A joint diagnosis system and method for reservoir dams using parallel electrical and transient electromagnetic techniques

Abstract

The invention discloses a reservoir dam parallel electrical method and transient electromagnetic technology joint diagnosis system and method, comprising a longitudinal detection system, the longitudinal detection system comprising a parallel electrical method detection device and a transient electromagnetic detection device, the parallel electrical method detection device comprising a parallel electrical method measurement line and a parallel electrical method instrument arranged on the central axis of the dam crest or the anti-seepage end surface, the parallel electrical method measurement line comprising copper rods inserted on the dam at adjacent intervals and cables connected to the copper rods; the transient electromagnetic detection device comprises a transient electromagnetic measurement line and a transient electromagnetic instrument arranged on the central axis of the dam crest or the anti-seepage section located at two dam shoulders and / or the dam crest hardening area, the transient electromagnetic measurement line comprising a coil arranged at a measuring point and a coil cable connected to the coil; the cable line and the coil cable are respectively connected to the parallel electrical method instrument and the transient electromagnetic instrument; the parallel electrical method instrument and the transient electromagnetic instrument are used to be connected to an analysis system.

Description

Technical Field

[0001] The present invention relates to the technical field of water conservancy project safety diagnosis, and specifically to a system and method for jointly diagnosing reservoir dam leakage using parallel electrical method and transient electromagnetic technology. The invention aims at the variable spatial position information of reservoir dam leakage hazards, and takes into account unfavorable conditions such as dam leakage around the dam and site hardening, and proposes a system and method for jointly diagnosing reservoir dam leakage hazards using parallel electrical method and transient electromagnetic technology. Background Art

[0002] The inspection and prevention of reservoir dam leakage is a difficult point in the standardized management of water conservancy projects. Filling the gaps in engineering hidden dangers is of great significance to ensuring the safety of infrastructure and sustainable water benefits. Earth-rock dams are granular structures of earth and rock formed by artificial or mechanical layered rolling and accumulation. Seepage problems occur in multiple stages of reservoir construction, operation, and maintenance. In the process of continuously solving the abnormal seepage risks of engineering series, researchers have achieved certain results in the understanding of the seepage mechanism of earth-rock dams, seepage safety evaluation, leakage hidden danger detection, and safety remediation. In particular, with the rapid development of efficient, convenient, and perspective non-destructive diagnostic technology, it provides a scientific basis for the precise locking of leakage target areas. For example: Utility model patent CN 205538138 U authorizes detection equipment for leakage detection and directional treatment of earth-rock dams. By introducing parallel electrical detection technology into earth-rock dam leakage detection and reasonably implementing grouting according to the detection results, the detection and treatment of hidden dangers are integrated, and the purpose of rapid directional treatment is achieved; invention patent CN 110082393 A discloses a real-time monitoring system and method for dams based on mobile communications and high-density electrical methods, which can monitor and warn the leakage of dams in real time. It is easy to implement, and the manual analysis process of data results is handed over to the computer to complete, while mining data to provide richer conclusions. However, reservoir leakage is the result of the continuous deterioration and accumulation of abnormal seepage inside the dam. It has the characteristics of unknown causes, unknown lesions, and diverse symptoms. It is manifested in complex and changeable spatial location information and cross-coupling of multiple hidden danger bodies, which causes the problem of misjudgment and omission when identifying hidden dangers by a single geophysical exploration method.

[0003] Invention patent CN 109782357 A discloses a method for detecting dam leakage by combining ground magnetic resonance method and high-density electrical method. The MRS method is used to accurately determine the leakage hidden danger attributes of the low-resistance abnormal area revealed by the high-density electrical method. The detection signal-to-noise ratio is effectively improved by optimizing the number of coil turns to improve the diagnostic efficiency and the accuracy of the interpretation of the inversion results. Invention patent CN 111381276 A discloses a monitoring method for the occurrence, development and positioning of dam leakage damage. By using the common points and respective advantages of micro-seismic and micro-seismic monitoring technologies, the accurate time and location of the seepage damage can be provided, which can save time for the treatment of hidden dangers and greatly improve the effect of hidden danger treatment. However, the current methods for detecting hidden dangers in water conservancy projects are diverse and have different applicable conditions. In most cases, it is impractical to use comprehensive geophysical methods for detection, which causes a waste of resources and a reduction in effectiveness to a certain extent. How to use the best matching combination to achieve efficient, accurate and economical full-perspective detection of reservoir dam hidden dangers has become the key. Leakage of reservoir dams occurs below the infiltration line. The most obvious difference in physical properties between the weak seepage area and the surrounding medium is mainly manifested in the high and low resistivity. Therefore, electrical methods play an important role in the diagnosis of leakage hazards. High-density electrical methods are widely used in reservoir dams, but the on-site work efficiency is low, and the hardening of the dam surface and the blind spots at both ends of the measuring line are becoming more and more prominent; transient electromagnetic technology can use non-contact coils to transmit and receive signals, and has a good application prospect in the detection of leakage hazards in complex sites, but the current transient electromagnetic detection equipment is large in size, and the instrument's shutdown time and the interference of the primary field signal cause blind spots in the shallow surface of the detection area. Therefore, in view of the characteristics of the geology, construction, and operation of reservoir dams, the orderly use of advanced technologies and corresponding combined technologies will help improve the reliability of diagnosis and increase the rake area for the precise treatment of reservoir dams. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of single means or poor combination optimization in geophysical exploration methods for reservoir dam leakage detection, and provide a reservoir dam parallel electrical method and transient electromagnetic technology joint diagnosis system and method. The invention has the characteristics of high resolution of leakage channels, fast on-site detection, and complementary advantages in detection accuracy of different parts of the dam. During use, the detection layout system and detection sequence are changed according to site conditions, thereby improving the accuracy and reliability of reservoir dam leakage diagnosis, and realizing efficient detection of the entire dam without blind spots.

[0005] A reservoir dam parallel electrical method and transient electromagnetic technology joint diagnosis system, including a longitudinal detection system, the longitudinal detection system including a parallel electrical method detection device and a transient electromagnetic detection device, the parallel electrical method detection device including a parallel electrical method measurement line and a parallel electrical method instrument arranged on the central axis of the dam crest or the anti-seepage end surface, the parallel electrical method measurement line including copper rods inserted on the dam at adjacent intervals and a cable connected to the copper rods; the transient electromagnetic detection device including a transient electromagnetic measurement line and a transient electromagnetic instrument arranged on the central axis of the dam crest or the anti-seepage section located at two abutments of the dam and / or the dam crest hardening area, the transient electromagnetic measurement line including a coil arranged at a measuring point and a coil cable connected to the coil; the cable and the coil cable are respectively connected to the parallel electrical method instrument and the transient electromagnetic instrument; the parallel electrical method instrument and the transient electromagnetic instrument are used to be connected to an analysis system.

[0006] Preferably, after the copper rod is inserted into the dam, a funnel-shaped pit is dug with the copper rod as the center and a radius of 10 cm, and the pit is filled with salt water.

[0007] Preferably, the coil is placed horizontally on the dam surface and the coil normal is vertically downward. Preferably, the parallel electrical method instrument has a wireless transmission module, a control module and an acquisition module, the acquisition module is connected to the cable, the control module is used to issue acquisition instructions and data recovery instructions to the acquisition module, and the wireless transmission module is used to remotely transmit the data recovered by the control module to the analysis system; the analysis system has the dual function of processing parallel electrical method data and transient electromagnetic data, the analysis system issues instructions for the recovery of transient electromagnetic data to the transient electromagnetic instrument, and the transient electromagnetic data is also remotely transmitted to the analysis system through the wireless transmission module to recover the data in the transient electromagnetic instrument.

