A non-invasive sand and soil coagulation method based on gelatin hydrogel

Abstract

The present invention relates to a non-invasive sand coagulation method based on gelatin hydrogel, comprising the following steps: preparing a gelatin solution; slowly injecting the gelatin solution into a sand sample to ensure uniform penetration, and waiting for it to gel to form a stable support network. This method only enhances the stability of the sample through physical filling and gelation, does not introduce foreign substances, and does not change the chemical composition or structure of the sand particles; the high fluidity of the hydrogel enables it to evenly fill the sand pores, avoiding the collapse or rearrangement of the local structure; the hydrogel forms an elastic network after solidification, while providing support, it does not affect the contact mode of the particles, so that the sand sample can maintain the original microstructure; it will not change the macroscopic mechanical properties of the sand; the sand after coagulation can be directly used for CT scanning and ESEM analysis to ensure the accuracy of microscopic analysis; gelatin is a biodegradable material, non-toxic and harmless, suitable for long-term experimental research and practical engineering applications.

Description

Technical Field

[0001] The invention relates to the technical fields of civil engineering, geotechnical engineering and soil reinforcement, and in particular to a non-invasive sand consolidation method based on gelatin hydrogel. Background Art

[0002] The macroscopic mechanical properties of sand are largely affected by its microstructure, especially the arrangement of particles, contact mode and pore distribution, which determine the deformation characteristics and bearing capacity of sand. However, when conducting microscopic analysis (such as CT scanning and ESEM testing), the preparation and processing of samples are often accompanied by inevitable sampling disturbances, which may lead to the destruction of the original structure and affect the accuracy of the test results. In addition, the limitation of sample size on CT scanning makes it impossible to capture the strain localization phenomenon and the complete force chain network distribution characteristics in large-scale sand piles. Therefore, achieving the stabilization of sand samples without destroying the particle contact mode has become a key challenge in microscopic research.

[0003] Existing sand solidification methods mainly include freezing, chemical reinforcement and biological reinforcement, which can enhance the self-stability of samples to a certain extent, but often change the original structure of sand and affect the reliability of microscopic tests. The freezing method improves the stability of samples by low-temperature freezing, but during the freezing and thawing process, the thermal expansion and contraction effect will change the contact state of particles and even cause the formation of microcracks, thus affecting the authenticity of microscopic tests. Although chemical reinforcement methods (such as cement or geopolymer solidification) can significantly improve the strength and durability of sand, they often introduce new chemical components, change the interaction between particles, and cause irreversible changes in the original structure. Biological reinforcement methods (such as microbial induced calcium carbonate deposition) can form stable calcium carbonate fillings in the pores and improve the overall stability of sand, but the deposition of exogenous minerals may obscure the original contact mode between particles, affecting the recognition of particle morphology and contact network by CT scanning.

[0004] Therefore, the existing solidification methods are difficult to meet the needs of high-precision microscopic analysis of sand, and a non-invasive sand solidification method is urgently needed to improve the self-stability of the sample without changing the original structure of the sand, and be compatible with microscopic research methods such as CT scanning and ESEM testing. The sand solidification method should have efficient pore filling ability to maintain the real contact state between particles, while providing flexible support to avoid structural damage to the sample during sampling, transportation and testing, thereby ensuring the accuracy of the microscopic analysis results. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a non-invasive sand coagulation method based on gelatin hydrogel, which can improve the self-stability of the sample without changing the original structure of the sand, and is compatible with micro-research methods such as CT scanning and ESEM testing.

[0006] In order to achieve the above-mentioned purpose, the present invention injects a flowable gelatin solution into the pores of sand to form a flexible support structure after gelation, thereby effectively preventing the displacement or collapse of sand particles and avoiding the destruction of the microstructure of sand by traditional solidification methods, thereby providing a reliable experimental basis for studying the real microscopic morphology and mechanical properties of sand.

[0007] The present invention adopts the following technical solution:

[0008] A non-invasive sand and soil coagulation method based on gelatin hydrogel comprises the following steps:

[0009] Weigh gelatin powder according to the mass ratio of gelatin powder to the sand sample to be cured of 0.25%-1.0%, add the weighed gelatin powder into water to prepare a gelatin solution, and the volume of water used is equal to the pore volume of the sand sample; the pore volume of the sand sample is calculated as follows:

[0010] ;

[0011] in, is the pore volume of the sand sample, is the total volume of the sand sample, is the mass of dry sand sample before curing, is the particle density of sand sample particles;

[0012] The gelatin solution is injected into a sand sample with a particle size of 1-2 mm and a relative density of 30% at a rate of 30-40 mL / min, so that it fills the pores of the sand sample by capillary action and gravity. After the gelatin solution is gelled, the sand sample maintains its original shape without collapse, subsidence or loose particles.

