Soil reinforcement method based on loaded calcium carbonate type graphene composite reinforcement material

Abstract

The invention relates to the field of soil reinforcement, and particularly discloses a soil reinforcement method based on a loaded calcium carbonate type graphene composite reinforcement material, which comprises the following steps: S1, preparing the loaded calcium carbonate type graphene composite reinforcement material: adding natural graphite into a sodium carboxymethyl cellulose aqueous solution, and uniformly stirring to obtain the loaded calcium carbonate type graphene composite reinforcement material; carrying out ball-milling treatment under a supercritical carbon dioxide condition to prepare a graphene dispersion liquid, and then sequentially adding a calcium chloride solution and a sodium carbonate solution to synthesize calcium carbonate in situ, so as to prepare a loaded calcium carbonate type graphene composite reinforcing material; s2, mixing the loaded calcium carbonate type graphene composite reinforcing material prepared in the step S1 with a dispersing agent and water to prepare turbid liquid; s3, a mixed solution of the turbid liquid and the water glass solution is added into the soil substrate, tamping and maintenance are conducted, and soil solidification is achieved. The novel soil reinforcement method provided by the invention solves the problem of soil alkalization caused by use of cement, lime and the like at present, and realizes an efficient, environment-friendly and economical soil reinforcement effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of soil reinforcement, and more particularly, to a soil reinforcement method based on a calcium carbonate-loaded graphene composite reinforcement material. BACKGROUND

[0002] Soil reinforcement refers to the process of making soil more solid, stable and dense through certain measures to meet the requirements of engineering construction. The main purpose of soil reinforcement is to obtain higher strength and better integrity than natural soil. Soil reinforcement plays a crucial role in civil engineering and geological engineering, mainly in the following aspects: Through soil reinforcement, the bearing capacity and stability of the foundation can be significantly improved to ensure the safe use of buildings and structures, which is particularly important for heavy-load structures such as high-rise buildings, large bridges and highways; soil reinforcement can effectively reduce the settlement and deformation of the foundation, avoiding structural damage caused by uneven settlement of the foundation, and prolonging the service life of the engineering structure; the reinforced soil has higher shear strength, compression modulus and permeability, which can meet the needs of different engineering properties of soil, improve engineering quality and reliability.

[0003] With the acceleration of urbanization and the continuous advancement of infrastructure construction, research and application of soil reinforcement technology are increasingly widespread. Traditional soil reinforcement methods mainly rely on cement, lime and other inorganic binders, but these materials have the problems of large dosage (usually 8-15%), high cost, and large environmental impact. Cement solidification can significantly increase the pH value of soil (pH>11), damaging the soil microbial environment; lime solidification has health risks and poor stability in sulfate environments, and both will produce a large amount of carbon dioxide emissions, which does not meet the carbon neutralization requirements. Although the microbial-induced calcium carbonate precipitation (MICP) technology is environmentally friendly, it has key technical limitations: the need for continuous supply of nutrients and suitable environmental conditions, slow reaction speed, usually 7-14 days, limited treatment depth, difficulty in maintaining bacterial activity in deep soil, high cost and uncertain stability.

[0004] In order to solve the limitations of the above-mentioned traditional soil reinforcement methods, new reinforcement materials need to be developed to solve the problem of soil alkalization caused by the use of cement, lime and other materials, and to achieve efficient, environmentally friendly and economical soil reinforcement effect. SUMMARY

[0005] In order to provide a new soil reinforcement method to solve the problem of soil alkalization caused by the use of cement, lime and other materials, the present application provides a soil reinforcement method based on a calcium carbonate-loaded graphene composite reinforcement material.

[0006] In a first aspect, the application provides a soil reinforcement method based on a calcium carbonate-loaded graphene composite reinforcement material, which adopts the following technical scheme: A soil reinforcement method based on a calcium carbonate-loaded graphene composite reinforcement material, comprising the following steps: S1, preparing a calcium carbonate-loaded graphene composite reinforcement material: adding natural graphite into a sodium carboxymethyl cellulose aqueous solution, performing ball milling treatment under supercritical carbon dioxide conditions, preparing a graphene dispersion liquid, and then sequentially adding a calcium chloride solution and a sodium carbonate solution to in-situ synthesize calcium carbonate, thereby preparing the calcium carbonate-loaded graphene composite reinforcement material; S2, mixing the calcium carbonate-loaded graphene composite reinforcement material prepared in step S1 with a dispersant and water to prepare a suspension liquid, and adjusting the pH value of the suspension liquid to 7.5-8.5; S3, adding a mixed solution of the suspension liquid and a water glass solution into a soil base, tamping, curing, and realizing soil solidification.

[0007] By adopting the above technical scheme, the application realizes uniform distribution of calcium carbonate on the surface of graphene through in-situ precipitation technology, avoids the agglomeration problem when used alone, and the calcium carbonate in the composite reinforcement material of the application provides cementation effect, forms a bridge between soil particles through precipitation reaction, increases the strength of the soil, and the two-dimensional sheet structure of graphene provides reinforcement of soil particle bridging and toughening effect. When the above composite material is added to the soil, the calcium carbonate in the composite material is partially dissolved in the soil pore water, and then recrystallized on the nucleation sites provided by graphene to form a cementation bridge between soil particles. The graphene sheet layer is combined with the soil particles through physical bridging and electrostatic action to enhance the overall stability, and the synergistic effect of the two can realize efficient reinforcement at very low output.

