High-density electrical method accurate detection method for interlayer cavities of concrete dam

Abstract

The invention provides a high-density electrical method accurate detection method for interlayer cavities of a concrete dam, and relates to the technical field of water conservancy and hydropower engineering.The method comprises the following steps that S1, an electrode array is arranged in a targeted mode based on a distribution track of an interlayer interface of the concrete dam; s2, interlayer targeted data acquisition: applying multi-frequency power supply current to the electrode array through a high-density electrical method instrument, and synchronously acquiring potential difference signals of each electrode pair under different power supply frequencies; s3, accurate inversion of interlayer holes is carried out, and the interlayer targeting apparent resistivity data set is input into a preset inversion model; s4, cavity parameters are quantitatively output, and based on a resistivity imaging profile, the high-density electrical method accurate detection method for the interlayer cavity of the concrete dam is adopted, centimeter-level positioning and tiny cavity recognition of the interlayer cavity of the concrete dam are achieved, the detection accuracy is improved, and a high-quality basis is provided for dam safety evaluation.

Description

Technical Field

[0001] This invention relates to the field of water conservancy and hydropower engineering technology, and in particular to a high-density electrical resistivity tomography method for the precise detection of voids between layers in concrete dams. Background Technology

[0002] Interlayer voids in concrete dams are a common structural defect in water conservancy and hydropower projects, mainly caused by construction defects (such as inadequate compaction and improper interface treatment), material problems (irrational mix proportions and substandard cement quality), and environmental influences (temperature deformation, seepage erosion, and seismic forces). These voids reduce the effective load-bearing area of ​​the dam body, causing stress concentration, leading to localized damage, and seriously threatening dam safety. Currently, the detection of interlayer voids in concrete dams mainly employs traditional non-destructive testing techniques such as electrical resistivity tomography, ground-penetrating radar, ultrasonic testing, and acoustic CT, as well as destructive testing methods such as core drilling. However, traditional testing methods generally suffer from insufficient accuracy, low resolution, and inability to accurately locate small-scale voids, making it difficult to meet the requirements of modern water conservancy projects for refined dam safety testing.

[0003] High-density electrical resistivity tomography (EPT), as an emerging array-based electrical exploration technology, has been widely used in the field of dam hazard detection due to its advantages such as high data acquisition density, high construction efficiency, and high resolution. It performs two-dimensional geoelectric cross-section measurements through high-density point deployment, simultaneously reflecting horizontal and vertical resistivity changes, making it particularly suitable for detecting cavities, seepage, and other hazards in dams. However, existing high-density EPT methods still face technical bottlenecks when detecting small-scale cavities between concrete dam layers, including inaccurate electrode placement, incomplete data acquisition, and insufficient accuracy of inversion algorithms, affecting the accuracy and reliability of the detection results. Summary of the Invention

[0004] The purpose of this invention is to provide a high-density electrical resistivity tomography method for the precise detection of voids between concrete dam layers, enabling centimeter-level localization of voids and identification of minute voids.

[0005] To achieve the above objectives, the present invention provides a high-density electrical resistivity tomography method for accurate detection of interlayer voids in concrete dams, comprising the following steps: Step S1: Targeted deployment of electrode arrays. Based on the distribution trajectory of the interlayer interface of the concrete dam, at least two sets of high-density electrode arrays are deployed on the water-facing or backwater-facing surface of the dam body along the direction of the interlayer interface. The contact between the electrodes and the dam body surface is filled with conductive gel and fixed with metal plates.

