A kind of river revetment embankment soil prepared by using low organic matter dewatered sludge and a preparation method thereof

Abstract

The application belongs to the technical field of resource recycling, and provides a kind of river revetment embankment soil prepared by using low organic matter dewatered sludge and a preparation method thereof.The river revetment embankment soil comprises low organic matter dewatered sludge, composite aggregate, composite solidifying agent and raw soil;the composite aggregate comprises cement-coated recycled aggregate, gravel and silane-modified waste rubber particles;the composite solidifying agent comprises cement, alkali-activated blast furnace slag, silane-modified montmorillonite and biochar.The application takes low organic matter dewatered sludge as one of the main raw materials, simultaneously absorbs a large amount of construction waste recycled aggregate, industrial blast furnace slag, waste rubber and other multi-source solid waste, realizes waste control by waste through the complementation of the functions of various components and the optimization of process parameters, and the on-site mixing and layered compaction process adopted is simple and easy to implement, has high construction efficiency, and has good engineering adaptability and application value.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically to a method for preparing riverbank protection soil using dewatered sludge with low organic matter. Background Technology

[0002] Under the wave of ecological construction in my country's water conservancy projects, the demand for high-quality soil for riverbank protection and embankment construction has been increasing year by year, with annual consumption exceeding 1 billion cubic meters. Traditional embankment soil mainly relies on the mining of natural clay, which not only leads to the increasing scarcity of high-quality soil resources but also causes ecological problems such as soil erosion and river siltation. At the same time, the pressure for large-scale disposal of low-organic-matter dewatered sludge continues to increase. The annual production of this type of sludge exceeds 30 million tons. It has a high proportion of inorganic components (≥70%), moderate clay content (10%-15%), and good plasticity, giving it natural advantages as a raw material for embankment soil. However, existing technologies have not fully explored its potential, resulting in sludge still being mainly landfilled and stockpiled, with both resource waste and environmental risks.

[0003] Existing sludge-based embankment soil technologies suffer from several key defects, failing to meet engineering requirements and environmental standards: First, performance compatibility is poor. Low-organic-matter sludge particles are highly dispersible, and when mixed with natural soil, inappropriate particle gradation makes it difficult to consistently achieve the required compaction degree. Furthermore, insufficient impermeability fails to resist river water seepage. In frigid northern regions, some products exhibit a mass loss rate of 1.32%-2.54% after 15 freeze-thaw cycles, far exceeding the standard limit of <1%, impacting their long-term stability and durability under harsh environments. Second, there is an imbalance between cost and environmental benefits. To improve performance, existing technologies often employ high-dosage solidifying agents (up to 12% in cement + lime composite systems). Furthermore, the utilization rate of industrial waste residue is generally low, failing to effectively implement the circular economy concept of treating waste with waste; thirdly, there are prominent environmental safety hazards. The trace amounts of highly toxic pollutants such as heavy metals (e.g., Cu, Pb, Cr, etc., with a total content of 50-100 mg / kg) remaining in the sludge are easily leached and migrated in the humid environment of the river. Existing single solidification agents can only achieve short-term physical encapsulation, and the leaching concentration of heavy metals is prone to exceed the standard during long-term service, polluting surface water and groundwater; fourthly, the process is complex. Some existing technical solutions involve cumbersome procedures such as deep drying of sludge, multiple conditioning, and aging, which extend the construction cycle by 50% compared to traditional embankment soil, making it difficult to adapt to the large-scale and fast-paced construction needs of water conservancy projects.

