A method for determining maximum adsorbed water content based on water density

Abstract

The present application discloses a method for determining the maximum adsorbed water content based on water density, comprising the following steps: S1, measuring the gas volume in a dried soil sample by a helium pycnometer to obtain the density of the solid particles of the soil sample; S2, measuring the gas volume in the soil samples under several different water content states, and obtaining the total volume of the solid particles and pore water of the soil sample under each water content state by calculation; S3, drying the soil samples with different water contents to obtain the mass of the pore water in the soil samples, and calculating the volume of the pore water in the soil samples with different water contents using the density of the solid particles of the soil samples in S1; S4, calculating the density of the pore water in the soil sample under each different water content state to obtain the average water density; or calculating the mass increment and volume increment of the pore water in the soil samples under two adjacent different water content states to obtain the incremental water density; S5, obtaining the maximum adsorbed water content of the soil sample according to the average water density or the incremental water density.

Description

Technical Field

[0001] The present application relates to the field of geotechnical engineering technology, and in particular to a method for determining maximum adsorbed water content based on water density. Background Art

[0002] The density of soil water is usually considered to be 1g / cm in geotechnical engineering applications. 3 , such as soil phase transitions, soil specific gravity measurements, and stress-strain measurements. However, due to hydration when water is adsorbed on the soil surface or between layers, it can cause an abnormal increase in soil water density and a corresponding change in the adsorbed water content. In traditional soil mechanics, the concept of residual water content is often used to describe the water-holding capacity of soil in a relatively dry state. Its physical essence is the amount of adsorbed water. When the water content in the soil decreases to a certain value with increasing suction, the water content no longer changes significantly with increasing external air pressure (or suction), and the residual water is adsorbed on the soil surface with a strong binding force. However, this water content is related to the rate of air pressure in the clay plate, so it is subject to human influence. In geology, the residual water content in minerals is determined using centrifuges, but the rate of water molecule separation is related to the centrifuge speed of the separation instrument, so it is also subject to human influence, and the specific residual water content is not a constant.

[0003] However, in the physical nature of intermolecular interactions, the interaction between soil and water is primarily governed by two physical processes: capillary action and adsorption. Capillary action occurs in soil pores when a curved gas-liquid interface exists under unsaturated conditions. Adsorption, on the other hand, occurs under both saturated and unsaturated conditions, primarily acting on the surface or interior of soil particles. Capillary action, influenced primarily by factors such as pore distribution, gas-liquid interfacial tension, and contact angle, is manifested as an internal interaction between water molecules, generating tensile stress and thereby reducing water density. Adsorption, influenced primarily by factors such as soil composition and specific surface area, is manifested as an external interaction between water molecules and the soil, generating compressive stress and thereby increasing water density. Therefore, soil water content can be physically divided into capillary water and adsorbed water, which have different physical properties and play a crucial role in several physical processes in the soil, such as fluid flow, thermal conductivity, and stress-deformation. However, most current theories or models describing the basic properties of soil do not distinguish between capillary water and adsorbed water, and the corresponding adsorbed water content and capillary water content cannot be measured separately. Therefore, in view of the limitations of the existing method of determining the maximum adsorbed water content based on water density, a method for measuring the adsorbed water content that can distinguish between adsorbed water and capillary water is needed. Summary of the Invention

[0004] The present application provides a method for determining the maximum adsorbed water content based on water density. The method determines the maximum adsorbed water content of soil based on incremental water density or average water density. The method effectively demarcates the boundary between adsorbed water content and capillary water content based on the physical nature of the pore water storage state, thereby overcoming the problems existing in the above-mentioned background technology. The technical solution is as follows:

