Solidified soil material based on soft matrix soil and preparation method

Abstract

The invention discloses a solidified soil material based on soft matrix soil and a preparation method, and relates to the technical field of soft matrix soil improvement. The solidified soil material comprises a solid component and a liquid component, the solid component comprises soft matrix soil, a composite gelling agent and modified bottom ash; the liquid component includes water and sulfonated oil. Wherein the composite gelling agent is formed by dry-mixing Portland cement, I-grade fly ash, S95-grade slag powder and desulfurized gypsum; the modified bottom ash is coal-fired power plant furnace bottom combustion residues subjected to pre-wetting treatment, and has a specific particle size range and particle composition; the sulfonated oil is an anionic surfactant containing a hydrophilic head group and a hydrophobic tail group, and the mass of the sulfonated oil and the total mass of the composite gelling agent meet a specific proportional relation. Through the synergistic effect of the inorganic gelling system, the physical framework material and the organic hydrophobic modifier, the problems that existing solidified soil is poor in water stability and low in industrial solid waste utilization rate are solved.

Description

Technical Field

[0001] This invention relates to the field of soft matrix soil improvement technology, and in particular to a solidified soil material based on soft matrix soil and its preparation method. Background Technology

[0002] In the backfilling and reinforcement of highway and railway subgrades, as well as building foundation pits, high liquid limit soils (such as high liquid limit silt, red clay, or weathered mica schist) are frequently encountered. These soils typically possess unfavorable engineering characteristics such as high natural water content, high liquid limit, large void ratio, and high water sensitivity. If such soils are directly used as subgrade fill material, they are prone to significant post-construction settlement under their own weight or long-term traffic loads. Especially in rainy southern regions or environments with frequent fluctuations in groundwater levels, the backfill soil is highly susceptible to softening due to water absorption, leading to strength reduction or even collapse, seriously threatening the long-term stability and safety of road engineering projects.

[0003] To improve the engineering performance of soft soil matrices, existing technologies typically employ chemical solidification methods. Traditional methods mainly rely on ordinary silicate cement or lime for stabilization. While this can improve strength to some extent, cement production is energy-intensive and generates significant carbon emissions, which contradicts the trend towards low-carbon and environmentally friendly practices. Furthermore, cement-solidified soil is brittle, prone to shrinkage cracks, and still lacks sufficient water resistance. Therefore, utilizing industrial solid waste (such as fly ash, slag, and power plant bottom ash) to replace cement in the preparation of low-carbon solidified soil materials has become a research hotspot. However, bottom ash emitted from coal-fired power plants is typically loose, porous, has high water absorption, and uneven gradation. Directly adding it as aggregate often competes for hydration water with cementitious materials, resulting in poor workability of fresh slurry, large fluctuations in the strength of the solidified body, and difficulty in ensuring density.

[0004] Furthermore, existing solidification technologies remain insufficient in addressing the contradiction between "high strength" and "high water stability." Simple inorganic solidification cannot fundamentally alter the hydrophilic nature of clay minerals, leaving the solidified soil at risk of softening after long-term immersion in water. While conventional organic modifiers can improve water resistance, they often hinder the hydration reaction of inorganic materials, resulting in lower early strength. In summary, there is currently a lack of a solidification technology for soft matrix soils that can efficiently utilize various industrial solid wastes, effectively address the negative impacts of porous, water-absorbing bottom ash, and simultaneously achieve high strength and high water stability through a synergistic physical-chemical process. Summary of the Invention

[0005] This invention provides a solidified soil material based on soft matrix soil and its preparation method, which solves the problems of poor water stability of soft matrix soil backfill materials, easy cracking of solidified soil, low utilization rate of bottom ash from coal-fired power plants, poor workability and large strength fluctuation caused by direct mixing in the prior art.

[0006] In a first aspect, embodiments of the present invention also propose a soil stabilization material based on soft matrix soil, the soil stabilization material comprising a solid component and a liquid component;

[0007] The solid component, by mass percentage, consists of the following raw materials: 50%–70% soft matrix soil, 20%–35% composite cementitious agent, and 10%–25% modified base lime;

[0008] The liquid component includes water and sulfonated oil, wherein the amount of water is 12%–18% of the total mass of the solid component, and the amount of sulfonated oil is 0.15%–0.35% of the total mass of the solid component; and the mass ratio of the sulfonated oil m_SO to the total mass of the composite gelling agent m_Binder satisfies the following mass ratio: 0.005 ≤ m_SO / m_Binder ≤ 0.01;

[0009] The composite cementitious agent is dry-mixed from the following raw materials by mass percentage: 40%–50% silicate cement, 20%–25% grade I fly ash, 15%–20% grade S95 slag powder, and 10%–15% desulfurized gypsum; the desulfurized gypsum contains SO3 by mass fraction greater than or equal to 40%, and the slag powder has a specific surface area of ​​400 m² / kg–450 m² / kg;

[0010] Modified bottom ash is the combustion residue of the bottom of a coal-fired power plant after pre-wetting treatment. The particle size range of modified bottom ash is 0.075mm–4.75mm, the moisture content is 3%–5%, and the particle size distribution of modified bottom ash meets the following requirements: curvature coefficient Cc is 1–3, and non-uniformity coefficient Cu is greater than or equal to 5.

