A device for simulating the diffusion of moisture in expansive rocks and a method for determining the moisture diffusion coefficient

Abstract

The present invention discloses an expansive rock moisture diffusion simulation device and a moisture diffusion coefficient determination method, comprising the following steps: making a rock sample and performing pretreatment; performing multiple groups of control tests to establish a strain data and moisture content relationship curve; performing rock moisture diffusion coefficient determination, determining the moisture content at different positions inside the rock sample at each time through the relationship curve between the strain data and the moisture content, and calculating the moisture diffusion coefficient at different positions of the rock sample at each time from the moisture content according to Fick's second law. The present invention can acquire and record moisture diffusion data in real time and accurately, greatly shortening the test cycle, using a non-destructive test method, not causing significant physical damage to the rock sample, and reducing the error between the measurement result and the actual result.

Description

Technical Field

[0001] The invention relates to the technical field of rock experiments, and in particular to a device for simulating the diffusion of moisture in expansive rocks and a method for determining a moisture diffusion coefficient. Background Art

[0002] Swelling rock refers to a type of rock that undergoes physical and chemical reactions with water, causing the water content of the rock to increase over time, and the volume to increase over time. When the swelling rock is disturbed and encounters groundwater, its properties change dramatically, resulting in volume expansion. For example, after the hydration and recrystallization of anhydrite, its volume can increase by about 30%, which will produce expansion stress on the structures therein and affect the stability of the project. Swelling rock is very sensitive to environmental factors, especially when the humidity conditions change, the physical and mechanical properties of the rock will change greatly. In addition to volume expansion, the strength will also decrease, which will have a great impact on the stability of the swelling rock project. Humidity is an important factor in the strength damage of rock-type tunnels. Measuring the rock humidity diffusion coefficient and the depth of humidity change are of great significance for evaluating the stability of rock projects under different humidity conditions. Swelling rock has the characteristics of swelling and disintegration when absorbing water, but some current humidity diffusion test methods have certain limitations. Existing test devices usually do not consider the disintegration characteristics of rocks and are not suitable for such rocks. On the other hand, the weight method and the resistance method are two commonly used methods to test the humidity diffusion performance of materials. The weight method evaluates the humidity diffusion performance by measuring the mass change of the material under a humidity environment. The resistance method uses the resistance change of the material under humidity changes to evaluate the humidity diffusion performance. The traditional weight method and resistance method may be disturbed by external conditions during the test process, and cannot provide real-time data on humidity changes, and cannot provide detailed information about the humidity diffusion depth and humidity diffusion coefficient at different positions. In addition, the traditional resistance method places the sensor inside the material to be tested, which will destroy the structure of the material to be tested. In view of the above-mentioned problems, it is necessary to study and design a new type of expansive rock humidity diffusion simulation device and humidity diffusion coefficient determination method to overcome the problems existing in the existing expansive rock humidity diffusion measurement. Summary of the invention

[0003] In order to solve the problems existing in the existing measurement of moisture diffusion of expansive rocks, namely, failure to consider the swelling and disintegration characteristics of expansive rocks due to water absorption, serious interference from external conditions during measurement, failure to provide detailed information on the moisture diffusion coefficient and destruction of the structure of the rock itself, the present invention provides an expansive rock moisture diffusion simulation device and a moisture diffusion coefficient determination method.

[0004] The technical scheme adopted by the present invention to achieve the above-mentioned purpose is: a method for determining the moisture diffusion coefficient of expansive rock, using an expansive rock moisture diffusion simulation device to determine the moisture diffusion coefficient, the expansive rock moisture diffusion simulation device comprising a constant temperature and humidity chamber, a sample slot, a strain gauge array and a data acquisition and control system; the constant temperature and humidity chamber is used to adjust the temperature and humidity of the test environment and maintain the stability of humidity and temperature; the sample slot is arranged inside the constant temperature and humidity chamber and has an open end, and is used to place rock samples; the strain gauge array is arranged on the outer surface of the sample slot, and is used to measure the strain data at different positions of the outer wall of the sample slot, and transmit the strain data to the data acquisition and control system; the data acquisition and control system is respectively connected to the constant temperature and humidity chamber and the strain gauge, and is used to receive the strain data and store, process and analyze it, and control the temperature and humidity inside the constant temperature and humidity chamber;