[0004] Furthermore, the unique service environment of river embankment projects (long-term immersion, water erosion, freeze-thaw cycles) places higher demands on soil performance, and existing technologies struggle to achieve synergistic optimization of multiple properties. Therefore, developing a low-organic-matter sludge-based soil for riverbank protection that balances engineering performance, environmental safety, and economic efficiency can not only solve the dual challenges of sludge disposal and natural soil shortages but also improve the ecological and environmental protection level of embankment projects, possessing significant engineering value and social significance. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a riverbank protection soil prepared using low-organic-matter dewatered sludge, comprising low-organic-matter dewatered sludge, composite aggregate, composite curing agent, and original soil; the composite aggregate comprises cement-coated recycled aggregate, crushed stone, and silane-modified waste rubber particles; the composite curing agent comprises cement, alkali-activated blast furnace slag, silane-modified montmorillonite, and biochar.

[0006] Furthermore, the mass ratio of pretreated sludge, composite aggregate and original soil is 1:(1-2):(2-4); the composite curing agent accounts for 2%-8% of the total mass of pretreated sludge, composite aggregate and original soil; the mass ratio of cement, alkali-activated blast furnace slag, silane-modified montmorillonite and biochar is 1:(0.5-0.6):(0.3-0.4):(0.05-0.1).

[0007] Furthermore, the moisture content of the low-organic-matter dewatered sludge is ≤50%.

[0008] Furthermore, the cement-coated recycled aggregate is a graded recycled aggregate, including cement-coated 0.5-5 mm recycled fine aggregate, cement-coated 5-10 mm recycled medium aggregate, and cement-coated 10-20 mm recycled coarse aggregate; the mass ratio of cement-coated 0.5-5 mm recycled fine aggregate, cement-coated 5-10 mm recycled medium aggregate, cement-coated 10-20 mm recycled coarse aggregate, and crushed stone is (3.5-4.5):(2.5-3.5):(1.5-2.5):(0.5-1.5), preferably 4:3:2:1; the crushed stone particle size is 5-20 mm; and the cement layer thickness is 0.2-0.6 mm.

[0009] Furthermore, alkali-activated blast furnace slag is obtained by roasting blast furnace slag with sodium carbonate at 280-350℃ for 20-60 minutes.

[0010] Furthermore, the preparation method of silane-modified montmorillonite includes: activating montmorillonite with 1%-10% hydrochloric acid for 1-5 hours at a liquid-to-solid ratio of (1-6):1, washing and drying with water, adding 3-8% by mass of silane coupling agent aqueous solution at a solid-to-liquid ratio of 1:(8-12), and reacting at 50℃-70℃ for 1-3 hours to obtain silane-modified montmorillonite; the silane coupling agent includes, but is not limited to, at least one of 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or γ-methacryloyloxypropyltrimethoxysilane.

[0011] Furthermore, the preparation method of silane-modified waste rubber granules includes: adding a silane coupling agent alcohol solution with a mass fraction of 5-10% at a solid-liquid ratio of 1:(3-6), reacting at 50℃-70℃ for 0.5-2h to obtain silane-modified waste rubber granules; the silane coupling agent includes, but is not limited to, at least one of 3-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, or vinyltriethoxysilane; in the composite aggregate, the mass of silane-modified waste rubber granules added accounts for 1%-5% of the total mass of the cement-coated recycled aggregate and crushed stone.

[0012] Furthermore, the biochar is corn stalk biochar with a particle size of 0.1-0.3 mm and a pore size of 1-20 μm.

[0013] This invention also provides a method for preparing riverbank protection soil using dewatered sludge with low organic matter, comprising the following steps:

[0014] (1) Cement-coated recycled aggregate, crushed stone and silane-modified waste rubber particles are mixed to obtain composite aggregate; cement, alkali-activated modified blast furnace slag, silane-modified montmorillonite and biochar are mixed to obtain composite curing agent; (2) Mix the low organic matter dewatered sludge, composite aggregate and original soil evenly to obtain a mixed component, add water to adjust the moisture content to 22%-28% to form a viscous and uniform wet material system; (3) Add composite curing agent to the viscous and uniform wet material system and mix evenly to obtain soil for riverbank protection.

