Method for comprehensively solidifying granite residual soil through microorganisms and jute fibers

Abstract

The invention relates to the technical field of environmental geotechnical engineering, and particularly discloses a method for comprehensively solidifying granite residual soil through microorganisms and jute fibers, and the method for comprehensively solidifying the granite residual soil through the microorganisms and the jute fibers comprises the following steps: (1) uniformly doping modified jute fibers into the granite residual soil, and performing compaction treatment to obtain a densified granite residual soil body; forming a fiber-soil body framework; (2) firstly injecting a compound bacteria solution into the fiber-soil body skeleton, and then injecting a cementing solution to obtain a preliminarily solidified soil body; and (3) maintaining the preliminarily solidified soil body, triggering automatic slurry supplementing when the resistivity is greater than 150 omega.m, and obtaining the microorganism-jute fiber comprehensive solidified granite residual soil after the slurry supplementing is ended. The prepared microorganism-jute fiber comprehensive solidified granite residual soil is excellent in performance, the mechanical strength, the water stability and the durability of the microorganism-jute fiber comprehensive solidified granite residual soil reach ideal effects, the pressure resistance is remarkably improved, the disintegration resistance is greatly improved, and the good mechanical stability can still be kept after dry-wet circulation.

Description

Technical Field

[0001] This application relates to the field of environmental geotechnical engineering technology, and more specifically, it relates to a method for the integrated solidification of granite residual soil by microorganisms and jute fibers. Background Technology

[0002] Granite residual soil is widely distributed in the hilly and coastal areas of southern my country. Due to its unique formation, it has characteristics such as high porosity, low shear strength, and easy softening upon contact with water. It is a key material for foundation treatment and slope protection in highway, railway, and building engineering projects, and its solidification quality directly determines the long-term stability and safety of the engineering structure. However, current mainstream reinforcement technologies have significant shortcomings, making it difficult to achieve efficient, coordinated, and ecologically compatible reinforcement goals. While single-microbial reinforcement methods have garnered significant attention due to their environmental friendliness, residual granite soils typically exhibit a low pH (<6.5) acidic environment, which inhibits microbial metabolic activity, resulting in mineralization efficiency below 40%. The generated cementing products are also scarce and unevenly distributed, failing to meet the engineering requirements for foundation bearing capacity. Traditional fiber reinforcement techniques utilize smooth and chemically inert materials like PP fibers, which cannot provide attachment sites or growth carriers for microorganisms. This disconnects reinforcement and microbial mineralization, hindering the formation of a synergistic effect of "mechanical support-mineralization cementation." While chemical solidifying agents can rapidly improve soil strength, they alter the soil's physicochemical structure, kill indigenous microorganisms, and disrupt the soil's ecological balance, clearly failing to meet the core ecological protection requirements of the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control (Trial)." These shortcomings severely restrict the widespread application of existing technologies in residual granite soil reinforcement projects. Therefore, developing technologies suitable for acidic environments, capable of synergistic reinforcement, and meeting ecological standards has become an urgent need in the field of geotechnical engineering. Summary of the Invention

[0003] To address the technical problems mentioned in the background section, this application provides a method for the integrated solidification of granite residual soil using microorganisms and jute fibers.

[0004] This application provides a method for comprehensively solidifying residual granite soil using microorganisms and jute fibers, employing the following technical solution:

[0005] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0006] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading to form a fiber-soil skeleton.

[0007] (2) First inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing solution to obtain the initially solidified soil;

[0008] (3) Cover the initially solidified soil with a breathable membrane to maintain soil moisture > 85% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity > 150 Ω·m, trigger automatic grouting. The grouting method is to inject the composite bacterial liquid and cementing liquid mentioned in step (2) in sequence. After the grouting is terminated, microbial-jute fiber integrated solidified granite residual soil is obtained.

[0009] Preferably, the method for preparing the modified jute fiber in step (1) is as follows:

[0010] Natural jute fiber is crushed, sieved, washed, and dried at 60-80℃ for 2-4 hours. It is then immersed in a NaOH solution with a mass fraction of 8-12%, and the solid-liquid mass ratio is controlled at 1-2:15-20. The mixture is then stirred at a constant temperature of 25-40℃ for 1-2 hours. After filtration, washing, and drying, modified jute fiber is obtained.

