Method for reinforcing loess foundation through cooperation of EICP and rice husks

Abstract

The invention belongs to the field of soil solidification, and particularly relates to a method for reinforcing a loess foundation through cooperation of EICP and rice husks. Comprising the following steps: 1, compounding long and short rice hull fibers, and sequentially carrying out alkali treatment activation, coupling agent modification and hydroxypropyl methyl cellulose reinforcement treatment; 2, calcining rice hulls, and grinding to obtain rice hull ash; 3, mixing a composite reinforcing agent obtained by compounding the modified and reinforced rice hull fibers and rice hull ash with loess to be reinforced; 4, mixing the urease extracting solution with a reinforcing solution containing urea and calcium ions, and adjusting the pH value to weak acidity to obtain mixed slurry; and 5, the mixed slurry is sprayed into the to-be-reinforced loess mixed with the composite reinforcing agent, and after grouting is finished, the surface of the soil body is covered with a film and subjected to water spraying maintenance. Through synergistic cooperation of the rice hull fibers and the rice hull ash, the common problems of non-uniform cementation and poor deep reinforcement effect during loess reinforcement by an EICP technology are effectively solved.

Description

Technical Field

[0001] This application belongs to the field of soil consolidation, and more specifically, relates to a method for reinforcing loess foundations with EICP in conjunction with rice husks. Background Technology

[0002] Loess deposits in my country are deep, long-lasting, and widely distributed. Their porous, loose, low-density, and easily waterlogged characteristics cause them to lose strength and collapse upon contact with water, leading to soil erosion, landslides, and debris flows—natural disasters that severely impact my country's ecological environment and engineering construction. Therefore, soil reinforcement and improvement are necessary during development to ensure soil properties meet engineering requirements. However, compared to coarse-grained soils like sand, loess exhibits a more loose and porous structure, with large pores larger than 5 mm accounting for approximately 25%. Furthermore, it has weak interparticle cohesion and poor permeability, making it highly susceptible to instability and collapse upon contact with water. These characteristics result in traditional physical reinforcement methods being labor-intensive and costly, while chemical reinforcement methods, such as cement and lime, easily cause soil shrinkage and cracking, significant ecological disturbance, and difficulty in achieving uniform penetration and effective cementation at deep loess layers.

[0003] With the development of biomineralization technology, enzyme-induced carbonate precipitation (EICP) technology has attracted widespread attention due to its mild reaction and environmental friendliness. For example, patent document CN115032365A discloses a soil reinforcement method based on improved EICP technology, which enhances the unconfined compressive strength of sand by adding carbon fiber, verifying the potential of EICP in improving the mechanical properties of soil. However, this type of method is mainly designed for sandy soils with uniform particles and good permeability, and it faces significant challenges when applied to loess. The large number of fine particles and complex pore structure in loess can strongly adsorb and impede the migration of urease and ions, easily forming local blockages near the grouting inlet, resulting in insufficient reinforcement depth, extremely uneven distribution of calcium carbonate deposition, and affecting urease activity. At the same time, loess is extremely sensitive to water content, and repeated injection of low-viscosity grout may induce collapse of the original structure, resulting in both strength deterioration and local hardening. It is evident that the existing EICP process developed for sandy soils cannot directly solve the special problems of loess foundations, such as complex pore structure, high fine particle content, and sensitivity to collapse. A loess foundation bio-solidification technology that balances the control of collapse, improvement of deposition efficiency, and environmental friendliness is needed to achieve efficient, uniform, and green reinforcement of loess foundations. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this application is to provide a method for reinforcing loess foundations with EICP and rice husks, which aims to overcome the technical problems of uneven cementation and poor deep reinforcement effect commonly encountered when reinforcing loess with EICP technology.

