An experimental device and test method for testing the gas diffusion coefficient of geomembrane

Abstract

The present invention relates to the technical field of experimental devices for testing diffusion coefficients, and more particularly to an experimental device and testing method for testing the gas diffusion coefficient of geomembranes. The device comprises an air supply mechanism, a testing mechanism, and a stretching mechanism. The testing mechanism comprises a reaction test cylinder, which comprises an upper chamber and a lower chamber. One side of the lower chamber is connected to the air supply mechanism. A placement assembly is provided between the upper and lower chambers. The clamping assembly of the stretching mechanism is detachably connected to the middle portion of the placement assembly. The present invention solves the problem in the prior art of being unable to simulate the gas diffusion coefficient test of geomembranes under the coupled effects of aging and tensile stress, and provides a reliable experimental device for evaluating the long-term anti-seepage performance of geomembranes under actual working conditions.

Description

Technical Field

[0001] The invention relates to the technical field of geomembrane testing devices, in particular to an experimental device and a testing method for testing the gas diffusion coefficient of a geomembrane. Background Art

[0002] Geomembranes are widely used in both temporary and final landfills in my country because they effectively block landfill gas emissions from the landfill cover layer, prevent rainwater infiltration, and reduce the generation of permeate within the landfill. However, their thinness inevitably leads to damage during installation and operation. Furthermore, exposure to temperature fluctuations and ultraviolet radiation in the environment accelerates these changes, placing high demands on the long-term performance of geomembranes.

[0003] At present, a large number of studies have focused on influencing factors such as temperature, humidity, ultraviolet intensity, texture, thickness, stress field, etc., and analyzed their mechanism of accelerated aging of geomembranes from the perspective of mechanical parameters such as crystallinity, yield strength and tensile fracture strength of geomembranes.

[0004] Existing research techniques have demonstrated that some environmental parameters have a significant impact on the diffusion capacity of geomembranes. Academician Rowe's team used BTEX aqueous solutions to compare the changes in the diffusion and distribution coefficients of geomembranes before and after long-term high-temperature aging, and further studied the changes in these coefficients at low and normal temperatures. Professor Lei Guoyuan's team at Wuhan University of Science and Technology used numerical models to further verify that the permeability coefficient of geomembranes increases with aging, thereby increasing the risk of contamination. Furthermore, geomembranes exposed to landfills are affected not only by environmental aging factors but also by external forces.

[0005] However, these methods present several challenges in practical applications. Existing analyses of environmental aging factors for membranes often lack adequate environmental parameter settings, with the assumed temperature range significantly differing from actual operating conditions. Furthermore, few studies consider ultraviolet radiation. Some studies have examined the effects of stress fields on the mechanical properties of geomembranes, but these studies have not integrated these with environmental aging factors, and lack methods for measuring diffusion coefficients under these coupled conditions.

[0006] Existing patent CN201810438534.0 discloses an experimental apparatus for testing the gas diffusion coefficient and permeability coefficient of unsaturated media. The apparatus primarily comprises a gas supply device, a main reaction device, and an outlet gas collection device. The gas supply device includes a water bath heating device for heating and transmitting gas, simulating the temperature changes generated by landfill waste degradation and external changes. The main reaction device consists of a lower chamber, a middle chamber, and an upper chamber, respectively simulating the landfill gas generation, the landfill cover (or GCL), and the upper soil sample environment. The upper chamber, loaded with a cylinder through a porous stainless steel plate, applies pressure to the soil sample (or GCL), simulating the earth pressure above the landfill cover. The outlet gas collection device, primarily consisting of a gas collection bottle, collects and processes the post-reaction gas to prevent post-experimental gas contamination. However, the apparatus can only simulate temperature and earth pressure alone and cannot implement tensile stress loading. It also lacks a module for the synergistic effect of aging and tensile stress, making it impossible to test the gas diffusion coefficient under the combined effects of these two factors. Consequently, it fails to meet the requirements for real-time diffusion testing of geomembranes under tension. Summary of the Invention

[0007] The purpose of the present invention is to provide an experimental device and a testing method for testing the gas diffusion coefficient of geomembranes, so as to solve the problem in the prior art that it is impossible to simulate the gas diffusion coefficient test of geomembranes under the coupling of aging and tensile stress, and to provide a reliable experimental device for evaluating the long-term anti-seepage performance of geomembranes under actual working conditions.

