Method for testing dynamic permeability coefficient of defective geomembrane impermeable layer

Abstract

The present application discloses a kind of defect geomembrane impermeable layer dynamic permeability coefficient test methods, to evaluate the permeability and stability of geomembrane with defects (such as holes) under different water head.The method includes determining soil sample particle size distribution, preparing defect geomembrane impermeable layer and carrying out water head saturation;Through multi-level permeation gradient parameter, permeation test is carried out step by step, and the amount of permeation, osmotic pressure and seepage phenomenon are recorded, and the permeability coefficient under each level of permeation gradient is calculated.Finally, the permeability coefficient data is fitted by statistical method, the change trend is analyzed, and the influence of defect on the performance of impermeable layer is evaluated.The present application establishes axisymmetric permeation model, assumes that water flow meets laminar flow condition and satisfies Darcy's law, and provides effective experimental basis for permeability analysis of geomembrane defect.The present application can be widely applied to performance evaluation and quality detection of geomembrane impermeable engineering.

Description

Technical Field

[0001] This invention relates to the field of water resources, and specifically to a method for testing the dynamic permeability coefficient of a defective geomembrane impermeable layer. Background Technology

[0002] In reservoir engineering, geomembranes, as an effective seepage control material, are significantly influenced by the geological conditions of the reservoir area. The seepage control performance of geomembranes and the assessment of their defects and leakage have become crucial aspects of reservoir design. Under ideal conditions, the permeability coefficient of geomembranes typically falls between [value missing]. m / s to The speed is between m / s. However, because the thickness of geomembrane material is only 0.3-2.0 mm, which is much smaller than the thickness of conventional strata, geomembranes are very prone to defects and pores during production, transportation, construction and operation, which can lead to reservoir leakage problems.

[0003] Defects in geomembrane seepage control layers can be broadly categorized into microscopic and macroscopic defects. Microscopic defects primarily originate from microscopic particulate impurities or inhomogeneities in the material, leading to uniform variations in geomembrane permeability. Macroscopic defects include damage caused by physical forces (such as tearing, puncture, bursting, and hydrostatic failure) and construction machinery, as well as joint damage caused by poor welding or adhesive bonding. These defects exhibit localized characteristics on a macroscopic level. According to the "Technical Specification for Geomembrane Seepage Control in Hydropower Engineering" (NB / T 35027-2014), the equivalent pore diameter of pores is generally 1mm-3mm, reaching up to 5mm in special locations. These localized macroscopic defects severely impact the seepage control performance of the engineering structure.

[0004] Taking the upper reservoir of a pumped storage power station as an example, the reservoir adopts a full-area geomembrane seepage prevention system. Monitoring data shows that the seepage at the bottom of the reservoir is 173-346. Localized damage leading to seepage not only causes seepage deformation of the sandy soil beneath the geomembrane, but can also cause localized subsidence of the embankment, exacerbating seepage and material erosion, and even posing a risk of dam collapse and breach. Furthermore, when the reservoir water level drops, defects in the geomembrane on the dam surface can create transient seepage fields, affecting the local anti-sliding stability of the dam. Therefore, accurately evaluating the impact of the degree of geomembrane defects on the amount of seepage has become a core issue in the design of geomembrane-lined reservoirs.

[0005] The factors influencing the leakage of geomembrane reservoirs are complex and varied. Leakage depends not only on the number and shape of defects but also on factors such as the permeability, stress level, and hydraulic head of the underlying contact layer. Experimental results show that the roughness and smoothness of the base layer significantly affect the leakage of geomembrane defects. Although there are existing studies on estimating geomembrane defect leakage both domestically and internationally, these studies are not yet suitable for direct application to actual reservoir projects because they have not fully considered the impact of variations in the permeability coefficient of the underlying support layer on defect leakage. Therefore, accurately assessing the leakage of geomembrane defects has become an urgent problem to be solved in current geomembrane defect testing research. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for testing the dynamic permeability coefficient of defective geomembrane impermeable layers.

[0007] This invention is achieved through the following technical solution:

[0008] This invention discloses a method for testing the dynamic permeability coefficient of a defective geomembrane impermeable layer, wherein the geomembrane impermeable layer comprises, from top to bottom, a geomembrane, a geotextile, a sand protective layer, and a sub-support layer, characterized in that the method includes the following steps:

[0009] Determine the particle size distribution curve of the original soil sample to obtain the particle size distribution information of the soil sample, provide the original soil sample information for the testing process, and ensure that the properties of the test soil sample are consistent with those of the original soil sample;

[0010] Prepare test materials. According to the geomembrane seepage prevention scheme, ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and membrane support layer are consistent with the scheme. Create a circular hole defect with radius R on the test geomembrane to obtain a defective geomembrane.

[0011] Based on the particle size distribution curve of the original soil sample, the membrane support layer is divided into several layered samples, which are mixed and filled in sequence. After each layer is filled, a compaction operation is carried out to ensure that the physical properties and particle size distribution of the membrane support layer are consistent with the original soil sample. A sand protective layer, geotextile and defective geomembrane are laid on top of the membrane support layer in sequence to form a defective geomembrane seepage prevention layer.

[0012] The sample was initially saturated, and the total thickness of the defective geomembrane seepage prevention layer was measured and recorded. Saturation was carried out using de-aired water via the head saturation method.

[0013] Set up multi-level permeability gradient parameters from small to large, and perform permeability tests under each level of permeability gradient in sequence. The permeation time under each level of permeability gradient should be controlled at 30-60 minutes. The permeation volume and permeability pressure data should be stabilized before proceeding to the next stage. Record the permeability pressure, permeation flow rate and permeation phenomena until the test fails or the water head can no longer be increased.