[0005] The method for determining the moisture diffusion coefficient of expansive rock comprises the following steps:

[0006] S1. Prepare rock samples and perform pretreatment: collect rock samples in the target area, process the rock samples to obtain multiple identical rock samples, dry the multiple rock samples to eliminate residual water inside, perform density tests on the multiple rock samples after treatment and record their dry densities;

[0007] S2. Conduct multiple groups of control tests to establish a relationship curve between strain data and moisture content: place the rock sample after drying treatment in step S1 inside the sample slot, weigh the sample slot and the rock sample as a whole, and after weighing, place the sample slot and the rock sample in a constant temperature and humidity chamber to stand for diffusion test. During the diffusion process, the data acquisition and control system continuously monitors the strain data of the outer side of the cylinder wall of the sample slot through the strain gauge array until the strain data is stable, weigh the sample slot and the rock sample as a whole, and the data acquisition and control system records the corresponding strain data of the outer side of the cylinder wall of the sample slot under the humidity condition, adjust the humidity inside the constant temperature and humidity chamber through the data acquisition and control system and repeat the above steps to prepare rock samples with different moisture contents, obtain the strain data of rock samples with different moisture contents through the strain data of the outer side of the sample slot cylinder, fit the relationship between the strain data and the moisture content of the rock sample using a regression formula, and draw a relationship curve between the strain data and the moisture content;

[0008] S3. Determination of rock moisture diffusion coefficient: The rock sample dried in step S1 is placed in the sample slot 2 to carry out a rock moisture diffusion test. The data acquisition and control system collects the strain data of the outer wall of the sample slot at different diffusion times through the strain gauge array. The moisture content at different positions inside the rock sample at each time is determined through the relationship curve between the strain data and the moisture content. The moisture diffusion coefficient at different positions of the rock sample at each time is calculated based on the moisture content according to Fick's second law.

[0009] According to the method for determining the moisture diffusion coefficient of expansive rock in some embodiments of the present application, the rock sample processed in step S1 is a cylindrical sample with a diameter of 50 mm and a height of 200 mm, and the drying process includes placing the rock sample in an oven, setting a constant temperature of 105°C, and continuously drying for 24 hours. After drying, the rock sample is placed in a dryer and cooled to room temperature, and the cooled rock sample is placed in a vacuum container. The rock sample is evacuated by a vacuum pump, and the vacuum pressure gauge reading of the vacuum pump is set to 100 kPa. The evacuation time is greater than 1 hour, and the air is evacuated until no bubbles escape.

[0010] According to the method for determining the moisture diffusion coefficient of expansive rock in some embodiments of the present application, in step S2, the humidity inside the constant temperature and humidity chamber is adjusted to 20%, 40%, 60%, 80%, and 100% respectively to obtain rock samples with different moisture contents. The moisture content is calculated as shown in formula (1):

[0011]

[0012] Where: m w is the moisture content, m a is the mass of the sample trough and the rock sample when the water in the rock sample is in equilibrium state, and m0 is the mass of the sample trough and the rock sample at the initial time.

[0013] According to the method for determining the moisture diffusion coefficient of expansive rock in some embodiments of the present application, in step S3, Fick's second law is as shown in formula (2):

[0014]

[0015] Where: C is the water concentration at the diffusion distance X of the rock sample, t is the diffusion time, D h is the humidity diffusion coefficient, X is the diffusion distance,

[0016] The moisture concentration C is shown in formula (3):

[0017] C=m w ×ρ d (3)

[0018] Where: m w is the moisture content, ρ d is the dry density of the rock sample,

[0019] According to Fick's second law, the humidity diffusion coefficient is shown in formula (4):

[0020]

[0021] Where: erfc -1 is the inverse function of erfc, t is the diffusion time, X is the diffusion distance, C is the water concentration at the corresponding diffusion distance X, C max is the water concentration at the diffusion starting point of the rock sample.

