WO2023240817A1 - 一种连续测试变吸力下非饱和土体气体渗透系数的装置和方法 - Google Patents

一种连续测试变吸力下非饱和土体气体渗透系数的装置和方法 Download PDF

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WO2023240817A1
WO2023240817A1 PCT/CN2022/119749 CN2022119749W WO2023240817A1 WO 2023240817 A1 WO2023240817 A1 WO 2023240817A1 CN 2022119749 W CN2022119749 W CN 2022119749W WO 2023240817 A1 WO2023240817 A1 WO 2023240817A1
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sample
suction
gas
testing
permeability coefficient
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PCT/CN2022/119749
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English (en)
French (fr)
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吴涛
徐浩青
张雷
王丽艳
吴思麟
侯贺营
李小娟
竺明星
王炳辉
刘顺青
周爱兆
孔德辉
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江苏科技大学
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Priority to KR1020237025532A priority Critical patent/KR20230125043A/ko
Publication of WO2023240817A1 publication Critical patent/WO2023240817A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
    • G01N15/082—Investigating permeability by forcing a fluid through a sample
    • G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
    • G01N13/04—Investigating osmotic effects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
    • G01N5/04—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by removing a component, e.g. by evaporation, and weighing the remainder
    • G01N5/045—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by removing a component, e.g. by evaporation, and weighing the remainder for determining moisture content
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N7/00—Analysing materials by measuring the pressure or volume of a gas or vapour
    • G01N7/10—Analysing materials by measuring the pressure or volume of a gas or vapour by allowing diffusion of components through a porous wall and measuring a pressure or volume difference
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/30—Landfill technologies aiming to mitigate methane emissions

Definitions

  • the invention relates to a device and method for continuously testing the gas permeability coefficient of unsaturated soil under variable suction, and belongs to the technical field of geotechnical engineering.
  • Gas permeability coefficient is an important indicator for judging the migration characteristics of gas in soil layers. It is mainly affected by factors such as soil structure and its changes, pore tortuosity, pore size and saturation.
  • the soil covering layer is an important part of the closure and covering system of solid waste landfills in my country. Its gas permeability coefficient is an important parameter for the analysis and design of gas migration in the covering layer, and has an important impact on the reduction of greenhouse gases and harmful gases in landfills. .
  • the present invention proposes a device and method for continuously testing the gas permeability system of unsaturated soil under variable suction.
  • This test device mainly uses dialysis method to achieve the required suction.
  • the negative pore pressure in the soil sample is close to the actual state on site. It also uses moisture desorption around the soil sample to shorten the time for the suction balance of unsaturated soil.
  • the dialysis method is used to apply the required suction force.
  • the principle is to utilize the dialysis force of the dialysis solution. Because dialysis solutions of different concentrations produce different osmotic suctions on the moisture of the unsaturated soil sample on the other side of the membrane through the barrier effect of the semipermeable membrane, and during the change process of the soil sample moisture, it can only absorb and retain moisture. Only when the matrix suction and the osmotic suction of the solution are balanced can the soil moisture remain unchanged. Therefore, using dialysis solutions of different concentrations to dialyse soil samples can achieve the purpose of applying and controlling suction to the soil samples.
  • a device for continuously testing the gas permeability coefficient of unsaturated soil under variable suction which is characterized by: including a gas supply device, a confining pressure device, a testing device, a suction control device and Exhaust device; the test device is divided into an inner chamber and an outer chamber.
  • the inner chamber is used to place soil samples, and the outer chamber is used to store a predetermined concentration of dialysis solution and apply confining pressure;
  • the air supply device includes an air compressor, One end of the pressure device is connected to an air compressor, and the other end of the confining pressure device is connected to the outer chamber of the testing device.
  • the air compressor is used to input confining pressure gas to the outer chamber of the testing device and transport test gas to the inner chamber of the testing device; so
  • the suction control device is used to apply and control suction to the soil sample;
  • the exhaust device is connected to the inner chamber of the testing device, and the exhaust device is used to discharge the test gas from the inner chamber.
  • the suction control device passes through the first suction channel and the first constant flow pump and the second suction channel and the second constant flow pump. One end continuously supplies the solution, and the other end continuously flows out the solution, so that the solution circulates in the outer chamber, and the air compressor passes through
  • the main air inlet pipe is connected to the air inlet pipe and the confining pressure air inlet pipe respectively.
  • the main air inlet pipe, the air inlet pipe and the confining pressure air inlet pipe are connected to each other through a tee joint.
  • the columnar soil sample is filled in the inner chamber.
  • the air inlet pipe is used to carry out the test.
  • the gas is passed into the lower chamber cavity at the bottom of the soil sample.
  • the confining pressure device is provided with an air source by an air compressor.
  • the testing device It is connected to the top of the testing device through a confining air inlet pipe and is used to transport confining pressure gas into the room where the dialysis solution is placed.
  • the air pressure is converted into gas-liquid pressure that outputs hydraulic pressure around the soil sample.
  • the confining pressure is equal to the air pressure of the lower chamber cavity at the bottom of the soil sample, which is beneficial to ensuring that the semi-permeable membrane is closely attached to the side wall of the soil sample.
  • the gas permeability coefficient is calculated by recording the data from the first pressure gauge at the bottom of the soil sample, the third pressure gauge at the top of the soil sample, and the second electronic soap film flow meter.
  • the air supply device includes an air inlet pipe.
  • One end of the air inlet pipe is connected to an air compressor and the test gas is passed into the inner chamber of the test device.
  • One end of the air inlet pipe close to the air compressor is sequentially provided with a first regulating valve and a first electronic soap film. Flow meter, first stop valve and first pressure gauge.
  • One end of the air inlet pipe is connected to the air compressor, and the other end is connected to the lower chamber cavity at the bottom of the soil sample.
  • the test gas is input into the lower chamber cavity, and then enters the soil sample through the porous plate.
  • the confining pressure device includes a confining pressure air inlet pipe.
  • the air compressor provides an air source and passes the confining pressure gas into the outer chamber of the test device through the confining pressure air inlet pipe.