[0014] Calculate the permeability coefficient of the defective geomembrane impermeable layer under each level of seepage slope. and the corresponding dry density of the under-membrane support layer Soil particle density Porosity Determine the dynamic permeability coefficient The changing trend.

[0015] This invention establishes a dynamic permeability coefficient testing method for defective geomembrane seepage barriers. This method can simulate the permeability performance of membrane materials under actual working conditions in a laboratory environment, evaluating the stability and permeability of the seepage barrier under defective conditions. By combining the physical properties of the underlying support layer with the analysis of permeability coefficient trends, this method can accurately reflect the impact of membrane defects on the permeability performance of the geomembrane seepage barrier, providing a scientific basis for the seepage prevention effect of geomembranes. This invention has good applicability and can be widely applied in civil engineering, environmental engineering, and other fields.

[0016] Furthermore, the determination of the particle size distribution curve of the original soil sample includes the following steps:

[0017] Original soil samples were selected, and the soil samples were sieved to determine the content of particles of different sizes.

[0018] Use sieving or laser particle size analysis to obtain the particle size distribution curve of the soil sample;

[0019] Based on the measured particle size distribution curve, determine the particle size distribution information of the original soil sample;

[0020] The particle size distribution data was recorded to provide benchmark data for the subsequent preparation of the membrane support layer, ensuring that the properties of the test soil sample were consistent with those of the original soil sample.

[0021] The determination of particle size distribution curves provides a detailed understanding of the particle size distribution of soil samples, offering a precise basis for the layered mixing and filling of the membrane support layer. The particle size distribution of a soil sample directly affects its permeability characteristics; therefore, ensuring the consistency of the soil sample with the original soil sample helps improve the reliability and repeatability of the test. Furthermore, determining the particle size distribution curves can provide important data support for subsequent permeability coefficient calculations and dynamic analysis, thereby enhancing the accuracy and scientific rigor of the entire testing method.

[0022] Furthermore, the preparation of the test materials includes the following steps:

[0023] Based on the established geomembrane seepage prevention scheme, prepare the corresponding test materials to ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and membrane support layer are consistent with the seepage prevention scheme.

[0024] At the center of the geomembrane used for testing, a circular hole with a radius of R is created by laser cutting or mechanical drilling; the circular hole is a circular hole with a radius of R of 2-5 mm, and the hole is located at least 10 mm away from the edge of the membrane.

[0025] The defective geomembrane is assembled with the sand protective layer, geotextile and the underlying support layer in sequence to ensure that each layer meets the design requirements of the impermeable structure.

[0026] Perform a visual inspection on the prepared defective geomembrane to ensure that the size and shape of the defects meet the test requirements.

[0027] This invention, through the precise fabrication of defective geomembranes, can simulate geomembrane damage that may occur in actual use, such as voids caused by wear during construction, transportation, or long-term use. This simulation of defects can help assess the degradation patterns of geomembrane impermeability under different conditions, thus providing a more scientific design basis for seepage control projects. Laser cutting or mechanical drilling techniques ensure the accuracy and consistency of defect dimensions, thereby improving the reliability and reproducibility of experimental results.

[0028] Furthermore, the preparation of the defective geomembrane impermeable layer includes the following steps:

[0029] Based on the measured particle size distribution curve of the original soil sample, the support layer under the membrane was divided into several layered samples, and the particle size distribution of each layer was ensured to be consistent with the original soil sample.

[0030] Following the principle of layering, the sample of the under-film support layer was mixed uniformly layer by layer, with the mixing uniformity of each layer controlled within ±2%.

[0031] Each layer of samples was filled in sequence and compacted using the standard compaction method to ensure that the dry density and compaction degree of each soil sample met the experimental requirements.

[0032] After each layer is filled and compacted, visually inspect each soil sample to ensure that it is uniform and free of loose areas, and that the compaction of each soil sample meets the standard and that there is no obvious looseness.

[0033] After the layered filling of the underlying support layer is completed, the sand protective layer, geotextile and defect geomembrane are laid in sequence to form a complete defect geomembrane seepage prevention layer structure.

[0034] The preparation of the defective geomembrane impermeable layer is crucial because the uniformity and compaction of the underlying support layer directly affect the accuracy and reliability of the permeability test. By strictly controlling the particle size distribution, mixing uniformity, and compaction of each soil sample layer, the stability of the geomembrane impermeable layer structure can be ensured, avoiding errors caused by soil inhomogeneity during testing. Furthermore, meticulous operational procedures ensure that the physical properties of each soil sample are consistent with the original soil sample, thereby guaranteeing the authenticity and validity of the test results.

[0035] Furthermore, the initial saturation of the sample includes the following steps:

[0036] Before the test begins, the defective geomembrane impermeable layer is initially saturated with deaerated water to ensure that the water flow can completely penetrate the geomembrane and the underlying support layer.

[0037] The head saturation method is used, in which a water head is applied to the test sample and the water level is gradually increased until the sample reaches a completely saturated state.

[0038] During the saturation process, the permeation of the sample is measured periodically, and the required time is recorded to ensure that the saturation of the sample meets the experimental requirements.

[0039] Measure and record the total thickness of the defective geomembrane seepage prevention layer to ensure it meets design requirements;

[0040] During the saturation process, the water temperature and room temperature should be checked regularly to ensure stable experimental conditions.

