A method for non-premixing spray reinforcement of low-viscosity soil surface layer based on urease phase rheological regulation and application

Abstract

The application provides a method for low-viscosity soil surface non-premixing spray reinforcement based on urease phase rheological regulation and application, and relates to the field of geotechnical engineering. The method comprises the following steps: adding calcium sulfate dihydrate into a plant source crude urease solution, stirring, standing and solid-liquid separation to obtain a purified urease solution; then adding 0.3-0.8 g / L xanthan gum into the purified urease solution to prepare a first treatment liquid; preparing a second treatment liquid by mixing calcium chloride and urea; spraying the first treatment liquid first during construction, and then spraying the second treatment liquid after standing for 1.5-2.5 hours, so that the two liquids only contact and react in the soil pores to form a calcium carbonate-xanthan gum composite reinforcement layer, and the spraying is cyclically carried out at intervals. The method can significantly reduce the solution turbidity and the risk of nozzle blockage while maintaining high urease activity, regulate infiltration and mineralization deposition, improve the compactness, uniformity and anti-infiltration performance of the reinforcement layer, and is suitable for the reinforcement and infiltration control of low-viscosity sandy soil, silt and bare slope surface.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, specifically to a method for non-premixed spraying reinforcement of low-cohesive soil surface based on urease phase rheology regulation, and the application of the above method in the reinforcement and infiltration control of low-cohesive soil surface. Background Technology

[0002] In engineering projects such as riverbank slope protection, roadbed treatment, and bare surface remediation, the surfaces of low-cohesion soils such as sand and silt are often subject to erosion, cracking, and soil loss due to rainfall, surface runoff, wet-dry cycles, and wind erosion. This leads to decreased surface strength and increased permeability, ultimately affecting the stability of the project. Therefore, reinforcing the surface of such soils to improve their surface strength, reduce infiltration, and enhance their overall integrity is of great significance for solving related geotechnical engineering problems.

[0003] In recent years, bio-geotechnical engineering technologies, represented by EICP (Enzyme-Induced Carbonate Precipitation), have been increasingly used for soil surface reinforcement due to their green, environmentally friendly, low-carbon, and energy-saving characteristics. The principle is as follows: urease extracted from plants (such as soybeans) hydrolyzes urea to produce carbonate ions, creating an alkaline environment. These carbonate ions combine with added calcium ions to form calcium carbonate precipitate, which then binds soil particles together, thereby improving the engineering properties of the soil. For surface reinforcement aimed at improving surface strength and reducing infiltration, spraying methods are widely used due to their low treatment solution volume and simple construction.

[0004] However, EICP spraying for surface reinforcement still faces a contradiction between "spraying operability" and "mineralization uniformity" in engineering: On the one hand, the crude urease solution extracted from plants contains a large amount of soluble organic matter and other impurities, which easily accumulate, bubble, and form flocs at the nozzle during spraying, clogging the nozzle and affecting the uniformity and continuity of spraying. The impurities also interfere with the uniform deposition of calcium carbonate. On the other hand, if the urease solution and cementing liquid are premixed before spraying, they react immediately upon contact to form calcium carbonate flocs, instantly clogging the nozzle, resulting in extremely poor engineering operability. Although the simple step-by-step spraying method can avoid premixed flocculation, the low-viscosity urease solution penetrates quickly and has a short residence time on the surface, resulting in low surface strength and uneven cementation between the surface and deep layers.

[0005] Therefore, there is an urgent need for a method that coordinates the above contradictions through a combination of processes, taking into account both sprayability and uniform mineralization. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for non-premixed spraying reinforcement of low-cohesion soil surface based on urease phase rheology regulation. By adding xanthan gum only to purified urease solution to form a first treatment solution and using its high viscosity to control the infiltration sequence, the solution is then sprayed in stages with a second treatment solution without premixing, so that calcium carbonate is generated in situ only in the soil pores, thereby achieving shallow, uniform, and dense reinforcement.

[0007] The second objective of this invention is to provide the application of the above-mentioned method in the reinforcement and infiltration control of low-cohesion soil surfaces, including windbreak and sand fixation of sandy or silty soil surfaces in arid and semi-arid regions, as well as seepage prevention and erosion protection of roadbed slopes, canal slopes, or exposed slope surfaces.