[0008] The calcium carbonate loaded graphene composite reinforcement material has good environmental compatibility, and compared with traditional cement and lime materials, can obviously improve the soil pH value. In the application, the composite material has a low dosage, reduces the input of alkaline substances, reduces the influence on the soil pH value, and the pH value is adjusted to be close to the initial pH value of the soil in the dispersion and addition stage of the composite reinforcement material, thereby avoiding local alkalization. More importantly, in the application, the calcium carbonate is precipitated in situ on the surface of graphene, and after the surface of graphene is functionalized by sodium carboxymethyl cellulose, the surface of graphene can regulate the crystal form of the generated calcium carbonate, and can promote the formation of calcite phase, which has lower solubility and is more stable and less likely to dissolve. On the other hand, when the calcium carbonate dissolves, the sodium carboxymethyl cellulose releases hydrogen ions to neutralize hydroxyl ions, thereby inhibiting the increase of pH value and forming a certain buffering effect to inhibit the sudden increase of pH value caused by the transition dissolution of calcium carbonate. Moreover, after the dissolution of calcium carbonate, the in-situ precipitation of calcium carbonate on graphene forms a cementing effect. The above comprehensive effects make the soil pH value stable in the range of 6.8-8.2 after the application of the calcium carbonate loaded graphene composite reinforcement material, and the pH value does not change significantly, thereby protecting the soil ecosystem.

[0009] Optionally, the proportion of calcite type calcium carbonate in the calcium carbonate loaded graphene composite reinforcement material in step S1 is greater than 80%.

[0010] By adopting the above technical solution, when the crystal form of calcium carbonate in the composite material is mainly calcite type calcium carbonate, the solubility of the calcite type calcium carbonate is lower than that of the vaterite type calcium carbonate, and the influence on the soil pH value is smaller, thereby further solving the problem of soil alkalization caused by the addition of reinforcement materials.

[0011] Optionally, the content of the water glass solution in step S3 is 10%, and the volume ratio of the suspension and the water glass solution is 1:(0.6-0.8).

[0012] By adopting the above technical solution, the addition of water glass makes the loose soil into a pellet structure, the water glass improves the water retention of the soil, facilitates planting, and slows down the loss of water.

[0013] Optionally, in step S2, the solid-liquid ratio of the calcium carbonate loaded graphene composite reinforcement material and water is 1:(5-10), and the mass concentration of the dispersant in the suspension is 0.2-0.5wt%.

[0014] By adopting the above technical solution, the above solid-liquid ratio controls the dispersion of the graphene composite material while maintaining the relative stability of the suspension, which is beneficial to the uniform mixing with the soil base in the subsequent process, and the amount of the dispersant is controlled to ensure the dispersion effect while taking into account the compatibility with the soil.

[0015] Optionally, the dispersant is one or both of polyacrylamide and sodium carboxymethyl cellulose.

[0016] By adopting the technical scheme, the polyacrylamide is adsorbed on the surface of the graphene or calcium carbonate particles by hydrogen bonding to form a steric hindrance layer, effectively preventing the aggregation of the calcium carbonate-loaded graphene composite particles. At the same time, the dispersing effect is further enhanced by electrostatic repulsion, and the sodium carboxymethyl cellulose disperses the particles by electrostatic repulsion. In addition, the long molecular chain of the sodium carboxymethyl cellulose forms a thick layer of adsorption on the surface of the composite particles, providing good steric hindrance to prevent agglomeration. The use of the above dispersant can improve the stability of the suspension and help the uniformity and stability of the composite material.

[0017] Optionally, in step S3, when the depth of the soil to be reinforced is 0-50 cm, the suspension is sprayed on the surface of the soil, and the spraying amount is controlled to be 2-5 L / m 2 Then, rotary tillage is mixed to a depth of 15-30 cm, and the travel speed is maintained at 2-5 km / h during the rotary tillage process. When the depth of the soil to be reinforced is 0.5-8 m, the suspension is grouted by a mixing pile machine with a drill bit diameter of 500-600 mm at a grouting pressure of 0.2-0.4 MPa, no grouting is performed during drilling, and grouting is performed while stirring after reaching the depth, the stirring speed is 15-30 rpm, the lifting speed is 1-2 m / min, and the suspension addition amount is 0.2-0.5 m 3 / m.

[0018] By adopting the technical scheme, for soil shallow reinforcement, rotary tillage mixing is used to destroy the original structure of the soil body through shear force, promote uniform mixing of the suspension and soil particles, form a dense surface layer through spraying and rotary tillage, resist surface load and erosion, and build rigid pile bodies in the deep layer through mixing pile grouting to improve the bearing capacity of the foundation.

[0019] Optionally, in step S3, when the soil substrate is soft clay with a water content of 20-35%, the calcium carbonate loading amount in the calcium carbonate-loaded graphene composite reinforcement material is 40-50 times the mass of the graphene. When the soil substrate is sand with a water content of 12-18%, the calcium carbonate loading amount in the calcium carbonate-loaded graphene composite reinforcement material is 30-40 times the mass of the graphene.