[0041] Initial saturation of the sample is a crucial step in ensuring the accuracy of test results, especially in testing defective geomembrane impermeable layers, where the degree of saturation directly affects the stability of the seepage process. Using degassed water for saturation can reduce interference from air bubbles and avoid errors in seepage flow rate caused by air bubbles in the water flow path. Simultaneously, strict control of water and room temperature ensures a stable experimental environment, further enhancing the controllability and repeatability of the experiment.

[0042] Furthermore, the penetration test includes the following steps:

[0043] Set up a multi-level permeability gradient parameter with an initial gradient of 0.02-0.03, gradually increasing to the target gradient, with each gradient parameter increment being 0.05;

[0044] At each level of seepage gradient, a seepage test is performed, and the seepage test data at each level of gradient is recorded, including seepage pressure, seepage flow rate, and seepage phenomena.

[0045] Measure and record the water pressure and seepage volume after each seepage test, and observe the seepage phenomena, including the turbidity of the water, the emergence of air bubbles, the jumping, movement or being carried out by the water flow of fine particles, the suspension of soil, and the change of water level in the piezometer.

[0046] Each infiltration test lasts 30 minutes to 1 hour, with a measurement interval of 10 to 20 minutes. If the water level and infiltration volume are basically stable after three consecutive measurements, the water head can be increased to the next level.

[0047] The penetration test ends when the test fails or the water head can no longer be increased.

[0048] The multi-stage gradient parameter setting for permeability testing is designed to simulate permeability conditions under different water heads, thereby comprehensively evaluating the permeability performance of the geomembrane impermeable layer. Under different water head conditions, the permeability of water flow may be affected by factors such as membrane defects and soil compaction. Therefore, gradually increasing the permeability gradient can reveal the permeability characteristics of the underlying support layer under different stress conditions. By observing the seepage phenomenon, we can further understand the influence mechanism of defective geomembranes on water flow, thus providing strong data support for subsequent permeability coefficient analysis.

[0049] Furthermore, determining the changing trend of the dynamic permeability coefficient includes the following steps:

[0050] Based on the recorded seepage flow rate, seepage pressure, and other test data at each seepage gradient, Darcy's law was used to calculate the dynamic permeability coefficient. Calculation;

[0051] Simultaneously, the dry density of the under-support layer of the test membrane was measured. Soil particle density and porosity And record its changes;

[0052] Permeability coefficient at each permeability gradient Perform statistical analysis to determine the permeability coefficient. The changing trend;

[0053] Based on the experimental results, statistical methods were used to determine the permeability coefficient under each permeability gradient. The data was fitted to identify and confirm the permeability coefficient. The changing trends and stability of the geomembrane were analyzed to assess the impact of defects and determine the stability and permeability of the impermeable layer.

[0054] Furthermore, determining the changing trend of the dynamic permeability coefficient includes the following steps:

[0055] During the permeation test, the flow pattern of water flowing through the support layer under the membrane is analyzed based on the axisymmetric permeation model, and it is assumed that the permeation meets the laminar flow condition and satisfies Darcy's law.

[0056] By analyzing test data and combining the seepage characteristics of the defect area of ​​the geomembrane, the stability of water permeability with different water heads was analyzed.

[0057] For the permeability coefficient data under each level of seepage gradient, statistical methods were used for fitting analysis to reveal the variation law of permeability coefficient with water head, and the permeability of the coarse soil layer under the membrane support layer and the influence of fine soil loss on the permeability coefficient were evaluated based on the experimental results.

[0058] At each water head level, the specific impact of geomembrane defects on the stability and permeability of the impermeable layer is evaluated, further verifying the applicability and reliability of the permeability model.

[0059] The dynamic trend of permeability coefficient variation is one of the core elements of the testing method in this invention. By calculating the permeability coefficient using Darcy's law and combining it with the physical properties of the underlying support layer (such as dry density and soil particle specific gravity), the actual impact of membrane defects on the permeability performance of the geomembrane can be revealed. Statistical analysis and data fitting methods can effectively identify the variation law of permeability coefficient, providing accurate quantitative analysis for evaluating the geomembrane's seepage prevention performance. Furthermore, the fitting results can provide a basis for relevant engineering designs, helping to optimize the structure and material selection of the geomembrane.

[0060] Furthermore, the calculation method is as follows:

[0061] The dry density Calculate using the following formula:

[0062]

[0063] In the formula: , The radius of the sample is (cm). The initial height of the sample (cm);

[0064] The specific gravity of soil particles The specific gravity of the mixture of coarse and fine particles is calculated using the following formula:

[0065]

[0066] In the formula: The specific gravity of soil particles with a diameter greater than 5 mm. The specific gravity of soil particles with a diameter not exceeding 5 mm. This represents the percentage by mass of soil particles with a diameter greater than 5 mm.

[0067] porosity Calculate using the following formula:

[0068]

[0069] In the formula: Porosity (%) The density of water ( );

[0070] The seepage velocity is calculated using the following formula:

[0071]

[0072] In the formula: The permeation velocity is (cm / s). Permeation ( ), For time (s), The area of ​​the sample ( );

[0073] The seepage gradient should be calculated using the following formula:

[0074]

[0075] In the formula: For seepage gradient, The pressure difference is measured in cm. To match the head difference The corresponding seepage path length (cm);

[0076] Permeability coefficient Then according to calculate.

