Test method for leakage stability of geomembrane defects in reservoir basin under simulated water level rise and fall conditions

Abstract

The invention discloses a test method for the leakage stability of geomembrane defects in a reservoir basin under simulated water level rise and fall conditions, including a pressure head system, a geomembrane defect leakage test system, and a measurement system. By applying variable head test conditions, the invention simulates the leakage process of geomembrane defects under water level rise, fall, and cyclic rise and fall in the actual reservoir basin project of a pumped storage power station. Through the change in the position of the dyed cushion material particles before and after the test, the radial migration distance of the cushion particles and the particle stability rate are obtained. Combining the size characteristics of the scour pit of the cushion, indicators are set to evaluate the seepage stability of the cushion after the leakage of the geomembrane defect, and the relationship between the leakage volume, the water head, and the characteristics of the geomembrane defect is established to quantitatively evaluate the leakage stability of the geomembrane defect under water head change, providing a theoretical basis for the anti-seepage design of geomembranes in reservoir basin projects, especially for the reservoir basin projects of pumped storage power stations with high anti-seepage requirements and large water level changes.

Description

Technical Field

[0001] The present invention relates to the field of geomembrane seepage prevention, in particular to a test method for the leakage stability of geomembrane defects in a reservoir basin under simulated water level rise and fall conditions. Background Art

[0002] Geomembrane is a new type of seepage prevention material made from polymer polymers by blow molding, calendering or brushing methods. It has the characteristics of excellent waterproof performance, strong adaptability to deformation, and obvious cost advantages. It has been widely used in seepage prevention projects such as reservoirs, cisterns and earth-rock dams. Especially in recent years, with the rapid construction of pumped storage power stations in China, geomembrane seepage prevention is adopted for the upper reservoirs of many power stations in the whole reservoir basin.

[0003] Due to reasons such as manufacturing processes and construction conditions, geomembranes in actual reservoir basin seepage prevention projects are inevitably damaged to varying degrees, such as being punctured, pierced, and welds being torn, and are prone to defects of various shapes such as circular holes, polygons and arcs. Under the action of water pressure, the concentrated leakage at the geomembrane defect site will scour the lower cushion layer, forming a scouring pit, causing the migration of cushion layer particles, resulting in the loss of cushion layer particles, making the geomembrane lose support, accelerating the expansion and evolution of geomembrane defects, further increasing the leakage volume of the defects, easily causing the leakage volume not to meet the requirements of reservoir basin seepage prevention, and directly affecting the seepage stability of the cushion layer material. Especially when the water pressure changes due to the change of water level, the cushion layer material is not easy to be stable, which may cause seepage failure and endanger the project safety.

[0004] Existing geomembrane defect leakage test devices mainly study the leakage volume of defects under constant head, and cannot simulate the operating characteristics of the reservoirs of pumped storage power stations with full reservoir basin geomembrane seepage prevention, such as water level changes such as rising, falling and cyclic storage and release of reservoir water; in addition, they cannot consider the influence of geomembrane defect leakage on the seepage stability of the cushion layer under the membrane, and lack quantitative research on the characteristics of scouring pits and the law of particle migration under the geomembrane after geomembrane defect leakage.

[0005] Therefore, it is necessary to design a test device and test method for the leakage stability of geomembrane defects in a reservoir basin under simulated water level rise and fall conditions. By applying variable head test conditions, simulate the leakage process of geomembrane defects under water level rise, fall and cyclic rise and fall in actual pumped storage power station reservoir basin projects. Through the position change of the dyed cushion layer particles before and after the test, obtain the radial migration distance of the cushion layer particles and the particle stability rate. Combining the size characteristics of the scouring pits in the cushion layer, set indicators to evaluate the seepage stability of the cushion layer after geomembrane defect leakage, and establish the relationship between the leakage volume, water head and geomembrane defect characteristics, and quantitatively evaluate the leakage stability of geomembrane defects under water head change, so as to provide a theoretical basis for the geomembrane seepage prevention design in reservoir basin projects, especially for the reservoir basin projects of pumped storage power stations with high seepage prevention requirements and large water level changes. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a test method for the leakage stability of geomembrane defects in the reservoir basin under simulated water level rise and fall conditions in view of the deficiencies of the above-mentioned prior art. The test method for the leakage stability of geomembrane defects in the reservoir basin under simulated water level rise and fall conditions simulates the leakage process of geomembrane defects under water level rise, fall and cyclic rise and fall in the actual pumped storage power station reservoir basin project by applying variable head test conditions. By the change of the position of the dyed cushion material particles before and after the test, the radial migration distance of the cushion particles and the particle stability rate are obtained. Combining the size characteristics of the cushion scouring pit, an index is set to evaluate the permeability stability of the cushion after the leakage of the geomembrane defect, and the relationship between the leakage volume, the water head and the characteristics of the geomembrane defect is established to quantitatively evaluate the leakage stability of the geomembrane defect under the change of the water head, providing a theoretical basis for the anti-seepage design of the geomembrane in the reservoir basin project, especially for the reservoir basin project of pumped storage power stations with high anti-seepage requirements and large water level changes.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A test method for the leakage stability of geomembrane defects in the reservoir basin under simulated water level rise and fall conditions includes the following steps.