[0005] The present application provides a method for determining the maximum adsorbed water content based on water density, comprising the following steps: S1, measuring the gas volume in a dried soil sample by a helium pycnometer, and obtaining the density of the solid particles of the soil sample by calculation; S2, measuring the gas volume in soil samples at several different water content states by a helium pycnometer, and obtaining the total volume of the solid particles and pore water of the soil sample at each water content state by calculation; S3, drying the soil samples at different water contents to obtain the mass of the pore water in the soil samples, and obtaining the volume of the pore water in the soil samples at different water contents by using the density of the solid particles of the soil samples in S1; S4, calculating the mass of the pore water in the soil samples according to the mass of the pore water in the soil samples in S3. and volume, calculate the density of the pore water in the soil sample at each different water content state to obtain the average water density; or according to the mass and volume of the pore water in the soil sample in S3, calculate the mass increment and volume increment of the pore water in the soil samples at two adjacent different water content states to obtain the incremental water density; S5, when the average water density in S4 decreases to a constant value as the water content of the soil sample increases, the water content of the corresponding soil sample at this time is the maximum adsorbed water content; or compare the incremental water density in S4 with the free water density. When the incremental water density decreases to equal the free water density as the water content of the soil sample increases, the water content of the corresponding soil sample at this time is the maximum adsorbed water content.

[0006] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, the helium pycnometer includes a sample chamber and a reference chamber connected in series, and the volume of the sample chamber is V c , the volume of the reference chamber is V r A first valve and a second valve are respectively provided on the air inlet side and the air outlet side of the sample chamber, a third valve is provided on the air outlet side of the reference chamber, and a pressure sensor is also provided on one side of the sample chamber to measure the air pressure in the sample chamber.

[0007] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S1, measuring the gas volume in the dried soil sample by a helium pycnometer includes the following steps: placing the dried soil sample in a sample chamber, first opening a first valve, and filling the sample chamber with helium until the internal pressure is P p , close the first valve; then open the second valve to allow gas to fill the reference chamber, reducing the pressure until the pressure in the sample chamber and the reference chamber are equal, recorded as P dFinally, keep the first valve closed and the second valve open, open the third valve to discharge the gas in the sample chamber and the reference chamber into the external environment. At this time, the air pressure on the pressure sensor is recorded as P a , the volume of gas in the dried soil sample V a The calculation formula is:

[0008]

[0009] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S1, the density of the solid particles of the soil sample ρ s The calculation formula is:

[0010]

[0011] Among them, m s is the mass of the dried soil sample, V t is the total volume of the oven-dried soil sample.

[0012] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S2, the gas volume V in the soil samples at several different water content states is measured by a helium pycnometer. a’ , to obtain the total volume V of solid particles and pore water in soil samples at different water contents w+s In step S3, the soil samples with different water contents are dried to obtain the mass m of pore water in the soil samples. w , using the density of the soil solid particles in S1, calculate the solid volume V in the soil samples with different water contents s , to obtain the volume V of pore water in soil samples with different water contents w , the volume of pore water V in soil samples with different water contents w The calculation formula is:

[0013]

[0014] Among them, V t is the total volume of soil samples at different water contents, m t is the total mass of soil samples at different water contents.

[0015] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S4, the average water density of the pore water in the soil sample at each different water content state is The calculation formula is:

[0016]

[0017] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S5, the mass increment Δmw and volume increment ΔVw of pore water in two adjacent soil samples at different water content states are calculated to obtain the incremental water density Incremental water density The calculation formula is:

[0018]

[0019] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S5, when When the water content of the soil sample increases, the water in the soil sample is adsorbed water; when the incremental water density decreases to When the water content of the soil sample is equal to the maximum adsorbed water content, it is used to distinguish the adsorbed water content and capillary water content in the water-containing soil sample.

[0020] The beneficial effects of a method for determining the maximum adsorbed water content based on water density provided in some embodiments of the present application are as follows: the method for determining the maximum adsorbed water content of a soil sample based on incremental water density or average water density effectively divides the boundary between the adsorbed water content and the capillary water content in the soil sample based on the physical nature of the pore water storage state, provides a reasonable and reliable method for defining and distinguishing adsorbed water and capillary water, avoids the interference of human factors in existing water content measurement methods, and solves the problem that most current theories or models describing the basic properties of soil do not distinguish between capillary water and adsorbed water, and the corresponding adsorbed water content and capillary water content cannot be measured separately from the physical nature of intermolecular interactions. The quantitative assessment of adsorbed water content in this application provides a new reference for optimizing the theories or models for predicting basic soil properties, such as pore water pressure, water viscosity, relative dielectric constant, soil matrix potential energy, freezing curve and permeability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 It is a simplified flow chart for measuring the volume of gas in a soil sample using a helium pycnometer;

