CN115508256A - Gas injection ball for measuring gas permeability coefficient and diffusion coefficient of soil in pre-embedded mode - Google Patents
Gas injection ball for measuring gas permeability coefficient and diffusion coefficient of soil in pre-embedded mode Download PDFInfo
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- 238000002347 injection Methods 0.000 title claims abstract description 70
- 239000007924 injection Substances 0.000 title claims abstract description 70
- 230000035699 permeability Effects 0.000 title claims abstract description 43
- 238000009792 diffusion process Methods 0.000 title claims abstract description 40
- 239000007789 gas Substances 0.000 claims abstract description 237
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- 238000005259 measurement Methods 0.000 claims abstract description 22
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- 239000004575 stone Substances 0.000 claims abstract description 10
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- 229920001778 nylon Polymers 0.000 claims abstract description 9
- 238000013508 migration Methods 0.000 claims description 11
- 230000005012 migration Effects 0.000 claims description 11
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- 238000011065 in-situ storage Methods 0.000 description 8
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- FBEHFRAORPEGFH-UHFFFAOYSA-N Allyxycarb Chemical compound CNC(=O)OC1=CC(C)=C(N(CC=C)CC=C)C(C)=C1 FBEHFRAORPEGFH-UHFFFAOYSA-N 0.000 description 1
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- 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
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Abstract
The invention provides a gas injection ball device and a method for pre-embedded measurement of a gas permeability coefficient and a diffusion coefficient of soil, which consist of a gas injection ball device and a gas supply device, wherein the gas injection ball device comprises a nylon net, a spherical bracket, broken stones, an expanding interface, a gas injection pipe, a gas taking interface and a gas taking pipe, and the gas supply device comprises an inert gas cylinder, a pressure stabilizing valve, a flow stabilizing valve, a U-shaped piezometer pipe, a flowmeter and a gas conveying pipe. The method is a single-point measurement, does not need any shape factor, and can obtain the gas diffusion coefficient and the permeability coefficient of the unsaturated soil through simple manual calculation by only measuring the gas pressure value, the gas concentration value and the corresponding gas flow value at one point position of the target depth in the unsaturated soil layer.
Description
Technical Field
The invention belongs to the technical field of environmental rock and soil, and particularly relates to a gas injection ball device and a gas injection ball method for pre-embedded measurement of gas permeability coefficient and diffusion coefficient of unsaturated soil at any depth on site.
Background
The quantitative migration of the gas in the unsaturated soil body has important scientific research and engineering application values in the fields of environmental geotechnics, agronomy, environmental engineering, ecology and the like. The main mechanisms of gas migration in unsaturated soils are convection and diffusion, which are controlled by the gas permeability coefficient and diffusion coefficient, respectively. The gas permeability coefficient and diffusion coefficient of the unsaturated soil body are affected by many factors including but not limited to pore size, pore connectivity, saturation, porosity, etc. of the unsaturated soil body, so that it is difficult to accurately estimate the gas permeability coefficient and diffusion coefficient of the unsaturated soil body on site through an empirical model. There are also currently available devices and methods for measuring gas permeability and diffusion coefficients in unsaturated soils in laboratories, but the samples for these tests are of small size, typically about 50mm in diameter and about 50mm in height. Because the field soil body has highly non-uniform and different dry-wet cycle histories, a large amount of original-state soil samples need to be collected on the field, and the diffusion coefficient and the permeability coefficient of the field soil body can be obtained through a laboratory measuring device and method, such as patents CN109883892B, a measuring device for the diffusion coefficient of gas in unsaturated soil, CN205157395U, a measuring instrument for the normal pressure gas permeability coefficient of unsaturated soil, and CN 108344668A, an experimental device for testing the diffusion coefficient and the permeability coefficient of unsaturated medium gas. However, collecting a large number of undisturbed soil samples and carrying out laboratory measurements consumes a large amount of manpower, material resources and financial resources, and disturbance to the soil samples is difficult to avoid in the process of collecting the undisturbed soil samples, so that the variability of the gas permeability coefficient and the diffusion coefficient of the onsite soil body in time and space is difficult to be described through the laboratory measurement device and method. Therefore, the development of a device and a method for measuring the diffusion coefficient and the permeability coefficient of the unsaturated soil gas in situ on site is urgently needed.
