Multi-scale research method for soil body strength degradation under dry-wet cycle action

Abstract

The invention discloses a multi-scale research method for soil body strength degradation under the dry-wet cycle effect. The multi-scale research method comprises the following steps: S1, preparing a sample from collected test soil under the dry-wet cycle effect; s2, testing the macroscopic shear strength of the soil body by using the triaxial sample prepared in the step S1; s3, the cutting ring sample prepared in the step S1 is used for soil microcosmic fracture testing; s4, carrying out a soil body micro-pore test by utilizing the microstructure sample prepared in the step S1; and S5, analyzing the soil body strength degradation rule of the collected test soil under the dry-wet cycle action by using the test results of the soil body macroscopic shear strength test, the soil body microcosmic crack test and the soil body microcosmic pore test. According to the method, through multi-scale analysis, related enterprises can more comprehensively evaluate the degradation rule of the soil body under the dry-wet cycle effect, so that an engineering construction design scheme is optimized, and the risks of landslide, collapse and other engineering accidents caused by soil body strength reduction are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering, and particularly relates to a multi-scale research method for soil strength degradation under the action of dry-wet cycles. Background Art

[0002] Wet-dry cycles are a key environmental factor contributing to soil strength degradation, creating significant engineering risks in slope engineering, roadbed stability, and geological disaster prevention. Traditional research has focused on macroscopic mechanical property testing, while methodological deficiencies exist in studying multi-scale synergistic degradation mechanisms, hindering the development of long-term remediation technologies.

[0003] Existing macroscopic shear strength measurement techniques primarily utilize triaxial and direct shear tests. Microscopic cracking studies utilize qualitative analysis through high-definition photography and quantitative analysis using CIAS software. Microstructural evolution studies primarily utilize CT scanning, SEM scanning, and other techniques. However, most existing methods focus on describing macroscopic phenomena, with limited explanations of microscopic mechanisms. These methods often focus on single-scale analysis and lack multi-scale correlations.

[0004] Therefore, it is necessary to design a multi-scale research method for soil strength degradation under the action of drying and wetting cycles. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-scale research method for the strength degradation of soil under the action of dry-wet cycles, so as to solve the problem that the existing methods proposed in the background technology are mostly based on the description of macroscopic phenomena, with little explanation of microscopic mechanisms, more single-scale analysis and less multi-scale correlation.

[0006] To achieve the above objectives, the present invention provides a multi-scale study method for soil strength degradation under dry-wet cycles, comprising the following steps:

[0007] S1. Prepare samples of the collected test soil according to the optimal moisture content and maximum dry density, and subject the samples to a dry-wet cycle; the samples include triaxial samples, ring knife samples, and microstructure samples;

[0008] The sample preparation process includes at least one dry-wet cycle process, and one dry-wet cycle process includes a dehumidification process and a humidification process. The dehumidification process adopts a natural air drying method, and the humidification process adopts a bidirectional water film humidification method;

[0009] S2. Performing a soil macroscopic shear strength test using the triaxial specimen prepared in step S1;

[0010] S3, using the ring cutter specimen prepared in step S1 to perform a soil micro-crack test;

[0011] S4. Performing soil micropore testing using the microstructure sample prepared in step S1;

[0012] S5. Use the test results of soil macro shear strength test, soil micro crack test and soil micro pore test to analyze the soil strength degradation law of the collected test soil under the action of dry-wet cycle.

[0013] In a specific embodiment, the testing equipment used for the soil macro-shear strength test includes an SLB-1A stress-strain controlled triaxial mainframe, a confining pressure and pore pressure measurement controller, and a back pressure and volume change measurement controller; the testing equipment used for the soil micro-crack test includes a high-definition camera; the testing equipment used for the soil micro-pore test includes a Scientz-N freeze dryer and an AutoPore V fully automatic mercury intrusion pore size analyzer.

[0014] In a specific embodiment, in said S1, when preparing the sample under the action of dry-wet cycle, the specific steps of preparing the triaxial sample include:

[0015] S1.1.1. First, obtain the maximum dry density and optimal moisture content of the test soil based on indoor compaction tests;

[0016] S1.1.2. Sieve and dry the test soil. Mix the test soil and water in a container to the optimal moisture content. Stir evenly and seal with plastic wrap for 23-25 hours.

[0017] S1.1.3. After the filling is completed, the total mass of the triaxial specimen is calculated based on the volume of the triaxial mold, the maximum dry density, and the optimal moisture content. The soil is then compacted into triaxial specimens using the triaxial mold using the layered compaction method.

[0018] S1.1.4. Place the sample in a saturation tank to saturate it;

[0019] S1.1.5. Perform a dry-wet cycle on the saturated triaxial specimens.

[0020] S1.1.6. During the dry-wet cycle, weigh the triaxial specimen regularly. When the triaxial specimen reaches the optimum moisture content, wrap it in plastic wrap and set aside.