[0008] Preferably, when laying out survey lines on site, the dam top survey line, the first-level backwater slope survey line, the second-level backwater slope survey line, the third-level backwater slope survey line to the n-level backwater slope survey line are laid out in sequence along the lateral width direction from the dam top to the dam foot, and the spacing between adjacent survey lines is 5m; the backwater slope survey line of the next level is determined by the range of the detection anomaly area of ​​the previous level.

[0009] Preferably, parallel electrical survey lines are arranged on the central axis of the dam crest or the anti-seepage section, and transient electromagnetic survey lines are arranged on the two shoulders of the dam. In combination with the spatial position of the leakage point of the dam and based on the results of the parallel electrical and transient electromagnetic detection on the dam crest, the position of the first-level backwater slope survey line is divided into a normal area and an abnormal area. Parallel electrical survey lines are arranged at the abnormal area of ​​the first-level backwater slope survey line, and transient electromagnetic survey lines are additionally arranged on the two shoulders of the dam. In combination with the spatial position of the leakage point of the dam and based on the results of the parallel electrical and transient electromagnetic detection on the first-level backwater slope survey line, the position of the first-level backwater slope survey line is divided into a normal area and an abnormal area. The position of the secondary back slope survey line is divided into a normal area and an abnormal area. A parallel electrical survey line is arranged at the abnormal area of ​​the secondary back slope survey line, and then a transient electromagnetic survey line is additionally arranged on the two dam shoulders; combined with the spatial position of the dam leakage point, and based on the results of the parallel electrical and transient electromagnetic detection of the secondary back slope survey line of the dam, the position of the tertiary back slope survey line is divided into a normal area and an abnormal area; and so on, until all the survey lines of the entire dam are detected, and through the detection of survey lines at different elevations, the scope of the abnormal area is gradually narrowed, and the direction of the leakage channel is finally determined.

[0010] Preferably, when there is a hardened area between the dam crest, the first-level backwater slope survey line position, the second-level backwater slope survey line position and the n-level backwater slope survey line position, a transient electromagnetic survey line is added in the hardened area.

[0011] Preferably, when there is leakage around the dam, a lateral detection system perpendicular to the dam is added at the dam shoulder. The lateral measurement line system of the lateral detection system also includes the parallel electrical detection device. The lateral measurement line arrangement starts at the dam top and ends at the dam foot. The back slope is divided into multiple measurement points with equal slope distance from the dam top to the dam foot. Each measurement point corresponds to the buried position of the copper rod. Each copper rod electrode is connected by a cable and formed into a parallel electrical detection device with a parallel electrical instrument.

[0012] The diagnostic method of the reservoir dam parallel electrical method and transient electromagnetic technology joint diagnostic system is characterized in that: the analysis system groups the received parallel electrical method data body and transient electromagnetic data body respectively to obtain the apparent resistivity contour line and inversion resistivity image, measuring point-induced electromotive force curve and apparent resistivity image of the dam crest or anti-seepage section; normalizes the overlapped part of the apparent resistivity contour line and the apparent resistivity image, uses the normalized ratio parameter to correct the apparent resistivity contour line and the apparent resistivity image, and splices them to obtain the apparent resistivity cloud map of the dam crest; gradually repeats the above steps for the data in the grouping, and then obtains the apparent resistivity cloud map of the whole dam from the first to the nth level backwater slope; the apparent resistivity cloud map of each group is mapped according to the three-dimensional coordinate system to form a three-dimensional apparent resistivity map of the whole dam.

[0013] Preferably, in the diagnostic method, if the low-resistance area in the horizontal abnormal area of ​​the three-dimensional apparent resistivity map of the whole dam has obvious connectivity features from the dam top to the dam foot, it indicates that there is a leakage channel in this section; if the low-resistance area in the abnormal area of ​​the low-resistance area does not have obvious connectivity features from the dam top to the dam foot, it indicates that the dam has a hidden danger of abnormal seepage; if in the normal area upstream of the dam, the downstream survey line has a low-resistance anomaly and the lateral survey line also has a low-resistance anomaly, then the dam has leakage around the dam; if the dam on each survey line appears to be in the normal area, then the dam has no hidden dangers.

[0014] The present invention is described in detail below:

[0015] The longitudinal detection system of the present invention preferentially arranges a parallel electrical detection device on the dam crest, quickly obtains the parallel electrical two-dimensional resistivity cross-sectional image of the dam, and uses a multi-turn overlapping small coil transient electromagnetic device to perform supplementary detection on the hardened part of the dam crest and the blind areas at both ends of the parallel electrical crest, thereby obtaining a transient electromagnetic two-dimensional resistivity cross-sectional image, and normalizes the data in the overlapping area of ​​the two, further corrects and calculates the parallel electrical two-dimensional resistivity cross-sectional image and the transient electromagnetic two-dimensional resistivity cross-sectional image, thereby obtaining a resistivity image of the entire cross-section of the dam; combined with The location of the dam leakage point is determined by dividing the back slope of the dam into multiple normal areas and abnormal areas according to the difference in resistivity. The above-mentioned longitudinal detection system is added to the abnormal areas. In particular, when the dam top detection results show that the dam has abnormal leakage around the dam, a transverse detection system should be added near the dam head. The transverse parallel electrical survey line starts from the dam top and ends at the dam foot. By combining the longitudinal detection system and the transverse detection system, the hidden dangers of reservoir leakage can be detected in an orderly manner, so as to achieve the purpose of accurate detection of dam hidden dangers, improve work efficiency and reduce the cost of blind detection of comprehensive geophysical exploration methods.

[0016] In order to achieve the above-mentioned purpose, the present invention provides a reservoir dam parallel electrical method and transient electromagnetic technology joint diagnosis system including an analysis system, a parallel electrical method instrument, a cable, a copper rod, a transient electromagnetic instrument, a coil, a coil cable, etc.

[0017] The parallel electrical method instrument includes a wireless transmission module, a control module and an acquisition module. The wireless transmission module is used to remotely transmit the data recovered by the control module to the analysis system. The control module issues acquisition instructions and data recovery instructions to the acquisition module. The acquisition module is connected to the cable, and the cable is connected to the copper rod. The copper rod is fully coupled with the dam fill. The analysis system has the dual function of processing parallel electrical method data and transient electromagnetic data. The analysis system issues instructions for recovering transient electromagnetic data to the transient electromagnetic instrument. The transient electromagnetic data is also remotely transmitted from the transient electromagnetic instrument to the analysis system through the wireless transmission module. The transient electromagnetic instrument is connected to the coil through a coil cable. The coil is horizontally placed on the dam surface and the coil normal is vertically downward.

[0018] The analysis system has the dual functions of recovering and processing parallel electrical method data and transient electromagnetic data.

[0019] The control module in the parallel electrical instrument collects data instructions AMN&MNB. The parallel electrical instrument has the characteristics of shielded electrodes. The cable includes taps at equal intervals, and each tap is connected to the copper rod via a double-clamp wire. The copper rod is 40 cm long and 2 cm in diameter. During detection, the copper rod enters the dam about 30 cm. At the same time, a funnel-shaped pit is dug with a radius of 10 cm with the copper rod as the center and filled with salt water.

[0020] The coil includes a transmitting coil and a receiving coil. The coil is cylindrical with a diameter of 50 cm and has the advantages of being easy to carry and quick to use.

[0021] The distance between the copper bars is 1m, and the point distance between the coils is 1m; there are multiple taps on the cable, and the length of the cable is related to the length of the dam crest;

[0022] The analysis system processes the parallel electrical method data and transient electromagnetic data respectively. The basis for the parallel electrical method judgment is mainly the apparent resistivity contour and the inversion resistivity image; the basis for the transient electromagnetic judgment is mainly the measuring point-induced electromotive force curve and the apparent resistivity image. The measuring point-induced electromotive force curve reflects the lateral changes of the dam, and the apparent resistivity image reflects the changes of the anomaly in the depth direction.

