A variable parameter microbial circulation grouting device and method based on permeability coefficient

Abstract

The present invention relates to the field of microbial engineering construction technology, specifically a variable-parameter microbial circulation grouting device and method based on permeability coefficient. The device includes a grouting stand, multiple grouting cylinders, a permeability coefficient measuring device, a slurry recovery device, and an auxiliary device; the method includes component splicing and installation, bacterial liquid cultivation, grouting reinforcement experiment, sample curing, and mechanical testing. This application can overcome the defects of existing MICP sample preparation technology, such as large disturbance and waste of grouting materials, and provides a grouting device and method with low sampling disturbance, slurry circulation, and grouting parameters that can be adjusted in real time according to changes in the sample permeability coefficient, thereby producing a geotechnical sample with good uniformity, low disturbance, high economic efficiency, and the ability to reasonably reflect the influence of grouting parameters on reinforcement strength.

Description

Technical Field

[0001] The present invention relates to the technical field of microbial engineering construction, and in particular to a variable-parameter microbial circulation grouting device and method based on permeability coefficient. Background Art

[0002] Infrastructure construction often requires modifying soils previously unsuitable for engineering to meet the requirements of modern construction. Traditional soil reinforcement techniques, including replacement filling, dynamic compaction, vibroflotation, and chemical grouting, are generally characterized by high energy consumption, high disturbance, and high pollution, which do not meet the national requirements for ecological civilization development. MICP (Microbial Induced Calcium Carbonate Precipitation) technology has garnered widespread attention in geotechnical engineering in recent years due to its green, environmentally friendly, and easy-to-use advantages. MICP utilizes microbial engineering to select and domesticate naturally occurring urease-producing bacteria (such as Bacillus subtilis, Bacillus licheniformis, and Sporosarcina pasteurii) as engineering bacteria. The bacteria decompose added urea in the soil environment to produce carbonate anions, which react with added calcium ions to form calcium carbonate colloidal particles. These colloidal calcium carbonate particles accumulate within the soil pores as the slurry penetrates, ultimately forming a stable bond between sand particles. This enhances the structural and stability of the reinforced soil, significantly improving its engineering properties. In order to explore the influencing factors of MICP reinforcement technology and improve its overall effect, sampling of the reinforced area is usually carried out under specific grouting parameters.

[0003] However, strong disturbances during sampling can introduce significant errors, affecting the objective analysis of the impact of various factors on the reinforcement effect. In addition, using a single grouting parameter throughout the entire grouting process can also lead to significant resource waste, so improvements are needed. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a variable parameter microbial circulation grouting device and method based on permeability coefficient.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A variable parameter microbial circulation grouting device based on permeability coefficient, comprising a grouting stand, a plurality of grouting cylinders, a permeability coefficient measuring device, a slurry recovery device and an auxiliary device;

[0007] Soil is provided in the grouting cylinder;

[0008] The upper surface of the grouting stand is provided with a plurality of circular holes at equal intervals; semicircular clamps are provided on both sides of the upper ends of the circular holes, the semicircular clamps are fixedly connected to the upper surface of the grouting stand, and a plurality of grouting cylinders are respectively arranged in the plurality of circular holes, and the two sides of the grouting cylinders are respectively in conflict with the corresponding two semicircular clamps.

[0009] Compared with the existing technology, the present application can effectively ensure the stability of the grouting cylinder after installation, and facilitate the addition of soil into it. At the same time, the permeability coefficient measuring device can detect the permeability situation, and the slurry recovery device and auxiliary device can avoid permeation leakage and realize the function of classified recovery, thereby improving the quality and efficiency of the device.

[0010] Preferably, the grouting cylinder is composed of two acrylic semi-cylinders that are in contact with each other, and water-stop tape is applied to the opposite sides of the two acrylic semi-cylinders.

[0011] Furthermore, the firmness of the grouting cylinder assembly can be ensured, and the water-stop tape can avoid leakage and make the connection between the two acrylic semi-cylinders more firmly.

[0012] Preferably, the permeability coefficient measuring device includes two water head sensors installed at the upper and middle parts of the grouting cylinder, and the two water head sensors are commonly connected to a computer).