[0013] Furthermore, the gelatin solution was prepared by dissolving gelatin powder having a Bloom value of 250 in distilled water at 60±2°C.

[0014] Furthermore, the mass ratio of gelatin powder to the sand sample to be cured is 0.5%.

[0015] Furthermore, the gelatin solution is injected in a staged manner.

[0016] Furthermore, after the gelatin solution was injected into the sand sample, it was left to stand in an environment of 23°C for 3 h. During the gelation process, the sample mass was monitored by weighing method to ensure that the water evaporation loss did not exceed 2%.

[0017] In general, the present invention has the following advantages:

[0018] (1) Non-invasive: Unlike freezing, chemical reinforcement or biological reinforcement, this method only enhances sample stability through physical filling and gelation, without introducing foreign substances and without changing the chemical composition or structure of sand particles;

[0019] (2) Efficient filling: The high fluidity of the hydrogel enables it to evenly fill the pores of sand, with a filling rate of up to 99.12%, avoiding the collapse or rearrangement of local structures;

[0020] (3) Flexible support: The hydrogel forms an elastic network after solidification, which provides support without affecting the contact pattern of particles, so that the sand sample can maintain its true microstructure;

[0021] (4) Mechanical stability: The experimental results show that this method does not change the macroscopic mechanical properties of sand. The stress-strain curve, internal friction angle and other parameters of sand samples treated with 0.5% gelatin solution by mass are consistent with those of untreated samples.

[0022] (5) Compatible with microscopic testing: The cured sand can be directly used for CT scanning and ESEM analysis, avoiding particle bonding, pore closure or structural distortion caused by traditional methods, thus ensuring the accuracy of microscopic analysis;

[0023] (6) Environmentally friendly: Gelatin is a biodegradable material, non-toxic and harmless, suitable for long-term experimental research and practical engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the process of non-invasive sand consolidation method based on gelatin hydrogel.

[0025] Figure 2 Schematic diagram of the morphological changes of gelatin-solidified sand samples with different mass ratios in the vibration test.

[0026] Figure 3 Schematic diagram of typical unconsolidated undrained test results of saturated sand and gelatin-coated sand, where (a) is different gelatin mass ratios and (b) is different confining pressures.

[0027] Figure 4 Schematic diagram of the Mohr circle and failure envelope of saturated sand sample and 0.5% gelatin-solidified sand sample by mass ratio, where (a) is the saturated sand sample and (b) is the 0.5% gelatin-solidified sand sample by mass ratio.

[0028] Figure 5Schematic diagram of CT slice comparison of sand samples before and after hydrogel coagulation, where (a) is the uncoagulated sand sample and (b) is the sand sample coagulated with 0.5% gelatin by mass.

[0029] Figure 6 Schematic diagram of the pore structure before and after hydrogel coagulation, where (a) is a comparison of the porosity and hydrogel fraction layer by layer, (b) is the three-dimensional pore structure of the uncoagulated sand sample, and (c) is the three-dimensional pore structure of the sand sample coagulated with 0.5% gelatin by mass.

[0030] Figure 7 Figure 1 is a schematic diagram showing the comparison of environmental scanning electron microscope images of sand samples before and after hydrogel coagulation, where (a) is an uncoagulated sand sample and (b) is a 0.5% gelatin coagulated sand sample. DETAILED DESCRIPTION

[0031] The present invention provides a non-invasive sand coagulation method based on gelatin hydrogel, which aims to improve the self-stability of sand without changing its original structure, and ensure its structural integrity in microscopic analysis such as CT scanning and ESEM testing.

[0032] The specific implementation process of the present invention is described in detail below in combination with experimental data.

[0033] Example 1: Preparation of hydrogel-coated sand sample

[0034] This embodiment introduces the selection, processing and curing process of sand samples.

[0035] (1) Sample selection and pretreatment

[0036] In this study, ISO standard sand from Fujian, China (provided by Xiamen ISO Standard Sand Co., Ltd.) was selected as the test material. The uniformity coefficient Cu=5.55 and the curvature coefficient Cc=1.59 of the sand are classified as poorly graded sand (SP) according to the Unified Soil Classification System (USCS). In order to improve the permeability of hydrogel in sand and ensure the uniformity of the sample, key parameters were strictly controlled during the sample preparation process. First, the sand was placed in a 60°C oven for 12 hours to remove residual moisture and avoid the hydrogel solution from reducing fluidity due to water saturation during the penetration process. Subsequently, the dried sand was sieved using a dry vibration sampler to select sand samples with a particle size range of 1-2 mm. In addition, in order to control the density of the sample, the sample was filled into the container using the vibration filling method, and the relative density (Dr=30%) was measured to simulate the stacking state of loose sand in actual engineering to improve the representativeness and comparability of the experimental data.

