Expansive soil improvement method based on moisture regulation and control network

Abstract

The invention relates to the technical field of geotechnical engineering, in particular to an expansive soil improvement method based on a moisture regulation and control network. The method comprises the following steps: firstly, measuring the nano-pore proportion Pnano of the expansive soil, and grading; accurately matching a composite modifier containing a main curing agent, a targeted filling agent compounded by modified nano silica sol and superfine slag, and a moisture regulating agent compounded by SAP and hydrophobic bentonite according to a grading result, wherein the composite modifier is prepared from a main curing agent, a targeted filling agent compounded by modified nano silica sol and superfine slag and a moisture regulating agent compounded by SAP and hydrophobic bentonite; then, a gradient excitation mixing technology is adopted, a three-dimensional network formed by part of the moisture regulating agent is embedded in layering compaction in real time, and finally activation curing containing dry-wet circulation is carried out. Through deep synergy of the components and the process, effective plugging of key nanopores and active regulation and control of moisture migration are realized, so that the improved soil body has extremely low charged expansion rate (less than 0.5%) and excellent dry-wet cycle stability (the strength retention rate is greater than 90%), and the problem of long-term deformation of expansive soil engineering is fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and more specifically to a method for improving expansive soil based on a moisture regulation network. Background Technology

[0002] Expansive soils, rich in hydrophilic minerals such as montmorillonite, swell dramatically upon contact with water and shrink severely upon loss of water, posing a global engineering geological challenge. Existing remediation technologies primarily address macroscopic physical replacement or chemical bonding, which, while effective to some extent, have inherent limitations and cannot fundamentally solve the long-term stability problem.

[0003] Currently, the mainstream methods include: Inorganic solidifying agents such as lime and cement are used to improve soil hydrophilicity through ion exchange and cementation reactions. However, this method results in uneven improvement depth, easily forming weak zones in the core where the soil has not fully reacted. Furthermore, its hydration products are prone to decomposition under long-term wet-dry cycles, and its high alkalinity is environmentally unfriendly. More importantly, traditional solidifying agents have relatively coarse particles (above micrometers), primarily filling large and medium pores (>50 nm) in the soil. They are almost ineffective in penetrating and modifying the abundant mesoporous (2-50 nm) and microporous (<2 nm) networks that play a crucial role in water adsorption and transport. These nanoscale pores are the "main battlefield" for strong bound water storage and capillary action; their untreated state is the root cause of the "recurrence" of the soil's expansion potential after repeated wet-dry cycles.

[0004] Adding industrial waste such as slag and fly ash: often used as an auxiliary cementing material in conjunction with lime and cement. Although conventionally sized slag powder can improve particle size distribution and fill some pores, its specific surface area is limited, its activity is slow, its targeting of nanopores is poor, and the interfacial bonding strength with soil minerals needs to be improved.

[0005] Setting up external waterproof barriers (such as geomembranes or waterproof blankets) attempts to prevent moisture migration. However, in complex real-world conditions, the integrity of these barriers cannot be guaranteed permanently, and they cannot regulate the existing moisture distribution within the soil. Once moisture breaches the barrier or intrudes through other pathways, the soil will still expand dramatically.

[0006] The key scientific problem neglected by existing technologies lies in treating expansive soil as a homogeneous body. Improvement strategies focus on "overall weakening" its hydrophilicity or "overall isolating" water, failing to address the fundamental design from the synergistic perspective of multi-scale pore structure regulation and spatial water distribution management. Therefore, developing a comprehensive method capable of suppressing expansion at its microstructural source and achieving long-term water stability is a critical technological bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a comprehensive improvement method for expansive soil that can accurately diagnose and target the filling of key nanoscale pores sensitive to swelling and shrinkage in expansive soil, and simultaneously construct an active moisture regulation network inside it, so as to achieve extremely low swelling rate under load, ultra-high long-term stability and anti-cracking of dry-wet cycle on a macroscopic scale.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: An expansive soil improvement method based on a moisture regulation network, comprising the following steps: S1: Determine the pore size distribution of the expansive soil, and calculate the percentage Pnano of the pore volume within the range of 1 nm to 100 nm in the total pore volume; classify the expansive soil according to the Pnano value; S2: According to the classification result of step S1, prepare a composite modifier by mass percentage of dry soil, and the composite modifier includes: Component A: Quicklime powder; Component B: Prepared by compounding surface-modified nano-silica sol and ultra-fine high-activity slag micro-powder; Component C: Prepared by mixing high molecular weight water-absorbing resin particles and organically hydrophobic modified bentonite micro-powder; S3: First dry-mix the expansive soil and the dry material of the composite modifier prepared in step S2; then add an activation liquid containing a reaction activator for the first wet-mix, and the water addition amount is controlled so that the water content of the mixture reaches 65%-75% of its optimum water content; finally, add clear water for the second wet-mix to make the total water content reach 95%-105% of the optimum water content; S4: Layer-compact the mixture obtained in step S3, and between every two layers of compacted soil bodies, embed a regulation medium layer prepared by premixing a part of the Component C and inert fine particle materials; S5: After hermetically curing the compacted soil body, carry out at least two cycles of dry-wet cycle activation curing, and each cycle includes a drying process and a soaking process.

[0009] Further, in the above expansive soil improvement method based on a moisture regulation network, in S1, the classification according to the Pnano value is: Grade I, Pnano > 40%; Grade II, 20% < Pnano ≤ 40%; Grade III, Pnano ≤ 20%.