[0009] Step 1, prepare the dyed cushion material: Prepare the cushion material from gravel and sand according to the set gradation, and divide the prepared cushion material into n groups equally, and each group is dyed with a different color.

[0010] Step 2, set the cushion chamber area and fill the cushion material: Set the cushion chamber as a transparent cylindrical barrel with an inner diameter of R. Then, with the axis of the cushion chamber as the center, divide it into n cushion areas at equal intervals from the inside to the outside, and mark them as cushion areas V1 to V n ; Fill the n groups of different-colored cushion materials prepared in Step 1 into the cushion areas V1 to V n respectively, and compact them layer by layer, and level the surface to form a cushion; the colors of the cushion materials in each cushion area are represented as C1 to C n , and the weights of the cushion material particles are represented as

[0011] Step 3, place the defective geomembrane: Lay the geomembrane with defects flat on the surface of the filled cushion, and make it closely fit with the cushion, and make the geomembrane defect located on the axis of the cushion chamber.

[0012] Step 4, install the pressure head system: Install the pressure head system above the defective geomembrane, and apply a pressure of a set water head to the cushion through the pressure head system.

[0013] Step 5, conduct the leakage test of the geomembrane defect, which specifically includes the following steps:

[0014] Step 5-1, Apply the initial pressure head h0: Use a pressure head system to apply the set initial pressure head h0 to the cushion chamber.

[0015] Step 5-2, Monitor the initial leakage rate: Use a flow monitor set at the bottom of the cushion chamber to monitor and record the initial leakage rate of the cushion chamber at set intervals; when the initial leakage rate remains stable and unchanged, it is recorded as the initial stable leakage rate q0.

[0016] Step 5-3, Variable head test: Variable head includes monotonic variable head and cyclic variable head.

[0017] Monotonic variable head: The pressure head system changes the pressure head at a set head change rate v until the final pressure head h1 is reached.

[0018] Cyclic variable head: The pressure head system changes the pressure head to h1 at a set head change rate v1, and then changes it back to h0 at a rate v2, and cycles the head change like this until the number of cycles reaches the set value n. 循 .

[0019] During the test, the pressure water will leak into the cushion through the defective part of the geomembrane and form an erosion pit on the cushion surface corresponding to the defective part of the geomembrane.

[0020] Step 5-4, Monitor the variable head leakage rate: During the process of the pressure head change, use a flow monitor to monitor and record the leakage rate at each moment; let the leakage rate corresponding to the pressure head h(t) at time t be q(t), and when the final pressure head no longer changes, the final stable leakage rate q1 is obtained and the test ends.

[0021] Step 6, Collect cushion erosion data: Cushion erosion data includes cushion erosion pit data, cushion radial migration data, and cushion erosion particle stability data. The specific collection method includes the following steps:

[0022] Step 6-1, Collect cushion erosion pit data: Remove the pressure head system, take out the defective geomembrane, and measure the geometric dimensions of the erosion pits on the cushion surface to obtain the erosion pit data;

[0023] Step 6-2, Collect cushion radial migration data: Observe and measure the spatial position distribution of each cushion material C1 to C n , and then combine with the initial filling positions of each cushion material C1 to C n to obtain the maximum radial migration distances l1 to l n of the cushion materials C1 to C n .

[0024] Step 6-3: Collect data on the stability of the cushion layer scouring particles: Take and dry the cushion layer materials in each cushion layer area and weigh them to obtain the particle weight Δ of the cushion layer material of the C color in the i-th cushion layer area, where 1 ≤ i ≤ n. i of the cushion layer material of the C color i ; where 1 ≤ i ≤ n.