[0013] Furthermore, a pipette is used to transfer bacterial liquid of one times the pore volume (Vv) of the soil to be reinforced from the cultured bacterial liquid to the grouting cylinder, and the permeability coefficient measuring device is started. When the liquid level reaches the permeability coefficient device at the upper part (at a height of H1 from the grouting cylinder), the device will record the time (T1) at this time and transmit it to the computer. When the liquid level reaches the permeability coefficient device at the lower part (at a height of H2 from the grouting cylinder), the device will record the time (T2) at this time and transmit it to the computer.

[0014] Preferably, the slurry recovery device includes a plurality of liquid collecting funnels fixed at equal intervals on the bottom of the upper table of the grouting stand, the lower end of the liquid collecting funnel is connected to a guide pipe, the lower ends of the plurality of guide pipes are commonly penetrated by a liquid collecting barrel, and the plurality of liquid collecting funnels are respectively arranged at the lower ends of the plurality of circular holes.

[0015] Furthermore, the bacterial liquid will move downward through the nylon gauze and fall into the liquid collecting funnel, and the falling bacterial liquid can be collected into the liquid collecting bucket through the diversion tube.

[0016] Preferably, the auxiliary device includes two annular fasteners sleeved on the upper and lower ends of the grouting cylinder, nylon gauze is laid in the circular hole, the grouting cylinder abuts against the upper end of the nylon gauze, and the soil abuts against the upper end of the nylon gauze; the upper end of the soil abuts against a buffer gasket.

[0017] Furthermore, the buffer pad can reduce the scouring effect of the slurry on the soil during grouting, which helps to obtain a smooth geotechnical test and reduce the test error of subsequent mechanical tests. At the same time, the nylon dense gauze uses 100-mesh nylon mesh gauze.

[0018] Preferably, the liquid collection barrels include a bacteria liquid collection barrel, a urea liquid collection barrel, a calcium chloride liquid collection barrel and a waste liquid barrel.

[0019] Furthermore, the collection of different bacterial liquids can be achieved.

[0020] Preferably, the diameter of the circular hole is 40 mm, the inner diameter of the grouting cylinder is 40 mm, the outer diameter is 45 mm, and the height is 120 mm; the inner wall of the grouting cylinder is covered with a PVC plastic sheet, and vaseline is provided on the inner wall of the grouting cylinder and both sides of the PVC plastic sheet.

[0021] Furthermore, it can be prepared according to needs to ensure that the components can be used in precise coordination.

[0022] The present invention also proposes a test method for a variable parameter microbial circulation grouting device based on a permeability coefficient, which is applicable to the above-mentioned variable parameter microbial circulation grouting device based on a permeability coefficient, and includes the following steps:

[0023] Step 1: Fix the two semi-cylinders at the upper and lower ends with circular fasteners. Seal the lower part with nylon gauze and apply water-stop tape at the joints to form a complete grouting cylinder.

[0024] Step 2: Apply vaseline evenly on the inner wall of the grouting cylinder and both sides of the PVC plastic sheet, and place the PVC plastic sheet coated with vaseline in the cylinder along the wall of the grouting cylinder;

[0025] Step 3: Weigh the weight of one sand column of soil to be reinforced according to the specified dry density and moisture content and mix it evenly with a certain amount of water. Then, divide the soil into four layers and fill it into the grouting cylinder and compact it to the specified height. Then, wrap it with plastic wrap and place it in a cool place for 24 hours to evenly distribute the moisture.

[0026] Step 4: Bacterial culture, urea solution preparation and calcium chloride solution preparation:

[0027] Step 4.1. Select different culture media according to different bacteria. Taking Sporosarcina pasteurii as an example, use a precision balance to weigh 15 g of casein peptone, 5 g of soy peptone, and 5 g of sodium chloride into a beaker, add 900 mL of deionized water, and adjust the pH of the solution to 7.3. After stirring, place the solution in a high-temperature autoclave to sterilize and dissolve the nutrients. After high-temperature sterilization, place the solution in a sterile UV operating table for one hour and cool to room temperature.

[0028] Step 4.2: Weigh 20 g of urea and dissolve it in 100 mL of water. Adjust the pH of the solution to 7.3 and filter out impurities using a filter in a sterile operating table. After UV irradiation for one hour, add the solution to the culture medium and UV irradiate for one hour. The liquid culture medium is ready.