Various researchers developed different methods for in situ measurement of gas diffusivity/permeability of porous media, the in situ gas permeability measurement being obtained mainly by gas permeation devices (e.g., CN102053054A, "a method for in situ measurement of gas permeability of landfill) or large-scale in situ gas injection/extraction tests (e.g., shan et al, 1992 (Water resource. Res.,28 (4): 1105-1120), olson et al, 2001 (J. Contam. Hydrol.,53 (1-2): 1-19)). Gas permeation devices are usually constructed from hollow cylinders or hollow probes, most of which are short in size (20-200 mm in diameter and 25-200mm in length), and most of which are limited to surface soil or depth measurements due to the size of the measurement device. Large-scale in-situ gas injection/extraction tests can determine gas permeability coefficients in a large range, but the construction cost is high, and the gas permeability coefficients are difficult to be widely applied. Acquisition of in situ measured gas diffusivity the diffusivity of tracer gas is typically pumped into surface Soil and determined by measuring the concentration of tracer gas at or some distance from the point of insufflation (Laemmel et al, 2017 (eur.j.soil sci.,68 (2): 156-166), werner et al, 2003 (environ.sci.technol., 37 (11): 2502-2510), tick et al, 2007 (Water Air Soil polut., 184 (1-4): 355-362)). Some of the current in-situ measurement devices require a plurality of measurement points to determine the gas diffusivity (Laemmel et al, 2017 (Eur. J. Soil Sci.,68 (2): 156-166)), and other measurement points have a long measurement period of about 4 days (Nioct et al, 1998 (J. Environ. Eng. -ASCE,124 (11): 1038-1046)), so that the measurement results are susceptible to weather changes and are susceptible to accuracy. Meanwhile, the calculation of the diffusion coefficient is complex, the test data needs to be fitted by using an analytic solution or numerical simulation with a very complex expression, and in addition, various parameters of the known soil body, such as the air inflation porosity, are mostly required by the analytic solution or the numerical simulation, but the parameters are very difficult to obtain, especially when the measurement point is deep.
In addition to some limitations, in the current field measurement devices, very individual devices can measure the gas diffusion coefficient and permeability coefficient of the soil body simultaneously, such as CN110455673B, "device and method for in-situ measuring gas migration parameters in unsaturated soil layer", and CN202210413988.9 "device and method for in-situ measuring gas diffusion coefficient and permeability coefficient of unsaturated soil". However, the patent CN110455673B has the following disadvantages: the theoretical calculation part of the device needs to assume the distribution of a spherical gas pressure contour line and a gas concentration contour line, but a porous gas permeable pipe used for gas injection of the device is actually a cylinder, and the gas concentration and the pressure are measured in the porous gas permeable pipe, so that the gas concentration and the pressure distribution are not spherical, and the theoretical assumption and the actual existence of the gas concentration and the pressure distribution cause certain measurement errors. CN110455673B and CN202210413988.9 both require a penetration operation, since the casing pipe or the steel pipe has a certain diameter, it is easy to compact the surrounding soil during the penetration process, and in addition, in dry weather, the soil shrinks, which is easy to cause the generation of gas dominant flow along the sidewall of the casing pipe or the steel pipe, and the accuracy of measurement is reduced. The device adopts a gas injection pipe and a gas production pipe with smaller diameters (such as 2-3mm outer diameter), a gas injection ball with the diameter of about 2cm is pre-buried in the soil body to a target depth, and then the gas injection pipe and the gas production pipe are drawn out to the ground surface, so that the side wall potential flow and the extrusion of a sleeve pipe to the surrounding soil body under the dry condition are avoided. Therefore, besides on-site in-situ measurement, the method provided by the invention has better applicability in model tests of soil columns, model tanks and the like: by selecting the air injection balloon with a smaller diameter (such as 1-2 cm), the air injection tube and the air production tube are pulled out from the side walls of the earth pillar, the model groove and the like along the horizontal direction, so that the real-time measurement of the gas permeability coefficient and the diffusion coefficient of the soil body in the model test can be realized, and the disturbance of the traditional sampling measurement on the model test is avoided.