[0011] Sulfonated oil is an anionic surfactant containing a hydrophilic head group -(SO2)OH- and a hydrophobic tail group hydrocarbon chain R.

[0012] Preferably, the overall porosity of the solidified soil material after 28 days of curing is less than or equal to 5.0%;

[0013] In the internal pore structure of the solidified soil material, the volume of pores with an equivalent diameter greater than 5 μm accounts for less than 10%, while the volume of pores with an equivalent diameter less than 1 μm accounts for more than 45%.

[0014] Furthermore, the distribution frequency of the ratio of the major axis to the minor axis of the pore structure in the range of 1.5–2.5 is greater than or equal to 40%.

[0015] Preferably, the unconfined compressive strength of the solidified soil material after preparation and standard curing for 28 days is greater than or equal to 5.5 MPa, and the water stability coefficient is greater than or equal to 85%.

[0016] Preferably, the solidified soil material further includes polypropylene fibers, the amount of which is 0.05%–0.15% of the total mass of the solid components, and the length of the polypropylene fibers is 6mm–12mm.

[0017] Preferably, when cured for 7 days at a temperature of 20±2℃ and a relative humidity of ≥95%, the microstructure characteristics of the solidified soil material are as follows: internal formation of ettringite crystals and CSH gel, with the ettringite crystals and CSH gel encapsulating the surface of the modified base ash particles.

[0018] Secondly, embodiments of the present invention also propose a method for preparing a solidified soil material based on soft matrix soil as proposed in the foregoing embodiments, comprising the following steps:

[0019] Step 1, raw material pretreatment: air-dry, crush and sieve the soft substrate soil; dry the bottom ash taken from the power plant, sieve and select the particle size range of 0.075mm-4.75mm, and adjust the moisture content to 3%-5% by adding water or drying to obtain modified bottom ash;

[0020] Step 2, dry powder premixing: Silicate cement, fly ash, slag powder and desulfurized gypsum are put into a mixer in proportion and dry premixed for 1-2 minutes to obtain composite cementitious agent; then soft matrix soil and modified bottom ash are added, and dry mixing is continued for 2-3 minutes to obtain dry mixture;

[0021] Step 3, preparation of liquid modifier: Dissolve sulfonated oil in water to prepare sulfonated oil aqueous solution;

[0022] Step 4, wet mixing: Add the sulfonated oil aqueous solution to the dry mixture and stir to form a wet mixture;

[0023] Step 5, Curing and Molding: Let the wet mixture stand under sealed conditions for 2–4 hours; then compact the cured wet mixture into shape.

[0024] Step 6, Curing: Place the molded specimens under conditions of 20±2℃ and relative humidity greater than or equal to 95% for curing.

[0025] Preferably, in step four, the sulfonated oil aqueous solution is sprayed into the dry mixture in three separate applications while stirring, and the shear rate of the stirring is controlled at 80 rpm–120 rpm.

[0026] Preferably, in step two, the pH value in the wet mixture system is maintained between 10 and 12 by adjusting the amount of desulfurized gypsum.

[0027] Seven days into the curing process, ettringite crystals and CSH gels are generated inside the solidified soil material, and the ettringite crystals and CSH gels coat the surface of the modified base coat particles.

[0028] Preferably, the solidified soil material prepared by steps one to six, after curing for 28 days, has an overall porosity of less than or equal to 5.0%, wherein the volume of pores with an equivalent diameter greater than 5 μm accounts for less than 10%, and the volume of pores with an equivalent diameter less than 1 μm accounts for more than 45%.

[0029] Preferably, the solidified soil material prepared by steps one to six and cured for 28 days at 20±2℃ and relative humidity greater than or equal to 95% has an unconfined compressive strength greater than or equal to 5.5MPa and a water stability coefficient greater than or equal to 85%.

