CN109459366B - Device and method for measuring permeability coefficient of unsaturated soil - Google Patents
Device and method for measuring permeability coefficient of unsaturated soil Download PDFInfo
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- CN109459366B CN109459366B CN201811392214.2A CN201811392214A CN109459366B CN 109459366 B CN109459366 B CN 109459366B CN 201811392214 A CN201811392214 A CN 201811392214A CN 109459366 B CN109459366 B CN 109459366B
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- 239000002689 soil Substances 0.000 title claims abstract description 94
- 230000035699 permeability Effects 0.000 title claims abstract description 49
- 238000000034 method Methods 0.000 title claims abstract description 35
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 123
- 239000011148 porous material Substances 0.000 claims abstract description 34
- 239000011159 matrix material Substances 0.000 claims abstract description 11
- 230000008569 process Effects 0.000 claims description 13
- 239000004744 fabric Substances 0.000 claims description 7
- 239000000758 substrate Substances 0.000 claims description 7
- 230000009471 action Effects 0.000 claims description 3
- 229920001971 elastomer Polymers 0.000 claims description 3
- 239000011521 glass Substances 0.000 claims description 3
- 238000002347 injection Methods 0.000 claims description 3
- 239000007924 injection Substances 0.000 claims description 3
- 239000007788 liquid Substances 0.000 claims description 3
- 239000000463 material Substances 0.000 claims description 3
- 230000003204 osmotic effect Effects 0.000 claims 2
- 230000008859 change Effects 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 239000000356 contaminant Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000008595 infiltration Effects 0.000 description 2
- 238000001764 infiltration Methods 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 230000004075 alteration Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 230000001052 transient effect Effects 0.000 description 1
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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
Abstract
The invention discloses a device for measuring the permeability coefficient of unsaturated soil, which comprises a container for containing an unsaturated soil sample, wherein a tensiometer is inserted into the unsaturated soil sample, the bottom of the container is provided with a screen, filter paper is laid on the upper surface of the screen, the bottom of the container is communicated with the top of a first measuring tube, the bottom of the first measuring tube is connected with one end of a connecting tube, the other end of the connecting tube is connected with the bottom of a second measuring tube, and the second measuring tube is provided with scale marks; in addition, the invention also discloses a corresponding method; the invention solves the technical problems of complex operation, high cost and long time consumption when the existing indirect method is used for measuring the permeability coefficient of the unsaturated soil body, can determine the permeability coefficients of soil samples with different saturation degrees according to the time t, the flow Q and the corresponding negative pore water pressure, and establishes the relation between the matrix suction and the permeability coefficients.
Description
Technical Field
The invention relates to the technical field of rock and soil experiments, in particular to a device and a method for measuring the permeability coefficient of unsaturated soil.
Background
Along with the gradual development of China in the field of geotechnical engineering, research on unsaturated soil is more and more emphasized by researchers, and the permeability coefficient of unsaturated soil is an important parameter for researching engineering problems such as rainwater infiltration, dam slope seepage and the like. At present, the permeability coefficient of saturated soil is relatively simple to measure, but the permeability coefficient of unsaturated soil can only be measured by a relatively complex steady-state test method and a transient profile method, and researchers also divide an experimentally measured soil-water characteristic curve into a plurality of sections, and assume that each section is a uniform matrix suction section to indirectly calculate the permeability coefficient of unsaturated soil.
Disclosure of Invention
The invention aims to overcome the defects, provides a device and a method for measuring the permeability coefficient of unsaturated soil, solves the technical problems of complex operation, high cost and long time consumption in the existing indirect method for measuring the permeability coefficient of unsaturated soil, and can determine the permeability coefficients of soil samples with different saturation degrees according to time t, flow Q and corresponding negative pore water pressure and establish the relationship between matrix suction and the permeability coefficient.