[0011] Preferably, the amount of modified jute fiber added in step (1) is 0.3-0.5 wt% of the mass of granite residual soil.

[0012] Preferably, the compound bacterial solution in step (2) is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 CFU / mL -1.5×10 7 A mixture of CFU / mL of compound bacteria, 0.5-1.0wt% sodium alginate, and 0.5-1.2M urea was prepared, and the pH was adjusted to 7.5±0.3.

[0013] Preferably, the compound bacteria consists of Bacillus pasteurellii, Bacillus mucilaginosus, and Bacillus megaterium with an effective live bacteria ratio of 10-12:3-5:1-3.

[0014] Preferably, the cementing solution in step (2) is prepared with deionized water and includes a mixture of 0.3-0.8M CaCl2 and 0.5-1.0M urea.

[0015] Preferably, the mass ratio of the composite bacterial solution, cementing solution and fiber-soil skeleton in step (2) is 5-8:3-7:10-15.

[0016] Preferably, in step (2), the grouting pressure of the composite bacterial solution and the cementing solution is controlled at 0.2-0.4 MPa, and the interval between the two grouting operations is 45-50 h.

[0017] Preferably, the grouting termination condition in step (3) is that the soil resistivity is stable in the range of 200-250 Ω·m for more than 24 hours.

[0018] Preferably, the mass ratio of the composite bacterial solution to the cementing solution in step (3) is 5-8:6-10.

[0019] In summary, this application has the following beneficial effects:

[0020] This application achieves a comprehensive improvement in the solidification effect of granite residual soil by synergistically applying modified jute fiber with a composite microbial system, combined with a combination of vacuum preloading, staged grouting, and automatic grouting. This effectively overcomes the shortcomings of traditional solidification methods, such as insufficient mechanical properties and poor water stability. By modifying jute fiber with NaOH solution, impurities on the fiber surface are removed and active groups are added, significantly enhancing the interfacial adhesion between the fiber and soil particles and microbial cementation products. This forms a stable fiber-soil interwoven skeleton, successfully inhibiting crack propagation under stress and improving overall shear and compressive strength.

[0021] By combining *Bacillus pasteurellii*, *Bacillus mucilaginosus*, and *Bacillus megaterium*, and utilizing the synergistic metabolic effects of these strains, along with urea as a substrate and sodium alginate as a stabilizer in the bacterial solution, microorganisms can continuously and efficiently generate cementing products. These products fill soil pores and cement the skeletal particles, further densifying the soil structure. An automatic grouting mechanism triggered by resistivity precisely replenishes the bacterial solution and cementing fluid according to the soil solidification process, significantly improving the uniformity of soil solidification, avoiding incomplete local solidification, and significantly enhancing resistance to disintegration and water stability.

[0022] By optimizing vacuum preloading parameters, grouting intervals, and grouting ratios, the synergistic effect of fiber reinforcement and microbial cementation is maximized. This leverages both the tensile and toughening properties of the fibers and the gap-filling and reinforcement effects of the microbial cementation, ensuring that the solidified soil maintains good mechanical stability under complex environments such as wet-dry cycles, meeting the needs of long-term engineering applications. Furthermore, by employing natural jute fiber and an environmentally friendly microbial system, the pollution problems of traditional chemical solidification agents are avoided, making the solidification process green, environmentally friendly, and controllable. It is suitable for various granite residual soil treatment scenarios, possessing broad practical value and promising prospects for widespread application. Detailed Implementation

[0023] The present application will be further described in detail below with reference to the embodiments.

[0024] The natural jute fiber used in the embodiments and comparative examples of this application was purchased from Feicheng Wenyang Oilseed Processing Plant; Bacillus pasteurellii (item number: B80469), Bacillus mucilaginosus (item number: B82482) and Bacillus megaterium (item number: B81563) were all purchased from Ningbo Mingzhou Biotechnology Co., Ltd.

[0025] Examples 1-3 provide a method for the integrated solidification of granite residual soil using microorganisms and jute fibers.

[0026] Example 1

[0027] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0028] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -70 kPa and the duration was 24 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.3 wt% of the mass of the residual granite soil.

