Dynamic permeability coefficient testing method for impervious layer of defective geomembrane

Abstract

The invention relates to a method for testing the dynamic permeability coefficient of a defective geomembrane impermeable layer, and aims to evaluate the permeability and stability of a geomembrane with defects (such as holes) under different water heads. The method comprises the following steps: measuring the grain composition of a soil sample, preparing a defective geomembrane impermeable layer and carrying out water head saturation; carrying out penetration test step by step according to the multi-stage penetration gradient parameters, recording the penetration amount, the seepage pressure and the seepage phenomenon, and calculating the penetration coefficient under each stage of penetration gradient. And finally, fitting permeability coefficient data through a statistical method, analyzing the change trend of the permeability coefficient data, and evaluating the influence of defects on the performance of the impermeable layer. According to the method, the axial symmetry penetration model is established, it is assumed that water flow meets laminar flow conditions and meets the Darcy law, and an effective experimental basis is provided for permeability analysis of geomembrane defects. The method can be widely applied to performance evaluation and quality detection of geomembrane anti-seepage engineering.

Description

Technical Field

[0001] The invention relates to the field of water affairs, and in particular to a method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer. Background Art

[0002] In the field of reservoir engineering, geomembranes are an effective anti-seepage material, and their application is significantly affected by the geological conditions of the reservoir area. The anti-seepage performance of geomembranes and the evaluation of their defects and leakage have become key links in reservoir design. In good condition, the permeability coefficient of geomembranes is usually between 1×10 -15 m / s to 1×10 -13 However, due to the thinness of the geomembrane material, which is only 0.3-2.0mm, much smaller than the thickness of the conventional stratum structure, the geomembrane is prone to defects and holes during production, transportation, construction and operation, thus leading to reservoir leakage problems.

[0003] The defects of the geomembrane anti-seepage layer can be divided into two categories: microscopic defects and macroscopic defects. Microscopic defects mainly originate from microscopic particle impurities or unevenness of the material, resulting in uniform changes in the permeability of the geomembrane. Macroscopic defects include damage caused by physical damage (such as tearing, bursting, puncture, liquid swelling damage, etc.) and construction machinery, as well as damage to the joints caused by poor welding or bonding. These defects are manifested as local characteristics at the macro level. According to the "Technical Specifications for Anti-seepage of Geomembranes for Hydropower Engineering" (NB / T35027-2014), the equivalent aperture of the hole is generally 1mm-3mm, and can reach 5mm in special parts. These local macroscopic defects have a serious impact on the anti-seepage performance of the engineering structure.

[0004] Taking the upper reservoir of a pumped storage power station as an example, the reservoir adopts a geomembrane anti-seepage system for the entire reservoir. Monitoring data shows that the leakage at the bottom of the reservoir is 173-346m 3 / d, the leakage problem caused by local damage not only causes the seepage deformation of the sandy soil under the geomembrane, but also may cause local subsidence of the embankment, aggravate leakage and material erosion, and even cause the risk of embankment collapse and breach. In addition, when the reservoir water level drops, the defective leakage of the geomembrane on the dam surface will form a transient seepage field, affecting the local anti-sliding stability of the dam body. Therefore, accurately evaluating the impact of the degree of geomembrane defects on the leakage has become a core issue in the design of geomembrane anti-seepage reservoirs.

[0005] The factors affecting the leakage of geomembrane reservoirs are complex and changeable. The leakage not only depends on the number and shape of defects, but is also closely related to factors such as the permeability, stress level and head of the contact layer under the geomembrane. The test results show that the thickness and flatness of the base layer have a significant effect on the leakage of geomembrane gap defects. Although there have been studies on the estimation of geomembrane defect leakage at home and abroad, these research results are not suitable for direct application in actual reservoir projects because they fail to fully consider the impact of changes in the permeability coefficient of the supporting layer under the geomembrane on defect leakage. Therefore, how to accurately evaluate the leakage of geomembrane defects has become an urgent problem to be solved in the current geomembrane defect test research. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer.

[0007] The present invention is achieved through the following technical solutions:

[0008] The present invention discloses a method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer, wherein the geomembrane anti-seepage layer comprises a geomembrane, a geotextile, a sand material protective layer and a support layer under the membrane arranged in sequence from top to bottom, and is characterized in that the method comprises the following steps:

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

[0010] Prepare test materials, and ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and supporting layer under the membrane are consistent with the plan according to the geomembrane anti-seepage plan, and make a circular hole-shaped defect with a radius of R on the test geomembrane to obtain a defective geomembrane;

[0011] According to the particle grading curve of the original soil sample, the supporting layer under the membrane is divided into several layered samples, which are mixed evenly and filled in sequence. After each layer is filled, compaction operation is performed to ensure that the physical properties and particle grading of the supporting layer under the membrane are consistent with the original soil sample; a sand protective layer, a geotextile and a defective geomembrane are laid on the top of the supporting layer under the membrane in sequence to form a defective geomembrane anti-seepage layer;

[0012] The specimen is initially saturated, and the total thickness of the impermeable layer of the defective geomembrane is measured and recorded. The specimen is saturated with air-free water using the head saturation method;

[0013] Set up multi-level infiltration gradient parameters from small to large, and perform infiltration tests at each level of infiltration gradient in turn. The infiltration time at each level of infiltration gradient is controlled to be 30-60 minutes. The infiltration volume and seepage pressure data must be stable before entering the next stage; and record the seepage pressure, seepage volume and seepage phenomenon until the test is destroyed or the water head cannot continue to increase;

[0014] Calculate the permeability coefficient k of the defective geomembrane anti-seepage layer under each level of permeability gradient T And the corresponding dry density of the support layer under the membrane ρ d , soil particle specific gravity G s , porosity ratio n, determine the dynamic permeability coefficient k T of the changing trend.