[0005] To achieve the above objectives, in a first aspect, this application provides a method for reinforcing loess foundations with EICP in conjunction with rice husks, comprising the following steps: Step 1: Two different sizes of rice husk fibers are blended together, and then the blended rice husk fibers are successively activated by alkali treatment, modified by coupling agent, and reinforced by organic binder to increase the specific surface area and the number of surface active sites of the rice husk fibers, thereby improving their stability and obtaining modified rice husk fibers. Step 2: Calcine the rice husks in an oxygen-containing atmosphere and then grind them to obtain rice husk ash; Step 3: Mix the modified rice husk fiber obtained in Step 1 with the rice husk ash described in Step 2 to obtain a composite reinforcing agent; uniformly incorporate the composite reinforcing agent into the loess to be reinforced; obtain the loess to be reinforced with the composite reinforcing agent. Step 4: Mix the urease extract with the consolidation solution containing urea and calcium ions, and adjust the pH to weakly acidic to obtain a mixed slurry; Step 5: Spray the mixed grout from Step 4 into the loess to be reinforced by adding the composite reinforcing agent as described in Step 3. After the grouting is completed, cover the soil surface with a film and spray water for curing.

[0006] Preferably, the two different sizes of rice husk fibers mentioned in step one include short rice husk fibers of 2-8 mm and long rice husk fibers of 10-20 mm. The mass ratio of short rice husk fiber to long rice husk fiber is 1:(1-3).

[0007] Preferably, the alkaline treatment activation in step one specifically involves placing rice husk fibers in a sodium hydroxide solution with a concentration of 3-8 wt% and stirring at 60-80 ℃ for 1-3 hours; The coupling agent modification specifically involves washing the alkali-treated fiber until it is neutral, then immersing it in a 1-5 wt% silane coupling agent ethanol solution and stirring for 30-60 minutes. The organic binder is hydroxypropyl methylcellulose, and the organic binder reinforcement specifically involves spraying a 1-3 wt% hydroxypropyl methylcellulose solution onto the rice husk fiber modified by the coupling agent, wherein the amount of the hydroxypropyl methylcellulose solution is 1-5% of the total mass of the rice husk fiber.

[0008] Preferably, step two specifically involves: washing and drying the rice husks, calcining them in an oxygen-containing atmosphere at 550-700 ℃ for 1-2 hours, cooling them, ball milling them, and sieving them to obtain rice husk ash with a particle size of less than 0.1 mm.

[0009] More preferably, in the composite reinforcing agent described in step three, the mass ratio of the modified rice husk fiber described in step one to the rice husk ash described in step two is (5-10):1.

[0010] Preferably, the amount of the composite reinforcing agent in step three in the loess to be reinforced is 0.5-2 wt%.

[0011] Preferably, the preparation of the urease extract includes the following steps: (a) mixing food-grade soybean flour and an aqueous ethanol solution at a solid-liquid ratio of 1:(8-10) to obtain a soybean flour solution; (b) stirring the soybean flour solution for 20-30 min at a speed of 8000-10000 r / min; (c) after the stirred soybean flour solution has been allowed to stand at 0-4℃ for 12-16 h, the supernatant is taken and centrifuged at 8000-10000 r / min at 0-4℃ for 8-15 min to obtain the urease extract.

[0012] Preferably, the stabilizing solution containing urea and calcium ions in step four is a mixture of CO(NH)2 and CaCl2 at a molar ratio of 1.2 to 1.5:1, wherein the CaCl2 concentration is 1 to 2 mol / L.

[0013] Preferably, step four involves adjusting the pH to 5-6.

[0014] More preferably, step five specifically involves spraying 100-200L of the mixed slurry described in step four onto each square meter of the loess to be reinforced with the composite reinforcing agent, repeating the spraying every 12-24 hours, and spraying a total of 4-8 times depending on the soil condition; after the grouting is completed, the soil surface is covered with a film and sprayed with water for curing at 15-35℃.

[0015] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: (1) Reinforcing and Filling Effects of Rice Husk Fibers. This invention involves graded processing of rice husks to form a fiber system with a combination of long and short fibers. During grouting, short fibers effectively fill the large pores (approximately 25% of the total pore volume) in the loess foundation with a diameter greater than 5 mm, reducing the overall porosity and providing abundant nucleation sites for calcium carbonate crystals generated by the EICP reaction, thus promoting interparticle cementation. Long fibers intertwine with soil particles, forming a spatial network structure through the frictional force at the fiber-soil interface. Under the wetting effect of the grouting fluid, a water film is adsorbed on the fiber surface, further enhancing the bond between the fiber and the soil. The combined effect of short fiber filling and long fiber reinforcement can significantly improve the large porosity and easy collapse problems inherent in loess, thereby enhancing the bearing capacity of the loess foundation.

