Geomembrane leakage simulation experiment method and device

Abstract

The present application belongs to the technical field of geomembrane defect leakage detection, and aims to solve the problem that the existing geomembrane leakage simulation experiment method and device cannot simulate and quantitatively study the coupling mechanism between the electrical shielding effect of the geomembrane, the reservoir water load and the defect leakage. The present application comprises the following steps: water is injected into the simulation experiment device to adjust the experimental water layer to a first target water level, and drainage is started to make the seepage field of the simulation experiment device reach a dynamic balance; in a stable state, apparent resistivity data at the first target water level are collected based on the ground high-density resistivity method and the water high-density resistivity method; the experimental variables are changed, and corresponding apparent resistivity data are collected after a new stable state is reached; the collected apparent resistivity data under different experimental conditions are compared and analyzed by inversion, and the response mechanism of the electrical shielding effect of the geomembrane, the influence of the reservoir water load or the defect leakage is explored.

Description

Technical Field

[0001] This invention belongs to the technical field of geomembrane defect leakage detection, and particularly relates to a geomembrane leakage simulation experiment method and device. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Geomembranes, with their superior impermeability, have become a key functional material in seepage prevention systems for plain reservoirs, artificial lakes, and other engineering projects. However, due to construction defects, material aging effects, and the influence of complex stress fields, geomembranes are prone to damage such as puncture holes, tears, and weld peeling, which can lead to leakage problems.

[0004] In geomembrane seepage prevention projects, defects and leakage are key issues affecting structural safety. Leakage not only leads to the ineffective dissipation of water resources, but may also induce seepage deformation and damage to the dam body, seriously endangering the structural safety of the project.

[0005] Existing technologies for simulating geomembrane leakage have been developed through various physical model experiments. On one hand, by using servo booster pumps and pressure water chambers to simulate the dynamic changes in overlying water head, real-time monitoring of leakage flow under variable water head conditions has been achieved, allowing for quantitative analysis of the relationship between water pressure fluctuations and leakage volume. On the other hand, by changing the moisture content of the underlying layer, setting different defect morphologies, and simulating water level rise and fall processes, the expansion law of the infiltration zone after defect leakage, as well as the migration of underlying layer particles and scour pit characteristics, have been observed, and an empirical model relating leakage volume to water head and defect size has been established. However, existing methods all focus on the response of hydraulic or soil mechanical parameters. As an insulating material, the leakage fluid at the defects of the geomembrane forms a conductive path. This electrical shielding effect has potential value for defect location and leakage monitoring, but existing experimental devices cannot simulate and quantitatively study the coupling mechanism between this effect and reservoir water load and defect leakage. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a method and apparatus for simulating geomembrane leakage, enabling quantitative research on the electrical shielding effect of geomembrane, the influence of reservoir water load, and the leakage response mechanism of defects.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a geomembrane leakage simulation experimental device, comprising: a test tank, a drainage device, a water injection device, and an electrode measurement system; The test tank contains, from bottom to top, an underlying soil layer, a geomembrane layer, and a soil covering layer on top of the membrane; the geomembrane layer is used to fix geomembrane samples with different integrity states. The drainage device is located at the bottom of the test tank and can be connected to the water injection device. The water injection device is used to add water above the soil covering layer on the membrane to form an experimental water layer with adjustable height. The electrode measurement system is used for electrical exploration. By changing the integrity state of the geomembrane sample or the water level of the experimental water layer, it collects the apparent resistivity data under the corresponding steady-state working conditions to explore the electrical shielding effect of the geomembrane, the influence of reservoir water load, or the defect leakage response mechanism.

[0008] Preferably, the electrode measurement system includes a ground-based high-density electrode and an underwater high-density electrode; the ground-based high-density electrode is disposed on the soil layer covering the membrane, and the underwater high-density electrode floats on the surface of the experimental water layer or is suspended in the experimental water layer.

[0009] Preferably, the geomembrane layer includes a bearing layer and a geomembrane sample laid on the surface of the bearing layer. The geomembrane sample has one or more defects of different sizes and shapes, such as pre-made holes, cracks, welds, or thinned areas, to simulate geomembranes with different integrity.

[0010] Preferably, the drainage device includes a multi-channel peristaltic pump, a circulating water injection pipe, and a manifold outlet; the manifold outlet is connected to the water injection device through the circulating water injection pipe, and the circulating water injection pipe is equipped with a multi-channel peristaltic pump; the water injection device includes a water source container and a water source injection pipe, and the water flow from the seepage port of the test tank returns to the water source container through the manifold outlet, the multi-channel peristaltic pump, and the circulating water injection pipe, and then returns to the test tank through the water source injection pipe to achieve water reuse.

[0011] Preferably, the soil layer on top of the membrane and the underlying stratum can be filled with one or more of sandy loam, silt, and clay, depending on the actual situation of the reservoir, to simulate the upper and lower strata of the geomembrane laid at the bottom of the reservoir.

[0012] Secondly, the present invention provides a method for simulating geomembrane leakage, employing the aforementioned geomembrane leakage simulation experimental apparatus, comprising the following method: Water is injected into the simulation experimental device to adjust the experimental water layer to the first target water level, and drainage is started to make the seepage field of the simulation experimental device reach dynamic equilibrium. Under steady conditions, apparent resistivity data at the first target water level are collected based on the ground high-density resistivity method and the water surface high-density resistivity method. After changing the experimental variables and reaching a new steady state, the corresponding apparent resistivity data were collected. The apparent resistivity data collected under different experimental conditions were inverted and compared to explore the electrical shielding effect of geomembrane, the influence of reservoir water load, or the response mechanism of defect leakage.

[0013] Preferably, the apparent resistivity data collected under different experimental conditions are inverted and compared to explore the electrical shielding effect of the geomembrane, the influence of reservoir water load, or the leakage response mechanism of defects. Specifically: Based on the apparent resistivity of the underlying stratum measured after the geomembrane is laid and the background resistivity under the condition without the geomembrane, the correction coefficient for the apparent resistivity data of the underlying stratum is determined. The correction coefficients of the apparent resistivity data of the strata under the membrane were analyzed, and the variation law of the geomembrane damage location, damage type and water level was analyzed to quantify the shielding strength and dynamic change characteristics of the geomembrane to the detection current. By comparing the differences in the correction coefficient values ​​of the apparent resistivity data of the underlying strata of geomembranes in different integrity states, the degree of weakening of the local shielding effect caused by geomembrane defects is quantitatively assessed.

[0014] Preferably, the method further includes: establishing a simulation model for numerical simulation verification, specifically: establishing Darcy's law and current field to describe the mechanical and electrical physical fields, in order to simulate the coupling behavior of water migration and current conduction during leakage; solving Darcy's equation at each time step to obtain the water content and pressure distribution; then updating the conductivity of each unit according to the water content, and then solving the current field equation to obtain the potential and current density distribution; and quantitatively comparing the apparent resistivity profile, low-resistivity anomaly morphology and amplitude change obtained from the numerical simulation with the measured data of the simulation experimental device to verify the effectiveness.

[0015] Preferably, it also includes: forming a defect diagnosis and identification chart based on the quantitative relationship between the apparent resistivity anomaly morphology, anomaly amplitude and defect size corresponding to different defect types of geomembrane.

[0016] Preferably, the relationship between the correction factor for the apparent resistivity data of the formation beneath the membrane and the water level. Specifically:

[0017] in, These are correction factors for the initial apparent resistivity data of the formation beneath the membrane; This is the compaction sensitivity coefficient; It is the shielding amplification factor; The compression factor is 1. It is the density of the water layer used in the experiment; Standard atmospheric pressure is the increased water level; S is the area of ​​the test tank viewed from above; g is the acceleration due to gravity.

[0018] The above one or more technical solutions have the following beneficial effects: In this invention, based on the ground high-density resistivity method and the water surface high-density resistivity method, apparent resistivity data under the first target water level are collected. By changing the experimental variables, a series of apparent resistivity data under steady-state conditions can be obtained in the same experimental device, which is convenient for carrying out multi-condition comparative analysis, and thus realizes quantitative research on the electrical shielding effect of geomembrane, the influence of reservoir water load and the defect leakage response mechanism.

