A test method for simulating the healing process of expansive rock and soil with cracks

Abstract

The present invention discloses a test method for simulating the healing process of expansive rock and soil containing cracks. The test method includes the following steps: S1, compaction sample preparation; S2, construction crack simulation; S3, crack healing test instrument assembly; S4, expansion force and permeability coefficient testing; S5, dry density and moisture content distribution testing. The test method for simulating the healing process of expansive rock and soil containing cracks of the present invention simulates construction cracks by setting a gap around the sample and a pressure chamber. The axial and radial expansion pressures under different construction cracks are measured using vertically arranged force sensors and radially arranged pressure sensors. The permeability coefficient of the cracked soil is determined based on the volume of injected water. The dry density distribution of the sample is determined by moisture content and dry density testing. The test results can be used to comprehensively evaluate the degree of crack healing.

Description

Technical Field

[0001] The invention relates to the technical field of buffer materials for high-level radioactive waste disposal repositories, and in particular to a test method for simulating the healing process of expansive rock and soil containing cracks. Background Art

[0002] Many countries utilize a multi-barrier system for deep underground disposal of radioactive waste, consisting of a radioactive waste container, a natural geological barrier (surrounding rock), a concrete lining, and sealing / backfill materials. Typically, the sealing / backfill materials are uniaxially compacted into blocks and then stacked between the surrounding rock and the radioactive waste container. This inevitably leaves construction cracks between the blocks, between the blocks and the container, and between the blocks and the surrounding rock. These construction cracks account for approximately 10% of the total tunnel volume. When groundwater intrudes from the surrounding rock, the compacted blocks expand and fill the construction cracks, gradually closing the preferential seepage channels. Subsequently, they expand under constant volume conditions, exhibiting sufficiently high expansion pressure to limit tunnel deformation after concrete lining failure and possessing a sufficiently low permeability coefficient to mitigate water migration. Therefore, the expansion force and permeability coefficient of expansive soil containing construction cracks are crucial foundations for the design and safety assessment of sealing / backfill materials for nuclear waste repositories.

[0003] Currently, research on the hydraulic behavior of compacted sealing / backfill materials primarily relies on laboratory and field testing. Preliminary quantitative relationships have been established between swelling pressure and the porosity ratio of montmorillonite, the dry density of expansive rock, the effective dry density of montmorillonite, and the initial saturation of montmorillonite. However, previous studies have rarely considered construction cracks. Hydration of the compacted sealing / backfill material due to cracks causes a rapid decrease in the dry density of the compacted mass near the cracks, resulting in an uneven distribution of dry density. The dry density is lower in the water-affected area, while the innermost area has a higher dry density. This distribution is roughly divided into two regions: a compressed region with a lower dry density than the average; and an expansive region with a lower dry density than the average. Over time, the expansive region continues to expand, while the compressed region is compressed by the swelling pressure. Over time, the dry density gradient decreases and approaches a relatively uniform state. This heterogeneity in the sealing / backfill material can in turn affect the overall swelling pressure and permeability, posing a threat to the safety of deep underground nuclear waste repositories. Therefore, research is necessary to investigate the healing process of expansive rock containing construction cracks and their long-term impact on the hydraulic behavior.

[0004] In summary, accurate evaluation of the healing process of expansive rock and soil containing construction cracks, as well as accurate measurement of expansion force and permeability, can provide engineers with a reference for the design of deep underground nuclear waste repositories and provide essential technical support for evaluating their long-term safety. However, to date, no researchers have proposed a standardized testing process or reasonable evaluation method for this issue. Summary of the Invention

[0005] The present invention provides a test method for simulating the healing process of expansive rock and soil containing cracks. The method is easy to implement, has a clear principle, is simple to operate, and has low cost. It can effectively solve the problem that current technical methods are difficult to directly and accurately evaluate the hydraulic properties of expansive rock and soil containing cracks.

[0006] The technical solutions of the present invention are as follows:

[0007] A test method for simulating the healing process of expansive rock and soil containing cracks, the test method comprising the following steps:

[0008] S1. Compaction sample preparation: Grind the expansive rock and soil sample into powder using a crusher. Then, add deionized water to the powder to make the powder reach the designed moisture content. Then, transfer the wetted powder into a sealed bag and store it for a set time to ensure uniform moisture distribution. Then, pour the powder into a rigid annular sample preparation mold and use a press to statically compact the powder to the designed dry density.