[0077] The beneficial effects of this invention are as follows: This invention proposes a method for testing the dynamic permeability coefficient of defective geomembrane seepage prevention layers. Considering the ultra-thin characteristics of geomembranes and the fact that defects typically manifest as small pores and localized distribution, this invention has the following innovative features:

[0078] (1) The concept of dynamic permeability coefficient of defective geomembrane impermeable layer is proposed for the first time. In the prior art, geomembrane and its upper and lower protective layers and support layers are often considered separately, ignoring the interaction of permeability between the materials of each layer. This has led to the long-standing problem of estimating the leakage of defective geomembrane, thus making it impossible to accurately assess the degree of defect of geomembrane. In this invention, the geomembrane and its upper and lower protective layers and support layers are regarded as an impermeable layer structure. Under laminar flow conditions, the flow of water through this structure satisfies Darcy's law. When the hydraulic gradient is stable and the loss of fine particles in the coarse-grained soil structure of the support layer under the membrane is relatively stable, the permeability coefficient of the impermeable layer can be regarded as approximately constant, thereby deepening the understanding of the permeability of defective geomembrane impermeable layer.

[0079] (2) An experimental device for the dynamic permeability coefficient of a defective geomembrane seepage barrier layer was designed. Based on the design scheme of the reservoir geomembrane seepage barrier structure, and combined with the characteristics of geomembrane defect leakage and coarse soil seepage deformation, this invention adds a defective geomembrane seepage barrier layer structure to the existing coarse soil seepage test device, forming an experimental device suitable for studying the dynamic permeability coefficient of a defective geomembrane seepage barrier layer, and providing experimental conditions for related research.

[0080] (3) A test method for the dynamic permeability coefficient of defective geomembrane impermeable layers is proposed. This invention draws upon the permeability test method for coarse-grained soil and, combined with the influencing factors of geomembrane defect leakage and coarse-grained soil permeability deformation, innovatively proposes this test method. The feasibility of this test method is verified by analyzing the relative stability of the dynamic permeability coefficient of defective geomembrane impermeable layers. Furthermore, this method can reveal the variation law of the permeability coefficient, reflecting the creative value of this invention. Attached Figure Description

[0081] Figure 1 Schematic diagram of seepage characteristics of defective geomembrane impermeable layer;

[0082] Figure 2 Isobaric plots from numerical simulation;

[0083] Figure 3 Evolution of permeability coefficient of defective geomembrane impermeable layer with reservoir water depth;

[0084] Figure 4 : Schematic diagram of the initial state of the permeability coefficient of the defective geomembrane seepage prevention layer;

[0085] Figure 5 : Schematic diagram of the permeability coefficient and pore blockage state of a defective geomembrane seepage prevention layer;

[0086] Figure 6 : Schematic diagram of the permeability coefficient of a defective geomembrane seepage prevention layer, with fine particles lost and pores enlarged;

[0087] Figure 7 : A schematic diagram of the permeability coefficient and pore structure stability of a defective geomembrane seepage prevention layer;

[0088] In the diagram: 2-1: Top surface; 2-2: Upper soil layer of geomembrane; 2-3: Defective geomembrane; 2-4: Lower soil layer of geomembrane; 2-5: Laminar flow; 2-6: Interfacial flow; 3-1: Reservoir water depth; 3-2: Permeability coefficient; 3-3: Time; 4-1: Seepage direction; 4-2: Sand protective layer; 4-3: Defect; 4-4: Geomembrane; 4-5: Support layer under the membrane; 4-6: Pores; 4-7: Coarse particles; 4-8: Fine particles. Detailed Implementation

[0089] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0090] Example: A method for testing the dynamic permeability coefficient of a defective geomembrane impermeable layer, wherein the geomembrane impermeable layer comprises, from top to bottom, a geomembrane, a geotextile, a sand protective layer, and a support layer beneath the membrane, characterized in that the method includes the following steps:

[0091] Determine the particle size distribution curve of the original soil sample to obtain the particle size distribution information of the soil sample, provide the original soil sample information for the testing process, and ensure that the properties of the test soil sample are consistent with those of the original soil sample;

[0092] Prepare test materials. According to the geomembrane seepage prevention scheme, ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and membrane support layer are consistent with the scheme. Create a circular hole defect with radius R on the test geomembrane to obtain a defective geomembrane.

[0093] Based on the particle size distribution curve of the original soil sample, the membrane support layer is divided into several layered samples, which are mixed and filled in sequence. After each layer is filled, a compaction operation is carried out to ensure that the physical properties and particle size distribution of the membrane support layer are consistent with the original soil sample. A sand protective layer, geotextile and defective geomembrane are laid on top of the membrane support layer in sequence to form a defective geomembrane seepage prevention layer.

[0094] The sample was initially saturated, and the total thickness of the defective geomembrane seepage prevention layer was measured and recorded. Saturation was carried out using de-aired water via the head saturation method.

[0095] Set up multi-level permeability gradient parameters from small to large, and perform permeability tests under each level of permeability gradient in sequence. The permeation time under each level of permeability gradient should be controlled at 30-60 minutes. The permeation volume and permeability pressure data should be stabilized before proceeding to the next stage. Record the permeability pressure, permeation flow rate and permeation phenomena until the test fails or the water head can no longer be increased.

[0096] Calculate the permeability coefficient of the defective geomembrane impermeable layer under each level of seepage slope. and the corresponding dry density of the under-membrane support layer Soil particle density Porosity Determine the dynamic permeability coefficient The changing trend.

[0097] This invention establishes a dynamic permeability coefficient testing method for defective geomembrane seepage barriers. This method can simulate the permeability performance of membrane materials under actual working conditions in a laboratory environment, evaluating the stability and permeability of the seepage barrier under defective conditions. By combining the physical properties of the underlying support layer with the analysis of permeability coefficient trends, this method can accurately reflect the impact of membrane defects on the permeability performance of the geomembrane seepage barrier, providing a scientific basis for the seepage prevention effect of geomembranes. This invention has good applicability and can be widely applied in civil engineering, environmental engineering, and other fields.