In order to solve the technical problems, the invention adopts the technical scheme that: the utility model provides a survey device of unsaturated soil permeability coefficient, is equipped with the tensiometer including the container that is used for splendid attire unsaturated soil sample, unsaturated soil sample interpolation, the container bottom is equipped with the screen cloth, and filter paper has been laid to the screen cloth upper surface, and the container bottom communicates with first survey buret top, and first survey buret bottom is connected with connecting pipe one end, and the connecting pipe other end is connected with second survey buret bottom, is equipped with the scale mark on the second survey buret.
Preferably, the first measuring tube is provided with a first valve, and the top of the second measuring tube is communicated with the bottom of the measuring cylinder through a second valve.
Preferably, the second valve is an electromagnetic valve, an infrared signal emitter and an infrared signal receiver are respectively arranged on two sides of the second measuring pipe, the infrared signal receiver is connected with a signal input end of the controller, and the controller is connected with a control end of the second valve.
Preferably, container, first buret of surveying and second buret are the transparent glass material, and the connecting pipe is the rubber pipe, the container is cylindrical structure, and the position department of container bottom and first buret of surveying top intercommunication sets up the screen cloth.
Preferably, the first measuring tube is mounted on a first support frame and the second measuring tube is mounted on a second support frame.
In addition, the invention also provides a method for measuring the permeability coefficient of unsaturated soil by using the device, which comprises the following steps:
step 1): installing a screen mesh at the bottom of the container, and paving filter paper on the screen mesh;
step 2): placing the unsaturated soil sample into a container and ensuring that the unsaturated soil sample is in complete contact with the filter paper;
step 3): installing a tensiometer in the unsaturated soil sample, and measuring the initial negative pore water pressure of the unsaturated soil sample;
step 4): injecting water into the measuring cylinder at the top of the second measuring tube, opening the second valve to enable the water to flow into the second measuring tube, the connecting tube and the first measuring tube in sequence, ensuring that the liquid level heights in the first measuring tube and the second measuring tube are flush with the filter paper in the cylindrical container after water injection, and then closing the second valve;
step 5): closing the first valve, reducing the height of the second measuring tube until the top of the second measuring tube is reduced to be below the horizontal position of the filter paper, wherein a water head difference formed by the first measuring tube and the second measuring tube generates downward negative pressure on the filter paper, the unsaturated soil sample generates upward negative pore water pressure on the filter paper, and the absolute value of the negative pressure generated by the water head difference on the filter paper is smaller than the absolute value of the negative pore water pressure generated by the unsaturated soil sample on the filter paper;
step 6): recording the water level of the measuring cylinder, and opening a first valve;
step 7): under the action of negative pore water pressure of the unsaturated soil sample, water in the first measuring tube gradually flows into the container through the filter paper, the water level of the second measuring tube communicated with the first measuring tube is lowered, the second valve is opened at the moment, water in the measuring cylinder enters the second measuring tube, and the second valve is closed again after the water head difference formed by the first measuring tube and the second measuring tube is ensured to be unchanged;
step 8): after a period of time, the negative pore water pressure of the unsaturated soil sample is gradually reduced until the absolute value of the negative pore water pressure is equal to the absolute value of the negative pressure, the permeation reaches balance, at the moment, the first valve is closed, and the negative pore water pressure of the unsaturated soil sample at the moment is measured by the tensiometer;
step 9): and recording the time interval t, reading the water supply quantity Q in the time through a measuring cylinder, and determining the unsaturated soil permeability coefficient k under the primary matrix suction according to Darcy's law Q = khtA/L (A, L is the area and the height of the unsaturated soil sample respectively, and h is the difference of water heads on two sides).
Preferably, the above method further comprises the steps of:
step 10): raising the height of the second measuring tube to reduce the water head difference formed by the first measuring tube and the second measuring tube, so that the absolute value of the negative pressure generated by the water head difference to the filter paper is smaller than the absolute value of the negative pore water pressure generated by the unsaturated soil sample to the filter paper again, then opening the first valve, and repeating the steps 6) to 9) to record the unsaturated soil permeability coefficient k under the suction of the primary matrix;
step 11): and (3) gradually increasing the height of the second measuring pipe for multiple times until the water head difference formed by the first measuring pipe and the second measuring pipe is 0, recording the unsaturated soil permeability coefficient k under each level of substrate suction according to the step 10) after the height of the second measuring pipe is increased every time, and making a relation curve graph of the substrate suction and the permeability coefficient.