[0022] The present invention also provides a swelling rock moisture diffusion simulation device used in the above method.

[0023] According to the expansive rock moisture diffusion simulation device of some embodiments of the present application, the sample slot is a cylindrical structure with one end sealed, the sample slot is made of steel, the inner diameter of the sample slot is 50 mm, and the length is 200 mm. The outer surface of the sample slot is provided with scale lines, and the scale lines are used to provide a positioning position for the strain gauge.

[0024] According to the expansive rock moisture diffusion simulation device in some embodiments of the present application, the strain gauge array includes 20 strain gauges arranged along the axial direction of the sample slot, 10 strain gauges are evenly arranged above and below the sample slot, and the strain gauges are staggered up and down above and below the sample slot.

[0025] According to the expansive rock moisture diffusion simulation device in some embodiments of the present application, the strain gauge includes an annular strain gauge and a radial strain gauge. The annular strain gauge is used to measure the axial strain data of the moisture absorption and expansion of the rock sample inside the sample slot, and the radial strain gauge is used to measure the radial strain data of the moisture absorption and expansion of the rock sample inside the sample slot.

[0026] According to the expansive rock moisture diffusion simulation device of some embodiments of the present application, the data acquisition and control system includes a data acquisition and analysis system, a humidity control system and a temperature control system. The data acquisition and analysis system is used to receive and store the strain data, establish a relationship model between strain and humidity diffusion by corresponding to the moisture content data of the rock sample, calculate the humidity diffusion coefficient of the rock sample at different positions by analyzing the strain data, and infer the humidity diffusion depth and water absorption rate distribution of the rock sample; the humidity control system is used to adjust and control the humidity of the environment during the test; the temperature control system is used to adjust and control the temperature of the environment during the test.

[0027] According to the expansive rock moisture diffusion simulation device of some embodiments of the present application, the data acquisition and control system is respectively connected to the constant temperature and humidity chamber and the strain gauge array through data transmission lines.

[0028] The present invention discloses an expansive rock moisture diffusion simulation device and a moisture diffusion coefficient determination method. By creating a single-direction moisture diffusion path at one end of an opening in a sample slot, the device can accurately simulate the moisture diffusion process in the actual expansive rock, and can accurately simulate the moisture absorption depth and moisture content changes of the rock sample at different times. The device is provided with strain gauges arranged along the axial direction of the sample slot, which can realize the monitoring and analysis of the moisture content and humidity diffusion coefficient at different positions. Through multi-point monitoring, the research on the humidity change inside the rock sample is more comprehensive and accurate, and the characteristics of the expansive rock swelling and disintegration due to water absorption are fully considered. Compared with the traditional weight method and resistance method, a more efficient and rapid humidity diffusion test method is provided, which can obtain and record humidity diffusion data in real time and accurately, and greatly shorten the test cycle. The humidity diffusion coefficient determination method adopts a non-destructive test method, which will not cause significant physical damage to the rock sample, and will not damage the internal structure of the rock sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the structure of a device for simulating moisture diffusion of expansive rocks according to an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of the position of the strain gauge array according to an embodiment of the present invention.

[0031] In the figure: 1. Constant temperature and humidity chamber, 2. Sample slot, 3. Data acquisition and control system, 4. Strain gauge array, 5. Data transmission line. DETAILED DESCRIPTION

[0032] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0033] In the description of the present invention, it should be noted that the orientations or positional relationships indicated by the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] This embodiment provides a method for determining the moisture diffusion coefficient of expansive rocks. The rock selected in this embodiment is skarn. Skarn often contains hydrophilic clay minerals such as kaolinite, chlorite, and talc. The crystal structure of clay minerals in rocks is active. When skarn encounters water or absorbs moisture in the air, water molecules will enter the crystal layers to form hydration film interlayers, resulting in lattice expansion, which is manifested as rock expansion in macroscopic terms. It has been determined that when the clay mineral content in skarn is 76%, its water absorption expansion rate can reach 84%.

