A PMM permafrost stabilizer

Abstract

The present application relates to the field of road engineering, and discloses a PMM frozen soil stabilizer.The stabilizer comprises an A agent and a B agent, the A agent comprises PSS-Al, a nucleation control agent, a water-retaining agent and water, and the B agent is a polymeric aluminum-iron salt.PSS-Al can continuously release aluminum ions between soil particles and form dense crystals, transform connected pores in coarse-grained soil into unconnected pores, and block water migration, thereby significantly inhibiting frost heaving.The B agent can activate the nucleation reaction early, and the nucleation control agent adjusts the crystal growth to ensure that a continuous reinforced layer is formed after the modified liquid penetrates.The stabilizer is suitable for in-situ improvement of graded gravel subgrade of a road that has been in operation for many years and has serious fine-grained soil intrusion, does not need to be turned over, and after modification, the frost heaving rate is significantly reduced, the permeability is improved, the water stability is improved, and the hidden danger of frost damage is fundamentally eliminated.

Description

Technical Field

[0001] This application relates to the field of road engineering technology, specifically to a PMM frozen soil stabilizer. Background Technology

[0002] Sections of the Jida-Yuanping High-Speed ​​Railway are located in seasonally frozen soil areas, with graded crushed stone as the subgrade fill material, and have been in operation for many years. During this long service period, fine-grained soil from the outside has continuously infiltrated the track bed and subgrade under the influence of train loads and rainwater erosion, gradually filling and blocking the original porous structure of the graded crushed stone. This has led to a significant decrease in subgrade permeability and severe degradation of drainage function. The presence of a large amount of fine-grained soil not only significantly increases the frost heave sensitivity of the subgrade fill material, but also makes it easier for retained water to cause significant volume changes during freeze-thaw cycles. The freeze-thaw cycle period in this region lasts up to 5 months. When the subgrade fill material freezes in winter, uneven frost heave easily occurs between areas rich in fine-grained soil and areas lacking it, causing local track geometry to exceed limits, resulting in unstable train operation and seriously threatening railway safety. Because the fine-grained soil has deeply infiltrated, is diffusely distributed, and is difficult to completely remove, traditional replacement methods are difficult to implement.

[0003] Currently, there are four main methods for preventing and controlling roadbed frost damage in China:

[0004] (1) Thermal insulation method: As a passive protection measure, it can only delay the impact of rising temperature on permafrost, but cannot solve the problem of expansion and contraction deformation of roadbed during winter freezing and summer thawing; at the same time, this method has the negative effect of both heat insulation and cold insulation, and its long-term service performance is difficult to guarantee.

[0005] (2) Crushed stone subgrade: Based on the principle of natural air convection in porous media, the natural cold source is used to continuously reduce the temperature field of the subgrade, which can keep the permafrost basically stable in winter and overcome the shortcomings of thermal insulation materials. However, it cannot solve the problem of permafrost thawing and settlement in summer. It is mostly suitable for newly built subgrades and is difficult to use directly for subgrades that have been in operation for many years and have fine soil intrusion.

[0006] (3) Heat pipe: When working in winter, the cold energy of the ground surface is evenly transported to the underground seasonal thawing layer, so that it freezes evenly to overcome the harm of uneven frost heave; however, the heat pipe does not work in summer, so it cannot solve the thawing settlement problem, and it cannot fundamentally solve the problem of fine-grained soil in the roadbed fill.

[0007] (4) Sunshade: As an auxiliary measure, it is only used to alleviate the problem of uneven heat absorption on the roadbed slopes, and its function is singular.

[0008] (5) Chemical modification: For example, patent DE5020150043067T2 provides a sulfonic acid soil stabilizer that reduces water adsorption on the surface of soil particles through ion exchange, thereby reducing frost heave sensitivity. However, this method requires mechanical loosening, mixing and compaction of the soil, lacks infiltration modification capabilities, relies on large construction equipment, and is also dependent on the aluminum ion content in the natural environment. The paper "Cure Mechanism of PAMCATS Curing Agent for Subgrade Soil in Cold Regions" (Journal of Chang'an University, 2010, Vol.30 No.3) discloses a curing agent compounded with polyacrylamide (PAM) and aluminum salt. Its mechanism is as follows: PAM amide group hydrogen bonds adsorb soil particles, and aluminum ions replace low-valence cations on the surface of soil particles (ion exchange thins the double electric layer) on the one hand, and form a flocculation network by coordination bridging between PAM molecular chains on the other hand, supplemented by lime volcanic ash reaction to provide strength. The significant drawback of this method is that although the spatial structure formed by cross-linking PAM and aluminum ions improves the stability of PAM to a certain extent, it seriously weakens its infiltration capacity in the soil. Once prepared, the solution is nearly gel-like and requires stirring before use. Therefore, this method is only suitable for preventative measures before construction and cannot be used for on-site repair of existing projects (such as track structures).