Preferably, in the step 7), the controller may automatically control the automatic opening and closing process of the second valve, and the specific steps are as follows:
firstly, the water level of the second measuring pipe communicated with the second measuring pipe is lower than the horizontal height of the infrared signal transmitter and the infrared signal receiver after the water level of the second measuring pipe is lowered, then the infrared signal receiver receives the signal transmitted by the infrared signal transmitter, the infrared signal receiver transmits the corresponding signal to the controller, the controller controls the second valve to be opened, the water in the measuring cylinder enters the second measuring pipe, when the water level in the second measuring pipe exceeds the horizontal height of the infrared signal transmitter and the infrared signal receiver, the signal transmitted by the infrared signal transmitter changes because of the blockage of the water, the infrared signal receiver transmits the corresponding signal to the controller, the controller controls the second valve to be closed, and the water in the measuring cylinder stops entering the second measuring pipe, the water level of the second measuring pipe can be guaranteed to be maintained at a fixed water level through the process, and therefore the water head difference formed by the first measuring pipe and the second measuring pipe is guaranteed to be unchanged.
The invention has the beneficial effects that:
1. the invention solves the technical problems of complex operation, high cost and long time consumption when the existing indirect method is used for measuring the permeability coefficient of the unsaturated soil body, can determine the permeability coefficients of soil samples with different saturation degrees according to the time t, the flow Q and the corresponding negative pore water pressure, and establishes the relation between the matrix suction and the permeability coefficients.
2. The device has simple structure and convenient use, and can control the soil body infiltration process to be slowly and uniformly carried out by gradually increasing the height of the second measuring tube in the measuring process, so that the measurement is more accurate.
3. By changing the dry density and the initial water content of the soil sample, the method can respectively carry out the same permeability coefficient test to obtain the relation between the unsaturated soil permeability coefficient curve and the initial dry density.
4. By changing the grain composition of the soil sample, the invention can respectively carry out the same permeability coefficient test to obtain the permeability coefficient curve of the unsaturated soil with different grain compositions.
5. When different types and concentrations of contaminants are added to water, the present invention can be used to analyze the rate and process of migration of contaminants in unsaturated soils.
6. The relation curve of the matrix suction and the permeability coefficient determined according to the invention can be used for calculating and describing the change development process of the seepage field in soil along with rainfall or running water soaking in a numerical analysis software.
Drawings
FIG. 1 is a schematic structural diagram of an apparatus for measuring the permeability coefficient of unsaturated soil;
FIG. 2 is a schematic view of a connection structure of an infrared signal receiver, a controller and a second valve;
FIG. 3 is a graph showing the permeability coefficient of a sand in this embodiment;
in the figure, a container 1, a tension meter 2, a screen 3, filter paper 4, a first measuring tube 5, a first valve 5.1, a connecting tube 6, a second measuring tube 7, a scale mark 7.1, a second valve 7.2, a measuring cylinder 8, an infrared signal transmitter 9, an infrared signal receiver 10, a controller 11, a first support frame 12 and a second support frame 13.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
As shown in fig. 1 and 2, a device for determining unsaturated soil permeability coefficient, including container 1 that is used for splendid attire unsaturated soil sample, unsaturated soil sample interpolation is equipped with tensiometer 2, container 1 bottom is equipped with screen cloth 3, and filter paper 4 has been laid to screen cloth 3 upper surface, and container 1 bottom and first survey buret 5 top intercommunication, first survey buret 5 bottom is connected with connecting pipe 6 one end, and the connecting pipe 6 other end is connected bottom the second survey buret 7, is equipped with scale mark 7.1 on the second survey buret 7. In this embodiment, the scale marks 7.1 can facilitate to clearly see the water level position in the second measuring pipe 7, and facilitate to determine the installation height of the infrared signal transmitter 9 and the infrared signal receiver 10.
