An experimental method for observing the evolution of mesostructure during loess collapse

Abstract

The present invention discloses an experimental method for observing the evolution of mesostructure during loess collapse, which relates to the field of mesoscopic observation technology and includes: preparing mesostructure evolution samples of loess samples in the same state; determining the collapse deformation of the original loess samples using a single-line immersion saturation compression method; performing additional tests on samples with significantly different test results from other parallel samples; dividing the collapse stage of the original loess into M stages according to arithmetic differences; taking N evolution samples in the same state, performing a single-line immersion saturation compression test, and removing ring knife samples in stages; freezing and drying the removed samples with liquid nitrogen, and cutting them into observation samples; performing scanning electron microscope observation tests and mercury intrusion tests on the observation samples; and obtaining the evolution characteristics of the loess collapse process based on statistical principles. By obtaining the complete mesostructure evolution characteristics of the entire loess collapse test process, the present invention can characterize the collapse evolution process, predict the macroscopic collapse deformation of loess, and better serve loess engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of microscopic observation, and in particular to an experimental method for observing microscopic structural evolution during loess collapse. Background Art

[0002] Microscopic processes determine macroscopic behavior, and a deep understanding of the microstructural characteristics of loess materials is crucial for revealing the underlying mechanisms of their macroscopic properties. With the continuous advancement of microscopic observation techniques in materials science—from the initial optical microscope to the scanning electron microscope (SEM), environmental scanning electron microscope (ESEM), X-ray computed tomography (CT), nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and nitrogen adsorption—scientists have conducted numerous experiments on the mesoscopic evolution of loess collapsibility based on these observational methods.

[0003] According to the evolution observation method, the observation of mesostructure evolution during loess collapse can be divided into two categories: the evolution experiment of the beginning and end observation and the dynamic evolution experiment (e.g. Figure 2 (As shown). The start-to-end observation evolution test uses mesoscopic observation techniques to obtain the mesoscopic characteristics of the loess collapsibility test at both the beginning and end stages. The start-to-end observation evolution test only observes the loess collapsibility test at its beginning and end stages, failing to capture the mesostructural evolution characteristics of the collapsibility process. The dynamic evolution of materials is crucial for revealing macroscopic internal mechanisms and accurately constructing evolution models. The dynamic observation evolution test effectively compensates for the shortcomings of the start-to-end observation evolution test. This method requires obtaining the microstructural characteristics of the sample at different collapsibility stages while simultaneously conducting dynamic mesostructural observations.

[0004] Three-dimensional, non-destructive, and dynamic computed tomography (CT) technology is perfectly suited for dynamic observation of collapsibility. CT scanning resolution is inversely proportional to sample size: the higher the CT resolution, the smaller the sample size. Medical and industrial CT scans can scan standard-sized samples indoors, but their resolution is on the millimeter scale, which cannot meet the micrometer-scale requirements for observing loess mesostructure. For example, Chinese utility model patent number CN201822150413.4 discloses a portable real-time loading test device for geotechnical mechanics, compatible with an industrial CT scanner. The invention requires a cylindrical specimen measuring φ50×100 mm. This device can only observe the dynamic evolution of cracks within the rock sample during loading failure and cannot capture the mesoscopic characteristics of the rock test during the loading process. Although micron CT scanners can observe the mesostructure of loess, the specimen size is only on the millimeter scale. For example, Chinese invention patent number CN201811062544.5 discloses a micro-soil sample hydraulic consolidation loading system. This device incorporates a micron CT scanner, requiring specimens with diameters of only 2 to 6 mm. The collapsible deformation of loess is closely related to boundary conditions, and there is a cross-effect between collapsible deformation and stress. The specimen size effect significantly impacts the evaluation of loess collapsibility. The "Building Standard for Collapsible Loess Areas" (GB 50025-2018) explicitly stipulates that specimen diameters for indoor single- and double-line compression collapsible tests must be no less than 79.8 mm. Furthermore, smaller specimens contain fewer regional geotechnical characteristics, making the test results less representative of the geotechnical material. Therefore, loess collapsibility evaluations obtained using millimeter-scale specimens are difficult to directly apply in practical engineering projects. Current dynamic observation evolution tests cannot simultaneously eliminate size effects and improve observation precision. Therefore, to address the shortcomings of current experimental methods, a new experimental method for observing the evolution of mesostructures during loess collapsibility is urgently needed.

