PMM permafrost stabilizer and its use

Abstract

The present application relates to the field of road engineering, and discloses a PMM frozen soil stabilizer and application thereof.The A agent of the stabilizer contains PSS-Al 60-80 g, citric acid 1.5-2.0 g, isopropyl alcohol 8.0-10.0 g, and EDTA-2Na 0.5-0.7 g per liter, and the pH is adjusted to 2.8-3.3 by using formic acid-ammonium formate buffer; and the stabilizer further contains a B agent containing PEG-400 and urea and polyether modified siloxane.During construction, the fine particle content, permeability coefficient and frost heaving rate of the original soil are measured; different amounts of the stabilizer are added in three portions, and the modified indexes are measured again to determine the single application amount of the modified soil sample.The PSS-Al ion exchange breaks down the water film, blocks the migration of frost heaving water, the acid slow-release realizes the penetration first and then the reaction to prevent the deposition of aluminum ions, the isopropyl alcohol reduces the freezing point to promote the penetration, the siloxane reduces the surface tension and viscosity, the B agent retains water to prolong the diffusion, and the buffer decomposes after penetration.The method can scientifically determine the amount, can adapt to different seasons, covers the construction throughout the year, and the modification is uniform.

Description

Technical Field

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

[0002] The Beijing-Yuanping Railway is located in a seasonally frozen soil region, where the lowest winter temperature can reach -28.2℃ and the maximum frost depth is about 1.5m. The roadbed is mostly loess that was originally filled with locally sourced soil, with fine-grained soil (less than 0.075mm in diameter) accounting for over 90%. This loess is characterized by strong hydrophilicity, loose structure, and highly developed capillary pores. Despite repeated compaction by long-term train loads, the inherent hydrophilic nature of the loess minerals remains unchanged; a thick film of water is still firmly adsorbed on the surface of its particles, preserving ample water sources and migration channels for frost heave.

[0003] Under the influence of sub-zero temperatures in winter, the frost heave process of dense loess is mainly driven by two mechanisms. First, when free water and bound water in the soil freeze in situ, the volume of ice expands by about 9% because the density of ice is less than that of water, directly generating frost heave force. Second, and more crucially, is the water migration and ice lensing effect: the temperature gradient drives water in the unfrozen area to continuously migrate towards the freezing front, where it continuously condenses into ice, forming ice interlayers or ice lenses. The growth of ice lenses not only significantly increases the total volume of the soil but also generates a huge expansion thrust on the surrounding soil, which is the dominant cause of severe frost heave. The unique pore structure of loess plays a promoting role in this process—numerous irregular capillary pores provide continuous migration channels for liquid water, and in the early stages of freezing, after ice crystals fill part of the capillary pores, the soil permeability decreases and the advance of the freezing front slows down, which in turn prolongs the duration of water accumulation towards the front, exacerbating the development of ice lenses and further increasing the amount of frost heave.

[0004] From a microscopic perspective, the strong frost heave of loess originates from the adsorbed water layer on the surface of its fine-grained soil particles. Loess particles are small in size and have a huge specific surface area. Due to lattice substitution and other processes, clay minerals give the particle surfaces a negative charge, which attracts hydrated cations and polar water molecules through electrostatic attraction, forming a double-layer structure that binds around the particles into a very strong adsorbed water film. This adsorbed water layer is difficult to remove even under high mechanical forces, and is the physical basis for soil water retention and migration. During freezing, the adsorbed water film not only directly supplies water for ice crystal growth but also maintains a continuous water film between particles, ensuring that liquid water can still be transported along the particle surface from the unfrozen area to the freezing front at sub-zero temperatures. Therefore, the adsorbed water layer of fine-grained soil essentially constitutes the water source and migration channel for frost heave. Coarse-grained soils such as gravel and sand lack this type of adsorbed water and basically do not experience water migration, resulting in minimal frost heave.

[0005] Because the problem of adsorbed water on the surface of loess particles remains unresolved, even with long-term compaction of the subgrade, traditional methods such as replacement or grouting are insufficient to effectively cut off the migration path of water due to frost heave. The treatment effect is limited and the construction cost is high. Therefore, there is an urgent need to develop a stabilizer technology that targets the hydrophilic characteristics of loess minerals, eliminating adsorbed water on the particle surface and blocking frost heave pathways at the source. This invention, PMM frozen soil stabilizer, is specifically developed for the long-term compacted and dense loess subgrade of the Beijing-Yuanping Railway. Through chemical action, it alters the hydrophilicity of loess particles, reducing or eliminating the adsorbed water film, thereby inhibiting water migration and frost heave, and achieving effective treatment of subgrade frost damage. Summary of the Invention

[0006] In view of the deficiencies in the existing technology, the purpose of this application is to provide a PMM frozen soil stabilizer and its application and construction method to achieve in-situ modification.

[0007] To address the aforementioned technical problems, this application provides a technical solution comprising agent A, wherein agent A is an aqueous solution, and per liter of agent A, agent A comprises the following components:

[0008] PSS-Al: 60~80 g / L

[0009] Citric acid: 1.5~2.0 g / L

[0010] Isopropanol: 8.0~10.0 g / L

[0011] EDTA-2Na: 0.5~0.7 g / L

[0012] And a pH-stabilized sustained-release agent for adjusting the pH of agent A to 2.8-3.3.

