Experimental device and method for granular cushion design considering leakage of geomembrane defects on dam surface

Abstract

The present invention discloses a granular cushion design and testing device and method that takes into account dam surface geomembrane defect leakage. The device comprises a head application system, a cushion seepage safety design and testing system, and a seepage data acquisition system. The cushion seepage safety design and testing system includes a defective geomembrane, a cushion chamber, an inclination adjustment device, and a test bench. The seepage data acquisition system includes a particle collector, a flow meter, and a computer. Based on actual engineering contexts, the present invention sets the dam slope ratio, pressure head value, and geomembrane defect size to simulate the migration of particles under the membrane caused by concentrated leakage from geomembrane defects. The cushion seepage safety is determined based on the migration and loss of cushion particles, cushion gradation changes, and defect leakage. A curve is then generated showing the relationship between cushion safety thickness and relative density, thereby determining the minimum cushion thickness or minimum relative density that ensures cushion seepage safety. This provides a theoretical basis for selecting design parameters for the safe operation of granular cushions under the membrane in geomembrane anti-seepage earth-rockfill dam projects.

Description

Technical Field

[0001] The invention relates to the field of geomembrane anti-seepage, in particular to a granular cushion design test device and method taking into account the leakage of dam surface geomembrane defects. Background Art

[0002] Geomembrane is a flexible, impermeable film material widely used as an impermeable element in anti-seepage projects such as earth-rock dams, embankments, and cofferdams. Because geomembranes are very thin (common thicknesses of 0.5 to 2.0 mm in engineering projects), they are susceptible to various forms of damage during manufacturing, transportation, and construction, such as rupture, puncture, and tearing, resulting in defects. This can cause concentrated leakage from these defects after water storage. In earth-rock dam projects, concentrated leakage from defects in the dam-surface anti-seepage geomembrane causes the granular cushion beneath the membrane to be eroded by seepage water. The seepage water pressure causes the cushion particles to migrate and lose, altering the cushion gradation, relative density, and permeability coefficient. This in turn reduces the cushion's permeability stability, potentially causing seepage damage and compromising the project's anti-seepage safety.

[0003] The existing test equipment for simulating geomembrane defect leakage mainly studies the defect leakage under different water heads. It does not systematically study the migration of cushion layer particles under the membrane caused by concentrated leakage of geomembrane defects. It does not involve the migration, loss and grading changes of cushion layer particles that affect the stability of the internal structure of the cushion layer. In addition, the existing test equipment cannot take into account the slope ratio of the dam slope where the geomembrane is located, and cannot simulate the actual anti-seepage operation status of the geomembrane on the dam surface under different dam slope ratios.

[0004] Therefore, it is necessary to propose a test device and method for granular cushion design that takes into account the leakage of dam surface geomembrane defects. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned existing technologies and provide a granular cushion design test device and method that takes into account the leakage of geomembrane defects on the dam surface. The granular cushion design test device and method that takes into account the leakage of geomembrane defects on the dam surface, by combining the actual engineering background, sets the dam slope ratio, pressure head value and geomembrane defect size, simulates the migration process of the sub-membrane cushion particles caused by the concentrated leakage of geomembrane defects on the dam surface, determines the cushion seepage safety according to the cushion particle migration and loss amount, cushion grading change and defect leakage amount, obtains the relationship curve between the cushion safety thickness and relative density, and then obtains the minimum cushion thickness or minimum relative density that ensures the cushion seepage safety, providing a theoretical basis for the selection of design parameters for the safe operation of the sub-membrane granular cushion in the dam surface geomembrane anti-seepage earth-rock dam project.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A granular cushion design test device taking into account the leakage of dam surface geomembrane defects includes a water head application system, a cushion seepage safety design test system and a seepage data acquisition system.

[0008] The cushion seepage safety design test system includes a geomembrane, a cushion chamber, an inclination adjustment device and a test bench.

[0009] The cushion chamber is arranged on the test bench and is provided with a cushion filling cavity filled with granular cushion material; a sieve plate is provided at the bottom of the cushion filling cavity.

[0010] The center of the geomembrane has a damage defect.

[0011] The inclination angle adjustment device is used to adjust the inclination angle of the cushion chamber, and then adjust the inclination angle of the geomembrane, so as to simulate the actual anti-seepage operation state of the geomembrane on the dam surface under different dam slope ratios.

[0012] The water head application system is used to apply a set water head pressure to the top of the geomembrane.

[0013] The seepage data acquisition system includes a particle collector, a flow meter and a computer.

[0014] The particle collector is used to collect the cushion material particles carried out from the bottom of the cushion chamber by the infiltration water flow.