[0008] One of the technical solutions adopted by this invention to achieve its objective is to provide a method for non-premixed spraying reinforcement of low-cohesion soil surface based on urease phase rheology regulation, comprising the following steps: S1. Purify the crude plant-derived urease solution using calcium sulfate dihydrate to obtain a purified urease solution. S2. Add xanthan gum to the purified urease solution and dissolve it to obtain a first treatment solution with a xanthan gum concentration of 0.3-0.8 g / L; S3. Mix the calcium chloride solution and the urea solution to obtain the second treatment solution; S4. Spray the first treatment solution evenly onto the soil surface and let it stand for 1.5-2.5 hours to allow it to seep in, thus obtaining soil with a pre-contained urease phase. S5. The second treatment liquid is evenly sprayed onto the soil surface with the pre-placed urease phase, so that the first treatment liquid and the second treatment liquid only come into contact and react within the soil pores to generate calcium carbonate and form a calcium carbonate-xanthan gum composite reinforcement layer together with xanthan gum. S6. Repeat steps S4 and S5 multiple times to gradually thicken the calcium carbonate-xanthan gum composite reinforcement layer, resulting in solidified soil.

[0009] The overall concept and inventive principle of this invention are as follows: This invention addresses the problems of uncontrollable reaction location and poor surface reinforcement effect caused by premixed spraying in existing EICP technology. It proposes a combined process of "calcium sulfate urease removal, low-dose xanthan gum modification, and two-stage non-premixed spraying," which achieves uniform reinforcement of low-cohesive soil surfaces by reconciling the contradiction between spraying operability and mineralization uniformity. Specifically, it includes the following key points: First, calcium sulfate dihydrate was used to salt out the crude plant urease solution to remove impurities. This step significantly reduced the turbidity of the solution with almost no loss of enzyme activity, reduced foaming and flocculent matter during spraying, lowered the risk of nozzle clogging, and improved the uniformity and continuity of spraying; the removal of impurities also created conditions for the subsequent uniform deposition of calcium carbonate.

[0010] Secondly, a low dose of xanthan gum (0.3-0.8 g / L) is added only to the purified urease solution to construct the first treatment solution and perform rheological regulation. In the solidification method provided by this invention, xanthan gum exists only in the urease phase and is not premixed with the second treatment solution. Extremely low concentrations of xanthan gum can increase the apparent viscosity of the urease phase, prolong its residence time on the soil surface, and regulate the infiltration sequence, while maintaining low turbidity to ensure continuous sprayability. After spraying the first treatment solution, the infiltration rate decreases and the distribution becomes more uniform, allowing urease to remain more fully within a certain depth below the surface. The negatively charged groups such as carboxyl groups on the side chains of xanthan gum can also help enrich calcium ions and provide nucleation sites for calcium carbonate, allowing calcium carbonate to preferentially deposit in situ at a controlled shallow depth, reducing the ineffective migration of the treatment solution to deeper areas. Therefore, compared with conventional EICP, the total thickness of the solidified layer obtained by this invention is slightly smaller, but within the effective reinforcement layer range, especially at a depth of 20 mm, the calcium carbonate content is higher, and the attenuation along the depth is lower.

[0011] Furthermore, a two-stage non-premixed spraying method is employed to achieve sequential separation of the first and second treatment solutions. First, the first treatment solution is uniformly sprayed onto the soil surface and allowed to infiltrate for 1.5-2.5 hours to allow urease to fully distribute below the surface. Then, the second treatment solution, calcium chloride-urea, is sprayed. The two solutions only meet and react within the soil pores, resulting in the in-situ deposition of calcium carbonate. This sequential separation completely avoids the problem of immediate flocculation and nozzle clogging caused by premixing the urease solution with the cementing liquid, making it highly operable in engineering. The rheological regulation of xanthan gum causes the urease phase to remain below the surface rather than rapidly infiltrate, allowing calcium carbonate to deposit at a more uniform depth. By controlling the intervals of cyclic spraying, the mineralized layer gradually thickens, the reinforcement effect is continuously enhanced, and the spraying method requires less treatment solution and has lower material costs.

[0012] Finally, based on the above-mentioned solidification method, this invention forms a calcium carbonate-xanthan gum composite mineralization layer within the pores of the low-viscosity soil surface, thereby improving its anti-infiltration stability. After dehydration, xanthan gum forms a film, encapsulates particles, and fills pores, together with the in-situ deposited calcium carbonate to constitute the composite mineralization layer: calcium carbonate crystals strengthen the cementing framework, while the xanthan gum film seals the interconnected pores between crystals and at pore throats. The synergistic effect of both results in a more uniform distribution of calcium carbonate along the depth direction in the treated soil surface, higher penetration strength, reduced saturated permeability coefficient, and improved anti-infiltration stability. It should be noted that the anti-infiltration performance here mainly stems from the sealing and interruption of pore connectivity by the composite mineralization layer, rather than the hydrophobicity of the xanthan gum or calcium carbonate materials themselves.

