A method for sand reinforcement that couples salting out urease with time-controlled grouting

Abstract

This invention relates to a method for reinforcing sandy soil by coupling salting-out optimized urease with time-controlled grouting. First, a urease solution and a cementing solution are prepared and stored separately. Then, an EICP solidification solution is injected into the sandy soil to be reinforced in batches. The EICP solidification solution is a mixture of the urease solution and the cementing solution, and the urease solution and cementing solution for each batch are mixed only before each batch is injected, until all batches of EICP solidification solution have been injected. Multiple rounds of grouting are then completed. Finally, static curing is performed. This invention applies the coupling of salting-out optimized urease and time-controlled grouting to the erosion-resistant reinforcement of poorly graded sandy soil. By coupling salting-out optimized and time-controlled grouting, the grouting method achieves coordinated control between the EICP reaction rate and deep penetration capacity, effectively reducing premature mineralization of calcium carbonate during transport, increasing the penetration depth and precipitation uniformity of the solidification solution within the soil, thereby enhancing the resistance of poorly graded sandy soil to internal erosion.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering, biomineralization reinforcement and soil erosion protection, specifically to a sand reinforcement method that couples salt precipitation-optimized urease with time-controlled grouting. Background Technology

[0002] Sand, as an important filling material, is widely used in civil engineering fields such as roadbeds, slopes, river embankments, coastal protection, and foundation treatment. However, sand particles lack effective bonding and have a loose structure. Under external forces such as natural rainfall erosion, surface runoff, seepage, and waves, fine particles are easily lost, forming poorly graded sand. Such sand has high porosity, weak interparticle cohesion, and a loose structure, resulting in significantly reduced erosion resistance. In severe cases, it can lead to engineering safety problems such as slope instability, foundation settlement, and dam failure.

[0003] To improve the erosion resistance of poorly graded sandy soils, microbial-induced calcium carbonate precipitation (MICP) and urease-induced calcium carbonate precipitation (EICP) technologies have become research hotspots in recent years. MICP technology utilizes urease secreted by microorganisms to catalyze the hydrolysis of urea, depositing calcium carbonate between soil particles to achieve particle cementation and thus enhance soil structure. EICP technology directly uses plant-derived urease instead of microbial urease, rapidly inducing calcium carbonate precipitation between soil particles without relying on living microorganisms.

[0004] Compared to traditional reinforcement methods such as cement and chemical grouting, MICP and EICP technologies demonstrate multiple advantages in improving poorly graded sandy soils, including being environmentally friendly, possessing superior mechanical properties, and exhibiting strong process adaptability. In terms of environmental friendliness, the energy consumption and carbon emissions of this technology are far lower than those of traditional cement. Regarding mechanical properties, the unconfined compressive strength of microbially reinforced sandy soil is significantly higher than that of cement-stabilized soil under the same curing conditions, while also drastically reducing the permeability coefficient, effectively resisting water erosion and earthquake liquefaction. In terms of process, the mineralized solution has good fluidity, allowing it to penetrate uniformly into the micropores of the sandy soil. The construction process essentially does not disturb the original structure. In terms of reinforcement mechanism, the generated calcium carbonate crystals form micron-level "bridges" and mechanical interlocks between particles, achieving biomimetic cementation. Furthermore, the raw material costs are relatively low, and the reaction rate is controllable, providing an efficient and sustainable reinforcement path for loose sandy soil structures.

