A system and method for testing and evaluating the permeability coefficient of modified expansive soil under dry-wet cycles

Abstract

This invention relates to a system and method for testing and evaluating the permeability coefficient of modified expansive soil under wet-dry cycles. The evaluation system includes a sample chamber, a support frame, a permeation system, a rainfall-evaporation device, a loading mechanism, a data acquisition system, and an evaluation module. The sample chamber is stably mounted on the support frame and contains the soil sample to be tested. The top of the sample chamber is connected to the loading mechanism via a pressure threaded rod. The rainfall-evaporation device is positioned above the sample chamber to simulate natural rainfall-evaporation. The permeation system is positioned on both sides of the sample chamber to saturate the soil sample through permeation. The data acquisition system can monitor the development of cracks in the soil sample during evaporation and the changes in swelling force, water content, and matrix suction in any direction during the soil sample permeation saturation process. The evaluation module processes the data transmitted from the data acquisition system and generates evaluation results.

Description

Technical Field

[0001] This invention relates to the field of expansive soil modification technology, and in particular to a system and method for testing and evaluating the permeability coefficient of modified expansive soil under wet-dry cycles. Background Technology

[0002] Expansive soil is a type of highly plastic clay mainly composed of strongly hydrophilic clay minerals. It is extremely sensitive to changes in moisture, expanding when exposed to water and shrinking when dehydrated. It has characteristics such as strong swelling and shrinkage, multiple fissures, and decreased strength when submerged in water. It can easily cause great damage during engineering construction and operation, such as slope instability, channel collapse, foundation heave, and road surface cracking.

[0003] Numerous studies and practices have shown that engineering problems in expansive soil areas are related to rainfall infiltration, and the permeability characteristics of expansive soil are crucial to the moisture content and changes in the soil under rainfall conditions. Typically, expansive soil or modified expansive soil exists in nature in an unsaturated state, making its permeability coefficient difficult to measure directly. Scholars both domestically and internationally often use soil-water characteristic curves to indirectly obtain the permeability coefficient of unsaturated soil. However, in reality, the alternating effects of rainfall and evaporation create numerous fissures in expansive soil, providing rapid pathways for rainfall infiltration and significantly altering its permeability characteristics.

[0004] Currently, many scholars are studying the permeability characteristics of expansive soil through experimental methods. For example, Chinese patent application 202010330596.7 discloses a device for measuring the permeability coefficient and swelling force of unsaturated expansive soil, which includes a sample chamber, a water supply system, a data acquisition system, and a weighing unit. The device can measure the permeability coefficient and swelling force of unsaturated expansive soil under three-dimensional confined conditions, but it only measures the vertical swelling force during the saturation process of expansive soil and does not consider the influence of the rainfall-evaporation cycle.

[0005] In summary, the following problems urgently need to be addressed regarding the permeability coefficient of expansive soil, especially modified expansive soil: First, there is a lot of testing and research on the vertical expansion force during the permeation saturation process of expansive soil, but little consideration is given to the changes in lateral confined expansion force; second, current research on the impact of rainfall-evaporation cycles on the permeability of expansive soil mostly involves conducting studies on samples undergoing several rapid saturation-drying cycles indoors, while in actual engineering, under most rainfall-evaporation alternations, expansive soil undergoes slow permeation saturation or evaporation drying; third, the evaluation of the permeability characteristics of modified expansive soil often only considers the changes in the permeability coefficient, without comprehensively considering the influence of internal and surface crack conditions of the expansive soil.

[0006] In conclusion, it is essential to develop a three-dimensional, unrestricted device for measuring the permeability coefficient of expansive soil under simulated natural rainfall-evaporation alternation indoors, and to provide a method for evaluating the permeability coefficient of modified expansive soil that considers the influence of cracks. Summary of the Invention

[0007] To address the aforementioned issues, a testing and evaluation system and method for the permeability coefficient of modified expansive soil under wet-dry cycles are provided. This system can monitor the crack development of a modified expansive soil under rainfall-evaporation cycles, test the swelling force, water content, matrix suction, and permeability coefficient of the soil sample in any direction during the permeability saturation process, and evaluate the permeability characteristics of the modified expansive soil based on the results.

[0008] The beneficial effects of the above scheme are:

[0009] 1) This invention can monitor the changes in swelling force, water content, and matrix suction in any direction during the seepage saturation process of expansive soil in real time by embedding an elastic pressure sensor and sensing optical fiber.