[0030] Beneficial Effects: This invention achieves high strength, high water stability, and low porosity in solidified soft matrix soil materials by synergistically combining a specific ratio of a cement-fly ash-slag-desulfurized gypsum composite cementitious system, pre-wetted modified coal-fired power plant bottom ash, and a sulfonated oil hydrophobic modifier, and optionally incorporating a certain amount of polypropylene fiber. Specifically, by controlling the bottom ash particle size to 0.075mm–4.75mm, the gradation parameters Cc to 1–3 and Cu≥5, and pre-wetting the bottom ash to a 3%–5% internal saturation state, the bottom ash particles can form a dense skeletal structure and serve as preferential nucleation sites for hydration products, thereby improving the density and interfacial bonding of the solidified body. Attached Figure Description

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0032] Figure 1 This is a schematic flowchart of a method for preparing a solidified soil material based on soft matrix soil, as described in Embodiment 2 of the present invention. Detailed Implementation

[0033] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the invention will be briefly introduced below in conjunction with the accompanying drawings and descriptions of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be noted that the description of these embodiments is for the purpose of helping to understand the invention, but does not constitute a limitation on the invention.

[0034] Example 1 presents a solidified soil material based on soft matrix soil. Addressing the engineering challenges of high natural water content, low strength, and poor water stability in soft matrix soils such as high liquid limit silt and red clay, this invention improves the mechanical properties and durability of the solidified soil by introducing specific modified base lime and sulfonated oil. In particular, it solves the problem of traditional solidified soils being prone to cracking and disintegration under wet-dry cycles. The specifications and parameters of the raw materials used in this invention are as follows. These parameters were determined through extensive screening experiments and are the foundation for achieving the high strength and high water stability of this invention.

[0035] The soft matrix soil selected in this embodiment is a high-liquid-limit silty clay taken from the roadbed of a highway in a rainy area in southern China. This type of soil is widely distributed in southern regions and has extremely poor engineering properties. Laboratory geotechnical tests showed that its natural moisture content was 42%, its liquid limit was 58%, its plasticity index was 29, and its pH value was 6.5, classifying it as a typical water-sensitive soil. Its mineral composition mainly consists of kaolinite, montmorillonite, and illite. Although the montmorillonite content is not high, it is sufficient to cause volume changes. Before use, the soil sample needs to be air-dried naturally to a moisture content of approximately 15%-18%, then crushed and sieved through a 2mm sieve. The purpose of pretreatment is to disrupt the original structure of the soil, facilitating uniform mixing with the curing agent later.

[0036] Composite cementitious agent: Employs a specific quaternary composite cementitious system of "cement-fly ash-slag-desulfurized gypsum". These four components exhibit complex synergistic effects.

[0037] Portland cement, specifically PO 42.5 ordinary Portland cement, is used as the alkaline activator and main cementitious component in the system. The cement hydrates rapidly, providing early strength support and releasing a large amount of... This provides an alkaline environment (pH > 12) for subsequent volcanic ash reactions.

[0038] Grade I fly ash, using Class F Grade I fly ash, with a water requirement of 92% and a loss on ignition of less than 5%. Fly ash is rich in active materials. and However, its glassy structure is dense, resulting in low early-stage reactivity. In this system, fly ash mainly participates in the later-stage pozzolanic reaction, consuming the substances produced during cement hydration. This generates CSH gel, which fills the pores and improves long-term strength and durability.

[0039] S95 grade slag powder, as a highly active potential hydraulic material. The slag powder contains a large amount of active calcium oxide and silicon dioxide, which can rapidly hydrate under alkaline activation. To ensure its rapid early reaction and good gradation complementarity with fly ash, this invention strictly limits its specific surface area to [specific value missing]. (The measured value in this embodiment is) While an excessively high specific surface area can improve early activity, it also increases water demand, making the solidified soil prone to cracking.

[0040] Desulfurization gypsum, a byproduct of flue gas desulfurization in power plants, mainly consists of calcium sulfate dihydrate. After drying and dehydration, among which... The mass fraction is 46% (meeting the ≥40% requirement). Desulfurized gypsum acts as a sulfate activator in this system. High concentrations of sulfate ions in an alkaline environment can activate active aluminum in slag and fly ash, generating ettringite (AFt). The needle-like crystals of ettringite can act as micro-reinforcement and fill large pores in the early stages, improving early strength.