[0037] (2) Gelatin hydrogel preparation

[0038] In this study, gelatin powder (Bloom value 250) was used as the hydrogel matrix. Gelatin powder was weighed according to the mass ratio of gelatin powder to the sand sample to be solidified at 0.25%, 0.5%, 0.75%, and 1.0%. The weighed gelatin powder was added into water to prepare four gelatin solutions with different mass ratios in order to evaluate the effect of different gelatin solutions on the stability of sand.

[0039] When preparing gelatin solution, the volume of water added should be equal to the pore volume of the sand sample.

[0040] ;

[0041] in, is the pore volume of the sand sample, is the total volume of the sand sample, is the mass of dry sand sample before curing, is the particle density of sand sample particles;

[0042] The preparation process of the hydrogel strictly controls the temperature and dissolution uniformity to ensure the optimal filling performance of the hydrogel. First, in a 60°C constant temperature water bath, gelatin powder is added to distilled water according to the target mass ratio, and a magnetic stirrer is used to stir continuously at a rate of 300rpm for 30 minutes until the gelatin is completely dissolved to form a transparent, uniform, bubble-free solution. The solution temperature is maintained at 60±2°C throughout the process to prevent the gelatin from gelling prematurely or the viscosity changes too much, which affects the subsequent penetration effect.

[0043] (3) Sand and soil consolidation process

[0044] The sand and soil coagulation adopts the liquid gelatin hydrogel infiltration filling method to ensure that the self-stability of the sand and soil is improved without changing the original microstructure of the sand and soil, and it is suitable for subsequent CT scanning and ESEM testing. First, the prepared gelatin solution is slowly injected into the pretreated sand and soil sample. The injection method adopts the staged injection method, that is, the gelatin solution is gradually added to diffuse in the pores of the sand and soil by capillary action and gravity to ensure the uniform filling process and prevent particle displacement or pore collapse due to local uneven penetration. Subsequently, the sample is placed at 23°C for 3 hours to allow the gelatin to fully gel and form a stable three-dimensional network structure inside the sand and soil to provide the necessary support. In addition, during the gelation process, the sample quality is monitored by weighing method to ensure that the water evaporation loss does not exceed 2% to maintain the stability and repeatability of the sample.

[0045] Example 2: Vibration Test

[0046] In this example, the anti-disturbance capability of the hydrogel-coated sand was evaluated through a vibration test.

[0047] (1) Test equipment

[0048] The vibration test used a HCZT-1 programmable disk vibration table, which can accurately simulate the dynamic response of sand under external disturbance. The samples were photographed with a high-resolution digital camera before and after the test, and their morphological changes were measured with an electronic vernier caliper to evaluate the stability and deformation characteristics of the samples. In addition, during the test, a high-frame rate camera was used to record the vibration behavior of the sand samples to analyze the particle rearrangement, local collapse and overall instability.

[0049] (2) Test parameters

[0050] The test set strict vibration conditions to ensure the comparability and repeatability of the experimental data. The vibration frequency was set to 47.67 Hz (i.e. 2860 times / minute) and the amplitude was set to 0.3–0.6 mm to simulate the disturbance amplitude in the actual engineering environment. The test lasted for 10 minutes, and the morphological changes of the sand samples were continuously observed during the test, including the overall collapse of the samples, particle peeling and local fracture. In order to avoid environmental factors affecting the experimental results, all tests were carried out in a laboratory environment with a constant temperature of 23°C and a humidity of 50%.

[0051] (3) Test results

[0052] The experimental results show that gelatin hydrogels with different mass ratios have a significant effect on the anti-disturbance ability of sand, and the gelatin solution with a mass ratio of 0.5% can maintain the stability of the sand while maintaining its microstructure unchanged. The specific results are as follows: within 30 seconds after the start of vibration, the untreated sand sample (0% gelatin by mass ratio) quickly disintegrated and collapsed as a whole. The particles were seriously unstable and could not maintain the original structure, indicating that the anti-disturbance ability of the uncured sand was extremely low; the integrity of the sand sample with a mass ratio of 0.25% gelatin was improved and it could maintain its shape for a short time, but after 6 minutes of vibration, local fractures occurred at the bottom, the particles slipped, and finally it still became unstable and collapsed; the sand sample with a mass ratio of 0.5% gelatin remained stable during the entire vibration process, and the volume change rate after vibration (Δ The sand particle arrangement remained basically the same, and no particle sliding, collapse or local fracture was observed, indicating that this mass ratio can effectively improve the anti-disturbance ability of sand. The morphology of sand samples solidified with gelatin at a mass ratio of 0.75%-1.0% was further stabilized, and the volume change rate after vibration was further reduced to 0.33%-0.19%. The particles were closely arranged with high structural integrity. However, due to the high mass ratio of hydrogel, there may be a weak bonding effect between the particles, resulting in further filling of local pores, which may affect the accuracy of micro-tests.