[0015] Furthermore, the construction conditions for the soil used for riverbank protection include: material placement, compaction, and curing; the compaction is gradient compaction, first statically compacting twice with a compaction energy of 500-700 kN·m / m³ to eliminate pores, then vibratingly compacting four times with a compaction energy of 2000-2500 kN·m / m³ to make it dense and formed, and finally statically compacting once with a compaction energy of 500-700 kN·m / m³ to level the surface.

[0016] The beneficial effects of this invention are as follows: 1. Significantly improves the engineering mechanical properties and freeze-thaw durability of embankment soil prepared from low-organic-matter sludge. This invention constructs a multi-level continuous gradation skeleton system composed of cement-coated recycled aggregate, crushed stone, and modified waste rubber particles. This effectively improves the particle size distribution and interfacial bonding of the soil, enhancing the overall integrity of the material's internal structure. Simultaneously, the elastic deformation capacity of the waste rubber particles and the porous buffering effect of biochar synergistically alleviate the volume expansion stress caused by water phase change during freeze-thaw cycles, significantly inhibiting surface spalling and mass loss. After multiple freeze-thaw cycles, the embankment soil maintains a low mass loss rate, meeting the stringent requirements for long-term freeze-thaw durability in riverbank protection and embankment projects.

[0017] 2. This invention modifies montmorillonite through organosilane grafting, introducing active functional groups capable of forming stable coordination bonds with heavy metal ions into the interlayer of montmorillonite. This modification transforms the physical adsorption and encapsulation of heavy metals by traditional curing materials into a more robust chemical chelation fixation, effectively inhibiting the leaching and migration of various heavy metals under complex environments such as alternating wet and dry conditions and long-term immersion, thus reducing the potential ecological risks posed by dike projects to surrounding water bodies and soil environments.

[0018] 3. This invention provides an efficient technical pathway for the synergistic resource utilization of multi-source solid waste. It uses low-organic-matter dewatered sludge as one of the main raw materials, while simultaneously utilizing a large amount of multi-source solid waste such as recycled aggregates from construction waste, industrial blast furnace slag, and waste rubber. Through the complementary functions of each component and the optimization of process parameters, it achieves waste-to-waste treatment. Furthermore, the on-site mixing and layered compaction processes employed are simple and easy to implement, with high construction efficiency, and possess good engineering adaptability and application value. Detailed Implementation

[0019] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0020] Example 1 S1. Low-organic-matter sludge dewatering and drying treatment (1) Add dewatering agent (industrial grade polyferric sulfate PFS, total iron content ≥20%) to low organic matter sludge (organic matter content 23%, water content 98.2%) at a dry basis ratio of 2%, mix and condition for 20 min, and then use plate and frame filter press for dewatering treatment to obtain dewatered sludge with a water content of 70%.

[0021] (2) Spread the dewatered sludge evenly on the impermeable ground and carry out static maturation and natural drying. Through the continuous coagulation and solidification effect of the agent and the evaporation of surface moisture, the moisture content of the sludge is initially reduced to 50%. Then, it is crushed and screened through a 5mm vibrating screen (vibration frequency 50Hz) to remove impurities such as gravel and fiber, and obtain pretreated sludge.

[0022] S2, Composite Aggregate Configuration (1) Modification of recycled aggregate from construction waste: The recycled aggregate from construction waste is graded by crushing, screening and impurity removal, and divided into three types according to particle size: fine aggregate (0.5-5 mm), medium aggregate (5-10 mm), and coarse aggregate (10-20 mm). The three types of aggregate are put into a mixer, and cement slurry (made of cement and water at a mass ratio of 2:1) is sprayed while mixing. The mixture is stirred for 5 minutes to make the surface of the aggregate uniformly coated with cement. The recycled aggregate coated with cement is placed in a ventilated place to air dry naturally to avoid clumping, resulting in fine aggregate coated with 0.3 mm thick cement, medium aggregate coated with 0.3 mm thick cement, and coarse aggregate coated with 0.3 mm thick cement. The cement slurry on the surface of the coated aggregate can react with the subsequent composite curing agent to form a continuous gel layer, eliminating the weak interfacial area of ​​the recycled aggregate and improving the bonding strength.