[0021] In a specific embodiment, the dehumidification process is as follows: the saturated triaxial specimen is removed from the mold and naturally air-dried until the mass of the triaxial specimen remains unchanged within 3 to 5 days, thus completing the dehumidification process;

[0022] The humidification process is:

[0023] The dehumidified triaxial specimen is placed between two permeable stones, with a piece of geotextile filter paper between the permeable stone and the triaxial specimen to prevent fine particles from clogging the pores of the permeable stone; the permeable stone is placed on an absorbent sponge, and the lower permeable stone absorbs water through the sponge to humidify the triaxial specimen, while the upper end is humidified by adding water to the permeable stone with an ear bulb at regular intervals; when the moisture on the sample surface cannot penetrate into the soil, wrap the triaxial specimen with plastic wrap for 12 hours to ensure uniform moisture distribution inside the soil sample, and the humidification process is completed.

[0024] In a specific embodiment, in said S1, when preparing the sample under the action of dry-wet cycle, the specific steps of preparing the ring knife sample include:

[0025] S1.2.1. First, obtain the maximum dry density and optimum moisture content of the test soil based on indoor compaction tests;

[0026] S1.2.2. Sieve and dry the test soil. Mix the test soil and water in a container to the optimal moisture content. Stir evenly and seal with plastic wrap for 23-25 hours.

[0027] S1.2.3. After the filling is completed, the total mass of the ring knife sample is calculated based on the volume of the ring knife mold, the maximum dry density and the optimal moisture content, and then the soil is made into a ring knife sample using the ring knife mold;

[0028] S1.2.4. Place the sample in a saturation tank to saturate it;

[0029] S1.2.5. Perform a dry-wet cycle on the saturated knife ring specimen;

[0030] S1.2.6. During the dry-wet cycle, weigh the ring knife sample regularly. When the moisture content of the ring knife sample reaches the optimal moisture content, wrap it with plastic wrap and set aside.

[0031] In a specific embodiment, in said S1, when preparing the sample under the action of dry-wet cycle, the specific steps of preparing the microstructure sample include:

[0032] S1.3.1. First, obtain the maximum dry density and optimum moisture content of the test soil based on indoor compaction tests;

[0033] S1.3.2. Sieve and dry the test soil. Mix the test soil and water in a container to the optimal moisture content. Stir evenly and seal with plastic wrap for 23-25 hours.

[0034] S1.3.3. After the filling is completed, the total mass of the ring knife sample is calculated based on the ring knife mold volume, maximum dry density and optimal moisture content, and then the soil is made into a ring knife sample using the ring knife mold;

[0035] S1.3.4. Place the sample in a saturation tank to saturate it;

[0036] S1.3.5. Perform a dry-wet cycle on the saturated ring knife specimen;

[0037] S1.3.6. During the dry-wet cycle, the mass of the ring knife sample should be weighed regularly. When the moisture content of the ring knife sample is the optimal moisture content, a volume of less than 1cm2 should be cut from the inside of the ring knife sample. 3 The samples are reserved, that is, the microstructure samples.

[0038] In a specific embodiment, the soil macroscopic shear strength test adopts an unsaturated soil triaxial consolidation undrained shear test, that is, based on the correspondence between suction and moisture content in the soil-water characteristic curve, the suction is controlled by controlling the moisture content, and equal suction consolidation and shear are directly performed. After that, the suction of the shear sample is measured by the filter paper method to check whether the suction is close to the suction of the soil-water characteristic curve.

[0039] In a specific embodiment, in the soil macro shear strength test, when the sample enters the shear stage, the shearing is completed when the sample is sheared to a maximum deformation of 15%.

[0040] In a specific embodiment, the soil micro-crack test specifically comprises the following steps:

[0041] First, use a camera to take pictures of the cracks produced during each dry-wet cycle;

[0042] The image is then grayscaled and imported into the CIAS crack image analysis software to obtain a binary image. After that, the noise is removed to obtain a denoised image.

[0043] Then, the Segmentation and Crack modules are used to analyze the crack area and crack local parameters respectively;

[0044] By obtaining the crack parameters, calculating the crack ratio and the average crack width, the crack change and development law are analyzed.

[0045] In a specific embodiment, the soil micropore test comprises the following steps:

[0046] First, the microstructure sample is freeze-dried to remove the moisture in the sample with minimal damage to the internal structure of the sample;

[0047] The pore structure of the sample was then analyzed using a fully automatic mercury intrusion pore size analyzer.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention adopts a method of controlling the moisture content to achieve control of the suction, directly performs consolidation and shear tests, and finally tests the suction of the sheared sample by a filter paper method, thereby saving overall test time.

[0050] The present invention considers the test results under two hydraulic paths, dehumidification and humidification, respectively.