[0020] By adopting the technical scheme, the soft clay has high pore water saturation, the soil intergranular water is mainly combined water, and the free water content is low, resulting in poor soil permeability. Therefore, the composite material with a higher calcium carbonate loading amount is added, which requires a higher content of calcium carbonate to form a continuous cementation network structure to make up for the lack of permeability, and the high calcium carbonate content can fill more pores to reduce the activity space of combined water and inhibit the plastic flow of the soil body. And the sand soil moisture content is moderate, the pore water is mainly free water, the combined water content is low, the soil permeability is high, under the action of dynamic load, the sand soil pore water pressure rises, the effective stress decreases, and the liquefaction instability is easy to occur, therefore, the low calcium carbonate loading ratio composite material is added in the application, the sand soil has high permeability, the slurry is easy to diffuse, the low calcium carbonate content can prevent the excessive filling of the pore, part of the free water is reserved to maintain the workability of the soil, and after the calcium carbonate fills the pore, the relative density of the sand soil is improved, the rising rate of the pore water pressure under the dynamic load is reduced, and the graphene sheet layer can also consume energy through sliding and fracture in the soil deformation process, and the liquefaction development is inhibited.

[0021] In summary, in the application, the high water content of soft clay leads to small and poorly connected pores, which requires high calcium carbonate content to fill the micropores and form a dense cement body, and the low permeability of soft clay can increase the viscosity of the slurry to prevent slurry loss; the medium water content of sand soil has large and well-connected pores, and low calcium carbonate content can fill the key pores and retain part of the permeability, and the high permeability of sand soil allows the slurry to diffuse quickly, and low calcium carbonate content maintains the fluidity of the slurry to avoid clogging the grouting pipeline.

[0022] Optionally, the specific operation in step S1 is: 1) Add natural graphite to a carboxymethyl cellulose sodium aqueous solution with a mass fraction of 1.5-2.0, then perform ball milling treatment under the conditions of supercritical carbon dioxide at 45-55℃ and 12-18MPa, to obtain a graphene nanosheet dispersion liquid with a graphene concentration of 50-100mg / mL; 2) Add calcium chloride solution to the graphene nanosheet dispersion liquid, adjust the pH value to 8-10, and stir at a temperature of 25-40℃ for 3-5min; 3) Then add sodium carbonate solution, and stir at a pH value of 9-10, a temperature of 20-30℃, and a stirring speed of 200-400rpm for 5-10min, to generate calcite type calcium carbonate nanoparticles; 4) After separation and purification, a calcium carbonate loaded graphene composite reinforcement material is obtained.

[0023] By adopting the technical scheme, the graphene nanosheet is prepared by ball milling under the supercritical carbon dioxide condition, the sodium carboxymethyl cellulose is adsorbed on the surface of the graphene to form a protective adsorption layer to prevent the sheet from re-aggregation, and the sodium carboxymethyl cellulose forms a stable anchor in the edge region of the graphene to provide additional stabilization effect and reduce the interface defects, the supercritical carbon dioxide environment is beneficial to the uniformity of the sodium carboxymethyl cellulose molecules and reduces the structural defects in the exfoliation process, the graphene dispersion liquid with good stability is prepared, the uniform distribution of the calcite type calcium carbonate is generated in situ on the surface of the graphene, then the calcium chloride solution is added, under the alkaline condition, the calcium ions are adsorbed on the surface of the graphene, and the carboxyl groups in the sodium carboxymethyl cellulose form a coordination effect with the calcium ions to regulate the distribution of the calcium ions on the surface of the graphene, which creates favorable conditions for the subsequent nucleation of the calcium carbonate, and a uniform calcium ion enrichment layer is formed on the surface of the graphene, which is helpful to improve the uniformity of the subsequent nucleation of the calcium carbonate, finally, the sodium carbonate is added, and the calcium carbonate is generated in situ on the surface of the graphene nanosheet, under the weak alkaline condition with a pH value of 9-10, the sodium carboxymethyl cellulose adjusts the crystal elongation rate through the interaction with the calcium ions to promote the formation of the calcite phase.

[0024] Especially, after the sodium carbonate is added subsequently, the calcium ions pre-adsorbed on the surface of the graphene are combined with the carbonate ions, the two-dimensional structure of the graphene plays a template role, and the low stirring speed and the short reaction time are beneficial to the formation of the calcite crystal, so that the calcium carbonate crystal is selected and regulated, and the calcite crystal is more helpful to stabilize the pH value in the soil reinforcement process and does not significantly change the pH value of the soil to prevent the soil from being alkalized when the pH value is greater than 9.

[0025] Optionally, the separation and purification in step 4) is specifically as follows: the product in step 3) is centrifuged and separated at 5000-8000 rpm for 5-10 min, washed with deionized water for 3-5 times, and then dried at 50-55 DEG C for 12-24 h to prepare the calcium carbonate loaded graphene composite reinforcement material.

[0026] By adopting the technical scheme, the unbound free sodium carboxymethyl cellulose molecules in the reaction system are removed, and an appropriate amount of functional sodium carboxymethyl cellulose molecules are retained as a dispersant and an interfacial compatibilizer.

[0027] Optionally, the dopamine is first added to the graphene nanosheet dispersion liquid in step 2), and ultrasonic dispersion is performed for 20-30 min, and then the calcium chloride solution is added, wherein the dopamine is added in an amount of 0.1-0.3 wt% of the graphene nanosheet dispersion liquid.