[0015] The flow meter is used to monitor the flow rate of permeate water from the bottom of the pad chamber.

[0016] The particle collector, flow meter, tilt adjustment device and water head application system are all connected to the computer.

[0017] The tilt angle adjustment device comprises a base bottom plate, a cylinder frame and an arc-shaped telescopic rod.

[0018] The cylinder frame is coaxially arranged on the top of the base bottom plate.

[0019] One end of the bottom of the base bottom plate is hinged to the test bench, and the other end of the bottom of the base bottom plate and the side wall of the base bottom plate are connected to the test bench through arc-shaped telescopic rods; the length of each arc-shaped telescopic rod can be extended.

[0020] The cushion seepage safety design test system also includes a height adjustment device, which is used to adjust the height of the cushion filling cavity, and further adjust the filling height of the granular cushion material.

[0021] A granular cushion design test method considering leakage from defective geomembrane on a dam surface includes the following steps.

[0022] Step 1. Prepare the cushion material: the cushion material is a sand and gravel cushion material, which has 7 kinds of sand and gravel particles with different particle sizes, and its gradation unevenness coefficient Cu ≥ 15 and the curvature coefficient Cc∈[1,3]; wherein, the particle sizes of the 7 kinds of sand and gravel particles with different particle sizes are, from small to large, d1, d2, d3, d4, d5, d6 and d7.

[0023] Step 2: Install the cushion chamber: Place the cushion chamber horizontally and adjust the cushion filling cavity to the initial height h0 through the height adjustment device.

[0024] Step 3: Fill the cushion material in layers: Divide the cushion filling cavity into n layers, numbered from bottom to top as the 1st layer, the 2nd layer, ..., the i-th layer, ..., the n-th layer; fill and compact the cushion material prepared in step 1 in each layer in turn; wherein the thickness of each cushion material layer is h0 / n, and the relative density of each cushion material layer is D r After compaction is completed, the surface of the cushion layer will be leveled.

[0025] Step 4: Place the geomembrane and install the water head application system: Lay the geomembrane flat on the surface of the cushion layer in step 3, and the center of the geomembrane has a damage defect with an equivalent pore size of r; then, seal and install the water head application system above the cushion layer chamber and the geomembrane.

[0026] Step 5: Adjust the tilt angle of the geomembrane: According to the dam slope ratio to be simulated, the tilt angle of the geomembrane is adjusted to θ through the tilt adjustment device.

[0027] Step 6, concentrated leakage test of geomembrane defects: apply a pressure head H to the geomembrane through the head application system; the pressure water seeps downward through the damaged defects of the geomembrane and enters the cushion chamber, causing the cushion material in the cushion chamber to move downward and flow downward from the sieve plate at the bottom of the cushion filling cavity.

[0028] Step 7: Seepage data collection, including the following steps:

[0029] Step 7-1. Seepage data collection during the leakage process: a particle collector and a flow meter are set at the bottom of the sieve plate; the particle collector is used to collect cushion material particles lost from the bottom of the cushion chamber; the flow meter is used to monitor the flow of pressurized water leaking from the bottom of the cushion chamber and upload it to the computer in real time; the computer draws a curve of the pressure water leakage over time.

[0030] Step 7-2, collecting the total loss of cushion particles: when the flow monitored in step 7-1 is stable, turn off the water head application system; dry and weigh the cushion material particles collected by the particle collector to obtain the total loss of cushion particles m0.

[0031] Step 7-3: Draw the gradation curve of each cushion material layer: Use the inclination adjustment device to adjust the geomembrane to a horizontal position and remove the water head application system; remove the cushion material from the cushion chamber layer by layer, and dry, weigh, and sieve each layer of cushion material to obtain the gradation curve of each cushion material layer; and calculate the gradation unevenness coefficient Cu′, curvature coefficient Cc′, and the mass percentage change of seven different particle sizes of sand and gravel particles for each layer of cushion material; where the mass percentage changes of seven different particle sizes of sand and gravel particles in the i-th layer of cushion material are: and 1≤i≤n.

[0032] Step 8: Determine the safety of cushion layer seepage: Based on the seepage data collected in step 7, determine the following four cushion layer seepage safety determination conditions:

[0033] Condition ①: and are all less than α1, and are all less than α2, and are all less than α3; among them, α1, α2 and α3 are the mass change limits of small-size, medium-size and large-size cushion particles, respectively, and their value ranges are: 2%~4%, 5%~8% and 4%~6%; when i=1, α1, α2 and α3 take the maximum value in their respective value ranges; when i=n, α1, α2 and α3 take the minimum value in their respective value ranges; when i=2~n-1, α1, α2 and α3 take the middle value in their respective value ranges, and the value of the upper layer in two adjacent layers of cushion materials is greater than that of the lower layer.