[0019] In this invention, by setting up an experimental tank, drainage device, water injection device, and electrode measurement system, the load exerted on the geomembrane seepage prevention system by the continuous change of reservoir water level during reservoir impoundment can be simulated with high fidelity. Furthermore, geomembrane samples with different prefabricated defects can be replaced, and the invention is not limited by various field water conditions. Simultaneously, it achieves high-precision electrical resistivity parameter acquisition synchronized with water level changes, thus providing a standardized experimental platform for quantitative research on the electrical shielding effect of geomembranes, the influence of reservoir water load, and the leakage response mechanism of defects. This not only verifies and optimizes leakage detection methods applicable to reservoir operation, but also significantly improves the efficiency, repeatability, and scientific rigor of related research.

[0020] In this invention, the apparent resistivity profile, low-resistivity anomaly morphology and amplitude changes obtained by numerical simulation are quantitatively compared with the measured data of the experimental device to verify the effectiveness of the model. A quantitative criterion for diagnosing geomembrane damage is established, providing a solid theoretical basis and experimental foundation for signal interpretation in actual reservoir leakage detection.

[0021] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a flowchart of the experimental method in an embodiment of the present invention; Figure 2 This is a schematic diagram of the main structure of the device in an embodiment of the present invention; Figure 3 This is a schematic diagram of the external protective structure of the test tank in an embodiment of the present invention; Figure 4 This is a schematic diagram of the experimental layer of the device in an embodiment of the present invention; wherein, (a) is a top view and (b) is a front view; In the diagram, 1. Electrical resistivity meter, 2. Multi-channel peristaltic pump, 3. Water source container, 4. Fixed pulley accessories, 5. Movable pulley accessories, 6. Moving rod, 7. Acrylic plate, 8. Measuring cable, 9. Water level observation pipe, 10. Circulating water injection pipe, 11. Water source injection pipe, 12. Cable height adjustment line, 13. Test tank, 14. Temperature and humidity sensor, 15. Corner seepage outlet, 16. Central seepage outlet, 17. Confluence outlet, 18. Confluence water pipe, 19. Load-bearing wheel, 20. Water level sensor, 21. Filter element, 22. Buffer pad, 23. Rigid frame, 24. Lateral deformation control rod, 25. Jack, 26. Underlying stratum, 27. Geomembrane layer, 28. Soil layer on top of membrane, 29. Experimental water layer, 30. Stainless steel metal fasteners. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0026] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0027] Example 1 Therefore, this embodiment proposes a geomembrane leakage simulation experimental device, including: a test tank, a drainage device, a water injection device, and an electrode measurement system; The test tank is arranged from bottom to top as follows: the underlying soil layer, the geomembrane layer, and the soil covering layer on the membrane; the geomembrane layer is used to fix geomembrane samples with different integrity states. The drainage device is located at the bottom of the test tank and can be connected to the water injection device. The water injection device is used to add water above the soil layer on the membrane to form an experimental water layer with adjustable height. The electrode measurement system is used for electrical exploration. By changing the integrity state of the geomembrane sample or the water level of the experimental water layer, it collects the apparent resistivity data under the corresponding steady-state working conditions to explore the electrical shielding effect of the geomembrane, the influence of reservoir water load, or the defect leakage response mechanism.

[0028] The experimental setup proposed in this embodiment can simulate with high fidelity the load exerted on the geomembrane seepage prevention system by the continuous change of reservoir water level during reservoir impoundment. It can also replace geomembrane samples with different prefabricated defects and simultaneously achieve high-precision electrical resistivity parameter acquisition synchronized with water level changes. This provides a standardized experimental platform for quantitative research on the electrical shielding effect of geomembrane, the influence of reservoir water load, and the leakage response mechanism of defects. It can not only verify and optimize leakage detection methods applicable to reservoir operation, but also significantly improve the efficiency, repeatability, and scientific rigor of related research.

[0029] like Figure 1 As shown, the geomembrane leakage simulation experimental device proposed in this embodiment includes a test tank 13. The test tank 13 is equipped with a rigid frame 23 with six load-bearing wheels 19 around its perimeter and bottom. A buffer pad layer 22 and a jack 25 are set at the contact position. Three transverse deformation control rods 24 are connected to the top and can be removed by nuts to control the transverse and longitudinal deformation of the device. The test tank 13 can be set with experimental layer simulation objects. For example, to simulate the damage of the geomembrane in a reservoir basin, the underlying soil layer, the geomembrane layer, and the soil covering layer on the membrane are laid flat from bottom to top. Water is then injected through a water injection device to form an experimental water layer to simulate the vertical infiltration process of geomembranes with different integrity during the reservoir operation period or water storage period. The drainage device at the bottom of the test tank 13 is used to collect leaked water. As needed, the central seepage port 16 and corner seepage ports 15 at the bottom of the test tank 13 are opened. Due to the slope of the drainage device, water naturally flows into the confluence outlet 17, which is equipped with a confluence pipe 18. Temperature and humidity sensors 14, water level sensors 20, and three sets of water level observation pipes 9 are buried at the bottom of the underlying stratum. Water is injected at the top of the test tank 13 to simulate the experimental water layer. A pulley system is installed at the top to suspend cables and adjust the measurement position. The test tank 13 and the drainage device below are detachable structures. Stainless steel metal fasteners 30 are used to tightly fix the test tank 13 and the drainage device in the rigid frame 23. The nuts can be removed and reinstalled, facilitating the cleaning of oxide accumulation caused by years of use in the drainage device.

[0030] like Figure 3 As shown, the upper part of the test tank 13 has an opening to expose the inner cavity of the test tank 13; the bottom wall of the test tank 13 has corner seepage outlets 15 and central seepage outlets 16. In this embodiment, there are 4 corner seepage outlets 15. The surface of these 5 seepage outlets is covered with a layer of stainless steel mesh and a layer of water-permeable fabric. Water seeping from the damaged geomembrane can flow naturally into the drainage device below through gravity potential energy. The seepage outlets have baffle-type switches, and the seepage outlets can be selected to be opened according to the experimental needs.

[0031] In this embodiment, in order to ensure a tight connection between the test tank 13 and the drainage device below, the test tank 13 and the drainage device below are detachable structures, such as... Figure 3As shown, after placing the test tank 13 on the drainage device, stainless steel metal fasteners 30 are used to secure the test tank and drainage device in the rigid frame 23 with one nut at the top, middle and bottom. The nuts can be removed and reinstalled, making it convenient to clean the oxide accumulation caused by the long-term use of the drainage device.

[0032] The test tank 13 and the drainage device are made of plexiglass. To prevent the drain outlet from loosening or leaking due to prolonged use, a stainless steel anti-seepage layer can be used to seal the entire drainage device at the confluence outlet 17. The edges of the anti-seepage layer can be treated with sealant or glass glue to make the edges of the stainless steel anti-seepage layer more firmly bonded to the countertop and to prevent mold or leakage after long-term use.

[0033] The drainage system consists of a manifold outlet 17, a manifold pipe 18, a filter element 21, a multi-channel peristaltic pump 2, and a circulating water injection pipe 10. The manifold outlet 17, with its basin-shaped design, allows seepage water to naturally converge and flow into the manifold pipe 18. The multi-channel peristaltic pump 2 is equipped with a filter element 21 to filter out large particles of soil and rock sediment. Water is then pumped back into the water source container 3 from the circulating water injection pipe 10 via the multi-channel peristaltic pump 2. The drainage system can discharge any leaked water back into the water source container 3 to replenish the experimental water leaking out of the container.

[0034] The water injection device consists of a water source container 3 and a water source injection pipe 11. One end of the water source injection pipe 11 is connected to the water source container 3, and the other end is attached to the inner wall of the test tank to meet the water requirements of the experiment. The water source injection pipe 11 has a backflow preventer structure inside, allowing water to be injected but not pumped out, ensuring that the seepage system consisting of the corner seepage port 15, the central seepage port 16, and the confluence outlet 17 serves as the only leakage channel. Water is redistributed in the water source container 3 to simulate reservoir water, and then injected back into the test tank 13 through the water source injection pipe 11 as needed, achieving water level control and stable water volume. The water flow from the seepage port returns to the water source container 3 through the confluence outlet 17, the confluence pipe 18, the multi-channel peristaltic pump 2, and the circulating injection pipe 10, and then returns to the experimental device through the water source injection pipe 11, thus achieving water reuse.

[0035] The circulating water injection pipe 10 has a check valve structure, which can only inject water but not discharge water. The leakage water in the manifold 18 is extracted by the multi-channel peristaltic pump 2 and directly injected into the circulating water injection pipe 10 to maintain the stability of the leakage and the balance of the water volume.

[0036] In this embodiment, the test tank 13 can be made of plexiglass for easy observation of the water level. In other embodiments, the material of the test tank can be set by the user.