[0009] In summary, existing methods are unable to effectively address the challenges of winter frost heave and summer thaw settlement faced by graded crushed stone subgrades that have been in operation for many years and where fine-grained soil has deeply penetrated the voids. Previous invasive modification methods required mixing and other processes, making in-situ modification impossible.

[0010] Therefore, there is an urgent need to develop specialized frozen soil stabilizers for such special working conditions, to improve the properties of the fill material itself in situ, fundamentally eliminate roadbed frost damage, and ensure the long-term stability of high-speed railway subgrades and the smooth operation of trains. Summary of the Invention

[0011] In view of the deficiencies in the existing technology, the purpose of this application is to provide a PMM frozen soil stabilizer that can achieve in-situ modification.

[0012] To address the aforementioned technical problems, this application provides a technical solution, comprising:

[0013] Agent A comprises the following components by mass percentage:

[0014] PSS-A1: 12% ~ 15%;

[0015] Nucleation regulator: 0.02% ~ 0.05%;

[0016] Water-retaining agent: 0.1%-0.15%;

[0017] Water: Balance;

[0018] Agent B comprises the following components:

[0019] Polyaluminum iron salt, wherein the amount of polyaluminum iron salt used is 0.2% to 0.3% of the total mass of agent A.

[0020] By adopting the above technical solution, PMM ("Prevent Moisture Migration") frozen soil stabilizer forms crystal particles in situ using aluminum ions, thus fixing the water of crystallization in place and fundamentally blocking the source of frost heave, preventing water from entering and migrating, and eliminating ice interlayers and ice lenses. Water migration is the direct cause of ice accumulation, ice interlayers, and ice lenses on freezing fronts. This invention utilizes the synergistic effect of Agent A (12%–15% PSS-Al, 0.1%–0.15% water-retaining agent) and Agent B (polyaluminum ferric salt): PSS-Al (polystyrene sulfonic acid-loaded aluminum) continuously releases aluminum ions, which nucleate and form crystals between fine soil particles, agglomerating fine particles and filling the interconnected pores between coarse particles; the water-retaining agent increases the viscosity of the system, preventing slurry infiltration and loss; Agent B activates the nucleation reaction early, significantly enhancing the retention of PSS on the surface of soil particles, and precisely retaining the active ingredients at the target depth. This process transforms the large, interconnected pores of coarse-grained soil into dense, non-interconnected pores, significantly reducing the permeability coefficient. It completely cuts off the migration channels of lower-level water to the freezing front, eliminating water sources in ice interlayers and ice lenses, and significantly reducing tangential and normal frost heave forces. The 0.02%–0.05% nucleation regulator in Agent A adjusts the initial size and growth rate of aluminum-based crystal nuclei, preventing premature formation of large crystals on the surface that block infiltration pathways. It ensures that the active ingredients infiltrate evenly to the designed depth before gradually completing nucleation and crystal growth, forming a continuous, dense, frost-heave-resistant reinforcement layer from top to bottom. This avoids the problem of unsustainable bonding reactions in traditional materials and also improves the issue of incomplete internal modification caused by excessively rapid infiltration of the modified liquid into graded gravelly soil, exceeding the freezing front depth. This significantly improves the effective reinforcement quality and engineering reliability. Although this formula is specifically designed for graded gravelly soil, its mechanism addresses the problem of soil moisture migration and frost heave with large interconnected channels. Therefore, it is applicable to similar media such as coarse-grained soil, gravelly soil, and sandy soil, demonstrating its versatility.

[0021] Preferably, the PSS-Al is made in the following manner:

[0022] Prepare a 20% aqueous solution of PSS-Na and slowly pass it through a chromatography column filled with hydrogen-form strong acid cation exchange resin. The effluent is PSS-H acid solution.

[0023] Highly active aluminum hydroxide was added to the PSS-H solution in portions under stirring at 40~50℃ until the reaction was complete, thus obtaining the PSS-Al mother liquor.

[0024] PSS-Al was obtained by filtration and purification.