[0010] 2) This invention simulates the natural rainfall-evaporation environment using a rainfall-evaporation device and records the crack parameters of soil samples during the evaporation process, thereby more realistically reflecting the crack characteristics of modified expansive soil under natural conditions and its influence on permeability.

[0011] 3) This invention not only considers the changes in permeability coefficient, permeability saturation time, and swelling force, but also monitors the changes in cracks in expansive soil during the evaporation process, thereby providing a more comprehensive analysis and evaluation of the permeability characteristics of modified expansive soil. Attached Figure Description

[0012] Picture 1 This is a schematic diagram of the evaluation system provided in an embodiment of the present invention;

[0013] Picture 2 This is a schematic diagram of the sample chamber in the evaluation system of the present invention;

[0014] Picture 3 This is a schematic diagram of the elastic pressure sensor in the evaluation system of the present invention.

[0015] Wherein: 1-Cylindrical cylinder; 2-Sleeve; 3-Soil sample to be tested; 4-Permeable structure; 5-Elastic pressure sensor I; 6-Protruding base; 7-Central hole of protruding base; 8-Top cover; 9-Top cover hole; 10-Rubber sealing ring; 11-Threaded rod; 12-Base plate; 13-Rubber support; 14-Bolt and nut; 15-Pressure threaded rod; 16-Handwheel; 17-Pressure beam; 18-Water tank; 19- 20-Water supply pipe; 21-Water supply valve; 22-Variable head pipe; 23-Drainage pipe; 24-Water storage bottle; 25-Carrier plate; 26-Water inlet pipe; 27-Water outlet pipe; 28-Blower; 29-Heating device; 30-High-definition camera; 31-Water delivery pipe; 32-Rain spray nozzle; 33-Rain valve; 34-Sensing fiber optic cable; 35-Data converter; 36-Computer; 37-Flexible structure; 38-Pressure sensor. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0019] like Picture 1 to Picture 3 As shown, the modified expansive soil permeability coefficient testing and evaluation system under wet-dry cycles provided in the embodiments of the present invention includes: a sample chamber, a support frame, a loading mechanism, a permeability system, a rainfall-evaporation device, a data acquisition system, and an evaluation module. The sample chamber includes a cylindrical cylinder 1 and a sleeve 2, with the sleeve 2 fitted over the outer side of the cylindrical cylinder 1. The cylindrical cylinder 1 contains a soil sample 3 to be tested. The bottom of the soil sample 3 is provided with a permeable structure 4, an elastic pressure sensor 5, and a raised base 6 in sequence. The raised base 6 has a base hole 7 in the center. The top of the soil sample 3 is arranged in sequence with a permeable structure, an elastic pressure sensor II, and a top cover 8. The top cover 8 has a top cover hole 9. The bottom surfaces of the sleeve 2 and the cylindrical tube 1 are flush with the bottom of the raised base 6. The top surfaces of the sleeve 2 and the cylindrical tube 1 are flush with the top surface of the top cover 8. A rubber sealing ring 10 is provided between the sleeve 2 and the cylindrical tube 1. The upper and lower ends of the cylindrical tube 1 are tightly fitted with the top cover 8 and the raised base 6 by means of the rubber sealing ring 10. An elastic pressure sensor III is arranged between the sleeve 2 and the cylindrical tube 1.

[0020] The support frame includes a threaded rod 11, a base plate 12, and a rubber support 13. The threaded rod 11 is fixed to the base plate 12 by the rubber support 13, and the raised base 6 is fixed to the base plate 12 by bolts and nuts 14.

[0021] The loading mechanism includes a pressure threaded rod 15, a handwheel 16, and a pressure crossbeam 17. The pressure threaded rod 15 passes through the pressure crossbeam 17 and contacts the top cover 8. The two ends of the pressure crossbeam 17 are connected to the threaded rods 11 on both sides. The handwheel 16 is installed on the pressure threaded rod 15.

[0022] The infiltration system includes a water tank 18, a water supply pipe 19, a water supply valve 20, a variable head pipe 21, a drain pipe 22, a water storage bottle 23, and a support plate 24. One end of the water supply pipe 19 is connected to the water tank 18, and the other end of the water supply pipe 19 is connected to the inlet pipe 25 and the variable head pipe 21 through a three-way flexible hose. The inlet pipe 25 is connected to the round hole 7 of the base. One end of the drain pipe 22 is connected to the outlet pipe 26 on the round hole 9 of the top cover through a flexible hose. The other end of the drain pipe 22 is connected to the water storage bottle 23. The water storage bottle 23 is placed on the support plate 24. The variable head pipe 21 and the side wall of the water storage bottle 23 are marked with graduations.

