Method for selecting a protective layer under a geomembrane under the action of circulating water head

Abstract

This invention belongs to the field of hydraulic engineering technology and provides a method for selecting a protective layer under geomembrane under circulating water head. The method includes the following steps: conducting stress-induced damage tests on geomembranes with different combinations of protective layer thickness and circulating water head characteristics on a granular cushion layer; establishing a quantitative relationship between the protective layer thickness and circulating water head characteristics to prevent geomembrane stress-induced damage; plotting a surface showing the relationship between circulating water head conditions and the thickness of the protective layer; defining the stress-induced damage conditions of the geomembrane; and determining the minimum thickness of different types of protective layers based on the circulating water head magnitude, duration, and cycle in actual engineering projects, thereby selecting the appropriate protective layer for the geomembrane. This invention has significant scientific research value and engineering application value for the selection and thickness design of protective layers to avoid geomembrane damage in practical engineering projects.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy engineering technology, and specifically relates to a method for selecting a protective layer under a geomembrane under the action of circulating water head. Background Technology

[0002] Geomembranes have excellent seepage prevention properties and are often used as seepage barriers in water conservancy, geotechnical and other engineering projects. For example, geomembranes are used as seepage barriers for the entire reservoir basin, with significant seepage prevention effects; in water storage ponds, geomembranes can effectively reduce water leakage losses and improve water resource utilization efficiency; in landfills, geomembranes can prevent leachate from polluting groundwater and avoid ecological damage.

[0003] In practical engineering applications, geomembranes face various complex stress environments, among which circulating water head is a common and significant factor. This is particularly true in projects such as pumped-storage power station reservoirs and flood control reservoirs, where periodic rises and falls in water level cause alternating stress on the geomembrane due to the circulating water head. When the water level is high or the water head fluctuation is large, the geomembrane will bear significant local tensile stress under the support of the underlying granular cushion layer, easily leading to damage. This not only severely reduces its seepage prevention effect but also triggers a series of engineering safety issues. To prevent geomembrane damage under stress, a lower protective layer is usually installed below the geomembrane. This lower protective layer acts as a buffer, dispersing the stress on the geomembrane and thus reducing the risk of damage.

[0004] In existing technologies, the selection of the lower protective layer thickness mainly relies on empirical methods. However, due to significant differences in the granular cushion conditions and circulating head characteristics of different projects, traditional methods cannot accurately account for the influence of these uncertainties, making it difficult to guarantee the rationality and reliability of the selected thickness. Furthermore, current research primarily focuses on the stress conditions of the geomembrane itself, lacking quantitative research on the relationship between the risk of geomembrane damage on granular cushion layers and the thickness of the protective layer and circulating head characteristics. This has resulted in the absence of a scientific and complete method for selecting the thickness of the lower protective layer for geomembranes.

[0005] Therefore, it is necessary to propose a method for selecting the lower protective layer of geomembrane under circulating water head. This method involves conducting stress-induced failure tests on geomembranes with different combinations of lower protective layer thickness and circulating water head characteristics on a granular cushion layer. A quantitative relationship between the lower protective layer thickness and circulating water head characteristics to prevent geomembrane stress-induced failure is established. A surface mapping the relationship between circulating water head conditions and the thickness of the lower protective layer is plotted, defining the stress-induced failure conditions of the geomembrane. Based on the magnitude, duration, and cycle of the circulating water head in actual engineering projects, the minimum thickness of different types of lower protective layers is determined, thereby enabling the selection of the lower protective layer for the geomembrane. This invention has significant scientific research value and engineering application value for the selection and thickness design of the lower protective layer to avoid geomembrane damage in practical engineering projects. Summary of the Invention

