Method and related equipment for determining pore size distribution based on relaxation distribution curve of rock and soil

Abstract

The present application discloses a method and related equipment for determining pore size distribution based on relaxation distribution curve of rock and soil, including the following steps: Step 1: Testing and inverting the moisture content before and after dehumidification to be w a and w b The clay relaxation time distribution curve; Step 2: The clay water content is w a and w b The first step is to obtain a difference relaxation distribution curve by taking the difference of the relaxation time distribution curve when the first step is reached; the third step is to convert the negative part of the nuclear magnetic resonance signal in the difference relaxation distribution curve into the pore size distribution and probability within the small pore range; the fourth step is to determine the pore size distribution and probability within the large pore range through the pore size distribution and probability within the small pore range; the fifth step is to repeat the first step to the fourth step until the pore water content reaches the single layer water content, and obtain the pore size distribution of the soil; the present application can eliminate the influence of the coupling effect between large and small pores on the relaxation time distribution, and obtain the pore size distribution curve of the rock and soil more accurately.

Description

Technical Field

[0001] The present application relates to the field of geotechnical engineering technology, and in particular to a method for determining pore size distribution based on a relaxation distribution curve of a rock mass and related equipment. Background Art

[0002] The engineering mechanical properties of soil mainly depend on the material composition and microstructure of the soil. The structure here usually refers to the comprehensive characterization of the internal structure of the soil formed by the different particle sizes, particle shape arrangement, contact mode, structural collapse and cementation, liquid and solid water content and occurrence mode inside the soil. Generally speaking, for the same type of soil, its material composition is relatively stable, but the microstructure of the soil is easily affected by changes in the external environment (such as temperature, pressure, chemistry, humidity, groundwater, etc.) and artificial disturbances (such as loading or unloading, injection or suction of pore liquid, artificial changes in temperature and chemical conditions, etc.). Therefore, slight changes in the external environment will cause changes in the soil structure, and then significantly change its physical and mechanical properties.

[0003] In terms of soil structure detection, the increasingly developed advanced micro-testing methods are gradually being applied to rock and soil structure testing, including: ① Time domain reflectometry (TDR), which calculates the water content in the soil based on the relationship between dielectric constant and water content. ② Computerized X-ray tomography (CT), which uses the different absorption and transmittance of soil materials to X-rays to form images, thereby calculating and observing the micro-structure of the soil. ③ Mercury injection method (MIP), the mercury injection test is designed based on the capillary phenomenon, assuming that the pressure and pore diameter required for mercury to penetrate the pores meet the Washburn formula, and then the pore size distribution of the soil is obtained. According to the range of mercury pressure applied, the pore size range measured by the mercury injection method is about 3.5nm~420μm. ④ Nuclear magnetic resonance (NMR), which uses the energy change of atomic nuclei in a magnetic field to obtain information about atomic nuclei, can simultaneously obtain the moisture content and distribution state in the soil, and is a high-resolution non-destructive detection technology. However, the first three technologies have certain limitations. TDR is relatively cheap, but the accuracy is not high. The accuracy of TDR testing is related to the occurrence form of liquid water in the soil. CT testing has high accuracy and can reflect the internal microstructure of the soil, but the cost is high. Only a few research institutions at home and abroad have used this method to conduct a few studies, and CT images can generally only be used for qualitative analysis, and the quantitative accuracy is not high. Mercury injection is currently one of the most widely used methods for testing the pore size distribution of rock and soil, but the test range is limited and there are many problems such as ink bottle effect, low-pressure conversion, freezing cracking, and high-pressure cracking during the test, which greatly reduce the test accuracy. Most of the above methods are based on certain assumptions to analyze the changes in soil structure through changes in soil sound, light, electricity and other physical parameters or mercury pressure, which are indirect test methods. Compared with other methods, the biggest advantage of nuclear magnetic resonance technology is that it is a direct and quantitative test method. The amount of nuclear magnetic signal is proportional to the hydrogen nucleus content in water molecules, which can be used to determine the water content of the soil. The speed of nuclear magnetic signal decay (relaxation time characterization) can reflect the distribution state of pore water. However, the traditional method of obtaining soil pore size distribution through NMR relaxation time distribution has an assumption that there is no diffusion coupling between different pores. In fact, there is data proving that during the pore water relaxation process, pore water between pores of different sizes undergoes diffusion coupling, resulting in the relaxation distribution curve of saturated rock and soil being inconsistent with its pore size distribution curve. Therefore, there is an urgent need for a method to solve the large error in obtaining pore size distribution using relaxation time distribution due to the coupling of water molecules between pores. Summary of the invention