[0015] The present invention can simulate the permeability performance of the membrane material under actual working conditions in a laboratory environment and evaluate the stability and permeability of the anti-seepage layer under defective conditions by establishing a dynamic permeability coefficient test method for a defective geomembrane anti-seepage layer. The test method combines the physical properties of the support layer under the membrane with the change trend analysis of the permeability coefficient, and can accurately reflect the influence of membrane defects on the permeability performance of the geomembrane anti-seepage layer, providing a scientific basis for the anti-seepage effect of the geomembrane. The present invention has good applicability and can be widely used in the fields of civil engineering, environmental engineering, etc.

[0016] Furthermore, the determination of the particle gradation curve of the original soil sample comprises the following steps:

[0017] Select the original soil sample, sieve the soil sample, and determine the content of particles with different particle sizes;

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

[0019] According to the measured particle size distribution curve, the particle gradation information of the original soil sample is determined;

[0020] The particle grading data is recorded to provide benchmark data for the subsequent preparation of the support layer under the membrane, ensuring that the properties of the test soil sample are consistent with those of the original soil sample.

[0021] By measuring the particle size distribution curve, we can understand the particle size distribution of the soil sample in detail, and provide an accurate basis for the layered mixing and filling of the support layer under the membrane. The particle size distribution of the soil sample directly affects its permeability characteristics, so ensuring the consistency of the soil sample with the original soil sample helps to improve the reliability and repeatability of the test. In addition, the determination of the particle size distribution curve can also provide important data support for the subsequent permeability coefficient calculation and dynamic analysis, thereby enhancing the accuracy and scientificity of the entire test method.

[0022] Further, the preparation of the test material comprises the following steps:

[0023] According to the determined geomembrane anti-seepage scheme, prepare the corresponding test materials to ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and supporting layer under the membrane are consistent with the anti-seepage scheme;

[0024] A circular hole defect with a radius of R is made at the center of the test geomembrane by laser cutting or mechanical drilling; the circular hole defect is a circular hole with a radius R of 2-5 mm, and the hole position is not less than 10 mm from the edge of the membrane;

[0025] Assemble the defective geomembrane with the sand protection layer, geotextile and the supporting layer under the membrane in sequence to ensure that each layer meets the design requirements of the anti-seepage structure;

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

[0027] The present invention can simulate the damage of geomembranes that may occur in actual use, such as holes caused by wear during construction, transportation or long-term use, by accurately manufacturing defective geomembranes. The simulation of such defects can help evaluate the degradation law of geomembrane anti-seepage performance under different conditions, thereby providing a more scientific design basis for anti-seepage projects. The accuracy and consistency of defect size are ensured by laser cutting or mechanical drilling technology, thereby improving the reliability and reproducibility of experimental results.

[0028] Furthermore, the preparation of the defective geomembrane anti-seepage layer comprises the following steps:

[0029] According to the measured particle gradation curve of the original soil sample, the support layer under the membrane is divided into several layered samples, and the particle gradation of each layer is ensured to be consistent with the original soil sample;

[0030] According to the layering principle, the samples of the supporting layer under the membrane are mixed evenly layer by layer, and the mixing uniformity of each layer is controlled within ±2%;

[0031] Each layer of samples is filled in sequence and compacted using the standard compaction method to ensure that the dry density and compaction degree of each layer of soil samples meet the experimental requirements;

[0032] After each layer is filled and compacted, visually check whether each layer of soil is uniform and has no loose areas, and whether the compaction degree reaches the specified standard, to ensure that the compaction degree of each layer of soil meets the standard and there is no obvious loose phenomenon;

[0033] After completing the layered filling of the supporting layer under the membrane, the sand protection layer, geotextile and defective geomembrane are laid in sequence to form a complete defective geomembrane anti-seepage layer structure.

[0034] The steps for preparing the imperfect geomembrane anti-seepage layer are crucial, because the uniformity and compaction of the supporting layer under the membrane directly affect the accuracy and reliability of the permeability test. By strictly controlling the particle grading, mixing uniformity, and compaction of each layer of soil sample, the stability of the geomembrane anti-seepage layer structure can be ensured, and errors caused by uneven soil layers during the test can be avoided. In addition, refined operating steps can ensure that the physical properties of each layer of soil sample are consistent with the original soil sample, thereby ensuring the authenticity and validity of the test results.

[0035] Furthermore, the sample is initially saturated, comprising the following steps:

[0036] Before the test begins, the imperfect geomembrane anti-seepage layer is initially saturated with degassed water to ensure that the water flow can fully penetrate the geomembrane and the supporting layer below it;

[0037] Using the head saturation method, a head of water is applied to the test sample, and the water level is gradually increased until the sample reaches a fully saturated state;

[0038] During the saturation process, the sample's permeability was measured regularly and the required time was recorded to ensure that the sample's saturation met the experimental requirements;

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

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

[0041] The initial saturation of the sample is a key step to ensure the accuracy of the test results, especially in the test of the defective geomembrane anti-seepage layer, where the saturation directly affects the stability of the infiltration process. Using degassed water for saturation can reduce the interference of bubbles and avoid the error of bubbles in the water flow path on the infiltration flow. At the same time, the water temperature and room temperature are strictly controlled to ensure the stability of the experimental environment and further enhance the controllability and repeatability of the experiment.

