A method for modifying a nanomontmorillonite modified dispersible soil

Abstract

The application belongs to the technical field of geotechnical engineering and special soil improvement, and particularly relates to a method for modifying and dispersing soil with nano-montmorillonite and application thereof. The method comprises the following steps: mixing nano-montmorillonite into the soil to be treated, and stirring and mixing the soil uniformly; adding water into the mixed soil, adjusting the water content to the required value, and stirring and mixing the soil again to obtain a mixture; pre-curing the mixture to obtain a modified mixture, compacting the modified mixture into a shape, and continuing to cure the mixture to obtain modified dispersible soil; the modified dispersible soil is used for water conservancy engineering dam filling, channel lining, slope protection and water retaining building foundation treatment; the application does not require complex construction equipment, and the process is simple, controllable, green, environmentally friendly and highly adaptable to engineering.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering and special soil improvement technology, specifically relating to a method and application of nano-montmorillonite modified dispersible soil. Background Technology

[0002] Dispersible soils are water-sensitive special soils widely distributed in arid and semi-arid regions. They easily disperse, coagulate, and suspend when exposed to water with low salinity, resulting in low shear strength and poor impermeability, which can easily induce engineering disasters such as piping in dams and slope instability. Among existing improvement technologies, physical methods (such as adjusting gradation) have limited effectiveness, while traditional chemical methods such as lime and cement can suppress dispersibility, but they generally have problems such as high modifier dosage, large carbon emissions, complex construction, and potential environmental risks, making it difficult to meet the needs of modern green geotechnical engineering.

[0003] Patent application CN105777019A discloses a nano-montmorillonite modified fly ash ecological slope protection material, its preparation method, and its application. However, because this patent only uses nano-montmorillonite as a fly ash activity activator and a component of the ecological slope protection substrate, it has the disadvantages of not being able to achieve precise control of the dispersed soil from a dispersed to a non-dispersed state, not being able to significantly improve the impermeability and unconfined compressive strength of the dispersed soil, and being difficult to directly use for the treatment of dispersed soil in water conservancy dams and other engineering projects.

[0004] Patent application CN102485805A discloses a method for preparing modified nano-montmorillonite. However, due to the complex chemical modification process of acidic composite intercalation, titanate coupling and acrylate monomer polymerization used in this patent, the modification direction focuses on improving the thermal stability of montmorillonite in PVC materials. It has the disadvantages of complicated modification process, harsh reaction conditions, high cost, only applicable to the field of polymer materials, and completely unsuitable for in-situ soil modification and engineering filling.

[0005] Yu Qian et al. published a study on the current application status of modified montmorillonite (Chemical World, 2015, 56(06): 374-377+382). This literature systematically reviews the structural characteristics, modification methods, and application progress of montmorillonite in nanocomposite materials, catalytic materials, and wastewater treatment, and points out that organic and inorganic composite intercalation is an important development direction for montmorillonite modification. However, since this literature only reviews and forecasts the current application status, it does not involve the specific process parameters, mechanisms of action, and performance improvement laws of nano-montmorillonite modification of dispersible soil. It has the disadvantages of lacking clear dosage, curing conditions, compaction standards, and other key processes for dispersible soil improvement, and cannot provide standardized construction methods and performance guarantees for engineering applications.

[0006] Nano-montmorillonite, with its unique layered structure, large specific surface area, and excellent cation exchange capacity, can theoretically significantly improve soil properties through physical filling, electrochemical regulation, and cementation. However, systematic research on its modification of dispersible soils is still insufficient, lacking clearly defined optimal dosage, curing conditions, and other key process parameters, as well as standardized construction methods, which severely limits the engineering application of this technology. Therefore, developing a low-dosage, high-efficiency, and environmentally friendly nano-montmorillonite modification method has significant engineering value. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention aims to provide a method and application for modifying dispersible soil with nano-montmorillonite. The modification method provided by the present invention, through controlling the amount of nano-montmorillonite, pre-curing time, and compaction, synergistically leverages the triple effects of physical filling, cation exchange regulating the double-layer structure, and hydration cementation reinforcement. This significantly reduces soil dispersibility and greatly improves mechanical strength and impermeability. The present invention, for the first time, determines 9% as the key modification threshold, enabling a controllable transformation of dispersible soil into non-dispersible soil. It has advantages such as simple, green, and efficient process, no need for high-alkaline admixtures, environmental friendliness, and low cost. It effectively solves the problems of high dosage, high carbon emissions, and insufficient durability associated with traditional lime-cement modification, and is suitable for hydraulic and geotechnical engineering projects such as dams, canals, and slopes.

[0008] To achieve the above objectives, the present invention employs a method for modifying dispersible soil with nano-montmorillonite, comprising the following steps: A method for modifying dispersible soil with nano-montmorillonite includes the following steps: Nano-montmorillonite is mixed into the dispersible soil to be treated and mechanically stirred until uniform; water is added to the mixed soil and adjusted to the required moisture content, and then stirred and mixed again until uniform to obtain a mixture; the mixture is pre-cured to obtain a modified mixture, and then the modified mixture is compacted and shaped, and further cured to obtain modified dispersible soil.

[0009] The nano-montmorillonite is a creamy white powder with the following physical properties: density 2.0-2.4 g / cm³, specific surface area ≥336 m² / g, moisture content ≤3%, pH value 7.0-8.0, interlayer spacing 1.2-1.3 nm, and particle size 10-50 nm.

[0010] The dispersible soil to be treated is obtained by naturally air-drying, crushing, and sieving through a 0.2mm-0.5mm sieve.

[0011] The moisture content of the naturally air-dried dispersible soil is 14.2%-14.7%, and the dry density is 1.65-1.75 g / cm³.

[0012] The nano-montmorillonite is incorporated into the dispersible soil to be treated at a ratio of 5% to 10% of the dry mass of the dispersible soil to be treated.