Preferably, the first measuring pipe 5 is provided with a first valve 5.1, and the top of the second measuring pipe 7 is communicated with the bottom of the measuring cylinder 8 through a second valve 7.2. The position of second survey buret 7 top and second valve 7.2 bottom intercommunication in this embodiment does not seal its and external atmosphere intercommunication, guarantees like this that top atmospheric pressure is the same with external atmosphere pressure in the second survey buret 7, and the hydrohead difference of first survey buret 5 and second survey buret 7 just can make things convenient for follow-up measurement process like this.
Preferably, the second valve 7.2 is an electromagnetic valve, the two sides of the second measuring pipe 7 are respectively provided with an infrared signal emitter 9 and an infrared signal receiver 10, the infrared signal receiver 10 is connected with a signal input end of a controller 11, and the controller 11 is connected with a control end of the second valve 7.2. When the height required to maintain the water level in the second measuring pipe 7 is determined, the installation height of the infrared signal transmitter 9 and the infrared signal receiver 10 is adjusted to be flush with a certain scale of the scale mark 7.1 according to the reading of the scale mark 7.1, when the water level is higher than the certain scale, the infrared signal receiver 10 transmits the signal change to the controller 11, the controller 11 controls the second valve 7.2 to be closed, when the water level is lower than the certain scale, the infrared signal receiver 10 transmits the signal change to the controller 11, and the controller 11 controls the second valve 7.2 to be closed, so that the automatic opening and closing process of the second valve 7.2 can be realized; in this embodiment, the controller 11 is preferably a Siemens S7-300 PLC controller.
Preferably, container 1, first survey buret 5 and second survey buret 7 are the transparent glass material, and connecting pipe 6 is the rubber tube, container 1 is cylindrical structure, and the position department of container 1 bottom and first survey buret 5 top intercommunication sets up screen cloth 3.
Preferably, the first measuring tube 5 is mounted on a first support frame 12 and the second measuring tube 7 is mounted on a second support frame 13.
In this embodiment, the method for determining the permeability coefficient of unsaturated soil by using the device comprises the following steps:
step 1): a screen 3 is arranged at the bottom of the container 1, and filter paper 4 is laid on the screen 3; the filter paper 4 is laid on the screen 3, the filter paper 4 with different thicknesses can generate different over-air pressure values, and the initially set negative water pressure can be changed by replacing the filter paper 4 with different thicknesses;
step 2): placing the unsaturated soil sample into the container 1 and ensuring that the unsaturated soil sample is in complete contact with the filter paper 4;
step 3): installing a tensiometer 2 in the unsaturated soil sample, and measuring the initial negative pore water pressure of the unsaturated soil sample; in the embodiment, two tensiometers 2 are respectively arranged in the unsaturated soil sample and used for measuring the negative pore water pressure value of different positions in the unsaturated soil sample at a certain moment, and the average value of the two readings is used for representing the negative pore water pressure value of the soil sample, so that the measurement is more accurate;
step 4): injecting water into a measuring cylinder 8 at the top of a second measuring pipe 7, opening a second valve 7.2 to enable the water to flow into the second measuring pipe 7, a connecting pipe 6 and the first measuring pipe 5 in sequence, ensuring that the liquid level heights in the first measuring pipe 5 and the second measuring pipe 7 are flush with the filter paper 4 in the cylindrical container after water injection, and then closing the second valve 7.2;
step 5): closing the first valve 5.1, reducing the height of the second measuring tube 7 until the top of the second measuring tube 7 is reduced to be below the horizontal position of the filter paper 4, wherein a water head difference formed by the first measuring tube 5 and the second measuring tube 7 generates downward negative pressure on the filter paper 4, the unsaturated soil sample generates upward negative pore water pressure on the filter paper 4, and the absolute value of the negative pressure generated by the water head difference on the filter paper 4 is smaller than the absolute value of the negative pore water pressure generated by the unsaturated soil sample on the filter paper 4;