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

[0043] Set the multi-level infiltration slope parameters from small to large, with the initial slope of 0.02-0.03, and gradually increase to the target slope, with the incremental value of each slope parameter being 0.05;

[0044] At each level of infiltration slope, the infiltration test is started and the infiltration test data at each level of slope is recorded, including the infiltration pressure, seepage volume and seepage phenomenon;

[0045] Measure and record the water pressure and water seepage after each penetration test, and observe the seepage phenomenon, including the turbidity of water, the emergence of bubbles, the jumping, movement or being carried out of fine particles by the water flow, the suspension of soil, and the change of the water level in the pressure measuring tube;

[0046] Each permeability test is carried out for 30 minutes to 1 hour, with a measurement interval of 10 to 20 minutes. If the water level and seepage volume are basically stable for three consecutive measurements, the next level of water head can be raised;

[0047] The penetration test is terminated until the test is destroyed or the water head can no longer increase.

[0048] The multi-level slope parameter setting of the permeability test is to simulate the permeability conditions under different water heads in order to comprehensively evaluate the permeability performance of the geomembrane anti-seepage 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 slope can reveal the permeability characteristics of the supporting layer under the membrane under different stress conditions. By observing the seepage phenomenon, we can further understand the influence mechanism of defective geomembranes on water flow, thereby providing strong data support for the subsequent permeability coefficient analysis.

[0049] Furthermore, the determination of the change trend of the dynamic permeability coefficient includes the following steps:

[0050] According to the recorded infiltration flow rate, infiltration pressure and other test data at each level of infiltration slope, Darcy's law is used to calculate the dynamic permeability coefficient k. T Calculation of

[0051] At the same time, the dry density of the support layer under the test membrane was measured. d Specific gravity of soil particles G s and porosity ratio n, and record their changes;

[0052] The permeability coefficient k for each level of permeability gradient T Perform statistical analysis to determine the permeability coefficient k T ;

[0053] According to the experimental results, the permeability coefficient k at each level of permeability slope is calculated using statistical methods. T The data were fitted to identify the permeability coefficient k T The changing trend and stability of geomembrane defects are evaluated to determine the stability and permeability of the anti-seepage layer.

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

[0055] During the permeation test, the flow pattern of water through the support layer under the membrane was analyzed based on the axisymmetric permeation model, and it was assumed that the seepage flow met the laminar flow conditions and satisfied Darcy's law.

[0056] Through the test data, combined with the seepage characteristics of the defective area of ​​the geomembrane, the stability of water permeability with different water heads is analyzed;

[0057] The permeability coefficient data under each level of permeability slope were fitted and analyzed using statistical methods to reveal the variation law of permeability coefficient with the change of water head, and the influence of the permeability of the coarse-grained soil layer under the membrane support layer and the loss of fine-grained soil on the permeability coefficient was 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 anti-seepage layer was evaluated to further verify the applicability and reliability of the permeability model.

[0059] The changing trend of the dynamic permeability coefficient is one of the core contents of the test method of the present invention. By using Darcy's law to calculate the permeability coefficient, combined with the physical properties of the supporting layer under the membrane (such as dry density, specific gravity of soil particles, etc.), the actual impact of membrane defects on the permeability of the anti-seepage layer can be revealed. The method of statistical analysis and data fitting can effectively identify the changing law of the permeability coefficient and provide accurate quantitative analysis for the evaluation of the anti-seepage performance of geomembranes. In addition, the fitting results can provide a basis for related engineering design and help optimize the structure and material selection of the anti-seepage layer.

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

[0061] The dry density ρ d Calculate as follows:

[0062]

[0063] Where: m d is the dry density of the sample (g / cm 3 ), r is the sample radius (cm), h0 is the sample initial height (cm);

[0064] The soil particle specific gravity G s is the mixing ratio of coarse and fine particles, calculated as follows:

[0065]

[0066] Where: G s1 G is the specific gravity of soil particles with a diameter greater than 5 mm. s2 is the specific gravity of soil particles with a particle size not greater than 5 mm, and P5 is the mass percentage (%) of soil particles with a particle size greater than 5 mm;

[0067] The void ratio n is calculated as follows:

[0068]

[0069] Where: n is the porosity (%), ρ w is the density of water (g / cm 3 );

[0070] The seepage velocity is calculated as follows:

[0071]

[0072] Where: v is the permeation velocity (cm / s), Q is the permeation volume (cm 3 ), t is time (s), A is sample area (cm 2 );

[0073] The infiltration slope should be calculated as follows:

[0074]

[0075] Where: i is the seepage slope, ΔH is the water head difference of the piezometer (cm), and L is the seepage path length corresponding to the water head difference ΔH (cm);

[0076] Permeability coefficient k T Then press calculate.