[0023] (2) Graded compounding: Coated fine aggregate, coated medium aggregate, coated coarse aggregate and 5-20 mm crushed stone aggregate are mixed at a mass ratio of 4:3:2:1 to form a continuous graded aggregate to improve the compaction of the material. Among them, coarse aggregate and crushed stone account for 30% to form a rigid main skeleton of composite aggregate, providing shear and scour resistance structural support for the soil of the dike. Medium aggregate accounts for 30% to fill the primary pores formed by coarse aggregate and crushed stone. Fine aggregate accounts for 40% to fill the secondary pores formed by the gaps between medium aggregate, realizing the tertiary pores are filled step by step, which greatly improves the compaction. In addition, the 40% fine aggregate can fully combine with the clay particles of low organic matter sludge, avoiding the separation of sludge and large-diameter aggregate, and at the same time providing attachment sites for the solidification agent hydration gel, strengthening the interfacial bonding between the cementing system and the aggregate.

[0024] (3) Composite aggregate preparation: Waste rubber particles with a particle size of 2-5 mm (derived from waste truck tires through mechanical crushing and grinding) are immersed in KH560 silane coupling agent modification solution (made by mixing KH560 and anhydrous ethanol at a mass ratio of 1:10). The mass ratio of waste rubber particles to KH560 silane coupling agent modification solution is 1:4. The mixture is stirred in a water bath at 60°C for 1 h, and then dried at 60°C to obtain modified waste rubber particles. 2% of the modified waste rubber particles are added to the continuous graded aggregate and mixed evenly to obtain composite aggregate.

[0025] S3, Modified Composite Curing Agent Preparation (1) Alkali activation of blast furnace slag: After passing blast furnace slag through a 100-mesh sieve, it is mixed with anhydrous sodium carbonate at a mass ratio of 100:3. Then, it is calcined at 300℃ for 30 min, cooled to room temperature, and ground to obtain alkali-activated modified blast furnace slag. In this process, sodium carbonate activates the aluminosilicate active sites of blast furnace slag at high temperature, which increases the secondary hydration reaction rate of blast furnace slag and cement hydration products (CSH), fills the pores and forms more hydration gel, thereby strengthening the compactness and impermeability of the soil used for dikes.

[0026] (2) Grafting modification of montmorillonite: Montmorillonite was activated for 3 hours with 3% hydrochloric acid at a liquid-to-solid ratio of 3:1 (activation of montmorillonite with hydrochloric acid removes interlayer impurities, increases the surface hydroxyl density, and improves the activity of subsequent grafting reaction). Then it was washed with water until the pH was close to neutral and dried. 5% 3-aminopropyltriethoxysilane (KH550) ethanol-water solution (ethanol:water mass ratio = 9:1) was added at a solid-to-liquid ratio of 1:10. The solution was stirred in a water bath at 60℃ for 2 hours, filtered, dried, ground, and passed through a 100-mesh sieve to obtain silane-modified montmorillonite. In the ethanol-water solution, the ethoxy groups of KH550 hydrolyze to generate active silanol groups, which undergo condensation reaction with the hydroxyl groups on the surface and interlayer edges of montmorillonite to form stable Si-O-Si covalent bonds, thereby introducing aminopropyl groups into the surface of montmorillonite. After grafting, the exposed amino groups can form stable complexes with heavy metal ions through coordination bonds. Due to the high grafting density on the surface of montmorillonite, multiple adjacent amino groups can form synergistic coordination with the same heavy metal ion, further enhancing the fixation effect. This chemical fixation mechanism overcomes the shortcomings of traditional cement hydration products that rely solely on physical encapsulation, achieving long-term stabilization of heavy metals.