[0041] Modified bottom ash (BTA) originates from combustion residues discharged from the bottom of coal-fired power plants. Unlike fly ash, bottom ash particles are coarser, porous, and have rough surfaces with irregular shapes. Particle size and gradation: Sieving was used to select particles ranging from 0.075mm to 4.75mm, removing excessively coarse particles (affecting compaction) and excessively fine dust (low activity and high water absorption). The curvature coefficient of its particle size distribution was measured. The coefficient of non-uniformity is 1.8. The moisture content is 7.2, meeting the requirements for well-graded skeleton packing. This means that the bottom ash particles can form a dense packing structure, reducing porosity. Pre-wetting modification is one of the key technical features of this invention. The high water absorption of the bottom ash is the main obstacle limiting its application in cementitious materials. If dry bottom ash is used directly, it will quickly absorb free water from the slurry, resulting in incomplete hydration of the cementitious material and weak interfacial bonding. Before use, this invention adjusts the moisture content of the bottom ash to 3%–5% (4.0% in this embodiment) through spray water addition and sealed static treatment. This state is the "internal saturated surface wet" state, that is, the pores inside the particles adsorb water, but there is no obvious water film on the surface. This prevents the porous bottom ash from absorbing water from the slurry, avoids the decrease in the strength of the interfacial transition zone (ITZ) due to an excessively thick free water film on the bottom ash surface, and provides a micro-humid environment for the nucleation of surface hydration products, promoting the growth and anchoring of hydration products on the bottom ash surface. Sulfonated oil (SO) is made with industrial-grade anionic surfactants, whose molecular structure contains hydrophilic head groups. The active ingredient content is 45%, consisting of a hydrophobic tail hydrocarbon chain R. The mechanism of action of sulfonated oil lies in its unique molecular structure: hydrophilic groups adsorb onto the surface of positively charged soil particles and hydration products through ion exchange, while hydrophobic groups align outwards, forming a dense monomolecular hydrophobic film. This film not only blocks the capillary channels through which liquid water penetrates the soil but also effectively inhibits the evaporation of moisture from within the soil, thus playing a dual role of "water retention" and "waterproofing." Furthermore, sulfonated oil can reduce the surface tension of pore water, acting as a lubricant during compaction and helping to improve the density of the solidified soil. Polypropylene fiber, using bundled monofilament polypropylene fiber, is 9mm long and 30mm in diameter. The tensile strength is >400MPa, and the elastic modulus is >3.5GPa. The fiber content is 0.1% of the total mass of the solid components. The fibers are distributed in a three-dimensional random pattern in the solidified soil, which can play a role in micro-reinforcement, crack prevention, and toughening, effectively improving the brittle failure characteristics of the solidified soil and enhancing its crack resistance and stability under dynamic loads.

[0042] The mixing water, ordinary tap water, must be clean and free of oil, with a pH value between 6 and 8.

[0043] This embodiment focuses on illustrating the composition and final performance indicators of the solidified soil material. For ease of comparison and calculation, a solidified soil material specimen with a mass of 1000g of solid components was prepared, with the specific formulation as follows:

[0044] The mix design is based on the results of orthogonal experimental optimization, aiming to balance strength, water stability, economy and workability.

[0045] Solid components (total 1000g): Soft matrix soil, 600g, accounting for 60% of the total solid component mass. This proportion ensures the basic properties of the solidified soil as a roadbed filler, while also making full use of on-site soil resources and reducing costs. Composite cementitious agent, 250g, accounting for 25% of the total solid component mass. The internal proportions of the composite cementitious agent are: silicate cement 112.5g (45%), Grade I fly ash 55g (22%), S95 grade slag powder 45g (18%), and desulfurized gypsum 37.5g (15%). This proportion maximizes the use of solid waste materials while ensuring early strength, and controls the alkalinity within a suitable range to facilitate the stable formation of ettringite. Modified base ash, 150g, accounting for 15% of the total solid component mass. The addition of base ash not only provides a physical skeleton but also acts as a micro-aggregate filler, further improving the density of the solidified soil.

[0046] Liquid components: Water, 150g, added at 15% of the total mass of the solid components. This water amount is slightly adjusted based on the optimum moisture content (OMC) determined by compaction tests to compensate for moisture loss during mixing and molding. Sulfonated oil (SO), 2.0g, added at 0.20% of the total mass of the solid components. Key parameter verification: Sulfonated oil mass. Total mass of composite gelling agent The ratio is calculated as follows: This ratio strictly falls within Within the specified range. This range is chosen based on the following considerations: if the ratio is less than 0.005, the sulfonated oil molecules are insufficient to cover most of the soil particle surface, and the hydrophobic effect is not obvious; if the ratio is greater than 0.01, excessive sulfonated oil molecules may coat the surface of cement particles, hindering the hydration reaction, leading to a decrease in strength, and may also cause slippage between soil particles, reducing shear strength.

[0047] Other components: Polypropylene fiber, 1.0g, with an admixture amount of 0.1% of the total mass of solid components.