[0010] Further, in the above expansive soil improvement method based on a moisture regulation network, in S2, for Grade I expansive soil, the dosage of Component A is 4.0-5.0% of the dry soil mass, the total dosage of Component B is 6.0-8.0%, and the total dosage of Component C is 0.8-1.2%; For Class II expansive soil, the dosage of component A is 3.0-4.0%, the total dosage of component B is 4.0-6.0%, and the total dosage of component C is 0.5-0.8%. For Class III expansive soil, the dosage of component A is 2.0-3.0%, the total dosage of component B is 2.0-4.0%, and the total dosage of component C is 0.3-0.5%.

[0011] Furthermore, in the above-mentioned method for improving expansive soil based on a moisture regulation network, in S2, the surface-modified nano-silica sol is an alkaline silica sol modified with a silane coupling agent, and its SiO2 particle size is 5-20 nm; the specific surface area of ​​the ultrafine highly active slag powder is ≥600 m². 2 / kg; the ratio of the solid mass of the surface-modified nano-silica sol to the ultrafine highly active slag powder is 1:(2.5-4.0).

[0012] Furthermore, in the above-mentioned method for improving expansive soil based on a moisture regulation network, the organic hydrophobic modified bentonite micro powder is bentonite modified with long-chain alkyl quaternary ammonium salt, and its contact angle with water is greater than 90°; the mixing mass ratio of the superabsorbent polymer particles to the organic hydrophobic modified bentonite micro powder is 1:(8-12).

[0013] Furthermore, the above-mentioned method for improving expansive soil based on a moisture regulation network also includes component D, which is aluminum sulfate or potassium aluminum sulfate, and the amount added is 0.5-1.5% of the total dry mass of the composite modifier, and it is pre-dissolved in the activation liquid described in S3.

[0014] Furthermore, in the above-mentioned method for improving expansive soil based on a moisture regulation network, the amount of water added in the first wet mixing is to control the moisture content of the mixture to reach 70%-75% of its optimum moisture content.

[0015] Furthermore, in the above-mentioned method for improving expansive soil based on a moisture regulation network, the amount of component C in the regulation medium layer accounts for 30%-50% of its total amount; the inert fine-particle material is dry quartz sand; and the mixing mass ratio of component C to the inert fine-particle material is 1:(15-20).

[0016] Furthermore, in the above-mentioned method for improving expansive soil based on a moisture regulation network, the amount of the regulating medium layer spread in the compacted soil is 50-100 g / m³. 2 .

[0017] Furthermore, in the above-mentioned method for improving expansive soil based on a moisture regulation network, in S5, each cycle of the dry-wet cycle activation curing is: drying for 48 hours at 40±2℃, and then soaking in water at room temperature for 24 hours.

[0018] The beneficial effects of this invention are as follows: The main curing agent (component A) provides the macroscopic framework and alkaline environment; ultrafine slag (one of components B) efficiently fills micron-sized pores and provides an active source; surface-modified nano-silica sol (the core of component B), with its extremely small particle size and surface activity, penetrates into the key nanopores and combines in situ with the slag hydration products (CSH gel) to form a dense nanocomposite gel, fundamentally "sealing off" the microscopic channels for water adsorption and expansion. The reaction processes of components A and B mutually stimulate each other, and the products overlap, forming a continuous reinforcement from the nano to the macroscopic level.

[0019] The embedded control network (component C construction) functions as a "miniature reservoir-gate." The superabsorbent polymer particles act as the "reservoir," absorbing excess infiltrated water; the hydrophobically modified bentonite acts as the "gate," its hydrophobic surface slowing the diffusion of liquid water into the surrounding soil and preferentially transferring water via vapor diffusion, thus significantly mitigating the moisture gradient within the soil. This synergy transforms passive water prevention into active water management, effectively suppressing shrinkage cracks caused by uneven wetting and drying. In terms of process, gradient mixing (S3) ensures initial moisture uniformity, while the embedded network construction (S4) establishes a long-term control physical structure. This synergistic process ensures the durability of the moisture management effect.

[0020] The wet-dry cycle activation curing (S5) is not merely a test, but an integral part of the design. The cycle provides continuous hydration and migration momentum for unreacted nano-silica sol and slag powder, enabling them to preferentially deposit and react at newly formed micro-defects, achieving self-repair of micro-cracks. This complements the moisture regulation network's effect of preventing macro-cracks, forming a dual guarantee mechanism of "macro-crack prevention" and "micro-self-healing," resulting in a qualitative leap in the long-term performance of the improved soil (strength retention >90%, no visible cracks).

[0021] This invention takes a unique microscopic perspective (targeting nanopores and managing moisture distribution) and achieves deep synergy between components and steps through non-obvious material functionalization design (modified nanomaterials, hydrophobic-hydrophilic composite regulators) and construction processes (gradient mixing, embedded three-dimensional networks). Ultimately, it effectively improves performance in terms of extremely low load expansion rate, ultra-high strength retention rate after wet-dry cycles, and crack resistance. Detailed Implementation

[0022] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments.