[0028] By adopting the technical scheme, the addition of dopamine reduces the concentration of free calcium ions in the solution because the catechol group in the molecular structure of dopamine forms a stable five-membered ring chelate with calcium ions, and the amino group of dopamine carries a positive point under alkaline conditions, and simultaneously forms a hydrogen bond with the carboxyl group at the edge of graphene through electrostatic attraction, which not only enhances the adsorption stability of the calcium carbonate precursor on the surface of graphene, but also provides favorable conditions for the formation of calcite nuclei. On the other hand, graphene is prone to aggregation due to strong interlayer π-π interaction, while the benzene ring structure of dopamine can be adsorbed on the surface of graphene through π-π stacking, and the amino group of dopamine forms a hydrogen bond with the carboxyl group at the edge of graphene. This dual action can effectively prevent the stacking of graphene layers, providing more attachment sites for calcium carbonate nanoparticles. Ultimately, the calcite type formed in the composite material prepared in the application is more stable, and the calcite type calcium carbonate has a more regular rhombohedron crystal structure, better matches the surface energy of soil particles, forms a stronger chemical bond, and can more effectively fill pores and cement particles in the soil, improving the unconfined compressive strength of the soil. Moreover, it has better stability and better maintains the cement body.

[0029] Optionally, after the suspension prepared in step S2 is prepared, a chitosan solution is also added, the chitosan solution is prepared by dissolving chitosan in an acetic acid solution, the pH value of the chitosan solution is 5.5-6.5, and the addition amount of chitosan is 3-5 wt% of the calcium carbonate-loaded graphene composite reinforcement material.

[0030] By adopting the technical scheme, the amino and hydroxyl groups in the molecular structure of chitosan form chemical adsorption with calcium on the surface of calcium carbonate through hydrogen bonds and salt bonds, and the long chain structure of chitosan can be wound around the surface of the graphene layer to form a "calcium carbonate-chitosan-graphene" three-dimensional structure, which can increase the number and strength of the cementing bridges, make the connection between soil particles more compact, and enhance the reinforcement effect.

[0031] In summary, the application has the following beneficial effects: 1. In the application, the in-situ precipitation technology is used to realize the uniform distribution of calcium carbonate on the surface of graphene, avoiding the agglomeration problem when used alone. Moreover, the calcium carbonate in the composite reinforcement material provides cementing action, forms bridges between soil particles through precipitation reaction, increases the strength of the soil, and the two-dimensional sheet structure of graphene provides additional bridging and toughening effect. When the composite material is added to the soil, the calcium carbonate in the composite material partially dissolves in the pore water of the soil, and then recrystallizes on the nucleation sites provided by graphene to form cementing bridges between soil particles. The graphene layers are combined with the soil particles through physical bridging and electrostatic attraction to enhance the overall stability, and the synergistic effect of the two can achieve efficient reinforcement at a very low yield. 2. The calcium carbonate-supported graphene composite reinforcement material of this application exhibits excellent environmental compatibility. Compared to traditional materials such as cement and lime, it significantly improves soil pH. The composite material content in this application is low, reducing the input of alkaline substances and minimizing its impact on soil pH. Furthermore, the pH is pre-adjusted to be close to the initial soil pH during the dispersion and addition stage of the composite reinforcement material, avoiding localized alkalization. More importantly, in this application, calcium carbonate is precipitated in situ on the graphene surface. Graphene, acting as a carrier, undergoes surface functionalization treatment with sodium carboxymethyl cellulose. This treatment can regulate the crystal form of calcium carbonate, selectively promoting the formation of the calcite phase, which has lower solubility and is more stable and less prone to dissolution. On the other hand, when calcium carbonate dissolves, sodium carboxymethyl cellulose releases hydrogen ions to neutralize hydroxide ions, thereby inhibiting pH increases and forming a buffer effect. This prevents a sudden pH increase caused by excessive calcium carbonate dissolution. Moreover, the in-situ precipitation of dissolved calcium carbonate on the graphene forms a cementing effect. The combined effects described above ensure that the application of the calcium carbonate-loaded graphene composite reinforcement material described in this application will stabilize the soil pH value within the range of 6.8-8.2, without causing significant pH changes, thus protecting the soil ecosystem. Attached Figure Description

[0032] Figure 1 This is a SEM scan of the calcium carbonate-loaded graphene composite reinforcement material prepared in step S1 of Embodiment 1 of this application; Figure 2 This is a SEM scan of the calcium carbonate-loaded graphene composite reinforcement material prepared in step S1 of Example 10 of this application. Detailed Implementation

