is obtained. Multiple interactive controls between the reference point power supply, the scanning instrument, and the bottom markers are achieved by setting a specific electric field frequency. Finally, the device is retrieved and data is collected. 3D data processing yields the three-dimensional shape of the pit bottom, accurately reflecting the flatness of the entire underwater excavation pit bottom.

[0078] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A device for detecting the flatness of the bottom of an underwater excavation pit, characterized in that, include A foundation pit (100) is excavated on the stratum (500). A retaining wall (600) is provided around the foundation pit (100). A mud-water layer (110) and a mud slurry layer (120) are arranged from top to bottom in the foundation pit (100). The mud slurry layer (120) is located on the upper side of the bottom of the foundation pit. A reference point power supply array (200) includes three or more reference point power supplies respectively set at the four sides above the water surface of the underwater excavation pit (100) to construct a reference coordinate system, and can transmit point power supply electric field signals of different electric field frequencies into the pit one by one. An inspection instrument (300) is designed to dive into a mud-water layer to detect flatness. The inspection instrument (300) can dive to a certain depth and start autonomous cruise detection at the junction of the mud-water layer (110) and the mud layer (120). The inspection instrument (300) and the reference point power array are connected by calculating the electric field strength between them and the distance between each power source. The absolute coordinate position of the inspection instrument (300) in the reference coordinate system is further determined. The inspection instrument (300) can import CAD data of the foundation pit plane and combine its own absolute coordinates with the foundation pit plane map to complete autonomous full-coverage cruise. A set of bottom marker arrays (400) distributed at the bottom of the underwater pit, the bottom marker array (400) including multiple bottom markers (410) set at the bottom of the pit, the bottom markers (410) and the inspection instrument (300) are interactively controlled by the electric field frequency, and the local coordinate relative position of the bottom markers and the inspection instrument is determined by the electric field strength.

2. The device for detecting the flatness of the bottom of an underwater excavation pit as described in claim 1, characterized in that, The base marker (410) includes a triangular cone shell (411) that is generally triangular in shape. A base marker power transmitter (412) and a base marker electric field strength detector (414) are respectively provided at the four apex corners of the triangular cone shell (411). A power supply and control compartment is provided inside the triangular cone shell (411). A base marker controller is provided in the control compartment. A folded buoyancy bag (413) is provided in the middle of the surface of the triangular cone shell (411). A gas generator is provided in the folded buoyancy bag (413). The base marker power transmitter (412), the base marker electric field strength detector (414) and the gas generator are respectively connected to the base marker controller.

3. The device for detecting the flatness of the bottom of an underwater excavation pit as described in claim 1, characterized in that, The inspection device (300) includes a head cover (310), a central rod (320), and a base (330) with an overall cross-shaped structure. The central rod (320) is located between the head cover (310) and the base (330).

4. The device for detecting the flatness of the bottom of an underwater excavation pit as described in claim 1, characterized in that, The helmet (310) is equipped with a top electric field strength detector (311), a hydraulic detector (319), a buoyancy control module (312), a ballast water tank (313), a thruster (315), a control processing host (314), a motion and attitude control module (316), a power supply module (317), and an electric field signal control module (318). The ballast water tank (313) is located at the upper end of the helmet (310). The hydraulic detector (319) and the buoyancy control module (312) are located inside the ballast water tank (313). The top electric field strength detector (311) is located at the top of the ballast water tank (313). The thruster (315) is symmetrically arranged on both sides of the helmet (310). The control processing host (314), motion and attitude control module (316), power supply module (317), and electric field signal control module (318) are respectively provided on the helmet (310). The motion and attitude control module (316), the power supply module (317), and the electric field signal control module (318) are all located inside the head cover (310). The control processing host (314) is connected to the top electric field strength detector (311), the hydraulic detector (319), the buoyancy control module (312), the ballast water tank (313), the thruster (315), the motion and attitude control module (316), and the electric field signal control module (318) respectively. The power supply module (317) is connected to the top electric field strength detector (311), the hydraulic detector (319), the buoyancy control module (312), the thruster (315), the control processing host (314), the motion and attitude control module (316), and the electric field signal control module (318) respectively.

5. The device for detecting the flatness of the bottom of an underwater excavation pit as described in claim 1, characterized in that, A point power supply array (331) is provided at three of the vertices of the base (330), and a bottom electric field strength detector (332) is provided at the center of the base (330).