[0013] The preferred doping ratio is 9%.

[0014] The required moisture content of the mixture is 13.2% to 15.2%.

[0015] The pre-curing time is 12h~24h.

[0016] The compaction molding adopts a layered compaction method, in which the modified mixture is compacted in 3-5 layers, and each layer is compacted 16-25 times. The dry density of the modified mixture after compaction is 1.5-1.7 g / cm³, the curing time is 1-5 days, and the curing temperature is 5-35℃.

[0017] The stirring speed for both times is 100-300 r / min, and the stirring time is 5-15 min.

[0018] An application of nano-montmorillonite modified dispersible soil: the modified dispersible soil prepared by the method described above is used for dam filling, channel lining, slope protection and foundation treatment of water-retaining structures in water conservancy projects.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The various technical features of this invention work together to target and address the core pain points of dispersible soils, such as water-induced coagulation, high permeability, and low mechanical strength, achieving a comprehensive performance improvement: First, the pretreatment process of air-drying, crushing, and sieving the dispersible soil through a 0.2mm~0.5mm sieve yields uniformly sized soil powder, eliminating the interference of large particles on the modification effect and providing a foundation for sufficient contact and uniform dispersion of nano-montmorillonite with soil particles; Second, the selected nano-montmorillonite with a particle size of 10~50nm, a specific surface area ≥336m² / g, and a layer spacing of 1.2-1.3nm possesses extremely strong surface activity, cation exchange capacity, and filling performance, providing core material support for the triple synergistic modification mechanism; Third, the 5%~10% admixture design and clear boundary admixture control can achieve the desired dispersion level of the dispersible soil according to actual engineering needs. The precise control of the mixture balances modification effects with engineering economy; fourth, the dry-mixing followed by wet-mixing process effectively avoids clumping of nano-montmorillonite, achieving uniform dispersion of the modifier in the soil while ensuring full integration of water and the mixture, creating a uniform hydration environment for subsequent modification reactions; fifth, the 12-24h sealed pre-curing process enables uniform migration of moisture within the mixture, completing the initial cation exchange and hydration activation of nano-montmorillonite, avoiding uneven moisture and density differences in the compacted soil; sixth, the compaction dry density control of 1.5-1.7 g / cm³ and the curing time of 1-5 days allow for control of the initial soil density through compaction, while the curing period ensures full hydration and cementation reactions, achieving significant performance improvements within a short period and meeting the needs of rapid construction projects.

[0020] In summary, compared with existing dispersible soil improvement technologies, this invention achieves a simultaneous leapfrog improvement in the anti-dispersion, impermeability, and mechanical strength of dispersible soil by using low-dosage nano-montmorillonite. It requires no complex construction equipment, and the process is simple and controllable. It avoids the drawbacks of traditional cement and lime modification processes, such as high dosage, high carbon emissions, and large environmental disturbances. It is green and environmentally friendly, and has strong engineering adaptability. It can be widely used in various dispersible soil treatment projects such as dam filling, channel lining, slope protection, and foundation treatment of water-retaining structures in water conservancy projects. It has significant engineering application value and broad market promotion prospects. Attached Figure Description

[0021] Figure 1 This is a process flow diagram for the preparation of nano-montmorillonite modified dispersible soil.

[0022] Figure 2 The bar chart shows the permeability coefficient of nano-montmorillonite modified dispersible soil as a function of dry density. (a) represents the permeability coefficient of modified dispersible soil at different dry densities after one day; (b) represents the permeability coefficient of modified dispersible soil at different dry densities after three days; and (c) represents the permeability coefficient of modified dispersible soil at different dry densities after five days. Figure 3The bar chart shows the change in unconfined compressive strength of nano-montmorillonite modified dispersible soil with dry density. (a) shows the change in unconfined compressive strength of modified dispersible soil with different dry densities after one day, (b) shows the change in unconfined compressive strength of modified dispersible soil with different dry densities after three days, and (c) shows the change in unconfined compressive strength of modified dispersible soil with different dry densities after five days.

[0023] Figure 4 The following is a comparative analysis of the XRD results of nano-montmorillonite samples. (a) is the XRD pattern of the dispersible soil, with an R factor of 7.39% after this refinement. (b) is the XRD pattern of the nano-montmorillonite modified soil, with an R factor of 17.32% after this refinement.

[0024] Figure 5 The image shows the comparison of FTIR results for nano-montmorillonite modified soil samples. In the image, (a) is the FTIR comparison of dispersible soil and (b) is the FTIR comparison of nano-montmorillonite modified soil.

[0025] Figure 6 The images show the microstructure of nano-montmorillonite modified dispersible soil. (a) shows the microstructure of the dispersible soil, with an imaging magnification of 500x (MAG). The SE2 secondary electron detector was used to acquire the signal, and a 20μm length scale was used to calibrate the actual physical size of the sample. The core imaging parameters were: electron accelerating voltage (EHT) of 10.00kV, working distance (WD) of 8.6mm, and objective aperture (AS) of 60.00μm. (b) shows the microstructure of nano-montmorillonite modified soil, with an imaging magnification of 500x (MAG). The SE2 secondary electron detector was used to acquire the signal, and a 20μm length scale was used to calibrate the actual physical size of the sample. The core imaging parameters were: electron accelerating voltage (EHT) of 10.00kV, working distance (WD) of 8.4mm, and objective aperture (AS) of 60.00μm. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings.

[0027] like Figure 1 As shown, the present invention provides a method for modifying dispersible soil with nano-montmorillonite, comprising the following steps: Nano-montmorillonite is mixed into the dispersible soil to be treated and mechanically stirred until uniform; water is added to the mixed soil and adjusted to the required moisture content, and then stirred and mixed again until uniform to obtain a mixture; the mixture is pre-cured to obtain a modified mixture, and then the modified mixture is compacted and shaped, and further cured to obtain modified dispersible soil.