[0004] In order to solve the above problems, the present application provides a method and related equipment for determining pore size distribution based on relaxation distribution curve of rock and soil, which can eliminate the influence of coupling between large and small pores on relaxation time distribution and more accurately obtain pore size distribution curve of rock and soil. The technical solution is as follows:

[0005] The present application provides a method for determining pore size distribution based on a relaxation distribution curve of a rock mass, comprising the following steps:

[0006] Step 1: Test and invert the moisture content before and after dehumidification as w a and w b Clay relaxation time distribution curve, where w a >w b ;

[0007] Step 2: The moisture content of the clay is w a and w b Taking a difference between the relaxation time distribution curves at 1 and 2, and obtaining a difference relaxation distribution curve;

[0008] Step 3: Convert the negative value of the NMR signal in the difference relaxation distribution curve into the pore size distribution and probability within the small pore range;

[0009] Step 4: Obtain the volume proportions of large and small pores through the difference relaxation distribution curve, and determine the pore size distribution and probability in the large pore size range through the pore size distribution and probability in the small pore size range;

[0010] Step 5: Repeat the first step to the fourth step until the pore water content reaches the single-layer water content to obtain the pore size distribution of the soil.

[0011] For example, in the method for determining the pore size distribution based on the relaxation distribution curve of a rock mass provided in one embodiment, in the second step, the negative portion of the nuclear magnetic resonance signal in the difference relaxation distribution curve represents the relaxation time distribution of small pores coupled with large pores, and the positive portion of the nuclear magnetic resonance signal in the difference relaxation distribution curve represents the relaxation time distribution of large pores coupled with small pores.

[0012] For example, in the method for determining the pore size distribution based on the relaxation distribution curve of a rock mass provided in one embodiment, in the third step, the negative value portion of the nuclear magnetic signal in the difference relaxation distribution curve is converted into the pore size distribution and probability within the small pore range according to the following formula:

[0013]

[0014] Among them, T 1b is the longitudinal relaxation time of pore water, ρ 1 is the surface longitudinal relaxation rate, S b and V b The water content is w b The pore surface area and volume size at r b is the radius of the smallest pore, F is the shape factor, and if the pore shape in the soil is cylindrical, then F=2.

[0015] For example, in the method for determining pore size distribution based on relaxation distribution curve of rock mass provided in one embodiment, in the fourth step, the volume proportion of small pores is p b It is equal to the ratio of the area of ​​the negative part to the positive part of the NMR signal in the difference relaxation distribution curve, and the volume proportion of macropores is p a =1-p b .

[0016] For example, in the method for determining the pore size distribution based on the relaxation distribution curve of the rock mass provided in one embodiment, the pore size distribution and probability within the large pore size range are determined according to the following formula:

[0017]

[0018] Among them, r a is the radius of the macropore r a , f a is the probability within the macropore range, f b is the probability within the small pore range.

[0019] The second aspect of the present application provides a device for determining pore size distribution based on a relaxation distribution curve of a rock mass, comprising: a relaxation time distribution curve generating unit for testing and inverting the moisture content before and after dehumidification, respectively w a and w b The clay relaxation time distribution curve is generated when the clay water content is w a and w b The relaxation time distribution curve at the time of the difference is taken to obtain the difference relaxation distribution curve; the calculation unit is used to obtain the volume proportion of large and small pores, and determine the pore size distribution and probability in the large pore size range through the pore size distribution and probability in the small pore size range.

[0020] The third aspect of the present application provides an electronic device, including: a memory, a processor, and the processor is used to implement the above-mentioned method of determining pore size distribution based on the relaxation distribution curve of rock and soil when executing a computer management program stored in the memory.

[0021] A fourth aspect of the present application provides a computer-readable storage medium having a computer management program stored thereon, which, when executed by a processor, implements the above-mentioned method for determining pore size distribution based on a relaxation distribution curve of a rock mass.

