A device for measuring porosity during seepage of sand

Abstract

The application provides a device for measuring porosity in the seepage process of sandy soil, comprising a soil sample containing unit and a water supply unit; the soil sample containing unit comprises a plurality of soil sample cylinders and a plurality of bottom covers; a screen is installed at the bottom end of the inner cavity of the soil sample cylinder, the screen and the inner cavity of the soil sample cylinder form a containing chamber for storing soil samples, an electrode is arranged on the outer side of the soil sample cylinder, one end of the electrode extends into the containing chamber, the other end of the electrode is used for being connected with a resistivity tester, the bottom cover is used for being installed at the bottom of the soil sample cylinder, a bottom passage is arranged on the bottom cover and communicates with the containing chamber, a plurality of soil sample cylinders are connected in a detachable mode to form a soil sample cylinder assembly extending along the height direction; the water supply unit is used for supplying water into the soil sample cylinder; and the device can measure the porosity of sandy soil samples before and after seepage under different infiltrations without destroying the structure of the soil samples.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical test, in particular to a device for measuring porosity in the process of sand seepage. BACKGROUND

[0002] The existing methods for measuring the porosity of sand mainly include the volume drainage method, the mercury intrusion method, the nuclear magnetic resonance method and the gas absorption method. The volume drainage method first measures the total volume Vtotal of the dry sample with a calibrated container, then puts the sand sample into a liquid container to make it fully submerged to calculate the drainage volume Vdrain, and calculates the porosity according to Vdrain and Vtotal. The disadvantage is that it may be difficult to obtain an accurate drainage volume for some very small or loose samples. The gas absorption method first dries the sand sample to a constant weight, then exposes the sample to a gas environment under a specific pressure, measures the volume of the absorbed gas, and calculates the porosity according to the known relationship between gas absorption and pore space. The disadvantage is that the measurement process is complex and the equipment cost is high. The mercury intrusion method dries and weighs the sand sample, puts the sample into a mercury intrusion device, gradually increases the pressure, records the volume of mercury under different pressures, calculates the pore volume according to the volume change of the intruded mercury, and thus obtains the porosity. The 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 the unconnected pores, and only the volume of connected pores can be effectively measured. The nuclear magnetic resonance method puts the sample into a nuclear magnetic resonance instrument, measures the reaction of water molecules in a magnetic field, and calculates the pore volume according to the signal intensity of water, and thus calculates the porosity. The disadvantage is that the equipment is expensive and the operation is complex.

[0003] Reverse grain sequence accumulation body is commonly found in the flow and accumulation zones of high-speed long-range landslides. Due to the effects of collision and crushing, vibration and size separation, and the dispersion pressure of large-diameter particles, the particle size of the accumulation body in the vertical direction presents an upper large and lower small structure. We can divide the accumulation body into three phases in the vertical direction: the top hard shell layer, the middle main body layer, and the bottom base layer. This special structure makes the upper porosity relatively large and the water permeability relatively strong. Under the action of water seepage, the water seepage may produce a strong drag force on fine particles, which may move in the pores formed by coarse particles. Due to the large difference in particle size distribution (composition) among the three phases, fine particles are easily lost in the hard shell layer due to large pore channels, fine particles in the main body layer are also migrated downward, and fine particles accumulate at the bottom. Therefore, it is necessary to analyze the change of soil porosity in three layers. SUMMARY

[0004] The application aims to provide a device for measuring the porosity of sand during seepage process, which can measure the porosity of sand before and after seepage under different seepage water heads without destroying the structure of the soil sample.

[0005] The application relates to a device for measuring the porosity of sand during seepage process, which comprises a soil sample containing unit and a water supply unit.

[0006] The soil sample containing unit comprises a plurality of soil sample cylinders and a plurality of bottom covers, the inner cavity bottom end of the soil sample cylinder is provided with a screen, the screen and the inner cavity of the soil sample cylinder enclose a containing chamber for storing the soil sample, an electrode is arranged on the outer side of the soil sample cylinder, one end of the electrode extends into the containing chamber, the other end of the electrode is used for being connected with a resistivity tester, the bottom cover is used for being mounted on the bottom of the soil sample cylinder, and a bottom passage is arranged on the bottom cover and communicates with the containing chamber, a plurality of soil sample cylinders are connected in a detachable mode to form a soil sample cylinder assembly extending along the height direction.