[0025] Step 7: Evaluate the seepage stability of the cushion layer, which specifically includes the following steps:

[0026] Step 7-1: Set the comprehensive evaluation index K for the stability of the cushion layer: Use the comprehensive evaluation index K of the cushion layer stability to judge the seepage stability of the cushion layer after leakage of the geomembrane defect; among them, the calculation formula of the K value is:

[0027]

[0028] Among them:

[0029]

[0030]

[0031]

[0032] In the formula, δ1 is the scouring degree index of the cushion layer scouring pit, which is the ratio of the geometric dimension data of the scouring pit in Step 6-1 to the size defect characteristic data of the geomembrane.

[0033] δ2 is the radial migration index of the cushion layer particles; l i is the maximum radial migration distance of the cushion layer material particles in the i-th cushion layer area.

[0034] δ3 is the cushion layer particle stability rate index; is the cushion layer particle stability rate of the i-th cushion layer area.

[0035] Step 7-2: Evaluate the seepage stability of the cushion layer: If K ≤ 3, it is judged that the seepage stability of the cushion layer is good; if 3 < K ≤ 6, it is judged that the seepage stability of the cushion layer is better; if K > 6, it is judged that the seepage stability of the cushion layer is poor.

[0036] It also includes Step 8: Establish a relationship model between the leakage rate q(t), the pressure head h(t), and the geomembrane defect characteristics.

[0037] In Step 3, when the geomembrane defect is a quasi-circular hole and the equivalent aperture of the quasi-circular hole is d, then in Step 6-1, the scouring pit on the cushion layer surface is a quasi-hemispherical scouring pit, and the scouring pit data includes the inner diameter d k and the depth h 1k of the quasi-hemispherical scouring pit; furthermore, in Step 7-1, the calculation formula of δ1 is:

[0038]

[0039] In Step 8, the relationship model expression among q(t), h(t), and the geomembrane defect characteristics is:

[0040]

[0041] where α1 and λ1 are fitting parameters obtained by fitting multiple groups of experimental data; T is the total duration of the experiment.

[0042] In Step 3, the geomembrane defect is a gap defect, and the equivalent length of the gap defect is The equivalent width of the gap defect is Then in Step 6-1, the scour pit on the cushion layer surface is a semi-elliptical scour pit, and the scour pit data includes the major axis a k of the semi-elliptical scour pit, the minor axis b k of the semi-elliptical scour pit, and the depth h 2k of the semi-elliptical scour pit; furthermore, in Step 7-1, the calculation formula for δ1 is:

[0043]

[0044] In Step 8, the relationship model expression among q(t), h(t), and the geomembrane defect characteristics is:

[0045]

[0046] where α2, β2, and λ2 are fitting parameters obtained by fitting multiple groups of experimental data; T is the total duration of the experiment.

[0047] In Step 5, by adjusting h0, v, h1, and n 循 , the simulation of three operating conditions in the pumped-storage power station project can be achieved; among them, the three operating conditions include the water level rising condition, the water level falling condition, and the reservoir water storage and release cycle condition; the simulation methods for the three operating conditions are as follows:

[0048] A. Water level rising condition: The initial pressure head h0 < the final pressure head h1, the water head change rate v > 0, and the number of cycles n 循 = 0.

[0049] B. Water level falling condition: The initial pressure head h0 > the final pressure head h1, the water head change rate v > 0, and the number of cycles n 循 = 0.

[0050] C. Reservoir water storage and release cycle condition: The initial pressure head h0 and the final pressure head h1 are different reservoir basin characteristic water levels, and the number of cycles n 循 > 0.

[0051] In Step 5-4, based on the pressure heads and corresponding leakage amounts recorded at each moment, a q(t)-h(t) relationship curve is plotted to analyze the influence of the water head magnitude and the water head change rate on the change of the leakage amount under different variable water head test conditions.

[0052] The test is carried out using a leakage test device for geomembrane defects in the reservoir basin. Among them, the leakage test device for geomembrane defects in the reservoir basin includes a geomembrane defect leakage test system, a pressure head system, and a measurement system.

[0053] The geomembrane defect leakage test system includes a base, a cushion chamber, and a geomembrane.

[0054] The cushion chamber is coaxially installed on the base, and the cushion chamber is a transparent cylindrical barrel; different colored cushion materials are filled in the cushion chamber at equal intervals; a permeable plate is arranged at the bottom of the cushion chamber.