[0033] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0034] Example 1 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material includes the following steps: S1. Preparation of calcium carbonate-supported graphene composite reinforcement material, specifically including the following steps: 1) Weigh 2.0g of natural graphite (thickness 3nm, lateral dimension 4μm) and add it to 100mL of sodium carboxymethyl cellulose aqueous solution with a mass fraction of 1.8%. Ball mill the solution for 4h under supercritical carbon dioxide conditions at a temperature of 50℃, a pressure of 15MPa, and a flow rate of 8L / min to obtain a highly exfoliated graphene nanosheet dispersion with a graphene nanosheet concentration of 80mg / mL. 2) Add 50 mL of calcium chloride solution with a molar concentration of 8 mM to the graphene dispersion prepared in step S1, adjust the pH value to 9.0, stir at 35℃ for 4 min to obtain a mixed solution, so that a calcium ion enrichment layer is formed on the graphene surface. 3) Add 50 mL of sodium carbonate solution with a molar concentration of 8 mM to the mixture at a flow rate of 100 mL / min, and then react for 10 min at pH 10, temperature 25℃ and stirring speed of 300 rpm to generate calcite-type calcium carbonate nanoparticles with a particle size of 600-800 nm in situ. 4) Then, centrifuge at 6000 rpm for 8 min, wash with deionized water 4 times, and dry at 50℃ for 18 h to obtain a calcium carbonate-loaded graphene composite reinforcement material. The mass ratio of graphene nanosheets to calcium carbonate in the calcium carbonate-loaded graphene composite reinforcement material is 1:30. S2. Take the calcium carbonate-loaded graphene composite reinforcement material obtained in step S1 and prepare a suspension at a ratio of 2 wt% of the dry weight of the soil. Specifically, mix the calcium carbonate-loaded graphene composite reinforcement material obtained in step S1 with the dispersant polyacrylamide and water to prepare a suspension, and adjust the pH of the suspension to 8. Among them, the solid-liquid ratio of the calcium carbonate-loaded graphene composite reinforcement material to water is 1:8, and the mass concentration of the dispersant in the prepared suspension is 0.3wt%. S3. Take sandy soil to simulate the surface soil matrix with a depth of 20cm and adjust the moisture content of the sandy soil to 15%. Mix the prepared suspension and 10% water glass solution (that is, the solution contains 10wt% sodium silicate) at a volume ratio of 1:0.7 to prepare a mixed solution. Then spray the mixed solution onto the surface of sandy soil with a moisture content of 15%, compact it to solidify the soil, and allow it to cure naturally for 7 days.

[0035] The calcium carbonate-supported graphene composite reinforcement material prepared in step S1 was observed by SEM as follows: Figure 1 As shown, the microstructure of calcium carbonate particles uniformly distributed on the surface of graphene nanosheets is illustrated. In this application, in-situ composite of graphene and calcium carbonate's dominant phase is achieved through liquid-phase co-precipitation-interface modulation technology. Furthermore, XRD characterization reveals that the calcite phase calcium carbonate in the composite material comprises approximately 85%, indicating that the calcium carbonate phase in the prepared composite material is primarily calcite.

[0036] Example 2 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, with the difference being... In step S1, the sodium carboxymethyl cellulose aqueous solution in step 1) has a mass fraction of 1.5%. It is ball-milled for 3 hours under supercritical carbon dioxide conditions at a temperature of 45℃ and a pressure of 12MPa to obtain a graphene nanosheet dispersion with a graphene nanosheet concentration of 50mg / mL. 2) Adjust the pH to 8.0 and stir for 5 minutes at 25℃; 3) The reaction was carried out at pH 9, temperature 20℃ and stirring speed 200rpm for 5min to generate calcite-type calcium carbonate nanoparticles in situ. Then, the material was centrifuged at 5000 rpm for 10 min, washed three times with deionized water, and dried at 50℃ for 24 h to obtain a calcium carbonate-loaded graphene composite reinforcement material. By adjusting the sodium carbonate solution and calcium chloride solution, the mass ratio of graphene nanosheets to calcium carbonate in the calcium carbonate-loaded graphene composite reinforcement material was 1:40. In step S2, the calcium carbonate-loaded graphene composite reinforcement material obtained in step S1 is used to prepare a suspension at a ratio of 1.5 wt% of the dry weight of the soil. Specifically, the calcium carbonate-loaded graphene composite reinforcement material obtained in step S1 is mixed with dispersant polyacrylamide and water to prepare a suspension, and the pH value of the suspension is adjusted to 7.5. Among them, the solid-liquid ratio of the calcium carbonate-loaded graphene composite reinforcement material to water is 1:5, and the mass concentration of the dispersant in the prepared suspension is 0.2wt%. S3. Take sandy soil to simulate the surface soil matrix with a depth of 5cm and adjust the moisture content of the sandy soil to 12%. Mix the prepared suspension and 10% water glass solution (that is, the solution contains 10wt% sodium silicate) at a volume ratio of 1:0.6 to prepare a mixed solution. Then spray the mixed solution onto the surface of sandy soil with a moisture content of 12%, compact it to solidify the soil, and allow it to cure naturally for 7 days.

[0037] Example 3 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, with the difference being... In step S1, the sodium carboxymethyl cellulose aqueous solution in step 1) has a mass fraction of 2%, and is ball-milled for 5 hours under supercritical carbon dioxide conditions at a temperature of 55℃ and a pressure of 18MPa to obtain a graphene nanosheet dispersion with a graphene nanosheet concentration of 100mg / mL. 2) Adjust the pH to 10.0 and stir for 3 minutes at 40℃; 3) The reaction was carried out at pH 10, temperature 30℃ and stirring speed 400rpm for 10min to generate calcite-type calcium carbonate nanoparticles in situ. Then, the graphene nanosheets were centrifuged at 8000 rpm for 5 min, washed 5 times with deionized water, and dried at 55℃ for 12 h to obtain the calcium carbonate-loaded graphene composite reinforcement material. By adjusting the sodium carbonate solution and calcium chloride solution, the mass ratio of graphene nanosheets to calcium carbonate in the calcium carbonate-loaded graphene composite reinforcement material was 1:50. In step S2, the calcium carbonate-loaded graphene composite reinforcement material obtained in step S1 is used to prepare a suspension at a ratio of 2.5 wt% of the dry weight of the soil. Specifically, the calcium carbonate-loaded graphene composite reinforcement material obtained in step S1 is mixed with dispersant polyacrylamide and water to prepare a suspension, and the pH value of the suspension is adjusted to 8.5. Among them, the solid-liquid ratio of the calcium carbonate-loaded graphene composite reinforcement material to water is 1:10, and the mass concentration of the dispersant in the prepared suspension is 0.5wt%. S3. Take sandy soil to simulate the surface soil matrix with a depth of 30cm and adjust the moisture content of the sandy soil to 25%. Mix the prepared suspension with a 10% water glass solution (that is, the solution contains 10wt% sodium silicate) at a volume ratio of 1:0.8 to prepare a mixed solution. Then spray the mixed solution onto the surface of the sandy soil with a moisture content of 25%, compact it and allow it to cure naturally for 7 days to achieve soil solidification.