[0098] Furthermore, the determination of the particle size distribution curve of the original soil sample includes the following steps:

[0099] Original soil samples were selected, and the soil samples were sieved to determine the content of particles of different sizes.

[0100] Use sieving or laser particle size analysis to obtain the particle size distribution curve of the soil sample;

[0101] Based on the measured particle size distribution curve, determine the particle size distribution information of the original soil sample;

[0102] The particle size distribution data was recorded to provide benchmark data for the subsequent preparation of the membrane support layer, ensuring that the properties of the test soil sample were consistent with those of the original soil sample.

[0103] The determination of particle size distribution curves provides a detailed understanding of the particle size distribution of soil samples, offering a precise basis for the layered mixing and filling of the membrane support layer. The particle size distribution of a soil sample directly affects its permeability characteristics; therefore, ensuring the consistency of the soil sample with the original soil sample helps improve the reliability and repeatability of the test. Furthermore, determining the particle size distribution curves can provide important data support for subsequent permeability coefficient calculations and dynamic analysis, thereby enhancing the accuracy and scientific rigor of the entire testing method.

[0104] Furthermore, the preparation of the test materials includes the following steps:

[0105] Based on the established geomembrane seepage prevention scheme, prepare the corresponding test materials to ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and membrane support layer are consistent with the seepage prevention scheme.

[0106] At the center of the geomembrane used for testing, a circular hole with a radius of R is created by laser cutting or mechanical drilling; the circular hole is a circular hole with a radius of R of 2-5 mm, and the hole is located at least 10 mm away from the edge of the membrane.

[0107] The defective geomembrane is assembled with the sand protective layer, geotextile and the underlying support layer in sequence to ensure that each layer meets the design requirements of the impermeable structure.

[0108] Perform a visual inspection on the prepared defective geomembrane to ensure that the size and shape of the defects meet the test requirements.

[0109] This invention, through the precise fabrication of defective geomembranes, can simulate geomembrane damage that may occur in actual use, such as voids caused by wear during construction, transportation, or long-term use. This simulation of defects can help assess the degradation patterns of geomembrane impermeability under different conditions, thus providing a more scientific design basis for seepage control projects. Laser cutting or mechanical drilling techniques ensure the accuracy and consistency of defect dimensions, thereby improving the reliability and reproducibility of experimental results.

[0110] Furthermore, the preparation of the defective geomembrane impermeable layer includes the following steps:

[0111] Based on the measured particle size distribution curve of the original soil sample, the support layer under the membrane was divided into several layered samples, and the particle size distribution of each layer was ensured to be consistent with the original soil sample.

[0112] Following the principle of layering, the sample of the under-film support layer was mixed uniformly layer by layer, with the mixing uniformity of each layer controlled within ±2%.

[0113] Each layer of samples was filled in sequence and compacted using the standard compaction method to ensure that the dry density and compaction degree of each soil sample met the experimental requirements.

[0114] After each layer is filled and compacted, visually inspect each soil sample to ensure that it is uniform and free of loose areas, and that the compaction of each soil sample meets the standard and that there is no obvious looseness.

[0115] After the layered filling of the underlying support layer is completed, the sand protective layer, geotextile and defect geomembrane are laid in sequence to form a complete defect geomembrane seepage prevention layer structure.

[0116] The preparation of the defective geomembrane impermeable layer is crucial because the uniformity and compaction of the underlying support layer directly affect the accuracy and reliability of the permeability test. By strictly controlling the particle size distribution, mixing uniformity, and compaction of each soil sample layer, the stability of the geomembrane impermeable layer structure can be ensured, avoiding errors caused by soil inhomogeneity during testing. Furthermore, meticulous operational procedures ensure that the physical properties of each soil sample are consistent with the original soil sample, thereby guaranteeing the authenticity and validity of the test results.

[0117] Furthermore, the initial saturation of the sample includes the following steps:

[0118] Before the test begins, the defective geomembrane impermeable layer is initially saturated with deaerated water to ensure that the water flow can completely penetrate the geomembrane and the underlying support layer.

[0119] The head saturation method is used, in which a water head is applied to the test sample and the water level is gradually increased until the sample reaches a completely saturated state.

[0120] During the saturation process, the permeation of the sample is measured periodically, and the required time is recorded to ensure that the saturation of the sample meets the experimental requirements.

[0121] Measure and record the total thickness of the defective geomembrane seepage prevention layer to ensure it meets design requirements;

[0122] During the saturation process, the water temperature and room temperature should be checked regularly to ensure stable experimental conditions.

[0123] Initial saturation of the sample is a crucial step in ensuring the accuracy of test results, especially in testing defective geomembrane impermeable layers, where the degree of saturation directly affects the stability of the seepage process. Using degassed water for saturation can reduce interference from air bubbles and avoid errors in seepage flow rate caused by air bubbles in the water flow path. Simultaneously, strict control of water and room temperature ensures a stable experimental environment, further enhancing the controllability and repeatability of the experiment.

[0124] Furthermore, the penetration test includes the following steps:

[0125] Set up a multi-level permeability gradient parameter with an initial gradient of 0.02-0.03, gradually increasing to the target gradient, with each gradient parameter increment being 0.05;

[0126] At each level of seepage gradient, a seepage test is performed, and the seepage test data at each level of gradient is recorded, including seepage pressure, seepage flow rate, and seepage phenomena.