[0013] By adopting the above technical solution, the PMM ("Prevent Moisture Migration") frozen soil stabilizer A agent provided by this invention, although developed for the long-term compacted loess subgrade of the Beijing-Yuanping Railway, has an action mechanism based on the ion exchange modification of the water adsorbed layer on the surface of fine-grained soil particles. Therefore, it is generally applicable to other soil types with similar compaction characteristics and frost heave sensitivity. Its beneficial effects are as follows: Utilizing the ion exchange function of PSS-Al (polystyrene sulfonic acid-supported aluminum), it replaces the hydrophilic cations in the double electric layer on the surface of soil particles, disintegrating the adsorbed water film, fundamentally cutting off the source of frost heave water and the migration channel, effectively inhibiting uneven frost heave. Citric acid and EDTA-2Na synergistically stabilize aluminum ions and regulate the nucleation process, ensuring that the active ingredient has a small and uniform particle size. Combined with isopropanol to reduce surface tension, the solution can smoothly penetrate into highly compacted soil, ensuring treatment depth and uniformity. Isopropanol also lowers the freezing point, preventing freezing during winter construction and meeting the needs of seasonal frozen soil window operations. The pH-stabilized slow-release agent controls the initial pH of the solution between 2.8 and 3.3, maintaining Al³⁺ stability and preventing sedimentation during the initial mixing and infiltration into the soil, ensuring full penetration of the active ingredients. Subsequently, under the continuous influence of the alkaline soil environment, the pH of the system gradually increases, and Al³⁺ begins to settle and complete ion exchange modification. The synergistic effect of multiple components endows Agent A with comprehensive properties such as antifreeze, deep penetration, antifreeze construction, and long-term maintenance.

[0014] Preferably, the PSS-Al is made in the following manner:

[0015] 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.

[0016] Highly active aluminum hydroxide was added to the PSS-H solution in portions under stirring at 40~50℃ until the reaction reached the endpoint, thus obtaining the PSS-Al mother liquor.

[0017] PSS-Al was obtained by filtration and purification.

[0018] 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 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 molar ratio of 1:0.2. 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 by filtration is the PSS-Al solution. When using, the actual mass of PSS-Al is used, not the total mass of the solution.

[0019] Preferably, the average molecular weight of the PSS-Na is 20,000 to 70,000.

[0020] By adopting the above technical solution, standard 21K PSS-Na with a weight-average molecular weight of 20,900 and standard 65K PSS-Na with a weight-average molecular weight of 64,000 can be selected, either alone or in combination, as the base raw material. Alternatively, self-synthesized PSS with a weight-average molecular weight of 20,000 to 70,000 can be used as the raw material. For dense soils such as loess, which have poor permeability, using higher molecular weight PSS will result in excessively high solution viscosity, preventing sufficient infiltration to the designated location. Conversely, lower molecular weight PSS is difficult to maintain its original ion exchange state for extended periods, reducing the durability of permafrost modification.

[0021] Preferably, agent A further comprises a poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer, the content of which is 1.0~1.5 g / L.

[0022] By adopting the above technical solution, the poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer, also known as dimethyl-3-hydroxypropyl-methylethoxylate, is a polyether-modified silicone oil with CAS number 67762-85-0. The poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer has limited compatibility with water, easily migrates to the surface of water, enhances the permeability of the solution in crevices, and can also reduce the interaction force between the solution and hydrophilic minerals. This is the principle behind the poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer as a leveling agent. The more important function is that the poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer does not chemically react with the substances in Agent A. In the solution state, it plays a occupant role, reducing the possibility of hydrogen bond entanglement between the two PSS chains and reducing the viscosity of the solution.

[0023] Preferably, it also includes agent B, wherein the mass amount of agent B is 13% to 15% of PSS-Al;

[0024] Each liter of Agent B is prepared as follows: 50-60g of PEG-400 and 20-25g of urea are added to 500ml of water, dissolved completely, and then diluted to 1L with water.

[0025] By adopting the above technical solution, PEG-400, officially named Polyethylene Glycol 400, with CAS number 25322-68-3, possesses strong water-retention properties, similar to urea. In dense soils, unmodified soil particles have a stronger adsorption capacity for water, preferentially adsorbing moisture and causing differences in the diffusion coefficients of different components in the solution. PSS, with its relatively weaker diffusivity, is highly susceptible to PSS-Al precipitation due to excessive water infiltration and loss. The water-retention properties of PEG-400 and urea can compete with soil particles for water adsorption, effectively reducing the diffusion differences between components. Simultaneously, both can reduce the surface tension of the solution, and urea can complex with Al ions, reducing premature deposition of active ingredients.

[0026] Preferably, the pH-stabilizing slow-release agent is a formic acid-ammonium formate buffer pair;

[0027] The method of applying the pH-stabilized sustained-release agent is as follows:

[0028] Formic acid is added to agent A until the pH is less than 2.2, and then ammonium carbonate is added until the pH of agent A is between 2.8 and 3.3, forming an in-situ formic acid-ammonium formate buffer pair.