[0029] Step 4.3: In a sterile operating table, use a pipette to extract the microbial strain and inoculate it into the prepared liquid culture medium. Mix evenly, seal it with kraft paper, and place it in a constant temperature shaker for 24 hours. The microbial culture solution is ready.

[0030] Step 4.4: Weigh 60 g of urea into a beaker and add 1 L of deionized water. Weigh 111 g of calcium chloride into a beaker and add 1 L of deionized water. Adjust the pH of each solution to 7. The binder solution is now ready.

[0031] Step 5: Grouting reinforcement experiment:

[0032] Step 5.1, Microbial Grouting: Before grouting, place a cushion on top of the soil column to be reinforced. Then, use a pipette to transfer a bacterial solution of one times the pore volume (Vv) of the soil to be reinforced from the cultured bacterial solution into the grouting cylinder. Start the permeability coefficient measuring device. When the liquid level reaches the permeability coefficient device at the upper part (at a height of H1 from the grouting cylinder), the device will record the time (T1) and transmit it to the computer. When the liquid level reaches the permeability coefficient device at the lower part (at a height of H2 from the grouting cylinder), the device will record the time (T2) and transmit it to the computer. The permeability coefficient can be calculated as follows:

[0033]

[0034] After the infiltration is completed, the bacterial solution in the collection bucket is transferred back to the grouting cylinder and the permeability coefficient is measured. This process is repeated three times. The average permeability coefficient of the three times is taken as the permeability coefficient of the bacterial solution and the slurry after three cycles is transferred to the waste liquid bucket;

[0035] Step 5.2, urea grouting: Pipette 1Vv of urea solution from the prepared urea solution and inject it into the grouting cylinder, repeating the relevant operations in step 5.1. The average permeability coefficient of the three times is recorded as the permeability coefficient of the urea solution;

[0036] Step 5.3, calcium chloride grouting: Pipette 1Vv of calcium chloride solution from the prepared calcium chloride solution and inject it into the grouting cylinder, repeat the relevant operations in step 5.1, and record the average permeability coefficient of the three times as the permeability coefficient of the calcium chloride solution;

[0037] Step 5.4, permeability coefficient calculation: take the average of the permeability coefficients of the bacterial solution, the urea solution, and the calcium chloride solution as the average permeability coefficient of this round of grouting;

[0038] Step 5.5: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.75, prepare 0.75 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting;

[0039] Step 5.6: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.5, prepare 0.5 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting;

[0040] Step 5.7: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.25, prepare 0.25 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting until it becomes impermeable. The grouting process is completed;

[0041] Step 6, sample curing: remove the grouting cylinder from the grouting stand, place it in a constant temperature drying oven, and cure it at 60°C for 4 days. The sample preparation is completed;

[0042] Step 7: Mechanical testing: Take the cured specimens out of the grouting cylinder and perform unconfined compression testing and triaxial compression testing.

[0043] Compared with the existing technology, this application clearly explains the method and steps for conducting the experiment, which makes it easier for staff to operate according to the experimental method so as to obtain accurate test values, while also realizing the recovery and secondary utilization of the slurry.

[0044] The beneficial effects of the present invention are:

[0045] 1. Controlling grouting parameters accordingly through permeability coefficient helps improve the uniformity and strength of the reinforced body;

[0046] 2. The three-phase grouting scheme helps to improve the penetration ability of slurry in dense sand and fine sand;

[0047] 3. Using a sample cylinder for grouting helps reduce the disturbance to the soil during the sampling process, reduces experimental errors, and makes the analysis of the impact of grouting parameters on the sample more objective;

[0048] 4. Using a liquid collecting device to recycle the slurry and perform secondary grouting can help improve the utilization rate of raw materials and reduce waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0050] Figure 2 It is a diagram of the grouting stand of the present invention;

[0051] Figure 3 It is a diagram of a grouting stand with a clamp of the present invention;

[0052] Figure 4 This is a diagram of a grouting stand with a liquid collecting device according to the present invention;

[0053] Figure 5 It is a diagram of a grouting stand with a sample preparation cylinder of the present invention;

[0054] Figure 6 is a flow chart of a method for implementing the present invention;

[0055] In the figure: 1 annular fastener, 2 buffer gasket, 3 nylon dense gauze, 4 grouting stand, 5 liquid collecting funnel, 6 diversion pipe, 7 liquid collecting bucket, 8 semicircular clamp, 9 soil, 10 head sensor, 11 grouting cylinder, 12 computer, 13 circular hole. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0057] Reference Figure 1-5 A variable parameter microbial circulation grouting device based on permeability coefficient includes a grouting stand 4, multiple grouting cylinders 11, a permeability coefficient measuring device, a slurry recovery device and an auxiliary device.