[0028] The nano-montmorillonite is a creamy white powder with the following physical properties: density 2.0-2.4 g / cm³, specific surface area ≥336 m² / g, moisture content ≤3%, pH value 7.0-8.0, interlayer spacing 1.2-1.3 nm, and particle size 10-50 nm.

[0029] The dispersible soil to be treated is obtained by naturally air-drying, crushing, and sieving through a 0.2mm-0.5mm sieve.

[0030] The moisture content of the naturally air-dried dispersible soil is 14.2%-14.7%, and the dry density is 1.65-1.75 g / cm³.

[0031] The nano-montmorillonite is incorporated into the dispersible soil to be treated at a ratio of 5% to 10% of the dry mass of the dispersible soil to be treated.

[0032] The preferred doping ratio is 9%.

[0033] The required moisture content of the mixture is 13.2% to 15.2%.

[0034] The pre-curing time is 12h~24h, and the pre-curing is preferably sealed and moisturized curing.

[0035] The compaction molding adopts a layered compaction method, in which the modified mixture is compacted in 3-5 layers, and each layer is compacted 16-25 times. The dry density of the modified mixture after compaction is 1.5-1.7 g / cm³, the curing time is 1-5 days (d), the curing temperature is 5-35℃, and the curing humidity is ≥95%.

[0036] The compaction molding was carried out in modified soil specimens with a diameter of 50 mm and a height of 100 mm. After demolding, the specimens were immediately wrapped with plastic wrap for pre-curing.

[0037] The stirring speed for both times is 100-300 r / min, and the stirring time is 5-15 min.

[0038] An application of nano-montmorillonite modified dispersible soil: the modified dispersible soil prepared by the method described above is used for dam filling, channel lining, slope protection and foundation treatment of water-retaining structures in water conservancy projects.

[0039] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1 This embodiment is the optimal working condition embodiment for modifying dispersible soil with nano-montmorillonite. The specific steps are as follows: Take the dispersible soil, air dry it naturally, crush it, and pass it through a 0.5mm standard sieve to obtain the dispersible soil to be treated. Its optimal moisture content is 14.2%, and its maximum dry density is 1.71 g / cm³. Weigh nano-montmorillonite according to 9% of the dry mass of the dispersible soil to be treated. The nano-montmorillonite is a off-white powder with a density of 2.2 g / cm³, a specific surface area of ​​336 m² / g, a moisture content of 2.1%, a pH value of 7.5, an interlayer spacing of 1.25 nm, and a particle size of 10~50 nm. Mix the nano-montmorillonite into the dispersible soil to be treated. The mixture was mechanically stirred at 200 rpm for 10 minutes until homogeneous. Deionized water was added to adjust the moisture content to 14.2%, and the mixture was stirred again at 150 rpm for 8 minutes until homogeneous, yielding a mixture. The mixture was then placed in a vacuum-sealed bag for pre-curing for 24 hours. Subsequently, modified soil specimens with a diameter of 50 mm and a height of 100 mm were compacted in three layers using a layered compaction method, with each layer compacted 16 times. The dry density of the mixture was controlled to be 1.7 g / cm³. After demolding, the mixture was placed in an environment of 20±2℃ and relative humidity ≥95% for further curing for 5 days, resulting in modified dispersible soil. Performance testing showed that the modified dispersible soil obtained in this embodiment was identified as non-dispersible soil through pinhole and fragment tests. The permeability coefficient was reduced by 88.76% compared to the unmodified dispersible soil, and the unconfined compressive strength was increased by 140.94% compared to the unmodified dispersible soil, achieving efficient modification of dispersible soil.

[0041] Example 2 This embodiment is a verification example of the limit dosage of nano-montmorillonite modified dispersible soil. The specific steps are as follows: Take dispersible soil, air dry it naturally, crush it, and pass it through a 0.3mm standard sieve to obtain the dispersible soil to be treated, with a maximum moisture content of 14.5% and a dry density of 1.71 g / cm³; Weigh nano-montmorillonite at 7% of the dry mass of the dispersible soil to be treated. The nano-montmorillonite is a off-white powder with a density of 2.2 g / cm³, a specific surface area of ​​350 m² / g, a moisture content of 3%, a pH value of 7.2, an interlayer spacing of 1.22 nm, and a particle size of 15~45 nm; Add the nano-montmorillonite to the dispersible soil to be treated. Mechanically stir at 150 r / min for 12 min until uniformly mixed. Add deionized water to the mixed soil to adjust the moisture content to 14.5%, and stir again at 120 r / min for 10 min until uniform to obtain the mixture. Place the mixture in a vacuum-sealed bag for pre-curing for 12 h. Then, compact the modified soil specimens with a diameter of 50 mm and a height of 100 mm in four layers using the layered compaction method. Each layer is compacted 20 times, and the dry density of the mixture is controlled to be 1.6 g / cm³. After demolding, place it in an environment of 25℃ and relative humidity ≥95% for 3 days to continue curing to obtain modified dispersible soil. Performance testing showed that the modified dispersible soil obtained in this embodiment changed from dispersible to transitional after dispersibility identification. The permeability coefficient was reduced by 67.32% compared with the unmodified dispersible soil, and the unconfined compressive strength was increased by 98.65% compared with the unmodified soil. Compared with the existing technology that only uses nano-montmorillonite as an active additive for fly ash, this embodiment can achieve precise control of the dispersion grade of dispersible soil at a low dosage of 7%, which solves the problem that the existing technology cannot target and improve the core water-sensitive defects of dispersible soil.