[0029] Using the above technical solution, the pH of domestic soils is generally between 4.5 and 8, and even greater than 7 in loess, all exceeding the pH range for complete precipitation of aluminum ions. Although citric acid has been added to the components to resist pH changes to some extent, ion exchange still occurs rapidly after the modified solution is injected, causing aluminum ions to be displaced and deposited, resulting in the loss of effective components and blockage of channels, often requiring increased application rates. Adding a pH buffer can stabilize aluminum ions and prevent precipitation in the early stages of application. The selected formic acid-ammonium formate buffer is inherently unstable and easily decomposes; it will decompose on its own after a period of time, ceasing to maintain a low pH, thus preventing the buffering effect in the soil from being too prolonged and affecting the construction progress. Considering the strong odor of ammonium formate powder and solution, it is very difficult to add it directly during construction. Therefore, the pH stabilizer slow-release agent adopts an in-situ generation method: formic acid is added in advance before the application of agent A, usually in excess until the pH is less than 2.2. During long-term storage, a small amount of decomposition and volatilization will occur, and the pH will drop. Ammonium carbonate is added just before application. The two react in situ to form a formic acid-ammonium formate buffer pair, which can not only meet the early aluminum stabilization requirements, but also overcome the inconvenience of construction caused by the odor.

[0030] This application also provides the application of the aforementioned PMM frozen soil stabilizer in soil modification.

[0031] Preferably, the soil is loess.

[0032] The beneficial effects of the technical solution provided in this application include:

[0033] Through the ion exchange of PSS-Al, hydrophilic cations in the double electric layer of fine-grained soil are replaced, breaking down the adsorbed water film and blocking the migration channels of water due to frost heave at the source. Citric acid and EDTA-2Na stabilize aluminum ions, making the active components fine and uniform; isopropanol reduces surface tension and freezing point, enhancing permeability in dense loess and preventing freezing during winter construction; pH-stabilizing slow-release agents control the initial pH at 2.8–3.3, ensuring that aluminum ions remain stable and do not settle in the early stages of infiltration, achieving "infiltration first, reaction later," effectively improving the utilization rate of active ingredients and the uniformity of treatment.

[0034] Poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer polyether-modified siloxane can further reduce the dynamic surface tension of the solution, enhance its permeability in mineral micropores, and reduce hydrogen bond entanglement between PSS chains through physical site occupation, thereby reducing viscosity and improving the uniformity of penetration and diffusion. PEG-400 in Agent B has a synergistic water-retention effect with urea, competing with soil particles for preferential adsorption of water, reducing the diffusion rate difference between water molecules and PSS-Al, and preventing premature precipitation of active ingredients. Urea also weakly complexes with aluminum ions, helping to extend the effective diffusion distance and ensuring sufficient ion exchange reaction. An in-situ generated formic acid-ammonium formate buffer pair is used as a pH-stabilizing slow-release agent. Formic acid and ammonium carbonate are added before use, which can maintain a low pH to stabilize aluminum ions in the early stages of construction. Furthermore, the buffer system itself is easily decomposed, automatically deactivating after penetration and triggering ion exchange, while avoiding the strong odor and construction inconvenience caused by directly adding ammonium formate.

[0035] Gradient admixture tests were conducted using undisturbed soil samples to quantitatively determine the unit application rate based on indicators such as fine-grained soil content, permeability coefficient, and frost heave rate, ensuring scientifically reliable construction parameters. The three provided construction schemes are applicable to the summer thaw period, spring thaw period, and winter freezing period, respectively, covering the entire year's construction window. The flexible construction methods ensure the modification depth and uniformity under different conditions. Attached Figure Description

[0036] 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.

[0037] Figure 1 This is a modified solution prepared by mixing agent A and agent B.

[0038] Figure 2 This is a diagram of the original soil sample before modification.

[0039] Figure 3 The modified sample is shown below. Detailed Implementation

[0040] 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.

[0041] 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.

[0042] In this application embodiment, the pharmaceutical products include the following types:

[0043] Sodium polystyrene sulfonate, abbreviated as PSS-Na, CAS: 9080-79-9. It has three weight-average molecular weights (Mw): 20,000, 40,000, and 65,000, all with a dispersion of K < 1.20.

[0044] Citric acid monohydrate, CAS No.: 77-92-9, purity > 99%.

[0045] Isopropanol, CAS: 67-63-0, analytical grade.

[0046] EDTA-2Na dihydrate, CAS: 6381-92-6, analytical grade.

[0047] Poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer: CAS: 67762-85-0, purity >99%.

[0048] PEG-400, CAS: 25322-68-3, analytical grade.

[0049] Urea, CAS: 57-13-6, analytical grade.

[0050] Formic acid, CAS: 64-18-6, analytical grade.

[0051] Ammonium carbonate monohydrate, CAS: 10361-29-2, analytical grade.