[0025] Using the above technical solution, commercially available PSS-H typically contains a high amount of sulfate and chloride salts, which easily leads to precipitates, affecting its performance, and its reaction with aluminum ions is relatively slow. PSS-H treated with ion exchange column exchange exhibits higher reactivity and better purity. The stoichiometric high-activity aluminum hydroxide refers to freshly prepared aluminum hydroxide, which has high reactivity and is easily loaded. In stoichiometry, the number of moles of the repeating unit is first calculated based on the weight-average molecular weight and molecular weight of the repeating unit of PSS-H, and then high-activity aluminum hydroxide is added at a 1:0.2 molar ratio. Since the molecular weight of polymers is measured through various indirect methods, there may be uneven distribution issues. To avoid errors and ensure complete reaction, in actual operation, after adding the calculated amount of aluminum hydroxide, aluminum hydroxide is added in small amounts several times until the solution is no longer clear (indicating the reaction has reached its endpoint). The clear liquid obtained after filtration is the PSS-Al solution. When using, the actual mass of PSS-Al is used for calculation, not the total mass of the solution.

[0026] Preferably, the average molecular weight of the PSS-Na is 130,000 to 270,000.

[0027] By adopting the above technical solution, standard 150K PSS-Na with a weight-average molecular weight of 147,000 and standard 270K PSS-Na with a weight-average molecular weight of 263,000 can be selected as the base raw materials, either alone or in combination. Alternatively, self-synthesized PSS with a weight-average molecular weight between 130,000 and 270,000 can be used as the raw material. Too low a molecular weight will significantly reduce the solution viscosity, making the solution too easily infiltrate, reducing its adhesion to soil particles, and decreasing the persistence of the modification; too high a molecular weight will make the solution too viscous, difficult to penetrate, and have too strong a binding force with soil particles, making it difficult to infiltrate to the appropriate location.

[0028] Preferably, the polyaluminum ferric salt is polyaluminum ferric chloride.

[0029] By adopting the above technical solution, polyaluminum ferric chloride is selected instead of simple polyaluminum salt for two reasons: first, polyaluminum ferric chloride is more likely to generate iron-based sedimentation nuclei, providing adsorption sites for PSS; second, a polymer with chloride ions is selected instead of sulfate ions, mainly because chloride ions do not participate in the reaction in the soil and have little impact on the soil environment, while sulfate ions easily form sulfates, which absorb water and swell, exacerbating the swelling effect of expansive soil.

[0030] Preferably, the nucleation regulator is one or a mixture of pyrogallol and tannic acid.

[0031] By adopting the above technical solution, pyrogallol and tannic acid are similar polyphenolic substances with similar physical properties. They mainly stabilize aluminum ions through phenolic hydroxyl groups, which not only prevents the aluminum loaded on PSS from hydrolyzing prematurely in water, but also avoids the premature hydrolysis of polyaluminum iron salt when Agent A and Agent B are mixed. Instead, after contacting the soil, they hydrolyze and generate coagulation nuclei by taking advantage of the alkaline conditions of the soil.

[0032] Preferably, the water-retaining agent is polyvinyl alcohol.

[0033] By adopting the above technical solution, polyvinyl alcohol can be used to adjust the viscosity of the solution, act as a lubricant, and absorb enough water to prevent the problem of hydrolysis due to lack of water during the modification of the stabilizer.

[0034] The beneficial effects of the technical solution provided in this application include:

[0035] By continuously releasing aluminum ions through PSS-Al, crystals are formed in situ between soil particles, transforming the large interconnected pores of coarse-grained soil into dense, non-interconnected pores. This significantly reduces the permeability coefficient, fundamentally blocking the migration of water to the freezing front, eliminating water sources in ice interlayers and ice lenses, and significantly reducing tangential and normal frost heave forces. Furthermore, the modifying agent provided in this solution differs from traditional adhesives; besides adsorption and exchange, it does not react with soil particles. Therefore, as long as the soil particles contain water, the soil can be modified in situ for a long time, exhibiting resistance to environmental changes. Moreover, this solution is an in-situ improvement method, eliminating the need for mixing and other processes, greatly reducing the amount of engineering work compared to traditional adhesive modification.

[0036] The water-retaining agent increases the viscosity of the system and prevents the slurry from seeping and escaping; Agent B activates the nucleation reaction in the early stage and enhances the retention of active ingredients on the surface of soil particles; the nucleation regulator adjusts the initial size and growth rate of crystal nuclei to prevent the premature formation of large crystals on the surface that block the infiltration pathways, ensuring that the active ingredients infiltrate evenly to the design depth before gradually completing nucleation and crystal growth, forming a continuous and dense anti-frost heave reinforcement layer from top to bottom. This solves the problems of poor bonding and incomplete internal modification of traditional materials, significantly improving the effective reinforcement quality and engineering reliability.