[0006] Step S2: Interlayer targeted data acquisition. A high-density electrical resistivity analyzer is used to apply multi-frequency power supply current to the electrode array and simultaneously acquire the potential difference signal of each electrode pair at different power supply frequencies. The target frequency with the most significant electrical response at the interlayer interface is selected and the interlayer targeted apparent resistivity dataset is obtained based on the target frequency. Step S3: Precise inversion of interlayer voids. The interlayer targeted apparent resistivity dataset is input into the preset inversion model. The inversion model is a two-dimensional / three-dimensional joint inversion algorithm that introduces preset electrical constraints on the interlayer interface, so that the inversion results focus on the interlayer interface, reduce interference from non-target areas, and achieve centimeter-level high-precision control of interlayer interface positioning. Compared with the existing unconstrained inversion method, the positioning accuracy is significantly improved, the error is greatly reduced, and the actual position of the interlayer interface can be more accurately locked. The resistivity imaging profile focused on the interlayer interface is generated through inversion calculation, and the interlayer interface resolution of the imaging profile is no greater than 2cm. Step S4: Quantitative output of void parameters. Based on resistivity imaging profiles and combined with dam seepage conditions, abnormal areas are identified. In dry environments, high-resistivity abnormal areas with an apparent resistivity of not less than 1500 Ω·m are identified; in water-filled environments, low-resistivity abnormal areas with an apparent resistivity of not more than 300 Ω·m are identified. Through matching and conversion between the electrode array coordinate system and the actual coordinates of the dam body, the actual planar position, burial depth, and three-dimensional dimensions of the abnormal areas in the interlayer of the concrete dam are obtained, and the quantitative detection results of interlayer voids are output.

[0007] Preferably, in step S1, the electrode array is a Winner-Schlumberger hybrid arrangement, wherein the electrodes along the interlayer interface are arranged in a Winner arrangement to improve lateral resolution, and the electrodes perpendicular to the interlayer interface are arranged in a Schlumberger arrangement to improve longitudinal resolution.

[0008] Preferably, in step S2, while acquiring the potential difference signal, the surface temperature and ambient humidity data of the dam body are simultaneously acquired, and the potential difference signal is corrected using a preset temperature-humidity correction formula. The correction formula is as follows: ; in, The corrected potential difference; The original potential difference was collected. This is a temperature correction factor, adapted according to the concrete grade of the dam body; This is a humidity correction factor, adapted to the ambient humidity range. The surface temperature of the dam body. This refers to ambient humidity.

[0009] Preferably, in step S3, the specific process of the two-dimensional / three-dimensional joint inversion algorithm is as follows: first, the longitudinal resistivity profile of the interlayer interface is obtained through two-dimensional inversion; then, the electrical distribution of the longitudinal profile is used as a constraint to perform three-dimensional inversion on the transverse resistivity data. During the inversion iteration process, L1 regularization constraint is used to suppress noise interference.

[0010] Preferably, in step S4, before outputting the quantitative detection results of interlayer voids, a verification step is also included: selecting at least one abnormal area corresponding to the dam surface location, drilling a verification hole with a diameter of no more than 50 mm, observing the interlayer interface state of the hole wall through an in-hole camera, and comparing the observation results with the detection results of the abnormal area; if the difference in void position between the two is no more than 5 cm and the difference in size is no more than 10%, then the detection results are confirmed to be valid.

[0011] Preferably, in step S4, based on the quantitative detection results of interlayer voids output in step S4, a detection report is generated that includes a void distribution heat map, void risk level, and repair suggestions. The repair suggestions recommend corresponding grouting materials and grouting pressures based on the void location and size.

[0012] Therefore, the present invention employs the above-mentioned high-density electrical resistivity tomography method for precise detection of interlayer voids in concrete dams, achieving centimeter-level positioning and identification of minute voids. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the overall process of a high-density electrical resistivity tomography method for accurate detection of interlayer voids in concrete dams according to the present invention. Detailed Implementation

[0014] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0015] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0016] Example 1 like Figure 1 As shown, this invention provides a high-density electrical resistivity tomography (EDT) method for accurate detection of interlayer voids in concrete dams, comprising the following steps: In the preliminary preparation phase, on-site surveys and parameter confirmation are conducted. Using dam construction drawings and geological survey reports, the distribution trajectory of the concrete dam interlayer interfaces, estimated thickness, and areas with potential voids are identified. The dam surface is inspected for debris, carbonized layers, microcracks, and other sources of interference. Effective areas for electrode placement are marked, ensuring no metal components (such as embedded parts) obstruct the view. Equipment and material preparation includes: a high-density electrical resistivity tomography (E tomography) instrument with multi-frequency power supply capabilities, metal electrodes, conductive gel, and metal pressure plates. Environmental monitoring equipment is also prepared, including temperature sensors, humidity sensors, and drilling equipment.