[0048] According to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009) and related standards, specimens cured to the specified age were tested. Six parallel specimens were tested at each age, and the average value was taken as the final result. The results are as follows:

[0049] Macroscopic mechanical properties: The 7-day unconfined compressive strength has an average measured value of 4.8 MPa. This strength meets the strength requirements of high-grade highway subgrade base courses (typically 3-4 MPa), indicating that the material has excellent early strength. The 28-day unconfined compressive strength has an average measured value of 6.2 MPa, meeting the preferred index of ≥5.5 MPa. The continuous increase in strength indicates that the pozzolanic reaction in the composite cementitious system is progressing steadily, indicating great potential for later strength. Water stability coefficient: The compressive strength of the 28-day cured specimen was measured after immersing it in water for 24 hours, and the result was 5.7 MPa. The calculated water stability coefficient HS = 5.7 / 6.2 × 100% = 91.9%, far exceeding the preferred index of 85%. This indicates that the solidified soil has extremely strong resistance to water erosion and can maintain stable mechanical properties in humid environments for a long time. The triaxial shear properties showed that under a confining pressure of 300 kPa, the deviatoric stress at failure reached 1250 kPa, and the stress-strain curve exhibited obvious strain hardening characteristics, with the failure strain exceeding 6.0%. This indicates that the addition of fibers effectively improved the toughness of the material, giving it better resistance to deformation.

[0050] Microscopic pore structure characteristics (28-day age, MIP mercury intrusion porosimetry):

[0051] The overall porosity is 4.2%, meeting the preferred requirement of ≤5.0%. Low porosity is the physical basis for the material's high strength and durability. The pore size distribution has an equivalent diameter greater than 5... The volumetric porosity is 5.8% (meeting <10%), and the equivalent diameter is less than 1. The micropore volume ratio is 58.3% (satisfying >45%). This indicates that the internal pore structure of the material is dominated by micropores, with large pores effectively filled or divided, reducing connectivity and thus improving impermeability. Regarding pore morphology, SEM image analysis shows that the ratio of the long axis to the short axis of the pores occurs most frequently in the range of 1.5–2.5 (satisfying ≥40%), indicating the formation of a dense, layered, compacted structure. This flattened pore structure is more conducive to preventing water penetration.

[0052] Example 2:

[0053] This embodiment focuses on the preparation process of the aforementioned solidified soil material, particularly the targeted construction of the material's microstructure through stepwise feeding, shear rate control, and pH environment regulation. The process flow is designed to maximize the effectiveness of each component and overcome problems such as uneven component dispersion and incomplete reaction in traditional processes. It includes the following steps:

[0054] Step 1, raw material pretreatment: air-dry, crush and sieve the soft substrate soil; dry the bottom ash taken from the power plant, sieve to select the particle size range of 0.075mm-4.75mm, and adjust the moisture content to 3%-5% by adding water or drying to obtain modified bottom ash.

[0055] The soft substrate soil was placed in a well-ventilated indoor area to air dry naturally, turning it regularly until its moisture content dropped below the plastic limit (approximately 15%-18%). It was then pulverized using a crusher and sieved through a 2mm sieve to remove particles larger than 2mm and organic impurities. The bottom ash from the power plant was naturally dried or oven-dried, and sieved to select a particle size range of 0.075mm–4.75mm. Before use, its moisture content was measured (0.5% in this example), and the required water was calculated. The bottom ash was placed in a mixer, and water was sprayed in while stirring until its moisture content reached 4.0%. After adding water, the bottom ash was sealed in a plastic bag and left to stand for 24 hours to allow moisture to fully penetrate into the internal pores of the particles and reach equilibrium through capillary action, thus obtaining the modified bottom ash. At this point, the bottom ash was in an "internal saturated surface wet" state, providing good interfacial conditions for the subsequent hydration reaction.

[0056] Step 2, dry powder premixing: Silicate cement, fly ash, slag powder and desulfurized gypsum are put into a mixer in proportion and dry premixed for 1-2 minutes to obtain composite cementitious agent; then soft matrix soil and modified bottom ash are added, and dry mixing is continued for 2-3 minutes to obtain dry mixture.

[0057] Silicate cement, fly ash, slag powder, and desulfurized gypsum were added to a twin-shaft forced mixer in a specific ratio. The mixer was started and dry-mixed at low speed (approximately 40-60 rpm) for 1-2 minutes to obtain a composite binder. In this embodiment, by controlling the desulfurized gypsum content to 15%, the pH value of the system was measured to be approximately 11.2 after subsequent addition of water to form a wet mixture (meeting the preferred range of 10-12). A suitable alkaline environment can both activate the activity of slag and fly ash and ensure the stable existence of ettringite (AFt), while avoiding the decomposition of sulfonated oil by a strongly alkaline environment. If the pH is too high (>12.5), ettringite may decompose, affecting early strength; if the pH is too low (<10), the pozzolanic reaction is difficult to proceed. Subsequently, the pretreated soft matrix soil, modified base ash, and polypropylene fiber were added, and dry mixing continued for 2-3 minutes. At this point, the stirring speed can be appropriately increased to 60-80 rpm to ensure that the components are fully dispersed and a dry mixture with uniform color is obtained.