[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 40,000. 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 solely of Agent A. Preparation of 1 liter of Agent A: Take 60 g of the PSS-Al mother liquor prepared according to Preparation Example 1 using PSS-Na with a weight-average molecular weight of approximately 20,000, based on pure PSS-Al, and place it in a 2 L beaker; add sequentially 1.64 g of citric acid monohydrate (equivalent to 1.50 g of anhydrous citric acid), 8.0 g of isopropanol, and 0.55 g of EDTA-2Na dihydrate (equivalent to 0.50 g of anhydrous EDTA-2Na), and then add deionized water to approximately 900 mL, stirring to dissolve. Adjust the pH to approximately 2.1 by adding formic acid dropwise, then add ammonium carbonate monohydrate in batches, finally adjusting the pH to 2.8 to form a formic acid-ammonium formate buffer pair in situ. Make up the volume to 1 L with deionized water to obtain Agent A.

[0063] Example 2

[0064] A PMM frozen soil stabilizer, consisting only of Agent A. To prepare 1 liter of Agent A: Take 80 g of PSS-Al mother liquor prepared according to the method of Preparation Example 1 using PSS-Na with a weight-average molecular weight of approximately 65,000, based on pure PSS-Al; add 2.19 g of citric acid monohydrate (equivalent to 2.00 g of anhydrous citric acid), 10.0 g of isopropanol, and 0.78 g of EDTA-2Na dihydrate (equivalent to 0.70 g of anhydrous EDTA-2Na), dissolve in the same manner as in Example 1, adjust the pH to 3.3 with formic acid and ammonium carbonate, and bring the volume to 1 L.

[0065] Example 3

[0066] A PMM frozen soil stabilizer, comprising agent A and agent B.

[0067] Preparation of Agent A: PSS-Na with a weight average molecular weight of approximately 20,000 and approximately 65,000 was mixed at a mass ratio of 1:1 to prepare PSS-Al mother liquor according to the method of Preparation Example 1. 70 g of this mother liquor, based on pure PSS-Al, was taken and added sequentially with 1.91 g of citric acid monohydrate (equivalent to 1.75 g of anhydrous citric acid), 9.0 g of isopropanol, and 0.66 g of EDTA-2Na dihydrate (equivalent to 0.60 g of anhydrous EDTA-2Na). Then, 1.0 g of poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer was added, and water was added to approximately 900 mL to dissolve. The pH was adjusted to 3.0 with formic acid and ammonium carbonate, and the volume was brought to 1 L.

[0068] Preparation of Agent B: Weigh 50 g of PEG-400 and 20 g of urea, dissolve them in about 500 mL of water, and then dilute to 1 L with deionized water.

[0069] The dosage of agent B is 13% of the mass of PSS-Al, that is, 9.1 g of agent B is added to every 1 LA agent, and the mixture is thoroughly mixed.

[0070] Example 4

[0071] A PMM frozen soil stabilizer, comprising agent A and agent B.

[0072] Preparation of Agent A: Using the PSS-Al mother liquor described in Example 3, take 70 g of pure PSS-Al, add 1.91 g of citric acid monohydrate (equivalent to 1.75 g of anhydrous citric acid), 9.0 g of isopropanol, 0.66 g of EDTA-2Na dihydrate (equivalent to 0.60 g of anhydrous EDTA-2Na), and then add 1.5 g of poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer. After dissolving, adjust the pH to 3.1 with formic acid and ammonium carbonate, and bring the volume to 1 L.

[0073] Preparation of Agent B: Weigh 60 g of PEG-400 and 25 g of urea, dissolve them in water, and then make up to 1 L.

[0074] The dosage of agent B is 15% of the mass of PSS-Al. Add 10.5 g of agent B to every 1 LA agent and mix thoroughly.

[0075] Example 5

[0076] A PMM frozen soil stabilizer, comprising agent A and agent B.

[0077] Preparation of Agent A: Using the PSS-Al mother liquor described in Example 3, take 70 g of pure PSS-Al, and add 1.91 g of citric acid monohydrate (equivalent to 1.75 g of anhydrous citric acid), 9.0 g of isopropanol, and 0.66 g of EDTA-2Na dihydrate (equivalent to 0.60 g of anhydrous EDTA-2Na). Then add 1.25 g of poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer. After dissolving, adjust the pH to 3.0 with formic acid and ammonium carbonate, and bring the volume to 1 L.

[0078] Preparation of Agent B: Weigh 55 g of PEG-400 and 22.5 g of urea, dissolve them in water, and then make up to 1 L.

[0079] The dosage of agent B is 14% of the mass of PSS-Al, with 9.8 g of agent B added per 1 LA unit. The prepared sample is shown below. Figure 1 It is an amber-colored transparent liquid.

[0080] Experimental Example 1

[0081] Indoor tests of loess modified with frozen soil stabilizers were conducted. Six samples of undisturbed loess from a section of the Beijing-Yuanping Railway subgrade were collected. The test results are shown in Table 1.

[0082] Table 1 Results of undisturbed soil samples

[0083]

[0084] It can be seen that the right shoulder of K239+110 has the highest content of fine-grained soil and the highest natural moisture content of 24.4%. Therefore, the right shoulder of K239+110 is taken as the original soil sampling point, and soil samples are collected as follows: Figure 2 As shown. Examples 1-5 were applied at a single application rate of 15% (V / V) for modification. Soil property tests were conducted on the modified samples, mainly in accordance with 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).