[0037] Optionally, the test tank 13 is set to 2m×1m×1m.

[0038] In this embodiment, the front view of the setup within the experimental layer is as follows: Figure 4 As shown in (b), the experimental layers, from bottom to top, are: underlying soil layer 26, geomembrane layer 27, overlying soil layer 28, and experimental water layer 29. A top view of the experimental layers is shown below. Figure 4 As shown in Figure (a), the figure illustrates different measuring line positions of the measuring cable 8, with the measuring line spacing typically set to 0.1m. All four of these settings are adjusted according to the actual engineering conditions of the reservoir to be simulated.

[0039] The soil layer 28 on the membrane and the underlying soil layer 26 are the upper and lower soil layers of the geomembrane laid on the actual bottom of the reservoir. They can be filled with sandy loam, silt, clay, etc., or filled with materials with similar gradation according to the actual situation of the reservoir. Their thickness, compaction degree and permeability parameters can be adjusted according to the experimental design.

[0040] Different experimental water levels were used to simulate the load of reservoir water on the geomembrane under different water level conditions. For example, pressures of 9.81 kPa and 49.05 kPa were used to simulate the load of water levels of 1m and 5m on the stratum.

[0041] The material of the geomembrane sample depends on the experimental reservoir or the experimental objective. For example, HDPE, or high-density polyethylene geomembrane, is often used for ordinary reservoirs; or geomembranes with conductive properties may be used for special scenarios.

[0042] The geomembrane sample includes a complete membrane sheet and a prefabricated membrane sheet with defects of different sizes and shapes. The defect types include at least one of holes, cracks, weld defects and local thinning areas to simulate different leakage test conditions. The geomembrane layer 27 is disposed between the geomembrane and the side wall of the test tank.

[0043] The geomembrane layer 27 is used as follows: First, the geomembrane layer 27 is fixed inside the test tank 13 to form a flat support base. Then, the geomembrane layer is laid on the upper surface of the underlying stratum 26. The edge of the membrane material is pressed and sealed to the test tank 13 using the flange edge. Its function is to provide continuous and uniform mechanical support for the geomembrane to disperse the lateral pressure of the sand and soil, prevent the membrane material from being punctured and torn, eliminate the deformation incoordination between the rigid box wall and the flexible membrane material to avoid boundary shear failure, provide a flat force application base for the mechanical pressing mechanism to ensure uniform transmission of sealing pressure, and enable the geomembrane to be quickly replaced in a detachable manner without damaging the box structure, thus achieving a balance between seepage prevention reliability and experimental operation convenience.

[0044] The reservoir water resistivity is referenced to the actual reservoir water resistivity range. Silty loam soil taken from the actual reservoir site is used to simulate the soil layer 28 on the membrane and the underlying stratum 26. Before the simulation, on-site water samples can be taken from the actual reservoir, and the on-site water temperature and conductivity can be measured respectively for the reservoir water comparison setting of the test tank.

[0045] In this embodiment, the test tank 13 is equipped with a temperature and humidity sensor 14, which is inserted into the soil layer 28 on the membrane to realize real-time monitoring of the temperature and humidity of the experimental environment. The temperature and humidity sensor 14 is connected to the host computer to transmit temperature and humidity information. Water level observation tubes 9 are respectively set at the three corners of the test tank 13. Water level sensors 20 are installed in the water level observation tubes 9. The data collected by the water level sensors 20 is uploaded to the host computer. The monitored data is displayed in real time according to the temperature and humidity sensors 14 and the water level sensors 20. If adjustment is required, the multi-channel peristaltic pump 2 can be controlled to circulate water.

[0046] Three vertical water level observation pipes 9 and three water level sensors 20 are fixedly installed in the inner cavity or outer wall of the test tank 13 to observe the water level at different locations, so as to observe the changes in water level at various locations in the bottom strata after leakage occurs. Temperature and humidity sensors 14 are also arranged in three groups at different locations and equal depths to monitor the temperature, humidity, and water content of the strata at different locations. The number and location of the water level observation pipes 9, water level sensors 20, and temperature and humidity sensors 14 can be set by those skilled in the art.

[0047] In this embodiment, after the experimental layer is filled, the experimental tank 13 may deform. To suppress deformation, a lateral deformation control rod 24 can be set, such as... Figure 3 As shown. The lateral deformation control rod 24 is a long screw, which is fixed to the rigid frame 23 with a nut and can be disassembled and reinstalled. The test tank 13 is embedded in the rigid frame 23, and a buffer pad 22 can be set at the contact part between the two. The rigid frame 23 controls the deformation of the test tank 13 after it is filled with water and sand. The test tank 13 and the rigid frame 23 are fixed on six load-bearing wheels 19, which can move and fix the entire system. If a heavy object is added to the test tank 13, the load-bearing wheels 19 alone cannot prevent its vertical deformation. In this case, multiple jacks 25 can be added under the entire device shell to prevent its deformation. The jacks can be replaced with other materials such as buffer wooden blocks.

[0048] Except for the rigid frame 23, all the outer shells, mainly the test tank 13, are made of high-strength non-metallic plexiglass material. Although not shown in the schematic diagram, it has a certain thickness (1~2cm). A buffer layer 22 of rubber or other material is added between the rigid frame 23 and the test tank 13, which solves the problems of deformation, damage, and instability caused by close contact, and does not interfere with the test results. If the overall weight of the test tank is too large, several buffer layers can be added to the bottom of the device. The material of the buffer layers can be rubber or wood.

[0049] In other embodiments, where the rigid frame 23 and the buffer pad 22 can effectively constrain the lateral deformation of the test tank 13, the use of the lateral deformation control rod 24 can be omitted, and can be selected by those skilled in the art.

[0050] In this embodiment, the electrode measurement system includes a measuring cable 8 parallel to the length of the test tank 13, an electrical resistivity meter 1, an acrylic plate 7, and a host computer connected to the electrical resistivity meter. Several high-density electrodes are arranged on the measuring cable. The function of the acrylic plate 7 is to constrain the electrodes in the lateral direction. The number of electrodes and the electrode spacing are determined according to the measurement situation. In this embodiment, there are 32 electrodes with an electrode spacing of 5 cm.

[0051] The electrode measurement system has two switchable measurement modes. The first is a high-density electrical resistivity tomography (ERT) cable measurement, in which the measuring cable 8 floats on the water surface or is suspended underwater (using a weight such as a lead weight to control buoyancy), allowing the high-density electrode to operate on the water surface. The second is a high-density electrical resistivity tomography (ERT) measurement on land, in which the measuring cable 8 is inserted into the soil layer 28 on the membrane, and the electrode area is submerged by the experimental water layer 29. Both measurement methods use a pulley system to fix the acrylic plate 7 in a suitable position.

[0052] The pulley system includes fixed pulley accessories 4, movable pulley accessories 5, a moving rod 6, and a cable height adjustment line 12. The pulley system can adjust the position and height of the measuring cable 8 through lateral and longitudinal operations. The moving rod 6 is a horizontal rod with fixed pulley accessories 4 installed on both sides and connected to the outer wall of the test tank 13, and movable pulley accessories 5 connected to the inner side. The main function of the moving rod 6 is to suspend the acrylic plate 7 that binds the electrode cable and control its position inside the test tank. By changing the position of the measuring cable 8, the measurement of the geomembrane gap in the water / land high-density electrical resistivity tomography is completed.

[0053] Except for the electrical resistivity meter 1, measuring cable 8, rigid frame 23 and lateral deformation control rod 24, all other components in the test tank 13 are made of high-strength non-metallic materials (such as plexiglass) that meet the requirements of rigidity and strength, thus avoiding the influence of metallic materials on the geophysical exploration results and ensuring the accuracy of the geophysical exploration results.

[0054] This embodiment adopts an integrated, movable, and detachable structure, which has the advantages of good controllability, simple use, rapid measurement, wide adaptability, and no interference with the experimental data of reservoir leakage detection. It can quickly verify various measurement methods and improve work efficiency and effectiveness.

[0055] While meeting the requirements for strength, stiffness, and deformation, it is not only easy to observe and use, but also ensures the stability of the system. It is not easily deformed or damaged during use, thus improving the effectiveness and efficiency of the test tank simulation experiment. It guarantees the exploration results and can be repeatedly simulated for geomembranes with various types of reservoirs and different defects. It is not limited by various field water conditions and effectively solves the problem of reservoir leakage detection being difficult or inconvenient due to field conditions.