[0005] Therefore, technicians in this field are committed to developing an experimental method to observe the evolution of mesostructure during loess collapse. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is that the microscopic structural evolution characteristics of the wetting process cannot be obtained in the initial and final observation evolution test, and the dynamic observation evolution test cannot take into account both eliminating the size effect and improving the observation precision.

[0007] To achieve the above object, the present invention provides an experimental method for observing the evolution of mesostructure during loess collapse, characterized in that the method comprises the following steps:

[0008] S101: preparing a sample of the same state of loess sample for the microscopic evolution of collapse, and wrapping the sample tightly with plastic wrap and placing it in a moisturizing cylinder;

[0009] S103: taking a predetermined number of parallel samples from the sample as the sample, and determining the collapsible deformation of the original loess sample using a single-line water immersion saturation compression method on the parallel samples;

[0010] S105: Additional testing of samples with significantly different test results: additional testing of the samples in the parallel test group with significantly different test results from the other parallel samples;

[0011] S107: Classifying the collapse of the original loess into stages: taking the average collapse deformation value of the parallel test group as the collapse deformation value of the original loess, and dividing the collapse stage of the original loess into M stages according to the arithmetic difference;

[0012] S109: the undisturbed loess staged collapsibility test: taking the N samples in the same state prepared in step S101 as evolution samples, and performing a single-line water immersion saturation compression test. When the load reaches the immersion pressure and the deformation of the evolution sample reaches stability, the ring cutter samples are removed in stages;

[0013] S111: Preparation of loess microscopic observation samples at the collapsible stage: subjecting the taken ring knife samples to liquid nitrogen freezing and drying, taking out the dried ring knife samples and cutting them into the observation samples;

[0014] S113: Microscopic observation test of loess at the collapsible stage: Scanning electron microscope observation test and mercury intrusion test are respectively performed on the observation samples at each collapsible stage;

[0015] S115: Analysis of microstructure evolution during loess collapse in a given state: Based on statistical principles, the evolution characteristics of loess collapse in a given state are obtained.

[0016] Furthermore, in the step S101, X parallel ring knife samples of the original loess in the same state are prepared. The samples in the same state refer to samples with equal water content and porosity ratio, the deposition direction of the samples is the same, and the samples are obtained at the same regional location.

[0017] Furthermore, M is 5, N is 15, X is 20, and the predetermined number of parallel samples is 5.

[0018] Furthermore, in step S107, the M collapse stages include the initial collapse stage C0, and the evolution sample deformation is h b ; Collapse I stage C Ⅰ , the evolution specimen deformation is h b -Δhc; Collapse II stage C Ⅱ , the evolution specimen deformation is h b -2Δhc; Collapse III stage C Ⅲ , the deformation of the evolution specimen is hb -3Δhc; final stage of collapse C E , the deformation of the evolution specimen is h b -4Δhc;

[0019] Among them, h b is the deformation of the evolution sample before stabilization by immersion in water, h a is the deformation of the evolution specimen after immersion in water and Δhc is the collapsible deformation, specifically:

[0020] Δhc=(h b -h a ) / 4.

[0021] Furthermore, in step S109, when conducting the single-line water immersion saturation compression test, the test instrument selected is an N-connected pneumatic consolidation instrument, and the pneumatic consolidation instrument includes N consolidation containers, which are marked as 1 to N respectively, and the N consolidation containers are loaded by the same air pressure in parallel.

[0022] Furthermore, the staged collapsibility test includes:

[0023] S1091: When the load reaches the immersion pressure and the deformation of the evolution specimen reaches stability, the evolution specimen reaches the initial collapsible stage C0, and the ring knife specimens No. 1 to 3 are taken out from the consolidation container;

[0024] S1092: Fill the remaining consolidation containers with water. When the deformation of the evolution sample reaches h b -Δhc, the evolution sample reaches the collapsible stage I C Ⅰ , taking out the ring knife samples No. 4 to 6 from the consolidation container;

[0025] S1093: When the deformation of the evolution sample reaches h b When -2Δhc, the evolution sample reaches the collapsible stage II C Ⅱ , taking out the ring knife samples No. 7 to 9 from the consolidation container;

[0026] S1094: When the deformation of the evolution sample reaches h b When -3Δhc, the evolution sample reaches the collapsible stage III C Ⅲ , taking out the ring knife samples No. 10 to 12 from the consolidation container;

[0027] S1095: When the deformation of the evolution sample reaches h b -4Δhc=h a When the evolution sample reaches the final stage of collapse C E , taking out the ring knife samples No. 13 to N from the consolidation container;

[0028] S1096: When all the ring knife specimens are taken out, the staged wetting test is completed.