[0013] Further, in step S1, the plant-derived crude urease solution is obtained by extraction from one or more of soybeans, sword beans, chickpeas, watermelon seeds, or mulberry leaves.

[0014] Further, in step S1, the amount of calcium sulfate dihydrate added is 8%-12% of the mass of the plant-derived crude urease solution, preferably 10%. Specifically, after adding calcium sulfate dihydrate, the mixture is stirred to fully disperse it and bind it with excess protein and soluble organic matter in the solution. After standing, it is centrifuged and filtered. Through salting out and particle sedimentation, the content of soluble organic matter and suspended impurities in the solution is reduced, and the settled impurities are removed. The supernatant is then taken to obtain the purified urease solution. This operation not only significantly reduces the turbidity of the urease solution, but also, as measured by the conductivity method, the urease activity remains above 15 mM / min.

[0015] Preferably, in step S1, the plant-derived crude urease solution is a soybean crude urease solution. Compared with other plant sources, soybeans have a high urease content and are inexpensive and readily available. In specific engineering projects, a suitable crop rich in urease can also be selected as the extract based on the material costs at the project location. The extraction method of soybean crude urease solution includes: drying and pulverizing soybeans, sieving to obtain soybean powder; preparing a soybean powder solution with a concentration of 50-100 g / L using deionized water, centrifuging and filtering, and obtaining the supernatant as the soybean crude urease solution.

[0016] Furthermore, in step S2, the apparent viscosity of the first treatment solution at 25 °C is 1.5-5 times that of the purified urease solution. In this step, the addition of low-concentration xanthan gum not only increases the residence time of the first treatment solution on the soil surface but also maintains the continuous sprayability of the first treatment solution.

[0017] Studies have shown that after spraying, the unevenness of calcium carbonate content along the depth direction in the soil is reduced compared to the treatment without xanthan gum, that is, the difference in calcium carbonate content between the surface and deep layers is reduced.

[0018] Further, in step S3, the concentration of calcium chloride in the second treatment solution is 0.8-1.2 mol / L, and the molar ratio of calcium chloride to urea is 1:1.

[0019] Furthermore, the spraying rate of the first treatment liquid in step S4 and the spraying rate of the second treatment liquid in step S5 are both 2-3 L / m³. 2 The spraying height is 5-10 cm from the soil surface.

[0020] Furthermore, in this invention, controlling the spraying interval between the first and second treatment solutions to be 1.5-2.5 h is a necessary condition for achieving shallow and uniform reinforcement. This set incubation time window allows urease in the first treatment solution to be fully adsorbed and distributed on the pore walls within a 2-8 cm depth range of the soil surface under the rheological regulation of xanthan gum, forming a pre-positioned urease distribution zone. If the incubation time is too short (e.g., 0.5 h), the urease has not fully completed its adsorption and distribution on the pore walls, and the subsequently sprayed second treatment solution cannot react with sufficient urease within the target depth range, resulting in insufficient calcium carbonate deposition, uneven distribution along the depth, and a significant decrease in reinforcement effect. If the incubation time is too long (e.g., 4 h), on the one hand, the urease remains in a liquid environment for a long time without a substrate, and its enzyme activity irreversibly decreases due to natural decay; on the other hand, the water in the first treatment solution continues to evaporate, disrupting the liquid environment within the pores. Both of these factors are detrimental to the efficient generation and uniform deposition of calcium carbonate after the introduction of the second treatment solution, similarly leading to a deterioration in the reinforcement effect.

[0021] Further, in step S6, the operations of steps S4 and S5 are repeated 2-8 times, with an interval of 18-32 hours between adjacent spraying cycles. Through multiple cycles, the second treatment solution is introduced into the urease distribution area pre-deployed by the first treatment solution in each cycle, and calcium carbonate is generated in situ, achieving the gradual thickening and densification of the reinforcement layer. During the cycle, it is always ensured that the first and second treatment solutions are not premixed before spraying, but only come into contact and react within the soil pores to generate calcium carbonate.

[0022] The second objective of this invention is to provide the application of the method described in the first objective of this invention in windbreak and sand fixation of sandy or silty soil in arid and semi-arid regions, or in seepage prevention and erosion protection of roadbed slopes, canal slopes, or exposed slope surfaces.

[0023] In applications for windbreak and sand fixation of sandy or silty soil surfaces in arid and semi-arid regions, conventional premixed EICP reinforcing solutions suffer from low efficiency in reinforcing wind-erosion-resistant layers within the 2-8 cm depth due to the large penetration depth and the migration of a large amount of effective components to deeper layers. This invention, through the time-sequential separation and spraying of the urease phase and the cementing solution, precisely positions the calcium carbonate-xanthan gum composite reinforcing layer within the shallowest 2-8 cm layer where wind erosion is most intense. With the same material consumption, its surface penetration strength and wind erosion resistance are significantly superior to conventional EICP methods, while also greatly conserving precious water resources in arid regions.