[0035] The method for determining the moisture diffusion coefficient of expansive rock adopts an expansive rock moisture diffusion simulation device to determine the moisture diffusion coefficient. The expansive rock moisture diffusion simulation device is as follows: Figure 1 As shown, it includes a constant temperature and humidity chamber 1, a sample tank 2, a strain gauge array 4 and a data acquisition and control system 3; the constant temperature and humidity chamber 1 is used to adjust the temperature and humidity of the test environment and maintain the stability of humidity and temperature; the sample tank 2 is arranged inside the constant temperature and humidity chamber 1 and is open at one end, and is used to place rock samples; the strain gauge array 4 is arranged on the outer surface of the sample tank 2, and is used to measure the strain data at different positions of the outer wall of the sample tank 2, and transmit the strain data to the data acquisition and control system 3; the data acquisition and control system 3 is respectively connected to the constant temperature and humidity chamber 1 and the strain gauge, and is used to receive the strain data and store, process and analyze it, and control the temperature and humidity inside the constant temperature and humidity chamber 1;

[0036] The method for determining the moisture diffusion coefficient of skarn includes the following steps:

[0037] S1. Prepare skarn rock samples and perform pretreatment: collect skarn rock samples in the target area, process the skarn rock samples, and process multiple identical rock samples. The rock samples are cylindrical samples with a diameter of 50 mm and a height of 200 mm. Dry the multiple rock samples to eliminate residual moisture inside. The drying process includes placing the rock samples in an oven, setting a constant temperature of 105°C, and drying them for 24 hours until the standards of constant mass and constant weight are met. The standards of constant mass and constant weight are that the mass change between two weighings is less than 0.1%. After drying, place the rock samples in a desiccator to cool to room temperature. Place the cooled rock samples in a vacuum container and evacuate the rock samples by a vacuum pump. Set the vacuum pressure gauge of the vacuum pump to 100 kPa. The evacuation time is greater than 1 hour, and the samples are evacuated until no bubbles escape. Density tests are performed on the multiple rock samples after treatment and their dry densities are recorded.

[0038] S2. Conduct multiple groups of control tests to establish a curve of strain data and moisture content: place the rock sample after drying in step S1 in the sample slot 2. The rock sample needs to be kept in the constant temperature and humidity chamber 2 for a sufficiently long time. In this embodiment, it is 7 days. The sample slot 2 and the rock sample are weighed as a whole. After weighing, the sample slot 2 and the rock sample are placed in the constant temperature and humidity chamber 1 for a diffusion test. The humidity in the constant temperature and humidity chamber 1 is adjusted to 20%. During the diffusion process, the data acquisition and control system 3 continuously monitors the strain data of the outer wall of the sample slot 2 through the strain gauge array 4 until the strain data is stable, indicating that the moisture content of the rock sample has reached a balanced state. The rock sample is weighed as a whole, and the data acquisition and control system 3 records the strain data of the outer side of the sample tank 2 under the humidity condition. The humidity inside the constant temperature and humidity chamber 1 is adjusted to 40%, 60%, 80% and 100% respectively through the data acquisition and control system 3, and the above steps are repeated respectively. Note that during the humidity adjustment process, the temperature in the constant temperature and humidity chamber 1 needs to be kept consistent, so as to prepare rock samples with different moisture contents. The strain data of rock samples with different moisture contents are obtained through the strain data of the outer side of the sample tank 2. The relationship between the strain data and the moisture content of the rock sample is fitted by using the regression formula, and the relationship curve between the strain data and the moisture content is plotted. The moisture content is calculated as shown in formula (1):

[0039]

[0040] Where: m w is the moisture content, m a is the mass of the sample trough and the rock sample when the water in the rock sample is in equilibrium state, and m0 is the mass of the sample trough and the rock sample at the initial time.