[0023] The reservoir dam parallel electrical method and transient electromagnetic technology joint diagnosis system also includes the layout plan of the on-site measurement line:

[0024] The combined diagnosis system includes a longitudinal detection system and a transverse detection system; the hardened area refers to the clay layer on the top of the dam covered by materials such as prefabricated concrete blocks (bricks), mortar masonry stones, asphalt, etc.

[0025] The number of on-site survey lines of the longitudinal detection system is related to the lateral width of the dam crest and dam foot. The spacing between adjacent survey lines is 5m. The survey lines are named in sequence as dam crest survey line, first-level backwater slope survey line, second-level backwater slope survey line, third-level backwater slope survey line...;

[0026] The survey lines of the longitudinal detection system are arranged in order, and the survey lines in the front of the corresponding order have the advantage of priority detection. The first survey line is the dam top survey line, the second survey line is the first-level backwater slope survey line, and so on;

[0027] The layout range of the first-level backwater slope survey line of the longitudinal detection system is determined by the detection abnormal area range of the dam top survey line, the layout range of the second-level backwater slope survey line is determined by the abnormal area range of the first-level backwater slope survey line, and so on;

[0028] The specific implementation is that the longitudinal detection system first arranges parallel electrical survey lines on the central axis of the dam crest or the anti-seepage section, and then arranges transient electromagnetic survey lines on the two dam shoulders. At the same time, if there is a hardened area on the dam crest, transient electromagnetic survey lines should also be added to this area; combined with the spatial position of the dam leakage point, and based on the results of the parallel electrical and transient electromagnetic detection of the dam crest survey lines, the position of the first-level backwater slope survey line is divided into a normal area and an abnormal area, and parallel electrical survey lines are arranged on the abnormal area of ​​the first-level backwater slope survey line, and then transient electromagnetic survey lines are additionally arranged on the two dam shoulders. At the same time, if there is a hardened area on the first-level backwater slope survey line, transient electromagnetic survey lines should also be added to this area; combined with the spatial position of the dam leakage point, and based on the results of the first-level dam leakage point, the first-level backwater slope survey line is divided into a normal area and an abnormal area. Based on the results of the parallel electrical method and transient electromagnetic detection of the secondary backwater slope survey line, the secondary backwater slope survey line position is divided into a normal area and an abnormal area. Parallel electrical method survey lines are arranged at the abnormal area of ​​the secondary backwater slope survey line, and transient electromagnetic survey lines are additionally arranged on the two dam shoulders. At the same time, if there is a hardened area at the location of the secondary backwater slope survey line, transient electromagnetic survey lines should also be added in this area; combined with the spatial location of the dam leakage point, and based on the results of the parallel electrical method and transient electromagnetic detection of the secondary backwater slope survey line of the dam, the third backwater slope survey line position is divided into a normal area and an abnormal area; and so on, until all the survey lines of the entire dam are detected, and through the detection of survey lines at different elevations, the scope of the abnormal area is gradually narrowed, and finally the direction of the leakage channel is determined;

[0029] In particular, if the dam has leakage problems around the dam, a transverse detection system perpendicular to the dam should be added at the dam shoulder. The transverse detection system also includes a parallel electrical method device. The transverse measuring line starts at the dam top and ends at the dam foot. The back slope is divided into multiple measuring points at equal oblique intervals from the dam top to the dam foot. Each measuring point corresponds to the buried position of the copper rod. Each copper rod electrode is connected by a cable and formed into a parallel electrical method device with a parallel electrical method instrument.

[0030] In particular, the normal and abnormal areas are determined based on the relative magnitude of the apparent resistivity values;

[0031] The combined diagnosis method of reservoir dam parallel electrical method and transient electromagnetic technology includes:

[0032] 1. Data Collection

[0033] According to the length of the dam, when detecting leakage of the dam body, parallel electrical measurement lines are arranged on the central axis of the dam top or the anti-seepage section, copper rods are arranged at the position of the cable line taps, and funnel-shaped pits with a radius of 10 cm are dug around each copper rod with the copper rod as the center, and filled with salt water, and the above work is carried out for all copper rods on the dam in turn; when all the copper rods are installed, the cable line taps and copper rods are connected in turn using double-clamp wires, and the cable is connected to the parallel electrical instrument, and the control module of the parallel electrical instrument is used to set the sampling parameters (data collection instructions, sampling time, sampling interval, power supply mode, shielding electrode) and send instructions to the acquisition module below. When the acquisition module receives the instructions, the copper rods on the cable line are powered on individually and sampled multiple times in turn, thereby realizing the collection of the natural electric field, primary field, and secondary field data of the dam. After the collection is completed, the control module recovers the collected data body in real time, and packages all the data as a whole and sends them remotely to the analysis system through the wireless transmission module;

[0034] Transient electromagnetic survey lines are also laid on the central axis of the dam crest or the anti-seepage section, located on the two shoulders of the dam or the hardened area of ​​the dam surface. Combined with the dam height and the blind spot position of the parallel electrical resistivity contour line, the transient electromagnetic detection section is delineated, and the measurement point is marked in the detection section. The center point of the transient electromagnetic coil is placed on the measurement point, and the transient electromagnetic coil is connected to the transient electromagnetic instrument through the coil cable. Then, the parameters such as the number of coil turns, the emission frequency, the emission current, the number of superpositions, and the measurement mode of the transient electromagnetic instrument are adjusted. The optimal detection parameters are obtained by observing the attenuation characteristics of the induced electromotive force, and each measurement point is sampled using transient electromagnetics. Finally, all the data are packaged as a whole through the wireless transmission module and sent remotely to the analysis system.

[0035] In particular, the parallel electrical survey line should be extended to both banks as far as possible. If the dam has leakage around the dam, a transverse detection system perpendicular to the dam should be added at the dam shoulder, which includes a parallel electrical device (i.e., a parallel electrical detection device). The transverse survey line starts at the dam top and ends at the dam foot. The back slope is divided into multiple measuring points at equal oblique intervals from the dam top to the dam foot. Each measuring point corresponds to the buried position of the copper rod. Each copper rod electrode is connected by a cable to form a parallel electrical device with a parallel electrical instrument. Specifically, a parallel electrical survey line is arranged on the back slope of the dam, copper rods are laid at the position of the cable tap, and a funnel-shaped pit with a radius of 10 cm is dug around each copper rod with the copper rod as the center, and filled with salt water. The above work is carried out for all the copper rods on the dam in turn; when all the copper rods are installed, the cable taps and the copper rods are connected in turn using double-clamp wires, and the cables are connected to the parallel electrical instrument. The control module of the parallel electrical instrument is used to set the sampling parameters (data collection instructions, sampling time, sampling interval, power supply method, shielding electrode) and send instructions to the acquisition module. When the acquisition module receives the instructions, it performs single power supply and multiple sampling on the copper rods on the cable in turn, thereby realizing the collection of the dam's natural electric field, primary field, and secondary field data. After the collection is completed, the control module recovers the collected data body in real time, and packages all the data as a whole and sends it remotely to the analysis system through the wireless transmission module.

[0036] Combined with the spatial location of the dam leakage point, and based on the results of the parallel electrical method and transient electromagnetic detection of the dam crest survey line, the position of the first-level backwater slope survey line is divided into a normal area and an abnormal area. A parallel electrical method survey line is arranged at the position of the abnormal area of ​​the first-level backwater slope survey line, and then a transient electromagnetic survey line is additionally arranged on the two dam shoulders. At the same time, if there is a hardened area on the position of the first-level backwater slope survey line, a transient electromagnetic survey line should also be added in this area; Combined with the spatial location of the dam leakage point, and based on the results of the parallel electrical method and transient electromagnetic detection of the first-level backwater slope survey line, the position of the second-level backwater slope survey line is divided into a normal area and an abnormal area. In the abnormal area of ​​the secondary back slope survey line, parallel electrical survey lines are arranged, and transient electromagnetic survey lines are additionally arranged on the two dam shoulders. At the same time, if there is a hardened area on the secondary back slope survey line, transient electromagnetic survey lines should also be added in this area; combined with the spatial position of the dam leakage point, and based on the results of parallel electrical and transient electromagnetic detection of the secondary back slope survey line of the dam, the position of the tertiary back slope survey line is divided into a normal area and an abnormal area; and so on, until all the survey lines of the entire dam are detected, and through the detection of survey lines at different elevations, the scope of the abnormal area is gradually narrowed, so as to finally find the direction of the leakage channel.