[0038] Example 4 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, except that in step 2), dopamine is first added to the graphene nanosheet dispersion, ultrasonically dispersed for 25 minutes with an ultrasonic power of 500W, and then calcium chloride solution is added, wherein the amount of dopamine added is 0.2wt% of the graphene nanosheet dispersion.

[0039] Example 5 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, except that in step 2), dopamine is first added to the graphene nanosheet dispersion, ultrasonically dispersed for 20 minutes with an ultrasonic power of 500W, and then calcium chloride solution is added, wherein the amount of dopamine added is 0.1wt% of the graphene nanosheet dispersion.

[0040] Example 6 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, except that in step 2), dopamine is first added to the graphene nanosheet dispersion, ultrasonically dispersed for 30 minutes with an ultrasonic power of 500W, and then calcium chloride solution is added, wherein the amount of dopamine added is 0.3wt% of the graphene nanosheet dispersion.

[0041] Example 7 A soil reinforcement method based on calcium carbonate-supported graphene composite reinforcement material is carried out according to the method in Example 1, except that after the suspension is prepared in step S2, a chitosan solution is added. The chitosan solution is prepared by dissolving chitosan in a 10% acetic acid solution, and the acetic acid is added until the pH value of the chitosan solution is 6. The amount of chitosan added is 4 wt% of the calcium carbonate-supported graphene composite reinforcement material.

[0042] Example 8 A soil reinforcement method based on calcium carbonate-supported graphene composite reinforcement material is carried out according to the method in Example 1, except that after the suspension is prepared in step S2, a chitosan solution is added. The chitosan solution is prepared by dissolving chitosan in a 10% acetic acid solution, and the acetic acid is added until the pH value of the chitosan solution is 5.5. The amount of chitosan added is 3 wt% of the calcium carbonate-supported graphene composite reinforcement material.

[0043] Example 9 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, except that after obtaining the suspension in step S2, a chitosan solution is added. The chitosan solution is prepared by dissolving chitosan in a 10% acetic acid solution, and the acetic acid is added until the pH value of the chitosan solution is 6.5. The amount of chitosan added is 5 wt% of the calcium carbonate-loaded graphene composite reinforcement material.

[0044] Example 10 A soil reinforcement method based on calcium carbonate-supported graphene composite reinforcement material is carried out according to the method in Example 1, except that the molar concentration of calcium chloride in step S1 2) is 6 mM, the pH value is adjusted to 11, and the mixture is stirred at 30°C for 3 min to obtain a mixed solution. 3) 50 mL of sodium carbonate solution with a molar concentration of 6 mM is added dropwise to the mixture at a flow rate of 80 mL / min. The mixture is then reacted for 10 min at a pH of 11, a temperature of 25 °C, and a stirring speed of 400 rpm to generate spheroidal calcium carbonate nanoparticles with a particle size of 400-600 nm in situ.

[0045] The remaining operations are the same as in Example 1. The SEM image of the calcium carbonate-type graphene composite material mainly composed of aragonite is shown below. Figure 2 As shown, spheroidal calcium carbonate nanoparticles are uniformly distributed on the surface of graphene nanosheets.

[0046] Comparative Example 1 A soil reinforcement method is carried out according to the method in Example 1, except that in step S2, the calcium carbonate-loaded graphene composite reinforcement material is replaced with an equal amount of calcium carbonate.

[0047] Comparative Example 2 A soil reinforcement method is performed according to the method in Example 1, except that in step S2, the calcium carbonate-loaded graphene composite reinforcement material is replaced by an equal amount of graphene (oxygen content of 30%, specific surface area of ​​180 m²). 2 / g).

[0048] Comparative Example 3 A soil reinforcement method is performed according to the method in Example 1, except that in step S2, the calcium carbonate-loaded graphene composite reinforcement material is replaced by an equal amount of graphene (oxygen content of 30%, specific surface area of ​​180 m²). 2 A mixture of graphene ( / g) and calcium carbonate, wherein the mass ratio of graphene to calcium carbonate is 1:30.

[0049] Comparative Example 4 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, except that in step S1, the sodium carboxymethyl cellulose solution in step 1) is replaced with water instead of added in step 2), and the sodium carboxymethyl cellulose is added to the mixture in step 2), and the amount of sodium carboxymethyl cellulose added is the same as in Example 1.

[0050] Comparative Example 5 A soil reinforcement method based on calcium carbonate-loaded graphene composite reinforcement material is carried out according to the method in Example 1, except that in step S1, the sodium carboxymethyl cellulose solution in step 1) is replaced with an equal amount of OP-10 solution, and the added volume and mass fraction of OP-10 solution are the same as in Example 1.