[0006] The technical problem this invention aims to solve is to address the shortcomings of existing technologies by proposing a method for selecting a protective layer under circulating water head conditions for geomembranes. This method involves conducting stress-induced damage tests on geomembranes with different combinations of protective layer thickness and circulating water head characteristics on a granular cushion layer. A quantitative relationship between the protective layer thickness and circulating water head characteristics to prevent geomembrane stress-induced damage is established. A surface mapping the relationship between circulating water head conditions and the thickness of the protective layer is plotted, defining the stress-induced damage conditions for the geomembrane. Based on the magnitude of the circulating water head, its duration, and the circulation cycle in actual engineering projects, the minimum thickness of different types of protective layers is determined, thereby enabling the selection of the geomembrane protective layer. This invention has significant scientific research value and engineering application value for the selection and thickness design of protective layers to avoid geomembrane damage in practical engineering projects.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for selecting a protective layer under a geomembrane under circulating water head includes the following steps: Step 1: Establish the relationship between the thickness D of the geomembrane under protective layer and the circulating water head H. max ~H min Duration of highest water head t max Minimum head duration t min The relationship between the circulation period T and the geomembrane thickness and the granular cushion design parameters is as follows: Based on the initially determined geomembrane type, thickness, and granular cushion design parameters, the lower protective layer material is selected, and different lower protective layer thicknesses are set. Different combinations of circulating water head conditions are then established, and geomembrane stress-damage tests are conducted under circulating water head conditions to obtain the relationship between different lower protective layer thicknesses and the corresponding circulating water head H at geomembrane stress-damage. max -H min The quantitative relationship between the duration of the highest and lowest water heads and the combination of cycle periods is established as follows: (1) In the formula, D is the thickness of the protective layer under the geomembrane; H max H is the highest circulating head. min The minimum circulating head; t max The duration of the highest water head; t min is the duration of the minimum head; α, β, and δ are fitting parameters; Step 2, Definition of Geomembrane Stress Failure: Based on the D and H established in Step 1 max H min t max t min The relationship between T and T is as follows: Using the x-axis as the base, Plot the thickness D of the geomembrane's lower protective layer against the z-axis. and The three-dimensional surface diagram shows that when the point (x, y, z) representing the circulating water head condition and the thickness of the protective layer under the geomembrane is below the three-dimensional surface, it indicates that the geomembrane will be damaged; when the point (x, y, z) is above the three-dimensional surface, it indicates that the geomembrane will not be damaged. Step 3: Select the thickness of the lower protective layer: based on the circulating water head H in the actual project. max -H min Duration of highest water head t max Minimum head duration t min Calculate the minimum thickness D of the lower protective layer to prevent geomembrane damage under stress, given the cycle period T. min The selected lower protective layer thickness should be greater than D. min If the geomembrane type, thickness, or granular cushion layer design parameters change, the geomembrane type, thickness, or granular cushion layer design parameters in step 1 must be replaced, and the corresponding fitting parameters α, β, and δ must be re-determined. Steps 1-3 must then be repeated. The selected geomembrane type, thickness, or granular cushion layer design parameters do not affect the formulas used in the calculation process; they only affect the determination of the fitting parameters α, β, and δ. Different projects use different geomembrane types, thicknesses, and cushion layer design parameters, which is determined by the engineering design.

[0008] As a preferred embodiment, the method for determining the fitting parameters α, β, and δ in formula (1) in step 1 includes the following steps: Step a, Filling the cushion layer: According to the design parameters of the granular cushion layer, fill the cushion layer into the cushion layer chamber, and the filling height is level with the top of the cushion layer chamber; Set the lower protective layer: Place the lower protective layer sample with a thickness of D1 on top of the padding layer; Geomembrane placement: Place the geomembrane sample above the lower protective layer; Install the pressure chamber: Install the pressure chamber above the geomembrane and fix the geomembrane and the lower protective layer; Step b, Set the circulating head conditions: Set the minimum circulating head (H) min1 H min2 ... H min6 ), duration of highest head (t) max1 t max2 t max3 ), minimum head duration (t) min1 t min2 t min3 An orthogonal combination of cycle periods (T1, T2, T3, T4) is input into the pressurization system; Set initial maximum circulating head: Set initial maximum circulating head H maxi (i=0), input the pressurization system; Step c, Geomembrane stress and damage test: Turn on the pressurization system and apply the set circulating water head condition to the geomembrane through the pressure chamber, and observe whether the geomembrane is damaged within the cycle T. Step d: Determine the maximum circulating head: If the geomembrane is not damaged, adjust the maximum circulating head to H. maxi =H maxi-1 +△h, repeat step b until the geomembrane is damaged, and the highest circulating head H max Take H maxi-1 If the geomembrane is damaged, adjust the maximum circulating water head to H. maxi =H maxi-1 -△h, repeat step b until the geomembrane is undamaged and the highest circulating head H is reached. max Take H maxi ; Step e: Obtain the distribution of circulating head conditions under the initial thickness D1: Repeat steps b-d until the six lowest circulating heads H are obtained. minb 3 types of maximum water head duration t maxc 3 types of minimum head duration t mind 4 types of cycle periods T e After the orthogonal combination operation is completed, the combination of the lower protective layer thickness D1 and each circulating head condition is obtained; Step f: Obtain the distribution of circulating head conditions under different lower protective layer thicknesses: Replace the lower protective layer thickness in step a with D2, D3, D4, and D5 in sequence, and repeat steps a-e to obtain the combination of different lower protective layer thicknesses and various circulating head conditions (D a H max H minb , t maxc , t mind T e ); where a = 1, 2, 3, 4, 5; b = 1, 2, 3, 4, 5, 6; c = 1, 2, 3; d = 1, 2, 3; e = 1, 2, 3, 4; Determine the fitting parameters α, β, δ: (D a H max H minb , t maxc Substituting ,tmind,Te into formula (1), we obtain the parameters α, β, and δ by fitting.