In order to solve the limitations of the existing measuring device and method, the invention develops the device and the method which can accurately and quickly measure the gas diffusion coefficient and the permeability coefficient of unsaturated soil at different depths in situ. Compared with the prior field measuring device, the gas injection ball device can be smaller in size (such as the diameter of 1-2 cm), and the disturbance to the field soil body is greatly reduced. Secondly, the measured data can be simply calculated by hand to obtain the gas permeability coefficient and the diffusion coefficient of the soil body, complex curve fitting or numerical simulation inverse analysis is not needed, and the measuring efficiency is improved. In addition, the device can be used for measuring the gas diffusion coefficient and the permeability coefficient of unsaturated soil on site and can also be used for model tests of soil columns, model tanks and the like.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a device and a method for pre-embedded measurement of gas migration parameters in an unsaturated soil layer, wherein the migration parameters comprise diffusion coefficients and permeability coefficients so as to meet the requirements of engineering application.
The technical scheme of the invention is as follows:
1. a gas injection ball for measuring gas permeability coefficient and diffusion coefficient of soil in an embedded mode is disclosed:
the gas injection device comprises a nylon net, a spherical support (made of stainless steel or plastic), broken stones, an expanding interface, a gas injection pipe, a gas taking interface and a gas taking pipe, wherein one end of the gas injection pipe is connected with the expanding interface, the expanding interface is arranged in the sphere center of the spherical support, the broken stones are filled in a cavity, then the nylon net is wrapped on the surface of the spherical support to form a gas injection ball, the gas taking interface is connected with one end of the gas taking pipe, and the other end of the gas taking pipe is 1cm away from the surface of the gas injection ball; the gas supply device comprises an inert gas cylinder, a pressure stabilizing valve, a flow stabilizing valve, a U-shaped pressure measuring pipe, a flowmeter and a gas conveying pipe, wherein the output end of the inert gas cylinder is connected to one end of the gas conveying pipe sequentially through the pressure stabilizing valve, the flow stabilizing valve, the U-shaped pressure measuring pipe and the flowmeter, and the other end of the gas conveying pipe is connected with the gas injection pipe.
The gas injection sphere center device is positioned at the depth of a required measuring point in an unsaturated soil layer.
The inert gas cylinder is used for generating the gas pressure required by gas introduction and is used as a tracer gas.
The pressure stabilizing valve and the flow stabilizing valve are used for adjusting the air inlet flow and the air pressure of the air transmission pipeline.
The U-shaped piezometric tube and the flowmeter are used for monitoring the air inflow and the air pressure of the gas transmission pipeline, so that the pressure is in a safe range.
The spherical cavity ball, the lower half part of the gas injection pipe and the lower half part of the gas taking pipe of the gas injection ball device are arranged in the unsaturated soil layer, and the upper half part of the gas injection pipe, the upper half part of the gas taking pipe and the gas taking interface extend out of the earth surface.
The gas injection tube can be adjusted according to the depth of the measuring point, including but not limited to using one gas injection tube, and the deep soil can be measured by using a longer gas injection tube.
2. The use method of the pre-embedded gas injection ball for measuring the gas permeability coefficient and the diffusion coefficient of soil comprises the following steps:
firstly, pre-burying the center of a spherical cavity ball of a gas injection ball device to the depth of an unsaturated soil layer to be measured, or drilling holes (the aperture is slightly larger than the spherical cavity ball), then installing the center of the spherical cavity ball in the depth of the unsaturated soil to be measured, and backfilling and compacting the drilled holes after a soil body taken out of the drilled holes passes through a 2mm sieve;
secondly, connecting an inert gas cylinder, a pressure stabilizing valve, a flow stabilizing valve, a U-shaped pressure measuring pipe and a flowmeter through a gas pipe to form a gas supply device, wherein the outlet end of the gas supply device is connected with a gas injection pipe through the gas pipe;
thirdly, extracting 1-3mL of gas at the gas extraction interface for measuring the background concentration of the inert gas in the unsaturated soil layer and recording the ambient atmospheric pressure and the ambient temperature at that time;