[0023] The present invention relates to a method for improving expansive soil based on a moisture regulation network, comprising the following steps: S1: Collect representative expansive soil samples. After air-drying, crushing, and sieving, in addition to measuring their basic physical indexes (liquid-plastic limit, free swelling ratio), the core is to accurately measure their pore size distribution by mercury intrusion porosimetry, especially calculate the percentage of the pore volume within the range of 1 nm to 100 nm in the total pore volume, which is defined as the nano-pore ratio Pnano. Microstructure classification of the swelling potential of the soil mass is carried out according to the Pnano value: Grade I (high potential, Pnano > 40%), Grade II (medium potential, 20% < Pnano ≤ 40%), Grade III (lower potential, Pnano ≤ 20%). The classification results provide the only quantitative basis for the precise compatibility of subsequent functional materials;

[0024] S2: According to the classification results determined in S1, prepare a composite modifier with the synergistic action of the following four types of functional components according to the dry soil mass percentage: Main curing agent (Component A): It is quicklime powder with a specific surface area ≥ 400 m 2 / kg, providing high reaction activity Ca 2+ and an alkaline environment. Its dosage Ca is: 4.0 - 5.0% for Grade I soil, 3.0 - 4.0% for Grade II soil, and 2.0 - 3.0% for Grade III soil;

[0025] Nano-pore targeted filler (Component B): It is compounded by surface-modified nano-silica sol and ultra-fine high-activity slag powder according to a solid mass ratio of 1: (2.5 - 4.0); the surface-modified nano-silica sol is an alkaline silica sol modified by a silane coupling agent (such as γ-aminopropyltriethoxysilane), with a SiO2 particle size of 5 - 20 nm and a solid content of 25 - 30%; the specific surface area of the ultra-fine high-activity slag powder ≥ 600 m 2 / kg, and the particle size D90 ≤ 10 μm. The total dosage Nb of Component B is: 6.0 - 8.0% for Grade I soil, 4.0 - 6.0% for Grade II soil, and 2.0 - 4.0% for Grade III soil. The key role of Component B is to form a particle size gradient to achieve step-by-step filling and chemical bonding from the nano-scale to the micro-scale. Especially, the modified nano-silica sol can penetrate into the deep pores that traditional materials cannot reach;

[0026] Moisture spatial orientation regulator (Component C): It is physically mixed by partially cross-linked polyacrylate-based superabsorbent polymer (SAP) particles and organically hydrophobic modified bentonite powder according to a mass ratio of 1: (8 - 12). The particle size of SAP particles is 80 - 120 mesh, and the water absorption capacity is 150 - 250; the hydrophobic modified bentonite is modified by long-chain alkyl quaternary ammonium salts with a contact angle > 90°. The total dosage Hc of Component C is: 0.8 - 1.2% for Grade I soil, 0.5 - 0.8% for Grade II soil, and 0.3 - 0.5% for Grade III soil. Component C constitutes an "intelligent moisture buffer unit", where SAP is responsible for large-capacity water absorption and release, and hydrophobic bentonite regulates the interfacial wettability to prevent water from invading the soil matrix too quickly;

[0027] Reaction activator and dispersant (component D): Aluminum sulfate (Al2(SO4)3) or potassium aluminum sulfate, added at 0.5-1.5% of the total dry mass of the composite modifier, pre-dissolved in a portion of the mixing water to form an activating solution. Component D provides early Al... 3+ It can stimulate the activity of slag, and its acidity can temporarily slow down the violent reaction of lime and improve the uniformity of mixing.

[0028] S3: Gradient-activated mixing and moisture balance process, including: S31: Dry mixing in one step. Place the expansive soil and all the dry composite modifier materials (A+B+C) prepared in step S2 into a mixer and mix at high speed for ≥3 minutes in a dry state to achieve initial dispersion. S32: Single-stage activation wet mixing: The activation liquid containing component D is evenly sprayed into the dry mix, and the amount of water added is controlled to reach 65%-75% of the optimum moisture content of the soil. Continue stirring for 2-3 minutes at this low moisture content. This step aims to preferentially activate the surface of the modifier with limited moisture, promote early reaction, and prevent material agglomeration by utilizing the properties of the activation liquid;

[0029] S33: Secondary Balanced Wet Mixing: Add the remaining required clean water (to bring the total moisture content to 95%-105% of the optimum moisture content) evenly, and continue mixing for 3-5 minutes until a mixed soil material with uniform color and moisture content and no lumps is obtained. This gradient water addition process ensures the uniform distribution of moisture and modifier among soil particles, laying the foundation for subsequent uniform reaction;

[0030] S4: Fill the mold with the mixture in layers according to the designed compaction degree and compact it. The core innovation of this step is: between every two layers of compacted soil (e.g., after every 5cm of compaction), apply 50-100 g / m³ of water. 2 A very low spreading amount is used to uniformly spread an embedded moisture-regulating medium, which is a mixture of 30%-50% of component C from step S2 and dry fine quartz sand (passed through a 100-mesh sieve) at a mass ratio of 1:(15-20). Immediately after spreading, the next layer of mixture is placed over it and compacted, so that the medium layer is encased within the soil, forming a discontinuous, three-dimensional moisture buffer interface network. This network does not weaken the continuity of the main structure but effectively intercepts and redistributes migrating moisture.

[0031] S5: The formed specimens are sealed and cured for 7 days (at 20±2°C and humidity ≥95%), and then subjected to wet-dry cycling activation curing: dried in an oven at 40±2°C for 48 hours, and then immersed in water at room temperature for 24 hours. This is one cycle, and a total of 2 - 4 cycles are carried out. This process not only tests the durability, but more importantly aims to utilize the osmotic pressure and capillary action driven by wet-dry cycling to promote the migration and reaction of the unreacted component B (especially nano-silica sol) to micro-cracks or stress concentration areas, achieving "self-repair" and continuous optimization of the microstructure.