[0008] To achieve the above-mentioned object, the present invention provides an experimental device for testing the gas diffusion coefficient of geomembrane, comprising an air supply mechanism, a testing mechanism and a stretching mechanism, wherein the testing mechanism comprises a reaction test cylinder, the reaction test cylinder comprises an upper chamber and a lower chamber, one side of the lower chamber is connected to the air supply mechanism, a placement assembly is provided between the upper chamber and the lower chamber, and a clamping assembly of the stretching mechanism is detachably connected to the middle part of the placement assembly;

[0009] The stretching mechanism also includes a support plate, a stretching assembly and a fixing assembly. The clamping assembly is detachably connected to the middle of the support plate. The fixing assembly is symmetrically arranged on both sides of the clamping assembly and is slidingly connected to the support plate. The stretching assembly is arranged at both ends of the support plate, and the inward side of the stretching assembly is connected to the fixing assembly.

[0010] Preferably, the upper chamber and the lower chamber are respectively provided with a plurality of openings equipped with valves, the top of the upper chamber is provided with a first detection port, and the side wall of the lower chamber is provided with a second detection port.

[0011] Preferably, the placement assembly includes a placement plate and a pressing plate arranged in parallel, the pressing plate is fixedly connected to the bottom of the upper chamber, and the placement plate is fixedly connected to the top of the lower chamber, and a ventilation channel is provided in the middle of the placement plate and the pressing plate.

[0012] Preferably, the gas supply mechanism comprises a gas cylinder, which is connected to the lower chamber through a vent pipe.

[0013] Preferably, the clamping assembly includes two clamping plates arranged in parallel up and down, a ventilation channel 2 is provided in the middle of the two clamping plates, and a plurality of evenly distributed fixing bolts are provided on both sides of the ventilation channel 2 on the clamping plates.

[0014] Preferably, the fixing assembly includes a fixing block and a fixing plate, the fixing block is slidably connected to the support plate, the fixing plate is connected to the upper side of the fixing block by bolts, and threaded adjustment holes are symmetrically provided on the front and rear sides of the fixing block.

[0015] Preferably, the stretching assembly includes a mounting block and an adjusting screw. The mounting block is fixedly connected to both ends of the support plate. Limiting holes are symmetrically provided on the front and rear sides of the mounting block. One end of the adjusting screw is connected to the limiting hole through a bearing, and the other end of the adjusting screw is connected to the threaded adjustment hole.

[0016] The present invention also provides a testing method using the above-mentioned experimental device for testing the gas diffusion coefficient of geomembrane, comprising the following steps:

[0017] S1. First, fix the aged geomembrane to both ends of the fixing assembly. Then, adjust the stretching assembly to drive the fixing assembly to move, apply a tensile force to the geomembrane until it reaches the preset tensile state. Then, fix the clamping assembly to the upper and lower sides of the geomembrane, lock the clamping assembly to ensure that the geomembrane is in the tensile state, release the fixing assembly, and then move the clamping assembly from the stretching mechanism to the middle of the placement assembly.

[0018] S2. Turn on the gas supply mechanism to allow the gas to enter the lower chamber at a set pressure and flow rate. The gas passes through the placement assembly to the bottom of the geomembrane, diffuses through the geomembrane, and then enters the upper chamber;

[0019] S3. Regularly measure the gas concentration in the upper chamber and the lower chamber until the gas diffusion in the lower chamber and the upper chamber reaches a state of equilibrium. Record the gas concentration in the lower chamber and the diffusion time at this time, and calculate the gas diffusion coefficient of the geomembrane.

[0020] Preferably, in S3, the gas diffusion coefficient is calculated by the following formula:

[0021] ;

[0022] Where, is the gas concentration in the lower chamber; D p is the effective diffusion coefficient of gas; ε is the gas porosity of the unsaturated medium; L is the thickness of the unsaturated medium, , is the height from the bottom of the unsaturated medium gas to the bottom of the lower chamber, α 1 for The first positive root of .

[0023] Beneficial effects of the present invention:

[0024] (1) The present invention discloses an experimental device for testing the gas diffusion coefficient of geomembranes, which can simulate the coupling effect of aging and tensile stress on geomembranes in actual environments. The stretching mechanism can apply different tensile forces and cooperate with external aging equipment to simulate environmental aging, making the test results more realistic and providing a reliable basis for evaluating long-term anti-seepage performance. The test mechanism has a modular design, and the reaction test cylinder has multiple openings to facilitate gas control and pressure monitoring. The ventilation channel for placing components avoids airflow disturbances, ensures the stability of the concentration gradient, and improves the accuracy of the diffusion test. The stretching mechanism can achieve uniform clamping of the geomembrane and precise application of tensile force, and is easy to operate and has high precision.