[0029] The preparation method of modified jute fiber is as follows:

[0030] Natural jute fibers were cut to a length of 20 mm, and fibers with a diameter of 0.1 mm were screened. After ultrasonic cleaning with deionized water for 10 min (ultrasonic power 100 W, ultrasonic frequency 40 kHz), the fibers were dried at 60℃ for 2 h. The fibers were then immersed in an 8% NaOH solution with a solid-liquid mass ratio of 1:15 and stirred at 25℃ for 1 h at a stirring speed of 200 rpm. After filtration, washing with deionized water three times, and drying at 50℃ for 2 h, modified jute fibers were obtained.

[0031] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.2 MPa, and the interval between the two groutings is 45 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 The mixture of CFU / mL of compound bacteria, 0.5wt% sodium alginate and 0.5M urea was adjusted to pH 7.2. The compound bacteria consisted of Bacillus pasteurellii, Bacillus mucilaginosus and Bacillus megaterium with an effective viable count ratio of 10:3:1. The cementing solution was prepared with deionized water and included a mixture of 0.3M CaCl2 and 0.5M urea. The mass ratio of the compound bacterial solution, cementing solution and fiber-soil skeleton was 5:3:10.

[0032] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 5:6. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.4MPa. The interval between two grouting is 45h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m for 30h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0033] Example 2

[0034] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0035] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -75 kPa and the duration was 36 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.4 wt% of the mass of the residual granite soil.

[0036] The preparation method of modified jute fiber is as follows:

[0037] Natural jute fibers were cut to a length of 25 mm, and fibers with a diameter of 0.2 mm were screened. After ultrasonic cleaning with deionized water for 15 min (ultrasonic power 150 W, ultrasonic frequency 50 kHz), the fibers were dried at 70℃ for 3 h. The fibers were then immersed in a 10% NaOH solution with a solid-liquid mass ratio of 1.5:18 and stirred at 35℃ for 1.5 h with a stirring speed of 300 rpm. After filtration, washing with deionized water three times, and drying at 65℃ for 3 h, modified jute fibers were obtained.

[0038] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.3 MPa, and the interval between the two groutings is 48 hours to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1.2 × 10⁻⁶. 7 The mixture of CFU / mL of compound bacteria, 0.8wt% sodium alginate and 0.8M urea was adjusted to pH 7.5. The compound bacteria consisted of Bacillus pasteurellii, Bacillus mucilaginosus and Bacillus megaterium with an effective viable count ratio of 11:4:2. The cementing solution was prepared with deionized water and included a mixture of 0.5M CaCl2 and 0.8M urea. The mass ratio of the compound bacterial solution, cementing solution and fiber-soil skeleton was 7:5:12.

[0039] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 7:8. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.6MPa. The interval between two grouting is 48h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m for 28h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0040] Example 3

[0041] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0042] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -80 kPa and the duration was 48 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.5 wt% of the mass of the residual granite soil.

[0043] The preparation method of modified jute fiber is as follows:

[0044] Natural jute fibers were cut to a length of 30 mm, and fibers with a diameter of 0.3 mm were screened. After ultrasonic cleaning with deionized water for 20 min (ultrasonic power 200 W, ultrasonic frequency 60 kHz), the fibers were dried at 80℃ for 4 h. The fibers were then immersed in a 12% NaOH solution with a solid-liquid mass ratio of 2:20 and stirred at 40℃ for 2 h at a stirring speed of 400 rpm. After filtration, washing with deionized water three times, and drying at 80℃ for 4 h, modified jute fibers were obtained.

[0045] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.4 MPa, and the interval between the two groutings is 50 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1.5 × 10⁻⁶. 7 The pH of the mixture of CFU / mL of compound bacteria, 1.0wt% sodium alginate and 1.2M urea was adjusted to 7.8. The compound bacteria consisted of Bacillus pasteurellii, Bacillus mucilaginosus and Bacillus megaterium with an effective viable count ratio of 12:5:3. The cementing solution was prepared with deionized water and included a mixture of 0.8M CaCl2 and 1.0M urea. The mass ratio of the compound bacterial solution, cementing solution and fiber-soil skeleton was 8:7:15.

[0046] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 8:10. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.8MPa. The interval between two grouting is 50h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m for 25h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0047] Comparative Example 1

[0048] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0049] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -70 kPa and the duration was 24 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.3 wt% of the mass of the residual granite soil.