[0037] 2. Data processing

[0038] The analysis system groups the received parallel electrical data bodies, including the dam crest survey line data body, the first-level backwater slope survey line data body, the second-level backwater slope survey line data body, the third-level backwater slope survey line data body, etc. Each group of data bodies is processed separately, with the data of the dam crest center axis or anti-seepage section being processed first, followed by the first-level backwater slope survey line data body, then the second-level backwater slope survey line data body, and so on; the processing steps include: coordinate input, signal denoising, data unpacking, apparent resistivity calculation, inversion calculation, etc. After processing, the apparent resistivity contour lines and inversion resistivity images of the dam crest or anti-seepage section are obtained;

[0039] In particular, the parallel electrical method dam crest data volume also includes the transverse survey line data volume;

[0040] The analysis system groups the received transient electromagnetic data bodies, including the dam crest data body, the first-level backwater slope data body, the second-level backwater slope data body, the third-level backwater slope data body, etc. Each group of data bodies is processed separately, with the data of the dam crest center axis or the anti-seepage section being processed first, followed by the first-level backwater slope data body, then the second-level backwater slope data body, and so on; the processing steps include: induced voltage display, track parameter modification, interference correction, and apparent resistivity mapping. After processing, the measuring point-induced electromotive force curve and apparent resistivity image of the dam crest or anti-seepage section are obtained;

[0041] In particular, the transient electromagnetic dam crest data volume also includes the transverse survey line data volume;

[0042] The overlapped parts of the parallel electrical apparent resistivity contour lines on the dam crest and the transient electromagnetic apparent resistivity image are normalized, and the apparent resistivity contour lines and the transient electromagnetic apparent resistivity image are corrected using the normalized ratio parameters, and then spliced ​​to obtain the apparent resistivity cloud map of the dam crest;

[0043] Similarly, the above steps are repeated step by step for the data in the grouping, and then the apparent resistivity cloud map of the entire dam, such as the first-level backwater slope, the second-level backwater slope, and the third-level backwater slope, is obtained.

[0044] 3. Data interpretation

[0045] The images involved in data interpretation include the apparent resistivity contour lines and inversion resistivity images of each marshaling, the measuring point-induced electromotive force curves and apparent resistivity images of each marshaling, and the apparent resistivity cloud map of each marshaling;

[0046] The apparent resistivity cloud map of each marshaling is composed of the apparent resistivity contour lines of each marshaling and the transient electromagnetic apparent resistivity image;

[0047] The inversion resistivity and the measuring point-induced electromotive force curve of each group are used to divide the normal area and abnormal area of ​​each group;

[0048] The apparent resistivity cloud maps of each group are mapped according to a three-dimensional coordinate system to form a three-dimensional apparent resistivity map of the entire dam;

[0049] Since the dam leakage occurs below the infiltration line, the basis for judging the leakage is the low-resistance feature of the apparent resistivity, combined with the construction and operation data of the reservoir dam and the location of the water outlet at the dam foot. If the low-resistance area in the horizontal abnormal area of ​​the three-dimensional apparent resistivity map of the whole dam has obvious connectivity from the dam top to the dam foot, it indicates that there is a leakage channel in this section; if the low-resistance area in the abnormal area of ​​the low-resistance area does not have obvious connectivity from the dam top to the dam foot, it indicates that the dam has a hidden danger of abnormal seepage; if in the normal area upstream of the dam, the downstream survey line has a low-resistance anomaly and the lateral survey line also has a low-resistance anomaly, then the dam has leakage around the dam; if the dams on each survey line appear to be in the normal area, then there is no hidden danger in the dam.

[0050] Advantages of the present invention:

[0051] 1. The present invention combines the parallel electrical method with the transient electromagnetic technology, effectively solving the problem of leakage around the dam abutment and dam hardening, and realizing efficient detection of the entire dam without blind spots;

[0052] 2. The dam top and backwater slope are grouped according to the width of the dam, and divided into multiple levels of normal and abnormal areas according to the detection components, effectively reducing the leakage phenomenon and achieving the effect of accurate diagnosis;

[0053] 3. The present invention is simple to operate, convenient to use, and feasible. The on-site parallel electrical method and transient electromagnetic detection are implemented successively, thus avoiding redundant workload;

[0054] 4. In the present invention, the overlapped parts of the parallel electrical resistivity contour lines and the transient electromagnetic resistivity images are normalized, thereby improving the ability to identify leakage hazards. At the same time, the three-dimensional apparent resistivity map of the entire dam can clearly show the buried depth, scale, direction and other information of the leakage channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Schematic diagram of the survey line layout of the reservoir dam parallel electrical method and transient electromagnetic technology joint diagnosis system,

[0056] Figure 2 This is a schematic diagram of the dam crest detection system.

[0057] Figure 3 It is a schematic diagram of the interpretation process of the present invention,

[0058] Figure 4 It is the reservoir dam scene diagram (a, b) and the plane diagram (c),

[0059] Figure 5 It is a high-density electrical arrangement and isolation coefficient.

[0060] Figure 6 is the quadratic field attenuation curve for different geological bodies,

[0061] Figure 7 It is the apparent resistivity diagram of different elevation lines.

[0062] Figure 8 It is the inversion of resistivity sections and drilling soil samples.

[0063] Fig. 9 is the transient electromagnetic induction voltage curve and apparent resistivity diagram,

[0064] Fig.10 It is the change of reservoir water level and leakage.

[0065] 1-dam body; 2-dam abutment; 3-dam crest; 4-copper rod; 5-cable; 6-parallel electrical instrument; 7-wireless transmission module; 8-analysis system; 9-hardened area on dam crest; 10-coil; 11-transient electromagnetic instrument; 12-coil cable; 13-backwater slope. DETAILED DESCRIPTION

[0066] 1. If Figure 1 As shown in the figure, according to the horizontal width from the dam crest to the dam foot, the detection survey lines are grouped and named in sequence as the dam crest survey line, the first-level backwater slope survey line, the second-level backwater slope survey line, the third-level backwater slope survey line...; when the dam has leakage around the dam, a horizontal survey line perpendicular to the dam should be added at the dam shoulder. The horizontal survey line starts at the dam crest and ends at the dam foot.

[0067] 2. If Figure 2 As shown, according to the dam length, when detecting leakage of the dam body 1, a parallel electrical method measuring line is arranged on the central axis of the dam crest 3 or the anti-seepage section, a copper rod 4 is arranged at the position of the cable line 5 tap, and a funnel-shaped pit with a radius of 10 cm is dug around each copper rod with the copper rod 4 as the center, and filled with salt water, and the above work is performed on all the copper rods 4 on the dam crest 3 in turn; when all the copper rods 4 are installed, the cable line tap and the copper rod 4 are connected in turn by double-clamp wires, and the cable 5 is connected to the acquisition module of the parallel electrical method instrument 6, and the sampling parameters (data acquisition instruction, sampling time, sampling interval, power supply mode, shielding electrode) are set by the control module of the parallel electrical method instrument 6 and instructions are sent to the lower part of the acquisition module. When the acquisition module receives the instruction, the copper rods on the cable line 5 are powered on individually and sampled multiple times in turn, thereby realizing the acquisition of the natural electric field, primary field, and secondary field data of the dam. After the acquisition is completed, the control module recovers the collected data body in real time, and packages all the data as a whole and sends them remotely to the analysis system 8 through the wireless transmission module 7;

[0068] The transient electromagnetic survey line is also arranged on the central axis of the dam crest 3 or the anti-seepage section, located on the two shoulders 2 of the dam or the hardened area 9 of the dam surface. In combination with the dam height and the blind spot position of the parallel electrical resistivity contour line, the transient electromagnetic detection section is delineated, and the measurement point is marked in the detection section. The center point of the transient electromagnetic coil 10 is placed on the measurement point, and the transient electromagnetic coil 10 is connected to the transient electromagnetic instrument 11 through the coil cable 12. Then, the parameters such as the number of coil turns, the emission frequency, the emission current, the number of superpositions, and the measurement mode of the transient electromagnetic instrument are adjusted. The optimal detection parameters are obtained by observing the attenuation characteristics of the induced electromotive force, and each measurement point is sampled using transient electromagnetics. Finally, all the data are packaged as a whole and sent to the analysis system 8 through the wireless transmission module 7.