[0023] Figure 2 It is a comparative diagram of the average water density and incremental water density change curves of a soil sample;

[0024] Figure 3It is a schematic diagram comparing the average water density and incremental water density of soil samples;

[0025] Figure 4 It is a graph showing the calculation of the incremental water density of a certain soil sample using the method of the present application;

[0026] Figure 5 It is the soil-water characteristic curve of a certain soil sample. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described in this method are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0028] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by persons of ordinary skill in the field to which this disclosure belongs. The words "first", "second" and similar terms used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0029] The present application provides a method for determining the maximum adsorbed water content based on water density, comprising the following steps: S1, measuring the gas volume in a dried soil sample by a helium pycnometer, and obtaining the density of the solid particles of the soil sample by calculation; S2, measuring the gas volume in soil samples at several different water content states by a helium pycnometer, and obtaining the total volume of the solid particles and pore water of the soil sample at each water content state by calculation; S3, drying the soil samples at different water contents to obtain the mass of the pore water in the soil samples, and obtaining the volume of the pore water in the soil samples at different water contents by using the density of the solid particles of the soil samples in S1; S4, calculating the mass of the pore water in the soil samples according to the mass of the pore water in the soil samples in S3. and volume, calculate the density of the pore water in the soil sample at each different water content state to obtain the average water density; or according to the mass and volume of the pore water in the soil sample in S3, calculate the mass increment and volume increment of the pore water in the soil samples at two adjacent different water content states to obtain the incremental water density; S5, when the average water density in S4 decreases to a constant value as the water content of the soil sample increases, the water content of the corresponding soil sample at this time is the maximum adsorbed water content; or compare the incremental water density in S4 with the free water density. When the incremental water density decreases to equal the free water density as the water content of the soil sample increases, the water content of the corresponding soil sample at this time is the maximum adsorbed water content.

[0030] According to the above embodiments, the present application provides a method for determining the maximum adsorbed water content of a soil sample based on incremental water density or average water density, which effectively divides the boundary between the adsorbed water content and the capillary water content in the soil sample, provides a reasonable and reliable method for defining and distinguishing adsorbed water and capillary water, avoids the interference of human factors in existing methods for measuring water content, and solves the problem that most of the current theories or models describing the basic properties of soil do not distinguish between capillary water and adsorbed water, and the corresponding adsorbed water content and capillary water content cannot be distinguished and measured from the physical essence of intermolecular interactions. The quantitative assessment of adsorbed water content in this application provides a new reference for optimizing the theories or models for predicting basic soil properties, such as pore water pressure, water viscosity, relative dielectric constant, soil matrix potential energy, freezing curve, and permeability.

[0031] Figure 1 A simplified flow chart of measuring the gas volume in a soil sample using a helium pycnometer is given in this application, as shown in FIG. Figure 1 As shown, the helium pycnometer includes two sample chambers and a reference chamber connected in series, and the volume of the sample chamber is V c , the volume of the reference chamber is V r A first valve V1 and a second valve V2 are respectively provided on the air inlet side and the air outlet side of the sample chamber, a third valve V3 is provided on the air outlet side of the reference chamber, and a pressure sensor is also provided on one side of the sample chamber to measure the air pressure in the sample chamber.