[0056] The device proposed in this embodiment can accurately simulate the continuous water storage process of a plain reservoir from low to high water levels. It can flexibly and systematically replace geomembrane samples with different prefabricated defects, and can synchronously and automatically collect multi-physical field data (such as water level, water pressure, resistivity, and flow field). Conducting systematic experiments with this device is an indispensable foundation for revealing the dynamic law of the electrical response of geomembrane defects during the water storage period, separating the interference of reservoir water load and geomembrane electrical shielding effect, and thus establishing a new method for accurate detection and interpretation suitable for the operational period.

[0057] Example 2 The purpose of this embodiment is to provide a method for simulating geomembrane leakage, using a geomembrane leakage simulation experimental device as described in Embodiment 1, and including the following methods: Water is injected into the simulation experimental device to adjust the experimental water layer to the first target water level, and drainage is started to make the seepage field of the simulation experimental device reach dynamic equilibrium. Under steady conditions, apparent resistivity data at the first target water level are collected based on the ground high-density resistivity method and the water surface high-density resistivity method. After changing the experimental variables and reaching a new steady state, the corresponding apparent resistivity data were collected. The apparent resistivity data collected under different experimental conditions were inverted and compared to explore the electrical shielding effect of geomembrane, the influence of reservoir water load, or the response mechanism of defect leakage.

[0058] The following is combined Figure 1 This embodiment provides a detailed description of a geomembrane leakage simulation experiment method, which specifically includes the following steps: S1: Prepare samples based on the actual strata and geomembrane conditions of the reservoir, construct simulated layers and install defective geomembranes, and prepare similar experimental water.

[0059] Based on the bottom strata conditions of the target plain reservoir, the specifications of the impermeable geomembrane, and the types of leakage defects, prepare experimental materials.

[0060] Using silty loam soil samples taken from the reservoir site or soil samples prepared according to similar gradations, the soil was filled in layers from bottom to top in the test trench: First, a drainage device with a slope at the bottom was installed, and the underlying soil layer was laid on top and compacted to the predetermined density; then, a pre-prepared geomembrane sample with specific defects (such as a complete geomembrane or a circular hole with a diameter of X cm or a crack with a length of Y cm) was installed on the geomembrane layer; finally, a soil cover layer was filled on top of the geomembrane and compacted.

[0061] Based on the test results of on-site water samples from the target reservoir, experimental water with similar temperature and conductivity to the reservoir water was prepared.

[0062] S2: Inject water to the target water level, maintain dynamic equilibrium and stability, and simulate the seepage field under reservoir water load.

[0063] Water is slowly injected using a water injection device. Exploration equipment (such as an electrical resistivity meter) is used to detect the geological conditions in the test tank. The leakage amount, leakage rate, and leakage location of the experimental water in the test tank are determined according to the detection method to be verified. The height of the experimental water layer is precisely adjusted to the first target water level H1 through the water level adjustment system, for example, to simulate the dead water level.

[0064] Specifically, water is first injected using a water injection device. Once the target water level is reached, the drainage device is activated to return the water that has seeped through the strata to the drainage device to the experimental water layer, so that the seepage field in the simulated experimental device reaches a dynamic equilibrium state, at which point the water level is stable.

[0065] S3: Deploy ground and water electrode arrays, collect apparent resistivity data, and calculate correction coefficients to analyze the membrane shielding effect.

[0066] According to the experimental design, the ground high-density resistivity method and the water high-density resistivity method were used respectively, and a four-pole symmetric device (i.e., the four-pole method) was used for data acquisition.

[0067] The four-electrode method refers to the simultaneous use of four electrodes in a single measurement: two power supply electrodes (A and B) and two measuring electrodes (M and N). In the standard forward measurement mode, a stable direct current (DC) of 10 mA (unit: I) is supplied to the ground (or the bottom of the water body) through the power supply electrodes A and B, establishing a stable artificial electric field in the underground medium. At this point, the potential difference between electrodes M and N is measured using a high-precision potentiometer. U. According to the distribution law of steady current field, the apparent resistivity ρ of the medium is related to the supply current I and the measured potential difference. There is a definite functional relationship between U and the device coefficient K, which is determined by the relative positions of the four electrodes A, B, M, and N. This is achieved by recording I and U at each measuring point. The U-value, combined with the known device coefficient K, allows us to calculate the apparent resistivity at the measuring point, which reflects the electrical distribution characteristics of the underground medium.

[0068] To eliminate the impact of factors such as spontaneous potential drift and polarization potential instability on data accuracy during the measurement process, and to improve the signal-to-noise ratio, this experiment will adopt an interchangeable observation (reciprocal observation) working method. The specific operation is as follows: Forward measurement (powered by electrodes A and B, measured by electrodes M and N): As described above, firstly, a 10 mA current is supplied using electrodes A and B as power supply electrodes, and the potential difference between electrodes M and N is observed simultaneously.

[0069] In reverse measurement (electrodes M and N supply power, electrodes A and B perform measurement), after completing the forward measurement, the same electrode system is used to interchange the power supply and measurement functions. That is, the original measuring electrodes M and N now act as power supply electrodes, supplying the same DC current (10 mA) to the medium; simultaneously, the original power supply electrodes A and B now act as measuring electrodes to observe the potential difference. Two potential difference values ​​are obtained from the forward and reverse measurements respectively. and Because interference from factors such as natural potential and electrode polarization potential may occur during the measurement process, simply taking one of these values ​​for calculation would introduce errors. Therefore, the arithmetic mean of the potential differences obtained from the two measurements is used as the effective potential difference value for the final apparent resistivity calculation. ,Right now:

[0070] The purpose of this is to eliminate natural potential drift and electrode polarization effects in the measurement system, thereby improving the signal-to-noise ratio and measurement accuracy. Subsequently, the effective potential difference value... Substitute into the apparent resistivity calculation formula:

[0071] Where K is the device coefficient; I is the power supply current, which is the same value for both forward and reverse measurements, such as 10 mA, which can be used to obtain the apparent resistivity value at the measurement point. The apparent resistivity is expressed in Ω·m.

[0072] The ground high-density resistivity method uses ground high-density electrodes embedded in the membrane and covered with soil, which has high accuracy; the water high-density resistivity method uses acrylic plates 7 to constrain the electrodes and arranges the electrodes according to the measuring cables 8 and floats on the water surface.

[0073] Start the electrical resistivity instrument and conduct electrical exploration through the electrode measurement system. Completely collect the apparent resistivity data under the steady-state condition, which is recorded as resistivity dataset D1(H1). Collect data from three experiments for comparison.

[0074] Optionally, the position of the measuring line can be changed, and the electrical parameter characteristics of the defect area can be collected at different measurement positions to analyze the impact of the measuring line offset on the measurement results of the damage anomaly.

[0075] The measuring device coefficient K is calculated based on the relative positions of the four poles, and the apparent resistivity of the geomembrane seepage prevention system is calculated in combination with the measured potential difference data. The apparent resistivity data of the intact state and the defect state are integrated to establish a quantitative mapping relationship between "defect characteristics and apparent resistivity". The current shielding effect of the geomembrane on the resistivity of the underlying stratum is analyzed. Based on the resistivity of the underlying stratum measured before and after the geomembrane is laid ( , (This sentence appears to be incomplete and requires more context.) By using the correction coefficient of the apparent resistivity data of the underlying stratum, the masking effect of geomembrane current shielding on the resistivity of the underlying stratum is revealed.

[0076] The formula for calculating the measuring device coefficient K is as follows:

[0077] In the formula, AM is the distance between the power supply electrode A and the measuring electrode M; BM is the distance between the power supply electrode B and the measuring electrode M; AN is the distance between the power supply electrode A and the measuring electrode N; and BN is the distance between the power supply electrode B and the measuring electrode N.

[0078] S4: Change experimental variables such as water level, membrane state, soil layer, and water quality, conduct control experiments, and repeat measurements to ensure reliability.

[0079] Reservoirs under different water levels, geological conditions, and water quality conditions, as well as geomembranes of different materials, damage shapes, damage locations, and damage sizes, were studied. After conducting electrical resistivity measurements, comparative analysis was performed to verify the effectiveness of the detection method and summarize the experience of the detection method.