[0051] The present invention comprehensively analyzes the strength degradation mechanism of soil under dry-wet cycles at three scales: macroscopic, microscopic and microscopic.

[0052] Through multi-scale analysis (macroscopic shear strength, microscopic crack development, and microscopic pore evolution), the present invention enables relevant companies to more comprehensively evaluate the deterioration patterns of soil under the action of dry-wet cycles, thereby optimizing engineering construction design plans and reducing the risks of engineering accidents such as landslides and collapses caused by the decline in soil strength.

[0053] According to the evolution laws of microscopic pores and microcracks of the present invention, relevant enterprises can delay the process of soil deterioration by screening or developing more effective soil improvement materials (such as curing agents) or optimizing construction processes (such as compaction control and drainage design).

[0054] By analyzing the changes in soil properties under different numbers of dry-wet cycles, the present invention can help relevant companies formulate more targeted maintenance cycles and measures, thereby extending the service life of the project.

[0055] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention is further described in detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0057] Figure 1 It is a schematic diagram of a flow chart of an embodiment of the present invention;

[0058] Figure 2 This is a macro shear strength test result of the dehumidification process of an embodiment of the present invention: stress-strain curve;

[0059] Figure 3 This is a macro shear strength test result of the humidification process of an embodiment of the present invention: stress-strain curve;

[0060] Figure 4 This is a graph showing changes in crack parameters with the number of dry-wet cycles during the dehumidification process of one embodiment of the present invention;

[0061] Figure 5This is a comparison diagram of the change in surface crack rate during the dehumidification and humidification process of an embodiment of the present invention;

[0062] Figure 6 This is a graph showing changes in pore density with the number of dry-wet cycles during the dehumidification process of one embodiment of the present invention;

[0063] Figure 7 This is a graph showing changes in pore density with the number of dry-wet cycles during the humidification process of an embodiment of the present invention. DETAILED DESCRIPTION

[0064] The embodiments of the present invention are described in detail below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0065] Example 1

[0066] The present invention provides a multi-scale research method for soil strength degradation under dry-wet cycles, comprising the following steps:

[0067] S1. Sample preparation under dry-wet cycle.

[0068] The collected test soil is subjected to dry-wet cycles to prepare samples; the samples include triaxial samples for shear strength tests, ring knife samples for crack tests, and microstructure samples with a volume of less than 1 cubic centimeter for mercury intrusion tests.

[0069] In order to more clearly highlight the influence of dry-wet cycles on the shear strength of soil, this test adopts the method of conducting dry-wet cycle tests at intervals to determine the test rules when the number of dry-wet cycles N = 1, 3, and 5. That is, when preparing samples under the action of dry-wet cycles, the triaxial samples were prepared with 1 dry-wet cycle, 3 dry-wet cycles, and 5 dry-wet cycles respectively; similarly, the ring knife samples were prepared with 1 dry-wet cycle, 3 dry-wet cycles, and 5 dry-wet cycles respectively; the microstructure samples were prepared with 1 dry-wet cycle, 3 dry-wet cycles, and 5 dry-wet cycles respectively.

[0070] S1.1. Preparation of triaxial specimens.

[0071] S1.1.1. According to the indoor compaction test, the maximum dry density of the test soil used in the present invention is 1.67 g / cm 3, the optimal moisture content is 18.3%. Different soils have different optimal moisture contents. Based on the indoor standard compaction test, the compaction curve of the soil can be obtained (moisture content on the horizontal axis, dry density on the vertical axis). The moisture content and dry density corresponding to the peak of the curve are the optimal moisture content and maximum dry density of the soil. The optimal moisture content is the moisture content at which the soil reaches its most compacted state under a given compaction energy, and the maximum dry density is the most compacted state that the soil can reach at the optimal moisture content. Both are important indicators for evaluating soil stability.

[0072] S1.1.2. Pass the test soil through a 2 mm sieve and oven dry at 105°C. Then, add the soil to the bucket in layers, setting the optimal moisture content at 18.3%, and mix thoroughly. Seal the bucket with plastic wrap and let it sit for 24 hours.

[0073] S1.1.3. After the filling is completed, according to the volume of the three-axis mold (diameter 3.91cm, height 8cm) and the maximum dry density 1.67g / cm 3 The required dry soil mass is calculated as:

[0074] According to the optimal moisture content of 18.3%, the mass of water to be added is: m w =m d *18.3%=160.32*18.3%=29.34g

[0075] Total mass: m 总 =m d +m w =29.34g+160.32g=189.66g

[0076] The soil is then compacted into triaxial specimens using a static triaxial mold using the layered compaction method: Divide the total amount of test soil obtained from the above formula by 5 to obtain the amount per layer. Add each layer to the triaxial mold and compact. Apply an appropriate amount of petroleum jelly to the bottom and mold walls before compaction. Add a layer of soil, level it, and then compact it using a static triaxial press. After compaction, roughen the surface before adding the next layer of soil and compacting it. Repeat this process to form the triaxial specimen. Immediately wrap the triaxial specimen in plastic wrap to prevent moisture loss.