[0016] (2) Improved curing agent. Rice husk ash is mixed with urease solution. The rice husk ash after low-temperature firing has a larger specific surface area and a stronger adsorption capacity. It can adsorb a large amount of urease, which improves the uniformity of spatial distribution and reaction efficiency of the soil. At the same time, it increases the viscosity of EICP slurry, avoiding collapsible damage to the pore structure of loess caused by water-based slurry, thereby achieving reinforcement of deep loess soil.

[0017] (3) Rice husk ash produced by low-temperature firing is rich in active SiO2. In the EICP reaction system, these active SiO2, upon contact with water at room temperature, can react with the OH- generated by the reaction. - and Ca in the solution 2+ A hydration reaction occurs, generating hydrated calcium silicate gel. This gel interweaves with the calcium carbonate crystals precipitated from the EICP reaction, forming a dense composite cement that significantly enhances the bond strength between soil particles. The composite gel can encapsulate urease molecules, protecting their activity, and the positive charge on the surface of hydrated calcium silicate can adsorb negatively charged urea, promoting urea hydrolysis and aiding in calcium carbonate deposition. This results in the formation of more composite cement, further enhancing the soil's density and skeletal structure, thus significantly consolidating the loess foundation.

[0018] (4) This invention effectively solves the common problems of uneven cementation and poor deep reinforcement effect in EICP technology for loess reinforcement by the synergistic combination of rice husk fiber and rice husk ash. Rice husk fiber forms a three-dimensional network structure in the soil, which not only enhances the integrity of the soil and provides a stable transport channel for the reaction, but also ensures the uniform distribution of rice husk ash. Rice husk ash, as a micron-level active component, protects urease activity through its porous structure and participates in the generation of CSH gel, forming a composite cementing system with calcium carbonate. This synergistic mechanism of fiber constructing a spatial framework and ash optimizing the reaction path allows the cement to be preferentially and uniformly deposited at key nodes in the soil, achieving an organic combination of physical reinforcement and chemical cementation, significantly improving the consolidation effect and engineering reliability of the loess foundation. This invention effectively solves the common problems of uneven cementation and poor deep reinforcement effect in EICP technology for loess reinforcement by the synergistic combination of rice husk fiber and rice husk ash. The method disclosed in this invention is efficient, economical, convenient, environmentally friendly, easy to promote, and suitable for large-scale processing. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method for reinforcing loess foundations with EICP in conjunction with rice husks, provided in an embodiment of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0022] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0023] The process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions.

[0024] This invention proposes a method for reinforcing loess foundations using EICP in conjunction with rice husks, such as... Figure 1 As shown, the specific steps include: Step 1: Preparation of rice husk fiber: Select dried, crystalline agricultural byproduct rice husks. First, crush and grade the rice husks, and prepare short fibers with a length of 2-8 mm and long fibers with a length of 10-20 mm by controlling the mechanical grinding parameters. Then, blend them according to a mass ratio of short fiber to long fiber of 1:(1~3).

[0025] Fiber surface modification: (1) Alkali treatment activation: Place the fiber in a 3-8 wt% sodium hydroxide solution and stir at 60-80 ℃ for 1-3 hours. After the reaction is complete, wash with deionized water until neutral and dry. This step can effectively clean and roughen the fiber surface, increase its specific surface area and the number of active sites such as hydroxyl groups, and provide favorable conditions for subsequent urease adsorption. (2) Coupling agent treatment: Wash the alkali-treated fiber until neutral, and then immerse it in a 1-5 wt% silane coupling agent (such as KH-550, KH-792, KH-560, etc.) ethanol solution, stir at a uniform speed for 30-60 minutes, and control the speed at 100-300 rpm. After completion, take it out and dry it thoroughly at 60-80 ℃ to enhance the biochemical affinity between the fiber and calcium carbonate crystals. Coupling agents can form a chemical bridging layer on the fiber surface, significantly enhancing the biochemical affinity and binding force between the fiber and the calcium carbonate crystals generated by the subsequent EICP reaction.