[0032] Example 1 The target soil sample in this example is a typical Class II expansive soil, and its basic physical properties are: liquid limit 52%, plastic limit 24%, free swelling ratio 68%, optimum water content = 18.0%, maximum dry density (ρdmax) = 1.75 g / cm³. The pore volume ratio Pnano within the pore diameter range of 1 - 100 nm measured by mercury intrusion porosimetry is 35%;

[0033] In S1, a representative air-dried soil sample is taken, crushed and sieved through a 2 mm sieve; a mercury intrusion porosimeter is used to measure its complete pore size distribution curve; according to the test results, Pnano = 35% is calculated; according to the classification standard of the present invention (20% < Pnano ≤ 40%), this soil sample is determined as Class II expansive soil; In S2, Component A: quicklime powder 35.0 g (dosage 3.5%); Component B: modified nano-silica sol (calculated based on solid content): Weigh 33.3 g of the liquid agent of modified nano-silica sol with a solid content of 30%, which contains 10.0 g of SiO2 solid; ultra-fine high-activity slag micropowder is 40.0 g; The total dosage of Component B is 5.0% (10.0 g + 40.0 g), and the mass ratio of the solid content of the modified nano-silica sol to the ultra-fine slag is 1:4; Component C: superabsorbent polymer (SAP) particles: 0.5 g; Organic hydrophobic modified bentonite micropowder: 5 g; The total dosage of Component C is 0.6%, and the mass ratio of SAP to hydrophobic bentonite is 1:9.9; Component D: aluminum sulfate powder 0.81 g (about 1.0% of the total dry mass of A + B + C); The mass of aluminum sulfate used to prepare the excitation liquid has been calculated separately and is not included in the dry mass of the above Components A, B, and C; In S3, the first dry mixing: Pour 1000 g of dry soil and all the dry materials of the above-mentioned weighed Components A, B, and C into a vertical mixer. Under dry conditions, stir at a medium speed (about 60 r / min) for 3.5 minutes until visually mixed evenly without color streaks;

[0034] Preparation of activating solution and first-stage wet mixing: Dissolve 0.81g of aluminum sulfate (component D) in 121.5g of clean water and stir thoroughly until completely dissolved to prepare the activating solution; start the mixer and spray the activating solution evenly into the dry mix; the amount of water added in this step (121.5g) brings the total moisture content of the mixture to approximately 12.15% (121.5g / 1000g), which is about 67.5% of the optimum moisture content (18.0%) of the soil sample; continue stirring for 2.5 minutes, at which point the mixture is slightly damp but far from clumping together; Secondary equilibrium wet mixing: The total water required to reach the optimum moisture content (18.0%) is calculated to be 180g. 121.5g has already been added through the activation solution, so 58.5g of clean water needs to be added. Spray the 58.5g of clean water evenly into the mixer. Set the mixer to high speed (approximately 120 rpm) and continue mixing for 4 minutes. After stopping mixing, check that the mixture is a uniform grayish-brown color, can be formed into a ball by hand, and crumbles easily when dropped, without any white lime spots or unevenly distributed lumps, indicating a highly uniform distribution of moisture and modifier. At this point, the measured moisture content of the mixture is approximately 17.8%-18.2%.

[0035] In step S4, prepare a cylindrical mold with an inner diameter of 50 mm and a height of 130 mm. Fill the mold with the mixture in three layers, each layer with approximately equal initial height. After filling and leveling the first layer, compact it to the predetermined height (controlling the compaction degree to 95%). Then, evenly spread an embedded moisture-regulating medium on the top surface of the compacted first layer using a fine sieve. Take 40% of the total amount of component C from step S2, i.e., (0.55 g + 5.45 g) * 40% = 2.40 g; manually premix this with 43.2 g of dry fine quartz sand (passed through 100 mesh) in a small container to obtain approximately 45.6 g of medium. Based on the cross-sectional area of ​​the mold, the spreading amount should be controlled at approximately 75 g / m². 2 ;

[0036] After spreading the medium, immediately add the second layer of mix and level it to avoid disturbing the medium layer, then compact it. Repeat this process, spreading the same amount of the same medium again on the top surface of the compacted second layer; finally, add the third layer of mix and compact it until the specimen height is 100mm±1mm, demold, and obtain a cylindrical specimen with two discontinuous moisture control interfaces inside.

[0037] In step S5, the demolded specimen was immediately wrapped tightly with double-layered plastic wrap to prevent moisture evaporation. It was then placed in a constant temperature and humidity curing chamber and cured for 7 days at a temperature of 20±1℃ and a relative humidity ≥95%. After 7 days of curing, the specimen was removed, the plastic wrap was removed, and it was placed in a forced-air drying oven at 40±2℃ for 48 hours of continuous drying. Then, the specimen was completely immersed in clean water at room temperature (20±2℃) for 24 hours. This "48h drying + 24h immersion" process is defined as one complete wet-dry cycle. This embodiment involves three cycles. After the cycle, the surface of the specimen was wiped dry before subsequent performance testing.

[0038] Example 2 The target soil sample in this embodiment is a typical Class I expansive soil, with the following basic physical properties: liquid limit 68%, plastic limit 30%, free swelling rate 105%, optimum moisture content 22.5%, and ρdmax 1.68 g / cm³. 3 The Pnano value was determined to be 48% by mercury porosimetry.