[0017] For electrode arrangement, a hybrid Wenner-Schlumberger arrangement is used. Electrodes along the interlayer interface are arranged using the Wenner arrangement, while those perpendicular to the interlayer interface are arranged using the Schlumberger arrangement. Spacing and coverage length are set as follows: the spacing between adjacent electrodes is set to 0.3-0.8m based on the estimated thickness of the interlayer interface, and the coverage length of each array is ≥ 3 times the longest diameter of the estimated void at the interlayer interface. Contact optimization and fixation: conductive gel is filled at the contact point between the electrodes and the dam surface, and then compacted and fixed with metal clamps to ensure that the contact resistance is stable below 500Ω.

[0018] Step S1: Targeted Electrode Array Deployment. Based on the distribution trajectory of the interlayer interfaces (including construction joints and the interface between old and new concrete) of the concrete dam, at least two sets of high-density electrode arrays are deployed along the interlayer interface on the upstream or downstream surface of the dam body. This ensures optimal coupling between the detection electric field and the interlayer interface, improving detection sensitivity. The spacing between adjacent electrodes in each array is set to 0.3-0.8m based on the estimated thickness of the interlayer interface, achieving a detection resolution of 1 / 10-1 / 20 of the interlayer interface thickness. This allows for the identification of tiny interlayer voids no larger than 2cm, overcoming the limitation of only identifying voids no smaller than 10cm. Furthermore, the contact between the electrodes and the dam surface utilizes conductive gel filling and metal clamping, effectively penetrating the carbonized layer of the concrete surface and eliminating interference from surface cracks. This stabilizes the contact resistance below 500Ω, improving stability by more than 10 times compared to traditional electrode contact methods (resistance fluctuation of 1-5kΩ), ensuring the reliability of measurement data and eliminating interference from the surface carbonized layer and tiny cracks on the contact resistance.

[0019] In step S1, the electrode array is a hybrid arrangement of Winner and Schlumberger, wherein the electrodes along the interlayer interface are arranged in Winner to improve lateral resolution, and the electrodes perpendicular to the interlayer interface are arranged in Schlumberger to improve longitudinal resolution, and the coverage length of each electrode array is not less than 3 times the estimated longest diameter of the void at the interlayer interface.

[0020] Multi-frequency power supply and signal acquisition: The high-density electrical resistivity meter is activated, and a multi-frequency power supply current of 5-50Hz is applied to the electrode array. The potential difference signal of each electrode pair under different power supply frequencies is acquired simultaneously, and the raw apparent resistivity data is recorded. Temperature and humidity sensors are activated simultaneously to acquire the surface temperature (T) and ambient humidity (RH) data of the dam body in real time, and the data is recorded once every 5 minutes.

[0021] Target frequency selection and data correction: Calculate the apparent resistivity difference between the interlayer interface and the dam body at different frequencies, select frequencies with a difference of not less than 30% as target frequencies, extract effective apparent resistivity datasets based on these frequencies, and correct the original potential difference using a preset correction formula.

[0022] Step S2: Interlayer Targeted Data Acquisition. A high-density electrical resistivity transilluminator is used to apply multi-frequency power supply current (frequency range 5-50Hz) to the electrode array. Potential difference signals of each electrode pair at different power supply frequencies are simultaneously acquired. The target frequency with the most significant electrical response at the interlayer interface (at this frequency, the apparent resistivity difference between the interlayer interface and the dam body is not less than 30%) is selected. This effectively distinguishes the interlayer interface from the dam body, improving the accuracy of interlayer void identification from conventional single-frequency detection, and enabling the identification of minute interlayer voids that conventional methods cannot detect. An interlayer targeted apparent resistivity dataset is obtained based on the target frequency acquisition.