[0077] S1.1.4. For saturated specimens, place the triaxial specimen in a triaxial saturator and secure it in a vacuum saturation cylinder. Add water until the water exceeds the triaxial saturator. Pump air into the vacuum saturation cylinder until it reaches a negative atmospheric pressure, then close the exhaust valve and wait 24 hours for it to be fully saturated.

[0078] S1.1.5. Dry-wet cycle. The dehumidification process uses natural air drying. After saturation, the triaxial specimens are removed from the mold and weighed at saturation. During the air drying process, if the specimen mass remains constant for 3–5 days, which is the lowest mass, the dehumidification process is considered complete. The humidification method uses a bidirectional water film humidification method. The dehumidified triaxial specimens are placed between two permeable stones. A piece of geotextile filter paper is placed between the permeable stones and the triaxial specimens to prevent fine particles from clogging the permeable stone pores. The permeable stones are placed on an absorbent sponge. The lower permeable stone absorbs water from the sponge to humidify the triaxial specimens. The upper permeable stone is periodically humidified by adding water to the permeable stone using an ear bulb. If the surface moisture of the specimens cannot penetrate the soil, wrap the triaxial specimens with plastic wrap for 12 hours to ensure uniform moisture distribution within the soil. The humidification process is considered complete.

[0079] S1.1.6. Obtain the samples required for the test. During the dehumidification and humidification process, weigh the sample regularly. When the moisture content of the sample reaches 18.3%, wrap it in plastic wrap and set aside.

[0080] S1.2. Preparation of ring knife specimens.

[0081] S1.2.1. According to the indoor compaction test, the maximum dry density of the test soil used in the present invention is 1.67 g / cm 3 , the optimal moisture content is 18.3%.

[0082] S1.2.2. Pass the test soil through a 2 mm sieve and oven dry at 105°C. Then, add the soil to a small bucket in layers to an optimal moisture content of 18.3% and mix thoroughly. Seal the bucket with plastic wrap and let it sit for 24 hours.

[0083] S1.2.3, after the stuffing is completed, according to the volume of the ring die (diameter 6.18cm, height 2cm) and the maximum dry density 1.67g / cm 3 The required dry soil mass can be calculated as:

[0084] According to the optimal moisture content of 18.3%, the mass of water to be added can be calculated as follows: m w =m d *18.3%=100.2*18.3%=18.3g

[0085] Total mass: m 总 =m d +m w =100.2g+18.3g=118.5g.

[0086] Then, use a ring knife mold to form a ring knife specimen: add the total mass of the test soil after the filling is completed according to the above formula to the ring knife mold and compact it. After the ring knife specimen is formed, immediately wrap it with plastic wrap to prevent moisture loss.

[0087] S1.2.4. For saturated samples, place the knife ring sample in a knife ring saturator and fix it in a vacuum saturation cylinder. Add water until the water exceeds the knife ring saturator. Pump air into the vacuum saturation cylinder until the pressure reaches one atmosphere below zero. Close the vacuum valve and wait for 24 hours for it to be fully saturated.

[0088] S1.2.5. Dry-wet cycle. The dehumidification process uses natural air drying. After saturation, the ring knife specimen is removed from the mold and weighed at saturation. During the air drying process, if the specimen mass remains unchanged for 3-5 days (the minimum specimen mass), the dehumidification process is considered complete. The humidification method uses a two-way water film humidification method. The dehumidified ring knife specimen is placed between two permeable stones. A piece of geotextile filter paper is placed between the permeable stone and the ring knife specimen to prevent fine particles from clogging the permeable stone pores. The permeable stone is placed on an absorbent sponge. The lower permeable stone absorbs water from the sponge to humidify the ring knife specimen. The upper end is humidified by periodically adding water to the permeable stone using an ear bulb. If the moisture on the sample surface cannot penetrate the soil, wrap the ring knife specimen with plastic wrap for 12 hours to ensure uniform moisture distribution within the soil sample. At this point, the humidification process is considered complete.

[0089] S1.2.6. Obtain the samples required for the test. During the dehumidification and humidification process, weigh the sample regularly. When the moisture content of the sample reaches 18.3%, wrap it in plastic wrap and set aside.

[0090] S1.3. Preparation of microstructure specimens.

[0091] S1.3.1. According to the indoor compaction test, the maximum dry density of the test soil used in the present invention is 1.67 g / cm 3 , the optimal moisture content is 18.3%.

[0092] S1.3.2. Pass the test soil through a 2 mm sieve and oven dry at 105°C. Then, add the soil to a small bucket in layers to achieve an optimal moisture content of 18.3% and mix thoroughly. Seal the bucket with plastic wrap and let it sit for 24 hours.