[0009] S2. Construction crack simulation: Trim the sample compacted in step S1 to a smaller diameter; place a pressure chamber on a base with a water inlet and an exhaust port. Place porous permeable stone and filter paper at the bottom of the pressure chamber, and then place the trimmed sample on the filter paper, ensuring that the sample is located in the center of the pressure chamber to simulate a test crack.

[0010] S3. Assembly of the Fracture Healing Test Instrument: Place filter paper and porous permeable stone on top of the specimen, followed by a cap with a drain / vent. Use a threaded rod mounted on a bracket to support the cap to ensure constant volume. Install a force sensor below the pressure chamber to measure axial expansion force. Additionally, drill a hole laterally in the pressure chamber to place a pressure sensor to measure radial pressure. Install an exhaust valve on the base's exhaust port. Install an inlet valve on the base's water inlet and connect it to a water pressure / volume controller to measure the specimen's permeability coefficient.

[0011] S4. Expansion force and permeability coefficient test: Before the test, apply initial axial pressure to the sample via a threaded rod. Then, open the water inlet valve. After the gas in the instrument pipeline is exhausted, close the exhaust valve and begin the water injection test. Use a force sensor and a pressure sensor to measure the axial and radial pressures of the sample. Use a water pressure / volume controller to record the amount of water injected at different times and calculate the permeability coefficient.

[0012] S5. Dry density and moisture content distribution test: For each construction crack, 7 identical specimens were prepared and water was injected for 0.5, 5, 15, 60, 240, 720 and 2160 hours respectively to analyze the crack healing process; after the set water injection time was reached, the crack-healed specimen was quickly taken out of the pressure chamber and divided into three parts: part I, part II and part III; part I was a ring located on the outer layer, corresponding to the initial pores; part III was a cylinder located in the center; part II was a ring between parts I and III; each part was cut into several soil blocks for the determination of moisture content, dry density, suction and microstructure; among them, the moisture content was determined by drying at 105°C for 24 hours, the dry density was determined by hydrostatic weighing after immersing the soil block in non-aromatic hydrocarbon liquid, the suction was measured by a cold mirror dew point tensiometer, and the microstructure was determined by mercury intrusion technology; the healing curve of the cracked soil was drawn based on the dry density and moisture content distribution time series data.

[0013] Furthermore, in step S1, the expansive rock and soil sample is ground into a powder with a particle size of less than 2 mm, added with deionized water, and stored for 48 hours; the diameter of the rigid annular sample mold is 50 mm, and during the compaction process, the displacement rate of the press is controlled at 0.05 mm / min, and the compacted sample height is 10 mm.

[0014] Furthermore, in step S2, the pressure chamber is made of a stainless steel cylinder with an inner diameter of 50 mm and a thickness of 20 mm, and the height of the pressure chamber is 40 mm.

[0015] Furthermore, the pressure chamber is made of 304 stainless steel.

[0016] Furthermore, in step S4, the initial axial pressure applied by the threaded rod is 0.05 MPa.

[0017] Furthermore, the threaded rod is made of 304 stainless steel.

[0018] Furthermore, in step S5, part I is a ring with an inner diameter and an outer diameter of 40 and 50 mm respectively, part II is a ring with an inner diameter and an outer diameter of 20 and 40 mm respectively, and the remaining cylinder with a diameter of 20 mm is part III.

[0019] Furthermore, the measuring range of the force sensor exceeds 10 kN.

[0020] Furthermore, the measuring range of the pressure sensor exceeds 5 MPa.

[0021] Furthermore, the measurement time interval between the force sensor and the pressure sensor should be less than 30s.

[0022] The principle of the test method for simulating the healing process of cracked expansive rock and soil of the present invention is to simulate construction cracks by setting gaps around the sample and the pressure chamber, use vertically arranged force sensors and radially arranged pressure sensors to measure the axial and radial expansion pressures under different construction cracks, determine the permeability coefficient of the cracked soil based on the volume of injected water, and determine the dry density distribution of the sample through water content and dry density tests. The test results can be used to comprehensively evaluate the degree of crack healing.