[0023] In step S2, while acquiring the potential difference signal, the surface temperature of the dam body (accuracy ±0.5℃) and the ambient humidity (accuracy ±2%RH) data are simultaneously acquired. The potential difference signal is then corrected using a preset temperature-humidity correction formula, which is as follows: ; in, The corrected potential difference; The original potential difference was collected. This is a temperature correction factor, adapted according to the concrete grade of the dam body; This is a humidity correction factor, adapted to the ambient humidity range. The surface temperature of the dam body. This refers to ambient humidity.

[0024] It can eliminate measurement errors caused by environmental factors and ensure the consistency of test results under different times and environmental conditions.

[0025] Accurate Inversion of Interlayer Voids: The inversion model parameters are set, incorporating pre-defined electrical constraints on the interlayer interface: under normal conditions, the apparent resistivity fluctuation range of the interlayer interface is 500-800 Ω·m; under void conditions, the apparent resistivity is greater than 1500 Ω·m and less than 300 Ω·m. Two-dimensional / three-dimensional joint inversion calculations are performed. Two-dimensional inversion is conducted on the corrected apparent resistivity data to generate a longitudinal resistivity profile of the interlayer interface. Using the two-dimensional longitudinal profile as a constraint, three-dimensional inversion is performed on the transverse resistivity data. L1 regularization constraints are applied during the inversion process, and the iteration termination condition is that the apparent resistivity error between two adjacent iterations is no greater than 2%. The final output is a three-dimensional resistivity imaging profile focused on the interlayer interface, with an interlayer interface resolution of no more than 2 cm.

[0026] Step S3: Precise inversion of interlayer voids. The interlayer targeted apparent resistivity dataset is input into a preset inversion model. The inversion model is a two-dimensional / three-dimensional joint inversion algorithm that incorporates preset electrical constraints on the interlayer interface (the apparent resistivity fluctuation range of the interlayer interface under normal conditions is 500-800 Ω·m, and the apparent resistivity under void conditions is greater than 1500 Ω·m and less than 300 Ω·m). This allows the inversion results to focus on the interlayer interface, reducing interference from non-target areas. The interlayer interface positioning achieves centimeter-level high-precision control. Compared with existing unconstrained inversion methods, the positioning accuracy is significantly improved, the error is greatly reduced, and the actual position of the interlayer interface can be more accurately locked. The resistivity imaging profile focused on the interlayer interface is generated through inversion calculation. The interlayer interface resolution of the imaging profile is no greater than 2 cm.

[0027] In step S3, the specific process of the two-dimensional / three-dimensional joint inversion algorithm is as follows: first, the longitudinal resistivity profile of the interlayer interface is obtained through two-dimensional inversion; then, the electrical distribution of the longitudinal profile is used as a constraint to perform three-dimensional inversion on the transverse resistivity data. During the inversion iteration process, L1 regularization constraint is used to suppress noise interference. The iteration termination condition is that the apparent resistivity error between two adjacent iterations is not greater than 2%.