[0050] The preparation method of modified jute fiber is as follows:

[0051] Natural jute fibers were cut to a length of 20 mm, and fibers with a diameter of 0.1 mm were screened. After ultrasonic cleaning with deionized water for 10 min (ultrasonic power 100 W, ultrasonic frequency 40 kHz), the fibers were dried at 60℃ for 2 h. The fibers were then immersed in an 8% NaOH solution with a solid-liquid mass ratio of 1:15 and stirred at 25℃ for 1 h at a stirring speed of 200 rpm. After filtration, washing with deionized water three times, and drying at 50℃ for 2 h, modified jute fibers were obtained.

[0052] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.2 MPa, and the interval between the two groutings is 45 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 The mixture of CFU / mL of compound bacteria, 0.5wt% sodium alginate and 0.5M urea was adjusted to pH 7.2. The compound bacteria consisted of Bacillus mucilaginosus and Bacillus megaterium with an effective viable count ratio of 3:1. The cementing solution was prepared with deionized water and included a mixture of 0.3M CaCl2 and 0.5M urea. The mass ratio of the compound bacterial solution, cementing solution and fiber-soil skeleton was 5:3:10.

[0053] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 5:6. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.4MPa. The interval between two grouting is 45h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m for 30h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0054] Comparative Example 2

[0055] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0056] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -70 kPa and the duration was 24 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.3 wt% of the mass of the residual granite soil.

[0057] The preparation method of modified jute fiber is as follows:

[0058] Natural jute fibers were cut to a length of 20 mm, and fibers with a diameter of 0.1 mm were screened. After ultrasonic cleaning with deionized water for 10 min (ultrasonic power 100 W, ultrasonic frequency 40 kHz), the fibers were dried at 60℃ for 2 h. The fibers were then immersed in an 8% NaOH solution with a solid-liquid mass ratio of 1:15 and stirred at 25℃ for 1 h at a stirring speed of 200 rpm. After filtration, washing with deionized water three times, and drying at 50℃ for 2 h, modified jute fibers were obtained.

[0059] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.2 MPa, and the interval between the two groutings is 45 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 The mixture of CFU / mL of compound bacteria, 0.5wt% sodium alginate and 0.5M urea was adjusted to pH 7.2. The compound bacteria consisted of Bacillus pasteurellii and Bacillus megaterium with an effective viable count ratio of 10:1. The cementing solution was prepared with deionized water and included a mixture of 0.3M CaCl2 and 0.5M urea. The mass ratio of the compound bacterial solution, cementing solution and fiber-soil skeleton was 5:3:10.

[0060] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 5:6. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.4MPa. The interval between two grouting is 45h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m for 30h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0061] Comparative Example 3

[0062] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0063] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -70 kPa and the duration was 24 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.3 wt% of the mass of the residual granite soil.

[0064] The preparation method of modified jute fiber is as follows:

[0065] Natural jute fibers were cut to a length of 20 mm, and fibers with a diameter of 0.1 mm were screened. After ultrasonic cleaning with deionized water for 10 min (ultrasonic power 100 W, ultrasonic frequency 40 kHz), the fibers were dried at 60℃ for 2 h. The fibers were then immersed in an 8% NaOH solution with a solid-liquid mass ratio of 1:15 and stirred at 25℃ for 1 h at a stirring speed of 200 rpm. After filtration, washing with deionized water three times, and drying at 50℃ for 2 h, modified jute fibers were obtained.

[0066] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.2 MPa, and the interval between the two groutings is 45 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 A mixture of CFU / mL of compound bacteria, 0.5wt% sodium alginate, and 0.5M urea was prepared, and the pH was adjusted to 7.2. The compound bacteria consisted of Bacillus pasteurellii and Bacillus mucilaginosus with an effective viable count ratio of 10:3. The cementing solution was prepared with deionized water and included a mixture of 0.3M CaCl2 and 0.5M urea. The mass ratio of the compound bacterial solution, cementing solution, and fiber-soil skeleton was 5:3:10.

[0067] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 5:6. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.4MPa. The interval between two grouting is 45h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m for 30h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0068] Comparative Example 4

[0069] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0070] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -70 kPa and the duration was 24 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.3 wt% of the mass of the residual granite soil.

[0071] The preparation method of modified jute fiber is as follows:

[0072] Natural jute fibers were cut to a length of 20 mm, and fibers with a diameter of 0.1 mm were screened. After ultrasonic cleaning with deionized water for 10 min (ultrasonic power 100 W, ultrasonic frequency 40 kHz), the fibers were dried at 60℃ for 2 h. The fibers were then immersed in an 8% NaOH solution with a solid-liquid mass ratio of 1:15 and stirred at 25℃ for 1 h at a stirring speed of 200 rpm. After filtration, washing with deionized water three times, and drying at 50℃ for 2 h, modified jute fibers were obtained.