[0025] (2) The present invention discloses a testing method for an experimental device for testing the gas diffusion coefficient of a geomembrane. The testing method simulates the stress on the geomembrane and the gas diffusion and penetration process in a landfill. The obtained parameters are more in line with reality, providing targeted data for landfill projects, helping to optimize the anti-seepage system and reduce pollution. The concentration-time curve is obtained by measuring the gas concentration and the diffusion coefficient is calculated.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of an experimental device for testing the gas diffusion coefficient of geomembranes according to the present invention;

[0028] Figure 2 is a schematic diagram of the testing mechanism of the present invention;

[0029] Figure 3 is a side view of the stretching mechanism of the present invention;

[0030] Figure 4 is a top view of the stretching mechanism of the present invention;

[0031] Figure 5 is a side view of a fixing plate of a stretching mechanism of the present invention;

[0032] Figure 6 It is a top view of the fixed block of the stretching mechanism of the present invention.

[0033] Reference numerals:

[0034] 1. Gas supply mechanism; 11. Gas cylinder; 12. Ventilation pipe;

[0035] 2. Test mechanism; 21. Reaction test cylinder; 211. Upper chamber; 212. Lower chamber; 213. Opening with valve; 22. Placement assembly; 221. Placement plate; 222. Press plate; 223. Ventilation channel 1;

[0036] 3. Stretching mechanism; 31. Support plate; 32. Stretching assembly; 321. Mounting block; 322. Adjusting screw; 33. Fixing assembly; 331. Fixing block; 332. Fixing plate; 333. Threaded adjustment hole; 34. Clamping assembly; 341. Clamping plate; 342. Ventilation channel 2. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to the accompanying drawings and examples. Unless otherwise defined, technical or scientific terms used herein shall have the same meanings as those commonly understood by persons of ordinary skill in the art to which the present invention pertains. The above-mentioned features or features described in the specific examples of the present invention may be combined in any manner. These specific examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0038] Example 1

[0039] like Figures 1 to 6 As shown, the present invention provides an experimental device for testing the gas diffusion coefficient of a geomembrane, comprising a gas supply mechanism 1, a testing mechanism 2, and a stretching mechanism 3. The testing mechanism 2 includes a reaction test cylinder 21, which includes an upper chamber 211 and a lower chamber 212. The upper chamber 211 is a diffusion chamber, and the lower chamber 212 is a gas source chamber. The gas supply mechanism 1 includes a gas cylinder 11, which is connected to the lower chamber 212 via a vent tube 12. The test gas enters the reaction test cylinder 21 through the vent tube 12, forming a unidirectional diffusion path within the upper chamber 211 and the lower chamber 212. A placement assembly 22 is provided between the upper chamber 211 and the lower chamber 212 to simulate the stretched state of the geomembrane. The upper chamber 211 and the lower chamber 212 are each provided with multiple openings 213 equipped with valves to facilitate gas inlet and outlet control and pressure monitoring. A first detection port is provided on the top of the upper chamber 211 , and a second detection port is provided on the side wall of the lower chamber 212 .

[0040] The placement component 22 includes a placement plate 221 and a pressing plate 222 arranged in parallel. The pressing plate 222 is fixedly connected to the bottom of the upper chamber 211, and the placement plate 221 is fixedly connected to the top of the lower chamber 212. A ventilation channel 223 is provided in the middle of the placement plate 221 and the pressing plate 222. The geomembrane is fixed between the placement plate 221 and the pressing plate 222. The edges of the ventilation channel 223 are chamfered to avoid airflow disturbance and ensure uniform passage of gas.

[0041] The clamping assembly 34 of the stretching mechanism 3 is detachably connected to the middle portion of the placement assembly 22. The stretching mechanism 3 also includes a support plate 31, a stretching assembly 32, and a fixing assembly 33. The clamping assembly 34 is detachably connected to the middle portion of the support plate 31. The clamping assembly 34 includes two clamping plates 341 arranged in parallel with each other. Ventilation channel 2 342 is provided in the middle of each clamping plate 341. Ventilation channel 2 342 corresponds to vent channel 1 223 of the placement assembly 22, ensuring a smooth gas diffusion path. Several evenly distributed fixing bolts are provided on both sides of the clamping plates 341 on either side of vent channel 2 342. The geomembrane is located between the two clamping plates 341. The two clamping plates 341 are locked together by the fixing bolts, thereby securing the geomembrane and transferring a uniform load to the geomembrane, simulating the pressure of the geomembrane in the landfill cover layer.