step 6): recording the water level of the measuring cylinder 8, and opening the first valve 5.1;
step 7): under the action of negative pore water pressure of the unsaturated soil sample, water in the first measuring tube 5 gradually flows into the container 1 through the filter paper 4, the water level of the second measuring tube 7 communicated with the first measuring tube is reduced, the second valve 7.2 is opened, water in the measuring cylinder 8 enters the second measuring tube 7, and the second valve 7.2 is closed again after the water head difference formed by the first measuring tube 5 and the second measuring tube 7 is ensured to be unchanged;
step 8): after a period of time, the negative pore water pressure of the unsaturated soil sample is gradually reduced until the absolute value of the negative pore water pressure is equal to the absolute value of the negative pressure, the permeation reaches balance, the first valve 5.1 is closed, and the negative pore water pressure of the unsaturated soil sample at the moment is measured by the tensiometer 2;
step 9): recording a time interval t, reading the water supply quantity Q in the time through the measuring cylinder 8, and determining the unsaturated soil permeability coefficient k under the primary matrix suction according to Darcy's law Q = khtA/L (A, L is the area and height of the unsaturated soil sample respectively, and h is the water head difference on two sides); in this embodiment, the time can be recorded by a computer, and the related data can be calculated in the computer;
step 10): raising the height of the second measuring tube 7 to reduce the water head difference formed by the first measuring tube 5 and the second measuring tube 7, so that the absolute value of the negative pressure generated by the water head difference to the filter paper 4 is smaller than the absolute value of the negative pore water pressure generated by the unsaturated soil sample to the filter paper 4 again, then opening the first valve 5.1, and repeating the steps 6) to 9), and recording the unsaturated soil permeability coefficient k under the primary matrix suction;
step 11): and (3) gradually increasing the height of the second measuring pipe 7 for multiple times until the water head difference formed by the first measuring pipe 5 and the second measuring pipe 7 is 0, and recording the unsaturated soil permeability coefficient k under each level of substrate suction according to the step 10) after increasing the height of the second measuring pipe 7 every time, and making a relation curve graph of the substrate suction and the permeability coefficient.
Preferably, in the step 7), the controller 11 can automatically control the automatic opening and closing process of the second valve 7.2, and the specific steps are as follows:
firstly, after the water level of the second measuring pipe 7 communicated with the second measuring pipe falls, the water level is lower than the horizontal height of the infrared signal emitter 9 and the infrared signal receiver 10, then the infrared signal receiver 10 receives the signal transmitted by the infrared signal emitter 9, then the infrared signal receiver 10 transmits a corresponding signal to the controller 11, the controller 11 controls the second valve 7.2 to open, the water in the measuring cylinder 8 enters the second measuring pipe 7, when the water level in the second measuring pipe 7 exceeds the horizontal height of the infrared signal emitter 9 and the infrared signal receiver 10, the signal transmitted by the infrared signal emitter 9 changes due to water blockage, the infrared signal receiver 10 transmits a corresponding signal to the controller 11, and the controller 11 controls the second valve 7.2 to close, the water in the measuring cylinder 8 stops entering the second measuring tube 7, and the water level of the second measuring tube 7 can be guaranteed to be maintained at a fixed water level through the process, so that the water head formed by the first measuring tube 5 and the second measuring tube 7 is guaranteed to be unchanged.