[0037] The optimized PSS-Al preparation method ensures high purity and reactivity. PSS-Na with a molecular weight of 147,000–263,000 is selected, balancing permeability and adhesion durability. Polyaluminum ferric chloride provides iron-based sedimentation nuclei as adsorption sites while avoiding the introduction of sulfate ions that could cause swelling. The nucleation regulator stabilizes aluminum ions through phenolic hydroxyl groups, allowing for hydrolysis and nucleation only after contact with alkaline soil conditions. Polyvinyl alcohol provides water retention and smoothness, preventing water shortage during the modification period. The components work synergistically, resulting in stable performance and environmental friendliness.

[0038] The formulation mechanism addresses the issues of soil moisture migration and frost heave with large interconnected channels, and is applicable to similar media such as coarse-grained soil, gravelly soil, and sandy soil, demonstrating its universality. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a modified solution prepared by mixing agent A and agent B.

[0041] Figure 2 A sample image taken from the left shoulder of a section of Jidayuan.

[0042] Figure 3 This is a sample of the soil under sieve before modification.

[0043] Figure 4 The modified sample is shown below. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0046] In this application embodiment, the pharmaceutical products include the following types:

[0047] Sodium polystyrene sulfonate, abbreviated as PSS-Na, CAS: 9080-79-9. Weight-average molecular weight (Mw) includes 1.47 × 10⁻⁶. 5 2×10 5 and 2.63×10 5 All three types maintained a dispersion of Đ < 1.20.

[0048] Tannic acid, also known as tannin, CAS: 1401-55-4, purity 96%.

[0049] Pyrogallic acid, CAS: 87-66-1, analytical grade.

[0050] Polyvinyl alcohol, CAS: 9002-89-5, analytical grade.

[0051] Polyaluminum ferric chloride, with an iron content of 3% and a basicity of 85%.

[0052] Example 1 of PSS-Al preparation

[0053] This preparation example illustrates the preparation process of PSS-Al.

[0054] Weigh 100g of analytical grade aluminum sulfate at room temperature (20~25℃), dissolve it in 500mL of deionized water, and stir until completely dissolved to obtain an aluminum sulfate solution. Separately weigh 40g of analytical grade sodium hydroxide, dissolve it in 300mL of deionized water to obtain a sodium hydroxide solution.

[0055] Under vigorous stirring, sodium hydroxide solution is added dropwise to aluminum sulfate solution at a rate of 2-3 drops per second, while monitoring the pH of the system. When the pH rises to 6.0-6.5, the dropping rate is slowed to 1 drop per second until the pH reaches 7.0, at which point the dropping is stopped. At this point, a large amount of white amorphous aluminum hydroxide precipitate is formed in the system.

[0056] After stirring for another 30 minutes, allow the mixture to settle and discard the supernatant. Wash the precipitate repeatedly with deionized water 4-5 times, separating it by vacuum filtration after each wash, until no sulfate ions are detected in the washing liquid using barium chloride solution (no white precipitate is formed), indicating that the free sulfate has been completely removed.

[0057] The resulting filter cake is highly active freshly prepared aluminum hydroxide, which is a hydrogel with a water content of approximately 75% to 85%. This product has extremely high chemical activity; its amorphous structure and abundant surface hydroxyl groups make it easy to undergo a loading reaction with the sulfonic acid groups in PSS-H acid solution. The reaction rate and conversion rate are significantly higher than those of commercially available aluminum hydroxide powder.

[0058] It should be noted that this highly active aluminum hydroxide must be freshly prepared and stored in a moist state before use. If it is dried or left for a long time, its activity will be significantly reduced due to aging and crystallization, thus affecting the subsequent preparation effect of PSS-Al. If the preparation scale needs to be expanded, the amount of each of the above materials can be increased proportionally, while keeping the stirring and washing conditions unchanged.

[0059] Prepare a 20% (w / w) aqueous solution of industrial-grade PSS-Na (sodium polystyrene sulfonate) standard with a weight-average molecular weight of 200,000. Slowly pass this aqueous solution through a chromatography column packed with hydrogen-form strong acid cation exchange resin at a flow rate of 1.5 column volumes per hour. Collect the eluent to obtain PSS-H acid solution.