  • the confining pressure air inlet pipe is provided with a second end near the air compressor. pressure regulating valve, second stop valve and second pressure gauge.
  • One end of the confining pressure air inlet pipe is connected to the air compressor, and the other end is connected to the top of the outer chamber.
  • the test device includes a sample barrel, a base and a top cover.
  • the base is set at the bottom of the sample barrel, and the top cover is set at the top of the sample barrel.
  • the sample barrel is divided into an outer sample barrel and an inner sample barrel.
  • the inner sample cylinder divides the testing device into an inner chamber and an outer chamber.
  • the inner chamber is a cylindrical container and the outer chamber is an annular container.
  • the inner sample cylinder includes an upper sample cylinder, a middle sample cylinder and a lower sample cylinder.
  • the upper section The sample cylinder, the middle sample cylinder and the lower sample cylinder are assembled into three sections to form an inner chamber; the upper sample cylinder and the top cover form the upper chamber cavity, and the upper and lower ends of the middle sample cylinder are equipped with porous plates.
  • the cylinder and two porous plates form a middle chamber for placing soil samples, and the lower sample tube and the base form a lower chamber cavity; the middle sample cylinder has a porous structure.
  • the testing device is a container surrounded by a sample cylinder, a base and a top cover. It is divided into an inner chamber and an outer chamber.
  • the inner chamber is composed of upper and lower chamber cavities and a middle chamber for placing cylindrical soil samples.
  • the bottom of the soil sample The lower chamber cavity is connected to the gas supply device, and the upper chamber cavity at the bottom of the soil sample is connected to the exhaust device.
  • the middle sample tube has a porous structure to allow the dialysis solution of a predetermined concentration to pass through the pores and the semipermeable membrane to maximize the contact to shorten dialysis time.
  • the suction control device includes a semipermeable membrane, a dialysis solution of a predetermined concentration, a first constant flow pump, and a second constant flow pump; the semipermeable membrane is arranged inside the middle sample tube and is close to the side wall of the soil sample;
  • the dialysis solution of the predetermined concentration adopts a dialysis solution with a layer of light oil floating on it; the opposite sides of the outer sample tube are respectively provided with a first suction channel and a second suction channel, and the first suction channel, the second suction channel and the outer
  • the chambers are connected;
  • the first constant flow pump is connected to one side of the outer sample cylinder through the first suction hole and supplies the solution, and the second constant flow pump is connected to the other side of the outer sample cylinder through the second suction hole and flows out the solution.
  • the first constant flow pump continuously supplies the solution through the end of the first suction hole connected to one side of the outer sample cylinder, and the second constant flow pump continuously flows out the solution through the end of the second suction hole connected to the other side of the outer sample barrel. , making it easy for the outer chamber to circulate, and the soil sample begins to dehumidify or absorb moisture.
  • the semipermeable membrane is sleeved in the middle sample tube.
  • the upper and lower ends of the semipermeable membrane are sleeved on the upper and lower ends of the middle sample sleeve.
  • the connection with the middle sample tube is sealed with sealing resin.
  • the outer wall of the outer sample tube is provided with a scale mark, and it is observed through the scale mark whether the suction force reaches balance.
  • the semipermeable membrane is an asymmetric membrane with a molecular weight cutoff of 1,000 to 50,000; the dialysis solution with a predetermined concentration is a macromolecular solution.
  • Semipermeable membranes are classified as asymmetric membranes according to structure, and semipermeable membranes are classified as ultrafiltration membranes according to pore size, and are used to separate macromolecular substances; the sample tube, base and top cover are all made of organic glass.
  • the exhaust device includes an exhaust pipe, and a third pressure gauge and a second electronic soap film flow meter are arranged at one end of the exhaust pipe near the testing device.
  • a method for continuously testing the gas permeability coefficient of unsaturated soil under variable suction which is characterized in that the steps are as follows:
  • the present invention has the following beneficial effects: 1.
  • the test device using the above dialysis method provided by the present invention is more operable, more convenient and faster, and the entire test process can be performed more stably.
  • This invention is based on the same soil sample test. Cavities are set at the bottom and top of the soil sample, and the test gas is input from the cavity at the bottom of the soil sample. This avoids disturbance of the soil sample, makes the soil sample evenly stressed, and can be monitored through monitoring.
  • the soil moisture content and suction change to obtain the gas permeability coefficient of the soil sample under different water content and suction; during the measurement process, the confining pressure is always equal to the air pressure of the cavity at the bottom of the soil sample to ensure that the semipermeable membrane is tightly connected to the side wall of the soil sample. It can avoid the loss of moisture in the soil sample caused by excessive air pressure in the bottom cavity, and avoid excessive moisture in the soil sample caused by excessive confining pressure, thereby avoiding factors that interfere with the accuracy of the measurement data.
  • the present invention does not use axis translation technology and can reproduce the negative pore pressure state of unsaturated soil under on-site conditions.
  • the present invention injects a predetermined concentration of dialysis solution into the outer chamber, and uses dialysis solutions of different concentrations to dialyse the soil sample to apply and control suction to the soil sample. Constant flow pumps and suction channels are respectively provided at both ends of the outer chamber to achieve soil sampling. Cyclically dehumidify and conduct gas permeability tests on unsaturated soils under different hydraulic histories.
  • the permeability coefficient calculation method of the present invention is simple and only needs to obtain the pressure and gas flow rate at the measurement point.
  • Figure 1 is a schematic structural diagram of the present invention.
  • Figure 2 is a schematic structural diagram of the reverse sleeve of the semipermeable membrane of the present invention.
  • Figure 3 is a partial cross-sectional schematic diagram of the middle section of the sample cylinder of the present invention.
  • this embodiment provides a device for continuously testing the gas permeability coefficient of unsaturated soil under variable suction, including: a gas supply device, a confining pressure device, a testing device, a suction control device, and an exhaust device. gas device;
  • the air supply device includes an air compressor 1, a first regulating valve 2-1, a first electronic soap film flow meter 3-1, a first stop valve 4-1 and a first pressure gauge 5-1;
  • the air compressor 1 is connected to the air inlet pipe and the confining pressure air inlet pipe respectively through the main air inlet pipe, and the main air inlet pipe, the surrounding pressure air inlet pipe and the air inlet pipe are connected to each other through a tee joint.