[0073] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.2 MPa, and the interval between the two groutings is 45 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 The pH of the mixture of CFU / mL of compound bacteria and 0.5wt% sodium alginate was adjusted to 7.2. The compound bacteria consisted of Bacillus pasteurellii, Bacillus mucilaginosus, and Bacillus megaterium with an effective viable count ratio of 10:3:1. The cementing solution was prepared with deionized water and included a mixture of 0.3M CaCl2 and 0.5M urea. The mass ratio of the compound bacterial solution, cementing solution, and fiber-soil skeleton was 5:3:10.

[0074] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 5:6. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.4MPa. The interval between two grouting is 45h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m and lasts for more than 24h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0075] Comparative Example 5

[0076] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0077] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -70 kPa and the duration was 24 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.3 wt% of the mass of the residual granite soil.

[0078] The preparation method of modified jute fiber is as follows:

[0079] Natural jute fibers were cut to a length of 20 mm, and fibers with a diameter of 0.1 mm were screened. After ultrasonic cleaning with deionized water for 10 min (ultrasonic power 100 W, ultrasonic frequency 40 kHz), the fibers were dried at 60℃ for 2 h. The fibers were then immersed in an 8% NaOH solution with a solid-liquid mass ratio of 1:15 and stirred at 25℃ for 1 h at a stirring speed of 200 rpm. After filtration, washing with deionized water three times, and drying at 50℃ for 2 h, modified jute fibers were obtained.

[0080] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.2 MPa, and the interval between the two groutings is 45 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 The mixture of CFU / mL of compound bacteria, 0.5wt% sodium alginate and 0.5M urea was adjusted to pH 7.2. The compound bacteria consisted of Bacillus pasteurellii, Bacillus mucilaginosus and Bacillus megaterium with an effective viable count ratio of 10:3:1. The cementing solution was prepared with deionized water and included a mixture of 0.3M CaCl2 and 0.5M urea. The mass ratio of the compound bacterial solution, cementing solution and fiber-soil skeleton was 5:3:10.

[0081] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. When the resistivity is >150Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. Control the mass ratio of composite bacterial solution to cementing solution to be 5:3. Control the grouting pressure of composite bacterial solution and cementing solution to be 0.4MPa. The interval between two grouting is 45h. The grouting termination condition is that the soil resistivity is stable in the range of 200-250Ω·m for 30h. Microbial-jute fiber integrated solidified granite residual soil is obtained.

[0082] Comparative Example 6

[0083] A method for solidifying residual granite soil using a microbial-jute fiber composite method includes the following preparation steps:

[0084] (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading. The vacuum preloading pressure was -70 kPa and the duration was 24 h to form a fiber-soil skeleton. The amount of modified jute fiber added was 0.3 wt% of the mass of the residual granite soil.

[0085] The preparation method of modified jute fiber is as follows:

[0086] Natural jute fibers were cut to a length of 20 mm, and fibers with a diameter of 0.1 mm were screened. After ultrasonic cleaning with deionized water for 10 min (ultrasonic power 100 W, ultrasonic frequency 40 kHz), the fibers were dried at 60℃ for 2 h. The fibers were then immersed in an 8% NaOH solution with a solid-liquid mass ratio of 1:15 and stirred at 25℃ for 1 h at a stirring speed of 200 rpm. After filtration, washing with deionized water three times, and drying at 50℃ for 2 h, modified jute fibers were obtained.

[0087] (2) First, inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing liquid. The grouting pressure is controlled at 0.2 MPa, and the interval between the two groutings is 45 h to obtain the initially solidified soil. The composite bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 The mixture of CFU / mL of compound bacteria, 0.5wt% sodium alginate and 0.5M urea was adjusted to pH 7.2. The compound bacteria consisted of Bacillus pasteurellii, Bacillus mucilaginosus and Bacillus megaterium with an effective viable count ratio of 10:3:1. The cementing solution was prepared with deionized water and included a mixture of 0.3M CaCl2 and 0.5M urea. The mass ratio of the compound bacterial solution, cementing solution and fiber-soil skeleton was 5:3:10.