[0053] Example 3: Triaxial shear test

[0054] In this example, the unconsolidated undrained (UU) triaxial test was used to evaluate the macroscopic mechanical properties of the consolidation sand.

[0055] (1) Test equipment

[0056] This study uses the GDS fully automatic triaxial test system, which can provide high-precision axial loading and confining pressure control to ensure the stability and repeatability of the test conditions. The specimen size strictly follows the standard triaxial test specifications, with a diameter of 39.1 mm and a height of 80 mm. The test system is equipped with a high-precision load sensor and a displacement measurement system to record the stress-strain curve of the specimen in real time and use a data acquisition system for analysis.

[0057] (2) Experimental process

[0058] In order to study the effect of gelatin hydrogel coagulation on the triaxial shear properties of sand, different confining pressure conditions were set in this test to simulate the mechanical response of sand under different burial depths. The specific loading procedure is as follows: confining pressures of 50 kPa, 100 kPa, and 150 kPa are applied to simulate the stratum stress state at shallow to medium depths. The confining pressure is accurately applied by the pressure control system and kept constant during the loading process. The axial loading rate of 0.7% / min is used to ensure the strain control accuracy during the test. The test ends at an axial strain of 20% to ensure that the sample reaches the peak strength and undergoes sufficient shear deformation. The sample is kept in an unconsolidated and undrained (UU) condition during the test, that is, no water is allowed to be discharged during the loading process, in order to evaluate the shear strength and deformation characteristics of the gelatin hydrogel coagulated sand.

[0059] (3) Test results

[0060] The experimental results show that the stress-strain curve of the sand sample with 0.5% gelatin by mass is basically the same as that of the untreated sand sample, indicating that the gelatin hydrogel's gelling effect will not significantly change the overall mechanical properties of the sand, but only slightly enhance the cohesion of the sand while improving the stability of the sample. The specific test data are as follows: Peak deviator stress: 192kPa (0.5% gelatin gelled sand sample) vs. 191kPa (untreated sand sample), the two are basically consistent, indicating that gelatin gelling will not affect the peak strength of the sand. Internal friction angle: 28° (0.5% gelatin gelled sand sample) vs. 28.3° (untreated sand sample), the difference between the two is only 0.3°, indicating that gelatin hydrogel will not affect the shear properties and sliding resistance between particles. The cohesion increased by 91%: 4.93 kPa → 9.4 kPa. The flexible bonding effect of gelatin hydrogel enhanced the weak bonding force between particles, which improved the overall stability of the sand, but did not form a rigid consolidation and still maintained the independent contact characteristics of the particles.

[0061] Example 4: CT Scan Analysis

[0062] This example uses CT scanning technology to evaluate the effect of hydrogel coagulation on the microstructure of sand.

[0063] (1) Test equipment

[0064] This experiment uses the GEVtomexS micron CT scanning system, which has high-precision X-ray imaging capabilities and a resolution of 44μm / voxel, which can clearly distinguish the morphology and pore structure of sand particles. During the test, the sand sample was placed in a transparent cylindrical container with high transmittance to ensure that there was no secondary disturbance during the CT scanning process to avoid the imaging results being affected by external forces or sample movement. During the scanning process, a voltage of 130kV and a current of 130μA were used to obtain the best contrast and clarity. All tests were carried out in a constant temperature laboratory environment of 23°C to ensure the comparability of the data.

[0065] (2) Scanning process

[0066] In order to comprehensively evaluate the curing effect of gelatin hydrogel, the experiment conducted two CT scans on the untreated sand and the cured sand to compare and analyze the porosity changes, filling rate and microstructural stability. The first scan (untreated sand sample): directly scan the sand sample without curing, analyze the particle distribution, porosity and contact network, and use it as the control group data. The second scan (cured sand sample): under the same scanning parameters, scan the sand sample treated with 0.5% gelatin hydrogel by mass, and analyze the hydrogel filling rate and microstructural changes after curing. In order to ensure the accuracy of the data, the CT image was processed using AVIZO software for three-phase segmentation (air-sand particles-hydrogel), and the watershed algorithm was used to automatically identify the particle contact points and calculate the particle morphological parameters and porosity changes.