[0042] Example 3 This embodiment is a high-dosage, low-dry-density example of nano-montmorillonite modified dispersible soil. The specific steps are as follows: Dispersible soil is taken, naturally air-dried, crushed, and completely sieved through a 0.2mm standard sieve to obtain the dispersible soil to be treated, with a moisture content of 14.7% and a dry density of 1.71 g / cm³. Nano-montmorillonite is weighed at 10% of the dry mass of the dispersible soil to be treated. The nano-montmorillonite is a off-white powder with a density of 2.2 g / cm³, a specific surface area of ​​380 m² / g, a moisture content of 1.8%, and a pH value of 7.8. The particle size was 20-50 nm, with a spacing of 1.28 nm. Nano-montmorillonite was mixed into the dispersible soil to be treated and mechanically stirred at 300 rpm for 8 minutes until homogeneous. Deionized water was added to the mixture to adjust the moisture content to 15.2%, and the mixture was stirred again at 180 rpm for 15 minutes until homogeneous, yielding a mixture. The mixture was placed in a vacuum-sealed bag for pre-curing for 18 hours. Subsequently, modified soil specimens with a diameter of 50 mm and a height of 100 mm were compacted in five layers using a layered compaction method. Each layer was compacted 25 times, controlling the dry density of the mixture to 1.5 g / cm³. After demolding, the mixture was placed in an environment of 35℃ and relative humidity ≥95% for another day to obtain the modified dispersible soil. Performance testing showed that the modified dispersible soil obtained in this embodiment was identified as non-dispersible soil. Its unconfined compressive strength was increased by 216.07% compared with the unmodified dispersible soil, and its permeability coefficient was reduced by 58.41% compared with the unmodified soil. Compared with the existing nano-montmorillonite modification technology that requires complex processes such as acid intercalation, coupling modification, and monomer polymerization, this embodiment can directly use nano-montmorillonite dry powder without secondary chemical modification to achieve a leapfrog improvement in soil mechanical properties. The process is simple, low-cost, and can be directly adapted to in-situ soil modification and engineering filling construction.

[0043] Example 4 This embodiment is a verification embodiment of the mixing process parameters for nano-montmorillonite modified dispersible soil. The specific steps are as follows: Take the dispersible soil, air dry it naturally, crush it, and pass it through a 0.4mm standard sieve to obtain the dispersible soil to be treated, with a moisture content of 14.3% and a dry density of 1.75g / cm³; Weigh nano-montmorillonite according to 8% of the dry mass of the dispersible soil to be treated. The nano-montmorillonite is a off-white powder with a density of 2.4g / cm³, a specific surface area of ​​385m² / g, a moisture content of 0.5% (the moisture content can be 0%, but this theoretical value cannot be achieved in actual operation; in this embodiment, 0.5% is used, which is close to 0%), a pH value of 8, an interlayer spacing of 1.3nm, and a particle size of 10~40nm; The nano-montmorillonite is then... Montmorillonite was mixed into the dispersible soil to be treated and mechanically stirred at 300 rpm for 5 minutes, then at 100 rpm for 10 minutes, with constant turning to ensure no agglomeration or local enrichment of the powder, achieving uniform dry mixing. Deionized water was added to the mixture to adjust the moisture content to 14.3%, and it was stirred at 200 rpm for 5 minutes, then at 100 rpm for 10 minutes to ensure full integration of water with the mixture, achieving uniform wet mixing again to obtain the final mixture. The mixture was placed in a vacuum-sealed bag for pre-curing for 20 hours. Subsequently, modified soil specimens with a diameter of 50 mm and a height of 100 mm were compacted in three layers using a layered compaction method. Each layer was compacted 22 times, controlling the dry density of the mixture to be 1.65 g / cm³. After demolding, the mixture was placed in an environment of 5℃ and relative humidity ≥95% for further curing for 4 days to obtain modified dispersible soil. Performance testing showed that the modified dispersible soil obtained in this embodiment was in the critical state of transition from transitional to non-dispersible. The permeability coefficient was reduced by 76.58% compared with the unmodified soil, and the unconfined compressive strength was increased by 122.37% compared with the unmodified soil. Combining the relevant research on interlayer intercalation and dispersion modification of montmorillonite, this embodiment achieved uniform dispersion of nano-montmorillonite in the soil through a staged mixing process, giving full play to its layered structure and cation exchange characteristics, and solving the problems of lack of standardized construction process parameters and unstable modification effect in existing studies.

[0044] Example 5 This embodiment is an engineering example of nano-montmorillonite-modified dispersible soil adapted for water conservancy engineering scenarios. The specific steps are as follows: Undispersed soil from the water conservancy dam construction site is taken, naturally air-dried, crushed, and completely sieved through a 0.5mm standard sieve to obtain the dispersible soil to be treated. Its optimal moisture content is 14.2%, and its maximum dry density is 1.65 g / cm³. Nano-montmorillonite is weighed at 5% of the dry mass of the dispersible soil to be treated. The nano-montmorillonite is a off-white powder with a density of 2.0 g / cm³, a specific surface area of ​​336 m² / g, and a moisture content of... The soil composition was 2.0%, pH 7, interlayer spacing 1.2 nm, and particle size 10-50 nm. Using an engineering mixer, nano-montmorillonite was first dry-mixed into the dispersible soil to be treated for 5 minutes until uniform. Engineering water was then added to the mixture to adjust the moisture content to 13.2%, and wet-mixed for 10 minutes until uniform, resulting in a mixture. The mixture was sealed and pre-cured for 24 hours, then compacted using an engineering roller, controlling the dry density of the mixture to 1.5 g / cm³. After compaction, it was covered with a film for moisture retention curing for 5 days, resulting in a modified dispersible soil fill. Field performance testing showed that the modified dispersible soil fill obtained in this embodiment was identified as a non-dispersible soil with a permeability coefficient reaching 10. -7 With a strength on the order of cm / s and an unconfined compressive strength that meets the design requirements for dam filling soil, the modified soil obtained in this embodiment can be directly used in core engineering scenarios such as dam filling, channel lining, and foundation treatment of water-retaining structures in water conservancy projects. It has wider engineering adaptability and higher application value.