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

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

[0009] A brass electrode sheet connected with the electrode is arranged on the side wall of the inner cavity of the soil sample cylinder, and the brass electrode sheets in the adjacent two soil sample cylinders of the soil sample cylinder assembly abut each other.

[0010] The soil sample cylinders are connected through flanges.

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

[0012] The application further discloses a method for measuring the resistivity and porosity of sand with reverse particle sequence structure during seepage process.

[0013] S1, standard samples with different sand porosities are prepared, and different layers of initial particle size gradations are used, and the content of fine particle diameters is changed;

[0014] S2, the sand standard samples prepared in S1 are loaded into the containing chambers of single soil sample cylinders, and the bottom covers are mounted, then the bottom passages on the bottom covers are connected with the water supply unit, water is slowly supplied to saturate the standard samples until the water surface is submerged, the water supply is stopped, the electrode is connected with the resistivity tester, and the resistivity is measured;

[0015] S3, the resistivity of the sand samples with different soil porosities is measured according to the operation of S2, and a relationship curve is established according to the known standard sample soil porosity and the corresponding measured resistivity.

[0016] S4, fill the to-be-tested sandy soil into the multiple soil sample cylinders from the bottom according to the reverse grain size order soil layer structure, then connect the multiple soil sample cylinders in sequence according to the reverse grain size order soil layer structure, install the bottom cover on the bottom of the bottommost soil sample cylinder, then connect the bottom passage on the bottom cover with the water supply unit, slowly supply water until saturation, that is, water is just observed on the surface of the soil sample in the topmost soil sample cylinder, disconnect the bottom passage on the bottom cover from the water supply unit and close the bottom passage;

[0017] S5, control the water supply unit to inject water into the topmost soil sample cylinder at a certain set water head;

[0018] S6, open the bottom passage on the bottom cover at the bottom of the bottommost soil sample cylinder, and close the water supply unit and the bottom passage on the bottom cover after no obvious particles are observed flowing out of the bottom passage;

[0019] S7, take another bottom cover, connect the topmost soil sample cylinder with the bottom cover after removing the topmost soil sample cylinder, supply water into the topmost soil sample cylinder through the bottom passage at the bottom of the bottom cover by the water supply unit, saturate the soil sample, close the bottom passage, connect the electrode of the topmost soil sample cylinder with the resistivity tester, and measure the resistivity of the soil sample in the topmost soil sample cylinder;

[0020] S8, take another bottom cover, connect the second topmost soil sample cylinder with the bottom cover after removing the second topmost soil sample cylinder, supply water into the second topmost soil sample cylinder through the bottom passage at the bottom of the bottom cover by the water supply unit, saturate the soil sample, close the bottom passage, connect the electrode of the second topmost soil sample cylinder with the resistivity tester, and measure the resistivity of the soil sample in the second topmost soil sample cylinder, and the resistivity of the soil sample in the remaining soil sample cylinders can be obtained in the same way;

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

[0022] S10, connect all the soil sample cylinders in sequence according to the reverse grain size order soil layer structure, install the bottom cover on the bottom of the bottommost soil sample cylinder, then connect the bottom passage on the bottom cover with the water supply unit, slowly supply water until saturation, that is, water is just observed on the surface of the soil sample in the topmost soil sample cylinder, disconnect the bottom passage on the bottom cover from the water supply unit and close the bottom passage;

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

[0024] S12, repeat the operations in S6-S9, and the porosity value corresponding to the resistivity of the soil sample in each soil sample cylinder under the water head in S11 can be obtained in the same way.