[0058] Step 3, preparation of liquid modifier: Dissolve sulfonated oil in water to prepare sulfonated oil aqueous solution.

[0059] Slowly add the weighed sulfonated oil (2.0g) to the measured water (150g). Using a high-speed shear emulsifier, stir at 2000-3000 rpm for 3-5 minutes to fully disperse the sulfonated oil in the water, preparing a homogeneous, milky-white aqueous solution of sulfonated oil. This solution should be prepared and used immediately before use to avoid separation caused by prolonged standing.

[0060] Step 4, wet mixing: Add the sulfonated oil aqueous solution to the dry mixture and stir to form a wet mixture.

[0061] The sulfonated oil aqueous solution is added to the dry mixture and stirred to form a wet mixture. To ensure uniform distribution of the liquid modifier without damaging the soil structure, this step employs a strategy of phased addition and controlled shear rate.

[0062] First spray: While the mixer is running, spray 30% of the total liquid volume, control the stirring speed at about 80 rpm, and stir for 30 seconds. The purpose is to initially wet the powder surface and suppress dust.

[0063] Second spray: Spray 40% of the total liquid volume, control the stirring speed at about 90 rpm, stir for 60 seconds to promote the liquid to penetrate into the soil particle aggregates;

[0064] Third spray: Spray the remaining 30% of the liquid volume and increase the stirring speed to 100 rpm, stirring continuously for 3 minutes.

[0065] Multi-stage spraying combined with an appropriate shear rate allows sulfonated oil droplets to be evenly coated onto the surface of soil particles and hydration products, forming a continuous hydrophobic film. Adding a large amount of liquid at once or stirring too quickly (>150 rpm) can easily lead to localized overwetting and clumping, and introduce a large number of unstable air bubbles, forming harmful large pores and severely reducing strength. If the stirring speed is too slow, sufficient shear force cannot be provided to break up the soil particle agglomerates, resulting in uneven dispersion of the modifier.

[0066] Step 5, Curing and Molding: Let the wet mixture stand under sealed conditions for 2–4 hours; then compact the cured wet mixture into shape.

[0067] Place the mixed wet material into a sealed container (such as a plastic bucket or sealed bag) and let it stand for 2–4 hours. This standing process utilizes the principle of ion diffusion to allow the sulfonated oil molecules to... Ions fully penetrate the double electrical layer inside the clay particles, completing ion exchange and hydrophobic modification. Simultaneously, the curing process helps to evenly distribute moisture within the mixture, eliminating uneven wetting. Subsequently, the wet mixture after curing is removed, and its moisture content is measured. If it is slightly below the optimum moisture content, a small amount of water can be added and mixed thoroughly. The mixture is then layered into test molds using a heavy compaction method, with each layer compacted the same number of times to ensure the overall compaction degree is controlled above 96%. For on-site construction, a heavy roller can be used for layered compaction.

[0068] Step 6, Curing: Place the molded specimens under conditions of 20±2℃ and relative humidity greater than or equal to 95% for curing.

[0069] After demolding, immediately wrap the specimens with plastic wrap to prevent excessive moisture evaporation and surface cracking. Place the wrapped specimens in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for curing. During curing, regularly check the condition of the specimens and maintain stable temperature and humidity in the curing room. For on-site construction, the subgrade surface should be covered with geotextile and watered for curing for no less than 7 days.

[0070] Microstructure evolution verification: To further investigate the influence of the preparation process of this invention on the microstructure, microscopic testing and analysis were performed on specimens cured for 7 days.

[0071] XRD analysis was performed on samples from the central portion of 7-day-old specimens, which were freeze-dried and ground before XRD testing. The spectra showed... Distinct characteristic diffraction peaks of ettringite (AFt) were observed at 9.1°, 15.8°, and 22.9°, with high peak intensity. This indicates that, under the stimulation of desulfurized gypsum, the active aluminum in the slag and fly ash underwent a rapid reaction in the early stages, generating a large amount of ettringite crystals. Furthermore, diffuse peaks of CSH gel were detected, indicating that the hydration reaction proceeded relatively fully.

[0072] SEM morphology: The fracture morphology of the samples was observed using scanning electron microscopy. Observations revealed densely packed needle-like ettringite crystals and flocculent CSH gel growing on the surface of the modified base ash particles, forming a "core-shell" encapsulation structure. This structure benefits from the pre-wetting treatment of the base ash, making its surface a preferential nucleation site for hydration reactions. Simultaneously, a very thin film-like substance (attributable to a hydrophobic film formed by sulfonated oil) was observed covering the soil particle surface, and the pores between particles were effectively filled by hydration products. This microstructure of "base ash skeleton + hydration product filling + hydrophobic film coating" enhances the interfacial bonding between aggregate and matrix, avoiding the interfacial delamination phenomenon commonly found in traditional solidified soils, and is key to achieving high strength and high water stability.