[0005] However, while MICP technology possesses the aforementioned advantages, it also has significant limitations in practical engineering applications: the microbial culture process is complex, microbial activity is easily affected by environmental conditions such as temperature and pH, and there are potential risks to the long-term ecological safety of microorganisms in soil, limiting its widespread application in large-scale soil reinforcement and slope protection projects. In contrast, EICP technology directly uses plant-derived urease to replace microbial urease, rapidly inducing calcium carbonate precipitation between soil particles without relying on living microorganisms. This method is simple to operate, has high reaction efficiency, and does not pose any microbial-related ecological safety risks, making it particularly suitable for sensitive areas. Furthermore, EICP is highly tolerant to environmental conditions such as pH and temperature, can operate stably under a wide range of environmental conditions, and can achieve effective cementation of sand particles without disturbing the original soil structure. Some studies have already improved the construction process of EICP technology. For example, patent application CN118894680A discloses a two-stage sand-fixing method based on soybean urease-induced calcium carbonate deposition. First, the soil is solidified using traditional EICP and then roughened. Then, soybean urease solution, calcium chloride solution, and urea solution are sequentially injected for secondary reinforcement. This method improves the solidification strength of the sand to some extent, but it still has the following shortcomings: the secondary injection process is complex and the construction period is long; the roughening treatment after the initial solidification may damage the already formed soil structure; and it fails to effectively solve the problem of pipeline blockage caused by premature mineralization when urease is mixed with the cementing solution. Another patent, CN119145397B, discloses a method for solidifying sand by urease-induced calcium carbonate precipitation. Urease-containing plant seeds are crushed, mixed with sand, and then cementing solution is injected. This method simplifies the process, but has obvious drawbacks: it is difficult to ensure the uniform distribution of urease powder in the soil when it is dry mixed with sand, and the reaction is rapid after the cementing liquid is injected, which can quickly form a dense calcium carbonate layer on the surface of the soil, hindering the subsequent cementing liquid from penetrating deeper, resulting in uneven solidification and limited overall reinforcement effect.

[0006] In summary, existing EICP technology generally suffers from the following problems in actual grouting processes: (1) The reaction rate is faster when urease solution is mixed with cementing solution, and calcium carbonate is more likely to be mineralized prematurely during transportation; (2) Pre-formed calcium carbonate can easily clog grouting pipes and surface pores of soil, affecting subsequent grout penetration; (3) When using traditional grouting methods, EICP curing liquid is difficult to fully penetrate into the deep soil area, resulting in uneven spatial distribution of calcium carbonate precipitation and difficulty in ensuring the overall anti-erosion effect.

[0007] Especially for poorly graded sandy soil, its internal pore structure is complex and fine particles are sensitive to migration, making it more prone to uneven reinforcement due to local blockage and difficult to effectively control internal erosion.

[0008] Therefore, there is an urgent need to develop a method for reinforcing poorly graded sandy soil that can reduce the risk of premature mineralization of EICP, improve the uniformity of calcium carbonate precipitation and deep permeability. Summary of the Invention

[0009] The purpose of this invention is to address the problems of premature mineralization, pore blockage, and uneven reinforcement in existing EICP technologies by providing a sand reinforcement method that couples salt-out optimized urease with time-controlled grouting. This method can also be called an anti-erosion reinforcement method for poorly graded sand based on salt-out optimized urease and time-controlled grouting.

[0010] This invention is the first to apply the coupling of salt-out optimization of urease and time-controlled grouting to the erosion-resistant reinforcement process of poorly graded sand. By coupling the salt-out optimization and time-controlled grouting, the grouting method achieves coordinated control between the EICP reaction rate and deep penetration capacity, effectively reducing the premature mineralization of calcium carbonate during transport, improving the penetration depth and precipitation uniformity of the solidification liquid in the soil, thereby enhancing the internal erosion resistance of poorly graded sand.

[0011] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for reinforcing sandy soil by coupling salting-out optimized urease with time-controlled grouting, comprising the following steps: (1) Prepare urease solution and cementation solution, and store them separately; (2) The EICP curing liquid is injected into the sand to be reinforced in batches. The EICP curing liquid is a mixture of urease solution and cementing solution. The urease solution and cementing solution of each batch are mixed before each batch of EICP curing liquid is injected until all batches of EICP curing liquid are injected. (3) Repeat step (2) to complete multiple rounds of grouting; (4) Allow to stand and solidify to complete the reinforcement.

[0012] In one embodiment of the present invention, the urease solution is a plant-derived urease extract.

[0013] More preferably, the plant-derived urease extract is a soybean urease extract.

[0014] More preferably, the urease solution is a urease solution that has undergone salting-out optimization treatment.

[0015] In one embodiment of the present invention, the salting-out optimization treatment includes: adding chloride salt to the crude urease extract solution for salting out, and obtaining the salting-out optimized urease solution after standing and centrifugation.