[0058] Reference Figure 1-5 The grouting cylinder 11 is provided with a soil body 9, through which a permeability test can be carried out to understand its permeability so as to select materials according to the test results; a plurality of circular holes 13 are provided on the upper surface of the grouting stand 4 at equal intervals, and the diameter of the circular hole 13 is 40 mm; the inner diameter of the grouting cylinder 11 is 40 mm, the outer diameter is 45 mm, and the height is 120 mm; the grouting cylinder 11 is composed of two acrylic semi-cylinders that are opposed to each other, and the opposite sides of the two acrylic semi-cylinders are covered with Water-stop tape can effectively prevent the occurrence of infiltration. At the same time, through precise numerical settings, the inner hole of the grouting cylinder 11 and the circular hole 13 can be accurately aligned, which is convenient for the infiltration and falling of the bacterial liquid. Semicircular clamps 8 are provided on both sides of the upper end of the circular hole 13. The semicircular clamps 8 are fixedly connected to the upper table of the grouting stand 4. Multiple grouting cylinders 11 are respectively arranged in multiple circular holes 13, and the two sides of the grouting cylinder 11 are respectively in conflict with the corresponding two semicircular clamps 8.

[0059] Reference Figure 1-5 The inner wall of the grouting cylinder 11 is covered with a PVC plastic sheet, and vaseline is provided on the inner wall of the grouting cylinder 11 and both sides of the PVC plastic sheet, which can fully ensure the tightness of the connection and the sealing effect, so that the bacterial liquid will only penetrate the soil 9, ensuring the accuracy of the penetration result.

[0060] Reference Figure 1-5 The permeability coefficient measuring device includes two water head sensors 10 installed at the upper and middle parts of the grouting cylinder 11, and the two water head sensors 10 are connected to a computer 12. A pipette is used to transfer a bacterial liquid with a pore volume (Vv) of one times the pore volume of the soil to be reinforced from the cultured bacterial liquid to the grouting cylinder 11, and the permeability coefficient measuring device is started. When the liquid level reaches the permeability coefficient device at the upper part (at a height H1 from the grouting cylinder 11), the device will record the time (T1) at this time and transmit it to the computer 12. When the liquid level reaches the permeability coefficient device at the lower part (at a height H2 from the grouting cylinder 11), the device will record the time (T2) at this time and transmit it to the computer 12.

[0061] Reference Figure 1-5 The slurry recovery device includes multiple liquid collecting funnels 5 fixed at equal intervals on the bottom of the upper table of the grouting stand 4. The lower end of the liquid collecting funnel 5 is connected to a guide pipe 6. The lower ends of the multiple guide pipes 6 are commonly penetrated by a liquid collecting barrel 7, which can centrally recover the bacterial liquid. The liquid collecting barrel 7 includes a bacterial liquid collecting barrel, a urea collecting barrel, a calcium chloride collecting barrel and a waste liquid barrel. Through the setting of multiple collection barrels, different bacterial liquids can be classified and collected for secondary utilization. Multiple liquid collecting funnels 5 are respectively arranged at the lower ends of multiple circular holes 13, which can accurately recover the falling infiltrated bacterial liquid.

[0062] Reference Figure 1-5 The auxiliary device includes two annular fasteners 1 sleeved on the upper and lower ends of the grouting cylinder 11, which can ensure the firmness of the grouting cylinder 11. Nylon dense gauze 3 is laid in the circular hole 13, which can facilitate the penetration of the bacterial liquid without causing the soil to penetrate. The grouting cylinder 11 is in contact with the upper end of the nylon dense gauze 3, and the soil 9 is in contact with the upper end of the nylon dense gauze 3; the upper end of the soil 9 is in contact with a buffer gasket 2, which can reduce the scouring effect of the slurry on the soil during grouting, help to obtain a smooth geotechnical test, reduce the test error of the subsequent mechanical test, help to make the soil 9 more solidified, and facilitate the adjustment of the test soil.