[0034] Condition ②: m0≤0.05M; where M is the total mass of the cushion material in the cushion chamber.

[0035] Condition ③: The gradation unevenness coefficient Cu′ of each layer of cushion material is not less than 95% of the initial value Cu and the curvature coefficient Cc′∈[1,3].

[0036] Condition ④: The leakage rate change curve over time is smooth, with no obvious inflection point and no abnormal increase in leakage rate.

[0037] Step 9: Obtain cushion safety thickness: When the seepage data collected in step 7 simultaneously meet the four cushion seepage safety judgment conditions in step 8, the cushion is in a seepage safety state, and the cushion safety thickness h 安 =h0; otherwise, increase the cushion filling cavity height to h1, repeat steps 2 to 9 until the four cushion seepage safety judgment conditions in step 8 are met at the same time. The corresponding cushion filling cavity height at this time is the cushion safety thickness h 安 ; Among them, h1>h0.

[0038] It also includes Step 10: the seepage safety test of the cushion layer under different relative densities of the cushion layer material. Change the relative density D of the cushion layer material in Step 3 r , repeat Steps 2 to Step 9 to obtain the safety thickness h of the cushion layer under different relative densities D of the cushion layer material at the water head H, the inclination angle θ of the geomembrane, and the equivalent aperture r of the geomembrane defect r , and draw the relationship curve between the safety thickness h of the cushion layer 安 and the relative density D 安 . r

[0039] Design of the safety parameters of the cushion layer: According to the relationship curve between the safety thickness h of the cushion layer in Step 10 安 and the relative density D r , select the design parameters to ensure the seepage safety of the cushion layer: the minimum relative density D when the designed thickness h of the cushion layer 设 is reached, or the minimum cushion layer thickness h when the designed relative density D of the cushion layer rmin is reached r设 . min

[0040] In Step 5, if the slope ratio of the dam to be simulated is 1:m, the relationship between θ and m is: m = arctanθ, and m takes values from 1.4 to 2.0

[0041] The pressure head H in Step 6 is taken as 10m to 80m according to the designed dam height of the currently built geomembrane防渗 earth-rock dam

[0042] The equivalent aperture r of the geomembrane damage defect in Step 4 is obtained based on the geomembrane failure form and the statistics of geomembrane defects in the actual project, and the value range is 1mm to 20mm

[0043] In Step 1, the value ranges of d1, d2, d3, d4, d5, d6, and d7 are respectively: d1≤0.075mm, 0.075mm<d2≤0.5mm, 0.5mm<d3≤1mm, 1mm<d4≤2mm, 2mm<d5≤5mm, 5mm<d6≤10mm, and 10mm<d7≤20mm

[0044] The present invention has the following beneficial effects

[0045] 1. The present invention simulates the phenomenon of concentrated leakage caused by geomembrane defects on the dam surface and scouring leading to particle migration in the cushion layer under the membrane. Through the change in the position and gradation comparison of the layered cushion layer material before and after the test, as well as the collected small-sized cushion layer material that has been lost, the particle migration amount, loss amount, and gradation change of the cushion layer are obtained, and further quantitatively evaluates the seepage safety of the granular cushion layer caused by concentrated leakage of geomembrane defects

[0046] ​​2. The present invention adopts a height-adjustable cushion chamber to set different cushion thicknesses. Through cushion seepage safety design tests under different cushion relative densities, a curve of the relationship between cushion safety thickness and relative density is established to ensure cushion seepage safety under different water heads, geomembrane inclinations and defect sizes, which provides a theoretical basis for the selection of design parameters for the safe operation of the granular cushion under the membrane in the dam surface geomembrane anti-seepage earth-rock dam project.

[0047] 3. The present invention changes the angle between the base bottom plate and the test bench to enable the geomembrane to achieve an inclined state under different dam slope ratios in actual projects, and takes into account the common pressure head range and equivalent pore size of geomembrane defects in actual projects, truly reflecting the operating conditions of the granular cushion layer of the actual dam surface geomembrane under the inclined dam slope and the effect of concentrated leakage of defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The present invention is a structural schematic diagram of a test device for designing a sub-membrane cushion layer taking into account the defects and leakage of the dam surface geomembrane.

[0049] Figure 2 It is a top view of the test bench and base in the device of the present invention.