[0055] The geomembrane is laid on the top of the cushion chamber, and the geomembrane has a defect located on the axis of the cushion chamber.

[0056] The pressure head system includes a water pressure chamber and a water tank; the water pressure chamber is coaxially and sealedly installed on the top of the geomembrane; the water tank is used to supply water to the water pressure chamber.

[0057] The measurement system includes a flow monitor arranged below the permeable plate for detecting the leakage amount of the cushion chamber.

[0058] The pressure head system further includes a hydraulic controller for controlling the water head pressure input by the water tank to the water pressure chamber; the measurement system further includes a computer, and both the hydraulic controller and the flow monitor are connected to the computer.

[0059] The present invention has the following beneficial effects:

[0060] 1. The present invention applies variable water head test conditions through a hydraulic control box, simulates the leakage process of geomembrane defects under the conditions of water level rise, fall, and reservoir water storage and release cycles in the actual pumped-storage power station reservoir basin project, and monitors the changes in water head and leakage amount during the test at a set interval to obtain the change curve of the leakage amount of defects with the water head under variable water head test conditions, providing a theoretical basis for the geomembrane anti-seepage design of the pumped-storage power station reservoir basin project.

[0061] 2. The present invention divides the cushion chamber area into several regions from the inside to the outside and fills the dyed cushion materials in different regions. By the change of the position of the dyed cushion materials before and after the test, the change of the spatial distribution of cushion particles caused by defect leakage is obtained, the migration law of cushion particles caused by geomembrane defect leakage is quantitatively characterized, and based on the quantitative test results such as the characteristics of the cushion scouring pit, the radial migration distance of cushion particles, and the retention rate of cushion particles, indicators are set to comprehensively evaluate the seepage stability of the cushion after geomembrane defect leakage.

[0062] 3. By setting the pore-like defects and seam-like defects of the geomembrane, the irregular-shaped geomembrane defects caused by different failure forms in actual engineering are simulated. Based on the area equivalence principle, the equivalent pore diameter, equivalent seam length, and equivalent seam width are proposed to quantitatively characterize the sizes of geomembrane defects with different shapes, and the relationship between the total leakage volume, test water head, and the shape and size of the geomembrane defects is established. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is a structural diagram of the test device for simulating the leakage stability of geomembrane defects in the reservoir basin under the condition of water level rise and fall according to the present invention.

[0064] Figure 2 It is a schematic diagram of the regional division of the cushion chamber according to the present invention; among them, Figure (a) shows a sectional view of the cushion chamber area divided along the diameter direction; Figure (b) shows a top view of the cushion chamber area division.

[0065] Figure 3 It is a schematic diagram of the scouring pit of the hemispherical cushion and the migration of cushion particles in the embodiment of the present invention.

[0066] Figure 4 It is a top view of the scouring pit of the hemispherical cushion in the embodiment of the present invention.

[0067] Figure 5 It is a top view of the geomembrane defect being a circular-like hole in the embodiment of the present invention.

[0068] Figure 6 It is a schematic diagram of the scouring pit of the semi-elliptical cushion and the migration of cushion particles in the embodiment of the present invention.

[0069] Figure 7 It is a top view of the scouring pit of the semi-elliptical cushion in the embodiment of the present invention.

[0070] Figure 8 It is a top view of the geomembrane defect being a gap in the embodiment of the present invention.

[0071] Among them: 1. Cushion chamber; 2. Water pressure chamber; 3. Geomembrane; 4. Defect; 5. Base; 6. Cushion material; 7. Scouring pit; 8. Hydraulic controller; 9. Water tank; 10. Water delivery pipe; 11. Permeable plate; 12. Flow monitor; 13. Computer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0072] The present invention will be further described in detail below in conjunction with the drawings and specific preferred embodiments.

[0073] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "left side", "right side", "upper part", "lower part", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second", etc. do not represent the importance of components, so it cannot be understood as a limitation to the present invention. The specific dimensions adopted in this embodiment are only for illustrating the technical solution by way of example and do not limit the protection scope of the present invention.

[0074] As Figure 1 shown, a test device for leakage of geomembrane defects in a reservoir basin under simulated water level rise and fall conditions includes a geomembrane defect leakage test system, a pressure head system, and a measurement system.

[0075] The geomembrane defect leakage test system includes a base 5, a cushion chamber 1, and a geomembrane 3.