[0023] The test method of the present invention includes specific steps suitable for testing the crack healing process in general expansive rock and soil. Step S3 provides a crack simulation method, cutting a prefabricated cylindrical specimen into cylinders of a designed diameter. The cut specimen is then placed in a pressure chamber, forming a pre-designed crack between the specimen and the chamber wall. Step S4 standardizes the testing process for axial and radial expansion pressures and permeability coefficients, facilitating effective testing of the hydraulic parameters of cracked soils under the same test conditions. Step S5 plots the healing curve of the cracked soil based on time series data of dry density and moisture content distribution, identifying the crack healing process and mechanism. Compared to existing methods for measuring hydraulic parameters in expansive rock and soil, the present invention offers technical advancements in focusing on the impact of crack evolution, quantitatively measuring the changes in axial and radial expansion pressures and permeability coefficients caused by cracks, and evaluating the impact of cracks on hydraulic performance degradation over long-term operation and the hazards posed to deep nuclear waste projects. The technical solution of the present invention is safe and stable, has low sample requirements, and has low implementation costs. The test device used in the test process is easy to build, and the repeatability of the test effect is good. Through multiple tests, the results of the test method can be made true and reliable with high precision, which has guiding significance for the safe operation of deep underground nuclear waste disposal repositories.

[0024] In summary, the technical solution of the present invention has the following beneficial effects:

[0025] 1) Low test cost. All test devices and materials are commonly used instruments and consumables, which can be recycled and reused, reducing the cost of the test.

[0026] 2) The principle is simple and easy to understand, making it easy for operators to use. Compared with traditional testing methods that study the interface effect of construction cracks, this method directly studies the evolution process of the construction crack interface, which is more conducive to revealing the feedback mechanism between soil and construction cracks.

[0027] 3) Simple operation. No large instruments are used, the instrument is easy to assemble, the test method is simple and easy to perform, and no professional technicians are required to operate it, thus reducing manpower and material resources.

[0028] 4) Improved data authenticity. The test process uses simple instruments and equipment, with good repeatability. Through multiple tests, the test results can be made true, reliable, and highly accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a test instrument used in the test method for simulating the healing process of expansive rock and soil containing cracks according to the present invention;

[0030] Figure 2 is the test result of the axial expansion pressure in Example 1;

[0031] Figure 3 is the detection result of the radial expansion pressure in Example 1;

[0032] Figure 4 is the test result of the permeability coefficient in Example 1;

[0033] Figure 5 This is the dry density and moisture content distribution test step in the embodiment, and the specific division of the sample into part I, part II and part III after the cracks are healed.

[0034] Figure 6 It is the water content test result in Example 1;

[0035] Figure 7 is the dry density test result in Example 1;

[0036] Figure 8 is the test result of the axial expansion pressure in Example 2;

[0037] Figure 9 is the detection result of radial expansion pressure in Example 2;

[0038] Figure 10 is the test result of the permeability coefficient in Example 2;

[0039] Figure 11 It is the water content test result in Example 2;

[0040] Figure 12 It is the dry density test result in Example 2. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments, but they are not intended to serve as the basis of the present invention.

[0042] All steps involved in basic geotechnical tests in this invention are strictly carried out with reference to the standard "Standard for Geotechnical Test Methods" (GB / T 50123-2019).

[0043] See also Figure 1The test apparatus used in the following embodiments includes a pressure chamber 1, a base 2, a porous permeable stone 3, filter paper 4, a top cap 5, and a threaded rod 6. The pressure chamber 1 is placed on the base 2, which is equipped with a water inlet and an exhaust port. The water inlet is equipped with a water inlet valve 9, and the exhaust port is equipped with an exhaust valve 10. A force sensor 7 is located below the base 2 to measure axial expansion pressure, and a pressure sensor 8 is located on the side of the pressure chamber 1 to measure radial expansion pressure. The porous permeable stone 3, filter paper 4, and top cap 5 have the same shape and size as the inner cavity of the pressure chamber 1. The top cap 5 is equipped with a drain / exhaust port, and a drainage tube 12 is provided on the drain / exhaust port. The threaded rod 6 is mounted on a bracket and can be adjusted in height. The pressure chamber 1 is located directly below the threaded rod 6. During the test, the sample is installed in the pressure chamber 1, with the porous permeable stone 3 and filter paper 4 placed at both ends of the sample, respectively. The top cap 5 covers the upper end of the pressure chamber and is supported by the threaded rod 6. The data from the force sensor 7 and pressure sensor 8 are read by a data acquisition device 11.