[0016] In one embodiment of the present invention, the specific preparation method of the salting-out optimized urease solution is as follows: Dry soybeans are pulverized using a grinder and passed through a sieve with a certain aperture to obtain soybean flour. The soybean flour is mixed with deionized water and stirred using a magnetic stirrer to prepare a soybean flour suspension of a certain concentration. A certain concentration of calcium chloride is added to the soybean flour suspension for salting out, and the mixture is stirred using a magnetic stirrer. After the stirred soybean flour suspension has been allowed to stand for a certain period of time, the supernatant is collected and centrifuged to obtain the salting-out optimized urease solution.

[0017] In one embodiment of the present invention, in the specific preparation of the salting-out optimized urease solution, at least one or more of the following conditions are selected: 1) The sieve used is a 100-mesh sieve; 2) The mixing time for the magnetic stirrer is 20-30 min (preferably 30 min); 3) The concentration of soybean flour suspension is 20-100 g / L (preferably 50-70 g / L). 4) The concentration of calcium chloride used for salting out is 0.002-0.01 mol / L (preferably 0.005-0.007 mol / L). 5) The settling time is 1 hour; 6) The centrifugation speed is 3000-4000 rpm (preferably 3500 rpm), and the centrifugation time is 8-15 min (preferably 15 min).

[0018] In one embodiment of the present invention, the cementing solution is an aqueous solution containing urea and calcium ions.

[0019] In one embodiment of the present invention, the cementing solution is prepared by mixing calcium chloride solution and urea solution in a volume ratio of 1:1, wherein the concentrations of the calcium chloride solution and urea solution are each independently 0.5–1.5 mol / L. Preferably, the cementing solution is prepared by mixing calcium chloride solution and urea solution in a volume ratio of 1:1, wherein the concentrations of both the calcium chloride solution and urea solution are 1.0 mol / L.

[0020] In one embodiment of the present invention, the EICP curing solution is a mixture of a urease solution and a bonding solution in a volume ratio of 1:1.

[0021] In one embodiment of the present invention, during a round of batch grouting, the EICP curing liquid is injected in 3 to 5 batches.

[0022] In one embodiment of the present invention, the volume of the urease solution taken is 0.5-1.0 times the total pore volume of the poorly graded sand to be reinforced.

[0023] In one embodiment of the present invention, the injection time for a single batch of EICP curing solution does not exceed 10 minutes. This ensures that the injection time for a single batch of EICP curing solution is less than its initial significant sedimentation time, thereby reducing pore blockage caused by premature mineralization of calcium carbonate.

[0024] In one embodiment of the present invention, the number of cyclic grouting cycles is 1 to 4.

[0025] In one embodiment of the present invention, the curing time is 24 hours.

[0026] In this application, the time-controlled grouting method refers to the time-series control of the batch equal-division, immediate mixing, time-limited rapid injection and cyclic curing process of urease solution and cementing solution.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a reinforcement method that combines salting out optimized urease with time-controlled grouting, which can effectively reduce the problem of premature mineralization of calcium carbonate during the EICP reaction process; (2) The present invention can reduce the phenomenon of surface pore blockage and increase the penetration depth of the curing liquid in poorly graded sand. (3) The present invention can improve the spatial distribution uniformity of calcium carbonate precipitation in soil, so that a continuous bridging cement structure is formed inside the sandy soil; (4) Through multiple rounds of cyclic grouting, the internal erosion and seepage of poorly graded sand can be significantly reduced, thereby improving the resistance to internal erosion. (5) This invention improves the stability of plant-derived urease through salting-out optimization treatment, without the need for microbial culture process, is simple to construct, and has high ecological safety; (6) This invention is applicable to slope protection, river management, coastal protection, dam seepage prevention and roadbed engineering, and has good engineering application prospects. Attached Figure Description

[0028] Figure 1 This is a flowchart of the grouting reinforcement method of the present invention; Figure 2 This is a schematic diagram of the apparatus for conducting internal erosion tests in an embodiment of the present invention; Figure 3 The relationship between the grouting reinforcement method of this invention and the erosion resistance of poorly graded sandy soil and urease concentration; Figure 4 This invention relates the grouting reinforcement method to the relationship between the erosion resistance of poorly graded sand and the concentration of the cementing solution. Figure 5 This invention relates the grouting reinforcement method to the relationship between improving the erosion resistance of poorly graded sandy soil and the number of reinforcement cycles. Figure 6This invention illustrates the impact of the grouting reinforcement method of this invention on the cumulative seepage flow of sandy soil compared to the traditional single-phase grouting method. Figure 7 This invention illustrates the impact of the grouting reinforcement method of this invention on the cumulative erosion of sandy soil compared to the traditional single-phase grouting method. Figure 8 This is a comparison of the uniformity of calcium carbonate produced by the grouting reinforcement method of the present invention and the traditional single-phase grouting method. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are used to illustrate the reinforcement effect of the grouting reinforcement method of the present invention on poorly graded sand, but should not be construed as limiting the scope of protection of the present invention. Without departing from the concept of the present invention, those skilled in the art can adjust the parameters according to the soil sample particle size distribution, porosity, number of treatments, and target reinforcement degree.