[0009] Preferred types of lower protective layers include geotextiles, geomats, and composite drainage nets.

[0010] Preferably, when the thickness of the protective layer is Di (i=1, 2, 3, 4, 5), the geomembrane will be damaged under stress under each combination of circulating head size, head duration and cycle period. Then, Di will be increased in increments of ΔD until the geomembrane does not be damaged under at least one combination of circulating head size, head duration and cycle period.

[0011] Preferably, the design parameters of the granular cushion layer include gradation, maximum particle size, minimum particle size, fine particle content, compaction method, and compaction degree.

[0012] Preferably, the minimum circulating head should be greater than the minimum water head during the normal operation cycle of the project.

[0013] Preferably, the pressurization system is programmable, which automatically applies a set circulating head load to the geomembrane by inputting the highest and lowest circulating head, the duration of the highest and lowest circulating head, and the circulation cycle.

[0014] As a preferred option, a liquid level sensor is installed on the upper part of the granular cushion layer. When the geomembrane is damaged by stress, water in the pressure chamber enters the cushion layer through the damaged area, and the liquid level sensor immediately issues a geomembrane damage alarm.

[0015] As a preferred option, the airtightness of the pressure chamber and the pressurization device must be tested and calibrated before the pressurization system is turned on.

[0016] As a preferred option, the fitting parameters α, β, and δ are determined using MATLAB software.

[0017] The present invention has the following beneficial effects: 1. This invention establishes a quantitative relationship between the thickness of the lower protective layer and the characteristics of circulating water head based on stress and failure tests of geomembranes with different combinations of lower protective layer thickness and circulating water head characteristics on a granular cushion layer. This allows for the determination of the type and thickness of the lower protective layer material of the geomembrane according to the circulating water head, water head duration, and circulation cycle in actual engineering projects. This avoids the subjectivity and uncertainty of traditional empirical methods, making the selection and thickness design of the lower protective layer more reliable and accurate.

[0018] 2. This invention fully considers the various complex circulating head environments faced by geomembranes by setting multiple orthogonal combinations of maximum and minimum circulating water heads, maximum and minimum water head durations, and circulation cycles, ensuring that the selected type and thickness design of the lower protective layer can prevent geomembranes from being damaged by stress under different circulating water head operating conditions in actual engineering projects.

[0019] 3. This invention visually demonstrates the selection area for the thickness of the lower protective layer of the geomembrane and the circulating water head conditions by drawing a three-dimensional surface diagram, which helps engineering designers quickly determine the minimum thickness of the lower protective layer based on actual engineering parameters, thereby improving design efficiency and facilitating its widespread application. Attached Figure Description

[0020] Figure 1 This invention relates to a geomembrane stress and failure test device with different combinations of lower protective layer thickness and circulating water head characteristics on a granular cushion layer. Figure 2 This is a three-dimensional curved surface diagram illustrating the circulating water head conditions and the thickness of the protective layer under the geomembrane in an embodiment of the present invention; Reference numerals in the attached diagram: 1. Geomembrane; 2. Lower protective layer; 3. Granular cushion layer; 4. Cushion chamber; 5. Pressurization chamber; 6. Pressurization system; 7. Fixing bolts; 8. Outlet; 9. Base. Detailed Implementation

[0021] Example 1: The geomembrane stress-damage test device with different combinations of lower protective layer thickness and circulating water head characteristics on the granular cushion layer in this example is shown below. Figure 1 .