[0093] S1.3.3, after the stuffing is completed, according to the volume of the ring die (diameter 6.18cm, height 2cm) and the maximum dry density 1.67g / cm 3 The required dry soil mass can be calculated as:

[0094] According to the optimal moisture content of 18.3%, the mass of water to be added can be calculated as follows: m w =m d *18.3%=100.2*18.3%=18.3g

[0095] Total mass: m 总 =md +m w =100.2g+18.3g=118.5g.

[0096] Then, use a ring knife mold to form a ring knife specimen: add the total mass of the test soil after the filling is completed according to the above formula to the ring knife mold and compact it. After the ring knife specimen is formed, immediately wrap it with plastic wrap to prevent moisture loss.

[0097] S1.3.4. For saturated samples, place the knife ring sample in a knife ring saturator and fix it in a vacuum saturation cylinder. Add water until the water exceeds the knife ring saturator. Pump air into the vacuum saturation cylinder until the pressure reaches one atmosphere below zero, then close the exhaust valve and wait for 24 hours for it to be fully saturated.

[0098] S1.3.5. Dry-wet cycle. The dehumidification process uses natural air drying. After saturation, the ring knife specimen is removed from the mold and weighed at saturation. During the air drying process, if the specimen mass remains unchanged for 3-5 days (the minimum specimen mass), the dehumidification process is considered complete. The humidification method uses a two-way water film humidification method. The dehumidified ring knife specimen is placed between two permeable stones. A piece of geotextile filter paper is placed between the permeable stone and the ring knife specimen to prevent fine particles from clogging the permeable stone pores. The permeable stone is placed on an absorbent sponge. The lower permeable stone absorbs water from the sponge to humidify the ring knife specimen. The upper end is humidified by periodically adding water to the permeable stone using an ear bulb. If the moisture on the sample surface cannot penetrate the soil, wrap the ring knife specimen with plastic wrap for 12 hours to ensure uniform moisture distribution within the soil sample. At this point, the humidification process is considered complete.

[0099] S1.3.6. Obtain the sample required for the test. When the ring knife sample is dehumidified or humidified to the optimal moisture content, cut a sample with a volume less than 1 cm from the inside of the ring knife sample. 3 The samples are reserved, that is, the microstructure samples.

[0100] S2. Macro shear strength test, namely triaxial consolidated undrained shear (CU) test of unsaturated soil.

[0101] The traditional shear strength test of unsaturated soil requires three steps (suction balance, isotropic consolidation, and shearing). However, this experiment controls the suction by controlling the moisture content based on the correspondence between suction and moisture content in the soil-water characteristic curve, directly performing isotropic consolidation and shearing. The suction of the shear specimen is then measured using the filter paper method to verify whether the suction is close to that of the soil-water characteristic curve.

[0102] S2.1. Specimen installation.

[0103] S2.1.1. Wrap the triaxial specimen with rubber film and place it in the instrument base. Secure it in the groove with three 2mm rubber bands at the top and bottom.

[0104] S2.1.2. After installing the pressure chamber, fill it with water until it is full and then tighten the bolts to isolate the pressure chamber from the outside atmosphere.

[0105] S2.1.3. Loosen the vent screw at the top of the pressure chamber and turn the ambient pressure three-way valve at the bottom of the pressure chamber to connect the internal pipes of the pressure chamber to the water storage bottle. Turn on the water pump and pump the water in the water storage bottle into the pressure chamber. When the water in the pressure chamber overflows, turn off the water pump and turn the ambient pressure valve to connect the internal pipes of the pressure chamber to the ambient pressure controller.

[0106] S2.1.4. Adjust the workbench, secure the force transmission rod to the specimen, and shorten the displacement sensor by 1 cm before fixing it in place.

[0107] S2.2. Software settings.

[0108] S2.2.1. After starting the SLB-1 triaxial test acquisition software, press the reset button for each item in the instrument status column to reset the ambient pressure, pore pressure, axial displacement, principal stress difference, back pressure 1, back pressure 2, and upper flow rate.

[0109] S2.2.2. Select CU test in the test method, set the soil sample number, fill in the test size (diameter 31.9 mm, height 80 mm) and the surrounding pressure (three confining pressure tests are performed: 30 kPa, 60 kPa, and 120 kPa respectively), set the back pressure 1 to 0, the strain rate to 0.08 mm / min, set the sampling method to 30 s time interval, and select the test end condition to be 15% of the deformation.

[0110] S2.2.3. After clearing and setting the test parameters, click Start Test.

[0111] S2.2.4. When the sample enters the consolidation stage and the water displacement per 2 hours is less than 0.02 ml, it is considered to have reached consolidation equilibrium and consolidation is stopped.