[0042] The fixing assembly 33 is symmetrically arranged on both sides of the clamping assembly 34 and is slidably connected to the support plate 31. The fixing assembly 33 includes a fixing block 331 and a fixing plate 332. The fixing block 331 is slidably connected to the support plate 31. The fixing plate 332 is connected to the upper side of the fixing block 331 by bolts. The front and rear sides of the fixing block 331 are symmetrically provided with threaded adjustment holes 333. The fixing block 331 and the fixing plate 332 cooperate to achieve clamping and fixing of the two ends of the geomembrane.

[0043] The stretching assembly 32 is fixedly connected to both sides of the support plate 31, and the inward side of the stretching assembly 32 is connected to the fixed assembly 33. The stretching assembly 32 includes a mounting block 321 and an adjusting screw 322. The mounting block 321 is fixedly connected to both ends of the support plate 31. The mounting block 321 is symmetrically provided with limiting holes on the front and rear sides. One end of the adjusting screw 322 is connected to the limiting hole through a bearing (the bearing is prior art and is not shown in the accompanying drawings), and the other end of the adjusting screw 322 is connected to the threaded adjustment hole 333 of the fixed block 331. By rotating the adjusting screw 322, the fixed block 331 can be driven to move on the support plate 31, thereby achieving the stretching of the geomembrane. The support plate 31 is provided with a scale corresponding to the stretching force, and the stretching force can be precisely controlled by controlling the distance the fixed block 331 moves.

[0044] Example 2

[0045] The present invention also discloses a testing method of an experimental device for testing the gas diffusion coefficient of a geomembrane according to embodiment 1, comprising the following steps:

[0046] S1. First, fix the aged geomembrane to the two ends of the fixing component 33, rotate the adjusting screws 322 on both sides of the stretching component 32 to drive the fixing component 33 to move, apply a preset tensile force to the geomembrane until it reaches the preset tensile state, and then fix the two clamping plates 341 of the clamping component 34 on the upper and lower sides of the geomembrane, and ensure that the test area completely covers the ventilation channel 2 342, and tighten the fixing bolts to clamp and fix the geomembrane in the stretched state to prevent the aged geomembrane from rebounding to its original state, loosen the fixing component 33, and then move the clamping component 34 from the stretching mechanism 3 to the middle of the placement component 22 to perform a gas diffusion reaction.

[0047] S2. First, close detection ports 1 and 2 of upper chamber 211 and lower chamber 212. Then, introduce nitrogen or nitrogen dioxide into lower chamber 212 to displace the air therein. Open one of the valved openings in upper chamber 211 as an air outlet and introduce nitrogen or nitrogen dioxide into upper chamber 211 to displace the air therein. Then, activate the air supply mechanism and open the vent pipe connected to lower chamber 212, allowing gas to enter lower chamber 212 at the set pressure and flow rate.

[0048] The gas is evenly distributed through the lower chamber 212 to the ventilation channel 223 of the placement plate 221 and reaches the bottom of the geomembrane. After diffusing through the geomembrane, it enters the upper chamber 211 through the ventilation channel 223 of the compression plate 222 until the pressure in the lower chamber 212 is equal to that in the upper chamber 211, and the ventilation pipe 12 and the air outlet of the upper chamber 211 are closed.

[0049] S3. Regularly measure the gas concentrations in the lower chamber 212 and the upper chamber 211 until the gas concentrations in the lower chamber 212 and the upper chamber 211 are equal, obtain the concentration-time curve of the lower chamber 212, and use COMSO software to fit to obtain the gas diffusion coefficient of the geomembrane under the action of aging-stretching coupling.

[0050] Example 3

[0051] The difference from Example 2 is that after obtaining the concentration-time curve of the lower chamber in S3, the gas diffusion coefficient of the geomembrane under the aging-stretching coupling effect is calculated using the formula. The rest is the same as Example 2.

[0052] The formula is:

[0053] ;

[0054] Where, is the gas concentration in the lower chamber; D p is the effective diffusion coefficient of gas; ε is the gas porosity of the unsaturated medium; L is the thickness of the unsaturated medium, , is the height from the bottom of the unsaturated medium gas to the bottom of the lower chamber, α 1 for The first positive root of .