[0022] A method for selecting a protective layer under a geomembrane under circulating water head includes the following steps: Step 1: Establish the relationship between the thickness D of the geomembrane lower protective layer and the circulating water head Hmax-Hmin, the duration of the highest water head tmax, the duration of the lowest water head tmin, and the circulation period T: Based on the preliminarily determined geomembrane type, thickness, and granular cushion layer design parameters, select the lower protective layer material, set different lower protective layer thicknesses, set different combinations of circulating water head conditions, and conduct stress-induced failure tests on the geomembrane under circulating water head. Obtain the quantitative relationship between different lower protective layer thicknesses and the corresponding combinations of circulating water head Hmax-Hmin, the duration of the highest and lowest water heads, and the circulation period when the geomembrane experiences stress-induced failure. Establish the following relationship: (1) In the formula, D is the thickness of the protective layer under the geomembrane; Hmax is the highest circulating head; Hmin is the lowest circulating head; tmax is the duration of the highest head; tmin is the duration of the lowest head; α, β, and δ are fitting parameters.

[0023] The method for determining the fitting parameters α, β, and δ in formula (1) in step 1 includes the following steps: Step 11, Filling the cushion layer: According to the design parameters of the granular cushion layer, fill the cushion layer into the cushion layer chamber, and the filling height is level with the top of the cushion layer chamber; Step 12: Set the lower protective layer: Place the lower protective layer sample with a thickness of D1 on top of the padding layer; Step 13, Place the geomembrane: Place the geomembrane sample above the lower protective layer; Step 14: Install the pressure chamber: Install the pressure chamber above the geomembrane and fix the geomembrane and the lower protective layer; Step 15: Set the circulating head conditions: Set an orthogonal combination of the minimum circulating head (Hmin1, Hmin2, ..., Hmin6), the maximum head duration (tmax1, tmax2, tmax3), the minimum head duration (tmin1, tmin2, tmin3), and the circulation period (T1, T2, T3, T4), and input it into the pressurization system. In this embodiment, the preferred circulating head conditions are Hmin(m)=[4,6,8,10,12,14], tmax(h)=[4,6,8], tmin(h)=[6,8,10], and T(h)=[12,16,20,24]. Step 16: Set the initial maximum circulating head: Set the initial maximum circulating head Hmax0 (i=0) and input it into the pressurization system. In this embodiment, Hmax0 is preferably 30m. Step 17, Geomembrane stress and damage test: Turn on the pressurization system and apply the circulating water head conditions set in Step 15 and Step 16 to the geomembrane through the pressure chamber, and observe whether the geomembrane is damaged within the circulation period T. Step 18: Determine the maximum circulating head: If the geomembrane is not damaged, adjust the maximum circulating head to Hmaxi = Hmaxi-1 + Δh, and repeat steps 16 and 17 until the geomembrane is damaged. The maximum circulating head Hmax is then set to Hmaxi-1. If the geomembrane is damaged, adjust the maximum circulating head to Hmaxi = Hmaxi-1 - Δh, and repeat steps 16 and 17 until the geomembrane is not damaged. The maximum circulating head Hmax is then set to Hmaxi. In this embodiment, Δh is preferably 4m. Step 19: Obtain the distribution of circulating head conditions under thickness D1: Repeat steps 15-18 until the orthogonal combination of 6 minimum circulating heads, 3 maximum head durations, 3 minimum head durations, and 4 circulation cycles is completed, and the lower protective layer thickness D1 and the combination of each circulating head condition are obtained. Step 110: Obtain the distribution of circulating head conditions under different lower protective layer thicknesses: Replace the lower protective layer thickness in Step 12 with D2, D3, D4, and D5 in sequence, and repeat Steps 13-19 to obtain different combinations of lower protective layer thicknesses and circulating head conditions (Da, Hmax, Hminb, tmaxc, tmind, Te); where a=1, 2, 3, 4, 5; b=1, 2, 3, 4, 5, 6; c=1, 2, 3; d=1, 2, 3; e=1, 2, 3, 4. Step 111: Determine the fitting parameters α, β, δ: Substitute (Da, Hmax, Hminb, tmaxc, tmind, Te) into formula (1) to obtain the fitting parameters α, β, δ. In this embodiment, the fitting parameters are α=0.140, β=7.774, and δ=1.131.

[0024] The types of lower protective layers in step 1 include geotextile, geomat, and composite drainage net; in this embodiment, geotextile is preferred.

[0025] When the thickness of the protective layer in step 12 is Di (i=1, 2, 3, 4, 5), the geomembrane will be damaged under stress under each combination of circulating head size, head duration and cycle period. Then, Di will be increased in increments of ΔD until the geomembrane does not be damaged under at least one combination of circulating head size, head duration and cycle period.