[0069] If the dam has leakage around the dam, a transverse measuring line system (i.e., transverse detection system) perpendicular to the dam should be added at the dam shoulder. The transverse detection system of the dam includes a parallel electrical device. The transverse measuring line starts at the dam top and ends at the dam foot. Specifically, the back slope is divided into multiple measuring points at equal oblique intervals from the dam top to the dam foot. Each measuring point corresponds to the buried position of the copper rod. Each copper rod electrode is connected by a cable to form a parallel electrical device with a parallel electrical instrument. Specifically, parallel electrical measuring lines are arranged on the back slope of the dam, copper rods are laid at the position of the cable tap, and funnel-shaped pits with a radius of 10 cm are dug around each copper rod with the copper rod as the center and filled with salt water. The dam is then tested in turn. The above work is performed on all copper rods; when all the copper rods are installed, the cable taps and the copper rods are connected in turn using double-clamp wires, and the cable is connected to the parallel electrical instrument. The control module of the parallel electrical instrument is used to set the sampling parameters (data collection instructions, sampling time, sampling interval, power supply method, shielding electrode) and send instructions to the acquisition module. When the acquisition module receives the instructions, it sequentially powers the copper rods on the cable and performs multiple sampling, thereby realizing the collection of the natural electric field, primary field, and secondary field data of the dam. After the collection is completed, the control module recovers the collected data body in real time, and packages all the data as a whole and sends them remotely to the analysis system through the wireless transmission module.

[0070] Combined with the spatial location of the dam leakage point, and based on the results of parallel electrical and transient electromagnetic detection of the four survey lines on the dam crest, the position of the first-level backwater slope survey line is divided into a normal area and an abnormal area. Parallel electrical survey lines are arranged in the abnormal area of ​​the first-level backwater slope survey line, and transient electromagnetic survey lines are additionally arranged on the two dam shoulders. At the same time, if there is a hardened area on the position of the first-level backwater slope survey line, transient electromagnetic survey lines should also be added in this area; Combined with the spatial location of the dam leakage point, and based on the results of parallel electrical and transient electromagnetic detection of the first-level backwater slope survey line, the position of the second-level backwater slope survey line is divided into a normal area and an abnormal area. In the abnormal area of ​​the secondary back slope survey line, parallel electrical survey lines are arranged, and transient electromagnetic survey lines are additionally arranged on the two dam shoulders. At the same time, if there is a hardened area on the secondary back slope survey line, transient electromagnetic survey lines should also be added in this area; combined with the spatial position of the dam leakage point, and based on the results of parallel electrical and transient electromagnetic detection of the secondary back slope survey line of the dam, the position of the tertiary back slope survey line is divided into a normal area and an abnormal area; and so on, until all the survey lines of the entire dam are detected, and through the detection of survey lines at different elevations, the scope of the abnormal area is gradually narrowed, so as to finally find the direction of the leakage channel.

[0071] 3. The analysis system groups the received parallel electrical data bodies, including the dam crest survey line data body, the first-level backwater slope survey line data body, the second-level backwater slope survey line data body, the third-level backwater slope survey line data body, etc. Each group of data bodies is processed separately, with the data of the dam crest center axis or anti-seepage section being processed first, followed by the first-level backwater slope survey line data body, then the second-level backwater slope survey line data body, and so on; the processing steps include: coordinate input, signal denoising, data unpacking, apparent resistivity calculation, inversion calculation, etc. After processing, the apparent resistivity contour lines and inversion resistivity images of the dam crest or anti-seepage section are obtained;

[0072] In particular, the parallel electrical method dam crest data volume also includes the transverse survey line data volume;

[0073] The analysis system groups the received transient electromagnetic data bodies, including the dam crest data body, the first-level backwater slope data body, the second-level backwater slope data body, the third-level backwater slope data body, etc. Each group of data bodies is processed separately, with the data of the dam crest center axis or the anti-seepage section being processed first, followed by the first-level backwater slope data body, then the second-level backwater slope data body, and so on; the processing steps include: induced voltage display, track parameter modification, interference correction, and apparent resistivity mapping. After processing, the measuring point-induced electromotive force curve and apparent resistivity image of the dam crest or anti-seepage section are obtained;

[0074] In particular, the transient electromagnetic dam crest data volume also includes the transverse survey line data volume;

[0075] The overlapped parts of the parallel electrical apparent resistivity contour lines on the dam crest and the transient electromagnetic apparent resistivity image are normalized, and the apparent resistivity contour lines and the transient electromagnetic apparent resistivity image are corrected using the normalized ratio parameters, and then spliced ​​to obtain the apparent resistivity cloud map of the dam crest;

[0076] Similarly, the above steps are repeated step by step for the data in the grouping, and then the apparent resistivity cloud map of the entire dam, such as the first-level backwater slope, the second-level backwater slope, and the third-level backwater slope, is obtained.

[0077] 4. Data interpretation

[0078] The images involved in data interpretation include the apparent resistivity contour lines and inversion resistivity images of each marshaling, the measuring point-induced electromotive force curves and apparent resistivity images of each marshaling, and the apparent resistivity cloud map of each marshaling;

[0079] The apparent resistivity cloud map of each marshaling is composed of the apparent resistivity contour lines of each marshaling and the transient electromagnetic apparent resistivity image;

[0080] The inversion resistivity and the measuring point-induced electromotive force curve of each group are used to divide the normal area and abnormal area of ​​each group;

[0081] The apparent resistivity cloud maps of each group are mapped according to a three-dimensional coordinate system to form a three-dimensional apparent resistivity map of the entire dam;

[0082] Since the dam leakage occurs below the infiltration line, the basis for judging the leakage is the low-resistance feature of the apparent resistivity, combined with the construction and operation data of the reservoir dam and the location of the water outlet at the dam foot. If the low-resistance area in the horizontal abnormal area of ​​the three-dimensional apparent resistivity map of the whole dam has obvious connectivity from the dam top to the dam foot, it indicates that there is a leakage channel in this section; if the low-resistance area in the abnormal area of ​​the low-resistance area does not have obvious connectivity from the dam top to the dam foot, it indicates that the dam has a hidden danger of abnormal seepage; if in the normal area upstream of the dam, the downstream survey line has a low-resistance anomaly and the lateral survey line also has a low-resistance anomaly, then the dam has leakage around the dam; if the dams on each survey line appear to be in the normal area, then there is no hidden danger in the dam.

[0083] Specific examples

[0084] Taking the leakage detection of Daijiawu Reservoir as the experimental object, the parallel electrical method was used to conduct multi-elevation hidden danger detection on the reservoir dam, and the distribution range of the dam leakage weak area was comprehensively determined based on the transient electromagnetic detection results. After directional treatment of the target area, the downstream leakage was significantly reduced, providing a reference for the optimization selection of comprehensive geophysical exploration methods for accurate diagnosis of hidden dangers in reservoir dam projects.