[0029] Furthermore, in step S111, the observation sample is 1.5×1.5×1.5 cm 3 The cubic specimen is marked with the direction of applied load.

[0030] Furthermore, four observation samples are prepared for each ring knife sample, two of which are used for scanning electron microscope observation and two for mercury intrusion testing.

[0031] Furthermore, in step S115, image processing software is used to extract microscopic characterization indicators from the image observed by scanning electron microscopy, and pore distribution characteristic parameters are obtained from the mercury injection test. The microscopic characterization indicators and the pore distribution characteristic parameters are combined to obtain the microscopic evolution characteristics of the loess collapse.

[0032] Furthermore, the microscopic characterization index includes a range index, a single particle index and a pore index, wherein:

[0033] The range index includes circularity R0, distribution dimension D V , grayscale entropy D f , orientation H and Euler number O indicators;

[0034] The single particle index includes the equivalent diameter D eq , particle long axis L l , particle short axis L s , particle specific surface area A and particle inclination index;

[0035] The pore index includes the porosity fractal dimension D n , pore orientation inclination and pore throat equivalent diameter index.

[0036] In a preferred embodiment of the present invention, by conducting different collapsibility tests on multiple parallel specimens in the same state, the collapsibility process of a single specimen is collectively described. This method can capture the complete microscopic evolutionary characteristics of the entire loess collapsibility process, revealing the mechanisms of the macroscopic physical and mechanical behavior during the loess collapsibility process and resolving the bottleneck issue between initial and final observational evolution tests and dynamic observational evolution tests. Furthermore, by capturing the complete microscopic evolutionary characteristics of the entire loess collapsibility test process, the present invention can characterize the collapsibility evolution process, predict the macroscopic collapse deformation of loess, and better serve loess engineering projects.

[0037] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the test method steps of a preferred embodiment of the present invention;

[0039] Figure 2 It is a schematic diagram of particle tracking of dynamic evolution and initial and final observation evolution in the prior art of the present invention;

[0040] Figure 3 This is a schematic diagram of the stages of undisturbed loess collapse in a given state according to a preferred embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of a loess step-by-step collapsible test route according to a preferred embodiment of the present invention;

[0042] Figure 5 It is a schematic diagram of the microscopic observation sample preparation route of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following describes several preferred embodiments of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0044] In the drawings, components with identical structures are denoted by the same reference numerals, and components with similar structures or functions are denoted by similar reference numerals. The size and thickness of each component shown in the drawings are arbitrary and are not limited by the present invention. For clarity, the thickness of components in some places in the drawings is appropriately exaggerated.

[0045] like Figure 1 As shown, an experimental method for observing the evolution of mesostructure during loess collapse provided by an embodiment of the present invention includes the following steps:

[0046] S101: Preparation of samples for the microscopic evolution of loess subsidence in the same state. After the sample preparation is completed, it is tightly wrapped with plastic wrap and placed in a moisturizing cylinder.

[0047] When preparing undisturbed loess samples in the same state, loess samples are obtained from the same area and location, and 20 parallel ring knife samples are made. The moisture content and porosity of these samples are equal, and the deposition direction of the samples is the same. Such samples are called samples in the same state.

[0048] S103: Taking a predetermined number of parallel samples from the sample, and determining the collapsible deformation of the original loess sample using a single-line water immersion saturation compression method for the parallel samples.

[0049] S105: Additional testing of samples with large differences in test results: Additional testing of samples with large differences in test results from other parallel samples in the parallel test group. The number of samples in the parallel test group is 5.

[0050] S107: Collapse of undisturbed loess: The average collapsible deformation value of the parallel test groups is taken as the collapsible deformation value of the loess in this state. The collapsible stages of the undisturbed loess are divided into 5 stages according to the arithmetic interval.