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

[0026] S1, make standard samples of different sand porosities, and specifically use different initial particle size gradations of layers, change the content of fine particle size;

[0027] S2, load the sand standard sample made in S1 into the containing chamber of a single soil sample cylinder, and install the bottom cover, then connect the bottom passage on the bottom cover with the water supply unit, slowly supply water to saturate the standard sample until the water surface is submerged, stop water supply, connect the electrode with the resistivity tester, and measure the resistivity;

[0028] S3, repeat the operation of S2 to measure the resistivity of sand samples with different soil porosities, and establish a relationship curve according to the known standard sample soil porosity and the corresponding measured resistivity;

[0029] S4, fill the sand to be measured into multiple soil sample cylinders from the bottom in reverse particle sequence soil layer structure, then connect the multiple soil sample cylinders in reverse particle sequence soil layer structure in turn, and install the bottom cover on the bottom of the bottommost soil sample cylinder, then connect the bottom passage on the bottom cover with the water supply unit, slowly supply water until saturation, that is, the soil sample surface in the topmost soil sample cylinder is just observed to be water, disconnect the bottom passage on the bottom cover from the water supply unit and close it;

[0030] S5, control the water supply unit to inject water into the topmost soil sample cylinder at a certain set water head, open the bottom passage, connect the resistivity tester with the electrode on one of the soil sample cylinders, and measure the porosity of the entire soil sample at a set frequency.

[0031] Optionally, the resistivity calculation formula is:

[0032]

[0033] In the formula, ρ is the resistivity of sand, w is the cross-sectional width of the current passing through the soil, h is the cross-sectional height of the current passing through the soil, L is the electrode spacing, and R is the measured saturated sand resistivity.

[0034] Optionally, the porosity calculation formula is:

[0035]

[0036] In the formula, n is the porosity, ρ is the resistivity of sand, ρ is the resistivity of pore water, a is an adjustment coefficient, and m is a porosity index. ω

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

[0038] 1. The device can measure the porosity of sand samples before and after infiltration under different infiltration water heads without damaging the soil sample structure, avoiding the problem that only one porosity change under one infiltration water head can be measured at a time in the traditional method. ​

[0039] 2、The device of the application measures porosity by resistance method without taking out the sample for drying and then measuring, simple operation and fast measurement speed.

[0040] 3、The device of the application can monitor porosity in real time for a whole soil and stone mixture.

[0041] 4、The device of the application is flexible in application, can be used separately, and a single soil sample cylinder can be taken out for outdoor measurement of sand porosity and is applicable to other types of soil other than sand. BRIEF DESCRIPTION OF DRAWINGS

[0042] The application will be further described below in combination with the drawings and examples.

[0043] Figure 1 A device for measuring porosity in the seepage process of sand provided by the application embodiment;

[0044] Figure 2 A top view of the soil sample cylinder provided by the application embodiment;

[0045] Figure 3 A structure schematic view of the bottom cover provided by the application embodiment; Figure 2 A section view along A-A of the above-mentioned structure;

[0046] Figure 4 A structure schematic view of the bottom cover provided by the application embodiment;

[0047] Figure 5 A structure schematic view of the top cover provided by the application embodiment;

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

[0049] The application embodiment will be further described below in combination with the drawings.

[0050] In order to realize the above technical features, the purpose of the application is realized as follows:

[0051] Example 1: see Figures 1-5The utility model provides a kind of device for measuring porosity in the process of sand seepage, including soil sample containing unit, water supply unit;Soil sample containing unit includes multiple soil sample cylinders 1, multiple bottom covers 2, top cover 9, the inner cavity bottom end of soil sample cylinder 1 is equipped with screen 3, screen 3 is enclosed with the inner cavity of soil sample cylinder 1 into the containing chamber 4 for storing soil sample, the outer side of soil sample cylinder 1 is equipped with electrode 5, one end of electrode 5 extends into containing chamber 4, the other end of electrode 5 is used to be connected with resistivity tester 6, bottom cover 2 is used to be installed in the bottom of soil sample cylinder 1, and bottom cover 2 is equipped with bottom passage 7 being connected with containing chamber 4, the bottom of bottom cover 2 is equipped with first valve 10, and bottom passage 7 is connected with outside through first valve 10, multiple soil sample cylinders 1 are connected by detachable way between head and tail and constitute soil sample cylinder assembly extending along the height direction, top cover 9 is installed on the top of soil sample cylinder 1 by detachable way, and top cover 9 is equipped with top passage 11 being connected with containing chamber 4, and top passage 11 is connected with outside through second valve 12;Water supply unit supplies water to soil sample cylinder 1 by being connected with first valve 10 and second valve 12 respectively.