[0024] For applications in seepage prevention and erosion protection of roadbed slopes, canal slopes, or exposed slope surfaces, this invention constructs a low-permeability composite mineralized layer in the shallow layer (2-8cm) of the slope surface through a non-premixed, staged spraying method. The saturated permeability coefficient is reduced by more than 74% compared to untreated soil, effectively blocking rainwater infiltration and inhibiting the development of slope erosion gullies. Conventional premixed EICP technology cannot achieve this type of efficient shallow seepage prevention function due to its excessive reinforcement depth and difficulty in controlling the seepage path.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a method for non-premixed spraying reinforcement of low-cohesive soil surface based on urease phase rheology regulation. The crude urease solution is salted out with calcium sulfate dihydrate to remove impurities. The content of soluble organic matter and suspended impurities in the solution is reduced with almost no loss of enzyme activity. This reduces foaming and flocculent matter during spraying, reduces the risk of nozzle clogging, improves the uniformity and continuity of spraying, and makes the subsequent deposition of calcium carbonate more uniform.

[0026] (2) The present invention provides a method for non-premixed spraying reinforcement of low-cohesion soil surface based on urease phase rheological regulation. Only a low dose of xanthan gum is added to the purified urease solution for rheological regulation, which increases the viscosity of the urease phase, prolongs its residence time on the soil surface and regulates the infiltration sequence, so that calcium carbonate is more dense and deposited more uniformly along the depth in the controlled shallow depth. Although the total depth of the solidified layer is slightly reduced compared with conventional EICP, it significantly improves the surface penetration strength and deep calcium carbonate content and reduces the saturation permeability coefficient.

[0027] (3) The present invention provides a method for non-premixed spraying reinforcement of low-cohesive soil surface based on urease phase rheology regulation. The method adopts a two-stage non-premixed spraying method. The first treatment liquid and the second treatment liquid only react in contact within the soil pores, avoiding the problem of flocculation and nozzle blockage immediately after the urease solution and cementing liquid are premixed. The method is highly operable in engineering. The spraying method uses less treatment liquid, which greatly reduces material costs and workload.

[0028] (4) The present invention provides a method for non-premixed spraying reinforcement of low cohesive soil surface based on urease phase rheology regulation. The calcium carbonate-xanthan gum composite mineralized layer formed after treatment is more uniformly distributed along the depth and has stronger anti-infiltration stability. After multiple spraying treatments, the integrity and anti-infiltration performance of the soil surface are significantly improved. It is suitable for reinforcement and infiltration control of low cohesive sandy soil or sandy silt surface. It has broad application prospects in the fields of windbreak and sand fixation in arid and semi-arid areas, seepage prevention and erosion resistance of roadbed slopes and canal slopes. Attached Figure Description

[0029] Figure 1This is a construction schematic diagram of a non-premixed spraying reinforcement method for low-cohesion soil surface based on urease phase rheology regulation provided by the present invention, wherein (a) is the first stage of spraying the first treatment liquid, (b) is the static infiltration process, and (c) is the second stage of spraying the second treatment liquid and solidifying. Figure 2 This describes the change in soil surface penetration strength with the number of spraying cycles in Embodiment 1 and Comparative Example 2 of the present invention. Figure 3 The changes in calcium carbonate content at the surface and 20 mm below the surface of the soil in Embodiment 1 and Comparative Example 2 of this invention are shown with the number of sprayings, where (a) is the surface layer and (b) is 20 mm deep. Figure 4 This describes the changes in the saturated permeability coefficient of soil with the number of spraying cycles in Embodiment 1 and Comparative Example 2 of the present invention. Among them, 1-sprayer; 2-nozzle; 3-droplet of the first treatment liquid (modified urease phase); 4-sand soil; 5-urease infiltration zone; 6-droplet of the second treatment liquid; 7-calcium carbonate-xanthan gum composite mineralization layer. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] This invention provides a method for non-premixed spraying reinforcement of low-cohesion soil surface based on urease phase rheology regulation, comprising the following steps: Step 1: Purify the plant-derived crude urease solution using calcium sulfate dihydrate to obtain a purified urease solution; the plant-derived crude urease solution is a soybean crude urease solution; the extraction method of the soybean crude urease solution includes: drying and pulverizing soybeans, sieving to obtain soybean powder; preparing a soybean powder solution with a concentration of 50-100 g / L using deionized water, centrifuging and filtering, and obtaining the supernatant as the soybean crude urease solution. The amount of calcium sulfate dihydrate added is 8%-12% of the mass of the plant-derived crude urease solution.