[0044] Example 1:

[0045] In Example 1, the test material used was a French deep underground nuclear waste repository buffer material. It consisted of a compacted mixture of American MX80 bentonite and French Callovo-Oxfordian (COx) claystone, with construction cracks accounting for 10% of the total volume. The mass ratio of MX80 bentonite to COx claystone in the mixture was 3:7, and the clay contents of MX80 bentonite and COx claystone were 86% and 26%, respectively.

[0046] In Example 1, the steps of the test method for simulating the healing process of expansive rock and soil containing cracks are:

[0047] 1. Preparation of compacted samples: Use a crusher to grind MX80 bentonite and COx clay rock into powder with a particle size of less than 2 mm. Then mix the MX80 bentonite and COx clay rock powders in a mass ratio of 3:7 and stir evenly. Then transfer the powder into a sealed bag and seal it for 48 hours to ensure uniform moisture distribution. The moisture content of the mixed powder is 7.7%. Then weigh 42.79 g of powder and pour it into a rigid annular sample preparation mold with a diameter of 50 mm. Use the press to control the displacement rate of the press at 0.05 mm / min to statically compact the powder to a height of 10 mm. At this time, the diameter and height of the compacted sample are 50 and 10 mm, respectively, and the density is 2.0 g / cm 3 .

[0048] 2. Simulate construction cracks: Trim the compacted specimen to a minimum diameter of 47.43 mm. Place a pressure chamber (1) with an internal diameter of 50 mm on a 30 mm thick base (2) equipped with a water inlet and exhaust port. At the bottom of the pressure chamber (1), place a porous permeable stone (3) with a diameter of 50 mm and then filter paper (4). Place the trimmed specimen on top of the filter paper (4). Use a vernier caliper to continuously adjust the specimen's position, ensuring that the specimen is centered in the pressure chamber (1). Ensure that the specimen's center coincides with the center of the chamber and that the distance between the specimen and the inner wall of the chamber is 1.28 mm. At this point, the construction crack between the specimen and the inner wall of the chamber accounts for 10% of the total volume.

[0049] 3. Assembly of the crack healing test instrument: After the construction crack is set, place filter paper 4, porous permeable stone 3 and upper cap 5 on the top of the sample, and use threaded rod 6 to support the upper cap 5 to ensure that the sample height remains unchanged. Place a force sensor 7 under the base 2 to measure the vertical expansion force. In addition, a pressure sensor 8 is arranged through the side hole drilled in the pressure chamber to measure the radial pressure. Figure 1 The water inlet of the base 2 is connected to a water pressure / volume controller to measure the permeability coefficient of the sample.

[0050] 4. Expansion force and permeability coefficient test: Before the test, an initial axial pressure of 0.05 MPa is applied to the sample through the threaded rod 6 to ensure that the sample maintains good contact with the instrument. In order to simulate the on-site conditions of the nuclear waste disposal repository, a salt solution is prepared according to the chemical composition of the on-site groundwater. The prepared salt solution is placed in the salt solution / deionized water converter. One end of the salt solution / deionized water converter is connected to the water pressure / volume controller, and the other end is connected to the water inlet. Then, the water pressure of the water pressure / volume controller is stabilized at 10 kPa, the water inlet valve is opened, and the salt solution begins to flow into the bottom of the water pressure chamber from the water inlet valve. After the gas in the instrument pipeline is exhausted, the exhaust valve 10 is closed, and the salt solution begins to be injected into the sample from bottom to top. The force sensor 7 at the bottom of the pressure chamber begins to measure the axial expansion pressure of the sample, Pa=4P / (πD 2 ), where Pa is the axial expansion pressure, P is the force sensor, and D is the sample diameter of 50 mm. Figure 2 As shown in the figure, the axial expansion force increases rapidly at first and then gradually stabilizes after 7.4 hours. The pressure sensor 8 on the side measures the radial expansion pressure, and the sample data is recorded every 30 seconds, as shown in the figure. Figure 3 As shown in the figure, the radial expansion force remains zero within 0.08h, increases rapidly after 0.08h, and gradually stabilizes after 7.5h. At the same time, the amount of water injected into the sample by the water pressure / volume controller at different times is recorded, kw = 4Q / (πD 2 △t), such as Figure 4 As shown in the figure, the permeability coefficient decreases rapidly with the wetting time and gradually stabilizes at 7.5h.