[0023] The rainfall-evaporation device includes a rainfall system, a blower 27, a heating device 28, and a high-definition camera 29. The rainfall system includes a water supply pipe 30, a rainfall nozzle 31, and a rainfall valve 32. One end of the water supply pipe 30 is connected to a water tank 18, and the other end of the water supply pipe 30 is connected to the rainfall nozzle 31. The high-definition camera 29 and the rainfall nozzle 31 are both positioned directly above the soil sample 3 to be tested. The blower 27 and the heating device 28 are symmetrically arranged on the threaded rods 11 on both sides.

[0024] The data acquisition system includes a sensing fiber optic cable 33, a data converter 34, an elastic pressure sensor I5, an elastic pressure sensor II, an elastic pressure sensor III, and a high-definition camera 29. The sensing fiber optic cable 33 is spirally arranged in the soil sample 3 to be tested. Both ends of the sensing fiber optic cable 33 are connected to the data converter 34. The elastic pressure sensor I5, the elastic pressure sensor II, the elastic pressure sensor III, and the high-definition camera 29 are connected to the data converter 34 via wireless signals.

[0025] The evaluation module includes a computer 35, and a data converter 34 transmits data signals to the computer 35 via a data cable 36.

[0026] Specifically, in this invention, the sensing optical fiber 33 is arranged in a spiral shape in the soil sample 3 to be tested. The spacing between each ring of sensing optical fiber 33 is 1 / 10 of the height of the soil sample, which can monitor the water content and matrix suction of the soil sample in real time.

[0027] Specifically, in this invention, the elastic pressure sensor III arranged between the sleeve 2 and the cylindrical tube 1 is distributed at equal intervals along the height of the soil sample 3 to be tested, with a spacing of 1 / 3 to 1 / 5 of the soil sample height; the elastic pressure sensor arranged between the upper permeable structure and the top cover 8, and between the lower permeable structure 4 and the raised base 6, is evenly arranged along the cross-section of the soil sample 3 to be tested.

[0028] Specifically, in this invention, the elastic pressure sensor I5, elastic pressure sensor II, and elastic pressure sensor III have the same structure and are composed of an elastic component 37 connected to a pressure sensor 38. The elastic component 37 reserves expansion and deformation space for the soil sample 3 to be tested, and can monitor the lateral and vertical expansion forces of the soil sample 3 to be tested in real time during the infiltration saturation process.

[0029] Specifically, in this invention, the cylindrical tube 1 is an ultra-flexible membrane to allow the soil sample 3 to be tested inside to undergo arbitrary lateral expansion and deformation.

[0030] The method for evaluating the permeability coefficient of modified expansive soil under wet-dry cycles in this invention includes the following steps:

[0031] Step 1, Preparation Stage:

[0032] Step 1.1: Prepare the expansive soil sample to be tested and the modified material;

[0033] Step 1.2: Determine the hydrological and meteorological data for the test expansive soil area, including rainfall duration, rainfall intensity, rainfall frequency, temperature, and wind speed data;

[0034] Step 2, Rainfall-Evaporation Cycle Stage:

[0035] Step 2.1: Check whether the sample chamber, support frame, rain-evaporation device, permeation system and data acquisition system of the test and evaluation system are fully connected and operating smoothly;

[0036] Step 2.2: Prepare the soil sample 3 to be tested inside the cylindrical tube 1 and embed the sensing optical fiber 33;

[0037] Step 2.3: Let the prepared soil sample 3 stand for a period of time to achieve a better modification effect;

[0038] Step 2.4: Activate the rainfall system and administer rainfall according to the surveyed rainfall intensity;

[0039] Step 2.5: After the required rainfall duration is reached, the rainfall system will be shut down.

[0040] Step 2.6: Turn on the blower 27, the heating device 28 and the high-definition camera 29, and set the blower 27 and the heating device 28 according to the wind speed and temperature investigated.

[0041] Step 2.7: Observe and record the data transmitted by the data converter 34 on the evaluation module;

[0042] Step 2.8: After the surface crack morphology of the soil sample 3 stabilizes, turn off the blower 27, heating device 28 and high-definition camera 29.