[0060] Freshly prepared highly active aluminum hydroxide was added to 45°C warm water and stirred until a turbid solution was formed. Under constant temperature and stirring conditions at 45°C, freshly prepared aluminum hydroxide was added in portions to the PSS-H acid solution until the stoichiometric ratio was reached. After the solution became clear, a small amount of freshly prepared highly active aluminum hydroxide was added until the solution became slightly turbid (indicating the reaction endpoint). Stirring was continued for 30 minutes, and then the solution was allowed to stand and cool. Excess aluminum hydroxide and insoluble matter were removed by filtration, yielding a clear PSS-Al mother liquor. After purification and drying, the PSS-Al product was obtained. The reaction was found to be complete and the product could be used immediately or, after purification, in solution form.

[0061] Example 1

[0062] A PMM frozen soil stabilizer, consisting of agent A and agent B, is packaged separately before use.

[0063] Formulation of Agent A (by mass percentage): PSS-Al (prepared from PSS-Al preparation example 1) 13.5%; nucleation regulator pyrogallic acid 0.03%; water-retaining agent polyvinyl alcohol 0.12%; balance water. Preparation method: Under stirring conditions, polyvinyl alcohol is added to hot water at 80°C until completely dissolved. After cooling to room temperature, PSS-Al and pyrogallic acid are added sequentially, and stirred until completely dissolved to obtain Agent A.

[0064] Agent B formulation: Polyaluminum ferric chloride, its mass is 0.25% of the total mass of Agent A. Agent B is a solid powder.

[0065] Example 2

[0066] A PMM frozen soil stabilizer differs from Example 1 in that the formulation of agent A is different, as detailed below:

[0067] Formula for Agent A: 15% PSS-Al (prepared from PSS-Al Preparation Example 1, but the raw material was replaced with standard PSS-Na with a weight average molecular weight of 263,000); 0.05% tannic acid as nucleation regulator; 0.15% polyvinyl alcohol as water-retaining agent; the balance being water.

[0068] Agent B formulation: Polyaluminum ferric chloride, its mass is 0.3% of the total mass of Agent A.

[0069] Example 3

[0070] A PMM frozen soil stabilizer differs from Example 1 in that the formulation of agent A is different, as detailed below:

[0071] Formula for Agent A: 12% PSS-Al (prepared from PSS-Al Preparation Example 1, but with the raw material replaced by standard PSS-Na with a weight average molecular weight of 147,000); 0.02% nucleation regulator, a 1:1 mass ratio mixture of pyrogallol and tannic acid; 0.1% water-retaining agent, polyvinyl alcohol; the balance being water.

[0072] Agent B formulation: Polyaluminum ferric chloride, its mass is 0.2% of the total mass of Agent A.

[0073] The PMM frozen soil stabilizer prepared in Examples 1, 2, and 3 was tested, and one of the samples was applied to the frost damage treatment of an operational section of the Jidayuan high-speed railway subgrade. The subgrade is graded crushed stone soil with severe fine soil intrusion. The maximum freezing depth in winter is about 1.68 meters, and frost heave is significant.

[0074] The specific steps are as follows:

[0075] (1) Obtaining original soil samples and determining parameters: Representative original soil samples were obtained by core drilling in the target construction section. The dry density ρ of the original soil samples was measured in the laboratory. d It has a density of 2.35 g / cm³, a natural moisture content ω of 6.75%, and a frost heave rate of... It is 1.75%.

[0076] (2) Preparation of the modified solution: On-site, slowly add the polyaluminum ferric chloride powder (Agent B) to the liquid A in proportion, stirring vigorously for 15 minutes while adding, until a homogeneous and stable modified solution is formed. It must be used within 4 hours. See [link to modified solution] for the completed modified solution. Figure 1 It is black, slightly viscous, and has no special odor.

[0077] (3) Sieve soil samples and conduct preliminary experiments: Pass the representative soil sample obtained in step (1) through a 2mm sieve, collect the undersized fine soil and mix it evenly. Calculate the volume percentage φ of the undersized fine soil in the original soil sample. f The average particle size D50 of the fine-grained soil was 0.635 mm, with a value of 0.42. The sieved fine-grained soil was divided into five portions: one as an unmodified control sample (original sample), and the other four as modified samples. The frost heave rate of the unmodified sample was determined. The content of the modified material was 1.73%, and the dry density ρ1 was 2.37 g / cm³. Four modified samples were uniformly mixed at volume application rates of 0.5%, 1.0%, 1.5%, and 2.0%, respectively, to prepare standard specimens for frost heave testing. After curing, the frost heave rate was determined according to the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019), "Standard for Geotechnical Classification of Railway Engineering" (TB 10077-2019), "Specifications for Geotechnical Testing of Railway Engineering" (TB 10102-2023), and "Specifications for Geotechnical Chemical Analysis of Railway Engineering" (TB 10103-2008). The data with the largest modification amount was selected as representative. The test results are shown in Tables 1, 2, and 3.