[0032] Step 2: Add xanthan gum to the purified urease solution and dissolve it to obtain a first treatment solution with a xanthan gum concentration of 0.3-0.8 g / L. The apparent viscosity of the first treatment solution at 25 °C is 1.5-5 times that of the purified urease solution.

[0033] Step 3: Mix the calcium chloride solution and the urea solution to obtain the second treatment solution; in the second treatment solution, the concentration of calcium chloride is 0.8-1.2 mol / L, and the molar ratio of calcium chloride to urea is 1:1.

[0034] Step 4: Spray the first treatment solution evenly onto the soil surface and allow it to infiltrate for 1.5-2.5 hours to obtain soil with a pre-contained urease phase; the spraying rate of the first treatment solution is 2-3 L / m². 2 .

[0035] Step 5: Spray the second treatment solution evenly onto the soil surface with the pre-placed urease phase. The spraying rate of the second treatment solution is 2-3 L / m². 2 The first and second treatment solutions react only within the pores of the soil to generate calcium carbonate, which together with xanthan gum forms a calcium carbonate-xanthan gum composite reinforcement layer. Step 6: Repeat steps 4 and 5 2-8 times, with an interval of 18-32 hours between adjacent spraying cycles. This allows the calcium carbonate-xanthan gum composite reinforcement layer to gradually thicken, resulting in solidified soil.

[0036] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the invention. The main parameters and variables of each embodiment of the present invention are shown in Table 1 below: Table 1

[0037] Example 1 This embodiment provides a method for non-premixed spraying reinforcement of low-cohesion soil surface based on urease phase rheology regulation. The materials used in this embodiment include deionized water, soybean flour, urea, calcium chloride, calcium sulfate dihydrate, and xanthan gum. The soil used is sandy soil taken from the test site, which is air-dried, sieved, and prepared into a smooth soil sample according to the designed dry density for later use.

[0038] The construction process of the second-stage non-premixed spraying is as follows: Figure 1 As shown. During spraying, the first treatment solution and the second treatment solution are respectively loaded into the sprayer, atomized through the nozzle, and sprayed onto the surface of the sandy soil; after the first treatment solution drips infiltrate, it forms a urease infiltration zone on the soil surface ( Figure 1 (a) Figure 1 (b) The second treatment liquid droplets sprayed again react with the soil pores only, depositing calcium carbonate in situ and forming a calcium carbonate-xanthan gum composite mineralization layer together with xanthan gum. Figure 1 (c)). The specific implementation steps are as follows: Step 1: Extract crude urease solution and remove impurities by salting out. Soybeans were dried in a 40 ℃ electric heating oven for 24 h, then pulverized and passed through a 100-mesh sieve to obtain dried soybean powder. A soybean powder solution with a concentration of 80 g / L was prepared using the dried soybean powder and deionized water, and stirred in a magnetic stirrer for 2 h to ensure uniform mixing. The stirred soybean powder solution was allowed to stand for 1 h, centrifuged, filtered, and the supernatant was collected to obtain the crude urease solution.

[0039] Add calcium sulfate dihydrate to the crude urease solution at 10% of its mass while stirring for 15 min. This reduces the content of soluble organic matter and suspended impurities in the solution through salting out, ionic strength adjustment, and particle sedimentation. After standing, centrifuge at 4000 r / min for 15 min, and collect the supernatant to obtain the purified urease solution. Store at 4 ℃ for later use. The turbidity of the purified solution is significantly lower than that before purification, spraying foaming is reduced, and the continuous spraying time can be extended.

[0040] The activity of the purified urease solution was measured using the conductivity method: A 1.11 mol / L urea solution was prepared, and 27 mL was placed in a beaker. 3 mL of the purified urease solution was added to bring the urea concentration in the mixed solution to 1 mol / L. The conductivity change of the mixed solution was measured using a conductivity meter at 25°C over 15 minutes (recorded every 5 minutes). The average conductivity change per minute was calculated, and the average of three measurements was taken. Urease activity was characterized by the amount of urea hydrolyzed by urease per minute; 1 mS / min conductivity change was converted to 11.1 mM / min of urea hydrolysis. The measured activity of the purified urease solution in this example was approximately 15 mM / min. Compared to before purification, the urease activity decreased only from about 16.1 mM / min to about 15.0 mM / min after purification (maintaining about 93%), while the turbidity after dilution by 40, 60, and 80 times decreased from about 500, 320, and 233 Ndu to about 178, 105, and 83 Ndu (a decrease of about 60%-67%). This indicates that calcium sulfate dihydrate treatment significantly removed impurities from the solution and significantly reduced turbidity with almost no loss of enzyme activity.