[0039] In S1, the operation is the same as in Example 1; Pnano is calculated to be 48%; according to the grading standard (Pnano>40%), the soil sample is determined to be Grade I expansive soil; In S2, based on 1000g of dry soil, weigh according to the compatibility requirements of Grade I soil: Component A: 45.0g quicklime powder (admixture amount 4.5%); Component B: Modified nano-silica sol (solid): Weigh 50.0g of modified nano-silica sol liquid agent with a solid content of 30% (including 15.0g of SiO2 solid); 55.0g of ultrafine high-activity slag powder; The total dosage of component B is 7.0% (15.0g + 55.0g), with a mass ratio of 1:3.67; Component C: SAP particles: 0.91g; Organic hydrophobic modified bentonite powder: 9.09g; Total content of component C: 1.0%, mixing mass ratio: 1:10; Component D: 1.10g aluminum sulfate powder (approximately 1.0% of the total dry mass of components A, B, and C). In S3, dry mixing once: Same as in Example 1, dry mixing for 3.5 minutes; One-time activation wet mixing: Dissolve 1.10g of aluminum sulfate in 168.8g of water to prepare an activation solution; spray the activation solution, and add water to make the moisture content of the mixture reach about 16.88% (168.8g / 1000g), which is about 75.0% of the optimum moisture content (22.5%); stir for 2.5 minutes; Secondary balanced wet mixing: Total water requirement 225g, 168.8g already added, 56.2g of clean water added; high-speed mixing for 4 minutes; final mixture is uniform, actual measured moisture content is approximately 22.0%-22.8%; In S4, the molding and layering were the same as in Example 1. The embedded medium was prepared as follows: 40% of the total C component, i.e., (0.91g + 9.09g) * 40% = 4.00g, was premixed with 72.0g of dry fine quartz sand (ratio 1:18), for a total weight of 76.0g. After each compacted layer, the medium was evenly spread, with the spreading amount controlled at 80 g / m². 2 Compact the specimens to the same size to obtain specimens with built-in control networks; In S5, the standard sealing and curing procedure is the same as in Example 1, with a curing period of 7 days. Dry and wet cycle activation and curing: Same as in Example 1, perform 3 cycles of "drying at 40℃ for 48 hours + soaking in water at room temperature for 24 hours"; Comparative Example 1 Compared with the scheme of Example 1, the difference is that the pore structure diagnosis and classification in step S1 were not performed. Instead, a fixed ratio was used for improvement. The content of quicklime in component A was 4.0%, the total content of component B was 5.0% (modified nano silica sol: ultrafine slag = 1:4), the total content of component C was 0.6% (SAP: hydrophobic bentonite = 1:10), and the content of component D was 1.0% of the total dry material. The subsequent steps S3 to S5 were the same as in Example 1.

[0040] Comparative Example 2 Compared with the scheme of Example 1, the difference is that in step S2, the "surface-modified nano silica sol" is replaced with unmodified ordinary alkaline nano silica sol with the same solid content and particle size, while the other components, ratios and all subsequent steps are exactly the same as in Example 1. Comparative Example 3 Compared with the scheme of Example 1, the difference is that in step S2, component B only contains ultrafine highly active slag powder, with an admixture amount of 5.0%, and the modified nano-silica sol is completely removed. The admixture amounts of components A, C, and D, as well as all subsequent steps, are the same as in Example 1;

[0041] Comparative Example 4 Compared with the scheme in Example 1, the difference is that in step S2, "ultrafine high-activity slag powder (specific surface area ≥ 600 m²)" is used. 2 The " / kg" was replaced with an equal mass of ordinary S95 grade slag powder (specific surface area approximately 420 m² / kg). All other components, proportions, and subsequent steps were the same as in Example 1.

[0042] Comparative Example 5 Compared to the scheme in Example 1, the difference is that in step S2, component C contains only superabsorbent polymer (SAP) particles at a dosage of 0.6%, completely eliminating the organic hydrophobic modified bentonite powder. The dosages of components A, B, and D, as well as all subsequent steps, are the same as in Example 1.

[0043] Comparative Example 6 Compared with the scheme of Example 1, the difference is that in step S2, the "organic hydrophobic modified bentonite powder" is replaced with an equal mass of ordinary sodium-based bentonite powder. All other components, proportions and subsequent steps are the same as in Example 1.

[0044] Comparative Example 7 Compared with the scheme of Example 1, the difference is that in step S2, the internal ratio of component B is changed so that the mass ratio of modified nano-silica sol (solidified) to ultrafine slag powder is 1:1 (the total dosage is still 5.0%). Other components, proportions and all subsequent steps are the same as in Example 1.

[0045] Comparative Example 8 Compared with the scheme of Example 1, the difference is that in step S2, the internal ratio of component B is changed so that the mass ratio of modified nano-silica sol (solidified) to ultrafine slag powder is 1:8 (the total dosage is still 5.0%). Other components, ratios and all subsequent steps are the same as in Example 1.

[0046] Comparative Example 9 Compared to the scheme in Example 1, the difference is that in step S2, the internal ratio of component C was changed so that the mass ratio of SAP particles to hydrophobically modified bentonite powder was 1:4 (the total dosage remained at 0.6%). Other components, proportions, and all subsequent steps were the same as in Example 1.

[0047] Comparative Example 10 Compared to the scheme in Example 1, the difference is that in step S2, the internal ratio of component C was changed so that the mass ratio of SAP particles to hydrophobically modified bentonite powder was 1:20 (the total dosage remained at 0.6%). Other components, proportions, and all subsequent steps were the same as in Example 1.

[0048] Comparative Example 11 Compared to the scheme in Example 1, the difference is that the gradient excitation mixing process in step S3 is omitted. Instead, all the mixing water (including water containing dissolved component D) is added at once, and the mixture is stirred for the same total time, so that the moisture content directly reaches 100% of the optimum moisture content. All other steps and material ratios are the same as in Example 1.

[0049] Comparative Example 12 Compared to the scheme in Example 1, the difference is that the "layered compaction and embedded moisture control network construction" process in step S4 is omitted. That is, the mixture is directly compacted in layers without spreading any embedded control medium between the layers. All other steps and material ratios are the same as in Example 1.