[0026] Physical reinforcement treatment of the fiber mesh: To improve the initial integrity of the modified fiber mesh and facilitate construction and laying, physical reinforcement is performed. A 1-3 wt% aqueous solution of hydroxypropyl methylcellulose (HPMC) is prepared as a binder. This solution is evenly sprayed onto the modified fibers obtained in step one using a spraying device, with the binder dosage controlled at 1-5% of the total fiber mass. After spraying, the fibers are slightly agitated at room temperature to ensure uniform mixing, and then dried at 60-80 ℃ for 30-60 minutes. This process forms weak water-soluble bonding points at fiber intersections, resulting in a prefabricated fiber mesh that is easy to handle and lay. When the subsequent EICP reaction solution is injected, the HPMC dissolves rapidly, and the fiber mesh maintains its shape under the constraint of the soil space, while all its active surfaces are completely released, thus not affecting the adsorption of urease and the cementation of calcium carbonate crystals.

[0027] Step 2: Preparation of Rice Husk Ash: Pre-treat rice husks in a 1-2.5% hydrochloric acid solution by heating in a boiling water bath for 1 hour or soaking at room temperature for 2-4 hours. Then, repeatedly wash with deionized water until neutral and dry at 80-105℃. Next, place the treated rice husks in a muffle furnace and calcine at 550-700℃ in air for 1-2 hours, allowing to cool naturally to room temperature. Transfer the calcined product to a ball mill and ball mill at 500-800 r / min for 10-30 minutes. Finally, sieve through a 150-mesh sieve (0.1 mm aperture) and collect the undersize material as the desired rice husk ash.

[0028] Step 3: Fiber Mixing: The modified rice husk fiber prepared in Step 1 and the rice husk ash prepared in Step 2 are uniformly mixed at a dry weight ratio of (fiber:ash) of (10~5):1 to form a composite reinforcing agent. Subsequently, the composite reinforcing agent is mixed with the crushed and air-dried loess sample at a mass dosage of 0.5-2% (percentage of dry soil mass) in a mixer for 5-15 minutes to ensure that the fiber and ash are evenly distributed in the soil.

[0029] Step 4, Preparation of EICP Urease Extract: (a) Mix food-grade soybean flour and (25%~30%) ethanol aqueous solution at a solid-liquid ratio of 1:(8-10) to obtain a soybean flour solution; (b) Stir the soybean flour solution with a magnetic stirrer for 20~30 min at a speed of 8000~10000 r / min; (c) After stirring, let the solution stand at 0~4℃ for 12~16 h, then take the supernatant and centrifuge at 8000~10000 r / min at 0~4℃ for 10 min to obtain the urease extract.

[0030] Step 5: Prepare a mixed solution of CO(NH)2 and CaCl2 with a concentration ratio of 1.2~1.5:1, wherein the concentration of CaCl2 is 1~2 mol / L, as a solidification solution.

[0031] Step 6: Mix the urease extract, the consolidation solution, and 1-2 mol / L dilute hydrochloric acid to form a mixed slurry with a pH of 5-6. By adjusting the pH, the formation of calcium carbonate is delayed, which facilitates the slurry's penetration into the soil and avoids surface blockage.

[0032] Step 7: Spray grouting. Spray 100-200L of mixed grout per square meter of soil, repeating the spraying every 12-24 hours. Depending on the soil conditions, spray a total of 4-8 times. After grouting, cure the soil surface with a film and water spraying at 15-35℃ for 7-14 days.

[0033] The embodiments of this application are described below with reference to the accompanying drawings.

[0034] Example 1 Step 1: Preparation of Rice Husk Fiber: Using dried, crystalline agricultural byproduct rice husks, the rice husks are first crushed and graded. The rice husks are placed in a hammer mill equipped with a screen with an aperture ≤2 mm and crushed at 1200 rpm for 60 seconds. All output is collected; the fiber length is mainly distributed between 2-8 mm. The rice husks are then placed in a hammer mill for preliminary crushing at 1200 rpm without a screen or with a screen with a large aperture (e.g., ≥10 mm) to loosen the husk clumps. Subsequently, the crushed product is graded through a set of standard sieves, collecting the portion that passes through an 8 mm screen but remains on a 2 mm screen; this portion consists of short fibers with a main length of 2-8 mm. Finally, the rice husks are placed in a toothed roller crusher, with the toothed roller gap adjusted to 8-12 mm, and crushed in one pass at 300 rpm. All output is collected; the fiber length is mainly distributed between 10-20 mm. The fibers prepared above are uniformly compounded at a mass ratio of short fiber to long fiber of 1:2 for subsequent modification and use.