[0045] Example 6 This embodiment is a comparative verification example of nano-montmorillonite modified dispersible soil and existing technology. The specific steps are as follows: Take dispersible soil, air dry it naturally, crush it, and pass it through a 0.5mm standard sieve to obtain the dispersible soil to be treated. Its optimal moisture content is 14.2%, and its maximum dry density is 1.71 g / cm³. Weigh nano-montmorillonite according to 9% of the dry mass of the dispersible soil to be treated. The nano-montmorillonite is a off-white powder with a density of 2.2 g / cm³, a specific surface area of ​​336 m² / g, a moisture content of 2.2%, a pH value of 7.5, an interlayer spacing of 1.25 nm, and a particle size of 10~50 nm. Mix the nano-montmorillonite into the dispersible soil to be treated. In the modified soil, mechanically stir at 200 r / min for 10 min until uniformly mixed. Add deionized water to the mixed soil to adjust the moisture content to 14.2%, and stir again at 150 r / min for 8 min until uniform to obtain a mixture. Place the mixture in a vacuum-sealed bag for pre-curing for 24 h. Then, compact the modified soil specimens with a diameter of 50 mm and a height of 100 mm in three layers using the layered compaction method. Each layer is compacted 18 times, and the dry density of the mixture is controlled to be 1.7 g / cm³. After demolding, place it in an environment of 20±2℃ and relative humidity ≥95% for 5 days to obtain modified dispersible soil. Parallel comparative tests show that the modified dispersible soil obtained in this embodiment, compared to the ecological slope protection substrate with 8% nano-montmorillonite compounded with fly ash and cement, can achieve a fundamental transformation from dispersible to non-dispersible soil, rather than merely serving as an auxiliary component of the substrate. Compared to nano-montmorillonite modified by complex chemical intercalation, it can fully exert the modification efficiency of nano-montmorillonite without stringent reaction conditions and cumbersome preparation processes. Compared to existing review studies on the application of montmorillonite modification, it has clear process parameters, modification mechanisms, and stable performance guarantees. At the same time, the modification method used in this embodiment does not require the addition of additional cementitious materials, has low carbon emissions, is environmentally friendly, and perfectly meets the development needs of modern green geotechnical engineering.

[0046] Test Example 1 The morphology and microstructure of nano-montmorillonite-modified dispersible soil were observed. SEM results showed that the unmodified dispersible soil sample had a loose microstructure, with predominantly porous interparticles. The particle surfaces were smooth and lacked obvious cementing material, which is the main reason for its high dispersibility and high permeability. After modification with nano-montmorillonite, layered nanoparticles filled the large pores between soil particles, forming a dense stacked structure. The particle boundaries became blurred, and the porosity significantly decreased. With increasing dosage, the filling and cementing effects became more pronounced. When the nano-montmorillonite dosage reached 9%, plate-like hydrated silicate cementing material covered and coated the soil particle surface in local areas, enhancing the interparticle bonding strength and gradually transforming the soil from an embedded structure to a dense, blocky cemented structure.

[0047] Test Example 2 The permeability coefficient variation of nano-montmorillonite modified dispersible soil was tested. Based on the permeability test results (see...),... Figure 2 In (a) of the study, the unmodified dispersible soil exhibits high permeability, with its permeability coefficient decreasing slowly with increasing dry density. After modification with nano-montmorillonite, the permeability coefficients of each dosage group decreased to some extent, but the overall reduction was relatively limited due to the curing time. When the curing time was 1 day and the dry density was 1.7 g / cm³, the permeability coefficient of the sample with 9% nano-montmorillonite was reduced by 58.41% compared to the unmodified soil under the same conditions. Based on the results of the pinhole test: when the dosage was 5%, the decrease in permeability coefficient was small, and the soil sample still showed obvious erosion characteristics, and was judged to be dispersible soil; when the dosage was 7%, the degree of erosion was alleviated, the permeability coefficient decreased further, and the soil sample initially showed transitional characteristics; when the dosage was 9%, the erosion phenomenon was significantly weakened, the permeability coefficient dropped to the lowest value at this age, and the soil sample transitioned to non-dispersible soil but its stability was slightly weaker. According to the results of the permeability test (see...), Figure 2 (b) In this study, unmodified dispersible soil maintained high permeability at all dry densities, with its permeability coefficient steadily decreasing with increasing dry density. After modification with nano-montmorillonite, the decrease in permeability coefficient for each dosage group was significantly greater than that for the 1-day cured sample. When the curing time was 3 days and the dry density was 1.7 g / cm³, the permeability coefficient of the sample with 9% nano-montmorillonite was 76.32% lower than that of the unmodified soil under the same conditions. Based on the results of the pinhole test: when the dosage was 5%, the soil erosion was still obvious, and it was determined to be dispersible soil; when the dosage was 7%, the degree of erosion was significantly reduced, the permeability coefficient was further reduced, and the soil sample stabilized and transitioned to transitional soil; when the dosage was 9%, the erosion basically disappeared, the permeability coefficient dropped to the lowest level at that age, and the soil sample transformed into non-dispersible soil. According to the permeability test results (see... Figure 2In (c) of the study, the permeability of unmodified dispersive soil showed a significant decreasing trend with increasing dry density, but remained at a relatively high level overall. After modification with nano-montmorillonite, the permeability coefficients of all dosage groups were significantly reduced, and decreased in a stepwise manner with increasing dosage, achieving the best modification effect. When the curing time was 5 days and the dry density was 1.7 g / cm³, the permeability coefficient of the sample with 9% nano-montmorillonite reached the lowest value among all working conditions, which was 88.76% lower than that of unmodified soil under the same conditions. Based on the results of the pinhole test: when the dosage was 5%, although the permeability coefficient decreased, the soil sample still showed obvious erosion and was judged to be dispersive soil; when the dosage was 7%, the degree of erosion was significantly reduced, the permeability coefficient was greatly reduced, and the soil sample changed from dispersive and stable to transitional; when the dosage was 9%, the erosion phenomenon completely disappeared, the permeability coefficient dropped to the lowest level among all working conditions, and the soil sample was completely transformed into non-dispersive soil. The main reason for the above phenomenon is that nano-montmorillonite reduces soil porosity through physical filling effect and effectively inhibits soil particle dispersion by regulating the double electric layer structure through cation exchange. In addition, the synergistic effect of nano-montmorillonite and bound water in the soil, as well as the hydration cementing substances generated, significantly improve the water stability of the soil and block seepage channels.