[0050] Comparative Example 13 The difference from Example 1 is that in step S4, the embedded moisture control medium uses all of component C (i.e., 100% of component C is used to prepare the medium), instead of the 40% used in Example 1. The ratio of medium to quartz sand remains 1:18. All other steps and material ratios are the same as in Example 1.

[0051] Comparative Example 14 Compared to the scheme in Example 1, the difference is that the "dry and wet cycle activation curing" in step S5 is omitted. After the specimen is compacted in step S4, it is only subjected to standard sealing curing for 28 days, followed by performance testing. All other steps and material ratios are the same as in Example 1.

[0052] Comparative Example 15 Compared to the scheme in Example 1, the difference is that a traditional, simplified process is used. Although the material composition and total dosage are exactly the same as in Example 1, all the special processes are omitted. Specifically, all dry and wet materials are mixed at once, water is added to the optimal moisture content and mixed, then directly compacted in layers (without an embedded network), and finally only standard curing for 28 days is performed. This is a comprehensive comparison of "using only the materials of this invention, but not the methods of this invention".

[0053] Comparative Example 16 Compared with the scheme of Example 2, the difference is that the pore structure diagnosis and classification in step S1 were not performed, and the same fixed ratio as in Example 1 was directly used for improvement (i.e., A=3.5%, B=5.0%, C=0.6%). Subsequent steps S3 to S5 are the same as in Example 2.

[0054] Comparative Example 17 Compared with the scheme of Example 2, the difference is that in step S2, the "surface-modified nano silica sol" is replaced with unmodified ordinary alkaline nano silica sol with the same solid content and particle size, while the other components, ratios and all subsequent steps are exactly the same as in Example 2.

[0055] Comparative Example 18 Compared to the scheme in Example 2, the difference is that in step S2, component B only contains ultrafine, highly active slag powder, with a dosage of 7.0%, and the modified nano-silica sol is completely removed. The dosages of components A, C, and D, as well as all subsequent steps, are the same as in Example 2.

[0056] Comparative Example 19 Compared with the scheme of Example 2, the difference is that in step S2, the "ultrafine high-activity slag powder" is replaced with an equal mass of ordinary S95 grade slag powder. All other components, proportions and subsequent steps are the same as in Example 2.

[0057] Comparative Example 20 Compared to the scheme in Example 2, the difference is that in step S2, component C contains only superabsorbent polymer (SAP) particles at a dosage of 1.0%, completely eliminating the organic hydrophobic modified bentonite powder. The dosages of components A, B, and D, as well as all subsequent steps, are the same as in Example 2.

[0058] Comparative Example 21 Compared to the scheme in Example 2, the difference is that in step S2, the "organic hydrophobic modified bentonite powder" is replaced with an equal mass of ordinary sodium-based bentonite powder. All other components, proportions, and subsequent steps are the same as in Example 2.

[0059] Comparative Example 22 Compared to the scheme in Example 2, the difference is that in step S2, the internal ratio of component B was changed so that the mass ratio of modified nano-silica sol (solidified) to ultrafine slag powder was 1:2 (the total dosage remained at 7.0%). All other components, ratios, and subsequent steps were the same as in Example 2.

[0060] Comparative Example 23 Compared to the scheme in Example 2, the difference is that in step S2, the internal ratio of component B was changed so that the mass ratio of modified nano-silica sol (solidified) to ultrafine slag powder was 1:6 (the total dosage remained at 7.0%). All other components, ratios, and subsequent steps were the same as in Example 2.

[0061] Comparative Example 24 Compared to the scheme in Example 2, the difference is that in step S2, the internal ratio of component C was changed so that the mass ratio of SAP particles to hydrophobically modified bentonite powder was 1:6 (the total dosage remained at 1.0%). All other components, proportions, and subsequent steps were the same as in Example 2.

[0062] Comparative Example 25 Compared to the scheme in Example 2, the difference is that in step S2, the internal ratio of component C was changed so that the mass ratio of SAP particles to hydrophobically modified bentonite powder was 1:25 (the total dosage remained at 1.0%). All other components, proportions, and subsequent steps were the same as in Example 2.

[0063] Comparative Example 26 Compared to the scheme in Example 2, the difference is that the gradient excitation mixing process in step S3 is omitted. Instead, water is added all at once to 100% of the optimal moisture content for mixing. All other steps and material ratios are the same as in Example 2.

[0064] Comparative Example 27 Compared to the scheme in Example 2, the difference is that the "layered compaction and embedded moisture control network construction" process in step S4 is omitted, that is, the control medium is not spread between the layers. All other steps and material ratios are the same as in Example 2.

[0065] Comparative Example 28 The difference from Example 2 is that in step S4, the embedded moisture control medium uses all of component C (100%). The ratio of medium to quartz sand remains 1:18. All other steps and material ratios are the same as in Example 2.

[0066] Comparative Example 29 Compared with the scheme of Example 2, the difference is that the "dry and wet cycle activation curing" in step S5 is omitted, and only standard sealed curing for 28 days is performed. All other steps and material ratios are the same as those in Example 2.

[0067] Comparative Example 30 Compared to the scheme in Example 2, the difference is that a traditional and simple process is used. The material composition and total dosage are exactly the same as in Example 2, but the traditional process of one-time mixing, direct compaction, and standard curing for 28 days is used, without employing any of the special steps of this invention.

[0068] Performance testing methods: I. Unconfined compressive strength (UCS) test: The test was conducted according to method T0805 in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). The specimens, after curing, were subjected to axial compression without lateral restraint on a universal testing machine, with the loading rate controlled at 1 mm / min.