[0051] The five stages of collapsibility mentioned above include:

[0052] At the initial stage of collapse, C0, the deformation of the evolving specimen is h b ;

[0053] Collapse Stage I C Ⅰ , the evolution specimen deformation is h b -Δhc;

[0054] Collapse II Stage C Ⅱ , the evolution specimen deformation is h b -2Δhc;

[0055] Collapse Stage III C Ⅲ , the evolution specimen deformation is h b -3Δhc;

[0056] Wet Collapse Final Stage C E , the evolution specimen deformation is h b -4Δhc;

[0057] Among them, h b is the deformation of the evolution specimen before immersion and stabilization, h a is the deformation of the evolving specimen after immersion in water and Δhc is the collapsible deformation, specifically:

[0058] Δhc=(h b -h a ) / 4.

[0059] S109: In-situ loess staged collapsibility test: Take 15 evolution samples in the same state prepared in step S101 and conduct a single-line immersion saturation compression test. When the load reaches the immersion pressure and the deformation of the evolution sample reaches stability, the ring knife samples are removed in stages.

[0060] When conducting a single-line water-saturated compression test, the test instrument selected is a 15-unit pneumatic consolidation instrument. The pneumatic consolidation instrument contains 15 consolidation containers, which are marked as 1 to 15 respectively. The 15 consolidation containers are loaded in parallel with the same air pressure to ensure the consistency of the air pressure.

[0061] The undisturbed loess step-by-step collapsibility test includes the following sub-steps:

[0062] S1091: When the load reaches the immersion pressure and the deformation of the evolution specimen reaches stability, the evolution specimen reaches the initial stage of wetting and collapsibility C0, and the ring cutter specimens No. 1 to 3 are taken out from the consolidation container;

[0063] S1092: Fill the remaining consolidation containers with water. When the evolution specimen deformation reaches h b -Δhc, the evolution sample reaches the collapsibility stage I C Ⅰ , take out No. 4 to No. 6 ring knife specimens from the consolidation container;

[0064] S1093: When the evolution specimen deformation reaches h b When -2Δhc, the evolution sample reaches the collapsible stage II C Ⅱ , take out the No. 7 to 9 ring knife specimens from the consolidation container;

[0065] S1094: When the evolution specimen deformation reaches h b When -3Δhc, the evolution sample reaches the collapsible stage III C Ⅲ , take out the No. 10 to No. 12 ring knife specimens from the consolidation container;

[0066] S1095: When the evolution specimen deformation reaches h b -4Δhc=h a When the evolution sample reaches the final stage of collapse C E , take out the No. 13 to No. 15 ring knife specimens from the consolidation container;

[0067] S1096: When all the ring knife specimens are taken out, the staged wetting test is completed.

[0068] S111: Preparation of loess microscopic observation samples in the collapsible stage: The cutter ring samples are frozen and dried with liquid nitrogen, and the dried cutter ring samples are taken out and cut into observation samples.

[0069] The observation sample is 1.5×1.5×1.5cm 3 The direction of load application is marked on the observation specimen. Four observation specimens are prepared for each ring knife specimen, two for scanning electron microscope observation and two for mercury intrusion testing.

[0070] S113: Microscopic observation test of loess at the collapse stage: Scanning electron microscope observation test and mercury intrusion test were carried out on the observation samples at each collapse stage;

[0071] S115: Analysis of microstructure evolution during loess collapse in a given state: Based on statistical principles, the evolution characteristics of loess collapse in a given state are obtained.

[0072] Image processing software is used to extract microscopic characterization indicators from scanning electron microscopy images, and pore distribution characteristic parameters are obtained from mercury injection tests. The microscopic evolution characteristics of loess collapse are obtained by combining the microscopic characterization indicators and pore distribution characteristic parameters.

[0073] The microscopic characterization indicators include range indicators, single particle indicators and pore indicators, among which,

[0074] Range indicators include circularity R0, distribution dimension D V , grayscale entropy D f , orientation H and Euler number O indicators;

[0075] Single particle index includes equivalent diameter D eq , particle long axis L l , particle short axis L s , particle specific surface area A and particle inclination index;

[0076] Porosity indicators include porosity fractal dimension D n , pore orientation inclination and pore throat equivalent diameter index.