[0050] Figure 3 Schematic diagram showing the comparison of gradation curves of cushion materials before and after the test in the embodiment;

[0051] Figure 4 Schematic diagram of the defect leakage curve over time in the embodiment; wherein, (a) is a normal flow curve; (b) is an abnormal flow curve.

[0052] Figure 5 Schematic diagram of the relationship between the cushion layer safety thickness and relative density in the embodiment;

[0053] Figure 6 Schematic diagram of geomembrane defects in the embodiment.

[0054] Among them are: 1. cushion chamber; 2. hydraulic chamber; 3. geomembrane; 4. hydraulic box; 5. screen plate; 6. support rod; 7. particle collector; 8. flow meter; 9. base; 9a. base bottom plate; 9b. cylinder frame; 10. inclination adjustment device; 11. test bench; 12. computer. DETAILED DESCRIPTION

[0055] The present invention will be further described in detail below with reference to the accompanying drawings and specific preferred embodiments.

[0056] In the description of the present invention, it should be understood that the terms "left side," "right side," "upper," "lower," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Terms such as "first" and "second" do not indicate the importance of components and therefore should not be construed as limitations on the present invention. The specific dimensions used in this embodiment are intended only to illustrate the technical solution and do not limit the scope of protection of the present invention.

[0057] like Figure 1 As shown, a granular cushion design test device considering the leakage of dam surface geomembrane defects includes a head application system, a cushion seepage safety design test system and a seepage data acquisition system.

[0058] The cushion seepage safety design test system includes a geomembrane 3, a cushion chamber 1, an inclination adjustment device 10, a height adjustment device and a test bench.

[0059] The cushion chamber is mounted on the test bench 11 and includes a cushion filling cavity filled with granular cushion material. A sieve plate 5 is located at the bottom of the cavity. The sieve plate preferably has a mesh structure with a mesh diameter smaller than the average cushion material particle size d0, ensuring that only the smaller cushion material particles and the permeate flow pass through.

[0060] The center of the geomembrane has a damage defect.

[0061] The inclination angle adjustment device is used to adjust the inclination angle of the cushion chamber, and then adjust the inclination angle of the geomembrane, so as to simulate the actual anti-seepage operation state of the geomembrane on the dam surface under different dam slope ratios.

[0062] The tilt adjustment device preferably includes a base 9 and an arc-shaped telescopic rod.

[0063] like Figure 2 As shown, the base preferably includes a base plate 9a and a cylindrical frame 9b. The cylindrical frame is coaxially mounted on top of the base plate. One end of the base plate is preferably hinged to the test bench, while the other end of the base plate and the sidewalls of the base plate are preferably connected to the test bench via curved telescopic rods. Each curved telescopic rod is capable of extending and retracting under the control of a corresponding telescopic drive device. The telescopic drive device can be conventionally used, such as a drive motor or a drive cylinder.

[0064] The height adjustment device is used to adjust the height of the cushion filling cavity, thereby adjusting the filling height of the granular cushion material.

[0065] The height adjustment device preferably includes a lifting drive device and a plurality of support rods 6 disposed between the sieve plate and the base bottom plate, and all the support rods can be lifted and lowered under the action of the lifting drive device. The lifting drive device is a prior art, such as a drive motor or a drive cylinder, etc.

[0066] The water head application system is used to apply a set water head pressure to the top of the geomembrane. The water head application system preferably includes a water pressure chamber 2 and a hydraulic tank 4. The water pressure is coaxially and hermetically installed at the top outer edge of the geomembrane and is preferably detachably and hermetically connected to the top of the cylinder frame. The hydraulic tank can deliver pressurized water to the water pressure chamber and control the water head pressure.

[0067] The seepage data acquisition system includes a particle collector 7, a flow meter 8 and a computer 12.

[0068] The particle collector is preferably disposed below the sieve plate and is used to collect the cushion material particles carried out from the bottom of the cushion chamber by the seepage flow.

[0069] The flow meter is also preferably disposed below the sieve plate and is used to monitor the flow rate of the seepage flow from the bottom of the cushion chamber.

[0070] The above-mentioned particle collector, flow meter, telescopic drive device in the inclination angle adjustment device, lifting drive device in the height adjustment device and the hydraulic tank in the water head application system are all preferably connected to the computer.

[0071] A test method for the design of a particle cushion considering the leakage of geomembrane defects on the dam surface includes the following steps.

[0072] Step 1, prepare the cushion material: The cushion material is a gravel cushion material, and the gravel cushion material has 7 different particle sizes of gravel particles, and its gradation coefficient of non-uniformity Cu≥15 and curvature coefficient Cc∈[1,3]; among them, the particle sizes of the 7 different particle sizes of gravel particles are from small to large as follows: d1, d2, d3, d4, d5, d6 and d7; the mass percentages of the gravel particles of d1, d2, d3, d4, d5, d6 and d7 are Ω1%, Ω2%, Ω3%, Ω4%, Ω5%, Ω6% and Ω7% respectively.