[0078] Table 1 Pre-experimental data

[0079] Table 2 Particle Size Table

[0080]

[0081] Table 3 Soil Properties

[0082]

[0083] Example 1 exhibits superior particle distribution, water retention, plasticity index, and free expansion rate, and uses industrial-grade PSS, while Examples 2 and 3 use standard-grade PSS, which is expensive. Considering both effectiveness and engineering cost, subsequent calculations will use Example 1 as the modified liquid, with the unmodified state as follows: Figure 3 The soil sample modified according to Example 1 is shown below. Figure 4 .

[0084] The formula shown in Example 1 was used to carry out in-situ construction modifications at three locations along the Jida-Yuanping High-Speed ​​Railway. Figure 2As shown, the sampling points for the graded crushed stone fill were located at kilometer markers K33+635, K56+550, and K102+770 on the Jida-Yuanping High-Speed ​​Railway. The control soil sample was taken from kilometer marker K33+631. During sampling, surface gravel was removed, and the top of the soil surface layer was used as the boundary. Since a stability assessment period of at least one year is required after the modification, the soil samples from the four locations have similar properties and can be used as control samples for comparison. This effectively eliminates the impact of climate change and train operation on soil quality during the one-year assessment period. In addition, to eliminate the influence of changes in environmental conditions, all sampling was completed at the same time. Specifically, samples were taken at depths of 0–20 cm and 20–40 cm at K33+635, at depths of 0–20 cm, 20–40 cm, and 40–60 cm at K56+550, and at depths of 0–20 cm, 20–40 cm, and 40–60 cm at K102+770. The control soil sample was taken from a depth of 0–20 cm at kilometer marker K33+631. Other soil samples were listed in ascending order of depth.

[0085] Particle size analysis results show that the content of particles smaller than 0.075 mm is 10.68%–12%, exceeding the requirement that the content of fine-grained soil in the graded crushed stone subgrade fill for high-speed railways should not exceed 5%. Moisture content tests show that the moisture content is 6.1%–6.9%, also greater than 5%. Existing technical data indicates that when both the fine-grained soil content and moisture content are less than 5%, the frost heave rate of the graded crushed stone subgrade is very small. The frost heave rate increases with increasing fine-grained soil content and moisture content. Fine-grained soil has high porosity and small pore size, strong water adsorption capacity, and strong water retention and absorption capabilities. When the moisture content reaches a certain value, liquefaction easily occurs, creating favorable conditions for water molecule migration during frost heave. This provides extremely convenient space and channels for frost heave, which is a major cause of frost damage to the subgrade.

[0086] Soil property tests were conducted at four sampling points, mainly in accordance with the "Standard for Geotechnical Testing Methods" (GB / T50123-2019), "Standard for Soil and Geotechnical Classification of Railway Engineering" (TB 10077-2019), "Specifications for Geotechnical Testing of Railway Engineering" (TB10102-2023), and "Specifications for Geotechnical Chemical Analysis of Railway Engineering" (TB 10103-2008). For items where it was inconvenient to test the original soil sample, fine soil was screened out for testing.

[0087] Table 4. Particle size distribution of in-situ modified soil

[0088]

[0089] Table 5 Soil Properties

[0090]

[0091] Table 6. Disintegration Status Table

[0092]

[0093] (1) The results of the liquid plasticity test show that the plasticity index of the graded crushed stone filler was 10.4 before modification and about 6-7 after modification, indicating that the hydrophilicity of the graded crushed stone filler was weakened.

[0094] (2) From the comparison table of particle size analysis, water holding capacity, and permeability test results, it can be seen that the fine-grained soil content in the graded crushed stone filler is about 11%. After modification with PMM frozen soil stabilizer, the fine-grained soil content is reduced to about 4.5%, the water holding capacity decreases from about 12% to about 10.5%, and the permeability coefficient decreases from about 5.2×10 -3 cm / s increased to approximately 5.5 × 10 -3 The modified graded crushed stone filler has reduced water retention and absorption capacity, enhanced drainage, reduced capillary action, and effectively prevented water migration.

[0095] (3) Based on the results of the frost heave test, the frost heave rate of the graded crushed stone filler is about 1.73%, which is classified as Class II frost heave according to the frost heave level. After the graded crushed stone filler is modified by PMM frozen soil stabilizer, the frost heave rate is reduced to about 0.23%, which is basically not frost heave, and it belongs to non-frost heave filler.