[0077] The beneficial effects of the present invention are as follows: the present invention proposes a method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer. In view of the ultra-thin characteristics of the geomembrane and the fact that the defects are usually small holes and are locally distributed, the present invention has the following innovative features:

[0078] (1) The concept of dynamic permeability coefficient of defective geomembrane anti-seepage layer was proposed for the first time. In the prior art, geomembrane and its upper and lower protective layers and supporting layers are often considered separately, ignoring the interaction between the permeabilities of the materials in each layer. This has led to the long-term failure to solve the problem of estimating the amount of leakage of geomembrane defects, making it impossible to accurately assess the degree of defects in the geomembrane. The present invention regards the geomembrane and its upper and lower protective layers and supporting layers as an anti-seepage layer structure. Under laminar flow conditions, the flow of water through the 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 supporting layer under the membrane is relatively stable, the permeability coefficient of the anti-seepage layer can be regarded as approximately constant, thereby deepening the understanding of the permeability of the anti-seepage layer of defective geomembrane.

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

[0080] (3) A test method for the dynamic permeability coefficient of the defective geomembrane anti-seepage layer is proposed. The present invention draws on the coarse-grained soil permeability test method, combines the influencing factors of geomembrane defect leakage and coarse-grained soil permeability deformation, and innovatively proposes this test method. The feasibility of this test method is verified by analyzing the relative stability of the dynamic permeability coefficient of the defective geomembrane anti-seepage layer. At the same time, this method can reveal the changing law of the permeability coefficient, reflecting the creative value of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 :Schematic diagram of seepage characteristics of defective geomembrane anti-seepage layer;

[0082] Figure 2 : Isobar map of numerical simulation;

[0083] Figure 3 : Evolution diagram of permeability coefficient of defective geomembrane anti-seepage layer and reservoir water depth;

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

[0085] Figure 5 : Schematic diagram of the state of fine particles blocking pores in the permeability coefficient of the defective geomembrane anti-seepage layer;

[0086] Figure 6 : Schematic diagram of the permeability coefficient of the defective geomembrane anti-seepage layer, the loss of fine particles, and the increase of pores;

[0087] Figure 7 : Schematic diagram of the stability of the permeability coefficient and pore structure of the defective geomembrane anti-seepage layer;

[0088] In the figure: 2-1: top surface; 2-2: soil layer above geomembrane; 2-3: defective geomembrane; 2-4: soil layer below geomembrane; 2-5: laminar flow; 2-6: interface 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: supporting layer under membrane; 4-6: pores; 4-7: coarse particles; 4-8: fine particles. DETAILED DESCRIPTION

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

[0090] Embodiment: A method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer, wherein the geomembrane anti-seepage layer comprises a geomembrane, a geotextile, a sand material protective layer and a support layer under the membrane arranged in sequence from top to bottom, characterized in that the method comprises the following steps:

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

[0092] Prepare test materials, and ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and supporting layer under the membrane are consistent with the plan according to the geomembrane anti-seepage plan, and make a circular hole-shaped defect with a radius of R on the test geomembrane to obtain a defective geomembrane;

[0093] According to the particle grading curve of the original soil sample, the supporting layer under the membrane is divided into several layered samples, which are mixed evenly and filled in sequence. After each layer is filled, compaction operation is performed to ensure that the physical properties and particle grading of the supporting layer under the membrane are consistent with the original soil sample; a sand protective layer, a geotextile and a defective geomembrane are laid on the top of the supporting layer under the membrane in sequence to form a defective geomembrane anti-seepage layer;

[0094] The specimen is initially saturated, and the total thickness of the impermeable layer of the defective geomembrane is measured and recorded. The specimen is saturated with air-free water using the head saturation method;

[0095] Set up multi-level infiltration gradient parameters from small to large, and perform infiltration tests at each level of infiltration gradient in turn. The infiltration time at each level of infiltration gradient is controlled to be 30-60 minutes. The infiltration volume and seepage pressure data must be stable before entering the next stage; and record the seepage pressure, seepage volume and seepage phenomenon until the test is destroyed or the water head cannot continue to increase;

[0096] Calculate the permeability coefficient k of the defective geomembrane anti-seepage layer under each level of permeability gradient T And the corresponding dry density of the support layer under the membrane ρ d Specific gravity of soil particles G s , porosity ratio n, determine the dynamic permeability coefficient k T 's changing trend.

[0097] The present invention can simulate the permeability performance of the membrane material under actual working conditions in a laboratory environment and evaluate the stability and permeability of the anti-seepage layer under defective conditions by establishing a dynamic permeability coefficient test method for a defective geomembrane anti-seepage layer. The test method combines the physical properties of the support layer under the membrane with the change trend analysis of the permeability coefficient, and can accurately reflect the influence of membrane defects on the permeability performance of the geomembrane anti-seepage layer, providing a scientific basis for the anti-seepage effect of the geomembrane. The present invention has good applicability and can be widely used in the fields of civil engineering, environmental engineering, etc.

[0098] Furthermore, the determination of the particle gradation curve of the original soil sample comprises the following steps:

[0099] Select the original soil sample, sieve the soil sample, and determine the content of particles with different particle sizes;

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

[0101] According to the measured particle size distribution curve, the particle gradation information of the original soil sample is determined;

[0102] The particle grading data is recorded to provide benchmark data for the subsequent preparation of the support layer under the membrane, ensuring that the properties of the test soil sample are consistent with those of the original soil sample.