[0085] 1. Project overview and exploration layout

[0086] Daijiawu Reservoir is located in Jiuli Village, Tianmushan Town, Lin'an District, Hangzhou. The reservoir was built in December 1957. The dam is a clay core dam with a total storage capacity of 111,000 m 3 Its main functions are urban water supply and irrigation. The dam crest is 54m long, 3.5m wide, 157.5m high, and 14.4m high. The spillway is located on the right bank of the dam and is a positive channel type. The water discharge facility is a siphon made of a steel pipe with an inner diameter of 20cm, and the hump level section is 152.8m high.

[0087] Reservoir dams are engineering structures with life. As the service life of the project continues to increase, the aging problem of the internal structure of the dam has become more and more prominent, especially with the frequent occurrence of extreme weather, which has led to increased safety risks. For example, in August 2009, the Daijiawu Reservoir was affected by Typhoon Morakot, and the dam experienced local pipe bursts, collapses and other dangerous conditions, and serious leakage occurred on the left dam slope. Because the cause and spatial location of the dam leakage were unclear, although the dam was reinforced for anti-seepage many times afterwards, the leakage risk was not fundamentally solved, and the reservoir could only be kept running at a low water level, affecting the normal performance of the reservoir's benefits. In order to solve the stubborn problem of leakage in reservoir dams, and considering the variable distribution of hidden dangers, a method combining parallel electrical method and transient electromagnetic is proposed to find the hidden dangers, providing a targeted target area for curing the leakage.

[0088] like Figure 4 As shown in (c), three parallel electrical survey lines (PL-1, PL-2, and PL-3) are laid on the dam crest and back slope. The survey lines all run from the right bank to the left bank. The starting point of the survey line PL-1 is located at stake number K0-006m (the right dam head is the starting point, the same below). The total number of electrodes in each survey line is 64, 48, and 41, respectively, and the minimum electrode spacing is 1m. The starting point of the transient electromagnetic survey line on the dam crest is located at the spillway on the left bank (stake number K0-011m), with a total of 67 measuring points, and the spacing between adjacent measuring points is 1m.

[0089] Working methods

[0090] 2.1 Parallel electrical technology

[0091] The parallel electrical method (Liu Shengdong et al., 2019) was first proposed by Anhui University of Science and Technology and Jiangsu Donghua Testing Co., Ltd. It absorbs the idea of ​​data collection in the process of seismic exploration. While using the power supply electrode to inject a steady current into the ground to form an electric field, all the measuring electrodes are arranged to synchronously and parallelly collect geoelectric data at different locations. Finally, the current and potential data combinations can be extracted, separated, and combined as needed to obtain data bodies of different devices and pan-device information. Therefore, the basic principle of the parallel electrical method is the same as that of the high-density electrical method, but in data collection, it is no longer limited to the serial collection idea of ​​sub-devices and sub-electric fields. It has higher work efficiency and stronger anti-interference ability. It is widely used in hydrology, environment, and engineering applications (Yue Jianhua et al., 2016).

[0092] The parallel electrical method uses a point power supply method in reservoir dam applications. Through a single point power supply, multi-pole acquisition can obtain two-pole, three-pole and high-resolution geoelectric information. In particular, the joint processing of multi-device data greatly improves the resolution of hidden dangers and the characterization of dam boundaries (Ma Huan et al., 2018). Figure 5 As shown;

[0093] 2.2 Transient electromagnetic method

[0094] Transient electromagnetic technology is to supply a step pulse square wave through an ungrounded return line or grounding electrode. During the power-off interval, the induced voltage of the secondary field is observed by using a probe or receiving coil. The spatiotemporal distribution of the geological body is inferred by analyzing the attenuation characteristics of the induced electromotive force at different times at a single point and the change trend of multiple points at the same depth (Xue Guoqiang et al., 2015). Since the research object of the transient electromagnetic method is the change of the pure secondary field, the signal response to the low-resistance anomaly is more obvious, and the antenna is laid parallel to the dam top to continuously obtain the signal of the entire dam, which has the characteristics of strong directivity. When using encapsulated and modular multi-turn small coils for detection on site, it is only necessary to move the coil according to the agreed step distance to meet the requirements of efficient and lightweight inspection of the dam. The interpretation of transient electromagnetic detection data of reservoir dams mainly relies on the attenuation curves and apparent resistivity images of different secondary fields. First, the lateral anomaly is preliminarily identified according to the characteristics of different measuring point-voltage curves, and then the depth information of the hidden danger is judged according to the calculated apparent resistivity.

[0095] 2.2 Optimization of detection methods

[0096] Under the action of dynamic and static water pressure in the reservoir area, the fine particles in the earth-rock dam will continue to be lost. When the normal seepage behavior deteriorates into a local leakage channel, the dam will have hidden dangers such as degassing, looseness or voids. The leakage of the dam occurs below the infiltration line. The hidden dangers in the saturated state have obvious low resistance characteristics compared with the surrounding medium, which provides a physical premise for the implementation of the parallel electrical method. However, for the leakage area at the junction of the two dam shoulders where hidden dangers are prone to occur, it is shielded by the high resistance of the rock foundation, and it is difficult for the parallel electrical method to effectively identify the low resistance information. At the same time, it is constrained by the site conditions of the dam, and this section is the blind spot of the parallel electrical method. The basic electromagnetic induction principle of the transient electromagnetic method has a weak response to high resistance and has the inherent advantage of checking low resistance in high resistance areas. The complementary advantages of the two methods will help improve the level of diagnosis of hidden dangers in the entire dam.

[0097] 3. Analysis and verification of test results

[0098] 3.1 Parallel electrical data processing and analysis

[0099] The WBD-1 parallel electrical instrument was used as the collector at the test site. The power supply mode was single positive method, the constant current time was 0.5s, and the sampling interval was 0.05s. Practice has proved that the single-point power supply mode is more suitable for finding leakage hazards of reservoir dams. One sampling can obtain the data of two-pole, three-pole and high-resolution electrical methods. The data at different elevations were decoded, extracted, denoised, and gridded to obtain the apparent resistivity cross-section of the Wenner three-pole right device (such as Figure 7 ), the reservoir water level was 153.8m during the test, and the apparent resistivity values ​​obtained by the survey line PL-1 ranged from 90 to 230Ω·m. The low-resistance anomaly area in the 25-35m section of the survey line was distributed in a closed shape with a burial depth of about 10m, while in the 0-20m section of the survey line, the low-resistance area within a depth of 5m was distributed in a strip shape and tended to extend to the right bank. Since the electrode could not penetrate the concrete and directly couple with the dam from the starting point of the survey line to the spillway section, a blind area for electrical profile measurement was formed on the right bank. Other methods are needed to determine whether there is a low-resistance anomaly area on the right bank. The low-resistance anomaly areas in the images of the survey lines PL-2 and PL-3 are more intuitive, and the shapes reflected by the two are basically the same, which may be related to the fact that the flow direction of the leakage channel on the back slope is more stable and the distance between the ground survey line and it is closer. Comparison Figure 7 The distribution of low-resistance abnormal areas in (a, b, c) shows that there is a low-resistance closed abnormal area in the dam body, but the position of the abnormal area on the backwater slope survey line has a certain lateral movement and also shows a certain tilt shape. It is inferred that the low-resistance abnormal area downstream of the backwater slope may be caused by the convergence of the low-resistance weak zone in the middle of the dam crest and the low-resistance weak zone in the right dam section. It should be pointed out that in Figure 7 (c) There is a low-resistance trap anomaly at 30 m, and Figure 7 (b) There is no obvious abnormality, so the location of the concentrated leakage point also needs to be considered when analyzing the abnormality here.

[0100] The apparent resistivity value obtained by the high-density electrical method is a local response to the geological body. The abnormal bodies reflected by different arrangements may have differences in depth, position, burial depth and morphology (Fang Yixiaosuo et al., 2019). The three-pole device adopts the potential gradient measurement mode, and the apparent resistivity images of AMN and MNB have certain asymmetry (Hu Xiongwu et al., 2018). Inversion is the best processing method for reconstructing the measurement data body model. Due to space limitations, the results of the dam crest survey line PL-1 are used to illustrate, such as Figure 8 This is the inversion result of the Wenner Triple Poles.