[0073] To more intuitively demonstrate the advantages of the embodiments of the present invention in terms of technical solutions and technical effects, the following comparative examples are provided:

[0074] Comparative Example 1: Conventional cement-stabilized soil (using only PO 42.5 cement, with an admixture of 15%, without base ash, and without sulfonated oil).

[0075] Comparative Example 2: Single organic modified soil (using only sulfonated oil, with an admixture of 0.2%, without composite cementitious agent, and without base ash).

[0076] Comparative Example 3: Conventional industrial solid waste consolidation soil (using CFSD system, directly mixed with dry bottom ash, without sulfonated oil).

[0077] Comparative Example 4: The formulation of this invention with unoptimized process parameters (one-time liquid addition, high-speed stirring >200 rpm).

[0078] Table 1. Comparison of overall performance between embodiments and comparative examples of the present invention.

[0079] Comparison Projects Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Component characteristics CFSD + Modified base ash + Sulfonated oil pure cement Sulfonated oil only CFSD + Dry Base Gray CFSD + Modified base ash + Sulfonated oil Process characteristics Pre-wetting + multi-stage spraying + low shear conventional mixing conventional mixing conventional mixing One-time liquid addition + high shear 28-day unconfined compressive strength 6.2 MPa 4.5 MPa 2.5 MPa 4.2 MPa 3.5 MPa Water stability coefficient (HS) 91.9% 75% 88% 70% 78% Porosity 4.2% 12% 15% 14% 12% Microstructural features Calcium alum / CSH encapsulated base gray, with a dense structure Gel filling, multiple microcracks Oil film coating, loose structure Interface stripping, porous Numerous pores and uneven structure Technical effect evaluation High strength, excellent water resistance, and uniform structure Its strength is acceptable, but its water resistance is poor and it is prone to cracking. It has good water resistance, but low strength and large deformation. High water demand, difficult molding, and fluctuating strength. Introducing air bubbles significantly reduces strength and density.

[0080] Data Analysis: Balance between Strength and Water Stability: Example 1 showed the highest strength (6.2 MPa) and extremely high water stability (91.9%). In contrast, Comparative Example 1, while having acceptable strength (4.5 MPa), exhibited poor water stability (75%), indicating that simple cement solidification cannot solve the problem of soil softening upon contact with water. Comparative Example 2 showed good water stability (88%), but its strength was too low (2.5 MPa), failing to meet the roadbed bearing requirements. This demonstrates the effectiveness of the synergistic effect of the "inorganic cementitious + organic hydrophobic" combination in this invention, utilizing both the high strength of inorganic materials and the high water stability of organic materials.

[0081] Compared with Comparative Example 3, the use of dried base ash increased water demand, disrupted the water-cement ratio balance, and resulted in decreased strength (4.2 MPa) and increased porosity (14%). SEM observation showed obvious peeling cracks at the interface between the base ash and the matrix in Comparative Example 3. This demonstrates the importance of "moisture content control of modified base ash," and pre-wetting treatment is key to the effective utilization of base ash.

[0082] Comparing Example 1 and Comparative Example 4, even with the same formulation, using an incorrect stirring process (such as high shear introducing air bubbles or uneven dispersion due to single-stage liquid addition) can lead to a surge in porosity (12%) and a decrease in strength (3.5 MPa). This fully supports the inventiveness of the technical features of "shear rate control" and "staged spraying" in the claims, demonstrating that process control is crucial for maximizing material performance.

[0083] In summary, this invention, through rational formulation design and refined preparation process, successfully prepared a soft soil stabilization material with high strength, high water stability, low porosity, and excellent durability. This material not only effectively solves the technical challenges in soft soil subgrade engineering but also makes extensive use of industrial solid waste, resulting in both economic and environmental benefits.