[0041] S3. Determination of rock moisture diffusion coefficient: The rock sample after drying in step S1 is placed in the sample tank 2 for rock moisture diffusion test. The data acquisition and control system 3 collects the strain data of the outer wall of the sample tank 2 at different diffusion times through the strain gauge array 4. The moisture content at different positions inside the rock sample at each time is determined through the relationship curve between the strain data and the moisture content. The moisture diffusion coefficient at different positions of the rock sample at each time is calculated from the moisture content according to Fick's second law. Fick's second law is shown in formula (2):

[0042]

[0043] Where: C is the water concentration at the diffusion distance X of the rock sample, t is the diffusion time, D h is the humidity diffusion coefficient, X is the diffusion distance,

[0044] The moisture concentration C is shown in formula (3):

[0045] C=m w ×ρ d (3)

[0046] Where: m w is the moisture content, ρ d is the dry density of the rock sample,

[0047] According to Fick's second law, the humidity diffusion coefficient is shown in formula (4):

[0048]

[0049] Where: erfc -1 is the inverse function of erfc, t is the diffusion time, X is the diffusion distance, C is the water concentration at the corresponding diffusion distance X, C max is the water concentration at the diffusion starting point of the rock sample.

[0050] The method first calibrates and corresponds the moisture content of the skarn rock specimen with the strain data of the outer side of the sample slot 2. After determining the corresponding relationship between the moisture content of the rock specimen 3 and the strain value of the outer side of the cylinder wall of the sample slot 2, the humidity diffusion coefficient is determined by measuring the strain value of the outer side of the cylinder wall of the sample slot 2, and the humidity change data is observed in real time. This method can avoid the situation of directly destroying the sample for moisture content testing.

[0051] A device for simulating the diffusion of moisture in an expansive rock according to this embodiment, such as Figure 1As shown, it includes a constant temperature and humidity chamber 1, a sample slot 2, a strain gauge array 4 and a data acquisition and control system 3; specifically, the sample slot 2 is a cylindrical structure with one end sealed, and the sample slot 2 is used to accommodate the rock sample and keep the rock sample in contact with the environment, so that one end of the rock sample can be exposed to humid air to form a single-direction humidity diffusion path. The sample slot 2 is made of steel to provide lateral restraint for the expansive rock sample. The inner diameter of the sample slot 2 is 50 mm and the length is 200 mm. The outer surface of the sample slot 2 is provided with scale lines, and the scale lines are used to provide a positioning position for the strain gauge.

[0052] like Figure 2 As shown, the strain gauge array 4 includes 20 pairs of strain gauges arranged above and below the sample slot 2, 10 pairs of strain gauges are evenly arranged above and below the sample slot 2, and the strain gauges are staggered above and below the sample slot 2. The strain gauges include annular strain gauges and radial strain gauges. The annular strain gauges are used to measure the axial strain data of the hygroscopic expansion of the rock sample inside the sample slot 2, and the radial strain gauges are used to measure the radial strain data of the hygroscopic expansion of the rock sample inside the sample slot 2. The strain gauges are used to measure the strain data of the outer wall of the sample slot 2 at different positions. By corresponding to the moisture content data of the sample, a relationship model between the strain data and the humidity diffusion is established. By analyzing the data, the humidity diffusion coefficient at different positions can be calculated, and the depth of humidity diffusion and the water absorption rate distribution can be deduced. The axial stress and radial stress of the hygroscopic expansion of the skarn inside the sample slot can be derived and calculated according to the generalized Hooke's law and the thin-walled cylinder theory.