[0041] Step 2: Preparation of the first treatment solution. Xanthan gum is slowly added to the purified urease solution while stirring. The addition amount is 0.5 g / L. Stirring continues until the xanthan gum is completely dissolved and the solution is homogeneous. This is the first treatment solution. Xanthan gum is not premixed with the second treatment solution. The apparent viscosity of the obtained first treatment solution at 25°C is 2.3 times that of the purified urease solution without xanthan gum, and the nozzle does not become clogged during continuous spraying.

[0042] Step 3: Prepare the second treatment solution. Prepare the second treatment solution with a calcium chloride concentration of 1 mol / L and a urea concentration of 1 mol / L (the molar ratio of calcium chloride to urea is 1:1).

[0043] Step 4: Two-stage non-premixed spraying. Load the first and second treatment solutions into two separate sprayers; keep the nozzles 5cm above the soil surface. First, spray the first treatment solution evenly onto the soil surface at a rate of 3 L / m². 2 Let it stand for 2 hours after infiltration; Step 5: Spray the second treatment solution evenly onto the soil surface at a rate of 3 L / m². 2It solidifies at room temperature, allowing calcium carbonate to fully deposit in the pores of the soil, thus completing one spraying cycle.

[0044] Step 6: Repeat the above spraying once every 24 hours, and complete the spraying treatment 2 times, 4 times, 6 times and 8 times respectively to obtain the solidified soil.

[0045] Example 2 The difference between this embodiment and Embodiment 1 is as follows: the soybean flour solution concentration is 50 g / L, the amount of calcium sulfate dihydrate added is 8% of the mass of the crude urease solution, the amount of xanthan gum added is 0.3 g / L, the concentration of calcium chloride in the second treatment solution is 0.8 mol / L, the concentration of urea is 0.8 mol / L, the nozzle is held at a distance of 7.5 cm from the soil surface, and the spraying rate of both the first and second treatment solutions is 2 L / m². 2 After infiltration and standing for 1.5 h, the remaining steps are the same as in Example 1.

[0046] Example 3 The difference between this embodiment and Embodiment 1 is as follows: the soybean flour solution concentration is 100 g / L, the amount of calcium sulfate dihydrate added is 12% of the mass of the crude urease solution, the amount of xanthan gum added is 0.8 g / L, the concentration of calcium chloride in the second treatment solution is 1.2 mol / L, the concentration of urea is 1.2 mol / L, the nozzle is held 10 cm away from the soil surface, and the spraying rate of both the first and second treatment solutions is 2.5 L / m². 2 After infiltration and standing for 2.5 hours, the remaining steps are the same as in Example 1.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that all raw materials are premixed and then sprayed in a single application. Specifically, the following steps are included: Step 1: The method for preparing the purified urease solution is the same as in Example 1.

[0048] Step 2: Slowly add xanthan gum to the purified urease solution while stirring. The addition amount is 0.5 g / L. Continue stirring until the xanthan gum is completely dissolved and the solution is homogeneous to obtain the first treatment solution. Prepare the second treatment solution with a calcium chloride concentration of 1 mol / L and a urea concentration of 1 mol / L (calcium chloride to urea molar ratio of 1:1). Mix the first and second treatment solutions at a volume ratio of 1:1 to obtain the mixed curing solution.

[0049] Step 3: Load the mixed curing solution into the sprayer; keep the nozzle 5cm away from the soil surface, and spray the mixed curing solution evenly onto the soil surface at a rate of 6 L / m. 2 ; Step 4: Repeat the above spraying once every 24 hours, and complete the spraying treatment 2 times, 4 times, 6 times and 8 times respectively to obtain the solidified soil.

[0050] Comparative Example 2 The difference between this comparative example and Example 1 is that xanthan gum was not added to the first treatment solution.

[0051] Step 1: The method for preparing the purified urease solution is the same as in Example 1.

[0052] Step 2: Use the purified urease solution obtained in Step 1 as the first treatment solution, without adding xanthan gum.

[0053] Step 3: Prepare the second treatment solution. Prepare the second treatment solution with a calcium chloride concentration of 1 mol / L and a urea concentration of 1 mol / L (the molar ratio of calcium chloride to urea is 1:1).

