Device for measuring porosity in sand seepage process

Abstract

The invention provides a device for measuring porosity in a sand seepage process. The device comprises a soil sample accommodating unit and a water supply unit, the soil sample accommodating unit comprises a plurality of soil sample barrels and a plurality of bottom covers, a screen is mounted at the bottom end of an inner cavity of each soil sample barrel, an accommodating chamber for storing a soil sample is defined by the screen and the inner cavity of each soil sample barrel, an electrode is arranged on the outer side of each soil sample barrel, one end of each electrode extends into the accommodating chamber, and the other end of each electrode is connected with a resistivity tester; the bottom cover is used for being mounted at the bottom of the soil sample barrel, a bottom channel communicated with the containing chamber is formed in the bottom cover, and the multiple soil sample barrels are detachably connected end to end to form a soil sample barrel assembly extending in the height direction; the device provided by the invention can measure the porosity of the sandy soil sample before and after seepage under different infiltration conditions without destroying the structure of the soil sample.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical testing, and in particular to a device for measuring the porosity of sand in the process of seepage. Background Art

[0002] The existing methods for measuring the porosity of sand are mainly volumetric drainage method, mercury intrusion method, nuclear magnetic resonance method and gas inhalation method. The volumetric drainage method first uses a calibrated container to measure the volume Vtotal of the dry sample, then puts the sand sample into a liquid container to completely immerse it to calculate the drainage volume Vrow, and calculates the porosity based on Vrow and Vtotal. Its disadvantage is that it may be difficult to obtain an accurate drainage volume for some very small or loose samples. The gas inhalation method first dries the sand sample to constant weight, then exposes the sample to a gas environment under a specific pressure, measures the volume of the adsorbed gas, and calculates the porosity based on the amount of gas adsorbed and the known relationship between gas adsorption and pore space. Its disadvantage is that the measurement process is complicated and the equipment cost is high. The mercury intrusion method dries the sand sample and weighs the mass, puts the sample into the mercury intrusion device, gradually increases the pressure, records the volume of mercury under different pressures, calculates the pore volume based on the volume change of the pressed mercury, and thus obtains the porosity. Its disadvantage is that the sample may be damaged and cannot be used for repeated experiments. Mercury does not wet the solid surface and cannot enter unconnected pores, so it can only effectively measure the volume of connected pores. The nuclear magnetic resonance method puts the sample into the nuclear magnetic resonance instrument, measures the reaction of water molecules in the magnetic field, and infers the pore volume based on the signal strength of water, and thus calculates the porosity. Its disadvantage is that the equipment is expensive and the operation is complicated.

[0003] The reversed grain order accumulation is common in the flow area and accumulation area of ​​high-speed long-distance landslides. Due to the impact of collision rolling, vibration screening and the dissipation pressure of large-size particles, the particle size of the accumulation body presents a structure of large top and small bottom in the vertical direction. We can divide the accumulation body into three phase zones in the vertical direction: the top hard shell layer, the middle main body layer, and the bottom base layer. This special structure makes its upper porosity relatively large and its water permeability relatively strong. Under the action of water flow, the penetration of water may produce a strong drag force on fine particles, thereby causing the fine particles to move in the pores formed by coarse sand particles. Since the three phase zones have large differences in particle grading (composition), that is, the hard shell layer is easy to lose fine particles due to its large pore channels, and the main layer has both fine particles from the hard shell layer and its own fine particles will migrate downward, and there will be accumulation of fine particles at the bottom, so it is necessary to analyze the changes in soil porosity in three layers. Summary of the invention

[0004] The purpose of the present invention is to provide a device for measuring the porosity of sandy soil during seepage, which can measure the porosity of sandy soil samples before and after seepage under different infiltration heads without destroying the soil sample structure. In order to achieve the above technical features, the purpose of the present invention is achieved as follows:

[0005] A device for measuring the porosity of sand during seepage, comprising a soil sample receiving unit and a water supply unit;

[0006] The soil sample accommodating unit comprises a plurality of soil sample tubes and a plurality of bottom covers, a screen is installed at the bottom end of the inner cavity of the soil sample tube, the screen and the inner cavity of the soil sample tube enclose a accommodating chamber for storing soil samples, an electrode is arranged on the outer side of the soil sample tube, one end of the electrode extends into the accommodating chamber, and the other end of the electrode is used to be connected to a resistivity tester, the bottom cover is used to be installed at the bottom of the soil sample tube, and a bottom channel communicating with the accommodating chamber is arranged on the bottom cover, and the head and tail of the plurality of soil sample tubes are detachably connected to form a soil sample tube assembly extending along the height direction;

[0007] The water supply unit is used to supply water into the soil sample cylinder.