[0103] By measuring the particle size distribution curve, we can understand the particle size distribution of the soil sample in detail, and provide an accurate basis for the layered mixing and filling of the support layer under the membrane. The particle size distribution of the soil sample directly affects its permeability characteristics, so ensuring the consistency of the soil sample with the original soil sample helps to improve the reliability and repeatability of the test. In addition, the determination of the particle size distribution curve can also provide important data support for the subsequent permeability coefficient calculation and dynamic analysis, thereby enhancing the accuracy and scientificity of the entire test method.

[0104] Further, the preparation of the test material comprises the following steps:

[0105] According to the determined geomembrane anti-seepage scheme, prepare the corresponding test materials to ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and supporting layer under the membrane are consistent with the anti-seepage scheme;

[0106] A circular hole defect with a radius of R is made at the center of the test geomembrane by laser cutting or mechanical drilling; the circular hole defect is a circular hole with a radius R of 2-5 mm, and the hole position is not less than 10 mm from the edge of the membrane;

[0107] Assemble the defective geomembrane with the sand protection layer, geotextile and the supporting layer under the membrane in sequence to ensure that each layer meets the design requirements of the anti-seepage structure;

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

[0109] The present invention can simulate the damage of geomembranes that may occur in actual use, such as holes caused by wear during construction, transportation or long-term use, by accurately manufacturing defective geomembranes. The simulation of such defects can help evaluate the degradation law of geomembrane anti-seepage performance under different conditions, thereby providing a more scientific design basis for anti-seepage projects. The accuracy and consistency of defect size are ensured by laser cutting or mechanical drilling technology, thereby improving the reliability and reproducibility of experimental results.

[0110] Furthermore, the preparation of the defective geomembrane anti-seepage layer comprises the following steps:

[0111] According to the measured particle gradation curve of the original soil sample, the support layer under the membrane is divided into several layered samples, and the particle gradation of each layer is ensured to be consistent with the original soil sample;

[0112] According to the layering principle, the samples of the supporting layer under the membrane are mixed evenly layer by layer, and the mixing uniformity of each layer is controlled within ±2%;

[0113] Each layer of samples is filled in sequence and compacted using the standard compaction method to ensure that the dry density and compaction degree of each layer of soil samples meet the experimental requirements;

[0114] After each layer is filled and compacted, visually check whether each layer of soil is uniform and has no loose areas, and whether the compaction degree reaches the specified standard, to ensure that the compaction degree of each layer of soil meets the standard and there is no obvious loose phenomenon;

[0115] After completing the layered filling of the supporting layer under the membrane, the sand protection layer, geotextile and defective geomembrane are laid in sequence to form a complete defective geomembrane anti-seepage layer structure.

[0116] The steps for preparing the imperfect geomembrane anti-seepage layer are crucial, because the uniformity and compaction of the supporting layer under the membrane directly affect the accuracy and reliability of the permeability test. By strictly controlling the particle grading, mixing uniformity, and compaction of each layer of soil sample, the stability of the geomembrane anti-seepage layer structure can be ensured, and errors caused by uneven soil layers during the test can be avoided. In addition, refined operating steps can ensure that the physical properties of each layer of soil sample are consistent with the original soil sample, thereby ensuring the authenticity and validity of the test results.

[0117] Furthermore, the sample is initially saturated, comprising the following steps:

[0118] Before the test begins, the imperfect geomembrane anti-seepage layer is initially saturated with degassed water to ensure that the water flow can fully penetrate the geomembrane and the supporting layer below it;

[0119] Using the head saturation method, a head of water is applied to the test sample, and the water level is gradually increased until the sample reaches a fully saturated state;

[0120] During the saturation process, the sample's permeability was measured regularly and the required time was recorded to ensure that the sample's saturation met the experimental requirements;

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

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

[0123] The initial saturation of the sample is a key step to ensure the accuracy of the test results, especially in the test of the defective geomembrane anti-seepage layer, where the saturation directly affects the stability of the infiltration process. Using degassed water for saturation can reduce the interference of bubbles and avoid the error of bubbles in the water flow path on the infiltration flow. At the same time, the water temperature and room temperature are strictly controlled to ensure the stability of the experimental environment and further enhance the controllability and repeatability of the experiment.

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

[0125] Set the multi-level infiltration slope parameters from small to large, with the initial slope of 0.02-0.03, and gradually increase to the target slope, with the incremental value of each slope parameter being 0.05;

[0126] At each level of infiltration slope, the infiltration test is started and the infiltration test data at each level of slope is recorded, including the infiltration pressure, seepage volume and seepage phenomenon;

[0127] Measure and record the water pressure and water seepage after each penetration test, and observe the seepage phenomenon, including the turbidity of water, the emergence of bubbles, the jumping, movement or being carried out of fine particles by the water flow, the suspension of soil, and the change of the water level in the pressure measuring tube;

[0128] Each permeability test is carried out for 30 minutes to 1 hour, with a measurement interval of 10 to 20 minutes. If the water level and seepage volume are basically stable for three consecutive measurements, the next level of water head can be raised;

[0129] The penetration test is terminated until the test is destroyed or the water head can no longer increase.

[0130] The multi-level slope parameter setting of the permeability test is to simulate the permeability conditions under different water heads in order to comprehensively evaluate the permeability performance of the geomembrane anti-seepage 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 slope can reveal the permeability characteristics of the supporting layer under the membrane under different stress conditions. By observing the seepage phenomenon, we can further understand the influence mechanism of defective geomembranes on water flow, thereby providing strong data support for the subsequent permeability coefficient analysis.