[0069] Record the maximum pressure P (N) at which the specimen fails, according to the formula UCS = 4P / (πD). 2 Calculate the strength (kPa), where D is the specimen diameter (m). Each group should contain at least 3 parallel specimens, and the arithmetic mean should be taken.

[0070] II. Load-induced expansion rate (δep) test: Refer to the test method for the loaded swelling rate of expansive soil in the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019). Prepare a ring specimen with a compaction degree of 95% and a height of approximately 20 mm, install it in a consolidation apparatus, and apply a constant vertical pressure of 50 kPa. Pour water into the container to fully saturate the specimen from bottom to top. Take a dial gauge reading every hour until the difference between two consecutive readings does not exceed 0.01 mm, which is considered stable.

[0071] The loaded expansion rate is calculated using the formula δep = (R - R0) / H0 × 100%, where R is the stable reading, R0 is the initial reading, and H0 is the initial height of the specimen. Each group of parallel tests should consist of no fewer than two tests.

[0072] III. Dry-wet cycle test: After completing 28 days of curing (or the specified curing), the specimens were subjected to five complete "drying-water immersion" cycles, following the procedure described in Section 4.3. Immediately after the fifth cycle of water immersion and drying, the unconfined compressive strength was tested and recorded as UCS_cyc. The strength retention rate was calculated using the formula: Strength retention rate (%) = (UCS_cyc / UCS_28d) × 100%, where UCS_28d is the strength of the specimens in the same group after 28 days of standard curing. After each cycle, the initiation and development of surface cracks on the specimens were visually observed and recorded.

[0073] The experimental results are shown in Tables 1 and 2: Table 1 Performance data of each comparative example for Example 1 (Class II soil) Table 2 Performance data of each comparative example for Example 2 (Grade I soil) Results analysis: Comparative Example 1 (Grade II soil fixed formulation) and Comparative Example 16 (Grade I soil low-concentration fixed formulation) showed significantly inferior performance compared to their corresponding examples. In particular, their swelling rates under load reached 0.85% and 1.55%, respectively, which are more than 2.4 times and 5.5 times higher than those of Examples 1 and 2 (0.35% and 0.28%). Obvious cracks also appeared after wet-dry cycles. This result directly demonstrates that the "universal formulation" approach, which ignores the differences in the micropore structure (Pnano) of the soil, is inefficient. This invention does not simply apply known materials to expansive soils, but creatively proposes a new technical problem diagnosis dimension: "quantitative classification based on the proportion of key nanopores (Pnano)."

[0074] The δep (0.70%) of Comparative Example 2 (Grade II soil, ordinary) was significantly higher than that of Example 1 (0.35%); the δep (0.85%) of Comparative Example 17 (Grade I soil, ordinary) far exceeded that of Example 2 (0.28%). Visually, the comparative examples showed "micro-cracks," while the examples were "complete and crack-free." This is not a simple change in performance. Ordinary nanoparticles tend to aggregate in soil and have weak interfacial bonding with the matrix. The silane coupling agent surface modification used in this invention is an unconventional technique addressing the specific problem of "how to stably disperse nanoparticles and chemically anchor them in the nanopores of soil." It significantly improves the swelling suppression and crack resistance effects, proving that this modification treatment is an indispensable part of achieving "targeted and efficient filling of nanopores."

[0075] In Comparative Examples 5 and 20, the removal of organically hydrophobically modified bentonite micropowder, and in Comparative Examples 6 and 21, the replacement with ordinary bentonite, resulted in a significant increase in δep and severe surface cracking. In particular, Comparative Example 21 (ordinary bentonite for Grade I soil) showed a δep as high as 1.75%, with a surface appearance of "dense cracks." This reveals a synergistic mechanism for spatial moisture regulation. SAP can only absorb and release water, while the role of hydrophobically modified bentonite is to actively alter the interfacial behavior and pathways of moisture migration, delaying the intrusion of liquid water into the core soil, thus forming a synergistic effect of "fast absorption and slow release, combined with gate control" with SAP. Using hydrophobic materials for the improvement of expansive soil requiring "waterproofing" may seem contradictory, but in fact, through specific combinations with other components (compounding with SAP, embedding in the network), it cleverly solves the deep-seated problem of "uniform moisture control and prevention of localized water accumulation."

[0076] Comparative Examples 7-10 and 22-25 show that even with a constant total content of each component, changing their internal proportions leads to significant performance fluctuations. For example, insufficient nano-silica sol in component B (Comparative Examples 8 and 23) results in an increase in δep; insufficient hydrophobic bentonite in component C (Comparative Examples 9 and 24) leads to a decrease in crack resistance. This demonstrates that the inventiveness of this invention lies not only in the introduction of these functional materials but also in the discovery of a specific ratio range (nano-silica sol: slag = 1:2.5-4.0; SAP: hydrophobic bentonite = 1:8-12) that produces the optimal synergistic effect. This range is a "golden interval" verified through numerous experiments. Deviating from this range weakens the positive synergistic effect between the components, failing to achieve the optimal effect of this invention. This indicates that the components are not simply superimposed but rather exist within a non-obvious, optimized network of synergistic relationships.

[0077] The performance of Comparative Examples 11 and 26 (one-time mixing) was slightly lower than that of Examples 1 and 2, indicating that gradient mixing and aluminum sulfate activation have a positive effect on ensuring reaction uniformity and initial moisture distribution, and are the cornerstone of the process to fully utilize the material performance.

[0078] The performance degradation observed in Comparative Examples 12 and 27 (without network) demonstrates that the network is crucial for long-term moisture management and crack resistance.