[0008] The inner cavity cross section of the soil sample cylinder is rectangular.

[0009] A brass electrode sheet connected to the electrode is installed on the side wall of the inner cavity of the soil sample tube, and the brass electrode sheets in two adjacent soil sample tubes on the soil sample tube assembly abut against each other.

[0010] The multiple soil sample cylinders are connected via flanges.

[0011] The soil sample tube is made of transparent and insulating materials.

[0012] A method for measuring the resistivity and porosity of sand with an inverse grain structure by using a device for measuring the porosity during sand seepage, comprising the following steps:

[0013] S1. Prepare standard samples of sand with different porosities, and use different layers of initial particle size grading to change the content of fine particle size;

[0014] S2. Place the sand and soil standard sample prepared in S1 into the holding chamber of a single soil sample tube and install the bottom cover. Then connect the bottom channel on the bottom cover to the water supply unit, slowly pass water to saturate the standard sample until the water surface is submerged, stop the water supply, connect the electrode to the resistivity tester, and measure the resistivity.

[0015] S3. Measure the resistivity of sandy soil samples with different soil porosities by the same operation as S2, and establish a relationship curve based on the known soil porosity of the standard sample and the corresponding resistivity obtained by the measurement;

[0016] S4. The sand to be tested is gradually filled into multiple soil sample tubes from the bottom according to the inverse grain sequence soil layer structure, and then the multiple soil sample tubes are connected in sequence according to the inverse grain sequence soil layer structure, and the bottom cover is installed at the bottom of the bottom soil sample tube, and then the bottom channel on the bottom cover is connected to the water supply unit, and water is slowly passed until saturation, that is, until water is just observed on the surface of the soil sample in the top soil sample tube, and the bottom channel on the bottom cover is disconnected from the water supply unit and closed;

[0017] S5, controlling the water supply unit to inject water into the soil sample tube at the top with a certain set water head;

[0018] S6. Open the bottom channel on the bottom cover at the bottom of the bottom soil sample tube. When no obvious particles are observed in the outflow of the bottom channel on the bottom cover, close the water supply unit and the bottom channel on the bottom cover.

[0019] S7, take another bottom cover, remove the top soil sample tube and connect it to the bottom cover, pass water into the top soil sample tube through the bottom channel at the bottom of the bottom cover through the water supply unit to saturate the soil sample, close the bottom channel, connect the top soil sample tube electrode to the resistivity tester, and measure the resistivity of the soil sample in the top soil sample tube;

[0020] S8. Take another bottom cover again, remove the soil sample tube of the second top layer and connect it to the bottom cover, pass water into the soil sample tube of the second top layer through the bottom channel of the bottom cover through the water supply unit to saturate the soil sample, close the bottom channel, connect the electrode of the soil sample tube of the second top layer to the resistivity tester, measure the resistivity of the soil sample in the soil sample tube of the second top layer, and similarly, obtain the resistivity of the soil samples in all the remaining soil sample tubes;

[0021] S9, according to the relationship between the porosity and resistivity curve of the standard sample obtained in S3, the porosity value corresponding to the resistivity of the soil sample in each soil sample tube under the water head in S5 can be found;

[0022] S10, reconnect all soil sample tubes in order according to the reverse grain sequence soil layer structure, and install the bottom cover at the bottom of the bottom soil sample tube, then connect the bottom channel on the bottom cover to the water supply unit, slowly pass water until saturation, that is, until water is just observed on the surface of the soil sample in the top soil sample tube, disconnect the bottom channel on the bottom cover from the water supply unit and close it;

[0023] S11, controlling the water supply unit to inject water into the soil sample cylinder at the top with a water head higher than that in S5;

[0024] S12. Repeat the operations of S6-S9. Similarly, the porosity value corresponding to the resistivity of the soil sample in each soil sample tube 1 under the water head in S11 can be obtained.