[0032] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S1, measuring the gas volume in the dried soil sample by a helium pycnometer includes the following steps: placing the dried soil sample in a sample chamber, first opening a first valve V1, and filling the sample chamber with helium until the internal pressure is P p , close the first valve V1; then open the second valve V2 to allow gas to fill the reference chamber, reducing the pressure until the pressure in the sample chamber and the reference chamber are equal, recorded as P d Finally, keep the first valve V1 closed and the second valve V2 open, open the third valve V3 to discharge the gas in the sample chamber and the reference chamber into the external environment. At this time, the air pressure on the pressure sensor is recorded as P a , the volume of gas in the dried soil sample V a The calculation formula is:

[0033]

[0034] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S1, the density of the solid particles of the soil sample ρ s The calculation formula is:

[0035]

[0036] Among them, m s is the mass of the dried soil sample, V t is the total volume of the oven-dried soil sample.

[0037] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S2, the gas volume V in the soil samples at several different water content states is measured by a helium pycnometer. a’ , to obtain the total volume V of solid particles and pore water in soil samples at different water contents w+s In step S3, the soil samples with different water contents are dried to obtain the mass m of pore water in the soil samples. w , using the density of the soil solid particles in S1, calculate the solid volume V in the soil samples with different water contents s , to obtain the volume V of pore water in soil samples with different water contents w , the volume of pore water V in soil samples with different water contents w The calculation formula is:

[0038]

[0039] Among them, V t is the total volume of soil samples at different water contents, m t is the total mass of soil samples at different water contents.

[0040] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S4, the average water density of the pore water in the soil sample at each different water content state is The calculation formula is:

[0041]

[0042] For example, in a method for determining the maximum adsorbed water content based on water density provided in one embodiment, in step S5, the mass increment Δmw and volume increment ΔVw of pore water in two adjacent soil samples at different water content states are calculated to obtain the incremental water density Incremental water density The calculation formula is:

[0043]

[0044] If the mass of pore water in the soil sample m w and the volume of pore water in the soil sample V w The density of pore water in the soil sample is directly calculated as the average water density like Figure 2 and Figure 3 As shown, the average water density As the water content of the soil increases, it gradually decreases to a certain value, but the density of free water is 1g / cm 3 There is still a certain difference. Average water density Describes all the water molecules present in the pores at a specific water content and is used to describe the overall density state of pore water. Due to the initial soil specific gravity, the change in average water density is always higher than the free water density. When the average water density As the moisture content of the soil sample increases and decreases to a constant level, the moisture content of the soil sample at this time is the maximum adsorbed water content.

[0045] In order to more conveniently and intuitively characterize the change of water density and thus calculate the content of adsorbed water, this application proposes a new form of water density change, namely incremental water density

[0046] like Figure 2 and Figure 3 As shown, the incremental water density Describes the addition of water molecules to a specific portion of the soil sample's pores, describing the local density of pore water and its impact on local density. The incremental water density is unaffected by the initial soil specific gravity and is determined solely by the water densities at the two different water contents. The incremental water density also decreases as the water content increases:

[0047] Specifically, if Figure 2 As shown, when the average water density When the water content of the soil sample increases and decreases to a constant value, the water content of the soil sample corresponding to this time is the maximum adsorbed water content; or when the incremental water density When , it indicates that the added water molecules are still adsorbed on the soil particles in an adsorbed state, and the water in the water-containing soil sample is adsorbed water; when Reduced to 1g / cm 3 It indicates that the water molecules in the soil sample are in a free state and there is no adsorption. After that, the water molecules will condense due to capillary action. The corresponding mass water content at this time is the maximum adsorbed water content, thereby distinguishing the adsorbed water content and capillary water content in the water-containing soil sample and dividing the boundary between adsorption and capillary action.

[0048] When the incremental water density is greater than 1g / cm 3 When , it indicates that the added water molecules are still adsorbed on the soil particles in an adsorbed state;

[0049] When the incremental water density is reduced to 1 g / cm 3 , that is, when it is equal to the free water density, it indicates that the water molecules are in a free state and no longer have adsorption. After that, the water molecules will condense due to capillary action. The corresponding mass water content at this time is the maximum adsorbed water content, which is recorded as

[0050] When the adsorbed water content is greater than the maximum adsorbed water content, the adsorbed water content no longer increases, and the capillary water content is the difference between the total water content of the soil sample and the maximum adsorbed water content.