[0076] The cushion chamber is coaxially installed on the base, and the cushion chamber is preferably a transparent cylindrical barrel with an inner diameter of R; different colored cushion materials 6 are filled in the cushion chamber at equal intervals; a permeable plate 11 is provided at the bottom of the cushion chamber.

[0077] The geomembrane is laid on the top of the cushion chamber, and the geomembrane has a defect 4 located on the axis of the cushion chamber.

[0078] The pressure head system includes a water pressure chamber 2, a hydraulic controller 8, and a water tank 9; the water pressure chamber is coaxially and hermetically installed on the top of the geomembrane; the water tank supplies water to the water pressure chamber through a water delivery pipe ၁၀; the hydraulic controller is used to control the head pressure input by the water tank to the water pressure chamber.

[0079] The measurement system includes a flow monitor 12 and a computer 13 provided below the permeable plate. Among them, the flow monitor is used to detect the leakage volume of the cushion chamber; the computer is respectively connected to the hydraulic controller and the flow monitor.

[0080] A test method for the leakage stability of geomembrane defects in a reservoir basin under simulated water level rise and fall conditions includes the following steps.

[0081] Step 1, prepare dyed cushion materials: Prepare cushion materials by forming gravel according to a set gradation, and divide the prepared cushion materials into n groups equally. In this embodiment, preferably n = 4. Each group is dyed with a different color.

[0082] Step 2, set the cushion chamber area and fill the cushion materials

[0083] As Figure 2 shown, with the axis of the cushion chamber as the center, it is equally divided into n (preferably 4) cushion areas at equal intervals from the inside to the outside, and is sequentially marked as cushion areas V1 to V n; The n groups of cushion materials with different colors prepared in Step 1 are respectively filled in the cushion areas V1 - V n and are compacted layer by layer, and the surface is leveled to form a cushion; the colors of the cushion materials in each cushion area are respectively represented as C1 - C n , and the particle weights of the cushion materials are respectively represented as Among them, the color of the cushion material in the i-th cushion area is represented as C i , and the particle weight of the cushion material in the i-th cushion area is represented as

[0084] Step 3, Place the defective geomembrane: Lay the defective geomembrane flat on the surface of the completed cushion, and closely fit it with the cushion, and make the defect of the geomembrane located on the axis of the cushion chamber. In this embodiment, it is preferred that the thickness of the geomembrane is 1 mm.

[0085] As Figure 5 and Figure 8 shown, the defect of the geomembrane in the present invention is preferably a quasi-circular hole or a crack.

[0086] Step 4, Install the pressure head system: Install the pressure head system above the defective geomembrane, and apply the pressure of the set head to the cushion chamber through the pressure head system.

[0087] Step 5, Conduct the leakage test of the geomembrane defect, which specifically includes the following steps:

[0088] Step 5-1, Apply the initial pressure head h0: Use the pressure head system to apply the set initial pressure head h0 to the cushion.

[0089] Step 5-2, Monitor the initial leakage rate: Use the flow monitor set at the bottom of the cushion chamber to monitor (such as measuring once every 1 minute, etc.) and record the initial leakage rate of the cushion chamber at the set interval; when the initial leakage rate remains stable and unchanged, it is recorded as the initial stable leakage rate q0.

[0090] Step 5-3, Variable head test: The variable head includes monotonic variable head and cyclic variable head.

[0091] Monotonic variable head: The pressure head system changes the pressure head at the set head change rate v until the final pressure head h1 is reached.

[0092] Cyclic variable head: The pressure head system changes the pressure head to h1 at the set head change rate v1, and then changes it to h0 at the rate v2, and so on to cycle the change of the head until the number of cycles reaches the set value n 循 .

[0093] During the test, the pressure water will leak through the defective part of the geomembrane into the cushion, and scour pits will be formed on the surface of the cushion corresponding to the defective part of the geomembrane.

[0094] Step 5-4, variable head leakage measurement: During the process of pressure head change, use a flow monitor to monitor and record the leakage at each moment; let the leakage corresponding to the pressure head h(t) at time t be q(t), and when the final pressure head no longer changes, the final stable leakage is q1, and the test ends.

[0095] In the present invention, by adjusting h0, v, h1, and n 循 , the simulation of three operating conditions in the pumped storage power station project can be achieved; among them, the three operating conditions include the water level rising condition, the water level falling condition, and the reservoir water storage and release cycle condition; the simulation methods for the three operating conditions are as follows:

[0096] A. Water level rising condition: The initial pressure head h0 < the final pressure head h1, the head change rate v > 0, and the number of cycles n 循 = 0.