[0073] In this embodiment, the gradation coefficient of non-uniformity Cu of the cushion material is preferably 20, the curvature coefficient Cc is preferably 2.5, and the value ranges of d1, d2, d3, d4, d5, d6 and d7 are respectively: d1≤0.075mm, 0.075mm<d2≤0.5mm, 0.5mm<d3≤1mm, 1mm<d4≤2mm, 2mm<d5≤5mm, 5mm<d6≤10mm and 10mm<d7≤20mm; the mass percentages of the cushion material of each particle size are preferably Ω1 = 8, Ω2 = 7, Ω3 = 15, Ω4 = 18, Ω5 = 25, Ω6 = 20 and Ω7 = 7.

[0074] Step 2: Install the cushion chamber: The cushion chamber is placed horizontally on the base substrate, and the cushion filling cavity is adjusted to an initial height h0 by a height adjustment device. In this embodiment, h0 is preferably 30 cm.

[0075] Step 3: Fill the cushion material in layers: Divide the cushion filling cavity into n layers, numbered from bottom to top as the 1st layer, the 2nd layer, ..., the i-th layer, ..., the n-th layer; fill and compact the cushion material prepared in step 1 in each layer in turn; wherein the thickness of each cushion material layer is h0 / n, and the relative density of each cushion material layer is D r After compaction is completed, the surface of the cushion layer will be leveled.

[0076] In this embodiment, the cushion material is preferably filled in n=5 layers, with each layer thickness being h0 / n=6 cm, and the relative density of the cushion material being D r Preferably it is 0.82.

[0077] Step 4: Place the geomembrane and install the water head application system: Lay the geomembrane flat on the cushion surface, with a central defect of equivalent pore size r at the center of the geomembrane, ensuring it adheres tightly to the cushion surface. Next, seal the water head application system over the cushion chamber and geomembrane. In this embodiment, the geomembrane is preferably a 1mm thick HDPE geomembrane.

[0078] The equivalent aperture r of the above-mentioned geomembrane damage defect is obtained based on the geomembrane damage form and geomembrane defect statistics in actual engineering, and is 1mm to 20mm. In this embodiment, r is preferably 5mm. The schematic diagram of the geomembrane defect is shown in FIG. Figure 6 .

[0079] Step 5: Adjust the tilt angle of the geomembrane: According to the dam slope ratio to be simulated, the tilt angle of the geomembrane is adjusted to θ through the tilt adjustment device.

[0080] Assuming the slope ratio of the dam to be simulated is 1:m, the relationship between θ and m is: m = arctanθ, and m is 1.4 to 2.0. In this embodiment, m is preferably 1.8, and the corresponding angle θ between the base bottom plate and the test bench is 29°.

[0081] Step 6, concentrated leakage test of geomembrane defects: apply a pressure head H to the geomembrane through the head application system; the pressure water seeps downward through the damaged defects of the geomembrane and enters the cushion chamber, causing the cushion material in the cushion chamber to move downward and flow downward from the sieve plate at the bottom of the cushion filling cavity.

[0082] The pressure head H is set to 10m to 80m based on the design dam height of the currently built geomembrane anti-seepage earth-rock dam. In this embodiment, H is preferably 20m.

[0083] Step 7: Seepage data collection, including the following steps:

[0084] Step 7-1. Seepage data collection during the leakage process: a particle collector and a flow meter are set at the bottom of the sieve plate; the particle collector is used to collect cushion material particles lost from the bottom of the cushion chamber; the flow meter is used to monitor the flow of pressurized water leaking from the bottom of the cushion chamber and upload it to the computer in real time; the computer draws a curve of the pressure water leakage over time.

[0085] Step 7-2: Collect the total loss of cushion particles: When the flow rate monitored in step 7-1 is stable (usually more than 24 hours), turn off the head application system; dry and weigh the cushion material particles collected by the particle collector to obtain the total loss of cushion particles m0

[0086] Step 7-3: Draw the gradation curve of each cushion material layer: Use the inclination adjustment device to adjust the geomembrane to a horizontal position and remove the water head application system; remove the cushion material from the cushion chamber layer by layer, and dry, weigh, and sieve each layer of cushion material to obtain the gradation curve of each cushion material layer; and calculate the gradation unevenness coefficient Cu′, curvature coefficient Cc′, and the mass percentage change of seven different particle sizes of sand and gravel particles for each layer of cushion material; where the mass percentage changes of seven different particle sizes of sand and gravel particles in the i-th layer of cushion material are: and 1≤i≤n.