[0035] Surface modification of rice husk fiber: (1) Alkali treatment activation: The fiber was placed in a 5 wt% sodium hydroxide solution and stirred at 70 ℃ for 2 hours. This step can effectively clean and roughen the fiber surface, increase its specific surface area and the number of active sites such as hydroxyl groups, and provide favorable conditions for subsequent urease adsorption. (2) Coupling agent treatment: The alkali-treated fiber was washed until neutral and then immersed in a 3 wt% silane coupling agent KH-550 ethanol solution and stirred at a constant speed for 45 minutes, with the speed controlled at 200 rpm. The coupling agent can form a chemical bridging layer on the fiber surface, which significantly enhances the biochemical affinity and binding force between the fiber and the calcium carbonate crystals generated by the subsequent EICP reaction.

[0036] Physical reinforcement treatment of the fiber mesh: A 2 wt% aqueous solution of hydroxypropyl methylcellulose (HPMC) was prepared as a binder. This solution was uniformly sprayed onto the modified fibers obtained in step one using a spraying device, with the binder dosage controlled at 3% of the total fiber mass. After spraying, the fibers were slightly agitated at room temperature to ensure uniform mixing, and then dried at 70°C for 45 minutes. This process forms weak water-soluble bonding points at fiber intersections, resulting in a prefabricated fiber mesh that is easy to handle and lay. When the subsequent EICP reaction solution is injected, the HPMC dissolves rapidly, and the fiber mesh maintains its shape under the constraint of the soil space, while all its active surfaces are completely released, thus not affecting the adsorption of urease and the cementation of calcium carbonate crystals.

[0037] Step 2: Preparation of rice husk ash: Rice husks were pretreated in a 2% hydrochloric acid solution, heated in a boiling water bath for 1 hour, repeatedly washed with deionized water until neutral, and dried at 85℃. The treated rice husks were then placed in a muffle furnace and calcined in air at 600℃ for 1.5 hours, followed by natural cooling to room temperature. The calcined product was transferred to a ball mill and ball-milled at 800 r / min for 20 minutes. Finally, it was sieved through a 150-mesh sieve (0.1 mm aperture), and the undersize material was taken as the desired rice husk ash.

[0038] Step 3: Fiber Mixing: The modified rice husk fiber prepared in Step 1 and the rice husk ash prepared in Step 2 are mixed evenly at a dry weight ratio of 8:1 (fiber:ash) to form a composite reinforcing agent. Subsequently, the composite reinforcing agent is mixed at a mass dosage of 1% (percentage of dry soil mass) with the crushed and air-dried loess sample in a mixer for 10 minutes to ensure that the fiber and ash are evenly distributed in the soil.

[0039] Step 4: Preparation of EICP urease extract: (a) Mix food-grade soybean flour and 30% ethanol aqueous solution at a solid-liquid ratio of 1:9 to obtain a soybean flour solution; (b) Stir the soybean flour solution with a magnetic stirrer for 25 min at a speed of 9000 r / min; (c) After stirring, let the solution stand in a refrigerator (0~4℃) for 15 h, then take the supernatant and centrifuge at 10000 r / min and 2℃ for 10 min to obtain the urease extract.

[0040] Step 5: Prepare a mixed solution of CO(NH)2 and CaCl2 with a concentration ratio of 1.4:1, wherein the concentration of CaCl2 is 1.5 mol / L, as a solidification solution.

[0041] Step 6: Mix the urease extract, the consolidation solution, and 1.5 mol / L dilute hydrochloric acid to form a mixed slurry with a pH of 5-6. By adjusting the pH, the formation of calcium carbonate is delayed, which facilitates the slurry's penetration into the soil and avoids surface blockage.

[0042] Step 7: Grouting. Spray 150L of mixed grout per square meter of soil, repeating the spraying every 18 hours. Depending on the soil conditions, spray a total of 6 times. After grouting, cure the soil surface with a film and water spraying at 25℃ for 7-14 days.

[0043] Example 2 The rest is the same as in Example 1, except that the mass ratio of short rice husk fiber to long rice husk fiber is 1:1, and the mass ratio of modified rice husk fiber in step one to rice husk ash in step two in the composite reinforcing agent is 10:1.

[0044] Example 3 The rest is the same as in Example 1, except that the amount of composite reinforcing agent in the loess to be reinforced is 0.8 wt%.