[0077] The experimental method for observing the evolution of mesostructure during loess subsidence provided by the embodiment of the present invention performs different loading stages on multiple parallel specimens in the same state, and jointly describes the experimental process of the specimen in one state. The complete mesostructure evolution characteristics of the entire loess test process can be obtained, the subsidence evolution process can be characterized, the macroscopic subsidence deformation of loess can be predicted, and the mechanism of the macroscopic physical and mechanical behavior during the loess test process can be revealed. The bottleneck problem of the beginning-end observation evolution test and the dynamic observation evolution test can be solved, and the loess engineering can be better served.

[0078] The present invention will be described in detail below in conjunction with the preferred embodiments of the present invention.

[0079] At present, in the micron-scale loess collapse mesoscopic observation test, except for the micro-soil sample loading system combined with the micron CT equipment, which can accurately observe the changes in the same area of ​​the same soil sample before and after the test, all other observations are different soil samples in the same state. For example, when the SEM electron microscope scanning method is used, since the SEM observation sample size is 1 to 2 cm, in order not to destroy the sample, it is necessary to use a soil sample in the same state as the sample for pre-test observation, and then perform final observation on the sample after the test. Therefore, the essence of the experimental method for observing the evolution of mesostructure during loess collapse proposed in the present invention is: multiple parallel loess samples in the same state are subjected to different collapse stages to jointly describe the entire collapse process of a loess sample in one state. Loess is formed by natural deposition, and there are still slight differences in the physical and mechanical properties of different original samples in the same state. The present invention needs to conduct a large number of parallel tests to eliminate the discreteness of the test results caused by the differences in samples based on statistics.

[0080] The specific implementation steps of the present invention for observing the microscopic evolution of the wetting collapse of a loess sample in a state are as follows:

[0081] Step 1: Prepare a single-state loess sample for the microscopic evolution of collapsibility: Prepare 20 parallel ring knife samples of undisturbed loess of the same state, with a sample size of φ79.8 × 20 mm. Samples of the same state refer to samples with identical physical properties, such as moisture content and void ratio, and are deposited in the same direction and sampled from the same location. For detailed sample preparation methods, refer to the "Standard for Geotechnical Test Methods" (GB / T 50123-2019). After preparation, tightly wrap the prepared samples with plastic wrap and place them in a moisture-retaining cylinder for subsequent testing.

[0082] Step 2: Obtain the collapsible deformation of an undisturbed loess specimen in a given state: The collapsible deformation of undisturbed loess is determined using the single-line immersion saturation compression method. For detailed experimental procedures, refer to the "Building Standard for Collapsible Loess Regions" (GB 50025-2018). The five specimens prepared in Step 1 were used as parallel specimens and subjected to the single-line immersion saturation compression method. The testing instrument was a GZQ-1 pneumatic consolidation apparatus. This system's multiple consolidation vessels are loaded in parallel using the same air pressure. All parallel tests for a single specimen in a given state are completed simultaneously, eliminating the influence of temporal and spatial effects on the test results.

[0083] Step 3: Additional testing of samples with significantly different test results: Additional testing of samples with significantly different test results from other samples in the 5 parallel test groups.

[0084] Step 4: Collapse of loess in a given state: The deformation h of the loess sample before it is stabilized by water b Deformation after immersion in water h a The difference is the collapsible deformation value h b -h a The average value of the collapsible deformation of 5 parallel samples is taken as the collapsible deformation value of the loess in this state. The collapsible deformation Δhc is taken as (h b -h a ) / 4, so the collapse stage can be divided into 5 stages according to the equal difference value Δhc. The initial collapse stage C0 (the specimen deformation is h b ), Collapse I stage C Ⅰ (The specimen deformation is h b -Δhc), collapsible stage II C Ⅱ (The specimen deformation is h b -2Δhc), collapsible stage III C Ⅲ (The specimen deformation is h b -3Δhc), final stage of collapse C E (The specimen deformation is h b -4Δhc=h a ). Schematic diagram of collapsibility stages, such as Figure 3 shown.