[0051] 5. Dry density and moisture content distribution test: 7 identical specimens were prepared and water was injected for 0.5, 5, 15, 60, 240, 720 and 2160 hours respectively. The crack healing process was analyzed and the specimens were quickly taken out of the pressure chamber after crack healing and divided into three parts: Part I, Part II and Part III. Figure 5 As shown. Part I corresponds to the initial pores, which refers to rings with inner and outer diameters of 40 and 50 mm respectively, Part II corresponds to rings with inner and outer diameters of 20 and 40 mm respectively, and the remaining cylinders with a diameter of 20 mm belong to Part III. Each part is cut into several soil blocks for the determination of moisture content and dry density. The moisture content is determined by drying at 105 ° C for 24 hours, weighing before and after drying, and calculating the moisture content in the wet state w = (mm s ) / m s , where m is the mass of the sample in the humidified state, m s is the mass of the sample when completely dried, such as Figure 6 As shown, the moisture content of section I, which is far from the center, is higher, while the moisture content of sections II and III, which are closer, is lower, showing a clearly uneven distribution. The dry density of the sample was determined by hydrostatic weighing the soil block after immersing it in a non-aromatic hydrocarbon liquid (Kerdane) (Bian, X., Cui, YJ & Li, XZ 2019b. Voids effect on the swelling behavior of compacted bentonite. Géotechnique 69, No. 7, 593-605). The dry density of the sample was calculated as ρ. d =m s ρ k / (mm k ), where m is the mass of the sample in the humidified state, m s is the mass of the sample when completely dried, m k is the mass after immersion in non-aromatic hydrocarbon liquid (Kerdane); ρ k is the dry density of the non-aromatic hydrocarbon liquid. As shown in 7, the dry density of part I far from the center is smaller, which is less than the average dry density of the sample 1.8Mg / m 3 , while the moisture content of Part II and Part III, which are close to each other, is higher, showing an obviously uneven distribution.

[0052] Example 2:

[0053] The test material used in Example 2 is also a compacted mixture of MX80 bentonite from the United States and Callovo-Oxfordian (COx) clay rock from France, wherein the construction cracks account for 20% of the total volume.

[0054] The steps of the test method for simulating the healing process of cracked expansive rock and soil in Example 2 are:

[0055] 1. Preparation of compacted samples: Use a crusher to grind MX80 bentonite and COx clay rock into powder with a particle size of less than 2 mm. Then mix the MX80 bentonite and COx clay rock powders in a mass ratio of 3:7 and stir evenly. Then transfer the powder into a sealed bag and seal it for 48 hours to ensure uniform moisture distribution. The moisture content of the mixed powder is 7.7%. Then weigh 42.79 g of powder and pour it into a rigid annular sample preparation mold with a diameter of 50 mm. Use the press to control the displacement rate of the press at 0.05 mm / min to statically compact the powder to a height of 10 mm. At this time, the diameter and height of the compacted sample are 50 and 10 mm, respectively, and the density is 2.0 g / cm 3 .

[0056] 2. Construction Crack Simulation: To simulate a 20% construction crack, the compacted specimen was trimmed to a smaller diameter of 44.72 mm. A pressure chamber (1) with an internal diameter of 50 mm was placed on a 30 mm thick base (2) with an inlet and exhaust port. A porous permeable stone (3) with a diameter of 50 mm and filter paper (4) were placed at the bottom of the chamber. The trimmed specimen was then placed on the filter paper (4). Using a vernier caliper, the specimen's position was continuously adjusted to ensure it was centered in the chamber, ensuring that the center of the specimen coincided with the center of the chamber and that the distance between the specimen and the chamber's inner wall was 2.64 mm. At this point, the construction cracks between the specimen and the inner wall of the chamber each accounted for 20% of the total volume.

[0057] 3. Assembly of the Crack Healing Test Instrument: After the construction crack is established, place filter paper 4, porous permeable stone 3, and a cap 5 on top of the specimen. Use a threaded rod 6 to support the cap 5 to ensure the specimen height remains constant. Install a force sensor 7 beneath the base 2 to measure vertical expansion force. Additionally, install a pressure sensor 8 through a hole drilled laterally in the pressure chamber to measure radial pressure. Connect the base's water inlet to a water pressure / volume controller to determine the specimen's permeability coefficient.