[0112] S2.2.5. When the specimen enters the shearing stage, close the drain valve. Shearing is completed when the specimen is sheared to 15% of the maximum deformation.

[0113] S2.2.6. After the test is completed, the data is exported.

[0114] S2.2.7. To unload the load, first unload the pressure inside the soil sample, i.e. the counter pressure or the axial pressure on the top of the soil sample, then unload the surrounding pressure, and then return the workbench to its original position.

[0115] S2.2.8. Drain the water in the pressure chamber and take out the soil sample.

[0116] S3. Microscopic crack test.

[0117] S3.1. Use a high-definition camera to capture the cracks generated on the sample surface during each drying and wetting cycle (dehumidification and humidification) to obtain the original RGB image.

[0118] S3.2. First, use Photoshop to grayscale the RGB image and crop any excess blank areas. Import the image into CIAS image analysis software, adjust the threshold, and click Segment to create a binary image. Then, click Edit Binary Image to remove noise, fully displaying the specimen cracks and obtaining a de-noised image.

[0119] S3.3, Segmentation module and Crack module correspond to crack area analysis and crack local parameter analysis respectively.

[0120] Click the Segmentation module to divide the crack image area. The pixels corresponding to the sample ring area are obtained through the divided area, and the conversion relationship between pixel units and actual units is established.

[0121] Click the Crack module to analyze the crack parameters, then click Auto analysis (Crack), wait 10-30 seconds to obtain the central axis of the crack network, and then click the Crack property table to pop up the crack geometry information table, from which you can obtain parameter information such as crack area, length, width, and direction. Based on the conversion relationship between pixel units and actual units, you can get the actual information of the crack parameters.

[0122] S3.4. By obtaining the crack parameters, the crack ratio is defined as the ratio of the total crack area to the total area of the ring cutter, and the average crack width is defined as the ratio of the total crack area to the total crack length. Then, the two important crack indicators, crack ratio and average crack width, can be calculated to analyze the change and development law of cracks.

[0123] S4. Micropore test.

[0124] S4.1. Freeze-dry the prepared sample to remove moisture from the sample with minimal damage to the internal structure of the sample.

[0125] S4.2. Analyze the pore structure of the sample using the AutoPore V fully automatic mercury intrusion pore size analyzer.

[0126] The steps are as follows: turn on the computer, then turn on the nitrogen switch and the mercury intrusion meter switch; weigh the sample mass, transfer the sample to the dilatometer, seal it, and weigh it; place the weighed dilatometer into the low-pressure chamber; select low-pressure test on the software interface, fill in the relevant information, and perform a low-pressure test (0.001MPa~0.1MPa); after the low-pressure test is completed, place the mercury-injected dilatometer into the high-pressure chamber and prepare for a high-pressure test (0.1MPa~400MPa); select high-pressure test on the software interface, fill in the relevant information, and perform a high-pressure test.

[0127] from Figure 2 and Figure 3 It can be seen that under the same confining pressure, the peak deviatoric stress gradually decreases with the number of dry-wet cycles. Compared to the same number of dry-wet cycles, the peak deviatoric stress generated during the wetting process is smaller than that during the dewetting process. This indicates that soil strength gradually deteriorates with increasing dry-wet cycles. (For curves with peaks, the peak value is taken as the shear strength value; for curves without peaks, the deviatoric stress corresponding to 15% strain is taken as the shear strength. Shear strength parameters such as cohesion can also be calculated using the Moore-Kunlun criterion.)

[0128] from Figure 4 and Figure 5 It can be seen that (1) the surface crack rate and average crack width go through three stages as the number of drying and wetting cycles increases: crack incubation stage (N = 0-1), crack expansion stage (N = 1-3), and crack equilibrium stage (N = 3-5); (2) during the dehumidification process, soil cracks gradually evolve, while during the wetting process, the overall performance is that the soil cracks heal. Specifically, during the dehumidification process, the surface crack rate gradually increases as the soil moisture content decreases, while during the wetting process, the surface crack rate first decreases rapidly as the soil moisture content decreases, and then increases very slowly.

[0129] from Figure 6 and Figure 7 It can be seen that with the increase of the number of drying and wetting cycles, the dominant pore diameters of small and large pores gradually increase during the dehumidification and wetting process, and the volume of large pores increases significantly, that is, the pore connectivity of the soil gradually increases.

[0130] The above experimental steps yielded macroscopic shear strength, microscopic crack index, and microscopic pore evolution index. The microscopic pore volume change index can be used to assess soil pore volume evolution; the microscopic crack development index is used to assess soil integrity; and the shear strength index is used to assess interparticle bonding and the long-term stability of soil engineering. Together, these three indicators form a multiscale evaluation system for soil strength degradation, which can provide multiscale evaluation for geological engineering disaster warnings (such as landslides) and a multiscale approach to long-term stability design in geotechnical engineering.