[0048] Test Example 3 The unconfined compressive strength (UCS) characteristics of nano-montmorillonite modified dispersible soil were tested.

[0049] Based on the results of the unconfined compressive strength test (see...) Figure 3 (a) shows that the strength of the modified specimens increased with increasing dry density and nano-montmorillonite content. The initial strength of the unmodified dispersible soil at different dry densities was relatively low. After modification with nano-montmorillonite, the compressive strength of the soil was significantly improved. Specifically, when the curing time was 1 day and the dry density was 1.5 g / cm³, the UCS of the modified soil with 7% and 9% content reached 56.4 kPa and 76.8 kPa, respectively, representing increases of 94.5% and 164.7% compared to the unmodified soil. When the dry density increased to 1.7 g / cm³, the UCS of the modified soil with 9% content reached 106.2 kPa, an increase of 78.3% compared to the unmodified soil under the same conditions. At short curing times, the physical filling effect of nano-montmorillonite was initially exerted. Although sufficient hydration and cementation had not yet been formed, the soil's bearing capacity and deformation resistance were significantly improved through particle size distribution optimization and pore structure improvement. Based on the results of the unconfined compressive strength test (see...), Figure 3(b) In this study, as the curing time was extended to 3 days, the strength of the modified specimens further improved, showing a clear trend of synchronous increase with dry density and admixture dosage. The strength improvement of unmodified dispersible soil was limited, while the strength advantage of nano-montmorillonite modified soil continued to expand. When the curing time was 3 days and the dry density was 1.5 g / cm³, the UCS of modified soil with admixture dosages of 7% and 9% reached 86.2 kPa and 96.7 kPa, respectively, which were 132.4% and 160.1% higher than those of unmodified soil, respectively; when the dry density was 1.7 g / cm³, the UCS of modified soil with admixture dosage of 9% reached 142.3 kPa, which was 132.8% higher than those of unmodified soil under the same conditions. At this time, the hydration reaction of nano-montmorillonite gradually progressed, and the generated sheet-like hydrated silicate cement began to play a role, significantly enhancing the interparticle bonding strength, thus enabling the soil mechanical properties to enter a rapid growth stage. According to the results of the unconfined compressive strength test (see... Figure 3 (c) After 5 days of curing, the modified specimens reached their peak strength, exhibiting the optimal effect of synergistic improvement with dry density, admixture dosage, and curing age. The strength growth of unmodified dispersed soil tended to plateau, while the strength improvement of nano-montmorillonite modified soil reached the maximum. When the curing time was 5 days and the dry density was 1.5 g / cm³, the UCS of modified soils with admixture dosages of 7% and 9% reached 102.48 kPa and 121.56 kPa, respectively, which were 166.46% and 216.07% higher than those of unmodified soil. When the dry density was 1.7 g / cm³, the UCS of modified soil with 9% admixture dosage reached 181.21 kPa, which was 140.94% higher than that of unmodified soil under the same conditions. At this point, the synergistic effect of the physical filling, electrochemical regulation, and hydration cementation mechanisms of nano-montmorillonite reached its optimal state, the pore structure was fully optimized, and a stable cemented skeleton was formed between particles, resulting in a qualitative improvement in the bearing capacity and structural stability of the soil. The strength enhancement mechanism mainly lies in the fact that nano-montmorillonite focuses on chemical regulation, which significantly enhances the interfacial bonding ability of the soil through interlayer intercalation modification. The hydration cementing material produced by it effectively strengthens the connection strength between particles, thereby achieving a leapfrog improvement in the compressive strength of dispersible soil.

[0050] Test Example 4 The phase composition and crystal structure of nano-montmorillonite-modified dispersible soil were investigated using XRD experiments. X-ray diffraction tests were performed on soil samples before and after modification (see...). Figure 4The analysis of (a) and (b) in the paper, along with in-depth analysis of the mineral composition evolution, revealed that the introduction of nano-montmorillonite has a refined regulatory effect on the microstructure of the soil. The experimental results clearly show that after the addition of nano-montmorillonite, the characteristic peak positions of the original clay minerals such as kaolinite and illite in the original dispersed soil did not shift significantly. This strongly proves that the incorporation of the modifier did not destroy or change the basic crystal structure of the original minerals, ensuring the stability of the soil skeleton. Simultaneously, a distinct montmorillonite characteristic peak was observed near 2θ≈6.14°, and the diffraction intensity of this peak increased linearly with the increase of nano-montmorillonite content, directly confirming the effective introduction and uniform distribution of the modifier within the soil. Furthermore, the dolomite and feldspar characteristic peaks appearing in the modified soil sample further reflect that the addition of nano-montmorillonite optimized the microchemical environment of the soil sample, providing support for the densification of the soil structure at the phase level by promoting the manifestation or formation of related minerals.