[0101] This paper adopts the least square method based on the smooth model (Loke et al, 2012), which is expressed as:

[0102] (J T J+λF)Δq k =J T g-λFq k-1

[0103] Where J is the Jacobi matrix; λ is the damping factor; g is the residual between the measured apparent resistivity value and the calculated value.

[0104] Figure 8 (a) Yes Figure 7 (a) The image obtained after inversion calculation shows that the inversion cross-section image depicts the details of the dam more finely, and the low-resistance anomaly area has also shifted to the right bank; Figure 8 (b) is the inversion profile of the left device of the Wenner tripolar system. The low-resistance anomaly area in the middle of the dam is enlarged compared with Figure (a). Figure 8 As can be seen from (a) and (b), the left and right devices of the Wenner Tripole show a large difference in the morphology of the dam shoulder rock foundation, which may be related to the power supply and measurement point locations of the two devices. In order to reduce the differences between different devices, joint inversion of the data volumes of the two devices is a solution. Figure 8 The joint inversion image (c) absorbs the advantages of both devices and is more reliable in describing the morphology of the dam abutment foundation and the low-resistance anomaly of the dam.

[0105] 3.2 Transient electromagnetic data processing and analysis

[0106] The transient electromagnetic field uses a multi-turn small loop coil for signal transmission and reception. The transmitting coil has 10 turns, the receiving coil has 67 turns, the transmitting frequency is 25HZ, and the number of superpositions is 512. The data body is obtained in the supporting processing software through the steps of flying point elimination, curve smoothing, coordinate setting, and resistivity calculation. Fig. 9 . Fig. 9(a) is the voltage change curve of all measuring points. From the late signal of the dam, it can be seen that there are obvious response characteristics of secondary field signals in the 6-13m, 24-27m, 42-45m and 54-60m sections on the measuring line, indicating that there may be a weak seepage zone in the low-resistance area in the lower part of this section; the apparent resistivity in the 3m burial depth range in Figure (b) is a strip-shaped low-resistance distribution, which may be related to the blind area formed by the shutdown time of the transient electromagnetic instrument (Xi Zhenzhu, 2016). Generally, the anti-seepage body and the infiltration line of the reservoir dam are lower than the blind area, and the blind area does not affect the judgment of the dam leakage hidden danger. From the apparent resistivity profile, it can be seen that the amplitude of the low-resistance anomaly at 6-12m on the measuring line is the largest, and there may be a leakage channel; the 24-27m section of the measuring line is located at the upper part of the siphon, and it is not ruled out that iron has caused certain interference to the electromagnetic field signal.

[0107] 3.3 Analysis of comprehensive detection results

[0108] The parallel electrical method and transient electromagnetic method obtain the geoelectrical signals of the reservoir dam from the perspectives of electrostatic field and electromagnetic field respectively. Both have obvious responses to the leakage risks of the reservoir dam. The results reflected by the parallel electrical method are more reliable for the leakage risks inside the dam body, while the transient electromagnetic method has more advantages in detecting leakage at the dam shoulder.

[0109] The apparent resistivity images of the three survey lines on the dam crest and back slope of the parallel electrical method can reflect the low-resistance leakage risk area, but the low-resistance leakage risk area of ​​the dam crest survey line is relatively regular, while the shape and spatial position of the two downstream survey lines are highly consistent, and the leakage channel has a tendency to extend to the riverbed section; the low-resistance area range of the joint inversion image of the dam crest (18-40m on the survey line) is further expanded, which is consistent with the flow direction of the leakage channel of the two downstream survey lines. The results of transient electromagnetic detection are relatively clearer. The weak seepage areas are mainly distributed in three sections, but the low-resistance anomaly at 24-27m on the survey line needs to consider the influence of the siphon.

[0110] Since the dam body section showed strong low-resistance anomalies in both the parallel electrical image (pile number K0+012~K0+034m) and the transient electromagnetic image (pile number K0-005~0+002m), drilling verification was carried out to further confirm the reliability of the results. Figure 8As shown in (d) and (e), it can be seen from the fill profile that the hole depth of 0 to 11m is silty clay containing gravel, and below 11m is gray-brown soft plastic silty clay, of which 9.5 to 10m is partially mixed with broken stones. Combined with the results of in-hole photography from 0 to 8m, it can be seen that the overall fill quality of the dam is poor, with a large amount of gravel and local looseness, indicating that the dam fill exposed by the drilling may have local seepage anomalies. Drilling at pile number K0+000 found that the hole depth above 5.3m is silty clay containing gravel, and below is strongly to weakly weathered sandstone. The rock mass is extremely broken and cracks are developed, and there is a serious leakage problem in the dam foundation.

[0111] In summary, based on the detection results of the two methods, the low-resistance abnormal area on the dam crest is mainly located in the sections with pile numbers K0-005~K0+002m, K0+012~K0+034m and K0+043~K0+049m. It is speculated that this section is the weak seepage area causing dam leakage.

[0112] 3.4 Targeted treatment of leakage hazards

[0113] The purpose of detecting leakage hazards in reservoir dams is to provide target areas for anti-seepage treatment design. Due to the complex distribution of weak seepage zones in earth-rock dams, grouting anti-seepage treatment is implemented in the low-resistance abnormal areas of the dam in order to more scientifically evaluate the detection results of comprehensive geophysical exploration. Fig.10 As shown in the figure, when the grouting of Daijiawu Reservoir started (July 12, 2018), the reservoir water level was 155.12m, and the concentrated leakage at the dam foot was 3.89L / s. During the entire anti-seepage treatment process, the reservoir water level remained basically stable, and the leakage changed in series. On July 18, the leakage dropped to 2.91L / s. On July 25, after grouting at pile number K0+046, the leakage dropped to 2.64L / s. After grouting at pile numbers K0-003 and K0+000, the leakage at the downstream dam foot dropped significantly, and the leakage dropped to 0.07L / s. Afterwards, the dam was enhanced with anti-seepage treatment, and the leakage dropped to near the allowable leakage, meeting the dam anti-seepage requirements.

[0114] in conclusion

[0115] This case uses the anti-seepage treatment project of Daijiawu Reservoir as the test object, combines parallel electrical method and transient electromagnetic technology to detect the hidden dangers of dam leakage, and uses engineering drilling and in-hole camera technology to verify local suspected weak areas. Finally, directional grouting treatment is carried out based on the detection results, successfully solving the problem of dam leakage.

[0116] (1) The parallel electrical method adopts a pseudo-seismic data acquisition mode, which can obtain multiple high-density electrical device data bodies in one acquisition, with high work efficiency. The direction of the dam leakage channel can be determined by comparing the apparent resistivity images at different elevations. At the same time, the joint inversion of the Wenner three-pole left and right devices is conducive to the location of the hidden danger body and the identification of the rock foundation of the dam shoulder.

[0117] (2) Multi-turn small coil transient electromagnetic technology is easy to operate and suitable for more complex sites. By interpreting the measuring point-voltage curve and apparent resistivity profile, it can effectively identify the low-resistance abnormal parts in the longitudinal and transverse directions of the dam.

[0118] (3) The parallel electrical method has a high accuracy in judging the hidden dangers of the dam body, and the transient electromagnetic method is more suitable for detecting the hidden dangers at the joint of the dam shoulder. The two technologies are combined to form a comprehensive detection technology for the diagnosis of leakage in the entire dam.

[0119] References

[0120] 1. Fang Yixiaosuo, Meng Yongdong, Tian Bin, et al. 2019. Study on the resolution response of high-density resistivity method to different electrode arrangements [J]. Progress in Geophysics, 34(6): 2421-2428, doi: 10.6038 / pg2019CC0313.