[0027] (3) Preparation of composite curing agent: Cement, alkali-activated modified blast furnace slag, silane-modified montmorillonite, and biochar (corn straw biochar, particle size 0.15-0.25 mm, average pore size 12 μm) were mixed in a mass ratio of 1:0.5:0.3:0.05 to obtain a quaternary composite curing agent. Among them, cement hydration gel is the matrix, alkali-activated blast furnace slag improves density, silane-modified montmorillonite achieves chemical chelation of heavy metals, and biochar is used as an auxiliary curing component. Its porous structure can work synergistically with modified montmorillonite to fix heavy metals, and the porous carbon skeleton of biochar can improve the freeze-thaw resistance of the curing system. Mechanism of biochar improving freeze-thaw resistance: The multi-level microporous structure of biochar plays a role in water regulation and stress buffering during the freeze-thaw cycle: in the positive temperature stage, it can absorb melt water and reduce the capillary saturation; in the negative temperature stage, the freezing point reduction effect of water confined in the pores delays the formation of ice crystals, and the elastic deformation of the porous carbon skeleton can absorb ice expansion stress. In addition, the micro-aggregate filling effect of biochar particles and the hydration nucleation effect of surface functional groups jointly improve the density and interfacial bonding strength of solidified soil, reducing the content of freezeable water and seepage channels from the source, thereby significantly improving the freeze-thaw resistance of the material.

[0028] S4. Pretreatment of original soil The original soil was taken from a riverbank protection area in Jin'an District, Lu'an City, Anhui Province. The soil was screened to remove impurities with a particle size greater than 5mm. The moisture content was adjusted to 20% by spraying or turning and drying to obtain pretreated original soil.

[0029] S5, Ingredient Mixing (1) The pretreated sludge obtained by S1, the composite aggregate obtained by S2, and the pretreated soil obtained by S4 are mixed at a mass ratio of 1:1.5:3 and dry-mixed at a speed of 200 rpm for 5 min to make the inorganic components uniformly mixed to obtain the mixed components.

[0030] (2) Add deionized water to adjust the total moisture content of the mixed components to 25%, reduce the speed to 150 rpm, and wet mix for 5 min to form a thick material; among them, medium-speed wet mixing can make the water evenly penetrate into the dry material mixture, and the sludge particles expand when they come into contact with water to form a colloid, which wraps the aggregate and original soil particles to form a viscous and uniform wet material system, providing a uniform liquid phase environment for the subsequent hydration reaction of the curing agent.

[0031] (3) Add the modified composite curing agent prepared by S3 to the viscous material at a ratio of 5% of the total mass of the mixed components, increase the speed to 180 rpm, and continue stirring for 5 min to ensure that the curing agent is evenly dispersed.

[0032] (4) Reduce the rotation speed to 100 rpm and stir at low speed for 1 minute to complete the final mixing. The low-speed final mixing eliminates the internal stress of the material generated by high-speed stirring, making the interface bonding of the curing agent, sludge and aggregate particles tighter, while avoiding premature curing caused by accelerated hydration reaction due to excessive stirring.

[0033] S6, Layered compaction (1) Use automated material spreading equipment to feed and spread the soil after final mixing in layers with a loose spreading thickness of 25 cm.

[0034] (2) Use a vibratory roller to implement gradient compaction: first, static compaction (compaction power 600kN·m / m³) for 2 passes to eliminate pores, then vibratory compaction (compaction power 2200kN·m / m³) for 4 passes to make it dense and formed, and finally static compaction (compaction power 600kN·m / m³) for 1 pass to level the surface.

[0035] S7, Maintenance (1) Cover with geotextile and moisture-retaining film immediately after compaction to avoid water loss due to rain and sun exposure.

[0036] (2) Sprinkle water once a day for the first 7 days, and once every 2 days for the next 7 days. The maintenance cycle is 14 days.

[0037] Example 2 Unlike Example 1, in step (3) of S3, the mass ratio of cement, alkali-activated modified blast furnace slag, silane-modified montmorillonite and biochar is 1:0.6:0.4:0.1, and the rest is the same as in Example 1.