fourthly, opening a valve of an inert gas cylinder, regulating the flow of the inlet gas to a constant volume flow value through a pressure stabilizing valve and a flow stabilizing valve, then conveying the inert gas to a gas injection ball device through a gas supply device, monitoring the pressure value and the flow value of the inert gas through a U-shaped piezometer tube and a flowmeter, and extracting 1-3mL of gas at a gas taking port every 30 minutes for measuring the concentration of the inert gas;
fifthly, after the concentration of the inert gas to be measured is stable, recording the concentration value C of the inert gas measured at the moment 1 And corresponding constant volume flow value q 1 ；
Sixthly, improving the gas inflow to a higher constant volume flow value through the pressure stabilizing valve and the flow stabilizing valve, enabling the gas pressure measured by the U-shaped pressure measuring tube to be higher than the atmospheric pressure and to have an obvious difference value (more than or equal to 0.1 kPa), and recording absolute gas pressure values P measured by the U-shaped pressure measuring tube and the flowmeter respectively at the moment after the reading of the U-shaped pressure measuring tube is stable 2 And a corresponding constant volume flow value q 2 ；
The seventh step, the measured inert gas concentration value C 1 And corresponding constant volume flow value q 1 Substituting the following formula to obtain the gas diffusion coefficient D g ：
In the formula, D g Gas diffusion coefficient (m) of unsaturated soil layer 2 s -1 )；C 1 Is the concentration value (m) of trace gas in the gas injection ball during the stable migration of gas 3 m -3 )；C hg Is the background concentration value (m) of the tracer gas in the soil layer 3 m -3 ) (ii) a r is the radius (m) of the multi-shot balloon;
the eighth step of measuring the absolute gas pressure value P 2 And corresponding constant volume flow value q 2 The gas permeability coefficient K is obtained by substituting the following formula g ：
In the formula, K g Gas permeability coefficient (ms) of unsaturated soil layer -1 )；P 2 Is the absolute air pressure value (Pa) of the soil body at a position 1cm away from the surface of the spherical cavity bead; ρ is a unit of a gradient a Is the density of air (kg m) -3 ) (ii) a g is the acceleration of gravity (9.8 ms) -2 )；P hg Is ambient atmospheric pressure (Pa).
Compared with the prior art, the invention has the beneficial effects that:
the method is single-point measurement, does not need any shape factor, and can obtain the gas diffusion coefficient and the permeability coefficient of the unsaturated soil through simple calculation only by measuring the gas pressure value, the gas concentration value and the corresponding gas flow value at one point position of the target depth in the unsaturated soil layer, thereby avoiding the measurement of a plurality of point positions in the conventional method.
The invention can measure the gas diffusion coefficient/permeability coefficient of unsaturated soil in any depth, and solves the limitation that the prior measuring device can only measure surface soil.
The invention has small size (the diameter of the gas injection ball is about 2 cm), and can avoid the extrusion of the prior injection device to the surrounding soil body and the influence of the side wall dominant flow by pre-embedding and then drawing the gas injection pipe and the gas production pipe with smaller diameter, thereby reducing the disturbance to the field soil body during installation. In addition, the invention has better applicability in indoor tests of soil columns, model tanks and the like.
The invention can directly obtain the measurement result by hand calculation without indoor complex curve fitting or numerical simulation inverse analysis.
Drawings
The invention is described in further detail below with reference to the following figures and detailed description:
FIG. 1 is a schematic view of the overall structure of the measuring device of the present invention;
FIG. 2 is a schematic structural view of the gas injection ball apparatus of the present invention;
FIG. 3 is a schematic diagram of one-dimensional steady-state gas migration corresponding to spherical cavity pellets in an unsaturated soil layer;
in the figure: 1-inert gas cylinder; 2-a valve; 3-gas pipe; 4-a pressure maintaining valve; 5-a flow stabilizing valve; 6-U type piezometric tube; 7-a flow meter; 8-a gas injection pipe; 9-expanding the interface; 10-nylon mesh; 11-breaking stone; 12-spherical cavity pellets; 13-taking the trachea; 14-gas taking interface; 15-spherical support.
Detailed Description
The invention is further illustrated by the following examples in conjunction with the drawings. It should be noted that the present embodiment is set forth to further illustrate the invention and is not intended to limit the invention.