[0043] Step 2.9: Repeat steps 2.4, 2.5, 2.6, 2.7, and 2.8 according to the designed number of rainfall-evaporation cycles;

[0044] Step 2.10: Observe the changes in data transmitted by the data converter 34 on the evaluation module, and record the surface porosity of the soil sample after the first and last rainfall-evaporation cycles. CIF 1 and CIF 2. The crack depths are respectively CD 1 and CD 2. The number of cracks are respectively NC 1 and NC 2. The number of fracture nodes are respectively NN 1 and NN 2. The total lengths of the cracks are respectively SL 1 and SL 2. The average width of the crack is AW 1 and AW 2. The number of soil clods is NCL 1 and NCL 2;

[0045] Step 3, Permeability and Expansion Force Testing Stage:

[0046] Step 3.1: Record the cross-sectional area of ​​the soil sample 3 to be tested as A, and the cross-sectional area of ​​the variable head pipe 21 as a;

[0047] Step 3.2: Assemble the complete sample chamber, loading mechanism, permeation system, and data acquisition system in sequence according to the test and evaluation system;

[0048] Step 3.3: Check again whether each part of the test evaluation system is functioning properly;

[0049] Step 3.4: Open water supply valve 1 201 and water supply valve 3 203 to allow the soil sample 3 to be tested to become saturated with water.

[0050] Step 3.5: Observe and record the data transmitted by the data converter 34 on the evaluation module;

[0051] Step 3.6: When there is a stable flow of water out of the drain pipe 22, close the water supply valve 1 201 and the water supply valve 3 203;

[0052] Step 3.7: Open water supply valve 1 201 and water supply valve 202 to fill water into the variable head pipe 21;

[0053] Step 3.8: When the water level in the variable head pipe 21 reaches the required height, close water supply valve 1 201 and water supply valve 2 202.

[0054] Step 3.9: Record the height of the initial water head position in the variable head pipe 21 from the circular hole 9 of the top cover 8. H 1;

[0055] Step 3.10: Open water supply valve 202 and water supply valve 303;

[0056] Step 3.11, experiencing Δ t After a certain time, close water supply valve 202 and water supply valve 303.

[0057] Step 3.12, record the height of the water head position in the variable head pipe 21 from the circular hole 9 of the top cover 8. H 2. The water output of drain pipe 22 is L The outlet temperature is T ;

[0058] Step 3.13, repeat steps 3.9, 3.10, 3.11 and 3.12 approximately 2 to 3 times;

[0059] Step 3.14, repeat steps 3.7, 3.8, 3.9, 3.10, 3.11, 3.12 and 3.13 approximately 5 to 6 times;

[0060] Step 3.15, calculate the permeability coefficient. ;

[0061] Step 3.16: Record the permeability coefficient of the soil sample to be tested, and use the average value of the permeability coefficients calculated from multiple tests as the final permeability coefficient of the soil sample to be tested. k ;

[0062] Step 3.17: Observe the changes in data transmitted by the data converter 34 on the evaluation module, and record the curves of water content change with time, matrix suction change with water content, and swelling force change with water content of the soil sample during the infiltration saturation process. Record the infiltration saturation time of the soil sample as follows: t、 The final matrix suction is s、 The final expansion force is p ;

[0063] Step 4: Organize the experimental equipment;

[0064] Step 5: Organize the experimental data;

[0065] Step 6, Evaluation Phase:

[0066] Step 6.1: Using the scoring method, assign different scores to the intervals of parameters in each test phase, and calculate the total score;

[0067] Step 6.2, the parameters for assigning fractures to the soil samples to be tested are shown in Table 1 and Table 2;

[0068] Table 1 Scoring of fissure parameters of soil samples after the first rainfall-evaporation.