[0053] The data acquisition and control system 3 includes a data acquisition and analysis system, a humidity control system and a temperature control system. The data acquisition and analysis system is used to receive and store strain data. By corresponding to the moisture content data of the rock sample, a relationship model between strain and humidity diffusion is established. By analyzing the strain data, the humidity diffusion coefficient at different positions of the rock sample is calculated, and the humidity diffusion depth and water absorption rate distribution of the rock sample are deduced; the humidity control system is used to adjust and control the humidity of the environment during the test; the temperature control system is used to adjust and control the temperature of the environment during the test. Rock humidity diffusion is not only related to the humidity environment, but temperature changes also affect the migration speed and spatial distribution of water vapor in the rock. The coupling effect of temperature and humidity in the rock mass causes the deformation of the rock mass to change with time and space. Therefore, the humidity control system and the temperature control system are set to provide different humidity and temperature environments for the experiment. The data acquisition and control system 3 is connected to the constant temperature and humidity chamber 1 and the strain gauge array 4 through the data transmission line 5, respectively. The data transmission line 5 can make the data transmission more stable.

[0054] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

Claims

1. A method for determining the moisture diffusion coefficient of expansive rock, characterized in that: A swelling rock humidity diffusion simulation device is used to measure humidity diffusion coefficient, the swelling rock humidity diffusion simulation device comprising a constant temperature and humidity chamber (1), a sample slot (2), a strain gauge array (4) and a data acquisition and control system (3); the constant temperature and humidity chamber (1) is used to adjust the temperature and humidity of the test environment and maintain the stability of humidity and temperature; the sample slot (2) is arranged inside the constant temperature and humidity chamber (1) and has an open end, and is used to place rock samples; the strain gauge array (4) is arranged on the outer surface of the sample slot (2) and is used to measure strain data at different positions of the outer wall of the sample slot (2) and transmit the strain data to the data acquisition and control system (3); the data acquisition and control system (3) is connected to the constant temperature and humidity chamber (1) and the strain gauge respectively, and is used to receive the strain data and store, process and analyze the strain data, and control the temperature and humidity inside the constant temperature and humidity chamber (1); The method for determining the moisture diffusion coefficient of expansive rock comprises the following steps: S1. Prepare rock samples and perform pretreatment: collect rock samples in the target area, process the rock samples to obtain multiple identical rock samples, dry the multiple rock samples to eliminate residual water inside, perform density tests on the multiple rock samples after treatment and record their dry densities; S2. Conduct multiple groups of control tests to establish a curve of the relationship between strain data and moisture content: place the rock sample after drying in step S1 inside the sample tank (2), weigh the sample tank (2) and the rock sample as a whole, and after weighing, place the sample tank (2) and the rock sample in a constant temperature and humidity chamber (1) to perform a diffusion test. During the diffusion process, the data acquisition and control system (3) continuously monitors the strain data of the outer wall of the sample tank (2) through the strain gauge array (4) until the strain data is stable. 2) and the rock sample as a whole are weighed, the data acquisition and control system (3) records the strain data of the outer side of the cylinder wall of the sample slot (2) corresponding to the humidity condition, the humidity inside the constant temperature and humidity chamber (1) is adjusted by the data acquisition and control system (3) and the above steps are repeated to prepare rock samples with different moisture contents, the strain data of rock samples with different moisture contents are obtained by the strain data of the outer side of the cylinder of the sample slot (2), the relationship between the strain data and the moisture content of the rock sample is fitted by using a regression formula, and a relationship curve between the strain data and the moisture content is drawn; S3. Determination of rock moisture diffusion coefficient: The rock sample dried in step S1 is placed in the sample slot (2) to carry out a rock moisture diffusion test. The data acquisition and control system (3) collects strain data of the outer wall of the sample slot (2) at different diffusion times through the strain gauge array (4). The moisture content at different positions inside the rock sample at each time is determined through a relationship curve between the strain data and the moisture content. The moisture diffusion coefficient at different positions of the rock sample at each time is calculated from the moisture content according to Fick's second law.