[0097] B. Water level falling condition: The initial pressure head h0 > the final pressure head h1, the head change rate v > 0, and the number of cycles n 循 = 0.

[0098] C. Reservoir water storage and release cycle condition: The initial pressure head h0 and the final pressure head h1 are different characteristic water levels of the reservoir basin (e.g., the initial pressure head is the normal storage water level of the reservoir basin, and the final pressure head is the dead water level of the reservoir basin), and the number of cycles n 循 > 0.

[0099] Step 6, collection of cushion scour data: The cushion scour data includes cushion scour pit data, cushion radial migration data, and cushion scour particle stability data. The specific collection method includes the following steps:

[0100] Step 6-1, collection of cushion scour pit data: Remove the pressure head system, take out the defective geomembrane, and measure the geometric dimensions of the scour pits on the cushion surface to obtain the scour pit data.

[0101] The above-mentioned scour pit shape needs to be determined specifically according to the type of geomembrane defect.

[0102] A. When the geomembrane defect is a quasi-circular hole, the scour pit is a quasi-hemispherical scour pit as shown in Figure 3 and Figure 4 . The scour pit data includes the inner diameter d k of the quasi-hemispherical scour pit and the depth h 1k of the quasi-hemispherical scour pit.

[0103] B. When the geomembrane defect is a gap, the scour pit is as shown in Figure 5 and Figure 6The semi-ellipsoid-shaped scouring pit shown, and the scouring pit data includes the major axis a of the semi-ellipsoid-shaped scouring pit k , the minor axis b of the semi-ellipsoid-shaped scouring pit k and the depth h of the semi-ellipsoid-shaped scouring pit 2k .

[0104] Step 6-2, Collect the radial migration data of the cushion layer: Observe and measure the spatial position distribution of each cushion material C1 to C n , and then combine with the initial filling positions of each cushion material C1 to C n to obtain the maximum radial migration distances l1 to l n of the cushion materials C1 to C n .

[0105] Step 6-3, Collect the stability data of the scoured particles of the cushion layer: Take and dry and weigh the cushion materials in each cushion layer area respectively, and obtain that the particle weight of the cushion materials in the i-th cushion layer area is Δ i ; where, 1 ≤ i ≤ n.

[0106] Step 7, Evaluate the seepage stability of the cushion layer, which specifically includes the following steps:

[0107] Step 7-1, Set the comprehensive evaluation index K of the cushion layer stability: Use the comprehensive evaluation index K of the cushion layer stability to judge the seepage stability of the cushion layer after leakage of the geomembrane defect; where, the calculation formula of the K value is:

[0108]

[0109] Where:

[0110]

[0111]

[0112]

[0113] In the formula, δ2 is the radial migration index of the cushion layer particles; l i is the maximum radial migration distance of the cushion layer particles in the i-th cushion layer area.

[0114] δ3 is the stable rate index of the cushion layer particles; is the stable rate of the cushion layer particles in the i-th cushion layer area.

[0115] The above δ1 is the scouring degree index of the scouring pit of the cushion layer, which is the ratio of the scouring pit data to the geomembrane defect characteristic data. The specific calculation methods are as follows two.

[0116] A. The geomembrane defect is a circular hole, and the equivalent aperture of the circular hole is d, then the calculation formula of δ1 is:

[0117]

[0118] B. The defect of the geomembrane is a crack defect, and the equivalent length of the crack defect is The equivalent width of the crack defect is Then the calculation formula of δ1 is:

[0119]

[0120] Step 7-2. Evaluation of the seepage stability of the cushion layer: If K ≤ 3, it is judged that the seepage stability of the cushion layer is good; if 3 < K ≤ 6, it is judged that the seepage stability of the cushion layer is relatively good; if K > 6, it is judged that the seepage stability of the cushion layer is poor. [[ID=!16]]

[0121] Step 8. Establish a relationship model among the leakage rate q(t), the pressure head h(t), and the geomembrane defect characteristics.

[0122] A. When the geomembrane defect is a quasi-circular hole, the expression of the relationship model among q(t), h(t), and the geomembrane defect characteristics is:

[0123]

[0124] In the formula, α1 and λ1 are fitting parameters obtained by fitting multiple groups of test data; T is the total test duration.