[0085] Step 5, staged collapsibility test of original loess in a given state: Take 15 loess samples of the same state prepared in step 1 and conduct a single-line water-immersion saturated compression test. The test instrument selected is a 15-unit GZQ-1 pneumatic consolidation instrument, that is, the instrument contains 15 consolidation containers, marked 1 to 15 respectively, and each consolidation container is loaded in parallel with the same air pressure. For specific test operation methods, please refer to the "Construction Standard for Collapsible Loess Areas" GB 50025-2018. When the load reaches the immersion pressure and the deformation of the sample reaches stability, that is, the sample reaches the initial stage of collapse C0, take out the ring knife samples No. 1 to 3 from the consolidation container. Fill the remaining consolidation containers with water, and when the sample deformation reaches h b -Δhc, that is, the sample reaches the wetting stage I C Ⅰ , take out the No. 4 to No. 6 ring knife specimens from the consolidation container; when the specimen deformation reaches h b -2Δhc, that is, the sample reaches the wetting stage II C Ⅱ , take out the No. 7 to No. 9 ring knife specimens from the consolidation container; when the specimen deformation reaches h b -3Δhc, that is, the sample reaches the wetting stage III C Ⅲ , take out the No. 10 to No. 12 ring knife specimens from the consolidation container; when the specimen deformation reaches h b -4Δhc=h a When the sample reaches the final stage of collapse, C E , take out the No. 13 to No. 15 ring knife specimens from the consolidation container. When all the ring knife specimens are taken out, the staged wetting test is completed. The staged wetting test route is as follows: Figure 4 shown.

[0086] Step 6. Preparation of loess microscopic observation samples at the collapsible stage: The ring knife samples taken at each stage in step 5 need to be immediately frozen with liquid nitrogen to ensure that the internal structure of the sample does not change as much as possible. Then, a vacuum freeze dryer is used to dry the frozen sample. The dried loess sample is slowly removed from the ring knife and cut into approximately 1.5×1.5×1.5cm 3 Cube specimens are prepared and the loading direction is indicated. Four cube specimens are required for each ring cutter sample, two of which are used for scanning electron microscope observation and two for mercury intrusion testing. Therefore, there are six cube specimens for scanning electron microscope observation and six cube specimens for mercury intrusion testing at each stage of wetting. The preparation route of microscopic observation specimens is as follows: Figure 5 shown.

[0087] Step 7: Microscopic observation test of loess at the collapsible stage: Scanning electron microscope observation test and mercury intrusion test were performed on the samples at each collapsible stage prepared in Step 6. Both types of tests have detailed experimental procedures and are not repeated here.

[0088] Step 8. Analysis of the evolution of microstructure during the wetting process of loess in a given state: Use image processing software to extract microscopic characterization indicators from the images observed by scanning electron microscopy, such as the range index system, circularity R0, and distribution dimension D. V , grayscale entropy D f , orientation H and Euler number O, etc.; single particle index system, equivalent diameter D eq , particle long axis L l , particle short axis L s , particle specific surface area A, particle inclination etc.; Porosity index system, porosity fractal dimension D n , pore orientation inclination Pore ​​throat equivalent diameter The pore distribution characteristic parameters obtained from the mercury injection test were analyzed and obtained. Based on statistical principles, the evolution characteristics of the loess collapse process in a given state were obtained.

[0089] In this way, the defects of the loess subsidence observation method and the loess subsidence dynamic observation method can be overcome, thereby obtaining the microscopic evolution characteristics of loess subsidence.

[0090] The preferred embodiments of the present invention have been described in detail above. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible without inventive effort by those skilled in the art. Therefore, any technical solution that can be derived by one skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. An experimental method for observing the evolution of mesostructure during loess collapse, characterized in that: The method comprises the following steps: S101: preparing a sample of the same state of loess sample for the microscopic evolution of collapse, and wrapping the sample tightly with plastic wrap and placing it in a moisturizing cylinder; S103: taking a predetermined number of parallel samples from the sample as the sample, and determining the collapsible deformation of the original loess sample using a single-line water immersion saturation compression method on the parallel samples; S105: Additional testing of samples with significantly different test results: additional testing of the samples in the parallel test group with significantly different test results from the other parallel samples; S107: Classifying the collapse of the original loess into stages: taking the average collapse deformation value of the parallel test group as the collapse deformation value of the original loess, and dividing the collapse stage of the original loess into M stages according to the arithmetic difference; S109: the undisturbed loess staged collapsibility test: taking the N samples in the same state prepared in step S101 as evolution samples, and performing a single-line water immersion saturation compression test. When the load reaches the immersion pressure and the deformation of the evolution sample reaches stability, the ring cutter samples are removed in stages; S111: Preparation of loess microscopic observation samples at the collapsible stage: subjecting the taken ring knife samples to liquid nitrogen freezing and drying, taking out the dried ring knife samples and cutting them into the observation samples; S113: Microscopic observation test of loess at the collapsible stage: Scanning electron microscope observation test and mercury intrusion test are respectively performed on the observation samples at each collapsible stage; S115: Analysis of microstructure evolution during loess collapse in a given state: Based on statistical principles, the evolution characteristics of loess collapse in a given state are obtained.