[0038] Example 3 Unlike Example 1, the cement layer thickness of the coated fine aggregate, coated medium aggregate, and coated coarse aggregate is 0.5 mm, while the rest is the same as in Example 1.

[0039] Example 4 Unlike Example 1, in step S2 (3), the 2-5 mm waste rubber particles are replaced with waste rubber powder with a particle size of 0.5-1 mm (made from waste car tires through freeze crushing), and the rest is the same as in Example 1.

[0040] Comparative Example 1 Unlike Example 1, step (1) of S2 omits the step of coating aggregates with cement. Specifically, step (1) of S2 involves classifying the recycled aggregates from construction waste by crushing, screening, and removing impurities, and classifying them into three types according to particle size: fine aggregates (0.5-5 mm), medium aggregates (5-10 mm), and coarse aggregates (10-20 mm). In step (2) of S2, the coated fine aggregates, coated medium aggregates, and coated coarse aggregates are replaced with uncoated fine aggregates, uncoated medium aggregates, and coarsely coated fine aggregates, while the rest is the same as in Example 1.

[0041] Comparative Example 2 Unlike Example 1, in step (3) of S3, the alkali-activated modified blast furnace slag is replaced with blast furnace slag that has passed through a 100-mesh sieve and is not subjected to any further treatment; the rest is the same as in Example 1.

[0042] Comparative Example 3 Unlike Example 1, biochar is omitted in step (3) of S3, and the mass ratio of cement, alkali-activated modified blast furnace slag and silane-modified montmorillonite is 1:0.6:0.4, while the rest is the same as in Example 1.

[0043] Comparative Example 4 Unlike Example 1, in step (3) of S2, the amount of modified waste rubber particles added is increased from 2% to 6%, and the rest is the same as in Example 1.

[0044] Comparative Example 5 Unlike Example 1, no waste rubber particles were added to the composite aggregate; otherwise, the process was the same as in Example 1.

[0045] Comparative Example 6 Unlike Example 1, in step (2) of S3, KH550 graft modification is omitted, and only acid activation is performed. Specifically, montmorillonite graft modification is performed by activating montmorillonite with 3% hydrochloric acid at a liquid-to-solid ratio of 3:1 for 3 hours (activating montmorillonite with hydrochloric acid removes interlayer impurities, increases surface hydroxyl density, and improves the activity of subsequent grafting reactions), followed by washing with water until the pH is near neutral, and drying to obtain modified montmorillonite. In step (3) of S3, silane-modified montmorillonite is replaced with modified montmorillonite. The rest is the same as in Example 1.

[0046] The soil layers of the above embodiments and comparative examples were subjected to performance tests after 14 days of curing. The test items and methods are as follows: Unconfined compressive strength: Tested in accordance with the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019).

[0047] Freeze-thaw loss rate: Samples are prepared into standard-shaped and sized blocks, typically cubes or cylinders. The samples are dried in a 105°C oven to constant weight, cooled to room temperature, and the initial dry weight is recorded. The dried samples are then immersed in 20°C water for 24 hours. After removing the samples and wiping off surface moisture, they are wrapped in plastic wrap and placed in a -15°C freezer for 5 hours. The plastic wrap is then removed, and the samples are thawed in 20°C water for 3 hours, completing one freeze-thaw cycle. After 15 repeated freeze-thaw cycles, the samples are dried in a 105°C oven to constant weight, and the mass loss is recorded. The freeze-thaw loss rate is then used to assess the overall weight loss.

[0048] Compaction degree: The compaction degree was tested by referring to the ring cutter test method in the "Specifications for Field Testing of Highway Subgrade and Pavement" (JTG 3450-2019).

[0049] Permeability coefficient: The test was conducted according to the variable head permeability test in the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019).