[0067] (3) Test results

[0068] The experimental results show that the filling rate of gelatin hydrogel in sand pores reaches 99.12%, which can effectively fill the pores, but will not affect the real contact relationship between particles. The specific data are as follows: Untreated sand sample: total porosity 0.340, clear particle contact network, uniform pore distribution. Sand sample after curing: hydrogel filling volume fraction 0.337, that is, the hydrogel filling rate reaches 99.12%, indicating that the hydrogel can fully penetrate the sand pores and provide support. The particle morphology remains unchanged. CT scan comparison shows that there is no significant change in the aspect ratio, equivalent diameter, sphericity and other parameters of the particles before and after hydrogel treatment. The contact network remains consistent, and the number and distribution characteristics of contact points between particles are not statistically different from those of the untreated sample, indicating that hydrogel filling will not affect the natural contact state between particles. The force chain distribution has not been reconstructed, and the force transmission path between particles is basically the same as that of the untreated sample, which further verifies the non-invasiveness of this method.

[0069] Example 5: ESEM microstructure analysis

[0070] In this example, an environmental scanning electron microscope (ESEM) was used to observe the changes in the microstructure of the sand.

[0071] (1) Test equipment

[0072] The experiment used the QUANTA200ESEM system, which has a low vacuum imaging mode and can directly observe non-conductive materials such as sand and hydrogel under a chamber pressure of 130Pa without the need for conductive spraying, thus avoiding microstructural changes caused by sample preparation. ESEM imaging uses a 20kV acceleration voltage to ensure high-resolution imaging of the particle surface and pore filling state, while adjusting the field of view to obtain detailed information on particle contact patterns, pore distribution, and gel phase distribution.

[0073] (2) Test results

[0074] ESEM image analysis shows that the pore filling effect of gelatin hydrogel curing sand is significant, but it does not affect the morphological characteristics and contact mode of the particles, as shown below: Untreated sand sample: The particles are loosely arranged, mainly in a multi-point contact mode, the particle surface is rough, the pore gaps are clearly visible, there is no additional filler between the particles, and the overall structure is a typical natural stacking structure. Sand sample after curing: A continuous gel phase appears in the pores, the hydrogel can evenly fill the sand pores and form a thin layer coating on the particle surface, but it does not affect the original angular characteristics of the particles, and the surface roughness of the particles remains unchanged. The particle contact mode remains stable. ESEM high-magnification imaging shows that there is no significant change in the number of particle contact points and contact mode before and after curing. The particles are still mainly in multi-point contact, and no obvious change in contact mode or particle slippage occurs. No particle agglomeration or structural rearrangement was observed, indicating that after the gelatin hydrogel penetrates into the sand pores, it will not cause the rearrangement of the particles or the formation of a new force chain network due to the bonding effect, which further verifies the non-invasive nature of this method.

[0075] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A non-invasive sand and soil coagulation method based on gelatin hydrogel, characterized in that: The following steps are included: First, the sand was placed in a 60°C oven and dried for 12 hours. Then, the dried sand was sieved using a dry vibrating sampler to select sand samples with a particle size range of 1-2 mm. Weigh gelatin powder according to the mass ratio of gelatin powder to 0.5% of the sand sample to be cured, add the weighed gelatin powder into water to prepare a gelatin solution, and the volume of water used is equal to the pore volume of the sand sample; the pore volume of the sand sample is calculated as follows: ； in, is the pore volume of the sand sample, is the total volume of the sand sample, is the mass of dry sand sample before curing, is the particle density of sand sample particles; The gelatin solution is injected into a sand sample with a particle size of 1-2 mm and a relative density of 30% at a rate of 30-40 mL / min, so that it fills the pores of the sand sample by capillary action and gravity. After the gelatin solution is gelled, the sand sample maintains its original shape without collapse, subsidence or loose particles, and maintains a real contact state between the particles.

2. The non-invasive sand and soil coagulation method based on gelatin hydrogel according to claim 1, characterized in that: The gelatin solution was prepared by dissolving gelatin powder with a Bloom value of 250 in distilled water at 60 ± 2°C.

3. The non-invasive sand and soil coagulation method based on gelatin hydrogel according to claim 1, characterized in that: The gelatin solution is injected in stages.

4. The non-invasive sand and soil coagulation method based on gelatin hydrogel according to claim 1, characterized in that: After the gelatin solution was injected into the sand sample, it was left to stand in an environment of 23°C for 3 hours. During the gelation process, the sample mass was monitored by weighing method to ensure that the water evaporation loss did not exceed 2%.

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