[0096] (4) Based on the comparative analysis of the swelling and shrinkage characteristics test results, after the graded crushed stone filler was modified by PMM frozen soil stabilizer, the free expansion rate decreased from about 22% to about 14%, and the swelling and shrinkage characteristics were greatly improved.

[0097] (5) The disintegration test can directly reflect the modification effect. The original sample disintegrated when it was put into water, and the disintegration amount was almost 100%, which fully reflects the strong water absorption of fine-grained soil. The modified sample after being modified by PMM frozen soil stabilizer basically does not absorb water, has extremely strong water stability, and does not disintegrate.

[0098] Comparative Example 1

[0099] A frozen soil stabilizer differs from Example 1 in that Agent A does not contain the nucleation regulator pyrogallic acid, while the remaining components and contents are the same as in Example 1. Specifically, Agent A consists of 13.5% PSS-Al, 0.12% polyvinyl alcohol as a water-retaining agent, and the remainder water; Agent B is polyaluminum ferric chloride, used at 0.25% of the total mass of Agent A.

[0100] Following the same preliminary experimental method as in Example 1, the frost heave rate was measured to be 0.58% and the disintegration rate to be 35% at a 2.0% application rate after modification. Furthermore, obvious white large-particle crystal enrichment was observed on the surface of the specimen, while the fine-grained soil in the lower part remained relatively loose.

[0101] Compared with the effect of 0.30% frost heave rate and basically no disintegration in Example 1, this comparative example lacks nucleation regulators, which causes aluminum crystals to grow too early and too fast on the surface, blocking the channels for downward penetration of the modification liquid. The deep fine-grained soil cannot be fully modified, and the overall frost heave resistance and water stability are significantly reduced.

[0102] Comparative Example 2

[0103] A frozen soil stabilizer differs from Example 1 in that Agent A does not contain the water-retaining agent polyvinyl alcohol, while the remaining components and contents are the same as in Example 1. Specifically, Agent A consists of 13.5% PSS-Al, 0.03% nucleation regulator pyrogallic acid, and the balance water; Agent B is the same as in Example 1.

[0104] Tests were conducted under the same conditions, and the frost heave rate at an application rate of 2.0% was measured to be 0.65%, and the disintegration rate was 52%. During the experiment, it was found that due to the low viscosity and poor water retention of the system, some of the modified liquid rapidly seeped down to the bottom of the coarse particles after injection, resulting in insufficient effective modified components in the upper fine-grained soil, poor modification uniformity, and frost heave inhibition effect and disintegration resistance far lower than in Example 1.

[0105] Comparative Example 3

[0106] A frozen soil stabilizer differs from Example 1 in that agent B uses an equal mass of polyaluminum chloride (iron-free) instead of polyaluminum ferric chloride, while the remaining components and contents are the same as in Example 1. That is, agent A has the same formulation as in Example 1; agent B is polyaluminum chloride, and its dosage is 0.25% of the total mass of agent A.

[0107] Under the same testing conditions, the frost heave rate at a 2.0% application rate was 0.45%, and the disintegration rate was 18%. Although the frost heave rate and disintegration rate were lower than those of the unmodified soil, the effect was significantly weaker than that of Example 1. The reason for this is that the lack of iron-based settling nuclei weakens the retention of PSS on the surface of soil particles, reduces early nucleation efficiency, and leads to insufficient aggregation of fine-grained soil and insufficient pore closure. Some connected channels still provide pathways for water migration, thereby reducing the frost heave resistance.

[0108] Comparative Example 4

[0109] A method for preventing frost damage to railway subgrade is proposed, which uses salt injection to lower the freezing point of the soil. This is a practical frost damage prevention measure used in railways in seasonally frozen soil areas.

[0110] After a railway in a seasonally frozen soil region opened for operation, the railway maintenance department implemented salt injection measures in frost-damaged sections. By injecting salt into specific areas, the freezing temperature of water was lowered, reducing uneven frost heave in the roadbed and mitigating the impact of frost damage on the roadbed. This method is widely used in railways in cold regions. Its principle is to use salt (mainly sodium chloride and calcium chloride) to lower the freezing point of pore water, allowing the water in the roadbed soil to remain liquid at lower temperatures, thereby reducing the volume expansion caused by freezing.