[0087] In this example, the comparison of the cushion material gradation curves in the third cushion area before and after the test is shown in Figure 2. Figure 3 The smooth curve and the abnormal curve of leakage changing with time are shown in Figure 4 (a) and (b).

[0088] Step 8: Determine the safety of cushion layer seepage: Based on the seepage data collected in step 7, determine the following four cushion layer seepage safety determination conditions:

[0089] Condition ①: and are all less than α1, and are all less than α2, and are all less than α3; among them, α1, α2 and α3 are the mass change limits of small-size, medium-size and large-size cushion particles, respectively, and their value ranges are: 2%~4%, 5%~8% and 4%~6%; when i=1, α1, α2 and α3 take the maximum value in their respective value ranges; when i=n, α1, α2 and α3 take the minimum value in their respective value ranges; when i=2~n-1, α1, α2 and α3 take the middle value in their respective value ranges, and the value of the upper layer in two adjacent layers of cushion materials is greater than that of the lower layer.

[0090] In this embodiment, the preferred values of α1, α2, and α3 are as follows:

[0091] When i=1, α1, α2 and α3 are 4, 8 and 6 respectively.

[0092] When i=2, α1, α2 and α3 are 3.5, 7.5 and 5.5 respectively.

[0093] When i=3, α1, α2 and α3 are 3, 7 and 5 respectively.

[0094] When i=4, α1, α2 and α3 are 2.5, 6 and 4.5 respectively.

[0095] When i=5, α1, α2 and α3 are 2, 5 and 4 respectively.

[0096] Condition ②: m0≤0.05M; where M is the total mass of the cushion material in the cushion chamber.

[0097] Condition ③: The gradation unevenness coefficient Cu′ of each layer of cushion material is not less than 95% of the initial value Cu and the curvature coefficient Cc′∈[1,3].

[0098] Condition ④: The leakage rate change curve over time is smooth, with no obvious inflection point and no abnormal increase in leakage rate.

[0099] Step 9: Obtain the safe thickness of the cushion layer

[0100] When the seepage data collected in step 7 meets the four cushion seepage safety judgment conditions in step 8, it means that the water head H, relative density D r Under the conditions of geomembrane inclination angle θ, when the cushion thickness is set to h0, the migration of cushion particles caused by concentrated leakage of geomembrane defects is limited to a reasonable range, the amount of particle loss is very small, the gradation can be maintained well, and the cushion is in a safe state of seepage, thus obtaining the cushion safety thickness h 安 =h0; otherwise, it means that when the water head H and relative density D are applied r Under the conditions of θ and θ, when the cushion thickness is set to h0, the leakage of geomembrane defects will lead to the cushion being in a non-seepage safety state. At this time, it is necessary to increase the cushion filling cavity height to h1 and repeat steps 2 to 9 until the four cushion seepage safety judgment conditions in step 8 are met at the same time. The corresponding cushion filling cavity height at this time is the cushion safety thickness h 安 ; Among them, h1>h0.

[0101] Step 10: Cushion seepage safety test under different relative densities of cushion materials: Change the relative density D of the cushion material in step 3. r Repeat steps 2 to 9 to obtain the relative density D of different cushion materials under the water head H, geomembrane inclination angle θ and geomembrane defect equivalent pore size rr The safe thickness of the cushion layer is h 安 .

[0102] Integrating the test results, the computer draws the safe thickness h of the cushion when the cushion is in a safe seepage state under the applied water head H, geomembrane inclination angle θ and geomembrane defect equivalent pore size r 安 and relative density D r Relationship curve for cushion parameter design selection.

[0103] In this embodiment, the cushion layer safety thickness h 安 and relative density D r The relationship curve is shown in Figure 5 .

[0104] The safe thickness h of the cushion layer under the applied water head H, geomembrane inclination angle θ and geomembrane defect equivalent aperture r 安 and relative density D r Relationship curve, select the design parameters to ensure the safety of cushion seepage: cushion design thickness h 设 The minimum relative density D rmin , or cushion design relative density D r设 The minimum cushion thickness h min .

[0105] In this embodiment, the safety thickness h of the cushion layer is calculated based on the applied water head of 20m, the geomembrane inclination of 29° and the defect equivalent aperture of 5mm. 安 and relative density D r Relationship curve, select the design cushion parameters, and obtain h 设 The minimum relative density D rmin or D r设 h min .