[0045] Example 4 The rest is the same as in Example 1, except that the amount of composite reinforcing agent in the loess to be reinforced is 1.8 wt%.

[0046] Example 5 The rest is the same as in Example 1, except that the mass ratio of short rice husk fiber to long rice husk fiber is 1:3, and the mass ratio of modified rice husk fiber in step one to rice husk ash in step two in the composite reinforcing agent is 5:1.

[0047] Comparative Example 1 Comparative Example 1 is identical to Example 1 except that rice husk fiber is not added. That is, step one is omitted, and the reinforcing agent in step three contains only rice husk ash.

[0048] Comparative Example 2 Comparative Example 2 is the same as Example 1 except that step two is omitted and the reinforcing agent in step three contains only rice husk fiber.

[0049] Comparative Example 3 The rest is the same as in Example 1, except that in step one, the rice husk fiber contains only one type with a size of 2-8mm.

[0050] Comparative Example 4 The rest is the same as in Example 1, except that in step one, the rice husk fiber contains only one type with a size of 10-20mm.

[0051] Comparative Example 5 The rest is the same as in Example 1, except that the rice husk fiber in step one is not modified and is directly a combination of long and short fibers after physical crushing.

[0052] Comparative Example 6 The rest is the same as in Example 1, except that the amount of composite reinforcing agent in step three is only 0.1%.

[0053] Comparative Example 7 The rest is the same as in Example 1, except that the amount of composite reinforcing agent in step three is only 2.5%.

[0054] Comparative Example 8 The rest is the same as in Example 1, except that in step two, the rice husks are directly carbonized at high temperature in a closed oxygen-free atmosphere at 700°C and then ground to obtain rice husk charcoal.

[0055] Test methods and results: Unconfined compressive strength tests were conducted on the loess foundations reinforced in Examples 1-5 and Comparative Examples 1-8 after curing for 7 and 14 days, respectively. The tests were performed in accordance with GB / T 50123-2019 Standard for Geotechnical Testing Methods.

[0056] Table 1. Strength of loess foundations reinforced in Examples 1-5 and Comparative Examples 1-7 after 7 and 14 days of curing.

[0057] As can be seen from Table 1, the reinforcement methods of Examples 1 to 5 significantly improved the strength of the loess foundation compared with Comparative Examples 1 to 8.

[0058] Comparative Example 1, lacking rice husk fiber, may have resulted in a lack of fibrous skeleton, poor soil structure, low strength, and slow strength growth. Comparative Example 2, lacking rice husk ash, may have lacked gel-assisted bonding; relying solely on dispersed calcium carbonate, the overall bonding was insufficient, limiting the strength improvement. Both rice husk fiber and rice husk ash are indispensable; their simultaneous introduction significantly enhances reinforcement strength.

[0059] Comparative Example 3 contained only short fibers, and Comparative Example 4 contained only long fibers. As can be seen from the data in Table 1, the combination of the two is also necessary. Short fibers alone may fill the pores but cannot build an effective load-bearing skeleton, thus failing to improve the structure of loess; long fibers alone, although they build the main skeleton, do not fill the pores well and fail to completely overcome the structural problems of loess.

[0060] Comparative Example 5, which uses completely unmodified rice husk fiber, also showed a weak strength improvement effect, indicating that the unmodified rice husk fiber has a weak interface with the soil and cannot effectively transfer stress. It also has a low urease adhesion rate and a relatively poor degree of cementation.

[0061] In Comparative Example 6, the dosage of the composite reinforcing agent was too low, and the reinforcing material might not be able to form a continuous network, resulting in strength close to that of pure EICP treatment. Furthermore, a small amount of the agent might affect the soil's inherent structure, leading to a slightly lower strength than pure EICP curing. In Comparative Example 7, the dosage was too high, which could easily lead to clumping and uneven reinforcement, failing to effectively increase strength.

[0062] Comparative Example 8 uses rice husk char obtained by high-temperature carbonization. The main component of high-temperature carbonized rice husk char is carbon, which may have some immobilization and adsorption capacity, but it is chemically inert and mainly functions as physical filler and adsorbent. Unlike the embodiments of this invention, it cannot form active SiO2 at a lower temperature during calcination, which can react with EICP to produce CSH gel, achieving a synergistic effect of physical filling and chemical bonding, i.e., a new cementing material, to help improve strength.