[0085] Table 2. Experimental Tables for Particle Analysis

[0086]

[0087] Table 3 Compaction Test Results

[0088]

[0089] Table 4 Basic Physical Properties

[0090]

[0091] Table 5 Disintegration Test Table

[0092]

[0093] As can be seen from the test results in Tables 2 to 5, Example 5 achieved the best performance in all key engineering indicators and had the best overall modification effect. Therefore, it was determined to be the optimal example. The modified sample of Example 5 is shown in Table 5. Figure 3 The specific details are as follows:

[0094] Regarding particle composition, the soil sample treated in Example 5 had the highest content of coarse particles (0.25–0.075 mm), reaching 68.12%, while the content of clay particles (<0.005 mm) was the lowest, at only 1.59%. This indicates that the treatment was most effective in agglomerating the strongly hydrophilic fine-grained soil in the original soil into coarse particles, fundamentally changing the engineering properties of the soil. In terms of compaction performance, Example 5 had the highest maximum dry density of 1.72 g / cm³, and the lowest optimum moisture content of 15.11%, demonstrating the best compactability and the lowest construction water requirement, which is beneficial for obtaining a high-density, high-stability fill.

[0095] Regarding hydrophysical and swelling / shrinkage properties, Example 5 exhibits a plasticity index reduced to 7.0, a water holding capacity reduced to 20.1%, a free expansion rate reduced to 20%, and a frost heave rate reduced to 0.79%, all of which are the lowest or tied for the lowest among all examples; simultaneously, its permeability coefficient increases to 8.53 × 10⁻⁻⁻⁶. 7 The value of cm / s was the highest among all embodiments. This indicates that Embodiment 5 most thoroughly weakened the hydrophilicity, water retention capacity, and water absorption capacity of the loess filler, most significantly enhanced drainage, most effectively suppressed water migration, and most significantly improved swelling and frost heave properties. Its frost heave rating is essentially that of a non-frost heave filler. In the disintegration test, Embodiment 5, like some embodiments, was completely non-disintegrating. Considering the aforementioned hard indicators, Embodiment 5 optimized all physical and mechanical properties while ensuring complete non-disintegration and extremely strong water stability.

[0096] Therefore, Example 5 demonstrates the most comprehensive and outstanding improvement advantages in terms of coarsening degree, compaction characteristics, water stability, frost heave resistance, and disintegration resistance, and most thoroughly reduces the engineering disadvantages of loess subgrade filler. Therefore, using Example 5 as the optimal example and as the basis for subsequent construction examples can ensure that the subgrade filler achieves optimal mechanical strength, water stability, and durability, maximizing the engineering improvement effect.

[0097] Untouched loess soil was taken from the right shoulder of the Beijing-Yuanping Railway at kilometer marker K239+110. The natural dry density was 1.63 g / cm³, and the content of fine-grained soil (particle size less than 0.075 mm) was over 90%. The untouched soil sample was divided into seven portions. One portion served as a blank control, recorded as a dosage of 0. The remaining six portions were sprayed with the modified liquid prepared in Example 5 at volume dosages of 5%, 8%, 10%, 12%, 15%, and 20%, respectively. The mixture was stirred evenly, compacted to the on-site dry density, and used to prepare test samples. After 7 days of sealed curing, various performance tests were conducted.

[0098] The particle analysis results of the modified samples with different dosages are shown in the table below.

[0099] Table 6. Results of particle analysis test

[0100]

[0101] As shown in Table 6, the content of fine particles with a diameter less than 0.075 mm in the undisturbed sample was over 90%. At a dosage of 5%, the content of fine particles decreased significantly from over 90% to approximately 35%, indicating that even a small amount of stabilizer could induce a significant particle agglomeration effect. As the dosage gradually increased from 5% to 15%, the content of fine particles further decreased from approximately 35% to approximately 13%, while the content of 0.25–0.075 mm particles in the coarse particle group steadily increased from 50.24% to 68.12%, and the content of clay particles smaller than 0.005 mm gradually decreased from 3.32% to 1.59%. The content of each particle size showed a continuous and gradual change at each dosage gradient. When the dosage was further increased from 15% to 20%, the variation range of particle size content at each level narrowed significantly. The total content of coarse particles larger than 0.25mm increased only from 85.46% to 85.54%, and the content of clay particles smaller than 0.005mm decreased only from 1.59% to 1.57%, indicating that the particle agglomeration effect had approached its upper limit.

[0102] The test results of the basic physical properties of the modified samples under different dosages are shown in Table 3.

[0103] Table 7 Results of Basic Physical Properties Tests

[0104]

[0105] As shown in Table 7, at a dosage of 5%, the hydrophilicity indicators of the sample were significantly lower than those of the original sample, with the frost heave rate decreasing from 3.26% to 1.52%, a reduction of more than half. As the dosage gradually increased from 5% to 15%, the liquid limit decreased from 24.6% to 18.1%, the plastic limit from 15.8% to 11.1%, the free expansion rate from 28% to 20%, the frost heave rate from 1.52% to 0.79% (below 1%), and the water holding capacity from 28.3% to 20.1%. All indicators showed a significant decreasing trend across the dosage gradients. When the dosage increased from 15% to 20%, the changes in each indicator became extremely limited; the frost heave rate decreased only from 0.79% to 0.78%, and the water holding capacity only from 20.1% to 20.0%, reaching a plateau. The permeability coefficient remained between 8.4 and 8.5 × 10⁻ ... 7 The magnitude was on the order of cm·s⁻¹, with no change in order of magnitude.