[0131] Furthermore, the determination of the change trend of the dynamic permeability coefficient includes the following steps:

[0132] According to the recorded infiltration flow rate, infiltration pressure and other test data at each level of infiltration slope, Darcy's law is used to calculate the dynamic permeability coefficient k. T Calculation of

[0133] At the same time, the dry density of the support layer under the test membrane was measured. d Specific gravity of soil particles G sand porosity ratio n, and record their changes;

[0134] The permeability coefficient k for each level of permeability gradient T Perform statistical analysis to determine the permeability coefficient k T ;

[0135] According to the experimental results, the permeability coefficient k at each level of permeability slope is calculated using statistical methods. T The data were fitted to identify the permeability coefficient k T The changing trend and stability of geomembrane defects are evaluated to determine the stability and permeability of the anti-seepage layer.

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

[0137] During the permeation test, the flow pattern of water through the support layer under the membrane was analyzed based on the axisymmetric permeation model, and it was assumed that the seepage flow met the laminar flow conditions and satisfied Darcy's law.

[0138] Through the test data, combined with the seepage characteristics of the defective area of ​​the geomembrane, the stability of water permeability with different water heads is analyzed;

[0139] The permeability coefficient data at each level of permeability slope were fitted and analyzed using statistical methods to reveal the variation of permeability coefficient with water head, and the influence of the permeability of the coarse-grained soil layer under the membrane support layer and the loss of fine-grained soil on the permeability coefficient was 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 anti-seepage layer was evaluated to further verify the applicability and reliability of the permeability model.

[0141] The changing trend of the dynamic permeability coefficient is one of the core contents of the test method of the present invention. By using Darcy's law to calculate the permeability coefficient, combined with the physical properties of the supporting layer under the membrane (such as dry density, specific gravity of soil particles, etc.), the actual impact of membrane defects on the permeability of the anti-seepage layer can be revealed. The method of statistical analysis and data fitting can effectively identify the changing law of the permeability coefficient and provide accurate quantitative analysis for the evaluation of the anti-seepage performance of geomembranes. In addition, the fitting results can provide a basis for related engineering design and help optimize the structure and material selection of the anti-seepage layer.

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

[0143] The dry density ρ d Calculate as follows:

[0144]

[0145] Where: m dis the dry density of the sample (g / cm 3 ), r is the sample radius (cm), h0 is the sample initial height (cm);

[0146] The soil particle specific gravity G s is the mixing ratio of coarse and fine particles, calculated as follows:

[0147]

[0148] Where: G s1 G is the specific gravity of soil particles with a diameter greater than 5 mm. s2 is the specific gravity of soil particles with a particle size not greater than 5 mm, and P5 is the mass percentage (%) of soil particles with a particle size greater than 5 mm;

[0149] The void ratio n is calculated as follows:

[0150]

[0151] Where: n is the porosity (%), ρ w is the density of water (g / cm 3 );

[0152] The seepage velocity is calculated as follows:

[0153]

[0154] Where: v is the permeation velocity (cm / s), Q is the permeation volume (cm 3 ), t is time (s), A is sample area (cm 2 );

[0155] The infiltration slope should be calculated as follows:

[0156]

[0157] Where: i is the seepage slope, ΔH is the water head difference of the piezometer (cm), and L is the seepage path length corresponding to the water head difference ΔH (cm);

[0158] Permeability coefficient k T Then press calculate.

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

[0160] 1. Experimental material preparation and geomembrane defect preparation

[0161] According to the method of the present invention, the materials of geomembrane, geotextile, sand protection layer and supporting layer under the membrane are first selected, and their thicknesses are determined according to the design requirements. Then, a circular hole defect with a radius of 5 mm is made at the center of the test geomembrane by mechanical drilling. The size and position of the defect hole strictly meet the test requirements to ensure the consistency and accuracy of the test conditions.

[0162] 2. Sample Preparation

[0163] According to the particle grading curve of the original soil sample, the support layer under the membrane is divided into several layers, and mixed, filled and compacted layer by layer according to the layering principle to ensure that the physical properties of each layer in the geomembrane anti-seepage layer are consistent with the original soil sample. After completing the layered filling of the support layer under the membrane, the sand protection layer, geotextile and defective geomembrane are laid in sequence to form a complete defective geomembrane anti-seepage layer.

[0164] 3. Saturation process and penetration test

[0165] The defective geomembrane anti-seepage layer is initially saturated, and the head saturation method is used to ensure that the geomembrane and the supporting layer below it are completely saturated. Then, the permeability test is carried out step by step according to the designed multi-level permeability gradient. At each level of permeability gradient, the test time is controlled within 30 to 60 minutes, and the permeability and seepage pressure data must be stable before entering the next level.

[0166] 4. Infiltration phenomenon and water flow changes

[0167] During the permeability test, as the water pressure increases, the hydraulic gradient on the geomembrane gradually increases. When the hydraulic gradient exceeds the critical value of fine particles, fine particles begin to flow and enter the supporting layer below the membrane through the defects of the geomembrane. This process occurs in the contact layer above the membrane, which manifests as local erosion, while the contact layer below the membrane begins to fill densely. As the reservoir water level continues to rise, when the hydraulic gradient under the geomembrane is greater than the critical value, the fine particles in the brecciated soil under the membrane begin to flow away, and gradually cause the permeability to increase. Finally, at higher water levels, the fine particles in the brecciated soil layer continue to flow away, resulting in more pore channels to penetrate, and the permeability reaches a relatively stable state.