[0080] Afterwards, tests and verifications can be conducted near an actual reservoir. The specific procedures are as follows: Condition A (Water Level Change): The experimental water layer height is adjusted to a new second target water level value H2 (such as design storage level, maximum storage level, beneficial storage capacity, flood level) using the water level regulation system. Different water levels impose different loads on the geomembrane. After reaching steady state again, step S3 is repeated to collect the resistivity dataset D2(H2). Condition B (Changes in the integrity of the geomembrane): Keeping the first target water level H1 unchanged, the geomembrane layer is extracted and replaced with a geomembrane layer with a different defect state (e.g., no membrane, complete membrane, incomplete membrane). The geomembrane is then reinserted. After the overburden structure stabilizes, step S3 is repeated, and resistivity dataset D3(H1) is collected.

[0081] The incomplete membranes are classified into the following types, and the control experiment can be formulated with reference to Table 1: Table 1. Comparison of test parameter settings for the incomplete geomembrane control group.

[0082] Condition C (Change in soil thickness): Change the thickness of the overlying soil layer or the underlying stratum, and remeasure. Condition D (Changes in Soil Properties): The compaction and permeability of the overlying soil layer or the underlying stratum were varied to observe the effect of different permeability on the seepage process. In addition, to investigate the influence of stratum heterogeneity, coarse sand and clay block anomalies were added to the overlying soil layer. Other measurement procedures were the same as in the above experiments.

[0083] Condition E (Water Quality Change): Simultaneously change the water level and the defect status of the geomembrane, and repeat the above process.

[0084] Condition F (change in seepage type): There are two types. The first is vertical seepage, which seeps down through the reservoir basin. The second is lateral seepage, which seeps down through the dikes around the reservoir.

[0085] The measurement of each of the above states was repeated more than three times to ensure the repeatability and reliability of the data and results.

[0086] S5: Invert electrical data, analyze the mapping relationship between water level, defects and resistivity, and evaluate the dynamic shielding effect of the membrane.

[0087] The series of electrical feature datasets D1, D2, ..., D obtained in steps S1~S4 are used to... n Inversion and comparative analysis are performed. Specifically, this includes: First, the raw apparent resistivity data is preprocessed, including removing bad pixels and smoothing the data; topographic correction may also be performed if necessary. Then, specialized high-density resistivity inversion software is used to perform two-dimensional or three-dimensional inversion imaging on the preprocessed data. During the inversion process, the least squares algorithm is employed, combined with water resistivity, water layer thickness, and electrode placement as prior information to suppress inversion ambiguity and obtain the true resistivity and resistivity distribution cross-sections. For time-lapse monitoring data, time-lapse inversion technology is used to directly invert the resistivity changes between different times (different water levels), thereby highlighting the subtle electrical anomalies caused by water level changes.

[0088] The inversion results are exported, and the minimum resistivity value and anomalous amplitude of the low-resistivity anomaly zone are observed; the geometric parameters of the anomaly body, such as horizontal extension length, vertical burial depth, and anomalous area or volume; and the anomaly gradient characteristics, such as the rate of change of the horizontal resistivity gradient. Image processing techniques are used to identify and track the boundary and center position changes of the anomaly zone under different water levels or defect conditions on the true resistivity distribution cross-sectional map. Regression analysis is employed to quantify the functional relationship between water level changes and changes in electrical parameters, with water level height H as the independent variable and electrical response parameters E (such as the minimum resistivity of the low-resistivity anomaly zone) as the independent variable. ) is the dependent variable.

[0089] First, construct the regression model:

[0090]

[0091] In the formula, is the electrical response parameter; H is the water level height; a, b are the regression coefficients obtained by least squares fitting; The fitting function form is selected based on the characteristics of electrical parameters. Electrical parameters can be conductivity (unit: S / m), real conductivity (unit: S / m), imaginary conductivity (unit: S / m), apparent resistivity (unit: Ω·m), resistivity (unit: Ω·m), phase (mrad), resistivity change rate (resistivity change per unit time per unit length / resistivity before change, dimensionless), abnormal amplitude (unit: Ω·m), etc. The unit of conductivity, S / m, represents Siemens per meter, and Siemens is abbreviated as S. To fit the coefficients of water level changes with electrical parameters, specific relationships are formulated based on image fitting software (including but not limited to Photo Math).

[0092] The calculation method for abnormal amplitudes is as follows: Data inversion software is used to invert the collected data to obtain a resistivity profile. Then, based on mathematical statistics methods, a threshold is set, and the average value of the apparent resistivity of the background in the survey area is calculated. Standard deviation Usually lower than - The area was designated as a low-resistivity anomaly zone, which will be higher than + The area was designated as a high-resistivity anomaly zone, and the horizontal extension length (in meters) and anomaly area (in square meters) of the anomaly zone were extracted accordingly. 2 ), and calculate its abnormal amplitude.

[0093] Define the sensitivity coefficient S, which represents the magnitude of change in electrical parameters caused by a unit change in water level.

[0094] Electrical response parameters Plot a graph to observe the functional relationship between water level changes and changes in electrical parameters, and summarize the patterns.

[0095] To separate and evaluate the dynamic electrical shielding effect of the geomembrane itself, a normalization method is introduced: a correction coefficient for the apparent resistivity data of the underlying stratum is defined. :

[0096]

[0097]

[0098] in, The apparent resistivity of the underlying stratum was measured after the geomembrane was laid. The background resistivity under membrane-free conditions; The three-dimensional resistivity distribution function of the underlying strata obtained by inversion when the water level is H before laying the geomembrane; The three-dimensional resistivity distribution function of the underlying strata is obtained by inversion when the water level is H after the geomembrane is laid. The integration region is the effective detection range of the underlying strata. The plane covers the entire electrode survey line, and the vertical direction extends from the lower interface of the geomembrane to the bottom of the model or the effective detection depth. If the detection is a two-dimensional plane, the triple integral is changed to the form of a double integral, and the double integral is only performed in the x and z directions. Other parameters in the formula remain unchanged.

[0099] When the water level changes, considering the increase in soil compaction, the resistivity will increase to a certain extent:

[0100] In the formula, Indicates the initial water level; This is the correction factor for the apparent resistivity data of the formation beneath the membrane before the water level increases, i.e., the initial correction factor for the apparent resistivity data of the formation beneath the membrane. This indicates an increase in water level.

[0101] The variation of the correction coefficient η for the apparent resistivity data of the underlying stratum under the geomembrane was analyzed with the location and type of geomembrane damage, and the water level H, to quantify the shielding strength of the geomembrane for the probe current and its dynamic variation characteristics. By comparing the differences in the correction coefficient η values ​​of the apparent resistivity data of the underlying stratum under geomembranes with different integrity states, the degree of weakening of the local shielding effect caused by defects can be quantitatively assessed. Through the above systematic data processing and analysis, the following conclusions can be drawn: First, the dynamic shielding effect of reservoir water load: As the water level rises, the background resistivity of the underlying strata changes regularly (e.g., as the water level increases, the compaction of the soil covering the membrane increases, leading to an increase in resistivity). A quantitative correction model between water level and background resistivity is established to eliminate the interference of water level changes on defect identification.

[0102] Second, establish the mapping relationship between defect characteristics and electrical response: clarify the quantitative relationship between the resistivity anomaly morphology (such as equiaxed and striped), anomaly amplitude and defect size (such as opening area and crack length) corresponding to different defect types (such as round holes, cracks and weld defects), and form a defect diagnosis and identification chart.

[0103] Third, quantify the dynamic electrical shielding effect of geomembranes and its spatiotemporal evolution characteristics: clarify the shielding strength of geomembranes on the underlying strata detection signals, i.e. the range of the correction coefficient η value of the apparent resistivity data of the underlying strata, and reveal the non-uniform variation characteristics of the shielding effect during water level changes, providing a theoretical basis for signal correction in actual reservoir detection.

[0104] Fourth, establish effective criteria for the selection of detection modes: compare the detection effects of ground and water surface electrode deployment methods at different water levels, clarify their respective optimal applicable ranges, and provide experimental support for the selection of detection schemes in practical engineering.

[0105] S6: Forward modeling and coupled modeling to simulate the seepage-electric field process, verify experimental results, and establish quantitative criteria for damage diagnosis.

[0106] First, multiple parameters, such as the strata, are modeled using simulation software. The parameters are strictly consistent with those inside the test tank. The simulation model consists of a soil layer on top of the membrane, a geomembrane layer, an underlying stratum, and an experimental water layer. The geomembrane layer can be pre-set with defects of different sizes and shapes according to the simulation requirements, such as circular holes and linear cracks.