[0058] 4. Expansion force and permeability coefficient test: Before the test, an initial axial pressure of 0.05 MPa is applied to the sample through the threaded rod 6 to ensure that the sample maintains good contact with the instrument. In order to simulate the on-site conditions of the nuclear waste disposal repository, a salt solution is prepared according to the chemical composition of the on-site groundwater. The prepared salt solution is placed in the salt solution / deionized water converter. One end of the salt solution / deionized water converter is connected to the water pressure / volume controller, and the other end is connected to the water inlet. Then, the water pressure of the water pressure / volume controller is stabilized at 10 kPa, the water inlet valve is opened, and the salt solution begins to flow into the bottom of the water pressure chamber from the water inlet valve. After the gas in the instrument pipeline is exhausted, the exhaust valve is closed, and the salt solution begins to be injected into the sample from bottom to top. The force sensor at the bottom of the pressure chamber begins to measure the axial expansion pressure of the sample, Pa=4P / (πD 2), where Pa is the axial expansion pressure, P is the force sensor, and D is the sample diameter of 50 mm. Figure 8 As shown in the figure, the axial expansion force increases rapidly at first, reaches a peak of 0.80 MPa at 0.68 h, then gradually decreases and gradually stabilizes after 5.8 h. The pressure sensor on the side measures the radial expansion pressure, and the sample data is recorded every 30 seconds, as shown in the figure. Figure 9 As shown in the figure, the radial expansion force remains zero within 0.18h, increases rapidly after 0.18h, and gradually stabilizes after 5.7h. At the same time, the amount of water injected into the sample by the water pressure / volume controller at different times is recorded, kw = 4Q / (πD 2 △t), such as Figure 10 As shown in the figure, the permeability coefficient decreases rapidly with the wetting time and gradually stabilizes at 5.8h.

[0059] 5. Dry density and moisture content distribution test: 7 identical specimens were prepared and injected with water for 0.5, 5, 15, 60, 240, 720 and 2160 hours respectively. The crack healing process was analyzed and the specimens were quickly taken out of the pressure chamber after crack healing and divided into three parts: Part I, Part II and Part III. Part I corresponds to the initial pores, which refers to the rings with inner and outer diameters of 40 and 50 mm respectively. Part II corresponds to the rings with inner and outer diameters of 20 and 40 mm respectively. The remaining cylinders with a diameter of 20 mm belong to Part III. Each part was cut into several soil blocks for determining the moisture content and dry density. The moisture content was determined by drying at 105°C for 24 hours. The weights were weighed before and after drying, and the moisture content w in the wet state was calculated as (mm s ) / m s , where m is the mass of the sample in the humidified state, m s is the mass of the sample when completely dried, such as Figure 11 As shown, the moisture content of section I, which is far from the center, is higher, while the moisture content of sections II and III, which are closer, is lower, showing a clearly uneven distribution. The dry density of the sample was determined by hydrostatic weighing the soil block after immersing it in a non-aromatic hydrocarbon liquid (Kerdane) (Bian, X., Cui, YJ & Li, XZ 2019b. Voids effect on the swelling behavior of compacted bent onite. Géotechnique 69, No. 7, 593-605). The dry density ρ of the sample was calculated. d =m s ρ k / (mm k ), where m is the mass of the sample in the humidified state, m s is the mass of the sample when completely dried, m k is the mass after immersion in non-aromatic hydrocarbon liquid (Kerdane); ρk is the dry density of the non-aromatic hydrocarbon liquid. As shown in 12, the dry density of part I far from the center is smaller, which is less than the average dry density of the sample 1.6Mg / m 3 , while the moisture content of Part II and Part III, which are close to each other, is higher, showing an obviously uneven distribution.

[0060] The above general description of the invention and the description of its specific embodiments involved in this application should not be understood as limiting the technical solutions of the invention. Based on the disclosure of this application, those skilled in the art may, without violating the constituent elements of the invention involved, add, subtract, or combine the disclosed technical features in the above general description and / or specific embodiments (including examples) to form other technical solutions within the scope of protection of this application.