[0131] Taking the dewetting process as an example, (1) it can be seen that as the number of dry-wetting cycles increases, the shear strength of the soil gradually decreases. Specifically, when the confining pressure is 30 kPa, the shear strength value of the soil decreases from 620 kPa in the first dewetting to 412 kPa in the third dewetting and 344 kPa in the fifth dewetting, respectively. The degradation of shear strength obviously occurs in the first three cycles. (2) As the number of dry-wetting cycles increases, the cracks in the soil gradually evolve. Specifically, the crack rate on the soil surface increases from 0% in the first dewetting to 3.51% in the third dewetting and 3.67% in the fifth dewetting; and the average crack width increases from 0 mm in the first dewetting to 0.22 mm in the third dewetting and 0.24 mm in the fifth dewetting. Therefore, the evolution of crack expansion is also mainly concentrated in the first three cycles. (3) As the number of dry-wetting cycles increases, the microscopic pores in the soil expand. Specifically, the dominant pore sizes of small pores and large pores increased, with the dominant pore size of small pores increasing from 0.020um in the first dewetting to 0.025um in the third dewetting and 0.030um in the fifth dewetting; while the dominant pore size of large pores increased from 12.2um in the first dewetting to 13.5um in the third dewetting and 16um in the fifth dewetting; at the same time, it can be found that the pore volume of large pores increased significantly.

[0132] Correlation between shear strength and crack evolution: With increasing drying and wetting cycles, the soil's shear strength decreased significantly (from 620 kPa to 344 kPa). Simultaneously, the crack fraction increased from 0% to 3.67%, and the average crack width increased from 0 mm to 0.24 mm. This indicates that crack development directly weakens the soil's structural integrity, leading to deterioration in shear strength.

[0133] Correlation between crack evolution and microscopic pore expansion: The crack ratio and pore expansion develop synchronously. For example, during the third drying-wetting cycle, the crack ratio jumped to 3.51%, accompanied by a phased increase in both small and large pore diameters (small pores 0.025 μm, large pores 13.5 μm). This indicates that pore expansion provides the foundation for crack development, and crack extension accelerates pore connectivity. The two mutually reinforce each other, driving soil degradation.

[0134] Through multi-scale analysis (macroscopic shear strength, microscopic crack development, and microscopic pore evolution), the present invention enables relevant companies to more comprehensively evaluate the deterioration patterns of soil under the action of dry-wet cycles, thereby optimizing engineering construction design plans and reducing the risks of engineering accidents such as landslides and collapses caused by the decline in soil strength.

[0135] According to the evolution laws of microscopic pores and microcracks of the present invention, relevant enterprises can delay the process of soil deterioration by screening or developing more effective soil improvement materials (such as curing agents) or optimizing construction processes (such as compaction control and drainage design).

[0136] By analyzing the changes in soil properties under different numbers of dry-wet cycles, the present invention can help relevant companies formulate more targeted maintenance cycles and measures, thereby extending the service life of the project.

[0137] The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A multi-scale study method for soil strength degradation under dry-wet cycles, characterized by: The following steps are involved: S1. Prepare samples of the collected test soil according to the optimal moisture content and maximum dry density, and subject the samples to a dry-wet cycle; the samples include triaxial samples, ring knife samples, and microstructure samples; The sample preparation process includes at least one dry-wet cycle process, and one dry-wet cycle process includes a dehumidification process and a humidification process. The dehumidification process adopts a natural air drying method, and the humidification process adopts a bidirectional water film humidification method; S2. Performing a soil macroscopic shear strength test using the triaxial specimen prepared in step S1; S3, using the ring cutter specimen prepared in step S1 to perform a soil micro-crack test; S4. Performing soil micropore testing using the microstructure sample prepared in step S1; S5. Use the test results of soil macro shear strength test, soil micro crack test and soil micro pore test to analyze the soil strength degradation law of the collected test soil under the action of dry-wet cycle.

2. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1 is characterized in that: The testing equipment used for the soil macro-shear strength test includes an SLB-1A stress-strain controlled triaxial main unit, a confining pressure and pore pressure measurement controller, and a back pressure and volume change measurement controller; the testing equipment used for the soil micro-crack test includes a high-definition camera; the testing equipment used for the soil micro-pore test includes a Scientz-N freeze dryer and an AutoPore V fully automatic mercury intrusion pore size analyzer.

3. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1 is characterized in that: In S1, when preparing the sample under the action of dry-wet cycles, the specific steps of preparing the triaxial sample include: S1.1.

1. First, obtain the maximum dry density and optimal moisture content of the test soil based on indoor compaction tests; S1.1.

2. Sieve and dry the test soil. Mix the test soil and water in a container to the optimal moisture content. Stir evenly and seal with plastic wrap for 23-25 hours. S1.1.