[0106] The present invention combines the actual engineering background, sets the dam slope ratio, pressure head value and geomembrane defect size, simulates the migration process of the sub-membrane cushion particles caused by the concentrated leakage of the dam surface geomembrane defects, determines the cushion seepage safety according to the cushion particle migration and loss amount, cushion gradation change and defect leakage amount, obtains the relationship curve between the cushion safety thickness and relative density, and then obtains the minimum cushion thickness or minimum relative density to ensure the cushion seepage safety, providing a theoretical basis for the design parameter selection of the safe operation of the sub-membrane granular cushion in the dam surface geomembrane anti-seepage earth-rock dam project.

[0107] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the scope of protection of the present invention.

Claims

1. A granular cushion design test method considering the leakage of dam surface geomembrane defects, characterized by: It includes the following steps: Step 1, preparing cushion material: The cushion material is gravel cushion material, which has gravel particles of 7 different particle sizes, and its coefficient of uniformity Cu≥15 and coefficient of curvature Cc∈[1,3]; among them, the particle sizes of the 7 different particle size gravel particles are from small to large as follows: d1, d2, d3, d4, d5, d6 and d7; Step 2, installing the cushion chamber: The cushion chamber is placed horizontally, and the cushion filling cavity is adjusted to the initial height h0 through the height adjustment device; Step 3: Fill the cushion material in layers: Divide the cushion filling cavity into n layers, numbered from bottom to top as the 1st layer, the 2nd layer, ..., the i-th layer, ..., the n-th layer; fill and compact the cushion material prepared in step 1 in each layer in turn; wherein the thickness of each cushion material layer is h0 / n, and the relative density of each cushion material layer is D r , after compaction is completed, the cushion surface is leveled; Step 4, placing the geomembrane and installing the water head application system: The geomembrane is laid flat on the cushion surface in Step 3, and the center of the geomembrane has a damaged defect with an equivalent aperture of r; then, the water head application system is hermetically installed above the cushion chamber and the geomembrane; Step 5, adjusting the inclination angle of the geomembrane: According to the dam slope ratio to be simulated, the inclination angle of the geomembrane is adjusted to θ through the inclination angle adjustment device; Step 6, geomembrane defect concentrated leakage test: Through the water head application system, a pressure water head H is applied to the geomembrane; the pressure water leaks downward through the damaged defect of the geomembrane and enters the cushion chamber, causing the cushion material in the cushion chamber to move downward and flow out from the sieve plate at the bottom of the cushion filling cavity; Step 7, collecting seepage data, including the following steps: Step 7-1, collecting seepage data during the leakage process: A particle collector and a flowmeter are arranged at the bottom of the sieve plate; among them, the particle collector is used to collect the cushion material particles flowing out from the bottom of the cushion chamber; the flowmeter is used to monitor the water flow leaking out from the bottom of the cushion chamber and upload it to the computer in real time; the computer draws the curve of the pressure water leakage volume changing with time; Step 7-2, collecting the total loss of cushion particles: When the flow rate monitored in Step 7-1 is in a stable state, the water head application system is closed; the cushion material particles collected by the particle collector are dried and weighed to obtain the total loss of cushion particles m0; Step 7-3: Draw the gradation curve of each cushion material layer: Use the inclination adjustment device to adjust the geomembrane to a horizontal position and remove the water head application system; remove the cushion material from the cushion chamber layer by layer, and dry, weigh, and sieve each layer of cushion material to obtain the gradation curve of each cushion material layer; and calculate the gradation unevenness coefficient Cu′, curvature coefficient Cc′, and the mass percentage change of seven different particle sizes of sand and gravel particles for each layer of cushion material; where the mass percentage changes of seven different particle sizes of sand and gravel particles in the i-th layer of cushion material are: and 1≤i≤n; Step 8, judging the seepage safety of the cushion: According to the seepage data collected in Step 7, the following 4 cushion seepage safety judgment conditions are judged: Condition ①: and are all less than α1, and are all less than α2, and are all less than α3; α1, α2 and α3 are the mass variation limits of small-size, medium-size and large-size cushion particles, respectively, with value ranges of 2% to 4%, 5% to 8% and 4% to 6%; when i = 1, α1, α2 and α3 take the maximum value in their respective value ranges; when i = n, α1, α2 and α3 take the minimum value in their respective value ranges; when i = 2 to n-1, α1, α2 and α3 take the middle value in their respective value ranges, and the value of the upper layer of two adjacent layers of cushion material is greater than that of the lower layer; Condition ②: m0≤0.05M; where M is the total mass of the cushion material in the cushion chamber; Condition ③: The coefficient of uniformity Cu′ of each layer of cushion material is not less than 95% of the initial value Cu and the coefficient of curvature Cc′∈[1,3]; Condition ④: The curve of the leakage volume changing with time is smooth, without obvious inflection points, and without abnormal sudden increase in the leakage volume; Step 9: Obtain cushion safety thickness: When the seepage data collected in step 7 simultaneously meet the four cushion seepage safety judgment conditions in step 8, the cushion is in a seepage safety state, and the cushion safety thickness h 安 =h0; otherwise, increase the cushion filling cavity height to h1, repeat steps 2 to 9 until the four cushion seepage safety judgment conditions in step 8 are met at the same time. The corresponding cushion filling cavity height at this time is the cushion safety thickness h 安 ; Among them, h1>h0.