[0030] Example 1: This embodiment provides a method for erosion-resistant reinforcement of poorly graded sand based on salting-out optimized urease and time-controlled grouting, referencing... Figure 1 Specifically, it includes the following steps: Step 1: Place the poorly graded sandy soil sample taken from Xiamen into an oven and dry it at 40℃ for 24 hours; Step 2: Based on a dry density of 1.8 g / cm³ 3 Weigh a certain mass of the poorly graded dry sand dried in step 1, and add deionized water to make wet sand with a moisture content of 10%. Step 3: The wet sand prepared in Step 2 is compacted in 5 layers, and the layers are roughened to obtain the sand column sample to be reinforced. Step 4: Take 50 mL of the optimized soybean urease solution after salting out, and divide the urease solution into 5 equal portions; Step 5: Take 50 mL of the cementing solution and divide it into 5 equal portions; Step 6: Take one part of the urease solution prepared in step 4 and one part of the cementing solution prepared in step 5, mix them to prepare one part of EICP curing liquid, and use a water pump to grout the sand column sample prepared in step 3 at a grouting rate of 6 mL / min. Step 7: Repeat step 6 until all five portions of curing liquid have been injected. Let the sand column sample stand for 24 hours to cure. After 24 hours of curing, one cycle of grouting is completed. Step 8: Repeat steps 4-7 until two cycles of grouting are completed; Step 9: Use an industrial-grade micro water pump to apply a constant water head pressure of 20 kPa to conduct an internal erosion test on the sand column. The scouring time is 60 min, during which data such as seepage flow and erosion volume are recorded.

[0031] In step 1, the non-uniformity coefficient of the poorly graded sandy soil sample is 12.3, and the curvature coefficient is 0.39.

[0032] In step 4, the preparation of the urease solution and the salting-out optimization method are as follows: Dry soybeans were pulverized using a grinder and passed through a 100-mesh sieve to obtain soybean flour. The soybean flour was mixed with deionized water and stirred with a magnetic stirrer for 30 min to prepare a soybean flour suspension with a concentration of 20 g / L. After the soybean flour suspension was allowed to stand for 1 h, the supernatant was collected, which was the crude urease extraction solution. Calcium chloride was added to the crude urease extraction solution at a concentration of 0.002 mol / L, and the mixture was stirred with a magnetic stirrer for 30 min. Subsequently, the mixture was centrifuged at 3500 rpm for 15 min to obtain the salting-out optimized soybean urease solution.

[0033] In step 5, the cementing solution is prepared by mixing calcium chloride solution and urea solution in a volume ratio of 1:1, and the concentrations of calcium chloride and urea are both 1 mol / L.

[0034] In step 9, the apparatus for conducting the internal erosion test is as follows: Figure 2 As shown, the sample tube 1 is in the middle. A top cover 2 is connected above the sample tube 1, and a bottom cover 3 is connected below the sample tube 1. A water pump 4 is connected to the top cover 3 through a pipeline. A pressure gauge 5 is connected to the upper space of the sample tube 1. Two porous plates 6 are set inside the sample tube 1. An EICP-reinforced sand column sample 7 is formed between the two porous plates 6. The pressure gauge 5 is connected to the top of the upper porous plate 6. A collection hopper 8 is set below the bottom cover 3.

[0035] Example 2: Compared with Example 1, the difference is that in step 4, the urease concentration is 60 g / L and the calcium chloride concentration used for salting out is 0.006 mol / L.

[0036] Example 3: Compared with Example 1, the difference is that in step 4, the urease concentration is 100 g / L and the calcium chloride concentration used for salting out is 0.01 mol / L.