[0063] Reference Figure 6 The present invention also proposes a test method for a variable parameter microbial circulation grouting device based on a permeability coefficient, which is applicable to the above-mentioned variable parameter microbial circulation grouting device based on a permeability coefficient, and includes the following steps:

[0064] Step 1: Fix the two semi-cylinders at the upper and lower ends with annular fasteners 1, seal the lower part with nylon gauze 3, and apply water-stop tape at the joints to form a complete grouting cylinder 11;

[0065] Step 2: Apply vaseline evenly on the inner wall of the grouting cylinder 11 and both sides of the PVC plastic sheet, and place the PVC plastic sheet coated with vaseline in the cylinder 11 along the wall.

[0066] Step 3: Weigh the weight of one sand column of soil to be reinforced according to the specified dry density and moisture content and mix it evenly with a certain amount of water. Then, divide the soil 9 into four layers and fill them into the grouting cylinder 11 and compact them to the specified height. Then, wrap it with plastic wrap and place it in a cool place for 24 hours to evenly distribute the moisture.

[0067] Step 4: Bacterial culture, urea solution preparation and calcium chloride solution preparation:

[0068] Step 4.1. Select different culture media according to different bacteria. Taking Sporosarcina pasteurii as an example, use a precision balance to weigh 15 g of casein peptone, 5 g of soy peptone, and 5 g of sodium chloride into a beaker, add 900 mL of deionized water, and adjust the pH of the solution to 7.3. After stirring, place the solution in a high-temperature autoclave to sterilize and dissolve the nutrients. After high-temperature sterilization, place the solution in a sterile UV operating table for one hour and cool to room temperature.

[0069] Step 4.2: Weigh 20 g of urea and dissolve it in 100 mL of water. Adjust the pH of the solution to 7.3 and filter out impurities using a filter in a sterile operating table. After UV irradiation for one hour, add the solution to the culture medium and UV irradiate for one hour. The liquid culture medium is ready.

[0070] Step 4.3: In a sterile operating table, use a pipette to extract the microbial strain and inoculate it into the prepared liquid culture medium. Mix evenly, seal it with kraft paper, and place it in a constant temperature shaker for 24 hours. The microbial culture solution is ready.

[0071] Step 4.4: Weigh 60 g of urea into a beaker and add 1 L of deionized water. Weigh 111 g of calcium chloride into a beaker and add 1 L of deionized water. Adjust the pH of each solution to 7. The binder solution is now ready.

[0072] Step 5: Grouting reinforcement experiment:

[0073] Step 5.1, microbial grouting: Before grouting, place the buffer pad 2 on the top of the soil column to be reinforced. Then, use a pipette to transfer a bacterial solution of one times the pore volume (Vv) of the soil to be reinforced from the cultured bacterial solution to the grouting cylinder 11. Start the permeability coefficient measuring device. When the liquid level reaches the permeability coefficient device at the upper part (at a height H1 from the grouting cylinder 11), the device will record the time (T1) at this time and transmit it to the computer 12. When the liquid level reaches the permeability coefficient device at the lower part (at a height H2 from the grouting cylinder 11), the device will record the time T2 at this time and transmit it to the computer 12. The permeability coefficient can be calculated according to the following formula:

[0074]

[0075] After the infiltration is completed, the bacterial solution in the liquid collection bucket 7 is transferred back to the grouting cylinder 11 and the permeability coefficient is measured. This process is repeated three times. The average permeability coefficient of the three times is taken as the permeability coefficient of the bacterial solution and the slurry after three cycles is transferred to the waste liquid bucket;

[0076] Step 5.2, urea grouting: pipette 1Vv of urea solution from the prepared urea solution and inject it into the grouting cylinder 11, repeating the relevant operations of step 5.1, and record the average permeability coefficient of the three times as the permeability coefficient of the urea solution;

[0077] Step 5.3, calcium chloride grouting: pipette 1Vv of calcium chloride solution from the prepared calcium chloride solution and inject it into the grouting cylinder 11, repeat the relevant operations of step 5.1, and record the average permeability coefficient of the three times as the permeability coefficient of the calcium chloride solution;

[0078] Step 5.4, permeability coefficient calculation: take the average of the permeability coefficients of the bacterial solution, the urea solution, and the calcium chloride solution as the average permeability coefficient of this round of grouting;

[0079] Step 5.5: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.75, prepare 0.75 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting;

[0080] Step 5.6: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.5, prepare 0.5 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting;

[0081] Step 5.7: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.25, prepare 0.25 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting until it becomes impermeable. The grouting process is completed;

[0082] Step 6, sample curing: remove the grouting cylinder 11 from the grouting stand 4, put it into a constant temperature drying oven, and cure it at 60°C for 4 days. The sample preparation is completed;

[0083] Step 7, mechanical test: the cured sample is taken out from the grouting cylinder 11 and subjected to an unconfined compression test and a triaxial compression test.