  • the other end of the air inlet pipe is connected to the lower chamber cavity at the bottom of the soil sample 6.
  • the air inlet pipe is used to pass the test gas into the lower chamber cavity at the bottom of the soil sample 6. From one end of the gas source, the air inlet pipe is connected and adjusted in sequence.
  • the first regulating valve 2-1 for the inlet pressure
  • the first electronic soap film flow meter 3-1 for regulating and measuring the inlet flow
  • the first stop valve 4-1 for controlling the introduction of the test gas and measuring the gas at the bottom of the soil sample 6 Pressure of the first pressure gauge 5-1.
  • the confinement pressure device is also provided with an air source by the air compressor 1.
  • One end of the confinement pressure inlet pipe is connected to the top of the outer chamber 13 of the test device for transporting confinement pressure gas into the outer chamber 13 where the dialysis solution is placed.
  • the confining pressure inlet pipe is connected in sequence to a second pressure regulating valve 2-2 for adjusting the confining gas pressure, a second stop valve 4-2 for controlling the introduction of the confining gas, and a second valve for measuring the confining gas pressure.
  • Pressure gauge 5-2 the outer chamber uses a dialysis solution with a layer of light oil floating on it to prevent the confining pressure gas from dissolving in the dialysis solution.
  • the confining pressure gas enters the outer chamber 13 through the confining pressure air inlet pipe, and the gas is converted into soil sample 6 The air-hydraulic pressure of the surrounding output hydraulic pressure.
  • the test device includes a sample cylinder, a base 10, a top cover 11 and a porous plate 7.
  • the test device is a container surrounded by the sample cylinder, the base 10 and the top cover 11.
  • the sample cylinder is divided into outer sample cylinders 12- 1 and an inner sample cylinder.
  • the inner sample cylinder divides the container into an inner chamber and an outer chamber 13.
  • the inner chamber is a cylindrical container and the outer chamber 13 is an annular container; the outer chamber 13 is used to store a predetermined concentration of dialysis solution, and the inner chamber It is composed of three sections: the upper sample cylinder 12-2, the middle sample cylinder 12-3 and the lower sample cylinder 12-4.
  • an upper chamber it is divided into three parts: an upper chamber, a middle chamber and a lower chamber; the upper chamber is composed of a top cover 11 and a lower chamber.
  • the upper chamber cavity is surrounded by the upper sample tube 12-2; the middle chamber is where the columnar soil sample 6 is placed, which is surrounded by two porous plates 7 and the middle sample tube 12-3.
  • Part of the masonry soil sample 6 has a porous structure to allow the dialysis solution of a predetermined concentration to have maximum contact with the semipermeable membrane 8 through the pores, so as to shorten the dialysis time.
  • the porous plates 7 are respectively provided at both ends of the middle sample cylinder 12-3, and the connection is sealed with a sealing medium to prevent gas from leaking from the pores during the gas permeability coefficient test.
  • the base 10 is provided at the bottom end of the sample cylinder.
  • the top cover 11 is arranged on the top of the sample tube to seal the annular container outer chamber 13 and the cylindrical container inner chamber.
  • the suction control device includes a semipermeable membrane 8, a predetermined concentration of dialysis solution, a first constant flow pump 15-1, and a second constant flow pump 15-2; the semipermeable membrane 8 is provided in the middle sample cylinder 12-3
  • the inner side of the cylindrical soil sample 6 is close to the side wall of the cylindrical soil sample 6, and extends along the outer edge of the middle sample tube 12-3 and is sleeved on the upper and lower ends of the middle sample sleeve 12-3.
  • the O-ring 9 clamps and defines the entire semipermeable membrane 8.
  • the sealing measures at the back sleeve of the semipermeable membrane 8 are specifically designed as follows: a closed O-ring is provided at the back sleeve of the semipermeable membrane 8 at the upper end of the middle sample tube 12-3. Ring 9, and at the same time, an annular groove is provided at the connection between the upper sample cylinder 12-2 and the middle sample cylinder 12-3. The annular groove corresponds to the O-ring 9 and is used to fix the O-ring 9; in the middle section The same sealing measures are adopted at the reverse sleeve of the semipermeable membrane 8 at the lower end of the sample tube 12-3. A first suction channel 14-1 and a second suction channel 14-2 are respectively provided on opposite sides of the outer chamber 13.
  • the first constant flow pump 15-1 communicates with one side of the outer sample cylinder 12-1 through the first suction channel 14-1.
  • One end of the connection continuously supplies solution
  • the second constant flow pump 15-2 continuously flows out from the end connected to the other side of the outer sample cylinder 12-1 through the second suction channel 14-2, causing the solution to circulate in the outer chamber 13.
  • the soil sample begins to dehumidify or absorb moisture.
  • the dialysis solution with a predetermined concentration is a macromolecule solution.
  • polyethylene glycol (PEG) solution is used.
  • PEG is the abbreviation of polyethylene glycol. It is a high molecular weight chemical reagent. It can be divided into many types according to different molecular weights, including PEG1500, PEG4000, PEG6000, PEG8000, PEG10000, PEG20000 and so on. The higher the concentration of the solution, the greater its osmotic suction.
  • the semipermeable membrane 8 generally uses the molecular weight cutoff MWCO to represent the size of the substance that can pass through.
  • a semipermeable membrane with PEG20000 and a molecular weight cutoff (MWCO) of 14000 was selected for the test.
  • the semipermeable membrane 8 is an asymmetric membrane.
  • the exhaust device is composed of a second electronic soap film flow meter 3-2 that accurately measures the air outlet flow rate and a third pressure gauge 5-3 that measures the gas pressure at the top of the soil sample.
  • the accuracy of the second electronic soap film flow meter 3-2 is is 0.1mL/min; one end of the second electronic soap film flow meter 3-2 is connected to the upper cavity of the columnar soil sample 6 through the exhaust pipe and the top cover 11, and the other end is connected to the atmosphere.