[0037] Example 4: Compared with Example 2, the difference is that in step 5, the concentrations of calcium chloride solution and urea solution are 0.5 mol / L.

[0038] Example 5: Compared with Example 2, the difference is that in step 5, the concentrations of calcium chloride solution and urea solution are 1.5 mol / L.

[0039] Example 6: Compared with Example 2, the difference lies in step 8, which continues until one grouting reinforcement is completed.

[0040] Example 7: Compared with Example 2, the difference lies in step 8, which continues until three grouting reinforcements are completed.

[0041] Example 8: Compared with Example 2, the difference lies in step 8, which continues until four grouting reinforcements are completed.

[0042] Comparative Example 1: Compared with Example 2, the difference is that the urease solution in step 4 is replaced with the same volume of deionized water.

[0043] Comparative Example 2: Compared with Example 2, the difference is that the calcium chloride solution and urea solution in step 5 are replaced with the same volume of deionized water.

[0044] Comparative Example 3: Compared to Example 6, the difference is that the number of reinforcements is 0.

[0045] Comparative Example 4: The conventional EICP single-phase grouting method includes the following steps: Step 1: Place the poorly graded sandy soil sample taken from Xiamen into an oven and dry it at 40℃ for 24 hours; Step 2: Based on a dry density of 1.8 g / cm³ 3 Weigh a certain mass of the poorly graded dry sand dried in step 1, and add deionized water to make wet sand with a moisture content of 10%. Step 3: The wet sand obtained in Step 2 is compacted in 5 layers, and the layers are roughened to obtain the sand column sample to be reinforced. Step 4: Take 50 mL of soybean urease solution and 50 mL of cementing solution, mix them together to prepare EICP curing solution; Step 6: Use a water pump to grout the sand column sample obtained in Step 3 at a grouting rate of 1 mL / min. Step 7: After the curing liquid completes the grouting, let the sand column sample stand for 24 hours to cure. Once the curing is complete, one grouting is finished. Step 8: Repeat steps 4-7 until the required number of grouting operations are completed; Step 9: Use an industrial-grade micro water pump to apply a constant water head pressure of 20 kPa to conduct an internal erosion test on the sand column. The scouring time is 60 min, during which data such as seepage flow and erosion volume are recorded.

[0046] In step 1, the non-uniformity coefficient of the poorly graded sandy soil sample is 12.3, and the curvature coefficient is 0.39.

[0047] In step 4, the urease solution is prepared as follows: Dry soybeans were pulverized using a grinder and passed through a 100-mesh sieve to obtain soybean flour. The soybean flour was mixed with deionized water and stirred with a magnetic stirrer for 30 min to prepare a soybean flour suspension with a concentration of 20 g / L. After the soybean flour suspension was allowed to stand for 1 h, the supernatant was taken, which was the crude urease solution. The crude urease solution was then centrifuged at 3500 rpm for 10 min to obtain soybean urease solution.

[0048] In step 4, the cementing solution is prepared by mixing calcium chloride solution and urea solution in a volume ratio of 1:1, and the concentrations of calcium chloride and urea are both 1 mol / L.

[0049] Comparative Example 5: Compared to Comparative Example 4, the difference is that the reinforcement was performed twice.

[0050] Comparative Example 6: Compared to Comparative Example 4, the difference is that the reinforcement was performed 3 times.

[0051] Comparative Example 7: Compared to Comparative Example 4, the difference is that the reinforcement was performed 4 times.

[0052] The specific differences between the different embodiments of the present invention and the comparative examples of the erosion-resistant reinforcement methods for poorly graded sand are shown in Table 1. The seepage flow, erosion amount and other data of the different embodiments and comparative examples of the erosion-resistant reinforcement methods for poorly graded sand are detailed in Table 1.