3. After the filling is completed, the total mass of the triaxial specimen is calculated based on the volume of the triaxial mold, the maximum dry density, and the optimal moisture content. The soil is then compacted into triaxial specimens using the triaxial mold using the layered compaction method. S1.1.

4. Place the sample in a saturation tank to saturate it; S1.1.

5. Perform a dry-wet cycle on the saturated triaxial specimens. S1.1.

6. During the dry-wet cycle, weigh the triaxial specimen regularly. When the triaxial specimen reaches the optimum moisture content, wrap it in plastic wrap and set aside.

4. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1 is characterized in that: The dehumidification process is as follows: the saturated triaxial specimen is removed from the mold and naturally air-dried until the mass of the triaxial specimen remains unchanged within 3 to 5 days, and the dehumidification process is completed; The humidification process is: The dehumidified triaxial specimen is placed between two permeable stones, with a piece of geotextile filter paper between the permeable stone and the triaxial specimen to prevent fine particles from clogging the pores of the permeable stone; the permeable stone is placed on an absorbent sponge, and the lower permeable stone absorbs water through the sponge to humidify the triaxial specimen, while the upper end is humidified by adding water to the permeable stone with an ear bulb at regular intervals; when the moisture on the sample surface cannot penetrate into the soil, wrap the triaxial specimen with plastic wrap for 12 hours to ensure uniform moisture distribution inside the soil sample, and the humidification process is completed.

5. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1 is characterized in that: In S1, when preparing the sample under the action of dry-wet cycle, the specific steps of preparing the ring knife sample include: S1.2.

1. First, obtain the maximum dry density and optimum moisture content of the test soil based on indoor compaction tests; S1.2.

2. Sieve and dry the test soil. Mix the test soil and water in a container to the optimal moisture content. Stir evenly and seal with plastic wrap for 23-25 hours. S1.2.

3. After the filling is completed, the total mass of the ring knife sample is calculated based on the volume of the ring knife mold, the maximum dry density and the optimal moisture content, and then the soil is made into a ring knife sample using the ring knife mold; S1.2.

4. Place the sample in a saturation tank to saturate it; S1.2.

5. Perform a dry-wet cycle on the saturated knife ring specimen; S1.2.

6. During the dry-wet cycle, weigh the ring knife sample regularly. When the moisture content of the ring knife sample reaches the optimal moisture content, wrap it with plastic wrap and set aside.

6. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1 is characterized in that: In said S1, when preparing the sample under the action of dry-wet cycle, the specific steps of preparing the microstructure sample include: S1.3.

1. First, obtain the maximum dry density and optimum moisture content of the test soil based on indoor compaction tests; S1.3.

2. Sieve and dry the test soil. Mix the test soil and water in a container to the optimal moisture content. Stir evenly and seal with plastic wrap for 23-25 hours. S1.3.

3. After the filling is completed, the total mass of the ring knife sample is calculated based on the ring knife mold volume, maximum dry density and optimal moisture content, and then the soil is made into a ring knife sample using the ring knife mold; S1.3.

4. Place the sample in a saturation tank to saturate it; S1.3.

5. Perform a dry-wet cycle on the saturated ring knife specimen; S1.3.

6. During the dry-wet cycle, the mass of the ring knife sample should be weighed regularly. When the moisture content of the ring knife sample is the optimal moisture content, a volume of less than 1cm2 should be cut from the inside of the ring knife sample. 3 The samples are reserved, that is, the microstructure samples.

7. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1 is characterized in that: The soil macroscopic shear strength test adopts an unsaturated soil triaxial consolidation undrained shear test, that is, based on the correspondence between suction and moisture content in the soil-water characteristic curve, the suction is controlled by controlling the moisture content, and constant suction consolidation and shear are directly performed. After that, the suction of the shear sample is measured by the filter paper method to check whether the suction is close to the suction of the soil-water characteristic curve.

8. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 7 is characterized in that: In the soil macro shear strength test, when the sample enters the shear stage, the shearing is completed when the sample is sheared to 15% of the maximum deformation.

9. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1 is characterized in that: The specific steps of the soil micro-crack test are as follows: First, use a camera to take pictures of the cracks produced during each dry-wet cycle; The image is then grayscaled and imported into the CIAS crack image analysis software to obtain a binary image. After that, the noise is removed to obtain a denoised image. Then, the Segmentation and Crack modules are used to analyze the crack area and crack local parameters respectively; By obtaining the crack parameters, calculating the crack ratio and the average crack width, the crack change and development law are analyzed.

10. The multi-scale research method for soil strength degradation under dry-wet cycles according to claim 1, characterized in that: The specific steps of soil micro-pore test are as follows: First, the microstructure sample is freeze-dried to remove the moisture in the sample with minimal damage to the internal structure of the sample; The pore structure of the sample was then analyzed using a fully automatic mercury intrusion pore size analyzer.

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