[0052] Further, the inner cavity of the soil sample cylinder 1 is rectangular in cross section.

[0053] Further, the inner cavity of the soil sample cylinder 1 is rectangular in cross section.

[0054] Further, the soil sample cylinders 1 are connected by flanges to achieve stable and reliable detachable connection.

[0055] Further, the soil sample cylinder 1 is made of transparent and insulating material, preferably acrylic plate, so that the soil sample can be directly observed through the soil sample cylinder.

[0056] Embodiment 2: A method for measuring the resistivity and porosity of sand with reverse particle sequence structure using the device for measuring porosity in the process of sand seepage, comprising the following steps:

[0057] S1, prepare standard samples with different sand porosities, and specifically use different initial particle size gradings, and change the content of fine particle size;

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

[0059] S3, measure the resistivity of sand samples with different soil porosities, and establish a relationship curve according to the known standard sample soil porosity and the corresponding measured resistivity;

[0060] S4, fill the to-be-tested sand soil into the three soil sample cylinders 1 from the bottom in reverse order of particle size, then connect the three soil sample cylinders 1 in reverse order of particle size, install the first bottom cover 2 on the bottom of the bottommost soil sample cylinder 1, then connect the first valve 10 at the bottom of the first bottom cover 2 with the water supply unit, slowly supply water until saturation, that is, just observe water on the surface of the soil sample in the topmost soil sample cylinder 1, close the first valve 10 and disconnect it from the water supply unit;

[0061] S5, connect the water supply unit with the second valve 12 and control it to inject water into the topmost soil sample cylinder 1 at a certain set water head;

[0062] S6, connect the first valve 10 with the receiving basin 15 through the bottom connecting water pipe, and open the first valve 10, then close the first valve 10 when no obvious particles are observed in the effluent from the first valve 10;

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

[0064] S8, take another third bottom cover 2, connect it with the middle soil sample cylinder 1 after removing it, switch the water supply unit to connect with the first valve 10 at the bottom of the middle soil sample cylinder 1, then supply water into the middle soil sample cylinder 1, saturate the soil sample in the middle soil sample cylinder 1, close the first valve 10, connect the electrode 5 of the middle soil sample cylinder 1 with the resistivity tester 6, and measure the resistivity of the soil sample in the middle soil sample cylinder 1, and similarly, the resistivity of the soil sample in the bottommost soil sample cylinder 1 can be obtained;

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

[0066] S10, connect all the soil sample cylinders 1 in reverse order of particle size, install the bottom cover 2 on the bottom of the bottommost soil sample cylinder 1, then connect the bottom channel 7 on the bottom cover 2 with the water supply unit, slowly supply water until saturation, that is, just observe water on the surface of the soil sample in the topmost soil sample cylinder 1, disconnect the bottom channel 7 on the bottom cover 2 from the water supply unit and close it;

[0067] S11, control the water supply unit to inject water into the topmost soil sample cylinder 1 at a higher water head than in S5;

[0068] S12, repeat the operations of S6-S9, and the porosity values corresponding to the resistivity of the soil sample in each soil sample cylinder 1 under the water head in S11 can be obtained.

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

[0070] S1, prepare standard samples of different sand porosities, and specifically use different initial particle size gradations of layers, and change the content of fine particle sizes;

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

[0072] S3, repeat the operation of S2 to measure the resistivity of the sand sample with different soil porosities, and establish a relationship curve according to the known standard sample soil porosity and the corresponding measured resistivity;

[0073] S4, fill the sand to be measured into the multiple soil sample cylinders 1 from the bottom in reverse particle sequence, then connect the multiple soil sample cylinders 1 in reverse particle sequence, install the bottom cover 2 on the bottom of the bottommost soil sample cylinder 1, then connect the bottom passage 7 on the bottom cover 2 with the water supply unit, slowly supply water until saturation, that is, the surface of the soil sample in the topmost soil sample cylinder 1 is just observed to be water, disconnect the bottom passage 7 on the bottom cover 2 from the water supply unit and close it;

[0074] S5, control the water supply unit to inject water into the topmost soil sample cylinder 1 at a certain set water head, open the bottom passage 7, connect the resistivity tester 6 with the electrode 5 on one of the soil sample cylinders 1, and measure the porosity of the entire soil sample at a 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, and the time for changing the water head is used as a basis for subsequent confirmation.