[0053] Table 1: EICP Grouting Reinforcement Scheme Plan Example 1 T1 20 1.0 1.0 2 6 69019.83 153.92 Example 2 T2 60 1.0 1.0 2 6 23924.78 81.39 Example 3 T3 100 1.0 1.0 2 6 17139.07 68.31 Example 4 T4 60 0.5 0.5 2 6 52641.67 102.34 Example 5 T5 60 1.5 1.5 2 6 41579.04 94.75 Example 6 T6 60 1.0 1.0 1 6 49468.71 121.64 Example 7 T7 60 1.0 1.0 3 6 3227.19 0.96 Example 8 T8 60 1.0 1.0 4 6 2144.2 0.57 Comparative Example 1 T9 0 1.0 1.0 2 6 134069.19 231.36 Comparative Example 2 T10 60 0 0 2 6 133518.33 229.67 Comparative Example 3 T11 60 1.0 1.0 0 6 132671.42 234.18 Comparative Example 4 T12 60 1.0 1.0 1 1 104450.57 173.44 Comparative Example 5 T13 60 1.0 1.0 2 1 47111.01 102.33 Comparative Example 6 T14 60 1.0 1.0 3 1 4847.8 7.07 Comparative Example 7 T15 60 1.0 1.0 4 1 2895.8 1.63 The calcium carbonate content of Examples 2, 8, 5, and 7 was also tested. The specific steps for testing the calcium carbonate content are as follows: Step 1: After the sand column test is cured, take a certain mass of sand from the top, middle and bottom of the sand column and bake it in an oven for 24 hours at a temperature of 105℃. Step 2: Place the dried sand into a test tube, acid wash it with 1 mol / L excess dilute sulfuric acid and stir until no bubbles are generated, then wash the sand with deionized water. Step 3: Place the cleaned sand back into the oven and bake for 24 hours at 105℃; Step 4: The formula for calculating calcium carbonate content (CCC) is shown in equation (1): (1) In formula (1): m1——mass of sand dried before pickling; m2——mass of sand dried after pickling.

[0054] The results of the calcium carbonate content distribution measured in the experiment are shown in Table 2.

[0055] Table 2: Distribution of Calcium Carbonate Example 2 T2 2 Coupled grouting method with salt precipitation optimization and time-series control 2.73 3.25 3.47 9.45 Example 8 T8 4 Coupled grouting method with salt precipitation optimization and time-series control 5.42 6.48 6.04 17.94 Comparative Example 5 T13 2 Traditional single-phase grouting method 5.14 3.71 1.47 10.32 Comparative Example 7 T15 4 Traditional single-phase grouting method 11.86 5.15 2.01 19.02 The results of the internal erosion test and the calcium carbonate content test were analyzed: Figure 3 This study investigates the relationship between the grouting reinforcement method of this invention and the erosion resistance of poorly graded sandy soil, and the concentration of urease. Figure 3 The experimental results show that, compared with Comparative Example 1, after EICP reinforcement treatment, the seepage flow of Examples 1, 2, and 3 decreased by 48.52%, 82.15%, and 87.22%, respectively, and the erosion amount decreased by 33.84%, 65.02%, and 70.47%, respectively. Specifically, from Example 1 to Example 2, increasing the urease concentration from 20 g / L to 60 g / L reduced the erosion amount from 153.92 g to 81.39 g, a decrease of 47.12%; when the urease concentration was further increased to 100 g / L in Example 3, the erosion amount only decreased by a further 5.45%. This indicates that the improvement slows down after 60 g / L, and higher urease concentrations offer limited improvement in anti-erosion performance, resulting in resource waste.

[0056] Figure 4 This study investigates the relationship between the grouting reinforcement method of this invention and the concentration of the cementing solution in improving the erosion resistance of poorly graded sand. Figure 4 The experimental results show that the erosion amounts in Examples 4, 2, and 5 were 102.34, 81.39, and 94.75 g, respectively, representing reductions of 55.44%, 64.56%, and 58.75% compared to Comparative Example 2; the seepage rates were reduced by 60.57%, 82.08%, and 68.86%, respectively. Among these, Example 2, with a cementing solution concentration of 1.0 mol / L, showed the best treatment effect, with an erosion amount reduced by 20.47% compared to the 0.5 mol / L cementing solution concentration in Example 4, and by 14.10% compared to the 1.5 mol / L cementing solution concentration in Example 5. This indicates that too low a cementing solution concentration results in insufficient calcium carbonate formation, while too high a concentration may inhibit urease activity; 1.0 mol / L is the optimal concentration.