[0084] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A test method for a variable parameter microbial circulation grouting device based on a permeability coefficient, which is adopted in a variable parameter microbial circulation grouting device based on a permeability coefficient, characterized in that: The following steps are involved: Step 1: The two semi-cylinders need to be fixed at the upper and lower ends with circular fasteners (1), the lower part of which needs to be sealed with nylon gauze (3), and water-stop tape is affixed at the seam to form a complete grouting cylinder (11); Step 2: Apply vaseline evenly on the inner wall of the grouting cylinder (11) and both sides of the PVC plastic sheet, and place the PVC plastic sheet coated with vaseline in the grouting cylinder (11) along the wall thereof; Step 3: Weigh the weight of a sand column of soil to be reinforced according to the specified dry density and moisture content and mix it evenly with a certain amount of water. Then, divide the soil (9) into four layers and fill them into the grouting cylinder (11) and compact them to the specified height. Then, wrap them with plastic wrap and place them in a cool place for 24 hours to evenly distribute the moisture. Step 4: Bacterial culture, urea solution preparation and calcium chloride solution preparation: Step 4.

1. Select different culture media according to different bacteria. For the bacteria used, use a precision balance to weigh 15 g of casein peptone, 5 g of soy peptone, and 5 g of sodium chloride into a beaker. Add 900 mL of deionized water and adjust the pH of the solution to 7.

3. After stirring, place the solution in a high-temperature autoclave to sterilize and dissolve the nutrients. After high-temperature sterilization, place the solution in a sterile UV operating table for one hour and cool to room temperature. Step 4.2: Weigh 20 g of urea and dissolve it in 100 mL of water. Adjust the pH of the solution to 7.3 and filter out impurities using a filter in a sterile operating table. After UV irradiation for one hour, add the solution to the culture medium and UV irradiate for one hour. The liquid culture medium is ready. Step 4.3: In a sterile operating table, use a pipette to extract the microbial strain and inoculate it into the prepared liquid culture medium. Mix evenly, seal it with kraft paper, and place it in a constant temperature shaker for 24 hours. The microbial culture solution is ready. Step 4.4: Weigh 60 g of urea into a beaker and add 1 L of deionized water. Weigh 111 g of calcium chloride into a beaker and add 1 L of deionized water. Adjust the pH of each solution to 7. The binder solution is now ready. Step 5: Grouting reinforcement experiment: Step 5.1, microbial grouting: before grouting, place the buffer pad (2) on the top of the soil column to be reinforced, then use a pipette to transfer the bacterial solution of one times the pore volume Vv of the soil to be reinforced from the cultured bacterial solution to the grouting cylinder (11), start the permeability coefficient measuring device, when the liquid level reaches the permeability coefficient device at a height H1 above the grouting cylinder (11), the device will record the time T1 at this time and transmit it to the computer (12), when the liquid level reaches the permeability coefficient device at a height H2 below the grouting cylinder (11), the device will record the time T2 at this time and transmit it to the computer (12), the permeability coefficient can be calculated according to the following formula: ； After the infiltration is completed, the bacterial solution in the liquid collection bucket (7) is transferred back to the grouting cylinder (11) and the permeability coefficient is measured. This process is repeated three times. The average permeability coefficient of the three times is taken as the permeability coefficient of the bacterial solution and the slurry after three cycles is moved into the waste liquid bucket; Step 5.2, urea grouting: pipette 1Vv of urea solution from the prepared urea solution and inject it into the grouting cylinder (11), repeat the relevant operations of step 5.1, and record the average permeability coefficient of the three times as the permeability coefficient of the urea solution; Step 5.3, calcium chloride grouting: pipette 1Vv of calcium chloride solution from the prepared calcium chloride solution and inject it into the grouting cylinder (11), repeat the relevant operations of step 5.1, and record the average permeability coefficient of the three times as the permeability coefficient of the calcium chloride solution; Step 5.4, permeability coefficient calculation: take the average of the permeability coefficients of the bacterial solution, the urea solution, and the calcium chloride solution as the average permeability coefficient of this round of grouting; Step 5.5: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.75, prepare 0.75 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting; Step 5.6: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.5, prepare 0.5 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting; Step 5.7: Repeat steps 5.1-5.4 until the permeability coefficient is reduced to the original 0.25, prepare 0.25 mol / L urea and calcium chloride solution, and use this concentration of urea and calcium chloride solution for grouting until it becomes impermeable. The grouting process is completed; Step 6, sample curing: remove the grouting cylinder (11) from the grouting stand (4), place it in a constant temperature drying oven, and cure it at 60°C for 4 days. The sample preparation is completed; Step 7, mechanical test: the cured sample is taken out from the grouting cylinder (11) and subjected to an unconfined compression test and a triaxial compression test.