[0051] The method for determining maximum adsorbed water content based on water density in this application is based on the physical nature of water molecule adsorption. It considers the two microscopic mechanisms of adsorbed water and capillary water, avoiding the interference of human factors in existing measurement technologies. It uses a helium pycnometer to measure the gas volume in the pores of the soil sample, indirectly calculating the volume of water in the soil, thereby determining the density of pore water in the soil sample at different water contents. The maximum adsorbed water content is determined using incremental water density or average water density, demarcating the boundary between adsorption and capillary action. The method of this application is simple and effective to operate, can accurately determine the maximum adsorbed water content of different soil samples in a relatively short time, and is suitable for unsaturated soil-related fields in geotechnical engineering.

[0052] This application's method for determining maximum adsorbed water content based on water density innovatively determines the maximum adsorbed water content of soil, reliably defining and distinguishing between adsorbed water and capillary water. Quantitative assessment of adsorbed water content provides a new approach for developing more accurate theories and models, and can be effectively applied to predicting basic soil properties such as suction stress, infiltration, water condensation and cavitation pressure, local pore water pressure, and soil freezing curves.

[0053] Effect verification

[0054] like Figure 4-5 As shown, the maximum adsorbed water content is calculated for a certain soil sample using the method of this application. See Figure 4 At the same time, the adsorption water and capillary water action curves of the soil sample were quantitatively fitted according to the soil-water characteristic curve model, and the maximum adsorption water content was obtained based on the fitting results. See Figure 5 ; The results are basically consistent with the calculation results using the method of this application, which verifies the rationality and authenticity of the method of this application.

[0055] Although the implementation scheme of the present application has been disclosed as above, it is not limited to the applications listed in the description and implementation mode. It can be fully applied to various fields suitable for the present application. For those familiar with this field, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present application is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for determining the maximum adsorbed water content based on water density, characterized in that: The following steps are involved: S1 measures the gas volume in the dried soil sample by using a helium pycnometer, including the following steps: placing the dried soil sample in the sample chamber, first opening the first valve, and filling the sample chamber with helium until the internal pressure is P p , close the first valve; then open the second valve to allow gas to fill the reference chamber, reducing the pressure until the pressure in the sample chamber and the reference chamber are equal, recorded as P d Finally, keep the first valve closed and the second valve open, open the third valve to discharge the gas in the sample chamber and the reference chamber into the external environment. At this time, the air pressure on the pressure sensor is recorded as P a , the volume of gas in the dried soil sample V a The calculation formula is: ； The density of the solid particles of the soil sample is obtained by calculation, and the density of the solid particles of the soil sample ρ s The calculation formula is: Among them, m s is the mass of the dried soil sample, V t is the total volume of the oven-dried soil sample; S2 Measure the gas volume V in soil samples at different water contents using a helium pycnometer a’ , to obtain the volume V of solid and water in soil samples at different water contents w+s Then, the soil samples with different water contents were dried to obtain the mass m of water in the soil samples. w , calculate the solid volume V in soil samples with different water contents using the density of the solid particles in S1 s , to obtain the water V in soil samples with different water contents w Volume: Among them, V t’ is the total volume of soil samples at different water contents, m t is the total mass of soil samples at different water contents; S3 Calculate the mass increment of water in two adjacent soil samples at different water contents and volume increment , and get the incremental water density , incremental water density The calculation formula is: ； S4 compares the incremental water density with the free water density. >1g / cm 3 When the incremental water density is reduced to be equal to the free water density, the water content of the soil sample corresponding to this time is the maximum adsorbed water content, in order to distinguish the adsorbed water content and capillary water content in the water-containing soil sample. The helium pycnometer comprises a sample chamber and a reference chamber connected in series, wherein the volume of the sample chamber is V c , the volume of the reference chamber is V r A first valve and a second valve are respectively provided on the air inlet side and the air outlet side of the sample chamber, a third valve is provided on the air outlet side of the reference chamber, and a pressure sensor is also provided on one side of the sample chamber to measure the air pressure in the sample chamber.

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