[0022] The beneficial effects brought about by a method for determining pore size distribution based on the relaxation distribution curve of a rock mass and related equipment provided in some embodiments of the present application are as follows: the present application solves the problem of large errors in obtaining pore size distribution using relaxation time distribution due to the coupling effect of water molecules between pores, eliminates the influence of the coupling effect between large and small pores on the relaxation time distribution, and obtains the pore size distribution curve of the rock mass more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

[0024] Figure 1 This is a schematic diagram of the real double porosity structure of the soil;

[0025] Figure 2 Schematic diagram of a single pore structure obtained by nuclear magnetic resonance in the prior art;

[0026] Figure 3 It is the relaxation distribution curve of clay before and after dehumidification;

[0027] Figure 4 It is the difference relaxation distribution curve of clay before and after dehumidification;

[0028] Figure 5 It is the pore size distribution diagram of the soil part determined before and after dehumidification;

[0029] Figure 6 It is a schematic diagram of the binary pore structure of soil. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can 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 described object changes, the relative positional relationship may also change accordingly.

[0032] The real dual porosity structure of the soil is Figure 1 As shown in the prior art, the soil pore structure obtained by nuclear magnetic resonance is as follows Figure 2 As shown in the figure: It is a single pore structure. The existing nuclear magnetic resonance method ignores the diffusion coupling of water molecules between different pores, resulting in a large error between the pore size distribution obtained by using the relaxation time distribution and the actual situation, making the relaxation distribution curve of the saturated rock mass inconsistent with its pore size distribution curve.

[0033] In view of this, the present application provides a method for determining pore size distribution based on a relaxation distribution curve of a rock mass, comprising the following steps:

[0034] Step 1: Test and invert the moisture content before and after dehumidification as w a and w b The clay relaxation time distribution curve is as follows: Figure 3 As shown, where w a >w b ;

[0035] Step 2: The moisture content of the clay is w a and w b The relaxation time distribution curves at the time of θ are subtracted to obtain the difference relaxation distribution curve, such as Figure 4 As shown in FIG. 1 , the negative NMR signal in the difference relaxation distribution curve represents the relaxation time distribution of small pores coupled with large pores, and the positive NMR signal in the difference relaxation distribution curve represents the relaxation time distribution of large pores coupled with small pores. Figure 4 It can be seen that the two water contents (w a and w b ) has two peaks, one large and one small. The NMR signal of the small peak is negative, which means that after dehumidification, the relaxation distribution curve of the soil at a low water content has an additional small peak, which represents the small pores coupled with the large pores. The large peak on the right represents the relaxation time distribution of the large and small peaks. After dehumidification, the water in the large pores of the large and small coupled pore units has been discharged, leaving the small pores saturated with water;

[0036] Step 3: Convert the negative value of the NMR signal in the difference relaxation distribution curve into the pore size distribution and probability within the small pore range;

[0037] The negative part of the NMR signal in the difference relaxation distribution curve is converted into the pore size distribution r in the small pore range according to the following formula: b With probability f b :

[0038]

[0039] Among them, T 1bis the longitudinal relaxation time of pore water, ρ 1 is the surface longitudinal relaxation rate, S b and V b The water content is w b The pore surface area and volume size at r b is the radius of the small pores, F is the shape factor, assuming that the pore shape in the soil is cylindrical, then F = 2, the probability f within the small pore range b Equal to the relaxation distribution curve (T 1 ) on the nuclear magnetic signal intensity.

[0040] Will Figure 4 The small peak in the above formula is converted into the pore size distribution within the small pore range, which is Figure 5 The shape of the small peak in the.

[0041] Step 4: Obtain the volume proportions of large and small pores through the difference relaxation distribution curve, and determine the pore size distribution and probability in the large pore size range through the pore size distribution and probability in the small pore size range;

[0042] Assume that the structural unit of large and small pore coupling is Figure 6 As shown, the volume of small pores accounts for p b It is equal to the ratio of the area of ​​the negative part to the positive part of the NMR signal in the difference relaxation distribution curve, that is: Figure 4 The ratio of the peak area of ​​small and medium peaks to the peak area of ​​large peaks, the volume proportion of large pores p a =1-p b .

[0043] The volume proportion of pores by size p a / p b , the pore size distribution and probability within the large pore size range are determined according to the following formula:

[0044]

[0045] Among them, r a is the radius of the macropore r a , f a is the probability within the macropore range, f b is the probability within the small pore range.

[0046] Thus, we obtain Figure 5 The large peak shape in the.

[0047] Step 5: Repeat the first step to the fourth step until the pore water content reaches the single-layer water content to obtain the pore size distribution of the soil.

[0048] The method of determining the pore size distribution based on the relaxation distribution curve of the rock mass in the present application solves the problem of large errors in obtaining the pore size distribution using the relaxation time distribution due to the coupling effect of water molecules between pores, eliminates the influence of the coupling effect between large and small pores on the relaxation time distribution, and obtains the pore size distribution curve of the rock mass more accurately.