[0025] A device for measuring the porosity of sand in the seepage process and a method for measuring the overall porosity of saturated sand in the seepage process, comprising the following steps:

[0026] S1. Prepare standard samples of sand with different porosities, and use different layers of initial particle size grading to change the content of fine particle size;

[0027] S2. Place the sand and soil standard sample prepared in S1 into the holding chamber of a single soil sample tube and install the bottom cover. Then connect the bottom channel on the bottom cover to the water supply unit, slowly pass water to saturate the standard sample until the water surface is submerged, stop the water supply, connect the electrode to the resistivity tester, and measure the resistivity.

[0028] S3, repeating the operation of S2 to measure the resistivity of sandy soil samples with different soil porosities, and establishing a relationship curve based on the known soil porosity of the standard sample and the corresponding resistivity obtained by measurement;

[0029] S4. The sand to be tested is gradually filled into multiple soil sample tubes from the bottom according to the inverse grain sequence soil layer structure, and then the multiple soil sample tubes are connected in sequence according to the inverse grain sequence soil layer structure, and the bottom cover is installed at the bottom of the bottom soil sample tube, and then the bottom channel on the bottom cover is connected to the water supply unit, and water is slowly passed until saturation, that is, until water is just observed on the surface of the soil sample in the top soil sample tube, and the bottom channel on the bottom cover is disconnected from the water supply unit and closed;

[0030] S5. Control the water supply unit to inject water into the topmost soil sample tube at a certain set water head, open the bottom channel, connect the resistivity tester to the electrode on one of the soil sample tubes, and measure the porosity of the entire soil sample at a set frequency.

[0031] Optionally, the resistivity is calculated by:

[0032]

[0033] Where: ρ is the resistivity of sand; w is the width of the cross section through which the current passes through the soil; h is the height of the cross section through which the current passes through the soil; L is the electrode spacing; and R is the measured resistance of saturated sand.

[0034] Optionally, the porosity is calculated by:

[0035]

[0036] Where: n is the porosity; ρ is the resistivity of sand; ρ ω is the resistivity of pore water; a is the adjustment coefficient; m is the porosity index.

[0037] The present invention has the following beneficial effects:

[0038] 1. The device of the present application can measure the porosity of sandy soil samples before and after seepage under different infiltration heads without destroying the soil sample structure, thus avoiding the situation that the traditional method can only measure the porosity change under one infiltration head at a time.

[0039] 2. The device of the present application adopts the resistance method to measure the porosity, and there is no need to take out the sample and dry it before measuring. The operation is simple and the measurement speed is fast.

[0040] 3. The device of the present application can monitor the porosity of an entire soil-rock mixture in real time.

[0041] 4. The device of the present application is flexible in application and can be disassembled for use. A single soil sample tube can be removed and used for outdoor measurement of sand porosity, and is suitable for other types of soil besides sand. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0043] Figure 1 A schematic diagram of a device for measuring porosity during sand seepage provided by an embodiment of the present invention;

[0044] Figure 2 A top view of a soil sample cylinder provided in an embodiment of the present invention;

[0045] Figure 3 The embodiment of the present invention provides Figure 2 Middle AA section;

[0046] Figure 4 A schematic diagram of the structure of a bottom cover provided by an embodiment of the present invention;

[0047] Figure 5 A schematic diagram of the structure of a top cover provided by an embodiment of the present invention;

[0048] In the figure: soil sample cylinder 1, bottom cover 2, screen 3, holding chamber 4, electrode 5, resistivity tester 6, bottom channel 7, brass electrode sheet 8, top cover 9, first valve 10, top channel 11, second valve 12, bottom bracket 13, flange 14, receiving basin 15. DETAILED DESCRIPTION

[0049] The embodiments of the present invention are further described below in conjunction with the accompanying drawings.