[0028] Anomaly identification: In the 3D resistivity imaging profile, anomaly areas are accurately marked in conjunction with the dam seepage conditions. In a dry environment (cavities filled with air), high-resistivity anomaly areas with an apparent resistivity of not less than 1500 Ω·m are marked; in a water-filled environment (cavities filled with water), low-resistivity anomaly areas with an apparent resistivity of not more than 300 Ω·m are marked. Actual parameter conversion: Through matching and calibration between the electrode array coordinate system and the actual coordinates of the dam body, the image coordinates of the anomaly areas (high or low resistance) are converted into the actual coordinates of the dam body, accurately obtaining the planar position, burial depth, and 3D dimensions of the cavities. Result verification: Select at least one anomaly area (high or low resistance) corresponding to the dam body surface position, drill a verification hole with a diameter not greater than 50 mm, and observe the interlayer interface state of the hole wall (simultaneously confirming the cavity filling medium: air or water) and the actual dimensions through an in-hole camera. Compare the observation results with the parameters obtained from the detection: if the deviation of the cavity position is not greater than 5 cm and the deviation of the size is not greater than 10%, the detection result is confirmed to be valid; if the deviation exceeds the range, return to step S2 to re-collect data and invert.

[0029] Step S4: Identify abnormal areas based on the dam's seepage conditions (dry environment / water-filled environment). In a dry environment (cavities are filled with air), identify high-resistivity abnormal areas with an apparent resistivity of not less than 1500 Ω·m (air resistivity is much higher than that of the concrete body, forming a high-resistivity contrast). In a water-filled environment (cavities are filled with water), identify low-resistivity abnormal areas with an apparent resistivity of not more than 300 Ω·m (water conductivity is better than that of the concrete body, forming a low-resistivity contrast). By matching and converting the electrode array coordinate system with the actual coordinates of the dam body, obtain the actual planar location, burial depth, and three-dimensional dimensions (length × width × thickness) of the abnormal areas between the concrete dam layers, and output the quantitative detection results of the interlayer cavities.

[0030] In step S4, before outputting the quantitative detection results of interlayer voids, a verification step is also included: select at least one abnormal area (high resistance or low resistance) corresponding to the dam surface location, drill a verification hole with a diameter of no more than 50 mm, observe the interlayer interface state of the hole wall through the hole camera (confirm the void filling medium and actual size), and compare the observation results with the detection results of the abnormal area; if the void position deviation between the two is no more than 5 cm and the size deviation is no more than 10%, the detection result is confirmed to be valid.

[0031] In the report output phase, the test results are visualized, generating a heat map of the interlayer void distribution; a 3D resistivity imaging profile and a void actual coordinate comparison table are attached. Repair recommendations are formulated, suggesting corresponding grouting materials based on the void location (e.g., surface / deep) and size: epoxy resin grout for small surface voids and cement grout for large deep voids; grouting pressure parameters are provided. The test process, inversion results, verification data, risk level, and repair recommendations are integrated to form a complete test report, serving as the engineering basis for the repair of interlayer voids in concrete dams.

[0032] In step S4, based on the quantitative detection results of interlayer voids output in step S4, a void distribution heatmap and void risk level (classified by void volume as minor: <0.1m) are generated. 3 Moderate: 0.1-1m 3 , Severity: >1m 3 The system includes a test report with repair recommendations, which recommend appropriate grouting materials and pressures based on the location and size of the voids. A closed-loop system of testing, verification, and correction is established to ensure the reliability of test results, providing authoritative evidence for project acceptance and solving the technical challenge of existing testing methods' inability to verify results.