[0069]

[0070] illustrate, CIF 1 ’ Modified expansive soil and unmodified expansive soil CIF The ratio of 1 to 1; CD 1 ’Modified expansive soil and unmodified expansive soil CD The ratio of 1 to 1; NC 1 ’ Modified expansive soil and unmodified expansive soil NC The ratio of 1 to 1; NN 1 ’ Modified expansive soil and unmodified expansive soil NN The ratio of 1 to 1; SL 1 ’ Modified expansive soil and unmodified expansive soil SL The ratio of 1 to 1; AW 1 ’ Modified expansive soil and unmodified expansive soil AW The ratio of 1 to 1; NCL 1 ’ Modified expansive soil and unmodified expansive soil NCL The ratio of 1 to 1;

[0071] Table 2 Scoring Table for Crack Parameters of Soil After Last Rainfall-Evaporation

[0072]

[0073] illustrate, CIF 2 ’ Modified expansive soil and unmodified expansive soil CIF The ratio of 2 values; CD 2 ’ Modified expansive soil and unmodified expansive soil CD The ratio of 2 values; NC 2 ’ Modified expansive soil and unmodified expansive soil NC The ratio of 2 values; NN 2 ’ Modified expansive soil and unmodified expansive soil NN The ratio of 2 values; SL 2 ’ Modified expansive soil and unmodified expansive soil SL The ratio of 2 values; AW 2 ’ Modified expansive soil and unmodified expansive soil AW The ratio of 2 values; NCL 2 ’ Modified expansive soil and unmodified expansive soil NCL The ratio of 2 values;

[0074] Step 6.3, according to the parameters in Table 1 CIF 1 ’ , CD 1 ’ , NC 1 ’ , NN 1’ , SL 1 ’ , AW 1 ’ , NCL 1 ’ The interval in which it is located determines the score for each parameter, and uses... S 1,1 Calculate the score of the fracture parameters of the soil sample after the first wet-dry cycle by summing the scores of each parameter. S 1,1 ;

[0075] Step 6.4, according to the parameters in Table 2 CIF 2 ’ , CD 2 ’ , NC 2 ’ , NN 2 ’ , SL 2 ’ , AW 2 ’ , NCL 2 ’ The interval in which it is located determines the score for each parameter, and uses... S 1,2 Calculate the score of the fracture parameters of the soil sample after the last wet-dry cycle by summing the scores of each parameter. S 1,2 ;

[0076] Step 6.5, combining the influence of the number of wet-dry cycles on the cracking characteristics of the soil, according to S 1 = 0.7 S 1,1 +0.3 S 1,2 Calculate the score of the fracture parameters of the soil sample to be tested. S 1;

[0077] Step 6.6, the permeability saturation parameter assignment table for the soil sample to be tested is shown in Table 3;

[0078] Table 3 Scoring Table for Permeability Saturation Parameters of Soil Samples to be Tested

[0079]

[0080] illustrate: t ’ Modified expansive soil and unmodified expansive soil t The ratio of values; s ’ Unmodified expansive soil and modified expansive soil s The ratio of values; p ’ Modified expansive soil and unmodified expansive soilp The ratio of values; k ’ Modified expansive soil and unmodified expansive soil k The ratio of values;

[0081] Step 6.7, according to the parameters in Table 3 t ’ 、s ’ , p ’ , k ’ The interval in which it is located determines the score for each parameter, and uses... S 2. Calculate the score for the permeability saturation parameter of the soil sample by summing the scores assigned to each parameter. S 2;

[0082] Step 6.8, combining the variation characteristics of the fracture parameters and permeability saturation parameters of the soil sample to be tested, and considering the magnitude of the influence of each parameter on the modification effect of expansive soil, according to... S =0.6 S 1 + 0.4 S 2. Calculate the final score S ;

[0083] Step 6.9, based on the final score S The modification effect of expansive soil after several rainfall-evaporation wet-dry cycles is shown in Table 4 below:

[0084]

[0085] This invention has been repeatedly tested and verified, and has achieved satisfactory trial results.