[0050] In order to realize the above-mentioned technical features, the purpose of the present invention is achieved as follows:

[0051] Example 1: See Figure 1-5A device for measuring the porosity of sand in the seepage process comprises a soil sample receiving unit and a water supply unit; the soil sample receiving unit comprises a plurality of soil sample tubes 1, a plurality of bottom covers 2, and a top cover 9; a screen 3 is installed at the bottom end of the inner cavity of the soil sample tube 1; the screen 3 and the inner cavity of the soil sample tube 1 enclose a receiving chamber 4 for storing soil samples; an electrode 5 is arranged on the outer side of the soil sample tube 1; one end of the electrode 5 extends into the receiving chamber 4; the other end of the electrode 5 is used to be connected to a resistivity tester 6; the bottom cover 2 is used to be installed at the bottom of the soil sample tube 1, and a top cover 9 is provided on the bottom cover 2 to connect to the receiving chamber 4; the bottom cover 2 is used to connect to the resistivity tester 6; the bottom cover 2 is used ... A bottom channel 7 connected to the chamber 4 is provided, and a first valve 10 is installed at the bottom of the bottom cover 2. The bottom channel 7 is connected to the outside through the first valve 10. A plurality of soil sample tubes 1 are connected head to tail in a detachable manner to form a soil sample tube assembly extending along the height direction. A top cover 9 is detachably installed on the top of the soil sample tube 1. A top channel 11 connected to the accommodating chamber 4 is provided on the top cover 9. The top channel 11 is connected to the outside through a second valve 12. The water supply unit supplies water to the soil sample tube 1 by being connected to the first valve 10 and the second valve 12 respectively.

[0052] Furthermore, the inner cavity cross-section of the soil sample tube 1 is rectangular.

[0053] Furthermore, a brass electrode sheet 8 connected to the electrode 5 by welding is installed on the side wall of the inner cavity of the soil sample tube 1, thereby indirectly increasing the contact area between the electrode and the soil sample in the soil sample tube; and the brass electrode sheets 8 in two adjacent soil sample tubes 1 on the soil sample tube assembly abut against each other to achieve mutual conduction among the brass electrode sheets in all soil sample tubes.

[0054] Furthermore, the multiple soil sample tubes 1 are connected by flanges to achieve a stable and reliable detachable connection.

[0055] Furthermore, the soil sample tube 1 is made of a transparent insulating material, preferably an acrylic plate, so that the soil sample can be visually observed through the soil sample tube.

[0056] Embodiment 2: A method for measuring the resistivity and porosity of sand with an inverse grain structure by a device for measuring the porosity during sand seepage, comprising the following steps:

[0057] S1. Prepare standard samples of sand with different porosities, and use different layers of initial particle size grading to change the content of fine particle size;

[0058] S2, put the sand and soil standard sample prepared in S1 into the containing chamber 4 of the single soil sample tube 1, and install the bottom cover 2, then connect the bottom channel 7 on the bottom cover 2 with the water supply unit, slowly pass water to saturate the standard sample until the water surface is immersed, stop the water supply, connect the electrode 5 with the resistivity tester 6, and measure the resistivity;

[0059] S3. Measure the resistivity of sandy soil samples with different soil porosities by the same operation as S2, and establish a relationship curve based on the known soil porosity of the standard sample and the corresponding resistivity obtained by the measurement;

[0060] S4, the sand to be tested is gradually filled into three soil sample tubes 1 from the bottom according to the inverse grain sequence soil layer structure, and then the three soil sample tubes 1 are connected in sequence according to the inverse grain sequence soil layer structure, and the first bottom cover 2 is installed at the bottom of the bottom soil sample tube 1, and then the first valve 10 at the bottom of the first bottom cover 2 is connected to the water supply unit, and water is slowly passed until saturation, that is, until water is just observed on the surface of the soil sample in the top soil sample tube 1, and the first valve 10 is closed and disconnected from the water supply unit;

[0061] S5, connecting the water supply unit to the second valve 12, and controlling water injection into the soil sample tube 1 at the top with a certain set water head;