[0054] Step 4: Two-stage non-premixed spraying. Load the first and second treatment solutions into two separate sprayers; keep the nozzles 5 cm above the soil surface. First, spray the first treatment solution evenly onto the soil surface at a rate of 3 L / m². 2 Let it stand for 2 hours after infiltration. Step 5: Spray the second treatment solution evenly onto the soil surface at a rate of 3 L / m². 2 It solidifies at room temperature, allowing calcium carbonate to fully deposit in the pores of the soil, thus completing one spraying cycle.

[0055] Step 6: Repeat the above spraying once every 24 hours, and complete the spraying treatment 2 times, 4 times, 6 times and 8 times respectively to obtain the solidified soil.

[0056] Comparative Example 3 The difference between this comparative example and Example 1 is that the infiltration and settling time of the first treatment solution in step 4 is adjusted from 2 hours to 0.5 hours, while the other operations and conditions remain unchanged.

[0057] Comparative Example 4 The difference between this comparative example and Example 1 is that the infiltration and settling time of the first treatment solution in step 4 is adjusted from 2 hours to 4 hours, while the other operations and conditions remain unchanged.

[0058] Application performance testing The reinforcement effect of the soil after spraying in each embodiment and comparative example was verified. The test items included surface penetration strength, calcium carbonate content (surface and 20mm depth) and saturated permeability coefficient.

[0059] The control group was conventional EICP without xanthan gum (Comparative Example 2); the present invention group (EICP-XG) consisted of urease purified by calcium sulfate dihydrate, with only 0.5 g / L xanthan gum added to the urease phase, and a two-stage non-premixed spraying process (Example 1). The number of spraying times was 2, 4, 6, and 8, and the spraying volume of both the urease phase and the cementing solution was 3 L / m³.2 .

[0060] (a) Surface penetration strength Figure 2 The results show that the surface penetration strength of both Example 1 and Comparative Example 2 increases with the number of sprays, but the EICP-XG in Example 1 is consistently higher (approximately 2660 kPa vs. 2140 kPa after 8 sprays, an increase of approximately 24%). This indicates that the EICP-XG in Example 1 has a denser surface bond, allowing for the achievement of equal or higher strength with fewer sprays, thus reducing costs and workload.

[0061] After eight spraying treatments, the surface penetration strength data of Examples 1-3 and Comparative Examples 1-4 are shown in Table 2 below.

[0062] Table 2

[0063] (ii) Calcium carbonate content Figure 3 The results show that the calcium carbonate content at both the surface and a depth of 20 mm in both Example 1 and Comparative Example 2 increased with the number of sprays. Compared to Comparative Example 2, the surface calcium carbonate content of Example 1 EICP-XG was slightly higher (approximately 2.61% vs. 2.33% after 8 sprays), consistent with the penetration strength trend. At a depth of 20 mm below the surface, the improvement in Example 1 was more significant (approximately 2.11% vs. 1.47% after 8 sprays, an increase of approximately 43.5%, far exceeding the approximately 12% increase at the surface).

[0064] Furthermore, after eight spraying treatments, the calcium carbonate content at different shallow depths in Example 1 and Comparative Example 2 is shown in Table 3 below.

[0065] Table 3

[0066] The comparison of shallow soil carbonate content in Table 3 shows that xanthan gum not only increases the total calcium carbonate content but also makes its distribution more uniform along depth. This is because xanthan gum has high viscosity and adsorption properties, which can retain the cementing liquid around the sand particles, slowing down infiltration and allowing for a more complete reaction.

[0067] Furthermore, after eight spraying treatments, the calcium carbonate content at a depth of 20 mm in Examples 1-3 and Comparative Examples 1-4 is shown in Table 4 below.

[0068] Table 4

[0069] As shown in Table 4, After eight spraying treatments, the calcium carbonate content at a depth of 20 mm in Examples 1-3 was higher than that in the comparative examples. Specifically, Example 1 (2.11%) showed an increase of approximately 137% compared to Comparative Example 1 (0.89%), and approximately 43.5% compared to Comparative Example 2 (1.47%). The calcium carbonate content at a depth of 20 mm in Comparative Example 3 (0.5 h) and Comparative Example 4 (4 h) was 1.65% and 1.57%, respectively, both lower than that in Example 1. This indicates that both excessively short and excessively long settling times are detrimental to the uniform deposition of deep calcium carbonate, and the 1.5-2.5 h settling infiltration time window is critical. This demonstrates that the present invention, through the synergistic effect of non-premixed staged spraying, xanthan gum rheological regulation, and the settling time window, can significantly increase the calcium carbonate content in the shallow soil layer (20 mm depth), and this effect is not a simple superposition of a single factor.