[0057] Figure 5 This study investigates the relationship between the grouting reinforcement method of this invention and the number of grouting cycles in improving the erosion resistance of poorly graded sand. Figure 5The experimental results show that the curing effect increases with the number of curing cycles, but the improvement slows down after a certain number of curing cycles. Examples 6, 2, 7, and 8 underwent EICP reinforcement 1, 2, 3, and 4 times respectively, with erosion amounts of 121.64, 81.39, 0.96, and 0.57 g, respectively, representing reductions of 48.06%, 65.24%, 99.59%, and 99.76% compared to Comparative Example 3; seepage rates also decreased by 62.71%, 81.97%, 97.57%, and 98.38%, respectively. From two reinforcement cycles in Example 2 to three reinforcement cycles in Example 7, the erosion amount plummeted from 81.39 g to 0.96 g, a reduction of 98.82%, indicating that internal erosion of the sand was basically controlled after three EICP reinforcement cycles. Continuing to increase to four EICP reinforcement cycles, the erosion amount only decreased further by 0.39 g, showing a limited improvement.

[0058] Figure 6 , Figure 7 This study investigates the effects of the salt precipitation optimization and time-series control coupled grouting method of this invention, compared with the traditional single-phase grouting method, on the seepage flow and erosion of sandy soil under different reinforcement cycles. Figure 6 It can be seen that, under reinforcement conditions 1, 2, 3, and 4, the cumulative seepage flow rate corresponding to the method of the present invention is lower than that of the traditional single-phase grouting method, decreasing from 104450.57, 47111.01, 4847.80, and 2895.80 mL to 49468.71, 23924.78, 3227.19, and 2144.20 mL, respectively, with reductions of 52.64%, 49.22%, 33.43%, and 25.95%. Figure 7 It can be seen that the cumulative erosion amount of the method of the present invention is significantly lower than that of the traditional single-phase grouting method at each reinforcement stage. When reinforcement is carried out 1, 2, 3, and 4 times, the erosion amount decreases from 173.44, 102.33, 7.07, and 1.63 g to 121.64, 81.39, 0.96, and 0.57 g, respectively, with reductions of 29.87%, 20.46%, 86.42%, and 65.03%. In particular, after 3 reinforcements, the erosion amount of the method of the present invention drops to 0.96 g, indicating that the loss of fine particles inside the sand is basically controlled.

[0059] Figure 8 This study investigated the distribution of calcium carbonate at the top, middle, and bottom of a sand column under different grouting methods. Figure 8 It can be seen that in the T2 and T8 samples corresponding to the method of the present invention, the calcium carbonate content is relatively evenly distributed between the top, middle and bottom; while in the T13 and T15 samples corresponding to the traditional single-phase grouting method, the calcium carbonate is mainly concentrated at the top of the sample, and the content at the bottom is significantly lower.

[0060] Based on the comprehensive analysis of the experimental data from Examples 1-8 and Comparative Examples 1-7, the optimal parameter combination for the salt precipitation optimization and time-series control coupled grouting method proposed in this invention, which balances reinforcement performance and resource utilization efficiency, is as follows: urease concentration 60 g / L, cementing solution (calcium chloride + urea) 1.0 mol / L each, 3 cycles of cyclic grouting, and grouting rate 6 mL / min (corresponding to Example 7). Under these conditions, the erosion of the sand column is as low as 0.96 g, which is 99.59% lower than the unreinforced group and 86.42% lower than the traditional single-phase grouting group with 3 cycles. The seepage flow is reduced by 97.57%, and the calcium carbonate precipitation is evenly distributed inside the sand column, avoiding the problems of surface blockage and insufficient deep reinforcement. Compared to two reinforcements, three reinforcements resulted in a sharp 98.82% reduction in erosion. While the erosion was slightly higher (0.39 g) compared to four reinforcements, it saved 25% on the number of grouting sessions and corresponding material consumption. Further increasing the urease concentration to 100 g / L or the cementing solution concentration to 1.5 mol / L offered limited performance improvement but significantly increased costs. Therefore, this optimal combination achieves over 99% internal erosion control while maintaining the best economic balance between material consumption, construction time, and reinforcement effect, making it suitable for engineering scenarios with high erosion resistance requirements and cost control needs. Overall, after reinforcement using the method of this invention, both the seepage flow and erosion of the sand decreased significantly. Under conditions such as four reinforcements (Example 8), the erosion could be reduced by up to 99.76%, and the seepage flow by up to 98.38%. Under the same conditions, the method of this invention improved the erosion resistance by up to 86.42% compared to the traditional single-phase grouting method, indicating that this method can improve the erosion resistance of poorly graded sand more effectively and quickly, and control internal erosion problems promptly and efficiently. In addition, during the traditional single-phase grouting process, the curing liquid is prone to premature mineralization in the early stage of entering the sand, resulting in surface precipitation enrichment and insufficient deep reinforcement. However, the method of the present invention can suppress premature precipitation and surface blockage at the inlet through salting-out optimization and timing control, improve the deep penetration ability of the curing liquid, and make calcium carbonate precipitate in the sand to form a more uniform cement structure, thereby further improving the overall anti-erosion reinforcement effect.