  • the O-ring material in this embodiment is neoprene; the connection is sealed with epoxy resin, and the porous plate 7 is a stainless steel porous plate; the sample tube, base 10 and top cover 11 are all made of It is made of organic glass; the test gas used is air; the columnar soil sample 6 is loess, with a diameter of 32mm and a height of 25mm.
  • This embodiment provides a method for continuously testing the gas permeability coefficient of unsaturated soil under variable suction.
  • the measurement method adopts the above-mentioned measurement device.
  • the measurement method includes the following steps:
  • Step 1 Place the device in a suitable location, ensuring that the place is clean, with appropriate temperature and humidity, no vibration, and no direct sunlight. Check the sealing performance of the device, and check the calibration and function of the instrument to ensure optimal operating performance. Best measurement results.
  • Step 2 Put the semipermeable membrane 8 back on the middle sample tube 12-3 and fix it with an O-ring 9, then prepare a loose soil body with a certain moisture content and dry density, and fill the columnar soil in two layers. Sample 6 is compacted and the soil sample is evacuated and saturated, and then the porous plate is placed. In order to ensure sealing, the pores connected to the edges of porous plate 7 are sealed with epoxy resin.
  • Step 3 Each concentration of PEG solution corresponds to a specific suction force. Find the suction value of the corresponding concentration through the calibration curve of concentration and suction force of that type of PEG solution.
  • s 11c 2 ; where s is suction (MPa), and c is PEG solution concentration (g/g water).
  • s suction
  • c PEG solution concentration
  • first suction channel 14-1 use the first constant flow pump 15-1 to inject a predetermined concentration of PEG solution into the outer chamber 13, and when it reaches a position slightly above the soil sample 6, open the second suction channel. 14-5 and the second constant flow pump 15-2 serve as the outflow channel for the PEG solution with changed concentration.
  • One end of the first constant flow pump 15-1 connected to the outer chamber 13 continuously supplies solution, while the second constant flow pump 15-2 at the other end continuously flows out, causing the solution to circulate in the outer chamber, and the soil sample begins to dehumidify or Hygroscopic. And there is a scale mark on the wall of the outer chamber 13.
  • the suction force of this stage reaches balance.
  • soil sample 6 reaches suction balance, the moisture content of the sample is calculated by weighing the change in mass of the PEG solution, and then the gas permeability coefficient of soil sample 6 is tested.
  • Step 4 Open the first stop valve 4-1 of the air inlet pipe, and the air compressor 1 delivers the test gas to the bottom cavity of the soil sample 6. After the gas passes through the soil sample 6 in the upper and lower porous plates 7, The top exhaust pipe is output to the atmosphere; at the same time, the second stop valve 4-2 of the confining pressure inlet pipe is opened, and the air compressor 1 transports the confining pressure gas to the outer chamber 13. Previously, a layer of light oil was added to the PEG solution.
  • the flow rate Q is recorded through the first pressure gauge 5-1 installed at the bottom cavity of the soil sample 6.
  • the lower chamber pressure P 1 of the soil sample 6 is recorded, and the soil sample is recorded through the third pressure gauge 5-3 installed at the top cavity of the soil sample 6.
  • the upper chamber pressure P 2 of 6 when the gas pressure at the measuring point remains constant and the gas flow rate remains basically unchanged, the system reaches a steady state, and the gas pressure at the measuring point is recorded at this time.
  • Step 5 The migration of gas in the covering layer includes convection and diffusion. This experiment mainly studies the convection of gas in the covering layer. Since there is a pressure gradient between the gas pressure and the atmospheric pressure under the covering layer, it is believed that the steady flow of gas in the covering layer obeys Darcy's law, that is, it satisfies the following relationship:
  • k g is the gas permeability coefficient (m 2 ); ⁇ g is the viscosity coefficient of the gas (Pa ⁇ s).
  • the value of air at normal temperature and pressure (20°C, one standard atmosphere) is 1.81 ⁇ 10 -5 Pa ⁇ s;
  • Q is the gas flow rate through the soil sample (m 3 ⁇ s -1 );
  • A is the cross-sectional area of the material (m 2 );
  • h is the height of the soil sample (m);
  • Step 6 Discharge the solution in the outer chamber 13, replace the PEG solution corresponding to the next level of suction, and use the same third, fourth, fifth, and sixth steps mentioned above to measure the gas permeability coefficient under this level of suction.