[0106] When the dosage increased from 0 to 5%, all indicators showed significant improvement, indicating that the stabilizer of this invention has high modifying activity even at low dosages. As the dosage gradually increased from 5% to 15%, all indicators showed continuous and gradual improvement, without any abrupt plateauing after a jump. When the dosage was further increased from 15% to 20%, the variation range of all indicators narrowed significantly, and core indicators such as particle size distribution, maximum dry density, frost heave rate, and disintegration rate became basically stable, indicating that the modification effect at 15% dosage was sufficient, and further increases in dosage resulted in a significant decrease in economic efficiency. Therefore, 15% is the economically optimal dosage of the PMM frozen soil stabilizer of this invention for modifying this loess.

[0107] Construction Example 2

[0108] This construction example corresponds to construction conditions from summer to autumn, when the frozen soil has completely thawed and there are large water channels and pores in the soil, allowing the modifying liquid to directly penetrate into the soil that needs modification.

[0109] The modified liquid prepared in Example 5 was used. The optimal volumetric dosage determined according to the experimental example was 15%, which was used as the unit application rate Q in construction.

[0110] A geological drilling rig was used to drill holes on the top surface of the roadbed, arranged in a quincunx pattern. The hole depth was 1.5 m, the maximum depth of the seasonally frozen soil thawed layer, and the hole spacing was 1.5 m. Each hole controlled approximately 3.4 m³ of earthwork. Based on the total earthwork volume and the application rate Q of 15%, the total amount of modified liquid was calculated. Before use, Agent A and Agent B were prepared according to Example 5 and mixed evenly. The modified liquid was injected into each hole at a uniform rate using a grouting pump, with an injection volume of approximately 510 L per hole.

[0111] After injection, a 3-day infiltration and diffusion reaction was maintained. On-site sampling confirmed that the penetration radius of the modified liquid was greater than 0.75 m, and the soil between the boreholes was effectively treated. Subsequently, the boreholes were backfilled and compacted in layers with cement and soil to restore the roadbed structure.

[0112] Construction Example 3

[0113] This construction example corresponds to construction conditions from spring to summer, when the frozen soil is gradually thawing. There is no need to drill deep holes. The modified liquid can be sprayed onto the soil in multiple applications as the thawing process progresses, allowing it to naturally penetrate as the ice crystals melt.

[0114] Agent A prepared in Example 5 was used, without adding Agent B, utilizing the antifreeze and penetration enhancement capabilities of isopropanol in the modified liquid.

[0115] The optimal volumetric dosage determined by the experimental example is 15%, the modified area is 200 m², the designed ice-melting depth is 1.5 m, and the total amount of modified liquid used is calculated to be 45 m³ based on the unit application rate Q of 15%. The modified liquid is divided into three groups of 15 m³ each, and sprayed evenly on the slope surface using a spraying device on the 1st, 5th, and 9th days, respectively.

[0116] After each spraying, the modified liquid seeps into the soil with the daytime snowmelt and diffuses deeper into the soil along capillary pores during the nighttime pause. After 20 days of natural melting and diffusion following the completion of the treatment, core sampling showed a significant reduction in the fine-grained soil content within a depth range of 1.2 m to 1.5 m. The frost heave rate decreased from 3.26% before modification to below 0.80%, and the soil disintegration rate decreased from 100% to 0, achieving complete non-disintegration. This method does not require large drilling equipment and is suitable for operation during the spring thaw window.

[0117] Construction Example 4

[0118] This construction example corresponds to winter construction conditions, at which time the soil has frozen and a pressurized infiltration method is required. If necessary, the modified liquid can be heated and then injected.

[0119] The modified liquid prepared in Example 5 was used. Given the unfavorable diffusion conditions in winter, the single application amount Q was determined to be 15% with reference to the optimal dosage of 15%. Heating and static pressure injection were used to ensure the effective diffusion of the modified liquid in the frozen soil.

[0120] Plastic drainage boards were vertically installed on both sides of the roadbed, spaced 1.0 m apart and 1.8 m deep, penetrating the seasonally frozen soil layer. The total amount of modified liquid used was calculated based on the volume of earthwork controlled by the drainage boards and the application rate Q per unit volume, which was 15%. The modified liquid was prepared according to Example 5 and heated to approximately 20°C before use. It was then injected statically through the core tube of the drainage board, with the injection volume per board calculated as 15% of the volume of earthwork it controlled.

[0121] A 30 cm thick medium-coarse sand cushion layer was laid on top of the drainage board, and horizontal drainage blind pipes were buried to form a longitudinal and transverse drainage system. Subsequently, a surcharge preloading of approximately 20 kPa was applied for 7 days. During preloading, the modified liquid gradually diffused and reacted in the soil as pore water was discharged, while the drainage system removed excess free water.