[0088] (3) Cover the initially solidified soil with a breathable membrane to maintain the soil moisture at 90% for curing. Use a resistivity tester to monitor the soil resistivity in real time. Curing is carried out until the resistivity is stable and lasts for more than 24 hours to obtain microbial-jute fiber integrated solidified granite residual soil.

[0089] Performance testing

[0090] The performance of the microbial-jute fiber integrated solidified granite residual soils prepared in Examples 1-3 and Comparative Examples 1-6 of this application was tested. The specific test items are as follows:

[0091] Unconfined compressive strength: Tested in accordance with the national standard GB / T 50123-2019 "Standard for Geotechnical Testing Methods";

[0092] Disintegration resistance: Tested in accordance with industry standard JTG 3430-2020 "Specifications for Geotechnical Testing of Highways";

[0093] Saturated water absorption rate: Tested in accordance with the national standard GB / T 50123-2019 "Standard for Geotechnical Testing Methods";

[0094] Mechanical retention rate after wet-dry cycle: Tested in accordance with industry standard CJJ / T 286-2018 "Technical Standard for Application of Soil Stabilizers";

[0095] The specific test items are shown in Table 1.

[0096] Table 1. Performance tests of granite residual soils prepared in Examples 1-3 and Comparative Examples 1-6

[0097] As shown in Table 1, the microbial-jute fiber composite solidified granite residual soil prepared in this application exhibits excellent performance and strong stability. Its mechanical strength, water stability, and durability all achieve ideal results, with significantly improved compressive strength, greatly enhanced anti-disintegration performance, and effectively controlled water absorption capacity. It also maintains good mechanical stability after wet-dry cycles.

[0098] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for solidifying residual granite soil using a microbial-jute fiber composite, characterized in that, The preparation steps include the following: (1) Modified jute fiber was uniformly added to the residual granite soil, and the residual granite soil with modified jute fiber was compacted by vacuum preloading to form a fiber-soil skeleton. (2) First inject the composite bacterial solution into the fiber-soil skeleton, then inject the cementing solution to obtain the initially solidified soil; (3) Cover the initially solidified soil with a breathable membrane to maintain soil moisture > 85% for curing. Monitor the soil resistivity. When the resistivity > 150 Ω·m, trigger automatic grouting. The grouting method is to inject composite bacterial solution and cementing solution in sequence. After the grouting is terminated, microbial-jute fiber integrated solidified granite residual soil is obtained.

2. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, The method for preparing the modified jute fiber in step (1) is as follows: Natural jute fiber is crushed, sieved, washed, and dried at 60-80℃ for 2-4 hours. It is then immersed in NaOH solution, with the solid-liquid mass ratio controlled at 1-2:15-20. The mixture is then stirred at a constant temperature of 25-40℃ for 1-2 hours. After filtration, washing, and drying, modified jute fiber is obtained.

3. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, In step (1), the amount of modified jute fiber added is 0.3-0.5 wt% of the mass of granite residual soil.

4. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, In step (2), the compound bacterial solution is prepared with sterile deionized water and contains a concentration of 1×10⁻⁶. 7 CFU / mL -1.5×10 7 A mixture of CFU / mL of compound bacteria, 0.5-1.0wt% sodium alginate, and 0.5-1.2M urea was prepared, and the pH was adjusted to 7.5±0.

3.

5. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 4, characterized in that, The compound bacteria consist of Pasteurella multocida, Bacillus mucilaginosus, and Bacillus megaterium with an effective live bacteria ratio of 10-12:3-5:1-3.

6. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, The cementing solution in step (2) is prepared with deionized water and includes a mixture of 0.3-0.8M CaCl2 and 0.5-1.0M urea.

7. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, In step (2), the mass ratio of the composite bacterial solution, cementing solution and fiber-soil skeleton is 5-8:3-7:10-15.

8. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, In step (2), the grouting pressure of the composite bacterial solution and the cementing solution is controlled at 0.2-0.4 MPa, and the interval between the two grouting is 45-50 h.

9. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, The grouting termination condition in step (3) is that the soil resistivity is stable in the range of 200-250 Ω·m for more than 24 hours.

10. The method for solidifying residual granite soil using a microbial-jute fiber composite method according to claim 1, characterized in that, In step (3), the mass ratio of the composite bacterial solution to the cementing solution is 5-8:6-10.

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