[0107] Tetrahedral elements were used to adaptively mesh the simulation model. Local mesh refinement was applied near geomembrane defects and in seepage channels to accurately capture high gradient changes in the seepage and electric fields. Based on experimental data from the test tank, corresponding material parameters, including permeability coefficient, resistivity, water storage coefficient, and porosity, were assigned to each layer.

[0108] To simulate the coupling behavior of moisture migration and current conduction during leakage, a seepage field and a current field are constructed to describe the mechanical and electrical physical fields, respectively.

[0109] The seepage field is described by Darcy's law in saturated-unsaturated porous media, and the governing equation is:

[0110]

[0111] In the formula, It is the independent variable of time, representing the duration of the seepage process, indicating the moment when the timer starts from the initial state (usually t=0), in seconds; It is porosity, which is dimensionless; This refers to fluid density, measured in kg / m³. 3 ; It is the Darcy velocity vector, with units of m / s; Source / sink, unit: kg / (m³) 3 ·s); k is the inherent permeability, which depends only on the pore structure of the porous medium, such as pore size, shape, and connectivity. It reflects the ability of the porous medium to allow fluid to pass through, and the unit is m. 2 ; It is the dynamic viscosity of a fluid, measured in Pa·s. It is the pore water pressure, in Pa.

[0112] In the unsaturated region, soil-water characteristic curves (Van Genuchten model) are introduced to describe matrix suction. The relationship between negative pore water pressure and volumetric water content (i.e., negative pore water pressure) and volumetric water content. :

[0113] In the formula, It is the volumetric water content, in m³ / m³. This is the residual moisture content, in m³ / m³. This is the saturated water content, in m³ / m³. It is the matrix suction, in Pa, a positive value; This is a parameter related to the intake air value, with the unit being 1 / Pa; It is the porosity distribution index, which is dimensionless. >1; c is the curve shape parameter, usually taken as c=1-1 / .

[0114] The physical meaning of this curve is that in the unsaturated region, the water content decreases as the matrix suction increases. This curve allows us to correlate the pressure term p in Darcy's law with the volumetric water content θ.

[0115] In the unsaturated region, the permeability according to Darcy's law It is no longer a constant, therefore it is corrected to:

[0116] Or written as:

[0117] In the formula, It is the relative permeability, dimensionless, and a function of water content θ; It is the fluid dynamic viscosity; k is the intrinsic permeability; It is the fluid density; It is unsaturated hydraulic conductivity, in m / s; It refers to pressure head, measured in meters (m). z is the height coordinate of a point in the test tank (such as a point in the soil layer on the membrane) relative to the bottom of the test tank. It is used to calculate the effect of gravity on the seepage process and is also called the position head. The unit is m. g is the acceleration due to gravity. Pore ​​water pressure; This is the gradient operator.

[0118] relative penetration Calculated using the model:

[0119] In the formula, It is the effective saturation, dimensionless. , It is the volumetric moisture content. It is the residual moisture content. It is the saturated moisture content; It is the porosity distribution index, which is dimensionless. >1; c is the curve shape parameter, usually taken as c=1-1 / .

[0120] Connecting the above relationships, we can obtain the complete governing equations for the unsaturated seepage field:

[0121] In the formula, This is due to matrix suction; Determined by soil-water characteristic curves; relative permeability Determined by the Van Genuchten model; k is the intrinsic permeability, in meters. 2 It is related to the soil structure and does not change with saturation. The viscosity is the dynamic viscosity of a fluid, measured in Pa·s. Fluid density, unit: kg / m³ 3 t represents the duration of the seepage process, in seconds.

[0122] In COMSOL, this equation is solved using the Richards equations module, and its standard form is:

[0123] The current field is approximated by a steady current field, and the governing equation is:

[0124]

[0125] In the formula, J is the current density vector, with units of A / m. 2 ; This is a current source term, unit: A / m 3 ; is the electrical conductivity, which is the reciprocal of the resistivity, with units of S / m; E is the electric field intensity vector, with units of V / m; V is the electric potential. is the gradient operator; z is the height coordinate of a point within the test tank (such as a point in the soil layer on the membrane) relative to the bottom of the test tank; It is the pressure head; It is unsaturated hydraulic conductivity.

[0126] In the permeation-electric field coupling, conductivity Set to volumetric water content Related functions :

[0127] In the formula, It is the conductivity under saturation, with units of S / m; It is the effective saturation, dimensionless; This is the saturation index, typically ranging from 1.5 to 2.5. This relationship reflects the dynamic impact of moisture migration on the conductivity of the medium during leakage.

[0128] The seepage field and the electric field are bidirectionally coupled through the dynamic change of conductivity with water content. Within each time step, the Darcy equation is first solved for the simulation model to obtain the water content and pressure distribution; then the conductivity of each element is updated according to the water content, and the current field equation is solved to obtain the potential and current density distribution.

[0129] A fully coupled solver combined with a transient time-stepping method is used to simultaneously solve the seepage field and the current field. The script uses loop control to achieve parameter updates, simulation model reconstruction, automated solving, and batch export of results for multiple operating conditions (different defect types, sizes, and water level conditions).

[0130] Through the above modeling and simulation process, the spatiotemporal evolution characteristics of resistivity anomalies with time and water level changes during leakage under different defect conditions can theoretically be obtained. Finally, the apparent resistivity profile, low-resistivity anomaly morphology, and amplitude changes obtained from numerical simulation are quantitatively compared with the experimentally measured data of the test tank to verify the effectiveness of the model.

[0131] Based on this, the characteristics of the "electricity-water" synergistic response are extracted, including: resistivity anomaly morphology (equiaxed, banded); the rate of change of anomaly amplitude over time; and the time lag effect of leakage front migration and electrical anomaly evolution. Finally, a quantitative criterion for geomembrane damage diagnosis integrating the above characteristics is established, providing a theoretical basis for the interpretation of electrical resistivity signals in actual reservoir leakage detection.

[0132] This embodiment uses Reservoir D in a plain as an example for detailed explanation: S1: Prepare samples based on the actual strata and geomembrane conditions of the reservoir, construct simulated layers and install defective geomembranes, and prepare similar experimental water.

[0133] According to the engineering geological survey report and design data of Reservoir D, the strata at the bottom of the reservoir are mainly silty loam, with an average dry density of 1.65 g / cm³ and a permeability coefficient of approximately 1.2 × 10⁻⁶. -5 cm / s. The reservoir uses a composite geomembrane (two layers of fabric and one layer of membrane, membrane thickness 0.5 mm) for full reservoir basin seepage prevention. Based on relevant studies in this region, this experiment aims to simulate the most common leakage defects in the geomembrane beneath the reservoir basin, including the intact state of the geomembrane, a 2 cm diameter circular hole defect (simulating air bursting defect), and a 5 cm long linear crack defect (simulating weld tearing defect).

[0134] Based on the above geological conditions, the experimental material was taken from silty loam near Reservoir D, and was air-dried, crushed and sieved through a 5 mm sieve before use. The test tank was filled in layers from bottom to top: First, a 5 cm thick gravel layer was laid at the bottom of the test tank as a filter layer; then, the underlying soil layer was filled on the gravel layer, compacted in two layers, each 10 cm thick, for a final thickness of 20 cm, with a compaction degree controlled at 0.95 and a dry density of 1.65 g / cm³; next, the pre-prepared geomembrane sample (intact membrane / porous membrane / cracked membrane) was laid flat on the underlying soil layer, and the geomembrane layer was fixed to the inside of the test tank to form a flat support base. Then, the geomembrane was laid on the surface of the bearing layer, and the edges of the membrane were pressed tightly and sealed to the bearing layer and the flange edge of the test tank; finally, a soil cover layer was filled on top of the geomembrane, also using silty loam from Reservoir D, compacted in two layers to a total thickness of 30 cm and a dry density of 1.60 g / cm³.

[0135] The test was conducted using a multi-parameter analyzer and outdoor water samples taken from Reservoir D for a week. Based on the water quality test report of Reservoir D, the test water was prepared using tap water and industrial salt to ensure that its conductivity was consistent with the measured value of Reservoir D water (approximately 220~280 µS / cm). The water temperature was adjusted to be close to the annual average water temperature of the reservoir (approximately 15℃). The test water was then stored in a water source container.

[0136] S2: Inject water to the target water level, maintain dynamic equilibrium and stability, and simulate the seepage field under reservoir water load.

[0137] Start the water injection switch and slowly inject water into the experimental water layer. Once the water level exceeds the geomembrane layer, simultaneously turn on the electrical resistivity tomography (EDT) instrument for preliminary monitoring. Continue injecting water to precisely control the water level of the experimental water layer at the first target water level H1, which corresponds to the dead water level elevation of Reservoir D of approximately 0.2 m (simulated water depth 2.0 m).