[0111] While salt injection can mitigate frost heave to some extent, it has several significant limitations: First, the salt content is gradually lost through precipitation infiltration and groundwater flow, resulting in a short effective period and requiring repeated application annually or seasonally, leading to high long-term maintenance costs. Second, chloride salts have a strong electrochemical corrosive effect on track metal fasteners and reinforced concrete structures; long-term, large-scale use will accelerate infrastructure aging, affecting railway lifespan and safety. Third, salt injection only delays freezing by lowering the freezing point; it does not alter the water-holding capacity and frost heave sensitivity of fine-grained soil. Water in fine-grained soil still migrates and undergoes phase changes during freeze-thaw cycles, and the uniform distribution of salt in the soil is difficult to control. Differences in salt concentration may even exacerbate localized frost heave variations, failing to completely solve the problem of uneven frost heave.

[0112] Compared with the mechanism of this invention, which forms water-insoluble crystal particles through in-situ nucleation of PSS-Al, and fixes the water of crystallization in situ to fundamentally block the water migration channel, the salt injection method is a temporary measure that only treats the symptoms and not the root cause. It cannot achieve the essential improvement of the roadbed filler and has secondary problems such as environmental corrosion.

[0113] Comparative Example 5

[0114] A method for preventing and controlling frost damage to railway subgrade, which adopts passive inspection and manual repair, is a frost damage maintenance scheme actually used in railways in seasonally frozen soil areas.

[0115] A section of high-speed railway was hit by a cold wave during its operation, resulting in dozens of instances of frost damage on the track, with millimeter-level undulations in the rail surface, severely impacting train operation safety. The railway maintenance department established multiple emergency repair teams, employing a combination of precision measurement and shim adjustment to address the frost damage. The main tasks involved utilizing the early morning "maintenance window" to detect rail surface deviations and adjusting rail surface accuracy by replacing shims. Nearly one hundred instances of frost damage were identified and repaired, achieving a 100% repair rate.

[0116] While this solution can promptly restore the track surface geometry and ensure short-term operational safety, it has fundamental limitations: First, this method is a passive response at the operation and maintenance level, compensating for track surface deformation caused by frost heave by only adjusting the thickness of the track fastener system's pads, without any improvement to the trackbed fill material itself. The root cause of frost heave—moisture migration and ice accumulation in fine-grained soil—remains completely unaddressed. Second, frost damage reappears or worsens after each cold wave, requiring repeated and substantial investment of manpower and resources for repairs, with maintenance costs increasing year by year with operational time. According to reports, dozens of new frost damage sites were added in this section within a short period due to cold waves, indicating that passive repairs cannot fundamentally curb the occurrence and spread of frost damage. Third, the "track maintenance window" operation time is short and the workload is heavy, limiting the accuracy and efficiency of repairs. Furthermore, frequent pad adjustments alter the stress state of the track fastener system, potentially affecting the long-term stability and durability of the track structure.

[0117] Compared with the technical solution of this invention, which can maintain the modification effect in the freeze-thaw cycle for a long time through the continuous release of aluminum ions after a single application and reduce the frost heave rate to 0.30% after treatment with basically no frost heave, passive inspection and manual repair are emergency measures. They lack the ability to fundamentally improve the frost heave sensitivity of roadbed filler, have high maintenance costs and insufficient reliability, and cannot meet the long-term strict requirements of high-speed railways in operation for track smoothness.

[0118] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0119] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0120] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A PMM frozen soil stabilizer, characterized in that, include: Agent A comprises the following components by mass percentage: PSS-A1: 12% ~ 15%; Nucleation regulator: 0.02% ~ 0.05%; Water-retaining agent: 0.1%-0.15%; Water: Balance; Agent B comprises the following components: Polyaluminum ferric salt, wherein the amount of polyaluminum ferric salt used is 0.2% to 0.3% of the total mass of agent A; The PSS-Al is manufactured in the following manner: Prepare a 20% aqueous solution of PSS-Na and slowly pass it through a chromatography column packed with hydrogen-form strong acid cation exchange resin. The effluent is PSS-H acid solution. Highly active aluminum hydroxide was added to the PSS-H solution in portions under stirring at 40~50℃ until the reaction was complete, thus obtaining the PSS-Al mother liquor. PSS-Al was obtained by filtration and purification; The average molecular weight of the PSS-Na is 130,000 to 270,000.

2. The PMM frozen soil stabilizer according to claim 1, characterized in that, The polyaluminum ferric salt is polyaluminum ferric chloride.

3. The PMM frozen soil stabilizer according to claim 1, characterized in that, The nucleation regulator is one or more of pyrogallol and tannic acid, or a mixture thereof.

4. The PMM frozen soil stabilizer according to claim 1, characterized in that, The water-retaining agent is polyvinyl alcohol.

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