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Abstract

一种连续测试变吸力下非饱和土体气体渗透系数的装置和方法，包括供气装置、围压装置、吸力控制装置和排气装置，测试装置的内室用于放置土样(6)，外室(13)用于储存预定浓度的渗析溶液和施加围压；供气装置包括空气压缩机(1)，围压装置一端连接空气压缩机(1)，围压装置的另一端连接测试装置的外室(13)，空气压缩机(1)用于向测试装置的外室(13)输入围压气体和向测试装置的内室输送测试气体；吸力控制装置用于对土样(6)施加和控制吸力；排气装置用于排出内室的测试气体；通过监控土样(6)吸力变化，获得土样(6)在不同含水量下的气体渗透系数，试验装置的可操作性更强，更加方便快捷。

Description

一种连续测试变吸力下非饱和土体气体渗透系数的装置和方法 技术领域
本发明涉及一种连续测试变吸力下非饱和土体气体渗透系数的装置和方法，属于岩土工程技术领域。
背景技术
气体渗透系数是判断气体在土层中运移特性的重要指标，主要受土体结构及其变化、孔隙曲折度、孔隙尺寸和饱和度等因素的影响。土质覆盖层是我国固体废物填埋场封场覆盖系统的重要组成部分，其气体渗透系数是覆盖层气体运移分析与设计的重要参数，对填埋场温室气体和有害气体减排有重要影响。
目前，国内外测试非饱和土的气体渗透特性时，大部分先通过轴平移技术来实现吸力控制，然后再通过三轴渗透仪或水气运动联合测定仪等各种装置测量气体渗透系数。传统方法的缺点是：(1)轴平移是将孔压增大为正值,同时也增大气压,通过二者的差值来施加设定的基质吸力，但是推广到现场状态时,非饱和土中的孔压都是负的,这种技术的适用性需要进一步考察并且轴平移可能会导致试样变形和内部结构变化，导致试验数据不准确；(2)由于轴平移技术能够达到的吸力值有限(0～1500kPa),因此研究试样处于高吸力条件进行试验时将受到限制；(3)测量时需要分别制备不同含水量的试样进行测试，不能直接测试单个试样的气体渗透系数随含水量的变化，可能因试样的个体差异导致试验结果波动；(4)测量时需要反复密封土样、连接装置，操作繁冗。
发明内容
为了克服上述现有技术的不足，本发明提出了一种连续测试变吸力下非饱和土体气体渗透系的装置和方法。本试验装置主要是采用渗析法来达到所需要的吸力，土样中的负孔压是接近于现场实际状态的,并采用土样周围脱吸湿,缩短了非饱和土吸力平衡的时间。
由于Darcy定律可以描述气体在非饱和土中的渗透，因此本试验 装置根据Darcy定律中需测的参数设计而来。此外采用渗析法施加所需的吸力,其原理是利用渗析溶液的渗析力。因为不同浓度的渗析溶液通过半透膜的隔挡作用对膜另一侧的非饱和土样的水分产生不同大小的渗透吸力,而土样水分在变化过程中,只有在对水分有吸持作用的基质吸力与溶液的渗透吸力达到平衡了,土样水分才能保持不变。因此采用不同浓度的渗析溶液渗析土样也就达到了对土样施加和控制吸力的目的。
本发明的目的是通过以下技术方案来实现的，一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：包括供气装置、围压装置、测试装置、吸力控制装置和排气装置；所述测试装置分为内室和外室，内室用于放置土样，外室用于储存预定浓度的渗析溶液和施加围压；所述供气装置包括空气压缩机，围压装置一端连接空气压缩机，围压装置的另一端连接测试装置的外室，所述空气压缩机用于向测试装置的外室输入围压气体和向测试装置的内室输送测试气体；所述吸力控制装置用于对土样施加和控制吸力；所述排气装置与测试装置的内室连接，排气装置用于排出内室的测试气体。
吸力控制装置通过第一吸力孔道与第一恒流泵和第二吸力孔道与第二恒流泵，一端不断地供应溶液，另一端不断地流出溶液，使溶液在外室内循环运动，空气压缩机通过总进气管分别连接进气管与围压进气管，总进气管、进气管和围压进气管之间通过三通接头相互连接，在内室中填筑柱形土样，进气管用于将测试气体通入土样下部的下室空腔中，围压装置由空气压缩机提供气源，通过围压进气管与测试装置的顶端连接，用于向放置渗析溶液的室内输送围压气体，进入外室后将气压转换为向土样周围输出液压的气液压力，在测量过程中始终保证围压等于土样底部的下室空腔气压，有利于保证半透膜与土样侧壁紧密贴合，最后通过记录土样底部的第一压力表、土样顶部的第三压力表以及第二电子皂膜流量计的数据计算气体渗透系数。
所述供气装置包括进气管，进气管的一端连接空气压缩机并将测试气体通入测试装置的内室中，进气管靠近空气压缩机一端依次设有 第一调节阀、第一电子皂膜流量计、第一截止阀和第一压力表。
进气管一端连接空气压缩机，另一端与土样底部的下室空腔连接，将测试气体输入下室空腔中，再通过多孔板进入土样。
所述围压装置包括围压进气管，空气压缩机提供气源并通过围压进气管将围压气体通入测试装置的外室中，围压进气管靠近空气压缩机一端依次设有第二调压阀、第二截止阀和第二压力表。
围压进气管一端与空气压缩机连接，另一端与外室的顶部连接。
所述测试装置包括试样筒、底座和顶盖，底座设置于试样筒的底端，顶盖设置于试样筒的顶端；所述试样筒分为外试样筒、内试样筒，内试样筒将测试装置分为内室和外室，内室为柱形容器，外室为环形容器；内试样筒包括上段试样筒、中段试样筒和下段试样筒，上段试样筒、中段试样筒和下段试样筒三段拼成内室；上段试样筒与顶盖围成上室空腔，中段试样筒上下两端均设有多孔板，中段试样筒与两块多孔板围成中室用于放置土样，下段试样管与底座围成下室空腔；所述中段试样筒为多孔结构。
测试装置由试样筒、底座和顶盖围成的容器，分内室和外室，内室由上、下室空腔和用于放置柱形的土样的中室组成，土样底部的下室空腔连接所述供气装置，土样底部的上室空腔连接所述的排气装置，中段试样筒为多孔结构、以允许预定浓度的渗析溶液通过孔道与半透膜有最大接触，以缩短渗析时间。
所述吸力控制装置包括半透膜、预定浓度的渗析溶液、第一恒流泵、第二恒流泵；所述半透膜设置于中段试样管内侧并紧贴于土样侧壁；所述预定浓度的渗析溶液采用上浮一层轻质油的渗析溶液；所述外试样筒相对两侧分别设有第一吸力孔道、第二吸力孔道，第一吸力孔道、第二吸力孔道与外室相通；第一恒流泵通过第一吸力孔道与外试样筒一侧连接并供应溶液，第二恒流泵通过第二吸力孔道与外试样筒另一侧连接并将溶液流出。