[0075] Further, the calculation formula of the resistivity in the present application is:

[0076]

[0077] In the formula, p is the resistivity of the sand, w is the cross-sectional width of the current passing through the soil, h is the cross-sectional height of the current passing through the soil, L is the electrode spacing, and R is the measured resistivity of the saturated sand.

[0078] Further, the calculation formula of the porosity in the application is as follows:

[0079]

[0080] In the formula, n is the porosity; p is the resistivity of the sand; p ω is the resistivity of the pore water; a is an adjustment coefficient; and m is a porosity index.

Claims

1. A method for measuring the resistivity and porosity of inverse graded sand, comprising a porosity measuring device, wherein the porosity measuring device includes a soil sample holding unit and a water supply unit; The soil sample holding unit includes multiple soil sample tubes (1) and multiple bottom covers (2). A sieve (3) is installed at the bottom of the inner cavity of the soil sample tube (1). The sieve (3) and the inner cavity of the soil sample tube (1) form a holding 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 holding chamber (4). The other end of the electrode (5) is used to connect to a resistivity tester (6). The bottom cover (2) is used to be installed at the bottom of the soil sample tube (1). The bottom cover (2) is provided with a bottom channel (7) that communicates with the holding chamber (4). Multiple soil sample tubes (1) are connected end to end in a detachable manner to form a soil sample tube assembly that extends along the height direction. The water supply unit is used to supply water into the soil sample tube (1); Its features are, The method for measuring the resistivity and porosity of inverse-grade sandy soils includes the following steps: S1. Prepare standard samples with different porosities of sand and soil, and use different initial particle size distributions of different layers to change the content of fine particles. S2. Put the sand standard sample prepared in S1 into the receiving 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. Using the same operation as S2, measure the resistivity of sandy soil samples with different soil porosities, and establish a relationship curve based on the known standard soil porosity and the corresponding measured resistivity. S4. The sand to be tested is gradually filled into multiple soil sample tubes (1) from the bottom according to the reverse order of granulation. Then, the multiple soil sample tubes (1) are connected in sequence according to the reverse order of granulation. The bottom cover (2) is installed at the bottom of the bottom soil sample tube (1). Then, the bottom channel (7) on the bottom cover (2) is connected to the water supply unit. Water is slowly introduced until saturation, that is, water is observed on the surface of the soil sample in the top soil sample tube (1). The bottom channel (7) on the bottom cover (2) is disconnected from the water supply unit and closed. S5. Control the water supply unit to inject water into the top soil sample tube (1) at a certain set water head; S6. Open the bottom channel (7) on the bottom cover (2) of the bottom soil sample tube (1). When no obvious particles are observed in the liquid flowing out 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). Use the water supply unit to supply water to the bottom channel (7) at the bottom of the bottom cover (2) to the top soil sample tube (1) so that the soil sample is saturated. Close the bottom channel (7) and connect the electrode (5) of the top soil sample tube (1) to the resistivity tester (6) to 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) of the second top layer and connect it to the bottom cover (2). Water is supplied to the second top layer soil sample tube (1) through the bottom channel (7) at the bottom of the bottom cover (2) by the water supply unit, so that the soil sample is saturated. Close the bottom channel (7), connect the electrode (5) of the second top layer soil sample tube (1) to the resistivity tester (6), and measure the resistivity of the soil sample in the second top layer soil sample tube (1). Similarly, the resistivity of the soil sample in all the remaining soil sample tubes (1) is obtained. S9. Based on the relationship between the porosity and resistivity curves 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. Reconnect all soil sample tubes (1) in reverse order of 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 and slowly pass water through until saturation, at which point water can be 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. S11, control the water supply unit to inject water into the top soil sample tube (1) with a water head higher than that in S5; S12. Repeat 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.