As shown in fig. 1-3, a pre-buried air injection balloon for measuring the gas permeability coefficient and diffusion coefficient of soil mainly comprises an air injection balloon device and an air supply device, wherein the air injection balloon device comprises a nylon net 10, a spherical support 15, broken stones 11, an expanding interface 9, an air injection pipe 8, an air taking interface 14 and an air taking pipe 13, one end of the air injection pipe 8 is connected with the expanding interface 9, the expanding interface 9 is arranged at the sphere center of the spherical support 15 to form a spherical cavity small ball 12, the broken stones 11 are filled in the cavity, the nylon net 10 is covered on the surface of the spherical support 15, the air taking interface 14 is connected with one end of the air taking pipe 13, and the other end of the air taking pipe 10 is positioned at 1cm position on the surface of the spherical cavity small ball 12; the gas supply device comprises an inert gas cylinder 1, a pressure stabilizing valve 4, a flow stabilizing valve 5, a U-shaped pressure measuring pipe 6, a flowmeter 7 and a gas pipe 3, wherein the output end of the inert gas cylinder 1 is connected to one end of the gas pipe 3 after sequentially passing through the pressure stabilizing valve 4, the flow stabilizing valve 5, the U-shaped pressure measuring pipe 6 and the flowmeter 7, and the other end of the gas pipe is connected with a gas injection pipe 8.
The inert gas cylinder 1 provides gas and air pressure which are transmitted to the gas injection ball device; the pressure stabilizing valve 4 and the flow stabilizing valve 5 accurately control the air inlet flow; the gas conveying pipe 3 and the gas injection pipe 8 play a role in conveying gas; the spherical cavity ball 12 provides a gas migration channel, and gravels 11 are filled in the spherical cavity ball 12, so that gas is uniformly and stably migrated to the surrounding soil body; the spherical support 15 makes the filled crushed stone 11 in a spherical shape; the flow meter 7 and the U-shaped piezometer tube 6 respectively monitor the magnitude of the air inflow and the air pressure.
The gas transmission pipe 3 adopts a wear-resistant and pressure-resistant Polytetrafluoroethylene (PTFE) pipe with the diameter of 6mm; the gas injection pipe 8 and the gas taking pipe 13 adopt wear-resistant and pressure-resistant PTFE pipes with the diameter of 3 mm; the specification of the nylon net 10 is 100 meshes; the diameter of the broken stone 11 is 3-4mm; the inner diameter of the expanding interface 9 is 6mm; the diameter of the spherical cavity pellet 12 is 40mm; the inert gas cylinder 1 adopts a high-purity helium gas cylinder; the pressure stabilizing valve 4, the flow stabilizing valve 5, the U-shaped piezometer tube 6 and the flowmeter 7 are all conventional parameter instruments.
Examples
Firstly, embedding a spherical cavity ball 12 of a gas injection ball device into a soil layer, wherein the center of the spherical cavity ball is positioned at the depth of an unsaturated soil layer to be measured, or drilling a hole (the aperture is slightly larger than that of the spherical cavity ball), then installing the center of the spherical cavity ball at the depth of the unsaturated soil to be measured, and backfilling and compacting the drilled hole after a soil body taken out from the drilled hole passes through a 2-mm sieve;
secondly, connecting a helium gas cylinder 1, a pressure stabilizing valve 4, a flow stabilizing valve 5, a U-shaped pressure measuring pipe 6 and a flowmeter 7 through a gas pipe 3 to form a gas supply device, wherein the outlet end of the gas supply device is connected with a gas injection pipe 8 through the gas pipe 3;
thirdly, 1-3mL of gas is extracted from the gas extraction interface 14 and used for measuring the background concentration (0 m) of helium in the unsaturated soil layer 3 m -3 ) Recording the ambient atmospheric pressure (100500 Pa) and the ambient temperature (298.15K) at the time;
fourthly, opening a gas cylinder valve 2, regulating the flow of inlet gas to a constant volume flow value (1 mL/min) through a pressure stabilizing valve 4 and a flow stabilizing valve 5, then conveying helium gas to a gas injection ball device through a gas supply device, monitoring the gas pressure value and the flow value of the helium gas through a U-shaped piezometer tube 6 and a flowmeter 7, and extracting 1-3mL of gas at a gas taking port 14 every 30 minutes to measure the concentration of the helium gas;
fifthly, after the helium concentration to be measured is stable, recording the concentration value C of the helium measured at the moment 1 (0.099m 3 m -3 ) And corresponding constant volume flow value q 1 (1mL/min)；