[0061] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for reinforcing sandy soil by coupling salting-out optimized urease with time-controlled grouting, characterized in that, Includes the following steps: (1) Prepare urease solution and cementation solution, and store them separately; (2) The EICP curing liquid is injected into the sand to be reinforced in batches. The EICP curing liquid is a mixture of urease solution and cementing solution. The urease solution and cementing solution of each batch are mixed before each batch of EICP curing liquid is injected until all batches of EICP curing liquid are injected. (3) Repeat step (2) to complete multiple rounds of grouting; (4) Allow to stand and solidify to complete the reinforcement.

2. The method for sand reinforcement coupled with salting-out optimized urease and time-controlled grouting according to claim 1, characterized in that, The urease solution is a plant-derived urease extract; Preferably, the plant-derived urease extract is a soybean urease extract; More preferably, the urease solution is a urease solution that has undergone salting-out optimization treatment.

3. The method for sand reinforcement coupled with salting-out optimized urease and time-controlled grouting according to claim 2, characterized in that, The specific preparation method of the salting-out optimized urease solution is as follows: Dry soybeans are pulverized using a grinder and passed through a sieve with a certain aperture to obtain soybean flour. The soybean flour is mixed with deionized water and stirred using a magnetic stirrer to prepare a soybean flour suspension of a certain concentration. A certain concentration of calcium chloride is added to the soybean flour suspension for salting out, and the mixture is stirred using a magnetic stirrer. After the stirred soybean flour suspension has been allowed to stand for a certain period of time, the supernatant is collected and centrifuged to obtain the salting out optimized urease solution. Preferably, in the specific preparation of the salting-out optimized urease solution, at least one or more of the following conditions are selected: 1) The sieve used is a 100-mesh sieve; 2) The mixing time for the magnetic stirrer is 20-30 minutes; 3) The concentration of soybean flour suspension is 20-100 g / L; 4) The concentration of calcium chloride used for salting out is 0.002-0.01 mol / L; 5) The settling time is 1 hour; 6) The centrifugation speed is 3000-4000 rpm and the centrifugation time is 8-15 min.

4. The method for sand reinforcement coupled with salting-out optimized urease and time-controlled grouting according to claim 1, characterized in that, The cementing solution is an aqueous solution containing urea and calcium ions; Preferably, the cementing solution is prepared by mixing calcium chloride solution and urea solution in a volume ratio of 1:1, and the concentrations of the calcium chloride solution and urea solution are each independently 0.5 to 1.5 mol / L.

5. The method for sand reinforcement coupled with salting-out optimized urease and time-controlled grouting according to claim 1, characterized in that, The EICP curing solution is a mixture of urease solution and cementing solution in a volume ratio of 1:

1.

6. The method for sand reinforcement coupled with salting-out optimized urease and time-controlled grouting according to claim 1, characterized in that, During a round of grouting, the EICP curing liquid is injected in 3 to 5 batches.

7. The method for sand reinforcement coupled with salting-out optimized urease and time-controlled grouting according to claim 1, characterized in that, The volume of the urease solution taken should be 0.5-1.0 times the total pore volume of the poorly graded sand to be reinforced.

8. The method for sand reinforcement according to claim 1, which couples salting out optimized urease with time-controlled grouting, is characterized in that, The injection time for a single batch of EICP curing solution should not exceed 10 minutes.

9. The method for sand reinforcement coupled with salting-out optimized urease and time-controlled grouting according to claim 1, characterized in that, The number of grouting cycles is 1 to 4.

10. The method for sand reinforcement according to claim 1, which couples salting out optimized urease with time-controlled grouting, is characterized in that, The curing time is 24 hours.

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