2. The method for measuring the resistivity and porosity of anti-sequential sandy soil according to claim 1, characterized in that: The inner cross-section of the soil sample tube (1) is rectangular.

3. The method for measuring the resistivity and porosity of anti-sequential sandy soil according to claim 2, characterized in that: The inner wall of the soil sample tube (1) is equipped with a brass electrode plate (8) connected to the electrode (5), and the brass electrode plates (8) in two adjacent soil sample tubes (1) of the soil sample tube assembly abut against each other.

4. The method for measuring the resistivity and porosity of anti-sequential sandy soil according to claim 2, characterized in that: Multiple soil sample tubes (1) are connected by flanges.

5. The method for measuring the resistivity and porosity of anti-sequential sandy soil according to claim 4, characterized in that: The soil sample tube (1) is made of transparent insulating material.

6. A method for measuring the overall porosity of saturated sand during seepage, comprising a porosity measuring device, wherein the porosity measuring device includes a soil sample holding unit and a water supply unit; The soil sample holding unit includes multiple soil sample tubes (1) and multiple bottom covers (2). A sieve (3) is installed at the bottom of the inner cavity of the soil sample tube (1). The sieve (3) and the inner cavity of the soil sample tube (1) form a holding 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 holding chamber (4). The other end of the electrode (5) is used to connect to a resistivity tester (6). The bottom cover (2) is used to be installed at the bottom of the soil sample tube (1). The bottom cover (2) is provided with a bottom channel (7) that communicates with the holding chamber (4). Multiple soil sample tubes (1) are connected end to end in a detachable manner to form a soil sample tube assembly that extends along the height direction. The water supply unit is used to supply water into the soil sample tube (1); Its features are, The method for measuring the overall porosity of saturated sand during seepage includes the following steps: S1. Prepare standard samples with different porosities of sand and soil, and use different initial particle size distributions of different layers to change the content of fine particles. S2. Put the sand standard sample that needs to be prepared in S1 into the container (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. Repeat operation S2 to measure the resistivity of sandy soil samples with different soil porosities, and establish a relationship curve based on the known standard soil porosity and the corresponding measured resistivity. S4. The sand to be tested is gradually filled into multiple soil sample tubes (1) from the bottom according to the reverse order of granulation. Then, the multiple soil sample tubes (1) are connected in sequence according to the reverse order of granulation. The bottom cover (2) is installed at the bottom of the bottom soil sample tube (1). Then, the bottom channel (7) on the bottom cover (2) is connected to the water supply unit. Water is slowly introduced until saturation, that is, water is just observed on the surface of the soil sample in the top soil sample tube (1). The bottom channel (7) on the bottom cover (2) is disconnected from the water supply unit and closed. S5. Control the water supply unit to inject water into the top soil sample tube (1) with a 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 a set frequency.

7. The method for measuring the overall porosity of saturated sand during seepage as described in claim 6, characterized in that, The formula for calculating resistivity is as follows: In the formula: ρ is the resistivity of sandy soil; 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; R is the measured resistivity of saturated sandy soil.

8. The method for measuring the overall porosity of saturated sand during seepage as described in claim 6, characterized in that, The formula for calculating porosity is as follows: In the formula: n is the porosity; ρ is the resistivity of the sand; ρ ω denoted as ρ, where ρ is the resistivity of pore water; a is the adjustment coefficient; and m is the porosity index.

9. The method for measuring the overall porosity of saturated sand during seepage according to claim 6, characterized in that: The inner cross-section of the soil sample tube (1) is rectangular.

10. A method for measuring the overall porosity of saturated sand during seepage according to claim 9, characterized in that: The inner wall of the soil sample tube (1) is equipped with a brass electrode plate (8) connected to the electrode (5), and the brass electrode plates (8) in two adjacent soil sample tubes (1) of the soil sample tube assembly abut against each other.

11. The method for measuring the overall porosity of saturated sand during seepage according to claim 10, characterized in that: Multiple soil sample tubes (1) are connected by flanges.

12. The method for measuring the overall porosity of saturated sand during seepage according to claim 11, characterized in that: The soil sample tube (1) is made of transparent insulating material.

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