[0033] Therefore, the present invention employs the above-mentioned high-density electrical resistivity tomography method for the precise detection of interlayer voids in concrete dams, achieving centimeter-level positioning and identification of minute voids, improving detection accuracy, and providing high-quality evidence for dam safety evaluation.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-density electrical resistivity tomography method for precise detection of interlayer voids in concrete dams, characterized in that, Includes the following steps: Step S1: Targeted deployment of electrode arrays. Based on the distribution trajectory of the interlayer interface of the concrete dam, at least two sets of high-density electrode arrays are deployed on the water-facing or backwater-facing surface of the dam body along the direction of the interlayer interface. The contact between the electrodes and the dam body surface is filled with conductive gel and fixed with metal plates. Step S2: Interlayer targeted data acquisition. A high-density electrical resistivity analyzer is used to apply multi-frequency power supply current to the electrode array and simultaneously acquire the potential difference signal of each electrode pair at different power supply frequencies. The target frequency with the most significant electrical response at the interlayer interface is selected and the interlayer targeted apparent resistivity dataset is obtained based on the target frequency. Step S3: Precise inversion of interlayer voids. The interlayer targeted apparent resistivity dataset is input into the preset inversion model. The inversion model is a two-dimensional / three-dimensional joint inversion algorithm that introduces preset electrical constraints on the interlayer interface, so that the inversion results focus on the interlayer interface, reduce interference from non-target areas, and achieve centimeter-level high-precision control of interlayer interface positioning. Compared with the existing unconstrained inversion method, the positioning accuracy is significantly improved, the error is greatly reduced, and the actual position of the interlayer interface can be more accurately locked. The resistivity imaging profile focused on the interlayer interface is generated through inversion calculation, and the interlayer interface resolution of the imaging profile is no greater than 2cm. Step S4: Quantitative output of void parameters. Based on resistivity imaging profiles and combined with dam seepage conditions, abnormal areas are identified. In dry environments, high-resistivity abnormal areas with an apparent resistivity of not less than 1500 Ω·m are identified; in water-filled environments, low-resistivity abnormal areas with an apparent resistivity of not more than 300 Ω·m are identified. Through matching and conversion between the electrode array coordinate system and the actual coordinates of the dam body, the actual planar position, burial depth, and three-dimensional dimensions of the abnormal areas in the interlayer of the concrete dam are obtained, and the quantitative detection results of interlayer voids are output.

2. The high-density electrical resistivity tomography method for precise detection of interlayer voids in concrete dams according to claim 1, characterized in that, In step S1, the electrode array is a hybrid arrangement of Winner and Schlumberger, wherein the electrodes along the interlayer interface are arranged in a Winner arrangement to improve lateral resolution, and the electrodes perpendicular to the interlayer interface are arranged in a Schlumberger arrangement to improve longitudinal resolution.

3. A high-density electrical resistivity tomography method for precise detection of interlayer voids in concrete dams according to claim 1, characterized in that, In step S2, while acquiring the potential difference signal, the surface temperature and ambient humidity data of the dam body are simultaneously acquired. The potential difference signal is then corrected using a preset temperature-humidity correction formula, which is as follows: ； in, The corrected potential difference; This represents the original potential difference acquired. This is a temperature correction factor, adapted according to the concrete grade of the dam body; This is a humidity correction factor, adapted to the ambient humidity range. The surface temperature of the dam body. This refers to ambient humidity.

4. A high-density electrical resistivity tomography method for precise detection of interlayer voids in concrete dams according to claim 1, characterized in that, In step S3, the specific process of the two-dimensional / three-dimensional joint inversion algorithm is as follows: first, the longitudinal resistivity profile of the interlayer interface is obtained through two-dimensional inversion; then, the electrical distribution of the longitudinal profile is used as a constraint to perform three-dimensional inversion on the transverse resistivity data. During the inversion iteration process, L1 regularization constraint is used to suppress noise interference.

5. A high-density electrical resistivity tomography method for precise detection of interlayer voids in concrete dams according to claim 1, characterized in that, In step S4, before outputting the quantitative detection results of interlayer voids, a verification step is also included: select at least one abnormal area corresponding to the dam surface location, drill a verification hole with a diameter of no more than 50 mm, observe the interlayer interface state of the hole wall through the hole camera, and compare the observation results with the detection results of the abnormal area; if the difference in void position between the two is no more than 5 cm and the difference in size is no more than 10%, then the detection results are confirmed to be valid.

6. A high-density electrical resistivity tomography method for precise detection of interlayer voids in concrete dams according to claim 1, characterized in that, In step S4, based on the quantitative detection results of interlayer voids output in step S4, a detection report is generated that includes a void distribution heat map, void risk level, and repair suggestions. The repair suggestions recommend corresponding grouting materials and grouting pressures based on the void location and size.

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