[0086] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for testing and evaluating the permeability coefficient of modified expansive soil under wet-dry cycles, characterized in that, include: The sample chamber comprises a support frame, a loading mechanism, a permeation system, a rainfall-evaporation device, a data acquisition system, and an evaluation module. The sample chamber includes a cylindrical tube (1) and a sleeve (2). The sleeve (2) is fitted over the outside of the cylindrical tube (1). The cylindrical tube (1) contains a soil sample (3) to be tested. The bottom of the soil sample (3) is provided with a permeable structure (4), an elastic pressure sensor I (5), and a raised base (6). The raised base (6) has a circular hole (7) in the center. The top of the soil sample (3) is provided with an upper permeable structure, an elastic pressure sensor II, and a top cover (4). 8), the top cover (8) is provided with a top cover round hole (9), the bottom surface of the sleeve (2) and the cylindrical tube (1) is flush with the protruding bottom end of the raised base (6), the top surface of the sleeve (2) and the cylindrical tube (1) is flush with the top surface of the top cover (8), a rubber sealing ring (10) is provided between the sleeve (2) and the cylindrical tube (1), the upper end and the lower end of the cylindrical tube (1) are tightly fitted with the top cover (8) and the raised base (6) respectively by the rubber sealing ring (10), and an elastic pressure sensor III is arranged between the sleeve (2) and the cylindrical tube (1); The support frame includes a threaded rod (11), a base plate (12) and a rubber support (13). The threaded rod (11) is fixed on the base plate (12) by the rubber support (13), and the raised base (6) is fixed on the base plate (12) by bolts and nuts (14). The loading mechanism includes a pressure threaded rod (15), a handwheel (16), and a pressure beam (17). The pressure threaded rod (15) passes through the pressure beam (17) and contacts the top cover (8). The two ends of the pressure beam (17) are connected to the threaded rods (11) on both sides. The handwheel (16) is installed on the pressure threaded rod (15). The permeation system includes a water tank (18), a water supply pipe (19), a water supply valve one (201), a water supply valve two (202), a water supply valve three (203), a variable head pipe (21), a drain pipe (22), a water storage bottle (23), and a carrying plate (24); one end of the water supply pipe (19) is connected to the water tank (18), and the other end of the water supply pipe (19) is connected to the inlet pipe (25) and the variable head pipe (21) respectively through a three-way flexible hose; the inlet pipe (25) is connected to the round hole (7) of the base; one end of the drain pipe (22) is connected to the outlet pipe (26) on the round hole (9) of the top cover through a flexible hose, and the other end of the drain pipe (22) is connected to the water storage bottle (23); the water storage bottle (23) is placed on the carrying plate (24); the variable head pipe (21) and the water storage bottle (23) are marked with graduations on their side walls; The rainfall-evaporation device includes a rainfall system, a blower (27), a heating device (28), and a high-definition camera (29). The rainfall system includes a water pipe (30), a rainfall nozzle (31), and a rainfall valve (32). One end of the water pipe (30) is connected to the water tank (18), and the other end of the water pipe (30) is connected to the rainfall nozzle (31). The high-definition camera (29) and the rainfall nozzle (31) are both positioned directly above the soil sample (3) to be tested. The blower (27) and the heating device (28) are symmetrically positioned on the threaded rods (11) on both sides. The data acquisition system includes a sensing fiber (33), a data converter (34), an elastic pressure sensor I (5), an elastic pressure sensor II, an elastic pressure sensor III, and a high-definition camera (29). The sensing fiber (33) is spirally arranged in the soil sample (3) to be tested. Both ends of the sensing fiber (33) are connected to the data converter (34). The elastic pressure sensor I (5), the elastic pressure sensor II, the elastic pressure sensor III, and the high-definition camera (29) are connected to the data converter (34) via wireless signals. The evaluation module includes a computer (35), and the data converter (34) transmits data signals to the computer (35) via a data line (36).

2. The permeability coefficient testing and evaluation system for modified expansive soil under wet-dry cycles according to claim 1, characterized in that, The sensing optical fiber (33) is spirally arranged in the soil sample (3) to be tested. The spacing between each ring of sensing optical fiber (33) is 1 / 10 of the height of the soil sample, which can monitor the water content and matrix suction of the soil sample in real time.

3. The permeability coefficient testing and evaluation system for modified expansive soil under wet-dry cycles according to claim 1, characterized in that, The elastic pressure sensor III, which is arranged between the sleeve (2) and the cylindrical tube (1), is distributed at equal intervals along the height of the soil sample (3) to be tested, with a spacing of 1 / 3 to 1 / 5 of the height of the soil sample; the elastic pressure sensor, which is arranged between the upper permeable structure and the top cover (8) and between the lower permeable structure (4) and the raised base (6), is evenly arranged along the cross-section of the soil sample (3) to be tested.

4. The permeability coefficient testing and evaluation system for modified expansive soil under wet-dry cycles according to claim 1 or 3, characterized in that, The elastic pressure sensor I (5), the elastic pressure sensor II, and the elastic pressure sensor III have the same structure and are composed of an elastic component (37) connected to a pressure sensor (38). The elastic component (37) provides expansion and deformation space for the soil sample (3) to be tested, and can monitor the lateral and vertical expansion forces of the soil sample (3) to be tested in real time during the infiltration saturation process.