在预定浓度的渗析溶液加入一层轻质油，避免围压气体溶解于渗析溶液中。第一恒流泵通过第一吸力孔道与外试样筒一侧连接的一端 不断地供应溶液，第二恒流泵通过第二吸力孔道与外试样筒另一侧连接的一端不断地流出溶液，使外室内的容易循环运动，土样开始脱湿或吸湿。
所述半透膜套于中段试样筒内，半透膜的上、下两端反套在中段试样筒的上、下两端，上、下两端反套处设有闭合的O型圈，所述上段试样筒的下端、下段试样筒的上端均设有与O型圈相匹配的环形凹槽，中段试样筒与上段试样筒、下段试样筒连接处及多孔板与中段试样筒连接处均采用密封树脂进行密封处理。
将半透膜的上端反套于中段试样筒的上端，并用O型圈限定，在上段试样筒的下端设置与O型圈相匹配的环形凹槽，用于固定O型圈，半透膜的下端与上端同样用O型圈限定，为保证密封性，连接处采用环氧树脂密封。
所述外试样筒外壁设有刻度线，通过刻度线观察吸力是否达到平衡。
打开第一吸力孔道，用第一恒流泵将预定浓度的渗析溶液注入外室，待达到比土样稍微靠上的位置时，开启第二吸力孔道和恒流泵，一端不断供应溶液，另一端不断流出，使溶液在外室中形成循环运动，土样开始脱湿或吸湿，当渗析溶液液面不变时，则此级吸力达到平衡。
所述半透膜为非对称膜，其截留分子量为1000～50000；所述预定浓度的渗析溶液为大分子溶液。
半透膜按结构分类属于非对称膜，半透膜按孔径划分属于超滤膜，用于分离大分子物质；所述试样筒、底座与顶盖均由有机玻璃加工而成。
所述排气装置包括排气管，排气管靠近测试装置一端依次设有第三压力表、第二电子皂膜流量计。
一种连续测试变吸力下非饱和土体气体渗透系数的方法，其特征在于：所述步骤如下：
1)固定半透膜，在中室内填筑柱形土样；
2)根据渗析溶液浓度与吸力的率定曲线，制备所测吸力对应的 预定浓度的渗析溶液13；
3)打开两侧的恒流泵，使渗析溶液在外室中循环运动，土样开始脱湿或吸湿，直至吸力平衡，然后称量渗析溶液质量变化计算出试样含水量；
4)开启围压装置与供气装置的截止阀，输送测试气体，在测量过程中始终保证围压等于土样底部空腔气压；
5)记录所需参数，根据达西定律，计算气体渗透系数；
6)调整渗析溶液浓度，采用上述同样方法进行下一级吸力的气体渗透系数测量。
本发明具有以下有益效果：1、本发明提供的采用上述渗析法的试验装置的可操作性更强，更加方便快捷，而且整个试验过程可更加稳定地进行。
2、本发明基于同一个土样试验，在土样的底部以及顶部设置空腔，将测试气体从土样底部的空腔输入，避免了土样扰动，使土样受力均匀，可以通过监控土体含水量与吸力变化，从而获得土样在不同含水量与吸力下的气体渗透系数；测量过程中始终保持围压等于土样底部空腔气压，从而保证半透膜与土样侧壁紧贴，避免底部空腔气压过大导致土样中水分丢失，也避免围压过大导致土样中水分过大，从而避免因素干扰测量数据的准确性。
3、本发明不采用轴平移技术,能够再现现场状态下非饱和土的负孔压状态。
4、本发明通过在外室注入预定浓度的渗析溶液，采用不同浓度的渗析溶液渗析土样从而达到对土样施加和控制吸力，在外室两端分别设置恒流泵和吸力孔道，能够实现土样循环脱吸湿,进行不同水力学历史下非饱和土的气体渗透测试。
5、本发明的渗透系数计算方法简单，只需获得测量点的压强和气体流量。
附图说明
图1是本发明结构示意图。
图2是本发明半透膜反套处结构示意图。
图3是本发明中中段试样筒部分截面示意图。
图中：1空气压缩机、2-1第一调压阀、2-2第二调压阀、3-1电子皂膜流量计、3-2电子皂膜流量计、4-1截止阀、4-2截止阀、5-1压力表、5-2压力表、6土样、7多孔板、8半透膜、9O型圈、10底座、11顶盖、12-1外试样筒、12-2上段试样筒、12-3中段试样筒、12-4下段试样筒、13外室、14-1第一吸力孔道、14-2第二吸力孔道、15-1第一恒流泵、15-2第二恒流泵。
具体实施方式
下面结合附图对本发明进行进一步的说明。下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有作出创造性劳动的前提下所获得的所有其他实施例，都属于本发明保护的范围。
实施例1
如附图1、2、3所示，本实施例提供一种连续测试变吸力下非饱和土体气体渗透系数的装置，包括：供气装置、围压装置、测试装置、吸力控制装置以及排气装置；
所述供气装置包括空气压缩机1、第一调节阀2-1、第一电子皂膜流量计3-1、第一截止阀4-1和第一压力表5-1；提供气源的空气压缩机1通过总进气管分别连通进气管与围压进气管，总进气管、围压进气管和进气管三者之间通过三通接头相互连接。进气管的另一端与土样6底部的下室空腔连通，所述进气管用于将测试气体通入土样6下部的下室空腔中，从气源一端，进气管上依次连接调节进气压力的第一调节阀2-1、调节与测量进气流量的第一电子皂膜流量计3-1、控制测试气体通入的第一截止阀4-1以及测量土样6底部气体压力的第一压力表5-1。
所述围压装置同样由空气压缩机1提供气源，围压进气管一端与测试装置的外室13顶端相连，用于向放置渗析溶液的外室13内输送 围压气体。从气源一端，围压进气管上依次连接调节围压气体压力的第二调压阀2-2、控制围压气体通入的第二截止阀4-2以及测量围压气体压力的第二压力表5-2，外室内采用上浮一层轻质油的渗析溶液，避免围压气体溶解于渗析溶液中，围压气体通过围压进气管进入外室13，将气体转化为向土样6周围输出液压的气液压力。
所述测试装置包括试样筒、底座10、顶盖11和多孔板7，测试装置是由试样筒、底座10和顶盖11围成的容器，试样筒分为外试样筒12-1和内试样筒，内试样筒将容器分为内室和外室13，内室为柱形容器，外室13为环形容器；外室13用来储存预定浓度的渗析溶液，内室由上段试样筒12-2、中段试样筒12-3和下段试样筒12-4三段拼成，分为上室、中室、下室三个部分；上室由顶盖11与上段试样筒12-2围成的上室空腔；中室由两块多孔板7与中段试样筒12-3围成的柱形土样6放置处，中段试样筒12-3围砌土样6部分为多孔结构，以允许预定浓度的渗析溶液通过孔道与半透膜8有最大接触，以缩短渗析时间。所述多孔板7分别设置于中段试样筒12-3的两端，连接处用密封介质密封，避免气体渗透系数测试过程中气体从孔隙中泄露，底座10设置在试样筒的底端，顶盖11设置在试样筒的顶端以封住环形容器外室13和柱形容器内室。