The above steps are prepared by specific experimental values as follows:
as shown in fig. 3, in step 3) of this embodiment, the initial negative pore water pressure of the unsaturated soil sample is measured to be-70 kPa through the tensiometer 2, then in step 5), the top of the second measuring tube 7 is lowered to 0.65m below the horizontal position of the filter paper 4, the water head difference is 0.65m, since the water pressure is in direct proportion to the height, the negative pressure generated by the water head difference to the lower surface of the filter paper 4 is calculated according to the water pressure formula, at this time, the negative pressure absolute value is slightly smaller than the negative pore water pressure absolute value, so the water in the first measuring tube 5 can gradually flow into the container 1 through the filter paper 4, after a while, the negative pore water pressure of the unsaturated soil sample gradually decreases until the negative pore water pressure absolute value is equal to the negative pressure absolute value, and the permeation reaches the balance; then, the second measuring tube is lifted by 0.05m, so that the water head difference formed by the first measuring tube 5 and the second measuring tube 7 is reduced, the absolute value of the negative pressure generated by the water head difference to the filter paper 4 is smaller than the absolute value of the negative pore water pressure generated by the unsaturated soil sample to the filter paper 4 again, and the water in the first measuring tube 5 can gradually flow into the container 1 through the filter paper 4 again; and analogizing in turn, gradually increasing the height of the second measuring tube 7 by 0.05m each time, repeating the process, determining the permeability coefficient under different substrate suction according to the formula in the step 9), and completing the determination of the permeability coefficient curve of the unsaturated soil body, wherein fig. 3 is a permeability coefficient curve chart of certain sandy soil.
The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and features in the embodiments and examples in the present application may be arbitrarily combined with each other without conflict. The protection scope of the present invention is defined by the claims, and includes equivalents of technical features of the claims. I.e., equivalent alterations and modifications within the scope hereof, are also intended to be within the scope of the invention.
Claims (7)
1. A method for measuring the permeability coefficient of unsaturated soil is characterized in that: the device used in the method comprises a container (1) for containing unsaturated soil samples, a tensiometer (2) is inserted into the unsaturated soil samples, a screen (3) is arranged at the bottom of the container (1), filter paper (4) is laid on the upper surface of the screen (3), the bottom of the container (1) is communicated with the top of a first measuring tube (5), the bottom of the first measuring tube (5) is connected with one end of a connecting tube (6), the other end of the connecting tube (6) is connected with the bottom of a second measuring tube (7), and a scale mark (7.1) is arranged on the second measuring tube (7); the method specifically comprises the following steps:
step 1): a screen (3) is arranged at the bottom of the container (1), and then filter paper (4) is laid on the screen (3);
step 2): placing the unsaturated soil sample into a container (1) and ensuring that the unsaturated soil sample is in complete contact with the filter paper (4);
step 3): installing a tensiometer (2) in the unsaturated soil sample, and measuring the initial negative pore water pressure of the unsaturated soil sample;
step 4): injecting water into a measuring cylinder (8) at the top of a second measuring pipe (7), opening a second valve (7.2) to enable the water to flow into the second measuring pipe (7), a connecting pipe (6) and the first measuring pipe (5) in sequence, ensuring that the liquid level in the first measuring pipe (5) and the second measuring pipe (7) is level with the filter paper (4) in the cylindrical container after water injection, and then closing the second valve (7.2);
step 5): closing the first valve (5.1), reducing the height of the second measuring tube (7) until the top of the second measuring tube (7) is reduced to be below the horizontal position of the filter paper (4), wherein a water head difference formed by the first measuring tube (5) and the second measuring tube (7) generates downward negative pressure on the filter paper (4), the unsaturated soil sample generates upward negative pore water pressure on the filter paper (4), and the absolute value of the negative pressure generated by the water head difference on the filter paper (4) is smaller than the absolute value of the negative pore water pressure generated by the unsaturated soil sample on the filter paper (4);
step 6): recording the water level of the measuring cylinder (8), and opening a first valve (5.1);
step 7): under the action of negative pore water pressure of an unsaturated soil sample, water in the first measuring pipe (5) gradually flows into the container (1) through the filter paper (4), the water level of the second measuring pipe (7) communicated with the first measuring pipe is reduced, the second valve (7.2) is opened, water in the measuring cylinder (8) enters the second measuring pipe (7), and the water head difference formed by the first measuring pipe (5) and the second measuring pipe (7) is ensured to be constant by controlling the opening and closing of the second valve (7.2);
step 8): the negative pore water pressure of the unsaturated soil sample is gradually reduced until the absolute value of the negative pore water pressure is equal to the absolute value of the negative pressure, the permeation is balanced, the first valve (5.1) is closed, and the negative pore water pressure of the unsaturated soil sample is measured by the tensiometer (2);
step 9): recording the time interval t, reading the water supply quantity Q in the time through a measuring cylinder (8), and determining the unsaturated soil permeability coefficient k under the primary matrix suction according to Darcy's law Q = khtA/L; a. L is the area and height of the unsaturated soil sample respectively, and h is the water head difference on two sides.