[0127] Measure and record the water pressure and seepage volume after each seepage test, and observe the seepage phenomena, including the turbidity of the water, the emergence of air bubbles, the jumping, movement or being carried out by the water flow of fine particles, the suspension of soil, and the change of water level in the piezometer.

[0128] Each infiltration test lasts 30 minutes to 1 hour, with a measurement interval of 10 to 20 minutes. If the water level and infiltration volume are basically stable after three consecutive measurements, the water head can be increased to the next level.

[0129] The penetration test ends when the test fails or the water head can no longer be increased.

[0130] The multi-stage gradient parameter setting for permeability testing is designed to simulate permeability conditions under different water heads, thereby comprehensively evaluating the permeability performance of the geomembrane impermeable layer. Under different water head conditions, the permeability of water flow may be affected by factors such as membrane defects and soil compaction. Therefore, gradually increasing the permeability gradient can reveal the permeability characteristics of the underlying support layer under different stress conditions. By observing the seepage phenomenon, we can further understand the influence mechanism of defective geomembranes on water flow, thus providing strong data support for subsequent permeability coefficient analysis.

[0131] Furthermore, determining the changing trend of the dynamic permeability coefficient includes the following steps:

[0132] Based on the recorded seepage flow rate, seepage pressure, and other test data at each seepage gradient, Darcy's law was used to calculate the dynamic permeability coefficient. Calculation;

[0133] Simultaneously, the dry density of the under-support layer of the test membrane was measured. Soil particle density and porosity And record its changes;

[0134] Permeability coefficient at each permeability gradient Perform statistical analysis to determine the permeability coefficient. The changing trend;

[0135] Based on the experimental results, statistical methods were used to determine the permeability coefficient under each permeability gradient. The data was fitted to identify and confirm the permeability coefficient. The changing trends and stability of the geomembrane were analyzed to assess the impact of defects and determine the stability and permeability of the impermeable layer.

[0136] Furthermore, determining the changing trend of the dynamic permeability coefficient includes the following steps:

[0137] During the permeation test, the flow pattern of water flowing through the support layer under the membrane is analyzed based on the axisymmetric permeation model, and it is assumed that the permeation meets the laminar flow condition and satisfies Darcy's law.

[0138] By analyzing test data and combining the seepage characteristics of the defect area of ​​the geomembrane, the stability of water permeability with different water heads was analyzed.

[0139] For the permeability coefficient data under each level of seepage gradient, statistical methods were used for fitting analysis to reveal the variation law of permeability coefficient with water head, and the permeability of the coarse soil layer under the membrane support layer and the influence of fine soil loss on the permeability coefficient were evaluated based on the experimental results.

[0140] At each water head level, the specific impact of geomembrane defects on the stability and permeability of the impermeable layer is evaluated, further verifying the applicability and reliability of the permeability model.

[0141] The dynamic trend of permeability coefficient variation is one of the core elements of the testing method in this invention. By calculating the permeability coefficient using Darcy's law and combining it with the physical properties of the underlying support layer (such as dry density and soil particle specific gravity), the actual impact of membrane defects on the permeability performance of the geomembrane can be revealed. Statistical analysis and data fitting methods can effectively identify the variation law of permeability coefficient, providing accurate quantitative analysis for evaluating the geomembrane's seepage prevention performance. Furthermore, the fitting results can provide a basis for relevant engineering designs, helping to optimize the structure and material selection of the geomembrane.

[0142] Furthermore, the calculation method is as follows:

[0143] The dry density Calculate using the following formula:

[0144]

[0145] In the formula: , The radius of the sample is (cm). The initial height of the sample (cm);

[0146] The specific gravity of soil particles The specific gravity of the mixture of coarse and fine particles is calculated using the following formula:

[0147]

[0148] In the formula: The specific gravity of soil particles with a diameter greater than 5 mm. The specific gravity of soil particles with a diameter not exceeding 5 mm. This represents the percentage by mass of soil particles with a diameter greater than 5 mm.

[0149] porosity Calculate using the following formula:

[0150]

[0151] In the formula: Porosity (%) The density of water ( );

[0152] The seepage velocity is calculated using the following formula:

[0153]

[0154] In the formula: The permeation velocity is (cm / s). Permeation ( ), For time (s), The area of ​​the sample ( );

[0155] The seepage gradient should be calculated using the following formula:

[0156]

[0157] In the formula: For seepage gradient, The pressure difference is measured in cm. To match the head difference The corresponding seepage path length (cm);

[0158] Permeability coefficient Then according to calculate.

[0159] Taking a 5mm hole in the center of a geomembrane as an example, the following is the process and experimental results of testing the dynamic permeability coefficient of the defective geomembrane impermeable layer according to the method provided by the present invention.

[0160] 1. Preparation of experimental materials and fabrication of defects in geomembranes

[0161] According to the method described in this invention, the materials for the geomembrane, geotextile, sand protective layer, and underlying support layer are first selected, and their thicknesses are determined according to design requirements. Next, a circular hole with a radius of 5 mm is mechanically drilled at the center of the geomembrane used for testing. The size and location of the defect hole strictly conform to the testing requirements to ensure the consistency and accuracy of the testing conditions.

[0162] 2. Sample Preparation

[0163] Based on the particle size distribution curve of the original soil sample, the underlying support layer is divided into several layers. Each layer is mixed, filled, and compacted according to the layering principle to ensure that the physical properties of each layer in the geomembrane seepage barrier are consistent with the original soil sample. After completing the layered filling of the underlying support layer, a sand protective layer, geotextile, and defective geomembrane are laid sequentially to form a complete defective geomembrane seepage barrier layer.