[0122] After construction, drilling verification showed that the soil frost heave rate within a depth of 1.5 m decreased to 0.79%, the soil disintegration decreased to 0, and the soil consolidation increased, achieving the dual goals of in-situ modification and drainage consolidation under winter freezing conditions.

[0123] The target locations for construction examples 2-4 are the right shoulders of K239+115, K252+150, and K239+110, respectively. Samples for construction examples 2-3 were taken at one-year intervals, with samples measuring 0-20cm, 20-40cm, and 40-60cm, and are presented from top to bottom in the table.

[0124] Table 8. Results of Particle Analysis

[0125]

[0126] Table 9 Compaction Test Results

[0127]

[0128] Table 10 Basic Physical Properties

[0129]

[0130] Table 11 Disintegration Test Results

[0131]

[0132] Field construction verified the successful adaptability of this technology to different seasons and geological formations. In the winter construction example implemented at the K239+110 undisturbed soil sample point, the heated static pressure injection method reduced the frost heave rate to 0.79% after treatment, and the soil did not disintegrate at all, achieving in-situ modification and consolidation under frozen conditions. In the summer and autumn drilling grouting construction example at K239+115 and the spring thaw surface spraying construction example at K252+150, both were carried out at the optimal dosage of 15%. After a one-year interval, stratified sampling and testing showed that the content of coarse particles (0.25-0.075mm) in the 0-20cm surface soil exceeded 67%, the frost heave rate remained at a low level of 0.79%-0.91%, the water holding capacity remained in a low range of 20.7%-22.4%, and the disintegration test showed only slight disintegration or no disintegration. The modification effect remained stable and excellent after a complete freeze-thaw cycle. It is evident that the modified liquid and its construction method of this invention can achieve the goals of coarse granulation, low frost heave, and complete non-disintegration under different soil types and construction conditions in different seasons, and have outstanding long-term durability, thus fully proving the success of the modification.

[0133] Comparative Example 1

[0134] A frozen soil stabilizer, whose composition is basically the same as that of Example 5, except that PSS-Al in Agent A is replaced with an equal mass of unloaded aluminum ion polystyrene sulfonic acid (PSS-H). The PSS-H is obtained by treating PSS-Na with an ion exchange resin, the same as in Example 5, but without reacting with aluminum hydroxide. Specifically, to prepare 1L of Agent A: Take 70g of PSS-H (based on pure PSS-H), add 1.91g of citric acid monohydrate, 9.0g of isopropanol, 0.66g of EDTA-2Na dihydrate, and 1.25g of poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer, add water to approximately 900mL to dissolve, adjust the pH to 3.0 with formic acid and ammonium carbonate, and bring the volume to 1L. Agent B is prepared and used in the same manner as in Example 5, mixed thoroughly to obtain the stabilizer of Comparative Example 1. The experimental method is also the same as in Example 5.

[0135] In Comparative Example 1, after PSS-H was replaced with PSS-Al, the agglomeration effect and hydrophilicity reduction effect on fine loess soil were greatly weakened due to the loss of aluminum ion loading and efficient ion exchange capacity, and the parameters were almost the same as the original soil sample.

[0136] Comparative Example 2

[0137] A frozen soil stabilizer, with a composition basically the same as in Example 5, except that isopropanol is not added to Agent A. Specifically, to prepare 1L of Agent A: Take 70g of the same PSS-Al mother liquor as in Example 5 (based on pure PSS-Al), and sequentially add 1.91g of citric acid monohydrate, 0.66g of EDTA-2Na dihydrate, and 1.25g of poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer. Add water to approximately 900mL to dissolve. Adjust the pH to 3.0 with formic acid and ammonium carbonate, and bring the volume to 1L. Agent B is prepared and used in the same manner as in Example 5. Mix thoroughly to obtain stabilizer of Comparative Example 2. The experimental method is also the same as in Example 5.

[0138] The lack of isopropanol in Comparative Example 2 resulted in an ineffective reduction of the surface tension of the solution, significantly weakening its penetration ability in dense loess. This limited the diffusion depth and uniformity of the active ingredient within the soil, leading to insufficient modification of the soil in deeper areas and far from the injection point. While its modified frost heave rate (1.22%) and disintegration rate (8%) were better than Comparative Example 1, they were still significantly inferior to Example 5.

[0139] Comparative Example 3

[0140] A frozen soil stabilizer, whose composition is basically the same as that of Example 5, differs in that a pH-stabilized slow-release system is not used. Specifically, when preparing agent A, only formic acid is used to directly adjust the pH of the solution to 3.0 without adding ammonium carbonate, thus no formic acid-ammonium formate buffer pair is formed. The remaining components and dosages are exactly the same as agent A in Example 5, and agent B is prepared and dosaged in the same way as in Example 5. After thorough mixing, stabilizer Comparative Example 3 is obtained. The experimental method is also the same as in Example 5.

[0141] Comparative Example 3 did not use a pH-stabilized slow-release system, which caused aluminum ions to rapidly deposit in the early stages of contact with the soil, blocking the permeation channels. The effective components failed to diffuse and react evenly in the soil. After modification, the fine particle content was still 32.07%, and the frost heave rate was 1.45%, which was significantly worse than Example 5.