[0070] (iii) Saturated permeability coefficient A lower permeability coefficient indicates more complete pore sealing. The permeability coefficient of untreated soil is approximately 3.7 × 10⁻⁶. -2 cm / s; the permeability coefficient of both Example 1 and Comparative Example 2 decreased with increasing spraying frequency, with Example 1's EICP-XG consistently showing a lower coefficient. After eight spraying treatments, Comparative Example 2 and Example 1 showed reductions of approximately 60% and 74% compared to untreated soil, respectively. This is attributed to xanthan gum dehydrating to form a film, filling pores, and synergistically sealing pore throats with calcium carbonate, thus cutting off infiltration channels and significantly improving anti-infiltration performance.

[0071] In summary, this invention addresses the bottlenecks of existing EICP technology, such as uncontrollable calcium carbonate deposition location and poor shallow reinforcement effects due to premixed spraying. It proposes a non-premixed spraying reinforcement method for low-cohesion soil surfaces based on urease phase rheological regulation. Through calcium sulfate salting-out for impurity removal, the addition of xanthan gum to the urease phase and its high viscosity to regulate infiltration timing, and the staged non-premixed spraying of the first and second treatment solutions, uniform and dense deposition of calcium carbonate within a 2-8 cm depth range on the soil surface is achieved. Experimental data show that after eight spraying treatments, the surface penetration strength of this invention is approximately 24% higher than conventional EICP, the calcium carbonate content at a depth of 20 mm is increased by approximately 43.5%, and the saturated permeability coefficient is reduced by approximately 74% compared to untreated soil, demonstrating both excellent reinforcement effect and anti-infiltration performance. This method is simple and low-cost, and has broad application prospects in arid and semi-arid regions for windbreak and sand fixation, roadbed slope protection, and canal slope seepage prevention and erosion control.

[0072] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for non-premixed spraying reinforcement of low-cohesion soil surface based on urease phase rheology regulation, characterized in that, Includes the following steps: S1. Purify the crude plant-derived urease solution using calcium sulfate dihydrate to obtain a purified urease solution. S2. Add xanthan gum to the purified urease solution and dissolve it to obtain a first treatment solution with a xanthan gum concentration of 0.3-0.8 g / L; S3. Mix the calcium chloride solution and the urea solution to obtain the second treatment solution; S4. Spray the first treatment solution evenly onto the soil surface and let it stand for 1.5-2.5 hours to allow it to seep in, thus obtaining soil with a pre-contained urease phase. S5. The second treatment liquid is evenly sprayed onto the soil surface with the pre-placed urease phase, so that the first treatment liquid and the second treatment liquid only come into contact and react within the soil pores to generate calcium carbonate and form a calcium carbonate-xanthan gum composite reinforcement layer together with xanthan gum. S6. Repeat steps S4 and S5 multiple times to gradually thicken the calcium carbonate-xanthan gum composite reinforcement layer, resulting in solidified soil.

2. The method according to claim 1, characterized in that, In step S1, the plant-derived crude urease solution is obtained by extraction from one or more of soybeans, sword beans, chickpeas, watermelon seeds, or mulberry leaves.

3. The method according to claim 1, characterized in that, In step S1, the amount of calcium sulfate dihydrate added is 8%-12% of the mass of the plant-derived crude urease solution.

4. The method according to claim 1, characterized in that, In step S1, the plant-derived crude urease solution is a soybean crude urease solution; the extraction method of soybean crude urease solution includes: drying and pulverizing soybeans, sieving to obtain soybean powder; preparing a soybean powder solution with a concentration of 50-100 g / L using deionized water, centrifuging and filtering, and the resulting supernatant is the soybean crude urease solution.

5. The method according to claim 1, characterized in that, In step S2, the apparent viscosity of the first treatment solution at 25 °C is 1.5-5 times that of the purified urease solution.

6. The method according to claim 1, characterized in that, In step S3, the concentration of calcium chloride in the second treatment solution is 0.8-1.2 mol / L, and the molar ratio of calcium chloride to urea is 1:

1.

7. The method according to claim 1, characterized in that, The spraying rate of the first treatment liquid in step S4 and the spraying rate of the second treatment liquid in step S5 are both 2-3 L / m³. 2 .

8. The method according to claim 1, characterized in that, In step S6, repeat steps S4 and S5 2-8 times, with an interval of 18-32 hours between two adjacent spray cycles.

9. The application of the method according to any one of claims 1-8 in windbreak and sand fixation of sandy or silty soil surface in arid and semi-arid regions.

10. The application of a method according to any one of claims 1-8 in the seepage prevention and erosion protection of roadbed slopes, canal slopes or exposed slope surfaces.

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