A device and method for reinforcing a tunnel starting well portal soil body by injecting a microbial slurry
By designing devices and methods suitable for microbial reinforcement, the separation, delivery, and deep mixing of bacterial solution and cementing solution into the soil were achieved. This solved the problems of pipe blockage and internal loosening in traditional microbial reinforcement technologies, improved the reinforcement effect of the soil at the tunnel starting shaft entrance, and met the construction requirements of tunnel boring machines.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2023-05-31
- Publication Date
- 2026-06-26
Smart Images
Figure CN116464459B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of tunnel soil reinforcement technology, and more specifically, relates to a device and method for reinforcing the soil at the entrance of a tunnel starting shaft by injecting microbial grout. Background Technology
[0002] During the initial construction of a tunnel using the shield tunneling method, there are certain requirements for the strength and impermeability of the soil at the tunnel entrance. Otherwise, if accidents such as collapse or water surge occur during the initial construction of the shield machine, it will result in huge losses of life and property.
[0003] Traditional methods for reinforcing the soil at the entrance of a launching shaft mainly use cement-based mortar and employ principles such as high-pressure jet grouting, deep mixing, and freezing reinforcement. However, these methods often lead to problems such as large in-situ disturbances, environmental pollution, and low economic efficiency. Furthermore, they are not conducive to the entry of large machinery into the confined space of a tunnel.
[0004] In recent years, emerging microbial soil reinforcement technologies, including microbial induced carbonate technology (MICP) and enzyme induced carbonate technology (EICP), have brought new ideas to the civil engineering industry. Compared with traditional cement mortar reinforcement, these microbial soil reinforcement technologies have advantages such as lower cost, no need for large construction equipment, and significantly reduced environmental pollution. However, in traditional microbial injection methods, the direct mixing and injection of bacterial solution and binder can lead to premature reactions, easily causing problems such as pipe blockage, excessively rapid sealing of the soil surface, and internal loosening. Summary of the Invention
[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a device and method for reinforcing the soil at the tunnel starting shaft entrance by injecting microbial slurry. The purpose is to reduce the internal loosening problem during microbial soil reinforcement and improve the soil reinforcement effect at the tunnel starting shaft entrance.
[0006] To achieve the above objectives, according to one aspect of the present invention, a device for reinforcing the soil at the entrance of a tunnel starting shaft by injecting microbial slurry is provided, comprising a storage component, a transport component, and an injection component, wherein:
[0007] The storage component includes two constant temperature chambers, which are used to hold bacterial solution and gelling solution respectively; the transmission component includes a multi-connected micro high-pressure pump, which has two independent liquid channels.
[0008] The injection component includes a grouting conduit and a rotating grouting head. The grouting conduit comprises two hollow semi-cylindrical tubes, the longitudinal surfaces of which are joined together to form a cylinder with two independent longitudinal cavities. The tops of the two independent longitudinal cavities are connected to two constant temperature chambers through different liquid channels. Multiple spray holes are evenly opened longitudinally on the arc surface of the hollow semi-cylindrical tubes. The rotating grouting head is used to drive the grouting conduit to rotate.
[0009] As a further preferred option, the nozzles on the two hollow semi-cylindrical tubes are arranged in a longitudinally staggered manner.
[0010] As a further preferred embodiment, the spacing between two adjacent nozzles on the hollow semi-cylindrical tube is 0.05m to 0.2m, and the nozzle diameter is 2mm to 4mm.
[0011] As a further preferred embodiment, the hollow semi-cylindrical tube is provided with a valve, which is used to control the opening and closing of the nozzle.
[0012] As a further preferred embodiment, the transmission component also includes a water shortage protection device and a check valve, wherein the water shortage protection device is disposed at the inlet of the multi-connected micro high-pressure pump and the check valve is disposed at the outlet of the multi-connected micro high-pressure pump.
[0013] As a further preferred embodiment, the transmission component also includes a high-pressure pump and a pressure sensor, wherein the high-pressure pump is used to provide pressurization for the multi-connected micro high-pressure pump, and the pressure sensor is used to test the pressure of the liquid at the outlet of the multi-connected micro high-pressure pump.
[0014] According to another aspect of the present invention, a method for reinforcing the soil at the entrance of a tunnel starting shaft by injecting microbial grout based on the above-described device is provided, comprising the following steps:
[0015] Detect the cracks in the soil at the tunnel's starting shaft entrance, and prepare appropriate amounts of bacterial solution and cementing solution, which are then placed in two constant temperature chambers respectively.
[0016] Drill grouting holes within the reinforcement area of the soil at the tunnel starting shaft entrance, insert grouting pipes into the grouting holes, and rotate the grouting pipes.