[0026] The design parameters for the granular cushion layer in step 1 include gradation, maximum particle size, minimum particle size, fine particle content, compaction method, and compaction degree.

[0027] The minimum circulating head set in step 15 must be greater than the minimum water head during the normal operation cycle of the project.

[0028] In step 15, the pressurization system is a programmable pressurization system. By inputting the highest and lowest circulating head, the duration of the highest and lowest head, and the cycle period, it automatically applies the set circulating head load to the geomembrane.

[0029] In step 11, a liquid level sensor is installed on the upper part of the granular cushion layer. When the geomembrane is damaged by stress, water in the pressure chamber enters the cushion layer through the damaged area, and the liquid level sensor immediately issues a geomembrane damage alarm.

[0030] Before starting the pressurization system in step 17, the airtightness of the pressure chamber and pressurization device must be tested and calibrated.

[0031] In step 111, the parameters α, β, and δ are determined by fitting using MATLAB software.

[0032] Step 2, Definition of Geomembrane Stress Failure: Based on the relationship between D and Hmax, Hmin, tmax, tmin, and T established in Step 1, ... Using the x-axis as the base, Plot the thickness D of the geomembrane's lower protective layer against the z-axis. and The three-dimensional surface diagram is shown below the geomembrane. When the point (x, y, z) representing the circulating water head condition and the thickness of the protective layer under the geomembrane is below the three-dimensional surface, it indicates that the geomembrane will be damaged; when the point (x, y, z) is above the three-dimensional surface, it indicates that the geomembrane will not be damaged. A schematic diagram of the three-dimensional surface diagram of the circulating water head condition and the thickness of the protective layer under the geomembrane in this embodiment is shown below. Figure 2 The results of the established three-dimensional surface points are shown in Table 1.

[0033] Table 1. Set of points for circulating water head conditions and thickness of the protective layer under the geomembrane. Step 3: Select the thickness of the lower protective layer: Based on the circulating water head Hmax-Hmin, the duration of the highest water head tmax, the duration of the lowest water head tmin, and the circulation period T in the actual project, calculate the minimum thickness of the lower protective layer Dmin to prevent the geomembrane from being damaged by stress. The selected thickness of the lower protective layer should be greater than Dmin. If the geomembrane type, thickness, or granular cushion layer design parameters change, the geomembrane type, thickness, or granular cushion layer design parameters in Step 1 need to be replaced, and Steps 1-3 need to be repeated.

[0034] This invention establishes a quantitative relationship between the thickness of the lower protective layer and the characteristics of circulating water head based on stress-induced failure tests of geomembranes with different combinations of lower protective layer thickness and circulating water head characteristics on a granular cushion layer. This allows for the determination of the type and thickness of the lower protective layer material for the geomembrane according to actual engineering conditions such as circulating water head, water head duration, and circulation cycle. This avoids the subjectivity and uncertainty of traditional empirical methods, making the selection and design of the lower protective layer more reliable and accurate. By setting multiple orthogonal combinations of maximum and minimum circulating water head, maximum and minimum water head duration, and circulation cycle, the invention fully considers the various complex circulating water head environments faced by the geomembrane, ensuring that the selected lower protective layer type and thickness design can prevent stress-induced failure of the geomembrane under different circulating water head operating conditions in actual engineering projects.

Claims

1. A method for selecting a protective layer under a geomembrane under circulating water head, characterized in that, Includes the following steps: Step 1: Establish the relationship between the thickness D of the geomembrane under protective layer and the circulating water head H. max ~H min Duration of highest water head t max Minimum head duration t min The relationship between the cycle period T; Step 2: Based on the above relationship, determine the fitting parameters and draw a three-dimensional surface plot; Step 3: Select the lower protective layer thickness: Based on the circulating water head, the duration of the highest water head, the duration of the lowest water head, and the circulation cycle in the actual project, calculate the minimum lower protective layer thickness D to prevent the geomembrane from being damaged by stress. min The selected lower protective layer thickness should be greater than D. min ; If the geomembrane type, thickness, or granular cushion layer design parameters change, the geomembrane type, thickness, or granular cushion layer design parameters in step 1 need to be replaced, and the corresponding fitting parameters α, β, and δ need to be re-determined. Then, steps 1-3 need to be repeated.

2. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 1, characterized in that, Step 1 specifically includes: based on the preliminarily determined geomembrane type, thickness, and granular cushion layer design parameters, selecting the lower protective layer material, setting different lower protective layer thicknesses, setting different combinations of circulating water head conditions, conducting stress-induced failure tests on the geomembrane under circulating water head, and obtaining the circulating water head H at different lower protective layer thicknesses and corresponding geomembrane stress-induced failure times. max ~H min The quantitative relationship between the duration of the highest and lowest water heads and the combination of cycle periods is established as follows: ； In the formula, D is the thickness of the protective layer under the geomembrane; H max H is the highest circulating head. min The minimum circulating head; t max The duration of the highest water head; t min α represents the minimum head duration; α, β, and δ are fitting parameters.

3. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 1, characterized in that, Step 2 specifically includes the following steps: Based on the relation established in step 1, Using the x-axis as the base, Plot the thickness D of the geomembrane's lower protective layer against the z-axis. and The three-dimensional surface diagram shows that when the point representing the circulating water head condition and the thickness of the protective layer under the geomembrane is below the three-dimensional surface, the geomembrane will be damaged; when the point is above the three-dimensional surface, the geomembrane will not be damaged.

4. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 1, characterized in that, The method for determining the fitting parameters specifically includes the following steps: Step a, Filling the cushion layer: According to the design parameters of the granular cushion layer, fill the cushion layer into the cushion layer chamber, and the filling height is level with the top of the cushion layer chamber; Set the lower protective layer: Place the lower protective layer sample with a thickness of D1 on top of the padding layer; Geomembrane placement: Place the geomembrane sample above the lower protective layer; Install the pressure chamber: Install the pressure chamber above the geomembrane and fix the geomembrane and the lower protective layer; Step b, Set the circulating head conditions: Set an orthogonal combination of minimum circulating head, maximum head duration, minimum head duration, and circulation cycle, and input it into the pressurization system; Set initial maximum circulating head: Set the initial maximum circulating head and input it into the pressurization system; Step c, Geomembrane stress and damage test: Turn on the pressurization system and apply the set circulating water head condition to the geomembrane through the pressure chamber, and observe whether the geomembrane is damaged within the circulation cycle; Step d: Determine the maximum circulating head: If the geomembrane is not damaged, adjust the maximum circulating head to H. maxi =H maxi-1 +△h, repeat step b until the geomembrane is damaged, and the highest circulating head H max Take H maxi-1 If the geomembrane is damaged, adjust the maximum circulating water head to H. maxi =H maxi-1 -△h, repeat step b until the geomembrane is undamaged and the highest circulating head H is reached. max Take H maxi ; Step e: Obtain the distribution of circulating head conditions under the initial thickness D1: Repeat steps b-d until all orthogonal combinations are traversed to obtain the lower protective layer thickness D1 and each circulating head condition combination; Step f: Obtain the data distribution of circulating head conditions under different lower protective layer thicknesses: Replace the lower protective layer thickness in step a with D2 to D5 in sequence, repeat steps a-e to obtain different combinations of lower protective layer thicknesses and circulating head conditions, and determine the fitting parameters.

5. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 1, characterized in that: The types of lower protective layers include geotextiles, geomats, and composite drainage nets.

6. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 4, characterized in that: When the thickness of the protective layer is D i When i=1, 2, 3, 4, 5, the geomembrane will be damaged under stress under each combination of circulating head size, head duration and cycle period. Then, Di will be increased in increments of ΔD until at least one combination of circulating head size, head duration and cycle period is satisfied that the geomembrane will not be damaged under stress.

7. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 4, characterized in that: The design parameters of the granular cushion layer include gradation, maximum particle size, minimum particle size, fine particle content, compaction method, and compaction degree.

8. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 4, characterized in that: The minimum circulating head is set to be greater than the minimum water head during the normal operation cycle of the project.

9. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 4, characterized in that: The pressurization system is a programmable pressurization system that automatically applies a set circulating head load to the geomembrane by inputting the highest and lowest circulating head, the duration of the highest and lowest circulating head, and the circulation cycle.

10. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 4, characterized in that: A liquid level sensor is installed on the upper part of the granular cushion layer. When the geomembrane is damaged by stress, water in the pressure chamber enters the cushion layer through the damaged area, and the liquid level sensor immediately issues a geomembrane damage alarm.

11. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 4, characterized in that: Before starting the pressurization system, the pressure chamber and pressurization device are tested and calibrated for airtightness.

12. The method for selecting a protective layer under a geomembrane under circulating water head as described in claim 4, characterized in that: The fitting parameters α, β, and δ were determined using MATLAB software.

Images