2. The method for determining the moisture diffusion coefficient of expansive rock according to claim 1, characterized in that: The rock sample processed in step S1 is a cylindrical sample with a diameter of 50 mm and a height of 200 mm. The drying process includes placing the rock sample in an oven, setting a constant temperature of 105°C, and continuously drying for 24 hours. After drying, the rock sample is placed in a dryer to cool to room temperature, and the cooled rock sample is placed in a vacuum container. The rock sample is evacuated by a vacuum pump, and the vacuum pressure gauge reading of the vacuum pump is set to 100 kPa. The evacuation time is greater than 1 hour, and the gas is evacuated until no bubbles escape.

3. The method for determining the moisture diffusion coefficient of expansive rock according to claim 1, characterized in that: In step S2, the humidity inside the constant temperature and humidity chamber (1) is adjusted to 20%, 40%, 60%, 80%, and 100% respectively to obtain rock samples with different moisture contents. The moisture content is calculated as shown in formula (1): Where: m w is the moisture content, m a is the mass of the sample trough and the rock sample when the water in the rock sample is in equilibrium state, and m0 is the mass of the sample trough and the rock sample at the initial time.

4. The method for determining the moisture diffusion coefficient of expansive rock according to claim 1, characterized in that: In step S3, Fick's second law is as shown in formula (2): Where: C is the water concentration at the diffusion distance X of the rock sample, t is the diffusion time, D h is the humidity diffusion coefficient, X is the diffusion distance, The moisture concentration C is shown in formula (3): C=m w ×ρ d (3) Where: m w is the moisture content, ρ d is the dry density of the rock sample. According to Fick's second law, the humidity diffusion coefficient is shown in formula (4): Where: erfc -1 is the inverse function of erfc, t is the diffusion time, X is the diffusion distance, C is the water concentration at the corresponding diffusion distance X, C max is the water concentration at the diffusion starting point of the rock sample.

5. A device for simulating moisture diffusion of expansive rocks used in the method as described in any one of claims 1 to 4.

6. The expansive rock moisture diffusion simulation device according to claim 5, characterized in that: The sample groove (2) is a cylindrical structure with one end sealed. The sample groove (2) is made of steel. The inner diameter of the sample groove (2) is 50 mm and the length is 200 mm. The outer surface of the sample groove (2) is provided with scale lines, and the scale lines are used to provide a positioning position for the strain gauge.

7. The expansive rock moisture diffusion simulation device according to claim 5, characterized in that: The strain gauge array (4) comprises 20 strain gauges arranged along the axial direction of the sample slot (2), 10 strain gauges are evenly arranged above and below the sample slot (2), and the strain gauges are arranged in an up-and-down staggered manner above and below the sample slot (2).

8. The expansive rock moisture diffusion simulation device according to claim 5, characterized in that: The strain gauge comprises an annular strain gauge and a radial strain gauge which are vertically connected to each other. The annular strain gauge is used to measure the axial strain data of the rock sample in the sample groove (2) due to moisture absorption and expansion, and the radial strain gauge is used to measure the radial strain data of the rock sample in the sample groove (2) due to moisture absorption and expansion.

9. The expansive rock moisture diffusion simulation device according to claim 5, characterized in that: The data acquisition and control system (3) comprises a data acquisition and analysis system, a humidity control system and a temperature control system. The data acquisition and analysis system is used to receive and store the strain data, establish a relationship model between strain and humidity diffusion by corresponding to the moisture content data of the rock sample, calculate the humidity diffusion coefficient at different positions of the rock sample by analyzing the strain data, and deduce the humidity diffusion depth and water absorption rate distribution of the rock sample; the humidity control system is used to adjust and control the humidity of the environment during the test; and the temperature control system is used to adjust and control the temperature of the environment during the test.

10. The expansive rock moisture diffusion simulation device according to claim 5, characterized in that: The data acquisition and control system (3) is respectively connected to the constant temperature and humidity chamber (1) and the strain gauge array (4) via data transmission lines (5).

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