[0164] 3. Saturation process and penetration test

[0165] Initial saturation of the defective geomembrane impermeable layer was performed using the head saturation method to ensure complete saturation of the geomembrane and its underlying support layer. Then, permeability tests were conducted progressively according to the designed multi-stage permeability gradient. At each permeability gradient, the test time was controlled between 30 and 60 minutes, and the permeability and pressure data had to stabilize before proceeding to the next stage.

[0166] 4. Infiltration and Changes in Water Flow

[0167] During the permeability test, the hydraulic gradient on the geomembrane gradually increases with increasing water pressure. When the hydraulic gradient exceeds the critical value for fine particles, it initiates the flow of fine particles and their entry into the underlying support layer through geomembrane defects. This process occurs in the upper contact layer of the membrane, manifesting as localized undercutting, while the lower contact layer begins to fill and compact. As the reservoir water level continues to rise, when the hydraulic gradient under the geomembrane exceeds the critical value, fine particles in the underlying gravelly soil begin to be lost, gradually leading to increased permeability. Ultimately, at higher water levels, the continuous loss of fine particles from the gravelly soil layer results in more pore channels being opened, and permeability reaches a relatively stable state.

[0168] 5. Penetration Model and Data Analysis

[0169] like Figure 1 and Figure 2As shown, the experimental results indicate that with changes in water flow through the defective pores, the isobars of the seepage pressure exhibit a circular diffusion trend centered on the defect. When the seepage pressure reaches 0.15 kPa, the water flow essentially transitions to a laminar state, which conforms to Darcy's law. Based on these test data, the dynamic permeability coefficient was calculated using Darcy's law, and the changing trend of the permeability coefficient was further analyzed by combining parameters such as the dry density, soil particle specific gravity, and porosity of the underlying support layer.

[0170] The variation law of dynamic permeability coefficient of defective geomembrane seepage prevention layer is as follows Figure 3 As shown, this indicates that the seepage effect caused by defects has significant piping characteristics. When seepage passes through the defective area, the physical changes of the geomembrane and the underlying support layer are closely related to the seepage characteristics. Statistical analysis of the permeability coefficient data under each seepage gradient shows that the permeability coefficient of the defective geomembrane seepage barrier increases with increasing water head, especially during the loss of fine particles, where the change in permeability is more significant.

[0171] 6. Conclusion

[0172] The experimental results of this embodiment show that the dynamic permeability coefficient of the defective geomembrane seepage barrier layer changes significantly under water pressure, and the permeability increases with the appearance of geomembrane defects and changes in water head. At higher water levels, fine particles are lost from the coarse-grained soil layer beneath the membrane support, leading to increased permeability, and this process exhibits obvious seepage characteristics, such as... Figure 4-7 As shown in the figure. This experiment verifies the permeability model of the present invention and its application, showing that the variation law of permeability performance of the defective geomembrane seepage prevention layer under different water head conditions is in line with expectations, and provides experimental basis for the evaluation of geomembrane seepage prevention performance.

[0173] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing the dynamic permeability coefficient of a defective geomembrane impermeable layer, wherein the geomembrane impermeable layer comprises, from top to bottom, a geomembrane, a geotextile, a sand protective layer, and a support layer beneath the membrane, characterized in that: The method includes the following steps: Determine the particle size distribution curve of the original soil sample to obtain the particle size distribution information of the soil sample, provide the original soil sample information for the testing process, and ensure that the properties of the test soil sample are consistent with those of the original soil sample; Prepare test materials. According to the geomembrane seepage prevention scheme, ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and membrane support layer are consistent with the scheme. Create a circular hole defect with radius R on the test geomembrane to obtain a defective geomembrane. Based on the particle size distribution curve of the original soil sample, the membrane support layer is divided into several layered samples, which are mixed and filled in sequence. After each layer is filled, a compaction operation is carried out to ensure that the physical properties and particle size distribution of the membrane support layer are consistent with the original soil sample. A sand protective layer, geotextile and defective geomembrane are laid on top of the membrane support layer in sequence to form a defective geomembrane seepage prevention layer. The sample was initially saturated, and the total thickness of the defective geomembrane seepage prevention layer was measured and recorded. Saturation was carried out using de-aired water via the head saturation method. Set up multi-level permeability gradient parameters from small to large, and perform permeability tests under each level of permeability gradient in sequence. The permeation time under each level of permeability gradient should be controlled at 30-60 minutes. The permeation volume and permeability pressure data should be stabilized before proceeding to the next stage. Record the permeability pressure, permeation flow rate and permeation phenomena until the test fails or the water head can no longer be increased. Calculate the permeability coefficient of the defective geomembrane impermeable layer under each level of seepage slope. and the corresponding dry density of the under-membrane support layer Soil particle density Porosity Determine the dynamic permeability coefficient The changing trend.

2. The method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 1, characterized in that: The determination of the particle size distribution curve of the original soil sample includes the following steps: Original soil samples were selected, and the soil samples were sieved to determine the content of particles of different sizes. Use sieving or laser particle size analysis to obtain the particle size distribution curve of the soil sample; Based on the measured particle size distribution curve, determine the particle size distribution information of the original soil sample; The particle size distribution data was recorded to provide benchmark data for the subsequent preparation of the membrane support layer, ensuring that the properties of the test soil sample were consistent with those of the original soil sample.