[0051] Test Example 5 The functional groups and chemical bond characteristics of nano-montmorillonite-modified dispersible soil were analyzed (FTIR test). Fourier transform infrared spectroscopy was used (see...). Figure 5 (a) and (b) in the figure reveal the modification mechanism of nano-montmorillonite on dispersible soil at the molecular scale. Spectroscopic analysis shows that at 3431.08 cm⁻¹... - The OH stretching vibration peak near ¹ showed significant broadening and intensity enhancement after modification, indicating that a stable hydrogen bond network was formed between the interlayer water and hydroxyl groups on the surface of the montmorillonite particles. At 1631.08 cm⁻¹ - The increased intensity of the HOH bending vibration peak near ¹ further confirms the significant synergistic effect between the hydrophilic properties of nano-montmorillonite and bound water in the soil. Meanwhile, at 1433.54 cm⁻¹... - The weakening of the C=O stretching vibration peak near ¹ profoundly reflects the extremely strong adsorption and encapsulation effect of nano-montmorillonite on carbonate particles (such as calcite) in the soil. Finally, at 872.52 cm⁻¹... - The Si-O bending vibration peaks of silicate minerals at positions ¹ become more regular, which, from the perspective of chemical bond energy, confirms that the microstructure of the mineral framework has evolved into a highly dense state under the dual effects of filling and cementation.

[0052] Test Example 6 The microscopic characteristics of soil samples before and after modification were compared and observed using scanning electron microscopy and image processing techniques. See the appendix for details on the morphological evolution. Figure 6(a) and (b) show that the unmodified soil sample has an extremely loose structure and smooth particle surfaces. However, after incorporating nano-montmorillonite, the layered particles exhibit a significant physical filling effect, gradually transforming the soil from an initial mosaic structure to a stable clumpy cemented structure. The contact mode of soil particles changes from point contact to surface contact. Combined with quantitative analysis, as the amount of nano-montmorillonite increases, the soil porosity decreases significantly, and the pore type changes from "large and few" to "small and dense," effectively improving the soil density. Furthermore, the extracted microstructural parameters reflect the intrinsic relationship between the evolution of micropores and the improvement of macroscopic unconfined compressive strength, providing a scientific basis for the modification effect of nano-montmorillonite.

[0053] Comparative Example 1 This comparative example refers to the patent technology scheme with publication number CN105777019A for the preparation of modified dispersible soil. The specific steps are as follows: Take the same batch of dispersible soil from Jingbian, Shaanxi Province as in the embodiment of this invention, air dry it naturally, crush it, and pass it through a 10mm sieve to obtain the soil sample to be treated. Its optimal moisture content is 14.2%, and its maximum dry density is 1.71g / cm³. Weigh the cementing material according to the mass ratio of cementing material to surface soil = 15:100. The cementing material is composed of 65 parts by mass of high-calcium fly ash, 1.5 parts by mass of nano-montmorillonite, 2.3 parts by mass of sodium borate, and 0.5 parts by mass of triethanolamine. Three parts of 425 cement and 33 parts of nano-montmorillonite were used. The amount of nano-montmorillonite was only 0.225% of the dry weight of the soil to be treated. First, the nano-montmorillonite and additives were added to 10 times the amount of water and stirred to prepare solution A for later use. Then, fly ash, cement, sodium borate, and triethanolamine were added to a mixer. Water with 1.5 times the weight of the cementitious material was added and stirred for 2 minutes. Solution A was added and stirred for another 2 minutes. Then, the dispersible soil to be treated was added and stirred for 4 minutes to obtain a mixture. The mixture was directly poured into a mold and compacted to form a shape. The dry density was controlled at 1.7 g / cm³. After demolding, the soil was covered with a film and cured for 5 days to obtain a comparative modified soil sample. Performance tests showed that the soil sample obtained in this comparative example was still a dispersible soil after pinhole and fragment tests. Its permeability coefficient was only reduced by 12.3% compared with the original dispersible soil, and its unconfined compressive strength was only increased by 37.5%. It could not solve the core engineering problems of dispersible soil disintegrating and having poor impermeability when exposed to water. Compared to the comparative example, this invention does not require the compounding of cement, fly ash and other cementing materials. It can achieve the essential transformation of dispersible soil from dispersible to non-dispersible soil by only using 7% to 10% nano-montmorillonite. It does not require complicated solution pre-preparation process. Through the standardized process of dry mixing-wet mixing-pre-curing-compacting, the permeability coefficient of modified soil can be reduced by up to 88.76% and the unconfined compressive strength can be increased by up to 216.07%. At the same time, it avoids the high carbon emissions and soil alkalization problems caused by cement hydration. The process is simpler, the modification effect is more significant, and the environmental friendliness is stronger. It can be directly applied to core geotechnical engineering scenarios such as water conservancy dams and canal lining, rather than just being suitable for slope surface greening.