[0050] Heavy metals: Samples were treated according to the standard "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method" (HJ557-2010), and the total amount of eight heavy metal pollutants (zinc, copper, lead, nickel, chromium, cadmium, mercury, and arsenic) in the leachate was tested. Zinc, copper, lead, nickel, chromium, and cadmium were tested according to the standard method of HJ 700-2014 "Determination of 65 Elements in Water - Inductively Coupled Plasma Mass Spectrometry," while mercury and arsenic were tested according to the standard method of HJ 694-2014 "Determination of Mercury, Arsenic, Selenium, Bismuth, and Antimony in Water - Atomic Fluorescence Spectrometry."

[0051] The test results are shown in Table 1.

[0052] Table 1

[0053] The mass loss rate of Example 1 after 15 freeze-thaw cycles was only 0.35%, which is far below the recommended limit of 1%, demonstrating excellent freeze-thaw resistance. In stark contrast, Comparative Example 1, lacking cement coating on the recycled aggregate, exhibited a loose aggregate-slurry interface transition zone, becoming a weak point for moisture accumulation and ice crystal expansion during freeze-thaw cycles. Its mass loss rate reached 2.35%, and its compaction and strength also significantly deteriorated. This demonstrates that cement coating is a core process for modifying aggregates to ensure the material's freeze-thaw resistance and overall structural integrity. Comparative Example 3, without biochar, lacked the moisture regulation and stress buffering functions of its microporous structure, resulting in a loss rate of 1.18%. Comparative Example 4, by increasing the rubber content to 6%, reduced the loss rate to 0.82%, but its unconfined compressive strength drastically decreased to 1.96 MPa. This indicates that while excessive rubber content can further inhibit freeze-thaw spalling, it comes at the cost of sacrificing mechanical properties, making it difficult to meet the bearing capacity requirements of embankment projects. Comparative Example 5, without waste rubber, lacked the elastic buffering effect to absorb relative frost heave stress, leading to a mass loss rate of 1.25%. The above comparison fully demonstrates that the synergistic combination of 2% modified waste rubber and 0.05 parts biochar determined in this invention is the optimal solution that balances high strength and low freeze-thaw loss rate.

[0054] The saturated permeability coefficient of Example 1 is 3.2 × 10⁻⁶. -7 The permeability coefficient is cm / s, which is classified as extremely low. Comparative Example 2, using unactivated blast furnace slag, saw its permeability coefficient increase to 7.6 × 10⁻⁶ cm / s. -6The increase in speed was more than an order of magnitude. This is because alkali activation treatment can effectively activate the pozzolanic activity of blast furnace slag, promoting the secondary hydration reaction to generate CSH gel that fills the pores.

[0055] The total leaching of eight heavy metals in Example 1 was 0.48 mg / L, which is within a safe level. Comparative Example 6, using unmodified montmorillonite, achieved a total leaching of 1.25 mg / L, approximately 2.6 times that of Example 1. This difference stems from the introduction of amino active sites on the montmorillonite surface through KH550 graft modification. These sites form stable surface complexes with heavy metal ions via coordination bonds, achieving a shift from physical adsorption to chemical fixation and ensuring the material's environmental safety under long-term water exposure.

Claims

1. A type of soil for riverbank protection and embankment preparation using low-organic-matter dewatered sludge, characterized in that, It includes low-organic-matter dewatered sludge, composite aggregate, composite curing agent and original soil; composite aggregate includes cement-coated recycled aggregate, crushed stone and silane-modified waste rubber particles; composite curing agent includes cement, alkali-activated blast furnace slag, silane-modified montmorillonite and biochar.

2. The riverbank protection soil prepared from low-organic-matter dewatered sludge according to claim 1, characterized in that, The mass ratio of pretreated sludge, composite aggregate and original soil is 1:(1-2):(2-4); the composite solidifying agent accounts for 2%-8% of the total mass of pretreated sludge, composite aggregate and original soil; the mass ratio of cement, alkali-activated blast furnace slag, silane-modified montmorillonite and biochar is 1:(0.5-0.6):(0.3-0.4):(0.05-0.1).