[0063] Therefore, the method for reinforcing loess foundations provided by this invention, which uses EICP in conjunction with rice husk fiber and rice husk ash to reinforce loess foundations, can effectively improve the deep reinforcement effect of loess foundations and can be widely used.

[0064] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for reinforcing loess foundations using EICP in conjunction with rice husks, characterized in that, Includes the following steps: Step 1: Two different sizes of rice husk fibers are blended together, and then the blended rice husk fibers are successively activated by alkali treatment, modified by coupling agent, and reinforced by organic binder to increase the specific surface area and the number of surface active sites of the rice husk fibers, thereby improving their stability and obtaining modified rice husk fibers. Step 2: Calcine the rice husks in an oxygen-containing atmosphere and then grind them to obtain rice husk ash; Step 3: Mix the modified rice husk fiber obtained in Step 1 with the rice husk ash described in Step 2 to obtain a composite reinforcing agent; uniformly mix the composite reinforcing agent into the loess to be reinforced to obtain loess to be reinforced with the composite reinforcing agent. Step 4: Mix the urease extract with the consolidation solution containing urea and calcium ions, and adjust the pH to weakly acidic to obtain a mixed slurry; Step 5: Spray the mixed grout from Step 4 into the loess to be reinforced by adding the composite reinforcing agent as described in Step 3. After the grouting is completed, cover the soil surface with a film and spray water for curing.

2. The method as described in claim 1, characterized in that, The two different sizes of rice husk fibers mentioned in step one include short rice husk fibers of 2-8 mm and long rice husk fibers of 10-20 mm. The mass ratio of short rice husk fiber to long rice husk fiber is 1:(1-3).

3. The method as described in claim 1, characterized in that, The alkaline treatment activation described in step one specifically involves placing rice husk fibers in a sodium hydroxide solution with a concentration of 3-8 wt% and stirring at 60-80 ℃ for 1-3 hours. The coupling agent modification specifically involves washing the alkali-treated fiber until it is neutral, then immersing it in a 1-5 wt% silane coupling agent ethanol solution and stirring for 30-60 minutes. The organic binder is hydroxypropyl methylcellulose, and the organic binder reinforcement specifically involves spraying a 1-3 wt% hydroxypropyl methylcellulose solution onto the rice husk fiber modified by the coupling agent, wherein the amount of the hydroxypropyl methylcellulose solution is 1-5% of the total mass of the rice husk fiber.

4. The method as described in claim 1, characterized in that, Step two is as follows: After washing and drying the rice husks, calcine them in an oxygen-containing atmosphere at 550-700℃ for 1-2 hours, then cool them and ball-mill them to obtain rice husk ash with a particle size of less than 0.1mm.

5. The method as described in claim 1, characterized in that, In step three, the mass ratio of the modified rice husk fiber described in step one to the rice husk ash described in step two in the composite reinforcing agent is (5-10):

1.

6. The method as described in claim 1, characterized in that, The amount of the composite reinforcing agent in the loess to be reinforced in step three is 0.5-2 wt%.

7. The method as described in claim 1, characterized in that, The preparation of the urease extract includes the following steps: (a) mixing food-grade soybean flour and an aqueous ethanol solution at a solid-liquid ratio of 1:(8-10) to obtain a soybean flour solution; (b) stirring the soybean flour solution for 20-30 min at a speed of 8000-10000 r / min; (c) allowing the stirred soybean flour solution to stand at 0-4℃ for 12-16 h, then centrifuging the supernatant at 8000-10000 r / min at 0-4℃ for 8-15 min to obtain the urease extract.

8. The method as described in claim 1, characterized in that, The stabilizing solution containing urea and calcium ions mentioned in step four is a mixture of CO(NH)2 and CaCl2 at a molar ratio of 1.2 to 1.5:1, wherein the concentration of CaCl2 is 1 to 2 mol / L.

9. The method as described in claim 1, characterized in that, Step 4: Adjust the pH to 5-6.

10. The method as described in claim 1, characterized in that, Step 5 specifically involves spraying 100-200L of the mixed grout from Step 4 onto each square meter of loess to be reinforced with the composite reinforcing agent. This spraying is repeated every 12-24 hours, and is carried out 4-8 times in total, depending on the soil condition. After grouting, the soil surface is covered with a film and sprayed with water for curing at 15-35℃.

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