[0051] Comparative Example 6 A soil reinforcement method based on calcium carbonate-type graphene composite reinforcement material is carried out according to the method in Example 1, except that in step S1, sodium carboxymethyl cellulose solution in step 1) is replaced with sodium dodecyl sulfate solution in equal volume, and the added volume and mass fraction of sodium dodecyl sulfate solution are the same as in Example 1.

[0052] Performance testing Soil reinforcement treatment was carried out according to the methods in the examples and comparative examples. The unconfined compressive strength of the reinforced soil was tested, and the results are shown in Table 1 below.

[0053] Table 1: In addition, the soil pH value after treatment in Example 1 was 7.2. The soil pH value after treatment in Examples 1-9 was tested and found to be in the range of 6.8-8.2, which will not cause soil alkalization. However, when the calcium carbonate crystal form in the composite material in Example 10 was aragonite, the soil pH value after treatment rose to 8.5. Compared with aragonite calcium carbonate, calcite calcium carbonate is more stable for soil pH.

[0054] Referring to the test results of Examples 1 and 4-6 in Table 1, when calcium carbonate is generated in situ on the graphene surface, the addition of dopamine enhances the adhesion stability of calcium carbonate on the graphene surface. Furthermore, the stabilizing effect on calcite-type calcium carbonate improves the unconfined compressive strength of the soil. Combined with the test results of Examples 7-9, the addition of chitosan solution to the suspension forms a three-dimensional structure of "calcium carbonate-chitosan-graphene," further enhancing the interparticle connections in the soil and improving the unconfined compressive strength. Combining the test results of Example 10, when the calcium carbonate in Example 10 is mainly in the spherulite phase, its unconfined compressive strength is somewhat reduced.

[0055] Referring to the test results of Examples 1 and Comparative Examples 1 and 2, when only calcium carbonate was used for soil reinforcement in Comparative Example 1, its unconfined compressive strength was significantly lower than that of Example 1, indicating that the reinforcement effect of calcium carbonate alone was limited. In Comparative Example 2, when only graphene was used for reinforcement, the reinforcement effect was even weaker, as the aggregation of graphene affected its effectiveness. Combining this with the test results of Comparative Example 3, when a physical mixture of graphene and calcium carbonate was added for reinforcement treatment in Comparative Example 3, the reinforcement effect was worse than that of Example 1, failing to leverage the combined effect of the two. Furthermore, considering the test results of Comparative Examples 4-6, when sodium carboxymethyl cellulose was added later than during the exfoliation process, or when other surfactants were added, the reinforcement effect was lower than that of Example 1.

[0056] In this application, when the suspension prepared based on calcium carbonate-loaded graphene composite reinforcement material is used as a reinforcement material for soil reinforcement, an appropriate construction method is selected according to the treatment depth. Specifically, when the soil depth to be reinforced is 0-50cm, the suspension is sprayed onto the soil surface, and the spraying volume is controlled at 2-5L / m. 2 Then, rotary tillage is carried out to a depth of 15-30cm, maintaining a travel speed of 2-5km / h during the rotary tillage process; When the soil depth to be reinforced is 0.5-8m, grouting is carried out using a mixing pile machine with a drill bit diameter of 500-600mm at a grouting pressure of 0.2-0.4MPa. Grouting is not performed during drilling; instead, grouting and mixing are carried out simultaneously after reaching the desired depth. The mixing speed is 15-30rpm, the lifting speed is 1-2m / min, and the amount of suspension added is 0.2-0.5m³. 3 / m.

[0057] For areas surrounding existing buildings or areas with strict deformation requirements, the calcium carbonate-loaded graphene composite reinforcement material is prepared as a grouting liquid and injected into the soil through pre-set grouting holes. The grouting pressure is 0.3-0.8 MPa, the grouting rate is controlled at 10-30 L / min, and the solid content in the grouting liquid, which is also the content of the calcium carbonate-loaded graphene composite reinforcement material, is 15-25%.

[0058] The methods described in Examples 1, 4, 7, and Comparative Example 3 were applied to soil reinforcement, specifically to the treatment of soft clay surface soil at a depth of 20 cm and sandy soil at a depth of 3 m. First, the moisture content of the soft clay was adjusted to 25%, and the moisture content of the sandy soil to 15%. Then, the methods from the examples were applied to the soil reinforcement. The difference was that for the 3 m sandy soil reinforcement, a deep mixing method was used. Specifically, a deep mixing pile machine was used with a drill bit diameter of 500 mm and a grouting pressure of 0.2 MPa. Grouting was not performed during drilling; grouting and mixing were carried out simultaneously after reaching the desired depth. The mixing speed was 20 rpm, the lifting speed was 1.5 m / min, and the suspension addition amount was 0.2 m³. 3 / m (meaning the amount of suspension added is 0.2m per 1m of reinforcement depth). 3 3m depth is 0.6m 3 In addition, the CBR value of the above-mentioned reinforced soil was tested by penetration test (penetration depth of 5 mm), and the results are shown in Table 2 below.

[0059] Table 2: Referring to the test results in Table 1 above, the calcium carbonate-loaded graphene composite reinforcement material prepared in this application embodiment has a good reinforcement effect on soil. Furthermore, the soil pH value of the treated soft clay and sandy soil was measured to be between 7 and 8. Compared with current lime and cement reinforcement materials, this application has less impact on soil pH, does not cause soil alkalization, reduces carbon emissions, and is more environmentally friendly. Moreover, it can achieve a good reinforcement effect with small dosages, making it more economical, simple, convenient, and efficient to use.