[0062] S6, connecting the first valve 10 to the receiving basin 15 through the bottom connecting water pipe, and opening the first valve 10. When no obvious particles are observed in the effluent discharged from the first valve 10, closing the first valve 10;

[0063] S7, take another second bottom cover 2, remove the top soil sample tube 1 and connect it to the second bottom cover 2, switch the water supply unit to connect to the first valve 10 at the bottom of the top soil sample tube 1, and then pass water into the top soil sample tube 1 to saturate the soil sample in the top soil sample tube 1, close the first valve 10, connect the electrode 5 of the top soil sample tube 1 to the resistivity tester 6, and measure the resistivity of the soil sample in the top soil sample tube 1;

[0064] S8, take another third bottom cover 2, remove the soil sample tube 1 of the middle layer and connect it to the third bottom cover 2, switch the water supply unit to connect it to the first valve 10 at the bottom of the soil sample tube 1 of the middle layer, and then pass water into the soil sample tube 1 of the middle layer to saturate the soil sample in the soil sample tube 1 of the middle layer, close the first valve 10, connect the electrode 5 of the soil sample tube 1 of the middle layer to the resistivity tester 6, and measure the resistivity of the soil sample in the soil sample tube 1 of the middle layer. Similarly, the resistivity of the soil sample in the soil sample tube 1 of the bottom layer can be obtained;

[0065] S9, according to the relationship between the porosity and resistivity curve of the standard sample obtained in S3, the porosity value corresponding to the resistivity of the soil sample in each soil sample tube 1 under the water head in S5 can be found;

[0066] S10, reconnect all soil sample tubes 1 in order according to the reverse grain sequence soil layer structure, and install the bottom cover 2 at the bottom of the bottom soil sample tube 1, then connect the bottom channel 7 on the bottom cover 2 to the water supply unit, slowly pass water until saturation, that is, until water is just observed on the surface of the soil sample in the top soil sample tube 1, disconnect the bottom channel 7 on the bottom cover 2 from the water supply unit and close it;

[0067] S11, controlling the water supply unit to inject water into the soil sample tube 1 at the top with a water head higher than that in S5;

[0068] S12. Repeat the operations of S6-S9. Similarly, the porosity value corresponding to the resistivity of the soil sample in each soil sample tube 1 under the water head in S11 can be obtained.

[0069] Embodiment 3: A device for measuring the porosity of sand during seepage. A method for measuring the overall porosity of saturated sand during seepage, comprising the following steps:

[0070] S1. Prepare standard samples of sand with different porosities, and use different layers of initial particle size grading to change the content of fine particle size;

[0071] S2, put the sand and soil standard sample prepared in S1 into the containing chamber 4 of a single soil sample tube 1, and install the bottom cover 2, then connect the bottom channel 7 on the bottom cover 2 to the water supply unit, slowly pass water to saturate the standard sample until the water surface is submerged, stop the water supply, connect the electrode 5 to the resistivity tester 6, and measure the resistivity;

[0072] S3, repeating the operation of S2 to measure the resistivity of sandy soil samples with different soil porosities, and establishing a relationship curve based on the known soil porosity of the standard sample and the corresponding resistivity obtained by measurement;

[0073] S4, the sand to be tested is gradually filled into multiple soil sample tubes 1 from the bottom according to the inverse grain sequence soil layer structure, and then the multiple soil sample tubes 1 are connected in sequence according to the inverse grain sequence soil layer structure, and the bottom cover 2 is installed at the bottom of the bottom soil sample tube 1, and then the bottom channel 7 on the bottom cover 2 is connected to the water supply unit, and water is slowly passed until saturation, that is, until water is just observed on the surface of the soil sample in the top soil sample tube 1, and the bottom channel 7 on the bottom cover 2 is disconnected from the water supply unit and closed;

[0074] S5. Control the water supply unit to inject water into the topmost soil sample tube 1 at a certain set water head, open the bottom channel 7, connect the resistivity tester 6 to the electrode 5 on one of the soil sample tubes 1, and measure the porosity of the entire soil sample at the set frequency. Whether the porosity of the entire soil sample continues to change can be used as a standard for the stability of the soil sample under this water head, which can serve as a basis for subsequent confirmation of the time to change the water head.