[0121] 2. Hu Xiongwu, Li Hongwen. 2018. Application of positive and negative three-electrode resistivity joint inversion in reservoir leakage detection [J]. Water Resources and Hydropower Engineering, 49(10):173-17, doi:10.13928 / j.cnki.wrahe.2018.10.024.

[0122] 3. Liu Shengdong, Liu Jing, Qi Jun, et al. 2019. Mine parallel electrical method technology system and new progress [J]. Journal of China Coal Society, 44(8): 2336-2345, doi:10.13225 / j.cnki.jccs.KJ19.0575.

[0123] 4. Ma Huan, Guo Yue, Wu Pingping, et al. 2018 Three-dimensional joint inversion of multiple resistivity data based on MPI parallel algorithm. Chinese Journal of Geophysics, 61(12): 5052-5065, doi: 10.6038 / cjg2018M0005.

[0124] 5. Xi Zhenzhu, Long Xia, Zhou Sheng, et al. 2016. Shallow transient electromagnetic method based on equivalent reverse flux principle[J]. Chinese Journal of Geophysics, 59(9):3428-3435, doi:10.6038 / cjg20160925.

[0125] 6. Xue Guoqiang, Yan Shu, Di Qingyun, et al. 2015. Analysis of Multi-channel Transient Electromagnetic Method (MTEM) Technology[J]. Journal of Earth Sciences and Environment, 37(1):94-100.

[0126] 7. Yue Jianhua, Xue Guoqiang. 2016. Review of 36-year development of coal electrical prospecting in China. Progress in Geophysics[J]. 31(4):1716-1724, doi:10.6038 / pg20160441.

Claims

1. A reservoir dam parallel electrical method and transient electromagnetic technology joint diagnosis system, comprising a longitudinal detection system, the longitudinal detection system comprising a parallel electrical method detection device and a transient electromagnetic detection device, the parallel electrical method detection device comprising a parallel electrical method measurement line and a parallel electrical method instrument arranged on the central axis of the dam crest or the anti-seepage end surface, the parallel electrical method measurement line comprising copper rods inserted on the dam at adjacent intervals and a cable connected to the copper rods; the transient electromagnetic detection device comprises a transient electromagnetic measurement line and a transient electromagnetic instrument arranged on the central axis of the dam crest or the anti-seepage section located at two abutments of the dam and / or the dam crest hardening area, the transient electromagnetic measurement line comprising a coil arranged at a measuring point and a coil cable connected to the coil; the cable and the coil cable are respectively connected to the parallel electrical method instrument and the transient electromagnetic instrument; The parallel electrical method instrument and the transient electromagnetic instrument are used to connect with the analysis system; The diagnostic method of the diagnostic system comprises: the analysis system groups the received parallel electrical method data body and transient electromagnetic data body respectively to obtain the apparent resistivity contour line and inversion resistivity image, measuring point-induced electromotive force curve and apparent resistivity image of the dam crest or anti-seepage section; normalizes the overlapped part of the apparent resistivity contour line and the apparent resistivity image, uses the normalized ratio parameter to correct the apparent resistivity contour line and the apparent resistivity image, and splices them to obtain the apparent resistivity cloud map of the dam crest; gradually repeats the above steps for the data in the grouping, and then obtains the apparent resistivity cloud map of the whole dam from the first to the nth level backwater slope; the apparent resistivity cloud map of each grouping is mapped according to the three-dimensional coordinate system to form a three-dimensional apparent resistivity map of the whole dam.

2. The diagnostic system according to claim 1, characterized in that: After the copper rod is inserted into the dam, a funnel-shaped pit is dug with a radius of 10 cm around the copper rod and filled with salt water.

3. The diagnostic system according to claim 1, characterized in that: The coil is placed horizontally on the dam surface with the coil normal pointing vertically downward.

4. The diagnostic system according to claim 1, characterized in that: The parallel electrical method instrument comprises a wireless transmission module, a control module and an acquisition module. The acquisition module is connected to the cable. The control module is used to issue acquisition instructions and data recovery instructions to the acquisition module. The wireless transmission module is used to remotely transmit the data recovered by the control module to the analysis system. The analysis system has the dual function of processing parallel electrical method data and transient electromagnetic data. The analysis system issues instructions for recovering transient electromagnetic data to the transient electromagnetic instrument. The transient electromagnetic data is also remotely transmitted from the transient electromagnetic instrument to the analysis system through the wireless transmission module.

5. The diagnostic system according to any one of claims 1 to 4, characterized in that: When laying out survey lines on site, the dam crest survey line, the first-level backwater slope survey line, the second-level backwater slope survey line, the third-level backwater slope survey line to the n-level backwater slope survey line are laid out in sequence along the horizontal width direction from the dam crest to the dam foot, and the spacing between adjacent survey lines is 5m; the backwater slope survey line of the latter level is determined by the range of the detection anomaly area of ​​the former level.

6. The diagnostic system according to claim 5, characterized in that: Parallel electrical survey lines are laid out on the central axis of the dam crest or on the anti-seepage section, and transient electromagnetic survey lines are laid out on the two shoulders of the dam. Combined with the spatial position of the leakage point of the dam and based on the results of the parallel electrical and transient electromagnetic detection on the dam crest, the position of the first-level backwater slope survey line is divided into a normal area and an abnormal area. Parallel electrical survey lines are laid out in the abnormal area of ​​the first-level backwater slope survey line, and transient electromagnetic survey lines are additionally laid out on the two shoulders of the dam. Combined with the spatial position of the leakage point of the dam and based on the results of the parallel electrical and transient electromagnetic detection on the first-level backwater slope survey line of the dam, the second-level backwater slope survey line is divided into a normal area and an abnormal area. The position of the back slope survey line is divided into normal area and abnormal area. Parallel electrical survey lines are arranged in the abnormal area of ​​the secondary back slope survey line, and transient electromagnetic survey lines are additionally arranged on the two dam shoulders. Combined with the spatial position of the dam leakage point and based on the results of the parallel electrical and transient electromagnetic detection of the secondary back slope survey line of the dam, the position of the tertiary back slope survey line is divided into normal area and abnormal area. This process is repeated until all the survey lines of the entire dam are detected. Through the detection of survey lines at different elevations, the scope of the abnormal area is gradually narrowed, and the direction of the leakage channel is finally determined.

7. The diagnostic system according to claim 6, characterized in that: When there is a hardened area between the dam crest, the first-level backwater slope survey line position, the second-level backwater slope survey line position and the n-level backwater slope survey line position, a transient electromagnetic survey line is added in the hardened area.

8. The diagnostic system according to claim 6, characterized in that: When there is leakage around the dam, a transverse detection system perpendicular to the dam is added at the dam shoulder. The transverse measuring line system of the transverse detection system also includes the parallel electrical detection device. The transverse measuring line arrangement starts at the dam top and ends at the dam foot. The back slope is divided into multiple measuring points with equal slope distance from the dam top to the dam foot. Each measuring point corresponds to the buried position of the copper rod. Each copper rod electrode is connected by a cable and formed into a parallel electrical detection device with a parallel electrical instrument.

9. The diagnostic system according to claim 1, characterized in that: If the low-resistance area in the horizontal abnormal area of ​​the three-dimensional apparent resistivity map of the whole dam has obvious connectivity from the dam crest to the dam foot, it indicates that there is a leakage channel from the dam crest to the dam foot; if the low-resistance area in the abnormal area of ​​the low-resistance area does not have obvious connectivity from the dam crest to the dam foot, it indicates that there is a hidden danger of abnormal seepage in the dam; If the downstream survey line shows a low resistance anomaly and the lateral survey line also shows a low resistance anomaly within the normal area upstream of the dam, then the dam has leakage around the dam; if the dams on each survey line appear to be in the normal area, then there are no hidden dangers in the dam.

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