[0017] The bacterial solution and cementing solution in the two constant temperature chambers are pressurized and pumped into two hollow semi-cylindrical pipes through a multi-connected micro high-pressure pump. The bacterial solution and cementing solution are injected into the soil through the nozzles on the hollow semi-cylindrical pipes and mixed in the soil to form a microbial slurry, thereby reinforcing the soil at the tunnel starting shaft entrance.
[0018] As a further preferred option, when preparing the cementitious solution, the pH value of the cementitious solution is lowered separately, so that the bacterial solution will not immediately begin to precipitate after mixing with the cementitious solution in the soil. Instead, after penetrating deep into the soil, as the bacterial solution hydrolyzes the urea in the cementitious solution, the pH value will continuously rise to neutral and the precipitation reaction will begin, thus reinforcing the soil.
[0019] As a further preferred embodiment, the bacterial solution is a Bacillus pasteurellii bacterial solution.
[0020] As a further preferred embodiment, the reinforcement range of the soil at the tunnel starting shaft entrance is all the soil within 5m longitudinally along the tunnel axis, 6m outside the tunnel centerline, 3m above the tunnel top, and 3m below the tunnel bottom.
[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:
[0022] 1. This invention designs a novel conduit suitable for microbial injection, allowing the bacterial solution and the cementing solution to enter the soil at the same time and position during rotary jet injection, while avoiding the problems of premature mixing of the two in the device leading to blockage and excessively rapid sealing of the soil surface. This reduces internal loosening during microbial reinforcement of the soil and improves the soil reinforcement effect at the tunnel starting shaft entrance.
[0023] 2. The longitudinally staggered arrangement of the nozzles on the two semi-cylindrical pipes in this invention allows the bacterial solution and cementing solution to mix later, thus enabling both liquids to penetrate deeper into the soil and increase the reinforcement depth. Simultaneously, the design of the spacing between adjacent nozzles on the semi-cylindrical pipes allows for proper mixing and reaction of the slurry from adjacent nozzles, avoiding excessive overlap due to overly close spacing or insufficient utilization of the slurry due to overly large spacing, thus preventing waste.
[0024] 3. The transmission component of this invention is equipped with a water shortage protection device, a booster pump, a pressure sensor, and a check valve. The water shortage protection device is located at the inlet of the multi-connected micro high-pressure pump, which can shut down the multi-connected micro high-pressure pump when there is a lack of liquid at the inlet. The check valve is located at the outlet of the multi-connected micro high-pressure pump to prevent backflow of liquid output from the outlet. An additional pump and a pressure sensor are also included to achieve pressure regulation and monitoring.
[0025] 4. This invention utilizes the high-pressure jet grouting principle to inject bacterial solution and cementing fluid into the soil in front of the tunnel entrance for reinforcement. It features a simple structure, convenient construction, and low cost. However, the reinforcement strength of the soil at the tunnel entrance cannot be too high; the soil strength needs to be controlled. If the soil strength is too high, the torque of the tunnel boring machine (TBM) cutterhead will increase significantly, making soil cutting difficult and increasing TBM wear. During TBM launch construction, a soil cohesion of 0.2–0.25 MPa and a compressive strength of 1.0–1.2 MPa are generally preferred. This invention's MICP-based microbial soil reinforcement technology can control the soil strength to around 1 MPa, meeting the strength requirements for the soil at the TBM launch tunnel entrance.
[0026] 5. Bacteria cannot be kept in a low pH environment for a long time, otherwise the activity of the bacterial solution will be greatly reduced. In this invention, the bacterial solution and the cementing solution are injected separately. The pH of the cementing solution can be adjusted according to actual needs by starting with the constant temperature box of the cementing solution, so as not to affect the activity of the bacteria. After the bacterial solution is mixed with the low pH cementing solution in the soil, it will not immediately start to precipitate. The bacterial-cement mixture slowly penetrates into the soil. As the bacterial solution hydrolyzes the urea in the cementing solution, the pH value continuously rises to neutral and then the precipitation reaction begins to reinforce the soil, thereby achieving effective reinforcement of the soil deep within the soil.
[0027] 6. This invention uses a Bacillus pasteurellium bacterial solution. The cell wall surface of Bacillus pasteurellium has a large number of negatively charged functional groups, which can effectively adsorb cementing fluids and soil containing calcium. 2+ The main component is metal cations; Bacillus pasteurellii produces urease during its metabolism, which hydrolyzes urea in the cementing solution to generate carbonate ions. The carbonate ions combine with the metal cations to form precipitates, thereby effectively cementing and solidifying the soil. The method is economical and environmentally friendly, with minimal in-situ disturbance, and aligns with the sustainable development concept of low-carbon emission reduction and environmental friendliness. Attached Figure Description
[0028] Figure 1 This is a schematic diagram of the device for reinforcing the soil at the tunnel starting shaft entrance with microbial grout according to an embodiment of the present invention;
[0029] Figure 2 This is a front view of the grouting conduit according to an embodiment of the present invention;
[0030] Figure 3 This is a top view of the grouting conduit according to an embodiment of the present invention;
[0031] Figure 4 A schematic diagram of the injection position and direction of microbial grouting at the construction site according to an embodiment of the present invention.