[0060] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A soil reinforcement method based on a calcium carbonate-supported graphene composite reinforcement material, characterized in that, Includes the following steps: S1. Preparation of calcium carbonate-loaded graphene composite reinforcement material: Natural graphite is added to an aqueous solution of sodium carboxymethyl cellulose and ball-milled under supercritical carbon dioxide conditions to obtain a graphene dispersion. Then, calcium chloride solution and sodium carbonate solution are added in situ to synthesize calcium carbonate, thus obtaining a calcium carbonate-loaded graphene composite reinforcement material. S2. The calcium carbonate-loaded graphene composite reinforcement material obtained in step S1 is mixed with a dispersant and water to prepare a suspension, and the pH value of the suspension is adjusted to 7.5-8.

5. S3. Add the mixture of suspension and water glass solution to the soil base, compact it, and cure it to achieve soil solidification.

2. The soil reinforcement method based on calcium carbonate-supported graphene composite reinforcement material according to claim 1, characterized in that: In step S1, the proportion of calcite-type calcium carbonate in the calcium carbonate-supported graphene composite reinforcement material is greater than 80%. And / or, the content of water glass solution in step S3 is 10%, and the volume ratio of suspension to water glass solution is 1:(0.6-0.8).

3. The soil reinforcement method based on calcium carbonate-supported graphene composite reinforcement material according to claim 1, characterized in that: In step S2, the solid-liquid ratio of the calcium carbonate-type graphene composite reinforcement material to water is 1:(5-10), and the mass concentration of the dispersant in the suspension is 0.2-0.5wt%.

4. The soil reinforcement method based on calcium carbonate-supported graphene composite reinforcement material according to claim 1, characterized in that: The dispersant is selected from one or both of polyacrylamide and sodium carboxymethyl cellulose.

5. A soil reinforcement method based on a calcium carbonate-supported graphene composite reinforcement material according to claim 1, characterized in that: In step S3, when the soil depth to be reinforced is 0-50cm, the suspension is sprayed onto the soil surface at a rate of 2-5L / m. 2 Then, rotary tillage is carried out to a depth of 15-30cm, maintaining a travel speed of 2-5km / h during the rotary tillage process; When the soil depth to be reinforced is 0.5-8m, grouting is carried out using a mixing pile machine with a drill bit diameter of 500-600mm at a grouting pressure of 0.2-0.4MPa. No grouting is carried out during drilling. After reaching the depth, grouting is carried out while mixing. The mixing speed is 15-30rpm, the lifting speed is 1-2m / min, and the amount of suspension added is 0.2-0.5m³ / m.

6. The soil reinforcement method based on a calcium carbonate-supported graphene composite reinforcement material according to claim 1, characterized in that: In step S3, when the soil substrate is soft clay with a moisture content of 20-35%, the calcium carbonate loading in the calcium carbonate-loaded graphene composite reinforcement material is 40-50 times the mass of graphene. When the soil substrate is sandy soil with a moisture content of 12-18%, the calcium carbonate loading in the calcium carbonate-loaded graphene composite reinforcement material is 30-40 times the mass of graphene.

7. A soil reinforcement method based on a calcium carbonate-supported graphene composite reinforcement material according to claim 1, characterized in that: The specific operation in step S1 is as follows: 1) Add natural graphite to an aqueous solution of sodium carboxymethyl cellulose with a mass fraction of 1.5-2.0, and then ball mill it under supercritical carbon dioxide conditions of 45-55℃ and 12-18MPa to obtain a graphene nanosheet dispersion with a graphene concentration of 50-100mg / mL. 2) Add calcium chloride solution to the graphene nanosheet dispersion, adjust the pH value to 8-10, and stir for 3-5 minutes at a temperature of 25-40℃; 3) Then add sodium carbonate solution and stir for 5-10 minutes at a pH of 9-10, a temperature of 20-30℃ and a stirring speed of 200-400 rpm to generate calcite-type calcium carbonate nanoparticles. 4) After separation and purification, a calcium carbonate-loaded graphene composite reinforcement material was obtained.

8. A soil reinforcement method based on a calcium carbonate-supported graphene composite reinforcement material according to claim 7, characterized in that: The specific separation and purification operation in step 4) is as follows: the product in step 3) is centrifuged at 5000-8000 rpm for 5-10 min, washed with deionized water 3-5 times, and then dried at 50-55℃ for 12-24 h to obtain the calcium carbonate-loaded graphene composite reinforcement material.

9. A soil reinforcement method based on a calcium carbonate-supported graphene composite reinforcement material according to claim 7, characterized in that: In step 2), dopamine is first added to the graphene nanosheet dispersion and ultrasonically dispersed for 20-30 minutes, and then calcium chloride solution is added. The amount of dopamine added is 0.1-0.3 wt% of the graphene nanosheet dispersion.

10. A soil reinforcement method based on a calcium carbonate-supported graphene composite reinforcement material according to claim 1, characterized in that: After obtaining the suspension in step S2, a chitosan solution is added. The chitosan solution is prepared by dissolving chitosan in acetic acid solution, and the pH value of the chitosan solution is 5.5-6.

5. The amount of chitosan added is 3-5 wt% of the calcium carbonate-type graphene composite reinforcement material.

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