[0125] B. When the geomembrane defect is a crack, the expression of the relationship model among q(t), h(t), and the geomembrane defect characteristics is:

[0126]

[0127] In the formula, α2, β2, and λ2 are fitting parameters obtained by fitting multiple groups of test data.

[0128] The present invention simulates the leakage process of the geomembrane defect under the rising, falling, and cyclic rising and falling of the water level in the actual pumped-storage power station reservoir basin project by applying variable-head test conditions. By the position change of the dyed cushion material particles before and after the test, the radial migration distance and particle stability rate of the cushion particles are obtained. Combining with the size characteristics of the scour pit of the cushion layer, indicators are set to evaluate the seepage stability of the cushion layer after the leakage of the geomembrane defect, and the relationship among the leakage rate, the water head, and the geomembrane defect characteristics is established to quantitatively evaluate the leakage stability of the geomembrane defect under the change of the water head, providing a theoretical basis for the geomembrane anti-seepage design in the reservoir basin project, especially for the reservoir basin project of the pumped-storage power station with high anti-seepage requirements and large water level changes.

[0129] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solution of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A method for testing geomembrane defects and leakage in a reservoir basin under simulated water level fluctuation conditions, characterized by: The steps include: Step 1: preparing dyed cushion materials: preparing sand and gravel according to a set gradation to form cushion materials, and dividing the prepared cushion materials into n groups, each group being dyed into a different color; Step 2: Set the cushion chamber area and fill the cushion material: Assume that the cushion chamber is a transparent cylinder with an inner diameter of R. Then, with the axis of the cushion chamber as the center, it is divided into n cushion areas from the inside to the outside at equal distances, and marked as cushion areas V1 to V n ; The n groups of cushion materials of different colors prepared in step 1 are filled in the cushion areas V1 to V n The cushion layer is formed by compacting the material layer by layer and leveling the surface. The cushion layer material colors in each cushion layer area are represented by C1 to C n , the weight of the cushion material particles is expressed as Step 3: Place the defective geomembrane: Lay the defective geomembrane flat on the surface of the completed cushion layer, making it fit tightly with the cushion layer, and make the defect of the geomembrane be located on the axis of the cushion layer chamber; Step 4: Install the pressure head system: Install the pressure head system above the defective geomembrane, and apply the set head pressure to the cushion layer through the pressure head system; Step 5: Conduct a geomembrane defect leakage test, which specifically includes the following steps: Step 5-1, applying an initial pressure head h0: using a pressure head system, applying a set initial pressure head h0 to the cushion chamber; Step 5-2, monitoring the initial leakage: using a flow monitor installed at the bottom of the cushion chamber, monitor and record the initial leakage of the cushion chamber at set intervals; when the initial leakage remains stable, it is recorded as the initial stable leakage q0; Step 5-3, variable head test: variable head includes monotonic variable head and cyclic variable head; Monotonic variable head: The pressure head system changes the pressure head according to the set head change rate v until it reaches the final pressure head h1; Cyclic head change: The pressure head system changes the pressure head to h1 at the set head change rate v1, and then changes it to h0 at the rate v2, and changes the head in this way until the number of cycles reaches the set value n 循 ; During the test, pressurized water will leak into the cushion layer through the defective parts of the geomembrane and form scour pits on the cushion layer surface corresponding to the defective parts of the geomembrane; Step 5-4, monitoring leakage under variable head conditions: During the pressure head change process, a flow monitor is used to monitor and record the leakage at each moment. Let the leakage corresponding to the pressure head h(t) at time t be q(t). When the pressure head stops changing, the final stable leakage is q1, and the test ends. Step 6: Collect cushion scour data: The cushion scour data includes cushion scour pit data, cushion radial migration data, and cushion scour particle stability data. The specific collection method includes the following steps: Step 6-1, collect cushion scour pit data: remove the pressure head system, remove the defective geomembrane, and measure the geometric dimensions of the scour pit on the cushion surface to obtain the scour pit geometric dimension data; Step 6-2, collect cushion radial migration data: observe and measure the radial migration data of each cushion material C1~C n The spatial distribution of each cushion material C1~C n The initial filling position is obtained by n The maximum radial migration distance l1~l n Step 6-3, collect cushion scour particle stability data: take out the cushion material in each cushion area and dry and weigh it, and get the C in the i-th cushion area i Color bedding material particle weight Δ i ; Where, 1≤i≤n; Step 7: Evaluation of cushion layer permeability stability, specifically including the following steps: Step 7-1. Set the comprehensive evaluation index K of cushion stability: Use the comprehensive evaluation index K of cushion stability to judge the cushion permeability stability after the geomembrane defect leakage; the calculation formula of K value is: in: Where δ1 is the scour degree index of the cushion scour pit, which is the ratio of the scour pit geometric size data in step 6-1 to the geomembrane defect size characteristic data; δ2 is the radial migration index of cushion particles; l i is the maximum radial migration distance of the cushion material particles in the ith cushion area; δ3 is the index of the stability rate of cushion particles; is the cushion particle stability rate of the ith cushion region; Step 7-2, cushion permeability stability evaluation: If K≤3, the cushion permeability stability is good; if 3<K≤6, the cushion permeability stability is relatively good; if K>6, the cushion permeability stability is poor.

2. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 1, characterized in that: The method also includes step 8, establishing a relationship model between leakage q(t), pressure head h(t) and geomembrane defect characteristics.

3. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 1 or 2, characterized in that: In step 3, if the geomembrane defect is a quasi-circular hole and the equivalent aperture of the quasi-circular hole is d, then in step 6-1, the scour pit on the cushion surface is a quasi-hemispherical scour pit. The scour pit data includes the inner diameter d of the quasi-hemispherical scour pit. k and the depth of the hemispherical scour pit h 1k ; Furthermore, in step 7-1, the calculation formula of δ1 is:

4. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 2, characterized in that: In step 8, the relationship model expression between q(t), h(t) and geomembrane defect characteristics is: Where α1 and λ1 are fitting parameters obtained by fitting multiple sets of test data; T is the total test time.

5. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 1 or 2, characterized in that: In step 3, the geomembrane defect is a gap defect, and the equivalent length of the gap defect is The equivalent width of the gap defect is In step 6-1, the scour pit on the cushion surface is a semi-ellipsoidal scour pit, and the scour pit data includes the long axis a of the semi-ellipsoidal scour pit. k 、Semi-ellipsoidal scour pit short axis b k and the depth of the semi-ellipsoidal scour pit h 2k ; Furthermore, in step 7-1, the calculation formula of δ1 is:

6. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 5, characterized in that: In step 8, the relationship model expression between q(t), h(t) and geomembrane defect characteristics is: Where α2, β2, and λ2 are fitting parameters obtained by fitting multiple sets of test data; T is the total test duration.

7. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 1, characterized in that: In step 5, by adjusting h0, v, h1 and n 循 , which can simulate three operating conditions in pumped storage power station projects; the three operating conditions include water level rising condition, water level falling condition and reservoir water storage and discharge cycle condition; the simulation methods of the three operating conditions are: A. Water level rising condition: initial pressure head h0 < final pressure head h1, head change rate v > 0, number of cycles n 循 =0; B. Water level drop condition: initial pressure head h0>final pressure head h1, head change rate v>0, number of cycles n 循 =0; C. Reservoir water storage and discharge cycle conditions: initial pressure head h0 and final pressure head h1 are different characteristic water levels of the reservoir basin, and the number of cycles n 循 >0.

8. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 1, characterized in that: In step 5-4, based on the pressure head and corresponding leakage recorded at each moment, a q(t)-h(t) relationship curve is drawn to analyze the effects of the head size and head change rate on the leakage change under different variable head test conditions.

9. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 1, characterized in that: The test is conducted using a reservoir basin geomembrane defect leakage test device, which includes a geomembrane defect leakage test system, a pressure head system, and a measurement system. The geomembrane defect leakage test system includes a base, a cushion chamber and a geomembrane; The cushion chamber is coaxially installed on the base and is a transparent cylindrical tube; cushion materials of different colors are filled in equidistant partitions in the cushion chamber; a permeable board is provided at the bottom of the cushion chamber; The geomembrane is laid on top of the cushion chamber, and the geomembrane has a defect located on the axis of the cushion chamber; The pressure head system includes a water pressure chamber and a water tank; the water pressure chamber is coaxially sealed and installed on the top of the geomembrane; the water tank is used to supply water to the water pressure chamber; The measuring system includes a flow monitor arranged below the permeable plate for detecting leakage in the cushion chamber.

10. The method for testing reservoir basin geomembrane defects and leakage under simulated water level fluctuation conditions according to claim 9, characterized in that: The pressure head system also includes a hydraulic controller, which is used to control the head pressure input from the water tank to the water pressure chamber; the measurement system also includes a computer, and the hydraulic controller and the flow monitor are both connected to the computer.

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