所述吸力控制装置包括半透膜8、预定浓度的渗析溶液、第一恒流泵15-1、第二恒流泵15-2；所述半透膜8设置于中段试样筒12-3的内侧并紧贴柱形土样6侧壁，沿中段试样筒12-3外沿处伸出并反套在中段试样套筒12-3的上、下端，在所述反套处采用O型圈9夹紧限定整个半透膜8，在半透膜8反套处的密封措施具体设计为，在中段试样筒12-3的上端半透膜8反套处设置闭合的O型圈9，同时在上段试样筒12-2与中段试样筒12-3之间连接部位设置环形凹槽，环形凹槽与O型圈9相对应，用于固定O型圈9；在中段试样筒12-3的下端半透膜8反套处采用同样的密封措施。外室13相对两侧分别设置第一吸力孔道14-1、第二吸力孔道14-2，第一恒流泵15-1通过第一吸力孔道14-1与外试样筒12-1一侧连接的一端不断地供应溶液， 第二恒流泵15-2通过第二吸力孔道14-2与外试样筒12-1另一侧连接的一端不断地流出，使溶液在外室13中循环运动，土样开始脱湿或吸湿。且外室13的外试样筒12-1的筒壁上标有刻度线，当渗析溶液液面不变时，则此级吸力达到平衡。
进一步，所述预定浓度的渗析溶液是大分子溶液。本实施例中，采用聚乙二醇(PEG)溶液。PEG是聚乙烯乙二醇的简称，是一种高分子量的化学试剂，按分子量的不同可以分为多种类型，有PEG1500、PEG4000、PEG6000、PEG8000、PEG10000、PEG20000等等。溶液的浓度越高，其渗透吸力也越大。半透膜8一般用截留分子量MWCO来表示所能透过物质的大小，MWCO越大，半透膜8的孔径及其渗透系数也越大，渗析达到平衡的时间越短。本实施例中，为缩短渗析时间，试验选用PEG20000，截留分子量(MWCO)为14000的半透膜。具体的，半透膜8是一种非对称膜。
所述排气装置由精确测量出气流量的第二电子皂膜流量计3-2和测量土样顶部气体压力的第三压力表5-3组成，第二电子皂膜流量计3-2的精度为0.1mL/min；所述第二电子皂膜流量计3-2一端通过排气管并穿过顶盖11与柱形土样6上部空腔相连，另一端与大气相连接。
进一步，本实施例中所述O型圈材质为氯丁橡胶；连接处采用环氧树脂进行密封，所述多孔板7为不锈钢多孔板；所述试样筒、底座10与顶盖11均由有机玻璃加工而成；所用测试气体为空气；所述柱形土样6为黄土，直径32mm，高度25mm。
实施例2
本实施例提供一种连续测试变吸力下非饱和土体气体渗透系数的方法，测量方法采用上述测量装置，测量方法包括以下步骤：
第一步：将装置摆放在合适的位置，保证放置所在干净，温度湿度适宜，无振动，无阳光直射，装置密封性能检查，仪器校准和功能必需检查，保证达到最佳操作性能，以得到最佳测量结果。
第二步：将半透膜8反套在中段试样筒12-3上用O型圈9固定 住后，然后制备一定含水量和干密度的松散土体，分两层填筑柱形土样6击实并将土样进行抽真空饱和，接着放置多孔板，为保证密封性，在多孔板7边缘连接的孔隙处，用环氧树脂密封。
第三步：PEG溶液每一种浓度对应特定的吸力，通过该种类型PEG溶液浓度与吸力的率定曲线查得对应浓度的吸力值。本实施例中，采用Delage等(1998)试验研究的吸力与PEG溶液浓度的关系式：s＝11c 2；式中：s为吸力(MPa)，c为PEG溶液浓度(g/g水)。此外由于土样中的微生物会使半透膜的使用寿命减小，因此需在溶液中加入少量青霉素。首先打开第一个吸力孔道14-1，用第一恒流泵15-1将预定浓度的PEG溶液注入外室13内，待达到比土样6稍微靠上的位置时，开启第二吸力孔道14-5和第二恒流泵15-2，作为浓度改变后的PEG溶液流出通道。第一恒流泵15-1与外室13连接的一端不断地供应溶液，而另一端的第二恒流泵15-2不断地流出，使溶液在外室中循环运动，土样开始脱湿或吸湿。且外室13筒壁上标有刻度线，当渗析溶液液面不变时，则此级吸力达到平衡。当土样6达到吸力平衡后，通过称量PEG溶液质量变化计算出试样含水量，然后测试土样6的气体渗透系数。
第四步：开启进气管的第一截止阀门4-1，由空气压缩机1向土样6底部空腔输送测试气体，气体在透过上、下多孔板7中的土样6后，经顶部排气管输出到大气中；同时开启围压进气管的第二截止阀门4-2，由空气压缩机1向外室13中输送围压气体，此前在PEG溶液加入一层轻质油，避免围压气体溶解于渗析溶液中，通过调压阀在测量过程中始终保证围压等于土样6底部空腔气压；通过第二电子皂膜流量计3-2测量通过土样6的流出气体流量Q，通过土样6底部空腔处安装的第一压力表5-1记录土样6的下室压强P 1，通过土样6顶部空腔处的第三压力表5-3记录土样6的上室压强P 2；当测量点处的气体压强保持恒定，且气体流量基本不变，则体系达到稳态，记录此时测量点气体压强。
第五步：气体在覆盖层中的运移包括对流和扩散，本试验主要研 究气体在覆盖层中的对流。由于在覆盖层下气体压力和大气压之间存在气压梯度，因而认为覆盖层中气体的稳态流动服从Darcy定律，即满足以下关系:
Figure PCTCN2022119749-appb-000001
式中：k g为气体渗透系数(m 2)；μ g为气体的粘滞系数(Pa·s)，在常温常压下(20℃、一个标准大气压)空气取值为1.81×10 -5Pa·s；Q为通过土样的气体流量(m 3·s -1)；A为材料的横截面积(m 2)；h为土样的高度(m)；ΔP为土样两端气压差(kPa；ΔP＝P 1-P 2)；为了得到气体渗透系数k g，试验中需要量测的主要参数为气体的压力梯度ΔP/h和流量Q。由于流量Q的测量受到压力和温度的影响，则需将试验时测得的流量修正为在常温常压下(20℃、一个标准大气压)的标准值。试验过程中，由于流量是在通向大气的末端测量，则无需进行压力修正；而温度为室温25±2℃，需进行温度修正，利用气体状态方程则可将其修正为20℃下的流量。