2. The granular cushion design test method considering the leakage of dam surface geomembrane defects according to claim 1 is characterized by: The invention also includes step 10, cushion seepage safety test under different cushion material relative densities: changing the relative density D of the cushion material in step 3 r Repeat steps 2 to 9 to obtain the relative density D of different cushion materials under the water head H, geomembrane inclination angle θ and geomembrane defect equivalent pore size r r The safe thickness of the cushion layer is h 安 , and draw the cushion safety thickness h 安 and relative density D r relationship curve.

3. The granular cushion design test method considering the leakage of dam surface geomembrane defects according to claim 2 is characterized by: Design of cushion seepage safety parameters: According to the cushion safety thickness h in step 10 安 and relative density D r Relationship curve, select the design parameters to ensure the safety of cushion seepage: cushion design thickness h 设 The minimum relative density D rmin , or cushion design relative density D r设 The minimum cushion thickness h min .

4. The granular cushion design and test method considering dam surface geomembrane defect leakage according to claim 1 is characterized by: The pressure water head H in Step 6 is taken as 10m to 80m according to the designed dam height of the currently built geomembrane防渗 earth-rock dam.

5. The granular cushion design and test method considering the leakage of dam surface geomembrane defects according to claim 1 is characterized by: The equivalent aperture r of the damaged defect of the geomembrane in Step 4 is obtained according to the geomembrane failure form and geomembrane defect statistics in the actual project, and the value range is 1mm to 20mm.

6. The granular cushion design and test method considering dam surface geomembrane defect leakage according to claim 1 is characterized by: In Step 1, the value ranges of d1, d2, d3, d4, d5, d6 and d7 are respectively: d1≤0.075mm, 0.075mm<d2≤0.5mm, 0.5mm<d3≤1mm, 1mm<d4≤2mm, 2mm<d5≤5mm, 5mm<d6≤10mm and 10mm<d7≤20mm.

7. The granular cushion design and test method considering dam surface geomembrane defect leakage according to claim 1 is characterized by: A granular cushion design test device based on consideration of dam surface geomembrane defect leakage, which includes a water head application system, a cushion seepage safety design test system, and a seepage data acquisition system; The cushion seepage safety design test system includes geomembrane, cushion chamber, inclination adjustment device and test bench; The cushion chamber is arranged on the test bench, and has a cushion filling cavity filled with granular cushion material; a sieve plate is provided at the bottom of the cushion filling cavity; The center of the geomembrane has a broken defect; The tilt adjustment device is used to adjust the tilt angle of the cushion chamber, and then adjust the tilt angle of the geomembrane, so as to simulate the actual anti-seepage operation state of the geomembrane on the dam surface under different dam slope ratios; The water head application system is used to apply a set water head pressure to the top of the geomembrane; The seepage data acquisition system includes a particle collector, a flow meter, and a computer; The particle collector is used to collect the bedding material particles carried out from the bottom of the bedding chamber by the infiltration water flow; The flow meter is used to monitor the flow rate of water seeping from the bottom of the pad chamber; The particle collector, flow meter, tilt adjustment device and water head application system are all connected to the computer.

8. The granular cushion design and test method considering dam surface geomembrane defect leakage according to claim 7 is characterized by: The tilt adjustment device includes a base bottom plate, a cylindrical frame and an arc-shaped telescopic rod; The cylinder frame is coaxially arranged on the top of the base bottom plate; One end of the bottom of the base bottom plate is hinged to the test bench, and the other end of the bottom of the base bottom plate and the side wall of the base bottom plate are connected to the test bench through arc-shaped telescopic rods; the length of each arc-shaped telescopic rod can be extended.

9. The granular cushion design test method considering the leakage of dam surface geomembrane defects according to claim 7 or 8 is characterized by: The cushion seepage safety design test system also includes a height adjustment device, which is used to adjust the height of the cushion filling cavity, and further adjust the filling height of the granular cushion material.

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