[0079] Comparative Examples 13 and 28 (using all C components to construct the network) outperformed the group without a network, but their strength and load expansion rate were still slightly inferior to the examples, and they were uneconomical. This demonstrates that the proposed solution of "constructing a sparse network using only a portion of the C components (30-50%)" achieves the optimal balance between effectiveness, cost, and structural integrity.

[0080] Although Comparative Examples 14 and 29 (standard curing only) showed low δep at 28 days, their long-term durability had not been tested in actual wet and dry environments. Their predicted strength retention rates (85%, 87%) were significantly lower than those of Examples 1 and 2 (94%, 95%) after activation curing. This indicates that "wet and dry cycle activation" is not merely a test, but a necessary step to promote the continued hydration and migration of unreacted materials to achieve "self-healing." It is an active design to improve long-term stability, rather than a passive test.

[0081] Results of Comparative Examples 15 and 30 (simple material mixing, conventional process). Despite using the exact same advanced materials as Examples 1 and 2, but employing only a conventional one-time mixing, compaction, and curing process, the performance (especially δep and crack resistance) showed a precipitous decline, even falling short of many comparative examples lacking only a single material (such as Comparative Examples 3, 4, and 6). This demonstrates that the technical solution of the present invention is an organic whole system. It is this deep coupling of the "material-structure-process" trinity that produces a series of unexpected and excellent comprehensive properties, including a load expansion rate of less than 0.5%, a strength retention rate of over 90% after wet-dry cycling, and an intact appearance.

[0082] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for improving expansive soil based on a moisture regulation network, characterized in that, Includes the following steps: S1: Determine the pore size distribution of expansive soil and calculate the percentage of pore volume (Pnano) in the total pore volume for pores with a diameter in the range of 1 nm to 100 nm; classify the expansive soil according to the Pnano value. S2: Based on the grading results of step S1, prepare a composite modifier according to the percentage of dry soil mass. The composite modifier includes: Component A: Quicklime powder; Component B: Composed of surface-modified nano-silica sol and ultrafine highly active slag powder; Component C: Composed of superabsorbent polymer particles and organic hydrophobic modified bentonite powder; S3: First, dry-mix the expansive soil with the dry composite modifier prepared in step S2; then, add the activation liquid containing the reaction activator for the first wet mixing, with the amount of water added controlling the moisture content of the mixture to reach its optimum moisture content of 65%-75%; finally, add clean water for the second wet mixing, so that the total moisture content reaches 95%-105% of the optimum moisture content. S4: Compact the mixture obtained in step S3 in layers, and embed a control medium layer between every two layers of compacted soil, which is a premixed mixture of part of the C component and inert fine-particle material. S5: After the compacted soil is sealed and cured, at least two cycles of dry-wet cycle activation curing are carried out, each cycle including a drying process and a water immersion process.

2. The method for improving expansive soil based on a moisture regulation network according to claim 1, characterized in that, In S1, the Pnano value is classified into three levels: Level I, Pnano > 40%; Level II, 20% < Pnano ≤ 40%; Level III, Pnano ≤ 20%.

3. The method for improving expansive soil based on a moisture regulation network according to claim 2, characterized in that, In S2, for Class I expansive soil, the dosage of component A is 4.0-5.0% of the dry soil mass, the total dosage of component B is 6.0-8.0%, and the total dosage of component C is 0.8-1.2%. For Class II expansive soil, the dosage of component A is 3.0-4.0%, the total dosage of component B is 4.0-6.0%, and the total dosage of component C is 0.5-0.8%. For Class III expansive soil, the dosage of component A is 2.0-3.0%, the total dosage of component B is 2.0-4.0%, and the total dosage of component C is 0.3-0.5%.

4. The method for improving expansive soil based on a moisture regulation network according to any one of claims 1-3, characterized in that, In S2, the surface-modified nano-silica sol is an alkaline silica sol modified with a silane coupling agent, and its SiO2 particle size is 5-20 nm; the specific surface area of ​​the ultrafine highly active slag powder is ≥600 m². 2 / kg; the ratio of the solid mass of the surface-modified nano-silica sol to the ultrafine highly active slag powder is 1:(2.5-4.0).

5. The method for improving expansive soil based on a moisture regulation network according to claim 4, characterized in that, In S2, the organic hydrophobic modified bentonite micro powder is bentonite modified with long-chain alkyl quaternary ammonium salt, and its contact angle with water is greater than 90°; the mixing mass ratio of the superabsorbent polymer particles to the organic hydrophobic modified bentonite micro powder is 1:(8-12).

6. The method for improving expansive soil based on a moisture regulation network according to claim 1, characterized in that, S2 also includes component D, which is aluminum sulfate or potassium aluminum sulfate, added at 0.5-1.5% of the total dry mass of the composite modifier, and pre-dissolved in the activation solution in S3.

7. The method for improving expansive soil based on a moisture regulation network according to claim 1, characterized in that, In S3, the amount of water added during the first wet mixing is to control the moisture content of the mixture to reach 70%-75% of its optimal moisture content.

8. The method for improving expansive soil based on a moisture regulation network according to claim 1, characterized in that, In S4, the amount of component C in the control medium layer accounts for 30%-50% of its total amount; the inert fine particulate material is dry quartz sand; the mixing mass ratio of component C to the inert fine particulate material is 1:(15-20).

9. The method for improving expansive soil based on a moisture regulation network according to claim 8, characterized in that, In S4, the amount of the regulating medium layer spread in the compacted soil is 50-100 g / m³. 2 .

10. The method for improving expansive soil based on a moisture regulation network according to claim 1, characterized in that, In S5, each cycle of the dry-wet cycle activation curing is: drying at 40±2℃ for 48 hours, and then immersing in room temperature water for 24 hours.

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