2. The method for determining the permeability coefficient of unsaturated soil according to claim 1, wherein: the first measuring pipe (5) is provided with a first valve (5.1), and the top of the second measuring pipe (7) is communicated with the bottom of the measuring cylinder (8) through a second valve (7.2).
3. The method for determining the permeability coefficient of unsaturated soil according to claim 2, wherein: the second valve (7.2) is an electromagnetic valve, an infrared signal transmitter (9) and an infrared signal receiver (10) are respectively arranged on two sides of the second measuring pipe (7), the infrared signal receiver (10) is connected with a signal input end of a controller (11), and the controller (11) is connected with a control end of the second valve (7.2).
4. The method for determining the permeability coefficient of unsaturated soil according to claim 1, wherein: container (1), first survey buret (5) and second survey buret (7) are the transparent glass material, and connecting pipe (6) are the rubber tube, container (1) are cylindrical structure, and position department that container (1) bottom and first survey buret (5) top communicate sets up screen cloth (3).
5. The method for determining the permeability coefficient of unsaturated soil according to claim 1, wherein: the first measuring pipe (5) is arranged on the first supporting frame (12), and the second measuring pipe (7) is arranged on the second supporting frame (13).
6. The method for determining the permeability coefficient of unsaturated soil according to claim 1, wherein: it also includes the following steps:
step 10): raising the height of the second measuring tube (7) to reduce the water head difference formed by the first measuring tube (5) and the second measuring tube (7), so that the absolute value of the negative pressure generated by the water head difference to the filter paper (4) is smaller than the absolute value of the negative pore water pressure generated by the unsaturated soil sample to the filter paper (4), then opening the first valve (5.1), repeating the steps 6) to 9), and recording the unsaturated soil permeability coefficient k under the primary matrix suction;
step 11): and (3) gradually increasing the height of the second measuring pipe (7) for multiple times until the water head difference formed by the first measuring pipe (5) and the second measuring pipe (7) is 0, recording the osmotic coefficient k of unsaturated soil under each level of substrate suction according to the step 10 after the height of the second measuring pipe (7) is increased every time, and making a relation curve graph of the substrate suction and the osmotic coefficient.
7. The method for determining the permeability coefficient of unsaturated soil according to claim 1, wherein: in the step 7), the controller (11) can automatically control the automatic opening and closing process of the second valve (7.2), and the specific steps are as follows:
firstly, after the water level of the second measuring pipe (7) communicated with the second measuring pipe is lowered, the water level is lower than the horizontal height of the infrared signal transmitter (9) and the infrared signal receiver (10), then the infrared signal receiver (10) receives a signal transmitted by the infrared signal transmitter (9), then the infrared signal receiver (10) transmits a corresponding signal to the controller (11), the controller (11) controls the second valve (7.2) to be opened, water in the measuring cylinder (8) enters the second measuring pipe (7), when the water level in the second measuring pipe (7) exceeds the horizontal height of the infrared signal transmitter (9) and the infrared signal receiver (10), the signal transmitted by the infrared signal transmitter (9) changes due to water blockage, and the infrared signal receiver (10) transmits the corresponding signal to the controller (11), the controller (11) can control the second valve (7.2) to close, and water in the measuring cylinder (8) stops entering the second measuring pipe (7), so that the water level of the second measuring pipe (7) can be maintained at a fixed water level through the process, and the water head difference formed by the first measuring pipe (5) and the second measuring pipe (7) is guaranteed to be unchanged.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103344538A (en) * | 2013-06-25 | 2013-10-09 | 西安科技大学 | Multifunctional unsaturated soil permeameter and testing method thereof |
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