[0075] Furthermore, the calculation formula of the resistivity in the present invention is:

[0076]

[0077] Where: ρ is the resistivity of sand; w is the width of the cross section through which the current passes through the soil; h is the height of the cross section through which the current passes through the soil; L is the electrode spacing; and R is the measured resistance of saturated sand.

[0078] Furthermore, the calculation formula of the porosity in the present invention is:

[0079]

[0080] Where: n is the porosity; ρ is the resistivity of sand; ρ ω is the resistivity of pore water; a is the adjustment coefficient; m is the porosity index.

Claims

1. A device for measuring the porosity of sand during seepage, characterized in that: It includes a soil sample holding unit and a water supply unit; The soil sample containing unit comprises a plurality of soil sample tubes (1) and a plurality of bottom covers (2); a screen (3) is installed at the bottom end of the inner cavity of the soil sample tube (1); the screen (3) and the inner cavity of the soil sample tube (1) enclose a containing chamber (4) for storing soil samples; an electrode (5) is provided on the outside of the soil sample tube (1); one end of the electrode (5) extends into the containing chamber (4); the other end of the electrode (5) is used to be connected to a resistivity tester (6); the bottom cover (2) is used to be installed at the bottom of the soil sample tube (1); and a bottom channel (7) communicating with the containing chamber (4) is provided on the bottom cover (2); and the plurality of soil sample tubes (1) are connected head to tail in a detachable manner to form a soil sample tube assembly extending in a height direction; The water supply unit is used to supply water into the soil sample cylinder (1).

2. The device for measuring porosity during sand seepage according to claim 1, characterized in that: The inner cavity cross section of the soil sample cylinder (1) is rectangular.

3. The device for measuring porosity during sand seepage according to claim 2, characterized in that: A brass electrode sheet (8) connected to the electrode (5) is installed on the inner cavity side wall of the soil sample tube (1), and the brass electrode sheets (8) in two adjacent soil sample tubes (1) on the soil sample tube assembly abut against each other.

4. The device for measuring porosity during sand seepage according to claim 2, characterized in that: The plurality of soil sample cylinders (1) are connected via flanges.

5. The device for measuring porosity during sand seepage according to claim 4, characterized in that: The soil sample tube (1) is made of transparent and insulating materials.