3. The riverbank protection soil prepared from low-organic-matter dewatered sludge according to claim 1, characterized in that, The moisture content of dewatered sludge with low organic matter content is ≤50%.

4. A type of riverbank protection soil prepared from low-organic-matter dewatered sludge according to claim 1, characterized in that, The cement-coated recycled aggregate is a graded recycled aggregate, including cement-coated 0.5-5 mm recycled fine aggregate, cement-coated 5-10 mm recycled medium aggregate, and cement-coated 10-20 mm recycled coarse aggregate; the mass ratio of cement-coated 0.5-5 mm recycled fine aggregate, cement-coated 5-10 mm recycled medium aggregate, cement-coated 10-20 mm recycled coarse aggregate, and crushed stone is (3.5-4.5):(2.5-3.5):(1.5-2.5):(0.5-1.5), preferably 4:3:2:1; the crushed stone particle size is 5-20 mm; and the cement layer thickness is 0.2-0.6 mm.

5. The riverbank protection soil prepared from low-organic-matter dewatered sludge according to claim 1, characterized in that, Alkali-activated blast furnace slag is obtained by roasting blast furnace slag with sodium carbonate at 280-350℃ for 20-60 minutes.

6. The riverbank protection soil prepared from low-organic-matter dewatered sludge according to claim 1, characterized in that, The preparation method of silane-modified montmorillonite includes: activating montmorillonite with 1%-10% hydrochloric acid for 1-5 hours at a liquid-solid ratio of (1-6):1, washing and drying with water, adding 3%-8% ethanol aqueous solution of silane coupling agent at a solid-liquid ratio of 1:(8-12), and reacting at 50℃-70℃ for 1-3 hours to obtain silane-modified montmorillonite; the silane coupling agent includes, but is not limited to, at least one of 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or γ-methacryloyloxypropyltrimethoxysilane.

7. The riverbank protection soil prepared from low-organic-matter dewatered sludge according to claim 1, characterized in that, The preparation method of silane-modified waste rubber granules includes: adding a silane coupling agent alcohol solution with a mass fraction of 5%-10% at a solid-liquid ratio of 1:3-6, reacting at 50℃-70℃ for 0.5-2h to obtain silane-modified waste rubber granules; the silane coupling agent includes, but is not limited to, at least one of 3-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, or vinyltriethoxysilane; in the composite aggregate, the mass of silane-modified waste rubber granules added accounts for 1%-5% of the total mass of recycled aggregate and crushed stone coated with cement.

8. The riverbank protection soil prepared from low-organic-matter dewatered sludge according to claim 1, characterized in that, The biochar is made from corn stalks, with a particle size of 0.1-0.3 mm and a pore size of 1-20 μm.

9. A method for preparing riverbank protection soil using low-organic-matter dewatered sludge according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Cement-coated recycled aggregate, crushed stone and silane-modified waste rubber particles are mixed to obtain composite aggregate; cement, alkali-activated modified blast furnace slag, silane-modified montmorillonite and biochar are mixed to obtain composite curing agent; (2) Mix the low organic matter dewatered sludge, composite aggregate and original soil evenly to obtain a mixed component, add water to adjust the moisture content to 22%-28% to form a viscous and uniform wet material system; (3) Add composite curing agent to the viscous and uniform wet material system and mix evenly to obtain soil for riverbank protection.

10. The preparation method according to claim 9, characterized in that, Construction conditions for soil used for riverbank protection include: material placement, compaction, and curing; compaction is gradient compaction, first statically compacting twice with a compaction energy of 500-700 kN·m / m³ to eliminate pores, then vibrating and compacting four times with a compaction energy of 2000-2500 kN·m / m³ to make it dense and formed, and finally statically compacting once with a compaction energy of 500-700 kN·m / m³ to level the surface.

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