[0168] 5. Penetration model and data analysis

[0169] like Figure 1 and Figure 2 As shown in the figure, the experimental results show that with the change of water flow in the defect hole, the seepage pressure contour shows an arc-shaped diffusion trend centered on the defect. When the seepage pressure reaches 0.15kPa, the water flow basically turns into a laminar flow state, which is in line with Darcy's law. Based on these test data, the dynamic permeability coefficient is calculated by Darcy's law, and the change trend of the permeability coefficient is further analyzed by combining the dry density, soil particle specific gravity and porosity of the supporting layer under the membrane.

[0170] The variation law of dynamic permeability coefficient of defective geomembrane anti-seepage layer is as follows Figure 3 As shown in the figure, this indicates that the permeability effect caused by defects has significant piping characteristics. When the seepage passes through the defective area, the physical changes of the geomembrane and the supporting layer under the membrane are closely related to the permeability characteristics. By statistically analyzing the permeability coefficient data at each level of permeability gradient, the fitting results show that the permeability coefficient of the defective geomembrane anti-seepage layer increases with the increase of water head, especially in the process of fine particle loss, the permeability change is more significant.

[0171] 6. Conclusion

[0172] The experimental results of this example show that the dynamic permeability coefficient of the defective geomembrane anti-seepage layer under water pressure changes significantly, and the permeability increases with the appearance of geomembrane defects and the change of water head. At higher water levels, fine particles are lost from the coarse-grained soil layer of the supporting layer under the membrane, resulting in increased permeability, and this process shows obvious seepage characteristics, such as Figure 4-7 This experiment verifies the permeability model of the present invention and its application, indicating that the permeability change law of the defective geomembrane anti-seepage layer under different water head conditions is in line with expectations, and provides an experimental basis for the evaluation of the anti-seepage performance of the geomembrane.

[0173] Finally, it should be noted that the above 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 aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer, wherein the geomembrane anti-seepage layer comprises a geomembrane, a geotextile, a sand protective layer and a support layer under the membrane arranged in sequence from top to bottom, characterized in that: The method comprises the following steps: Determine the particle gradation curve of the original soil sample, obtain the particle size distribution information of the soil sample, provide the original soil sample information for the test process, and ensure that the properties of the test soil sample are consistent with those of the original soil sample; Prepare test materials, and ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and supporting layer under the membrane are consistent with the plan according to the geomembrane anti-seepage plan, and make a circular hole-shaped defect with a radius of R on the test geomembrane to obtain a defective geomembrane; According to the particle grading curve of the original soil sample, the supporting layer under the membrane is divided into several layered samples, which are mixed evenly and filled in sequence. After each layer is filled, compaction operation is performed to ensure that the physical properties and particle grading of the supporting layer under the membrane are consistent with the original soil sample; a sand protective layer, a geotextile and a defective geomembrane are laid on the top of the supporting layer under the membrane in sequence to form a defective geomembrane anti-seepage layer; The specimen is initially saturated, and the total thickness of the impermeable layer of the defective geomembrane is measured and recorded. The specimen is saturated with air-free water using the head saturation method; Set up multi-level infiltration gradient parameters from small to large, and perform infiltration tests at each level of infiltration gradient in turn. The infiltration time at each level of infiltration gradient is controlled to be 30-60 minutes. The infiltration volume and seepage pressure data must be stable before entering the next stage; and record the seepage pressure, seepage volume and seepage phenomenon until the test is destroyed or the water head cannot continue to increase; Calculate the permeability coefficient k of the defective geomembrane anti-seepage layer under each level of permeability gradient T And the corresponding dry density of the support layer under the membrane ρ d Specific gravity of soil particles G s , porosity ratio n, determine the dynamic permeability coefficient k T 's changing trend.

2. The method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 1, characterized in that: The method of determining the particle gradation curve of the original soil sample comprises the following steps: Select the original soil sample, sieve the soil sample, and determine the content of particles with different particle sizes; Use sieving method or laser particle size analysis method to obtain the particle size distribution curve of soil samples; According to the measured particle size distribution curve, the particle gradation information of the original soil sample is determined; The particle grading data is recorded to provide benchmark data for the subsequent preparation of the support layer under the membrane, ensuring that the properties of the test soil sample are consistent with those of the original soil sample.

3. The method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 1, characterized in that: The preparation of the test material comprises the following steps: According to the determined geomembrane anti-seepage scheme, prepare the corresponding test materials to ensure that the material type and thickness of the geomembrane, geotextile, sand protective layer and supporting layer under the membrane are consistent with the anti-seepage scheme; A circular hole defect with a radius of R is made at the center of the test geomembrane by laser cutting or mechanical drilling; the circular hole defect is a circular hole with a radius R of 2-5 mm, and the hole position is not less than 10 mm from the edge of the membrane; Assemble the defective geomembrane with the sand protection layer, geotextile and the supporting layer under the membrane in sequence to ensure that each layer meets the design requirements of the anti-seepage structure; Perform a visual inspection on the prepared defective geomembrane to ensure that the defect size and shape meet the test requirements.