[0142] Comparative Example 4

[0143] This comparative example demonstrates the borehole-and-pipe salt injection method actually used in the Laiyuan area of ​​the Beijing-Yuanping Railway. This method involves drilling holes in the roadbed to the depth of the frost layer and quantitatively injecting an industrial salt solution to lower the freezing point of pore water in the soil, thereby inhibiting frost heave. The amount of salt injected is determined based on the frost heave height; approximately 10 kg of salt is injected per sleeper when the frost heave height is below 20 mm, and this increases to 30 kg when the frost heave height exceeds 50 mm. The operation employs refined salt injection technology, using borehole positioning to achieve targeted salt distribution.

[0144] This method has the following drawbacks: Salt injection only delays freezing by lowering the freezing point; it does not alter the hydrophilicity and water-adsorbing film on the surface of loess particles. Moisture migration channels still exist, and if sub-zero temperatures persist, ice lenses will continue to develop, making frost heave impossible to eliminate. The injected salt will gradually be lost through rainwater leaching and groundwater seepage, leading to a continuous decline in its antifreeze effect and necessitating repeated replenishment, resulting in accumulating maintenance costs. Furthermore, the large amount of salt seeping into the soil and groundwater poses a long-term pollution risk to the ecological environment along the route.

[0145] Comparative Example 5

[0146] This comparative example illustrates the partial replacement method actually used in severely frost-damaged sections of the Beijing-Yuanping Railway. This method involves excavating the existing frost-sensitive loess and replacing it with coarse-grained, non-frost-sensitive soil (such as gravel), compacting it in layers to the designed compaction degree, and the replacement depth being the maximum frost depth of the seasonally frozen soil.

[0147] This method has the following drawbacks: it requires closing the railway line for large-scale excavation, severely disrupting normal railway operations and significantly impacting transportation order. The amount of earthwork excavation and replacement is enormous, resulting in high project costs. The large amount of waste loess generated during excavation requires separate land acquisition and transportation for disposal, placing significant environmental pressure and incurring high additional costs. The construction period lasts for several months, making it impossible to complete within limited operating windows and unsuitable for existing lines with heavy traffic.

[0148] Comparative Example 6

[0149] This comparative example illustrates the comprehensive roadbed drainage treatment method actually implemented on the Beijing-Yuanping Railway, adhering to the maintenance philosophy of "treating winter diseases in summer and preventing them throughout the year." Specific measures include: promptly clearing drainage facilities after summer rainfall to prevent roadbed water accumulation; cleaning and screening the track in autumn to maintain smooth drainage of the ballast bed; strengthening ballast bed cleaning and screening in winter and spreading frost-damaging salts for emergency antifreezing in extremely cold weather; and simultaneously laying composite geomembrane waterproof layers and longitudinal drainage blind ditches on both sides of the roadbed to cut off surface water infiltration and capillary upwelling channels for groundwater.

[0150] This method has the following drawbacks: drainage and water-blocking measures can only block external water supply and remove some free water, but they are ineffective against the bound water film firmly adsorbed on the surface of loess particles through physicochemical processes. Water sources within the soil cannot be eradicated, water migration channels remain, and frost heave cannot be fundamentally addressed. Geomembranes are at risk of aging and damage, drainage blind ditches are prone to siltation and failure, and long-term reliability is difficult to guarantee. The entire solution requires continuous investment of manpower and resources for repeated maintenance, resulting in considerable accumulated costs, and the approach remains in a reactive state.

[0151] 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.

[0152] 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.

[0153] 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 permafrost stabilizer, characterized in that, It includes Agent A, which is an aqueous solution, and per liter of Agent A, Agent A contains the following components: PSS-Al: 60~80 g / L Citric acid: 1.5~2.0 g / L Isopropanol: 8.0~10.0 g / L EDTA-2Na: 0.5~0.7 g / L And a pH-stabilized sustained-release agent for adjusting the pH of agent A to 2.8-3.3; 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 reached the endpoint, thus obtaining the PSS-Al mother liquor. PSS-Al was obtained by filtration and purification; The average molecular weight of the PSS-Na is 20,000~70,000; The pH-stabilizing slow-release agent is a formic acid-ammonium formate buffer pair; The method of applying the pH-stabilized sustained-release agent is as follows: Formic acid is added to agent A until the pH is less than 2.2, and then ammonium carbonate is added until the pH of agent A is between 2.8 and 3.3, forming an in-situ formic acid-ammonium formate buffer pair.

2. The PMM permafrost stabilizer of claim 1, wherein, Agent A further comprises a poly(dimethylsiloxane)-60%(propylene oxide)-40%(ethylene oxide) copolymer, the content of which is 1.0~1.5 g / L.

3. The PMM permafrost stabilizer of claim 1, wherein, It also includes agent B, wherein the mass amount of agent B is 13% to 15% of PSS-Al; Each liter of Agent B is prepared as follows: 50-60g of PEG-400 and 20-25g of urea are added to 500ml of water, dissolved completely, and then diluted to 1L with water.

4. The application of the PMM frozen soil stabilizer according to any one of claims 1-3 in soil modification.

5. Use according to claim 4, characterized in that, The soil in question is loess.

Images