[0049] The second aspect of the present application provides a device for determining pore size distribution based on a relaxation distribution curve of a rock mass, comprising: a relaxation time distribution curve generating unit for testing and inverting the moisture content before and after dehumidification, respectively w a and w b The clay relaxation time distribution curve is generated when the clay water content is w a and w b The relaxation time distribution curve at the time of the difference is taken to obtain the difference relaxation distribution curve; the calculation unit is used to obtain the volume proportion of large and small pores, and determine the pore size distribution and probability in the large pore size range through the pore size distribution and probability in the small pore size range.

[0050] The third aspect of the present application provides an electronic device, including: a memory, a processor, and the processor is used to implement the above-mentioned method of determining pore size distribution based on the relaxation distribution curve of rock and soil when executing a computer management program stored in the memory.

[0051] A fourth aspect of the present application provides a computer-readable storage medium having a computer management program stored thereon, which, when executed by a processor, implements the above-mentioned method for determining pore size distribution based on a relaxation distribution curve of a rock mass.

[0052] Although the implementation scheme of the present application has been disclosed as above, it is not limited to the applications listed in the specification and implementation modes, and it can be fully applicable to various fields suitable for the present application. For those familiar with the art, 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 the illustrations shown and described herein.

Claims

1. A method for determining pore size distribution based on relaxation distribution curve of rock and soil mass, characterized in that: The following steps are involved: Step 1: Test and invert the moisture content before and after dehumidification as w a and w b Clay relaxation time distribution curve, where w a >w b ; Step 2: The moisture content of the clay is w a and w b Taking a difference between the relaxation time distribution curves at 1 and 2, and obtaining a difference relaxation distribution curve; Step 3: Convert the negative value of the NMR signal in the difference relaxation distribution curve into small pores according to the following formula Pore ​​size distribution and probability within the gap range: Among them, T 1b is the longitudinal relaxation time of pore water, ρ1 is the longitudinal relaxation rate of the surface, S b and V b The water content is w b The pore surface area and volume size at r b is the radius of the small pore, F is the shape factor, assuming that the pore shape in the soil is cylindrical, then F = 2; Step 4: Obtain the volume proportions of large and small pores through the difference relaxation distribution curve, and determine the pore size distribution and probability in the large pore size range through the pore size distribution and probability in the small pore size range; Among them, the volume of small pores accounts for p b It is equal to the ratio of the area of ​​the negative part to the positive part of the NMR signal in the difference relaxation distribution curve, and the volume proportion of macropores is p a =1-p b , the pore size distribution and probability within the large pore size range are determined according to the following formula: Among them, r a is the macropore radius, f a is the probability within the macropore range, f b is the probability within the small pore range; Step 5: Repeat the first step to the fourth step until the pore water content reaches the single layer water content, The pore size distribution of the soil is obtained.

2. The method for determining pore size distribution based on relaxation distribution curve of rock and soil mass according to claim 1, characterized in that: In the second step, the negative part of the NMR signal in the difference relaxation distribution curve represents the relaxation time distribution of small pores coupled with large pores, and the positive part of the NMR signal in the difference relaxation distribution curve represents the relaxation time distribution of large pores coupled with small pores.

3. The device for determining the pore size distribution based on the relaxation distribution curve of rock and soil mass according to any one of claims 1 to 2, characterized in that: include: The relaxation time distribution curve generation unit is used to test and invert the moisture content before and after dehumidification, which is w a and w b Clay relaxation time distribution curve; The difference relaxation distribution curve is generated to convert the clay moisture content into w a and w b Taking a difference between the relaxation time distribution curves at 1 and 2, and obtaining a difference relaxation distribution curve; The calculation unit is used to obtain the volume proportion of large and small pores, and determine the pore size distribution and probability in the large pore size range through the pore size distribution and probability in the small pore size range.

4. An electronic device, characterized in that: include: A memory and a processor, wherein the processor is used to implement the method for determining pore size distribution based on relaxation distribution curve of rock and soil mass as described in any one of claims 1 to 2 when executing the computer management program stored in the memory.

5. A computer-readable storage medium having a computer management program stored thereon, characterized in that: When the computer management program is executed by the processor, the method for determining the pore size distribution based on the relaxation distribution curve of the rock and soil mass as described in any one of claims 1 to 2 is implemented.

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