4. The method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 1, characterized in that: The method for preparing the defective geomembrane anti-seepage layer comprises the following steps: According to the measured particle gradation curve of the original soil sample, the support layer under the membrane is divided into several layered samples, and the particle gradation of each layer is ensured to be consistent with the original soil sample; According to the layering principle, the samples of the supporting layer under the membrane are mixed evenly layer by layer, and the mixing uniformity of each layer is controlled within ±2%; Each layer of samples is filled in sequence and compacted using the standard compaction method to ensure that the dry density and compaction degree of each layer of soil samples meet the experimental requirements; After each layer is filled and compacted, visually check whether each layer of soil is uniform and has no loose areas, and whether the compaction degree reaches the specified standard, to ensure that the compaction degree of each layer of soil meets the standard and there is no obvious loose phenomenon; After completing the layered filling of the supporting layer under the membrane, the sand protection layer, geotextile and defective geomembrane are laid in sequence to form a complete defective geomembrane anti-seepage layer structure.

5. The method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 1, characterized in that: The sample is initially saturated, comprising the following steps: Before the test begins, the imperfect geomembrane anti-seepage layer is initially saturated with degassed water to ensure that the water flow can fully penetrate the geomembrane and the supporting layer below it; Using the head saturation method, a head of water is applied to the test sample, and the water level is gradually increased until the sample reaches a fully saturated state; During the saturation process, the sample's permeability was measured regularly and the required time was recorded to ensure that the sample's saturation met the experimental requirements; Measure and record the total thickness of the defective geomembrane anti-seepage layer to ensure that it meets the design requirements; During the saturation process, check the water temperature and room temperature regularly to ensure stable experimental conditions.

6. The method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 1, characterized in that: The penetration test comprises the following steps: Set the multi-level infiltration slope parameters from small to large, with the initial slope of 0.02-0.03, and gradually increase to the target slope, with the incremental value of each slope parameter being 0.05; At each level of infiltration slope, the infiltration test is started and the infiltration test data at each level of slope is recorded, including the infiltration pressure, seepage volume and seepage phenomenon; Measure and record the water pressure and water seepage after each penetration test, and observe the seepage phenomenon, including the turbidity of water, the emergence of bubbles, the jumping, movement or being carried out of fine particles by the water flow, the suspension of soil, and the change of the water level in the pressure measuring tube; Each permeability test is carried out for 30 minutes to 1 hour, with a measurement interval of 10 to 20 minutes. If the water level and seepage volume are basically stable for three consecutive measurements, the next level of water head can be raised; The penetration test is terminated until the test is destroyed or the water head can no longer increase.

7. The method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 1, characterized in that: The determination of the variation trend of the dynamic permeability coefficient comprises the following steps: According to the recorded infiltration flow rate, infiltration pressure and other test data at each level of infiltration slope, Darcy's law is used to calculate the dynamic permeability coefficient k. T Calculation of At the same time, the dry density of the support layer under the test membrane was measured. d Specific gravity of soil particles G s and porosity ratio n, and record their changes; The permeability coefficient k for each level of permeability gradient T Perform statistical analysis to determine the permeability coefficient k T ; According to the experimental results, the permeability coefficient k at each level of permeability slope is calculated using statistical methods. T The data were fitted to identify the permeability coefficient k T The changing trend and stability of geomembrane defects are evaluated to determine the stability and permeability of the anti-seepage layer.

8. The method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 7, characterized in that: The determination of the variation trend of the dynamic permeability coefficient comprises the following steps: During the permeation test, the flow pattern of water through the support layer under the membrane was analyzed based on the axisymmetric permeation model, and it was assumed that the seepage flow met the laminar flow conditions and satisfied Darcy's law. Through the test data, combined with the seepage characteristics of the defective area of ​​the geomembrane, the stability of water permeability with different water heads is analyzed; The permeability coefficient data at each level of permeability slope were fitted and analyzed using statistical methods to reveal the variation of permeability coefficient with water head, and the influence of the permeability of the coarse-grained soil layer under the membrane support layer and the loss of fine-grained soil on the permeability coefficient was evaluated based on the experimental results. At each water head level, the specific impact of geomembrane defects on the stability and permeability of the anti-seepage layer was evaluated to further verify the applicability and reliability of the permeability model.

9. A method for testing the dynamic permeability coefficient of a defective geomembrane anti-seepage layer according to claim 7 or 8, characterized in that: The dry density ρ d Calculate as follows: Where: m d is the dry density of the sample (g / cm 3 ), r is the sample radius (cm), h0 is the sample initial height (cm); The soil particle specific gravity G s is the mixing ratio of coarse and fine particles, calculated as follows: Where: G s1 G is the specific gravity of soil particles with a diameter greater than 5 mm. s2 is the specific gravity of soil particles with a particle size not greater than 5 mm, and P5 is the mass percentage (%) of soil particles with a particle size greater than 5 mm; The void ratio n is calculated as follows: Where: n is the porosity (%), ρ w is the density of water (g / cm 3 ); The seepage velocity is calculated as follows: Where: v is the permeation velocity (cm / s), Q is the permeation volume (cm 3 ), t is time (s), A is sample area (cm 2 ); The infiltration slope should be calculated as follows: Where: i is the seepage slope, ΔH is the water head difference of the piezometer (cm), and L is the seepage path length corresponding to the water head difference ΔH (cm); Permeability coefficient k T Then press calculate.

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