[0138] After the water level stabilizes, the drainage device is turned on, and the water that seeps through the defects in the geomembrane and flows into the drainage device through the seepage port at the bottom of the test tank. The seepage water is then reinjected into the test water layer through a multi-channel peristaltic pump and circulating water injection pipe.

[0139] By adjusting the reinjection flow rate and the leakage flow rate to achieve a dynamic balance, the seepage field and water level in the experimental system are ensured to reach a stable state.

[0140] S3: Deploy ground and water electrode arrays, collect apparent resistivity data, and calculate correction coefficients to analyze the membrane shielding effect.

[0141] According to the experimental design, two electrode placement methods were used simultaneously for data acquisition: Ground high-density resistivity method: A measuring line consisting of 30 stainless steel electrodes is laid out along the long axis of the test tank on the surface of the soil covering the membrane, with an electrode spacing of 5 cm. A Wenner apparatus (four-electrode method) is used for data acquisition. Electrodes A and B are supplied with a stable 10 mA DC current, and the potential difference ΔU between electrodes M and N is measured. Simultaneously, to eliminate the influence of electrode polarization, measurements are performed by reversing the electrodes (i.e., MN is powered, AB is measured).

[0142] High-density resistivity method in water: Thirty specially designed electrodes, spaced 5 cm apart, are fixed to an acrylic plate of equal width to the water surface of the test tank, forming equidistant measuring cables. The acrylic plate is placed on the water surface, ensuring the electrodes are submerged approximately 2 cm below the water level. Data acquisition is performed using a Winner device.

[0143] The electrical resistivity meter was activated to probe the geomembrane defect model using both ground and floating survey lines, and the apparent resistivity data under the stable condition of the first target water level H1 was fully collected, denoted as resistivity dataset D1(H1). To ensure data reliability, the experimental data were collected three times under this condition.

[0144] After completing the center survey line measurement, the survey line was moved parallel by 5 cm and 10 cm. Electrical parameters of the defect area were collected at different locations to analyze the impact of survey line offset on defect anomaly identification.

[0145] Calculate the apparent resistivity of the seepage prevention system using the formula for calculating the coefficient K of the four-electrode method:

[0146]

[0147] In the formula, AM is the distance between the power supply electrode A and the measuring electrode M, in meters; BM is the distance between the power supply electrode B and the measuring electrode M, in meters; AN is the distance between the power supply electrode A and the measuring electrode N, in meters; BN is the distance between the power supply electrode B and the measuring electrode N, in meters; I is the current collected, in mA; and ΔU is the potential difference, in V.

[0148] By integrating apparent resistivity data from intact and defective geomembranes, a preliminary mapping relationship between "defect characteristics" and "apparent resistivity" is established. Simultaneously, the current shielding effect of the geomembrane is quantitatively analyzed, and the correction coefficient η for the apparent resistivity data of the underlying strata under this condition is calculated.

[0149] In the formula, ρ 前 This is the apparent resistivity of the underlying stratum measured before laying the geomembrane, in units of Ω·m and ρ. 后 It is the apparent resistivity of the underlying stratum measured after the geomembrane is laid, in Ω·m.

[0150] S4: Change experimental variables such as water level, membrane state, soil layer, and water quality, conduct control experiments, and repeat measurements to ensure reliability.

[0151] To fully verify the effectiveness of the detection method, this embodiment designed and executed multiple sets of control conditions: Operating Condition A (Water Level Change): Using the water level adjustment system, the experimental water layer height is sequentially adjusted to the design storage level (0.4 m, corresponding to the second target water level H2) and the highest storage level (0.55 m, corresponding to the third target water level H3) of the simulated reservoir D. After each adjustment, once the system seepage field reaches dynamic equilibrium again, the measurement procedure in step S3 is repeated to collect datasets D2(H2) and D3(H3) respectively.

[0152] Condition B (Changes in Geomembrane Integrity): While maintaining the first target water level H1, the experiment was paused, the overlying soil layer was drained, and the original intact membrane support layer module was removed and replaced with prefabricated support layers containing 2 cm diameter circular holes, 5 cm long cracks, and no geomembrane (control). After refilling the overlying soil layer and allowing the structure to stabilize, step S3 was repeated, and datasets D4 (H1, circular hole), D5 (H1, crack), and D6 (H1, no membrane) were collected. This process strictly followed the parameter settings for the control group in Table 1. For example, complex defect states such as weld cracking and irregular holes were also simulated in subsequent experiments.

[0153] Condition C (Soil layer thickness variation): Keeping other conditions unchanged, change the thickness of the soil layer covering the membrane (set to 20cm and 40cm respectively), and repeat the above measurements.

[0154] Condition D (Change in soil properties): The compaction degree of the soil layer under the membrane was changed, resulting in dry densities of 1.55 g / cm³ and 1.75 g / cm³, to simulate different permeability. Furthermore, to investigate the influence of soil heterogeneity, a 10 cm × 10 cm clay block and a 5 cm × 5 cm coarse sand lens were artificially buried in the overlying soil layer to observe their impact on the electrical resistivity tomography (EDT) results.

[0155] Condition E (Water Quality Change): Change the conductivity of the experimental water (prepare solutions of 100 µS / cm, 400 µS / cm and 800 µS / cm respectively), and measure it in conjunction with different defect states in Condition B.

[0156] Condition F (Change in seepage type): Simulate side seepage by closing the bottom drainage system and opening the drain outlets on the side wall of the test tank.

[0157] As a further implementation method, the measurements under each of the above operating conditions are repeated more than three times to ensure the repeatability and reliability of the data and results.

[0158] S5: Invert electrical data, analyze the mapping relationship between water level, defects and resistivity, and evaluate the dynamic shielding effect of the membrane.

[0159] The series of electrical characteristic datasets D1~D2 obtained in steps S1~S4 n Preprocessing, inversion imaging, and comparative analysis are performed. Specifically, this includes: We analyzed the resistivity gradient of the low-resistivity anomaly zone in the apparent resistivity cross-section diagram under the same geomembrane condition (e.g., an intact membrane) as the water level H increased. We found that as the water level rises, the load from the reservoir water enhances the compaction effect of the underlying soil, leading to a regular, slight increase in its apparent resistivity. This quantifies the dynamic shielding effect of the reservoir water load.

[0160] The electrical anomaly characteristics corresponding to different defect types (circular holes and cracks) and sizes were compared at the same water level. The results showed that circular holes exhibited an approximately equiaxed low-resistivity anomaly region, while cracks exhibited a strip-shaped low-resistivity anomaly. The anomaly amplitude was positively correlated with the opening area of ​​the defect, thus establishing a preliminary mapping relationship between defect characteristics and electrical response.

[0161] Through specific experiments, the measurement results of the geomembrane without membrane, with intact membrane, and with defective membrane were compared. The resistivity profiles were integrated to successfully separate and evaluate the electrical shielding effect of the geomembrane itself. Correction factor for apparent resistivity data of the formation beneath the membrane under complete membrane operating conditions. <1 reflects the electrical shielding effect of the intact geomembrane, such as 0.3~0.4; Under defective membrane conditions, due to the formation of leakage channels, a localized low-resistivity anomaly will appear directly below the defect, and the shielding effect will be locally weakened, i.e., the correction factor for the apparent resistivity data of the formation beneath the membrane. <1, but this value is improved compared to the intact membrane condition, such as 0.7~0.9; As the water level rises, the reservoir water load compacts the soil layer beneath the membrane, leading to an increase in soil resistivity. Simultaneously, the high-resistivity shielding effect of the geomembrane is further enhanced with rising water levels. These two effects combined result in a greater relative increase in the apparent resistivity of the underlying stratum under membrane-layment conditions compared to those without membrane. Therefore, the correction coefficient η(H) for the apparent resistivity of the underlying stratum increases with rising water levels.