3. The method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 1, characterized in that: The preparation of the test materials includes the following steps: Based on the established geomembrane seepage prevention scheme, prepare the corresponding test materials to ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and membrane support layer are consistent with the seepage prevention scheme. At the center of the geomembrane used for testing, a circular hole with a radius of R is created by laser cutting or mechanical drilling; the circular hole is a circular hole with a radius of R of 2-5 mm, and the hole is located at least 10 mm away from the edge of the membrane. The defective geomembrane, sand protective layer, geotextile and membrane support layer are assembled in sequence to ensure that each layer meets the design requirements of the impermeable structure. Perform a visual inspection on the prepared defective geomembrane to ensure that the size and shape of the defects meet the test requirements.

4. The method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 1, characterized in that: The preparation of the defective geomembrane impermeable layer includes the following steps: Based on the measured particle size distribution curve of the original soil sample, the support layer under the membrane was divided into several layered samples, and the particle size distribution of each layer was ensured to be consistent with the original soil sample. Following the principle of layering, the sample of the under-film support layer was mixed uniformly layer by layer, with the mixing uniformity of each layer controlled within ±2%. Each layer of samples was filled in sequence and compacted using the standard compaction method to ensure that the dry density and compaction degree of each soil sample met the experimental requirements. After each layer is filled and compacted, visually inspect each soil sample to ensure that it is uniform and free of loose areas, and that the compaction of each soil sample meets the standard and that there is no obvious looseness. After the layered filling of the underlying support layer is completed, the sand protective layer, geotextile and defect geomembrane are laid in sequence to form a complete defect geomembrane seepage prevention layer structure.

5. The method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 1, characterized in that: The initial saturation of the sample includes the following steps: Before the test begins, the defective geomembrane impermeable layer is initially saturated with deaerated water to ensure that the water flow can completely penetrate the geomembrane and the underlying support layer. The head saturation method is used, in which a water head is applied to the test sample and the water level is gradually increased until the sample reaches a completely saturated state. During the saturation process, the permeation of the sample is measured periodically, and the required time is recorded to ensure that the saturation of the sample meets the experimental requirements. Measure and record the total thickness of the defective geomembrane seepage prevention layer to ensure it meets design requirements; During the saturation process, the water temperature and room temperature should be checked regularly to ensure stable experimental conditions.

6. The method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 1, characterized in that: The penetration test includes the following steps: Set up a multi-level permeability gradient parameter with an initial gradient of 0.02-0.03, gradually increasing to the target gradient, with each gradient parameter increment being 0.05; At each level of seepage gradient, a seepage test is performed, and the seepage test data at each level of gradient is recorded, including seepage pressure, seepage flow rate, and seepage phenomena. Measure and record the water pressure and seepage volume after each seepage test, and observe the seepage phenomena, including the turbidity of the water, the emergence of air bubbles, the jumping, movement or being carried out by the water flow of fine particles, the suspension of soil, and the change of water level in the piezometer. Each infiltration test lasts 30 minutes to 1 hour, with a measurement interval of 10 to 20 minutes. If the water level and infiltration volume are basically stable after three consecutive measurements, the water head can be increased to the next level. The penetration test ends when the test fails or the water head can no longer be increased.

7. The method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 1, characterized in that: The determination of the changing trend of the dynamic permeability coefficient includes the following steps: Based on the recorded seepage flow rate, seepage pressure, and other test data at each seepage gradient, Darcy's law was used to calculate the dynamic permeability coefficient. Calculation; Simultaneously, the dry density of the under-support layer of the test membrane was measured. Soil particle density and porosity And record its changes; Permeability coefficient at each permeability gradient Perform statistical analysis to determine the permeability coefficient. The changing trend; Based on the experimental results, statistical methods were used to determine the permeability coefficient under each permeability gradient. The data was fitted to identify and confirm the permeability coefficient. The changing trends and stability of the geomembrane were analyzed to assess the impact of defects and determine the stability and permeability of the impermeable layer.

8. The method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 7, characterized in that: Determining the trend of the dynamic permeability coefficient includes the following steps: During the permeation test, the flow pattern of water flowing through the support layer under the membrane is analyzed based on the axisymmetric permeation model, and it is assumed that the permeation meets the laminar flow condition and satisfies Darcy's law. By analyzing test data and combining the seepage characteristics of the defect area of ​​the geomembrane, the stability of water permeability with different water heads was analyzed. For the permeability coefficient data under each level of seepage gradient, statistical methods were used for fitting analysis to reveal the variation law of permeability coefficient with water head, and the permeability of the coarse soil layer under the membrane support layer and the influence of fine soil loss on the permeability coefficient were evaluated based on the experimental results. At each water head level, the specific impact of geomembrane defects on the stability and permeability of the impermeable layer is evaluated, further verifying the applicability and reliability of the permeability model.

9. A method for testing the dynamic permeability coefficient of a defective geomembrane seepage prevention layer as described in claim 7 or 8, characterized in that: The dry density Calculate using the following formula: ； In the formula: , The radius of the sample is (cm). The initial height of the sample (cm); The specific gravity of soil particles The specific gravity of the mixture of coarse and fine particles is calculated using the following formula: ； In the formula: The specific gravity of soil particles with a diameter greater than 5 mm. The specific gravity of soil particles with a diameter not exceeding 5 mm. This represents the percentage by mass of soil particles with a diameter greater than 5 mm. porosity Calculate using the following formula: ； In the formula: Porosity (%) The density of water ( ); The seepage velocity is calculated using the following formula: ； In the formula: The permeation velocity is (cm / s). Permeability ( ), For time (s), The area of ​​the sample ( ); The seepage gradient should be calculated using the following formula: ； In the formula: For seepage gradient, The pressure difference is measured in cm. To match the head difference The corresponding seepage path length (cm); Permeability coefficient Then according to calculate.

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