第六步：将外室13中的溶液排出，更换下一级吸力对应的PEG溶液，采用上述同样第三、四、五、六步进行此级吸力下的气体渗透系数测量。
以上结合附图对本发明的具体实施方式作了说明，但这些说明不能被理解为限制了本发明的范围，本发明的保护范围由随附的权利要求书限定，任何在本发明权利要求基础上的改动都是本发明的保护范围。

Claims (10)

  1. 一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：包括供气装置、围压装置、测试装置、吸力控制装置和排气装置；所述测试装置分为内室和外室(13)，内室用于放置土样(6)，外室(13)用于储存预定浓度的渗析溶液和施加围压；所述供气装置包括空气压缩机(1)，围压装置一端连接空气压缩机(1)，围压装置的另一端连接测试装置的外室(13)，所述空气压缩机(1)用于向测试装置的外室(13)输入围压气体和向测试装置的内室输送测试气体；所述吸力控制装置用于对土样(6)施加和控制吸力；所述排气装置与测试装置的内室连接，排气装置用于排出内室的测试气体。
  2. 根据权利要求1所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述供气装置包括进气管，进气管的一端连接空气压缩机(1)并将测试气体通入测试装置的内室中，进气管靠近空气压缩机(1)一端依次设有第一调节阀(2-1)、第一电子皂膜流量计(3-1)、第一截止阀(4-1)和第一压力表(5-1)。
  3. 根据权利要求1所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述围压装置包括围压进气管，空气压缩机(1)提供气源并通过围压进气管将围压气体通入测试装置的外室(13)中，围压进气管靠近空气压缩机(1)一端依次设有第二调压阀(2-2)、第二截止阀(4-2)和第二压力表(5-2)。
  4. 根据权利要求1所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述测试装置包括试样筒、底座(10)和顶盖(11)，底座(10)设置于试样筒的底端，顶盖(11)设置于试样筒的顶端；
    所述试样筒分为外试样筒(12-1)、内试样筒，内试样筒将测试装置分为内室和外室(13)，内室为柱形容器，外室(13)为环形容器；
    内试样筒包括上段试样筒(12-2)、中段试样筒(12-3)和下段试样筒(12-4)，上段试样筒(12-2)、中段试样筒(12-3)和下段试样筒(12-4)三段拼成内室；上段试样筒(12-2)与顶盖(11)围成上室空腔，中段试样筒(12-3)上下两端均设有多孔板(7)，中段试样筒(12-3)与两块多孔板(7)围成中室用于放置土样(6)，下段试样管(12-4)与底座(10)围成下室空腔；所述中段试样筒(12-3)为多孔结构。
  5. 根据权利要求4所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述吸力控制装置包括半透膜(8)、预定浓度的渗析溶液、第一恒流泵(15-1)、第二恒流泵(15-2)；所述半透膜(8)设置于中段试样管(12-3)内侧并紧贴于土样(6)侧壁；所述预定浓度的渗析溶液采用上浮一层轻质油的渗析溶液；所述外试样筒(12-1)相对两侧分别设有第一吸力孔道(14-1)、第二吸力孔道(14-2)，第一吸力孔道(14-1)、第二吸力孔道(14-2)与外室(13)相通；第一恒流泵(15-1)通过第一吸力孔道(14-1)与外试样筒(12-1)一侧连接并供应溶液，第二恒流泵(15-2)通过第二吸力孔道(14-2)与外试样筒(12-1)另一侧连接并将溶液流出。
  6. 根据权利要求5所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述半透膜(8)套于中段试样筒(12-3)内，半透膜(8)的上、下两端反套在中段试样筒(12-3)的上、下两端，上、下两端反套处设有闭合的O型圈(9)，所述上段试样筒(12-2)的下端与中段试样筒(12-3)连接处、下段试样筒(12-4)的上端于中段试样筒(12-3)连接处均设有与O型圈(9)相匹配的环形凹槽，中段试样筒(12-3)与上段试样筒(12-2)、下段试样筒(12-4)连接处及多孔板(7)与中段试样筒(12-3)连接处均采用密封树脂进行密封处理。
  7. 根据权利要求4所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述外试样筒(12-1)外壁设有刻度线，通过刻度线观察吸力是否达到平衡。
  8. 根据权利要求5所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述半透膜(8)为非对称膜，其截留分子量为1000～50000；所述预定浓度的渗析溶液为大分子溶液。
  9. 根据权利要求1所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置，其特征在于：所述排气装置包括排气管，排气管靠近测试装置一端依次设有第三压力表(5-3)、第二电子皂膜流量计(3-2)。
  10. 利用权利要求1-9任一一项所述的一种连续测试变吸力下非饱和土体气体渗透系数的装置的方法，其特征在于：所述方法的步骤如下：
    1)固定半透膜(8)，在中室内填筑柱形土样(6)；
    2)根据渗析溶液浓度与吸力的率定曲线，制备所测吸力对应的预定浓度的渗析溶液；
    3)打开两侧的恒流泵，使渗析溶液在外室(13)中循环运动，土样开始脱湿或吸湿，直至吸力平衡，然后称量渗析溶液质量变化计算出试样含水量；
    4)开启围压装置与供气装置的截止阀，输送测试气体，在测量过程中始终保证围压等于土样底部空腔气压；
    5)记录所需参数，根据达西定律，计算气体渗透系数；
    6)调整渗析溶液浓度，采用上述同样方法进行下一级吸力的气体渗透系数测量。
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