2. The method according to claim 1, wherein In step S101, X parallel ring knife samples of the original loess in the same state are prepared. The samples in the same state refer to samples with equal moisture content and porosity ratio, the deposition direction of the samples is the same, and the samples are obtained at the same regional location.

3. The method according to claim 2, wherein The M is 5, the N is 15, the X is 20, and the predetermined number of parallel samples is 5.

4. The method according to claim 1, wherein In step S107, the M collapsible stages include the initial collapsible stage C0, the deformation of the evolution sample is h b； Collapse Stage I C Ⅰ， The evolution specimen deformation is h b -Δhc; Collapse II stage C Ⅱ， The evolution specimen deformation is h b -2Δhc; Collapse III stage C Ⅲ， The deformation of the evolution specimen shown is h b -3Δhc; final stage of collapse C E， The deformation of the evolution specimen shown is h b -4Δhc; Among them, h b is the deformation of the evolution sample before stabilization by immersion in water, h a is the deformation of the evolution sample after immersion and stabilization, Δhc is the collapsible deformation, specifically: Δhc= (h b -h a ) / 4.

5. The method according to claim 4, wherein In step S109, when performing the single-line water immersion saturation compression test, the test instrument selected is an N-connected pneumatic consolidation instrument, which includes N consolidation containers, which are marked as 1 to N respectively, and the N consolidation containers are loaded by the same air pressure in parallel.

6. The method according to claim 5, wherein The staged collapsibility test includes: S1091: When the load reaches the immersion pressure and the deformation of the evolution specimen reaches stability, the evolution specimen reaches the initial collapsible stage C0, and the ring knife specimens No. 1 to 3 are taken out from the consolidation container; S1092: Fill the remaining consolidation containers with water. When the deformation of the evolution sample reaches h b -Δhc, the evolution sample reaches the collapsible stage I C Ⅰ , taking out the ring knife samples No. 4 to 6 from the consolidation container; S1093: When the deformation of the evolution sample reaches h b When -2Δhc, the evolution sample reaches the collapsible stage II C Ⅱ , taking out the ring knife samples No. 7 to 9 from the consolidation container; S1094: When the deformation of the evolution sample reaches h b When -3Δhc, the evolution sample reaches the collapsible stage III C Ⅲ , taking out the ring knife samples No. 10 to 12 from the consolidation container; S1095: When the deformation of the evolution sample reaches h b -4Δhc=h a When the evolution sample reaches the final stage of collapse C E , taking out the ring knife samples No. 13 to N from the consolidation container; S1096: When all the ring knife specimens are taken out, the staged wetting test is completed.

7. The method according to claim 1, wherein In step S111, the observation sample is 1.5×1.5×1.5 cm 3 The cubic specimen is marked with the direction of applied load.

8. The method according to claim 7, wherein Four observation samples were prepared for each ring knife sample, two of which were used for scanning electron microscope observation and two for mercury intrusion testing.

9. The method according to claim 1, wherein In step S115, image processing software is used to extract microscopic characterization indicators from the scanning electron microscopy image, and pore distribution characteristic parameters are obtained from the mercury injection test. The microscopic characterization indicators and the pore distribution characteristic parameters are combined to obtain the microscopic evolution characteristics of the loess collapse.

10. The method according to claim 9, wherein The microscopic characterization indicators include range indicators, single particle indicators and pore indicators, among which, The range index includes circularity R0, distribution dimension D V , grayscale entropy D f , orientation H and Euler number O indicators; The single particle index includes the equivalent diameter D eq , particle long axis L l , particle short axis L s , particle specific surface area A and particle inclination index; The pore index includes the porosity fractal dimension D n , pore orientation inclination and pore throat equivalent diameter index.

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