6. A method for detecting the flatness of the bottom of an underwater excavation pit, the method being implemented based on the underwater excavation pit flatness detection device described in any one of claims 1-5, characterized in that... Includes the following steps First step: Evenly throw multiple bottom markers onto the bottom surface of the foundation pit, and then place the inspection instrument at the junction of the mud-water layer and the mud slurry layer; The second step: During the inspection process, the power supply of one of the reference points is turned on. At this time, the electric field frequency is the target activation frequency, and the electric field strength is higher than the target activation field strength. When the inspection device approaches a target, the target electric field strength detector on the target senses an electric field with a frequency of the target activation frequency, which exceeds a certain threshold, and no electric field with a frequency of the target emission frequency is sensed. Then the target is "wake up and activated". After the target is "activated", it turns on its own point power supply and generates an electric field with the target emission frequency. The third step: When the bottom electric field strength detector of the inspection instrument detects the presence of an electric field with the emission frequency of the base target in the current electric field environment, it then adjusts to a horizontal hovering posture. Based on the right-angled arrangement of point power sources, it measures the electric field strength of the base target's own point power source, calculates the straight-line distances, and finally converts them into the coordinate matrix of the base target with the inspection instrument as the local coordinate. After completing the calculation, it saves the local coordinate matrix, the direction parameters of the inspection instrument, and the time series. Fourth step: After saving the local data, the inspection instrument will turn off the point power array. The current base electric field detection is lower than the base activation field strength, that is, it is "hypnotized" and turns off its own point power electric field to enter the "complete" state, that is, it will no longer respond to the base activation frequency. Fifth step: The inspection instrument remains stationary. Based on the electric field strength detector at its top, the overall coordinate matrix in the coordinate system determined by the reference point power supply in the previous step is measured. Based on the size of the inspection instrument itself, the actual conversion relationship between the local coordinates and the reference coordinates is obtained from the electric field strength detector at its top and the point power supply array arranged in the rectangular coordinate system at its bottom. This allows us to determine the actual coordinate position of the base point in the reference coordinate system. Step 6: The inspection instrument reactivates the power supply array, replans the inspection route based on its own coordinates calculated above, adjusts its direction and attitude, and completes the measurement of the overall coordinate position of each bottom marker on the entire pit through full-coverage inspection. Step 7: After completing the survey, turn off the power to the activation point on the survey instrument. The power to the reference point is activated at the "flying" frequency. After the electric field strength detectors on the survey instrument and each bottom marker identify that the current frequency is "flying", the buoyancy control module of the survey instrument performs the ascent operation, while each bottom marker starts the gas generator, opens the folded buoyancy bag, and the survey instrument and each bottom marker float to the upper side of the water surface in the pit, thus completing the recovery operation. Step 8: After the inspection device is retrieved, it is imported into the computer via the wireless transmission module or by removing its memory card. Finally, all coordinate data is read through 3D graphics processing software, which can complete the interpolation and smoothing of the pit bottom plane, thereby completing the surface detection of the entire pit bottom plane and intuitively displaying the flatness of the pit bottom plane.

7. The detection method of the underwater excavation pit bottom flatness detection device as described in claim 6, wherein the algorithm for calculating the distance between the inspection instrument (300) and the reference point power array through the electric field strength between them and the power supply at each point, and determining the current coordinate position of the inspection instrument includes: First step: Taking the minimum number of three point power sources as an example, the electrical signal frequencies emitted by the three point power sources O, A, and B are freq1, freq2, and freq3, respectively. Assume that they are directly arranged to form a rectangular coordinate system, with the origin at O ​​and the three orthogonal coordinate axes OX, OY, and OZ, where point O is at coordinates (0, 0, 0), point A is at coordinates (a, 0, 0), and point B is at coordinates (0, b, 0). The second step: The underwater inspection device is equipped with an electric field frequency detector and an electric field strength detector. The frequency of the electric signal, freq1, freq2, and freq3, is measured by the electric field frequency detector to identify which point power source, O, A, or B, the signal originates from. The electric field strength detector can measure the electric field strength E(r) at this point. For a point power source in a uniform medium, its electric field strength distribution is directly proportional to the resistivity ρ and the current I, and inversely proportional to the square of the distance, d^2. in, ρ is the resistivity of the liquid, I is the total current flowing from the point source, r is the distance to the point source, and E(d) is the magnitude of the electric field strength; the formula can be used to calculate the electric field strength. Third step: Based on the above method for calculating the distance r and the method for the distribution of the electric field source, it can be known that the distances between the underwater inspection instrument P and the three points O, A, and B are d_op, d_ap, and d_bp, respectively. Then, based on geometric principles, the coordinates of point P in a given coordinate system can be calculated: Thus, the method for locating the inspection instrument in the relatively homogeneous upper mud and water layer (approximately tens of meters high) can be determined.

8. The detection method of the underwater excavation pit bottom flatness detection device as described in claim 6, wherein the bottom marker (410) and the inspection instrument (300) are interactively controlled by the electric field frequency, and the local coordinate relative position of the bottom marker and the inspection instrument is determined by the electric field strength.

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