5. A method for evaluating the permeability coefficient of modified expansive soil under wet-dry cycles, characterized in that, The application of the permeability coefficient testing and evaluation system for modified expansive soil under wet-dry cycles as described in any one of claims 1-4 includes the following steps: Step 1, Preparation Stage: Step 1.1: Prepare the expansive soil sample to be tested and the modified material; Step 1.2: Determine the hydrological and meteorological data for the test expansive soil area, including rainfall duration, rainfall intensity, rainfall frequency, temperature, and wind speed data; Step 2, Rainfall-Evaporation Cycle Stage: Step 2.1: Check whether the sample chamber, support frame, rain-evaporation device, permeation system and data acquisition system of the test and evaluation system are completely connected and operating smoothly; Step 2.2: Prepare the soil sample (3) to be tested inside the cylindrical tube (1) and embed the sensing optical fiber (33). Step 2.3: Let the prepared soil sample (3) stand for a period of time to achieve a better modification effect; Step 2.4: Activate the rainfall system and administer rainfall according to the surveyed rainfall intensity; Step 2.5: After the required rainfall duration is reached, the rainfall system will be shut down. Step 2.6: Turn on the blower (27), the heating device (28) and the high-definition camera (29), and set the blower (27) and the heating device (28) according to the wind speed and temperature investigated; Step 2.7: Observe and record the data transmitted by the data converter (34) on the evaluation module; Step 2.8: After the surface crack morphology of the soil sample (3) is stable, turn off the blower (27), heating device (28) and high-definition camera (29). Step 2.9: Repeat steps 2.4, 2.5, 2.6, 2.7, and 2.8 according to the designed number of rainfall-evaporation cycles; Step 2.10: Observe the changes in data transmitted by the data converter (34) on the evaluation module, and record the surface porosity of the soil sample after the first and last rainfall-evaporation cycles. CIF 1 and CIF 2. The crack depths are respectively CD 1 and CD 2. The number of cracks are respectively NC 1 and NC 2. The number of fracture nodes are respectively NN 1 and NN 2. The total lengths of the cracks are respectively SL 1 and SL 2. The average width of the crack is AW 1 and AW 2. The number of soil clods is NCL 1 and NCL 2; Step 3, Permeability and Expansion Force Testing Stage: Step 3.1: Record the cross-sectional area of ​​the soil sample (3) to be tested as A, and the cross-sectional area of ​​the variable head pipe (21) as a; Step 3.2: Assemble the complete sample chamber, loading mechanism, permeation system, and data acquisition system in sequence according to the test and evaluation system described above; Step 3.3: Check again whether each part of the test evaluation system is functioning properly; Step 3.4: Open water supply valve one (201) and water supply valve three (203) to saturate the soil sample (3) to be tested; Step 3.5: Observe and record the data transmitted by the data converter (34) on the evaluation module; Step 3.6, when there is a stable flow of water out of the drain pipe (22), close the water supply valve one (201) and the water supply valve three (203). Step 3.7: Open water supply valve one (201) and water supply valve two (202) to fill water into the variable head pipe (21); Step 3.8: When the water level in the variable head pipe (21) reaches the required height, close water supply valve one (201) and water supply valve two (202). Step 3.9, record the height of the initial water head position in the variable head pipe (21) from the circular hole (9) of the top cover (8). H 1; Step 3.10: Open water supply valve 2 (202) and water supply valve 3 (203); Step 3.11, experiencing Δ t After a certain time, close water supply valve 2 (202) and water supply valve 3 (203). Step 3.12, record the height of the water head position in the variable head pipe (21) from the circular hole (9) of the top cover (8). H 2. The water output of the drain pipe (22) is L The outlet temperature is T ; Step 3.13, repeat steps 3.9, 3.10, 3.11 and 3.12 2 to 3 times; Step 3.14, repeat steps 3.7, 3.8, 3.9, 3.10, 3.11, 3.12 and 3.13 5 to 6 times; Step 3.15, calculate the permeability coefficient. ; Step 3.16: Record the permeability coefficient of the soil sample to be tested, and use the average value of the permeability coefficients calculated from multiple tests as the final permeability coefficient of the soil sample to be tested. k ; Step 3.17: Observe the data changes transmitted