Sixthly, improving the gas inflow to a higher constant volume flow value through the pressure stabilizing valve 4 and the flow stabilizing valve 5, enabling the gas pressure measured by the U-shaped pressure measuring pipe 6 to be higher than the atmospheric pressure and to have an obvious difference value (more than or equal to 0.1 kPa), and recording the absolute gas pressure value P measured by the U-shaped pressure measuring pipe 6 and the flowmeter 7 at the moment after the reading of the U-shaped pressure measuring pipe 6 is stable 2 (100700 Pa) and corresponding constant volume flow value q 2 (200mL/min)；
The seventh step, the measured inert gas concentration value C 1 And corresponding constant volume flow value q 1 The gas diffusion coefficient D was obtained by substituting the following equation g ：
In the formula, D g Gas diffusion coefficient (m) of unsaturated soil layer 2 s -1 )；C 1 Is the concentration value (m) of trace gas in the gas injection ball during the stable migration of gas 3 m -3 )；C hg Is the background concentration value (m) of trace gas in the soil layer 3 m -3 ) (ii) a r is the radius (m) of the multi-shot balloon;
the eighth step of measuring the absolute gas pressure value P 2 And corresponding constant volume flow value q 2 The gas permeability coefficient K is obtained by substituting the following formula g ：
In the formula, K g Unsaturated soilGas permeability coefficient (ms) of the layer -1 )；P 2 Is the absolute air pressure value (Pa) of the soil body at a position 1cm away from the surface of the spherical cavity; rho a Is the density of air (kg m) -3 ) (ii) a g is the acceleration of gravity (9.8 ms) -2 )；P hg Is ambient atmospheric pressure (Pa). .
After the in-situ measurement is finished, the gas permeability coefficient and diffusion coefficient of the unsaturated soil obtained by the device and the laboratory measurement method are compared by collecting a field undisturbed soil sample and carrying out laboratory measurement (table 1). Therefore, the device can accurately measure the gas permeability coefficient and the diffusion coefficient of the soil body.
TABLE 1 comparison of the gas migration parameters of the inventive device and laboratory measurements
a. The measurement difference is defined as:
Claims (4)
1. the utility model provides a gas permeability coefficient of soil and diffusion coefficient's notes balloon is measured to pre-buried formula which characterized in that includes gas injection ball device, air feeder: the gas injection ball device comprises a nylon net (10), a spherical support (15), broken stones (11), an expanding interface (9), a gas injection pipe (8), a gas taking interface (14) and a gas taking pipe (13), wherein one end of the gas injection pipe (8) is connected with the expanding interface (9), the expanding interface (9) is arranged at the ball center position of the spherical support (15) to form a spherical cavity ball (12), the broken stones (11) are filled in the cavity, the nylon net (10) is covered on the surface of the spherical support (15), the gas taking interface (14) is connected with one end of the gas taking pipe (13), and the other end of the gas taking pipe (13) is positioned at a position of 1cm on the surface of the spherical cavity ball (12); the gas supply device comprises an inert gas cylinder (1), a pressure stabilizing valve (4), a flow stabilizing valve (5), a U-shaped pressure measuring pipe (6), a flowmeter (7) and a gas conveying pipe (3), wherein the output end of the inert gas cylinder (1) sequentially passes through the pressure stabilizing valve (4), the flow stabilizing valve (5), the U-shaped pressure measuring pipe (6) and the flowmeter (7) and then is connected to one end of the gas conveying pipe (3), and the other end of the gas conveying pipe (3) is connected with a gas injection pipe (8).
2. The air injection balloon for measuring the gas permeability coefficient and the diffusion coefficient of the soil in an embedded mode according to claim 1, wherein the air injection balloon is characterized in that: the sphere center of the spherical cavity small ball (12) is positioned at the depth of a required measuring point in an unsaturated soil layer.
3. The gas injection balloon for pre-buried measurement of the gas permeability coefficient and the diffusion coefficient of soil according to claim 1, wherein: the spherical cavity ball (12), the lower half part of the gas injection pipe (8) and the lower half part of the gas taking pipe (13) of the gas injection ball device are arranged in an unsaturated soil layer, and the upper half part of the gas injection pipe (8), the upper half part of the gas taking pipe (13) and the gas taking interface (14) extend out of the earth surface.