6. The method for measuring the resistivity and porosity of sand with an inverse grain structure by using the device for measuring the porosity in the seepage process of sand according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Prepare standard samples of sand with different porosities, and use different layers of initial particle size grading to change the content of fine particle size; S2, placing the sand and soil standard sample prepared in S1 into the containing chamber (4) of a single soil sample tube (1), and installing the bottom cover (2), then connecting the bottom channel (7) on the bottom cover (2) to the water supply unit, slowly passing water to saturate the standard sample until the water surface is submerged, stopping the water supply, connecting the electrode (5) to the resistivity tester (6), and measuring the resistivity; S3. Measure the resistivity of sandy soil samples with different soil porosities by the same operation as S2, and establish a relationship curve based on the known soil porosity of the standard sample and the corresponding resistivity obtained by the measurement; S4, the sand to be tested is gradually filled into a plurality of soil sample tubes (1) from the bottom according to the inverse grain sequence soil layer structure, and then the plurality of soil sample tubes (1) are sequentially connected according to the inverse grain sequence soil layer structure, and the bottom cover (2) is installed at the bottom of the bottom soil sample tube (1), and then the bottom channel (7) on the bottom cover (2) is connected to the water supply unit, and water is slowly passed until saturation, that is, until water begins to be observed on the surface of the soil sample in the top soil sample tube (1), and the bottom channel (7) on the bottom cover (2) is disconnected from the water supply unit and closed; S5, controlling the water supply unit to inject water into the soil sample tube (1) at the top with a certain set water head; S6. Open the bottom channel (7) on the bottom cover (2) at the bottom of the bottom soil sample tube (1). When no obvious particles are observed in the outflow of the bottom channel (7) on the bottom cover (2), close the water supply unit and the bottom channel (7) on the bottom cover (2); S7, take another bottom cover (2), remove the top soil sample tube (1) and connect it to the bottom cover (2), pass water into the top soil sample tube (1) through the bottom channel (7) at the bottom of the bottom cover (2) through the water supply unit to saturate the soil sample, close the bottom channel (7), connect the top soil sample tube (1) electrode (5) to the resistivity tester (6), and measure the resistivity of the soil sample in the top soil sample tube (1); S8, take another bottom cover (2), remove the soil sample tube (1) at the second top layer and connect it to the bottom cover (2), pass water into the soil sample tube (1) at the second top layer through the bottom channel (7) at the bottom of the bottom cover (2) through the water supply unit, so that the soil sample is saturated, close the bottom channel (7), connect the electrode (5) of the soil sample tube (1) at the second top layer to the resistivity tester (6), measure the resistivity of the soil sample in the soil sample tube (1) at the second top layer, and similarly obtain the resistivity of the soil samples in all the remaining soil sample tubes (1); S9, according to the relationship between the porosity and resistivity curve of the standard sample obtained in S3, the porosity value corresponding to the resistivity of the soil sample in each soil sample tube (1) under the water head in S5 can be found; S10, all soil sample tubes (1) are reconnected in sequence according to the reverse grain sequence soil layer structure, and the bottom cover (2) is installed at the bottom of the bottom soil sample tube (1), and then the bottom channel (7) on the bottom cover (2) is connected to the water supply unit, and water is slowly passed until saturation occurs, that is, water begins to be observed on the surface of the soil sample in the top soil sample tube (1), and the bottom channel (7) on the bottom cover (2) is disconnected from the water supply unit and closed; S11, controlling the water supply unit to inject water into the soil sample tube (1) at the top with a water head higher than that in S5; S12. Repeat the operations S6-S9 to obtain the porosity value corresponding to the resistivity of the soil sample in each soil sample tube (1) under the water head in S11.

7. The method for measuring the overall porosity of saturated sand during seepage according to the device for measuring the porosity of sand during seepage according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Prepare standard samples of sand with different porosities, and use different layers of initial particle size grading to change the content of fine particle size; S2, place the sand and soil standard sample prepared in S1 into the containing chamber (4) of a single soil sample tube (1), and install the bottom cover (2), then connect the bottom channel (7) on the bottom cover (2) to the water supply unit, slowly pass water to saturate the standard sample until the water surface is submerged, stop the water supply, connect the electrode (5) to the resistivity tester (6), and measure the resistivity; S3, repeating the operation of S2 to measure the resistivity of sandy soil samples with different soil porosities, and establishing a relationship curve based on the known soil porosity of the standard sample and the corresponding resistivity obtained by measurement; S4, the sand to be tested is gradually filled into a plurality of soil sample cylinders (1) from the bottom according to the inverse grain sequence soil layer structure, and then the plurality of soil sample cylinders (1) are sequentially connected according to the inverse grain sequence soil layer structure, and the bottom cover (2) is installed at the bottom of the bottom soil sample cylinder (1), and then the bottom channel (7) on the bottom cover (2) is connected to the water supply unit, and water is slowly passed until saturation, that is, until water is just observed on the surface of the soil sample in the top soil sample cylinder (1), and the bottom channel (7) on the bottom cover (2) is disconnected from the water supply unit and closed; S5, controlling the water supply unit to inject water into the topmost soil sample tube (1) at a certain set water head, opening the bottom channel (7), connecting the resistivity tester (6) to the electrode (5) on one of the soil sample tubes (1), and measuring the porosity of the entire soil sample at a set frequency.

8. The device for measuring porosity during sand seepage according to claim 7, characterized in that: The calculation formula of the resistivity is: Where: ρ is the resistivity of sand; w is the width of the cross section through which the current passes through the soil; h is the height of the cross section through which the current passes through the soil; L is the electrode spacing; and R is the measured resistance of saturated sand.

9. The device for measuring porosity during sand seepage according to claim 7, characterized in that: The porosity is calculated by: Where: n is the porosity; ρ is the resistivity of sand; ρ ω is the resistivity of pore water; a is the adjustment coefficient; m is the porosity index.

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