by the data converter (34) on the evaluation module, record the curves of water content change with time, matrix suction change with water content, and swelling force change with water content of the soil sample during the infiltration saturation process, and record the infiltration saturation time of the soil sample as follows: t、 The final matrix suction is s、 The final expansion force is p ; Step 4: Organize the experimental equipment; Step 5: Organize the experimental data; Step 6, Evaluation Phase: Step 6.1: Using the scoring method, assign different scores to the intervals of parameter division for each test stage, and calculate the total score; Step 6.2, the parameters for assigning fractures to the soil samples to be tested are shown in Table 1 and Table 2; Table 1. Scoring of fracture parameters of soil samples after the first rainfall-evaporation. illustrate, CIF 1 ’ Modified expansive soil and unmodified expansive soil CIF The ratio of 1 to 1; CD 1 ’ Modified expansive soil and unmodified expansive soil CD The ratio of 1 to 1; NC 1 ’ Modified expansive soil and unmodified expansive soil NC The ratio of 1 to 1; NN 1 ’ Modified expansive soil and unmodified expansive soil NN The ratio of 1 to 1; SL 1 ’ Modified expansive soil and unmodified expansive soil SL The ratio of 1 to 1; AW 1 ’ Modified expansive soil and unmodified expansive soil AW The ratio of 1 to 1; NCL 1 ’ Modified expansive soil and unmodified expansive soil NCL The ratio of 1 to 1; Table 2 Scoring Table for Crack Parameters of Soil After Last Rainfall-Evaporation illustrate, CIF 2 ’ Modified expansive soil and unmodified expansive soil CIF The ratio of 2 values; CD 2 ’ Modified expansive soil and unmodified expansive soil CD The ratio of 2 values; NC 2 ’ Modified expansive soil and unmodified expansive soil NC The ratio of 2 values; NN 2 ’ Modified expansive soil and unmodified expansive soil NN The ratio of 2 values; SL 2 ’ Modified expansive soil and unmodified expansive soil SL The ratio of 2 values; AW 2 ’ Modified expansive soil and unmodified expansive soil AW The ratio of 2 values; NCL 2 ’ Modified expansive soil and unmodified expansive soil NCL The ratio of 2 values; Step 6.3, according to the parameters in Table 1 CIF 1 ’ , CD 1 ’ , NC 1 ’ , NN 1 ’ , SL 1 ’ , AW 1 ’ , NCL 1 ’ The interval in which it is located determines the score for each parameter, and uses... S 1,1 Calculate the score of the fracture parameters of the soil sample after the first wet-dry cycle by summing the scores of each parameter. S 1,1 ; Step 6.4, according to the parameters in Table 2 CIF 2 ’ , CD 2 ’ , NC 2 ’ , NN 2 ’ , SL 2 ’ , AW 2 ’ , NCL 2 ’ The interval in which it is located determines the score for each parameter, and uses... S 1,2 Calculate the score of the fracture parameters of the soil sample after the last wet-dry cycle by summing the scores of each parameter. S 1,2 ; Step 6.5, combining the influence of the number of wet-dry cycles on the cracking characteristics of the soil, according to S 1 = 0.7 S 1,1 +0.3 S 1,2 Calculate the score of the fracture parameters of the soil sample to be tested. S 1; Step 6.6, the permeability saturation parameter assignment table for the soil sample to be tested is shown in Table 3; Table 3 Scoring Table for Permeability Saturation Parameters of Soil Samples to be Tested illustrate: t ’ Modified expansive soil and unmodified expansive soil t The ratio of values; s ’ Unmodified expansive soil and modified expansive soil s The ratio of values; p ’ Modified expansive soil and unmodified expansive soil p The ratio of values; k ’ Modified expansive soil and unmodified expansive soil k The ratio of values; Step 6.7, according to the parameters in Table 3 t ’ 、s ’ , p ’ , k ’ The interval in which it is located determines the score for each parameter, and uses... S 2. Calculate the score for the permeability saturation parameter of the soil sample by summing the scores assigned to each parameter. S 2; Step 6.8, combining the variation characteristics of the fracture parameters and permeability saturation parameters of the soil sample to be tested, and considering the magnitude of the influence of each parameter on the modification effect of expansive soil, according to... S =0.6 S 1 + 0.4 S 2. Calculate the final score S ; Step 6.9, based on the final score S The score is determined by assessing the modification effect of expansive soil after several rainfall-evaporation wet-dry cycles. S The effects of modification are shown in Table 4 below; Table 4 Scoring Table for the Modification Effect of Expansive Soil 。

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