[0162] Due to soil compression, density increases, porosity decreases, conductive pathways diminish, and resistivity rises. Considering the compaction effect, the correction factor for the apparent resistivity data of the formation beneath the membrane is inferred to be related to the water level as follows:

[0163] In the formula, These are correction factors for the initial apparent resistivity data of the formation beneath the membrane; This is the compaction sensitivity coefficient, which is dimensionless and usually ranges from 2 to 8. Smaller values ​​are used for cohesive soils and larger values ​​are used for sandy soils. This is the compressibility coefficient, dimensionless, and depends on the soil type; for cohesive soils, it is typically taken as 0.05 to 0.15. It is the shielding amplification factor, dimensionless, representing the degree to which the geomembrane amplifies the compaction effect caused by reservoir water load, under the condition of an intact geomembrane. A value of 1.5 to 3.0 reflects strong shielding and amplification, while under defective geomembrane conditions, A value close to 1 indicates that the shielding effect is weakened by local leakage channels; It is the density of the water layer used in the experiment; Standard atmospheric pressure S is the increase in water level height, in meters (m); S is the area of ​​the test tank viewed from above, in square meters (m²). 2 g is the acceleration due to gravity.

[0164] When considering water level changes, both are affected by the compaction effect, but under the membrane laying condition, the current is shielded by the geomembrane, and the impact of the compaction effect on the resistivity of the underlying stratum is amplified.

[0165] S6: Forward modeling and coupled modeling to simulate the seepage-electric field process, verify experimental results, and establish quantitative criteria for damage diagnosis.

[0166] First, using Res2Dmod forward modeling software, parameters consistent with those used in the experimental trench were input: a two-dimensional model 2 m long and 1 m deep was established, including a water layer (0.4 m thick, resistivity 12.5 Ω·m), a soil layer overlying the membrane (0.30 m thick, resistivity 50 Ω·m), a geomembrane layer (assumed to have infinite resistance), and an underlying soil layer (0.20 m thick, resistivity 45 Ω·m). A low-resistivity channel (1 Ω·m) 2 cm wide was set at the center of the geomembrane layer to simulate damage. Measurement lines were laid out on the water surface and the underwater soil surface, respectively, and forward modeling calculations were performed to simulate high-density electrical resistivity methods on water and land, collecting theoretical apparent resistivity data. Subsequently, using inversion software, the Robust-constrained inversion method was employed, incorporating water resistivity and water layer thickness as prior information, to invert the forward modeling data. The inversion results were compared with the inversion results of the measured data in the experimental tank. The two results were highly consistent in terms of anomaly morphology, location and amplitude, which verified the accuracy of the physical experiment.

[0167] Secondly, a three-dimensional seepage-electric field coupling model perfectly matching the experimental trench was established using simulation software. Through parametric modeling and batch simulation, the variation patterns of electric field distribution and current density under different defect sizes and water levels were systematically analyzed. The numerical simulation results not only reproduced the resistivity anomaly characteristics observed in the experimental trench but also revealed the influence mechanism of the movement of the "wetting front" on the spatiotemporal evolution of the electric field during seepage. Finally, by cross-validating the numerical simulation results with the experimental trench results, the "electric-water" synergistic response characteristics integrating resistivity anomaly morphology, amplitude changes, and time effects were extracted. A preliminary quantitative criterion for geomembrane damage diagnosis was established, providing a solid theoretical basis and experimental foundation for signal interpretation in actual reservoir seepage detection.

[0168] In further embodiments, the following is also provided: An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor. When executed by the processor, the computer instructions perform the method described in Embodiment 2. For brevity, further details are omitted here.

[0169] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0170] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0171] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in Embodiment 2.

[0172] The method in Example 2 can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0173] Those skilled in the art will recognize that the units and algorithm steps described in conjunction with the embodiments herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0174] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for simulating geomembrane leakage, employing a geomembrane leakage simulation experimental device, characterized in that, include: The apparatus includes: a test tank, a drainage device, a water injection device, and an electrode measurement system. Within the test tank, from bottom to top, are an underlying soil layer, a geomembrane layer, and a soil cover layer. The geomembrane layer is used to fix geomembrane samples with different integrity states. The drainage device is located at the bottom of the test tank and can be connected to the water injection device, which adds water above the soil cover layer to form an adjustable-height experimental water layer. The electrode measurement system is used for electrical resistivity exploration, collecting apparent resistivity data under corresponding steady-state conditions by changing the integrity state of the geomembrane samples or the water level of the experimental water layer, to investigate the geomembrane's electrical shielding effect, the influence of reservoir water load, or the defect leakage response mechanism. The electrode measurement system includes a ground-based high-density electrode and a surface-based high-density electrode. The ground-based high-density electrode is placed on the soil cover layer, while the surface-based high-density electrode floats on the surface of the experimental water layer or is suspended in the experimental water layer. The method includes: injecting water into the simulation experimental device to adjust the experimental water layer to the first target water level, and starting drainage to make the seepage field of the simulation experimental device reach dynamic equilibrium. Under steady conditions, apparent resistivity data at the first target water level are collected based on the ground high-density resistivity method and the water surface high-density resistivity method. After changing the experimental variables and reaching a new steady state, the corresponding apparent resistivity data were collected. The apparent resistivity data collected under different experimental conditions were inverted and compared to explore the electrical shielding effect of geomembrane, the influence of reservoir water load, or the response mechanism of defect leakage. Among them, based on the apparent resistivity of the underlying stratum measured after the geomembrane is laid and the background resistivity under the condition without the geomembrane, the correction coefficient for the apparent resistivity data of the underlying stratum is determined, and the relationship between the correction coefficient for the apparent resistivity data of the underlying stratum and the water level is determined. Specifically: in, These are correction factors for the initial apparent resistivity data of the formation beneath the membrane; This is the compaction sensitivity coefficient; It is the shielding amplification factor; The compression factor is 1. It is the density of the water layer used in the experiment; Standard atmospheric pressure is the increased water level; S is the area of ​​the test tank viewed from above; g is the acceleration due to gravity.

2. The method for simulating geomembrane leakage according to claim 1, characterized in that, The geomembrane layer includes a bearing layer and a geomembrane sample laid on the surface of the bearing layer. The geomembrane sample has one or more defects of different sizes and shapes, such as pre-made holes, cracks, welds, or thinned areas, to simulate geomembranes with different integrity.

3. The method for simulating geomembrane leakage according to claim 1, characterized in that, The drainage device includes a multi-channel peristaltic pump, a circulating water injection pipe, and a manifold outlet. The manifold outlet is connected to the water injection device via the circulating water injection pipe, which is equipped with the multi-channel peristaltic pump. The water injection device includes a water source container and a water source injection pipe. Water flowing from the seepage port of the test tank returns to the water source container through the manifold outlet, the multi-channel peristaltic pump, and the circulating water injection pipe, and then returns to the test tank through the water source injection pipe, thereby achieving water reuse.

4. The method for simulating geomembrane leakage according to claim 1, characterized in that, The soil layer on top of the membrane and the underlying strata can be simulated by filling one or more of sandy loam, silt, and clay, depending on the actual situation of the reservoir, to simulate the upper and lower strata of the geomembrane laid at the bottom of the reservoir.

5. The geomembrane leakage simulation test method as described in claim 1, characterized in that, Inversion and comparative analysis were performed on the apparent resistivity data collected under different experimental conditions to explore the electrical shielding effect of geomembranes, the influence of reservoir water load, or the leakage response mechanism of defects. Specifically: Based on the apparent resistivity of the underlying stratum measured after the geomembrane is laid and the background resistivity under the condition without the geomembrane, the correction coefficient for the apparent resistivity data of the underlying stratum is determined. The correction coefficients of the apparent resistivity data of the strata under the membrane were analyzed, and the variation law of the geomembrane damage location, damage type and water level was analyzed to quantify the shielding strength and dynamic change characteristics of the geomembrane to the detection current. By comparing the differences in the correction coefficient values ​​of the apparent resistivity data of the underlying strata of geomembranes in different integrity states, the degree of weakening of the local shielding effect caused by geomembrane defects is quantitatively assessed.

6. The geomembrane leakage simulation test method as described in claim 1, characterized in that, It also includes: establishing a simulation model for numerical simulation verification, specifically: establishing Darcy's law and current field to describe the mechanical and electrical physical fields, in order to simulate the coupling behavior of water migration and current conduction during leakage; solving Darcy's equation at each time step to obtain the water content and pressure distribution; then updating the conductivity of each unit according to the water content, and then solving the current field equation to obtain the potential and current density distribution; and quantitatively comparing the apparent resistivity profile, low-resistivity anomaly morphology and amplitude changes obtained from the numerical simulation with the measured data of the simulation experimental device to verify the effectiveness.

7. The geomembrane leakage simulation test method as described in claim 1, characterized in that, Also includes: Based on the quantitative relationship between the apparent resistivity anomaly morphology, anomaly amplitude and defect size corresponding to different defect types of geomembranes, a defect diagnosis and identification chart is formed.

Images