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An experimental device for testing the gas diffusion coefficient of geomembrane, characterized by: The apparatus comprises an air supply mechanism, a testing mechanism and a stretching mechanism. The testing mechanism comprises a reaction test cylinder, which comprises an upper chamber and a lower chamber. One side of the lower chamber is connected to the air supply mechanism. A placement assembly is provided between the upper chamber and the lower chamber. The clamping assembly of the stretching mechanism is detachably connected to the middle of the placement assembly. The stretching mechanism also includes a support plate, a stretching assembly and a fixing assembly. The clamping assembly is detachably connected to the middle of the support plate. The fixing assembly is symmetrically arranged on both sides of the clamping assembly and is slidably connected to the support plate. The stretching assembly is arranged at both ends of the support plate, and the inward side of the stretching assembly is connected to the fixing assembly. The clamping assembly is used to clamp and fix the geomembrane in a stretched state, and includes two clamping plates arranged in parallel above and below. The middle part of each clamping plate is provided with a second ventilation channel, and a number of evenly distributed fixing bolts are provided on both sides of the second ventilation channel on the clamping plate; The fixing assembly is used to fix the two ends of the aged geomembrane, including a fixing block and a fixing plate. The fixing block is slidably connected to the support plate. The fixing plate is connected to the upper side of the fixing block by bolts. The front and rear sides of the fixing block are symmetrically provided with threaded adjustment holes. The tensile assembly is used to apply different tensile forces to the geomembrane. It includes a mounting block and an adjusting screw. The mounting block is fixedly connected to both ends of the support plate. Limiting holes are symmetrically provided on the front and back sides of the mounting block. One end of the adjusting screw is connected to the limiting hole through a bearing, and the other end of the adjusting screw is connected to the threaded adjustment hole. The fixing component fixes the two ends of the aged geomembrane, applies a preset tensile force to the geomembrane through the tensile component, and then the clamping component clamps and fixes the geomembrane in the stretched state. The fixing component is released and the clamping component is moved from the tensile mechanism to the middle of the placement component for gas diffusion testing.

2. The experimental device for testing the gas diffusion coefficient of geomembrane according to claim 1, characterized in that: The upper chamber and the lower chamber are respectively provided with a plurality of openings equipped with valves. The top of the upper chamber is provided with a first detection port, and the side wall of the lower chamber is provided with a second detection port.

3. The experimental device for testing the gas diffusion coefficient of geomembrane according to claim 1, characterized in that: The placement assembly includes a placement plate and a pressing plate arranged in parallel. The pressing plate is fixedly connected to the bottom of the upper chamber, and the placement plate is fixedly connected to the top of the lower chamber. A ventilation channel is provided in the middle of the placement plate and the pressing plate.

4. The experimental device for testing the gas diffusion coefficient of geomembrane according to claim 1, characterized in that: The gas supply mechanism comprises a gas cylinder, which is communicated with the lower chamber through a vent pipe.

5. A testing method using the experimental device for testing the gas diffusion coefficient of geomembrane according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. First, fix the aged geomembrane to both ends of the fixing assembly. Then, adjust the stretching assembly to drive the fixing assembly to move, apply a tensile force to the geomembrane until it reaches the preset tensile state. Then, fix the clamping assembly to the upper and lower sides of the geomembrane, lock the clamping assembly to ensure that the geomembrane is in the tensile state, release the fixing assembly, and then move the clamping assembly from the stretching mechanism to the middle of the placement assembly. S2. Turn on the gas supply mechanism to allow the gas to enter the lower chamber at a set pressure and flow rate. The gas passes through the placement assembly to the bottom of the geomembrane, diffuses through the geomembrane, and then enters the upper chamber; S3. Regularly measure the gas concentration in the upper chamber and the lower chamber until the gas diffusion in the lower chamber and the upper chamber reaches a state of equilibrium. Record the gas concentration in the lower chamber and the diffusion time at this time, and calculate the gas diffusion coefficient of the geomembrane.

6. The test method of the experimental device for testing the gas diffusion coefficient of geomembrane according to claim 5, characterized in that: In S3, the gas diffusion coefficient is calculated by the following formula: ； Where, is the gas concentration in the lower chamber; is the effective diffusion coefficient of gas; is the gas porosity of the unsaturated medium; is the thickness of the unsaturated medium, , is the height from the bottom of the unsaturated medium gas to the bottom of the lower chamber, for The first positive root of .

Images