[0084] Finally, it should be noted that the above are merely preferred embodiments of the invention and are not intended to limit the scope of protection of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A soil stabilization material based on soft matrix soil, characterized in that, The solidified soil material includes solid components and liquid components; The solid component, by mass percentage, consists of the following raw materials: 50%–70% soft matrix soil, 20%–35% composite cementitious agent, and 10%–25% modified base lime; The liquid component comprises water and sulfonated oil, wherein the amount of water is 12%–18% of the total mass of the solid components, and the amount of sulfonated oil is 0.15%–0.35% of the total mass of the solid components; and the mass ratio of the sulfonated oil m_SO to the total mass m_Binder of the composite gelling agent satisfies the following mass ratio: 0.005 ≤ m_SO / m_Binder ≤ 0.01; The composite cementitious agent is dry-mixed from the following raw materials by mass percentage: 40%–50% silicate cement, 20%–25% grade I fly ash, 15%–20% grade S95 slag powder, and 10%–15% desulfurized gypsum; the desulfurized gypsum contains SO3 by mass fraction greater than or equal to 40%, and the slag powder has a specific surface area of ​​400 m² / kg–450 m² / kg; The modified bottom ash is the combustion residue of the bottom of a coal-fired power plant after pre-wetting treatment. The particle size range of the modified bottom ash is 0.075mm–4.75mm, the moisture content is 3%–5%, and the particle size distribution of the modified bottom ash satisfies the following: curvature coefficient Cc is 1–3, and non-uniformity coefficient Cu is greater than or equal to 5. The sulfonated oil is an anionic surfactant containing a hydrophilic head group -(SO2)OH- and a hydrophobic tail group hydrocarbon chain R.

2. The soil stabilization material based on soft matrix soil according to claim 1, characterized in that, The total porosity of the solidified soil material after 28 days of curing is less than or equal to 5.0%. In the pore structure inside the solidified soil material, the volume of pores with an equivalent diameter greater than 5 μm accounts for less than 10%, and the volume of pores with an equivalent diameter less than 1 μm accounts for more than 45%. Furthermore, the distribution frequency of the ratio of the major axis to the minor axis of the pore structure in the range of 1.5–2.5 is greater than or equal to 40%.

3. The soil stabilization material based on soft matrix soil according to claim 1, characterized in that, The solidified soil material, after preparation and standard curing for 28 days, has an unconfined compressive strength greater than or equal to 5.5 MPa and a water stability coefficient greater than or equal to 85%.

4. The soil stabilization material based on soft matrix soil according to claim 1, characterized in that, The solidified soil material also includes polypropylene fibers, the amount of which is 0.05%–0.15% of the total mass of the solid components, and the length of which is 6mm–12mm.

5. The soil stabilization material based on soft matrix soil according to claim 1, characterized in that, When cured for 7 days at a temperature of 20±2℃ and a relative humidity of ≥95%, the microstructure of the solidified soil material is characterized by the formation of ettringite crystals and CSH gel inside, and the ettringite crystals and CSH gel encapsulate the particle surface of the modified base coat.

6. A method for preparing a solidified soil material based on soft matrix soil as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1, raw material pretreatment: The soft substrate soil is air-dried, crushed and sieved; the bottom ash taken from the power plant is dried, sieved to select a particle size range of 0.075mm–4.75mm, and the moisture content is adjusted to 3%–5% by adding water or drying treatment to obtain the modified bottom ash; Step 2, dry powder premixing: The silicate cement, fly ash, slag powder and desulfurized gypsum are put into a mixer in proportion and dry premixed for 1-2 minutes to obtain the composite cementitious agent; then the soft matrix soil and the modified bottom ash are added, and dry mixing is continued for 2-3 minutes to obtain the dry mixture; Step 3, preparation of liquid modifier: Dissolve the sulfonated oil in the water to prepare an aqueous solution of sulfonated oil; Step 4, wet mixing: The sulfonated oil aqueous solution is added to the dry mixture and stirred to form a wet mixture; Step 5, Curing and Molding: The wet mixture is left to stand under sealed conditions for 2–4 hours; then the cured wet mixture is compacted and molded. Step 6, Curing: Place the molded specimens under conditions of 20±2℃ and relative humidity greater than or equal to 95% for curing.

7. The preparation method according to claim 6, characterized in that, In step four, the sulfonated oil aqueous solution is sprayed into the dry mixture in three separate applications while stirring, and the shear rate of the stirring is controlled at 80 rpm–120 rpm.

8. The preparation method according to claim 6, characterized in that, In step two, the pH value of the wet mixture system is maintained between 10 and 12 by adjusting the amount of desulfurized gypsum. When the curing process reaches 7 days, ettringite crystals and CSH gel are generated inside the solidified soil material, and the ettringite crystals and CSH gel coat the surface of the modified base coat particles.

9. The preparation method according to claim 6, characterized in that, The solidified soil material prepared by steps one to six, after curing for 28 days, has an overall porosity of less than or equal to 5.0%, wherein the volume of pores with an equivalent diameter greater than 5 μm accounts for less than 10%, and the volume of pores with an equivalent diameter less than 1 μm accounts for more than 45%.

10. The preparation method according to claim 6, characterized in that, The solidified soil material prepared by steps one to six and cured for 28 days at 20±2℃ and relative humidity greater than or equal to 95% has an unconfined compressive strength greater than or equal to 5.5MPa and a water stability coefficient greater than or equal to 85%.

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