4. An embedded type air injection balloon for measuring the gas permeability coefficient and the diffusion coefficient of soil, which is applied to the device of any one of claims 1 to 3, and is characterized in that: the method comprises the following steps:
firstly, pre-embedding a spherical cavity ball (12) of a gas injection ball device into a soil layer, wherein the center of the spherical cavity ball is positioned at the depth of unsaturated soil to be measured, or installing the center of the spherical cavity ball (12) at the depth of the unsaturated soil to be measured by drilling (the aperture is slightly larger than the spherical cavity ball (12)), and backfilling and compacting the drilled hole after the soil body taken out by drilling passes through a 2mm sieve;
secondly, connecting an inert gas cylinder (1), a pressure stabilizing valve (4), a flow stabilizing valve (5), a U-shaped pressure measuring pipe (6) and a flowmeter (7) through a gas pipe (3) to form a gas supply device, wherein the outlet end of the gas supply device is connected with a gas injection pipe (8) through the gas pipe (3);
thirdly, extracting 1-3mL of gas at the gas taking interface (14) for measuring the background concentration of the inert gas in the unsaturated soil layer and recording the ambient atmospheric pressure and the ambient temperature at that time;
fourthly, opening an inert gas cylinder valve (1), adjusting the flow of inlet gas to a constant volume flow value through a pressure stabilizing valve (4) and a flow stabilizing valve (5), then conveying the inert gas to a gas injection ball device through a gas supply device, monitoring the gas pressure value and the flow value of the inert gas through a U-shaped piezometer tube (6) and a flowmeter (7), and extracting 1-3mL of gas at a gas taking port (14) every 30 minutes for measuring the concentration of the inert gas;
fifthly, after the concentration of the inert gas to be measured is stable, recording the concentration value C of the inert gas measured at the moment 1 And corresponding constant volume flow value q 1 ；
Sixthly, improving the gas inflow to a higher constant volume flow value through the pressure stabilizing valve (4) and the flow stabilizing valve (5), enabling the gas pressure measured by the U-shaped pressure measuring tube (6) to be higher than the atmospheric pressure and to have an obvious difference value (more than or equal to 0.1 kPa), and recording absolute gas pressure values P measured by the U-shaped pressure measuring tube (6) and the flowmeter (7) respectively at the moment after the reading of the U-shaped pressure measuring tube (6) is stable 2 And a corresponding constant volume flow value q 2 ；
The seventh step, the measured inert gas concentration value C 1 And corresponding constant volume flow value q 1 The gas diffusion coefficient D was obtained by substituting the following equation g ：
In the formula, D g Gas diffusion coefficient (m) of unsaturated soil layer 2 s -1 )；C 1 Is the concentration value (m) of trace gas in the gas injection ball during the stable migration of gas 3 m -3 )；C hg Is the background concentration value (m) of trace gas in the soil layer 3 m -3 ) (ii) a r is the radius (m) of the balloon;
the eighth step of measuring the absolute gas pressure value P 2 And corresponding constant volume flow value q 2 The gas permeability coefficient K of the unsaturated soil is obtained by substituting the following formula g ：
K g Is gas of unsaturated soil layerCoefficient of volume permeability (ms) -1 )；P 2 Is the absolute air pressure value (Pa) of the soil body at a position 1cm away from the surface of the spherical cavity; rho a Is the density of air (kg m) -3 ) (ii) a g is the acceleration of gravity (9.8 ms) -2 )；P hg Is ambient atmospheric pressure (Pa).
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| WO1998046858A1 (en) * | 1997-04-15 | 1998-10-22 | Science & Engineering Associates, Inc. | In situ measurement apparatus and method of measuring soil permeability and fluid flow |
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| CN110455673A (en) * | 2019-09-03 | 2019-11-15 | 浙江大学 | The device and method of gas migration parameter in penetration type in situ measurement unsaturation soil layer |
| CN111458274A (en) * | 2020-04-20 | 2020-07-28 | 福州大学 | Soil column device and method for measuring gas permeability and diffusion coefficient of unsaturated soil body |
| CN115165675A (en) * | 2022-04-14 | 2022-10-11 | 福州大学 | Device and method for in-situ measurement of gas diffusion coefficient and permeability coefficient of unsaturated soil |
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| WO1998046858A1 (en) * | 1997-04-15 | 1998-10-22 | Science & Engineering Associates, Inc. | In situ measurement apparatus and method of measuring soil permeability and fluid flow |
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