Claims

1. A test method for simulating the healing process of expansive rock and soil containing cracks, characterized in that: The test method includes the following steps: S1. Compaction sample preparation: Grind the expansive rock and soil sample into powder using a crusher. Then, add deionized water to the powder to make the powder reach the designed moisture content. Then, transfer the wetted powder into a sealed bag and store it for a set time to ensure uniform moisture distribution. Then, pour the powder into a rigid annular sample preparation mold and use a press to statically compact the powder to the designed dry density. S2. Construction crack simulation: trim the sample compacted in step S1 into a smaller diameter; place the pressure chamber (1) on a base (2) with a water inlet and an exhaust port, place porous permeable stone (3) and filter paper (4) at the bottom of the pressure chamber (1), and then place the trimmed sample on the filter paper, ensuring that the sample is located in the middle of the pressure chamber to simulate the test crack; S3. Assembly of the crack healing test instrument: Filter paper (4) and porous permeable stone (3) are placed on the top of the sample in sequence, and then an upper cap (5) with a drainage / exhaust port is placed and a threaded rod (6) mounted on the bracket is used to support the upper cap (5) to ensure a constant volume condition; a force sensor (7) is set below the pressure chamber (1) to measure the axial expansion force, and a pressure sensor (8) is arranged by drilling a hole on the side of the pressure chamber (1) to measure the radial pressure; an exhaust valve (10) is installed on the exhaust port of the base (2); an inlet valve (9) is installed on the water inlet of the base (2) and connected to a water pressure / volume controller to measure the permeability coefficient of the sample; S4. Expansion force and permeability coefficient test: Before the test, an initial axial pressure is applied to the sample through the threaded rod (6); then the water inlet valve (9) is opened, and after the gas in the instrument pipeline is exhausted, the exhaust valve (10) is closed and the water injection test is started. The axial and radial pressures of the sample are measured using the force sensor (7) and the pressure sensor (8), and the amount of water injected at different times is recorded using the water pressure / volume controller to calculate the permeability coefficient; S5. Dry density and moisture content distribution test: For each type of construction crack, 7 identical specimens were prepared and water was injected for 0.5, 5, 15, 60, 240, 720 and 2160 hours respectively to analyze the crack healing process; after reaching the set water injection time, the crack-healed specimen was quickly taken out of the pressure chamber (1) and divided into three parts: part I, part II and part III; part I is the ring located in the outer layer, corresponding to the initial pores; Part III is the central cylinder; Part II is the ring between Part I and Part III; each part is cut into several soil blocks for measuring moisture content, dry density, suction, and microstructure; among them, the moisture content is determined by drying at 105°C for 24 hours, the dry density is determined by hydrostatic weighing after immersing the soil blocks in non-aromatic hydrocarbon liquid, the suction is measured by a chilled mirror dew point tensiometer, and the microstructure is determined by mercury intrusion technology; the healing curve of the cracked soil is drawn based on the time series data of dry density and moisture content distribution.

2. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 1, characterized in that: In step S1, the expansive rock and soil sample is ground into a powder with a particle size of less than 2 mm, added with deionized water, and stored for 48 hours; the diameter of the rigid annular sample mold is 50 mm, and during the compaction process, the displacement rate of the press is controlled at 0.05 mm / min, and the compacted sample height is 10 mm.

3. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 2, characterized in that: In step S2, the pressure chamber (1) is made of a stainless steel cylinder with an inner diameter of 50 mm and a thickness of 20 mm, and the height of the pressure chamber (1) is 40 mm.

4. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 3, characterized in that: The pressure chamber is made of 304 stainless steel.

5. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 4, characterized in that: In step S4, the initial axial pressure applied by the threaded rod (6) is 0.05 MPa.

6. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 5, characterized in that: The threaded rod (6) is made of 304 stainless steel.

7. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 6, characterized in that: In step S5, part I is a ring with an inner diameter and an outer diameter of 40 and 50 mm respectively, part II is a ring with an inner diameter and an outer diameter of 20 and 40 mm respectively, and the remaining cylinder with a diameter of 20 mm is part III.

8. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 7, characterized in that: The measuring range of the force sensor (7) exceeds 10 kN.

9. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 8, characterized in that: The measuring range of the pressure sensor (8) exceeds 5 MPa.

10. The test method for simulating the healing process of expansive rock and soil containing cracks according to claim 7, 8 or 9, characterized in that: The measurement time interval between the force sensor (7) and the pressure sensor (8) should be less than 30 seconds.

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