2. The test method of the variable parameter microbial circulation grouting device based on permeability coefficient according to claim 1 is characterized in that: The variable parameter microbial circulation grouting device based on permeability coefficient comprises a grouting stand (4), a plurality of grouting cylinders (11), a permeability coefficient measuring device, a slurry recovery device and an auxiliary device; and is characterized in that: A soil body (9) is provided in the grouting cylinder (11); The upper surface of the grouting stand (4) is provided with a plurality of circular holes (13) at equal intervals; semicircular clamps (8) are provided on both sides of the upper ends of the circular holes (13); the semicircular clamps (8) are fixedly connected to the upper surface of the grouting stand (4); a plurality of grouting cylinders (11) are respectively arranged in the plurality of circular holes (13), and the two sides of the grouting cylinders (11) are respectively in contact with the corresponding two semicircular clamps (8).

3. The test method of the variable parameter microbial circulation grouting device based on permeability coefficient according to claim 2 is characterized in that: The grouting cylinder (11) is composed of two acrylic semi-cylinders that are in contact with each other, and water-stop tape is applied to the opposite sides of the two acrylic semi-cylinders.

4. The test method of the variable parameter microbial circulation grouting device based on permeability coefficient according to claim 2 is characterized in that: The permeability coefficient measuring device comprises two water head sensors (10) installed at the upper and middle parts of the grouting cylinder (11), and the two water head sensors (10) are commonly connected to a computer (12).

5. The test method of the variable parameter microbial circulation grouting device based on permeability coefficient according to claim 2 is characterized in that: The slurry recovery device comprises a plurality of liquid collecting funnels (5) fixed at equal intervals on the bottom of the upper table of the grouting stand (4); the lower ends of the liquid collecting funnels (5) are connected to a guide pipe (6); the lower ends of the plurality of guide pipes (6) are penetrated by a liquid collecting barrel (7); and the plurality of liquid collecting funnels (5) are respectively arranged at the lower ends of the plurality of circular holes (13).

6. The test method of the variable parameter microbial circulation grouting device based on permeability coefficient according to claim 2 is characterized in that: The auxiliary device comprises two annular fasteners (1) sleeved on the upper and lower ends of the grouting cylinder (11); a nylon gauze (3) is laid in the circular hole (13); the grouting cylinder (11) abuts against the upper end of the nylon gauze (3); the soil (9) abuts against the upper end of the nylon gauze (3); and the upper end of the soil (9) abuts against a buffer gasket (2).

7. The test method of the variable parameter microbial circulation grouting device based on permeability coefficient according to claim 5 is characterized in that: The liquid collecting barrel (7) comprises a bacterial liquid collecting barrel, a urea liquid collecting barrel, a calcium chloride liquid collecting barrel and a waste liquid barrel.

8. The test method of the variable parameter microbial circulation grouting device based on permeability coefficient according to claim 2 is characterized in that: The diameter of the circular hole (13) is 40 mm, the inner diameter of the grouting cylinder (11) is 40 mm, the outer diameter is 45 mm, and the height is 120 mm; the inner wall of the grouting cylinder (11) is affixed with a PVC plastic sheet, and the inner wall of the grouting cylinder (11) and both sides of the PVC plastic sheet are provided with vaseline.

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