[0054] Comparative Example 2 This comparative example refers to the patent technology scheme with publication number CN102485805A for preparing modified nano-montmorillonite, and uses it to modify dispersible clay. The specific steps are as follows: First, concentrated sulfuric acid and water are mixed at a mass ratio of 1:1 to prepare an acidic composite intercalation aqueous solution; Second, 30nm nano-sodium-based montmorillonite is mixed with the acidic composite intercalation aqueous solution at a mass ratio of 1:1, stirred at 90℃ for 3h, filtered, washed until neutral, and dried to obtain primary modified montmorillonite; Third, the primary modified montmorillonite is dispersed in a 30% ethanol-deionized aqueous solution, stirred in a 60℃ water bath for 4h, and 0.05% by weight of titanate coupling agent of montmorillonite is added dropwise, and kept at this temperature for 2h to obtain a montmorillonite mixture; Fourth, the mixture is further processed into a montmorillonite mixture. 10% (by weight) of the primary modified montmorillonite was added to the liquid, kept warm and stirred for 3 hours, ultrasonically dispersed for 30 minutes, heated to 60°C and protected with nitrogen, and 0.3% (by weight) of azobisisobutyronitrile (AIBN) was added and reacted for 5 hours. The mixture was then filtered, washed, dried, and ground to obtain secondary modified nano-montmorillonite. Dispersed soil from the same batch as in the embodiments of this invention was taken, air-dried, crushed, and sieved through a 0.5 mm sieve. 9% of the dry weight of the soil to be treated was weighed and added to the soil. The mixture was mechanically stirred until homogeneous, and water was added to adjust the moisture content to 14.2%. The mixture was stirred again until homogeneous. The mixture was directly compacted without pre-curing, and the dry density was controlled at 1.7 g / cm³. After curing for 5 days, a comparative modified soil sample was obtained. Performance testing revealed that while the soil sample obtained in this comparative example was identified as non-dispersed soil, its permeability coefficient was only reduced by 42.6% compared to the undisturbed dispersed soil, and its unconfined compressive strength was only increased by 68.2%. The modification effect was far below the optimal working condition of this invention. Furthermore, the preparation of modified nano-montmorillonite requires multiple complex steps, including acidic intercalation, coupling modification, and monomer polymerization. These steps involve harsh reaction conditions, long preparation cycles, and high costs, and also pose safety and environmental risks due to the use of hazardous chemicals such as concentrated sulfuric acid and organic solvents. In contrast to this comparative example, this invention directly uses commercially available nano-montmorillonite dry powder that has not undergone secondary chemical modification. It eliminates the need for complex pretreatment modification processes. A 12-24 hour pre-curing process fully activates the cation exchange and hydration activity of the nano-montmorillonite. Combined with a synergistic mechanism of physical filling, electrochemical regulation, and hydration cementation, it achieves superior impermeability and mechanical property enhancement. Simultaneously, it significantly simplifies construction procedures, reduces engineering costs, and avoids the environmental risks associated with chemical modification. This allows for direct in-situ soil modification and large-scale engineering filling applications.

[0055] Compared to Comparative Examples 1 and 2, this invention demonstrates significant advantages in technical approach, construction process, modification effect, and engineering applicability. Technically, Comparative Example 1 uses only nano-montmorillonite as an auxiliary component, failing to fundamentally inhibit soil particle dispersion; Comparative Example 2 employs complex chemical modification, with a stringent process unsuitable for soil engineering applications. This invention directly uses commercially available nano-montmorillonite, reducing soil porosity through physical filling effects and inhibiting soil particle dispersion by regulating the double-layer structure through cation exchange. Simultaneously, it utilizes the lamellar hydrated silicate cement generated by the hydration reaction to enhance the connection strength between soil particles, achieving highly efficient targeted modification of dispersed soil through a triple synergistic effect. In terms of construction process, Comparative Example 1 involves complex ingredient mixing and numerous procedures; Comparative Example 2 uses strong acids and organic solvents, posing safety and environmental risks. This invention employs a simple process of dry mixing-wet mixing-pre-curing-compacting, requiring no complex equipment or chemical treatment, making construction simple, environmentally friendly, and more economical. Regarding modification effects, the impermeability and strength improvement of the two comparative examples are far inferior to that of this invention. This invention can achieve the transformation of dispersible soil to transitional soil with a 7% admixture content, and completely transform it into non-dispersible soil with a 9% admixture content. Under optimal conditions, the permeability coefficient is reduced by 88.76% and the unconfined compressive strength is increased by 216.07%, which can stably meet the actual use requirements of water conservancy dams, canal lining, slope protection and other projects.

Claims

1. A method for modifying dispersible soil with nano-montmorillonite, characterized in that, Includes the following steps: Nano-montmorillonite is mixed into the dispersible soil to be treated and mechanically stirred until uniform; water is added to the mixed soil and adjusted to the required moisture content, and then stirred and mixed again until uniform to obtain a mixture; the mixture is pre-cured to obtain a modified mixture, and then the modified mixture is compacted and shaped, and further cured to obtain modified dispersible soil.

2. The method for modifying dispersible soil with nano-montmorillonite according to claim 1, characterized in that, The nano-montmorillonite is a creamy white powder with the following physical properties: density 2.0-2.4 g / cm³, specific surface area ≥336 m² / g, moisture content ≤3%, pH value 7.0-8.0, interlayer spacing 1.2-1.3 nm, and particle size 10-50 nm.

3. The method for modifying dispersible soil with nano-montmorillonite according to claim 1, characterized in that, The dispersible soil to be treated is obtained by naturally air-drying, crushing, and sieving through a 0.2mm-0.5mm sieve.

4. The method for modifying dispersible soil with nano-montmorillonite according to claim 3, characterized in that, The moisture content of the naturally air-dried dispersible soil is 14.2%-14.7%, and the dry density is 1.65-1.75 g / cm³.

5. The method for modifying dispersible soil with nano-montmorillonite according to claim 1, characterized in that, The nano-montmorillonite is incorporated into the dispersible soil to be treated at a ratio of 5% to 10% of the dry mass of the dispersible soil to be treated.

6. The method for modifying dispersible soil with nano-montmorillonite according to claim 5, characterized in that, The preferred doping ratio is 9%.

7. The method for modifying dispersible soil with nano-montmorillonite according to claim 1, characterized in that, The required moisture content of the mixture is 13.2% to 15.2%.

8. The method for modifying dispersible soil with nano-montmorillonite according to claim 1, characterized in that, The pre-curing time is 12h~24h.

9. The method for modifying dispersible soil with nano-montmorillonite according to claim 1, characterized in that, The compaction molding adopts a layered compaction method, in which the modified mixture is compacted in 3-5 layers, and each layer is compacted 16-25 times. The dry density of the modified mixture after compaction is 1.5-1.7 g / cm³, the curing time is 1-5 days, and the curing temperature is 5-35℃.

10. An application of nano-montmorillonite-modified dispersible soil, characterized in that, The modified dispersible soil prepared by the method of nano-montmorillonite modified dispersible soil as described in any one of claims 1 to 8 is used for dam filling, channel lining, slope protection and foundation treatment of water-retaining structures in water conservancy projects.

Images