[0032] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-thermostatic chamber A, 2-thermostatic chamber B, 3-multi-connected micro high-pressure pump, 4-water shortage protection device, 5-booster pump, 6-pressure sensor, 7-check valve, 8-rotary grouting head, 9-grouting conduit, 10-conduit orifice valve. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0034] This invention provides a device for reinforcing the soil at the entrance of a tunnel starting shaft with microbial slurry, comprising a storage component, a transmission component, and an injection component, wherein:
[0035] The storage component includes two or more constant temperature chambers, with the bacterial solution and the cementing solution placed in different chambers. The transmission component includes a multi-connected micro high-pressure pump, which has two or more independent liquid channels. The inlets of the liquid channels are connected to the constant temperature chambers via conduits, and the outlets of the liquid channels are connected to the injection component via conduits. The injection component is a combined grouting device, which consists of a rotatable grouting head and a grouting conduit. The grouting conduit includes two semi-cylindrical rigid tubes of the same length and diameter, which are joined together to form a cylinder with two independent longitudinal cavities. Several spray holes are evenly arranged at the apex of each of the two semi-cylindrical rigid tubes along the longitudinal direction. The rotatable grouting head is installed on the top of the grouting conduit, driving the grouting conduit to rotate and achieve separate spraying of the bacterial solution and the cementing solution.
[0036] Furthermore, the length of the grouting pipe is 3m to 5m and the diameter is 1cm to 3cm; 3m to 5m is the general reinforcement depth of the soil after tunnel lining, while the fluidity of the microbial liquid can extend the reinforcement depth by 0.5 to 1m, which meets the requirements of most tunnel reinforcement situations.
[0037] Furthermore, the spacing between two adjacent nozzles is 0.05m to 0.2m, which allows the slurry from adjacent nozzles to mix and react appropriately. If the distance is too close, the slurry will overlap too much, and if it is too far, the slurry may not be fully utilized, both of which will result in waste. The nozzle diameter is 2mm to 4mm. Considering that both the bacterial solution mixture and the cementing solution are in a liquid state without solid particles, the nozzle diameter is designed accordingly, which can save materials and increase the pressure at the injection port.
[0038] Furthermore, depending on actual needs, if it is necessary for the bacterial solution and cementing solution to mix earlier in the soil to achieve rapid surface and shallow sealing, the small holes on both sides of the grouting conduit can be processed to be arranged in a horizontal line. If it is necessary for the bacterial solution and cementing solution to mix later, allowing both liquids to penetrate deeper into the soil, the small holes on both sides of the grouting conduit can be processed to be staggered, with the small holes on both sides offset by 3-5 cm. Valves can be installed on the side of the conduit to control the closure of adjacent small holes, allowing the small holes to be opened or closed during grouting according to the required soil layer depth.
[0039] Furthermore, this invention designs the storage components to store the bacterial solution and cementing fluid separately in constant temperature chambers. This facilitates the separate treatment of the bacterial solution and cementing fluid to meet actual engineering needs. The soil at the tunnel launch shaft entrance differs from other parts of the tunnel. A large area of soil, from shallow to deep, must achieve a certain strength to ensure the safe launch of the tunnel boring machine. Therefore, even deep soil must be uniformly and effectively reinforced. One method for achieving effective deep soil reinforcement using microbial reinforcement is to lower the pH value of the grouting fluid, delaying the calcium carbonate precipitation reaction. While the bacteria in the MICP method can tolerate a pH of up to 4.0, they cannot be kept in a low pH environment for extended periods, otherwise the bacterial activity will be significantly reduced. Therefore, the uncertainty of actual on-site construction time makes the method of lowering the pH value difficult to apply. This invention addresses this by using a constant temperature chamber for the cementing fluid. The pH of the cementing fluid can be adjusted according to actual needs without affecting bacterial activity. For example, to reinforce soil 5-7m deep, the pH value of the cementing fluid can be lowered to 5-6 when preparing the cementing fluid. When the bacterial solution is mixed with the low-pH cementitious solution in the soil, it does not immediately begin to precipitate. The bacterial-cement mixture slowly penetrates deep into the soil. As the bacterial solution hydrolyzes the urea in the cementitious solution, the pH value continuously rises until it reaches neutral, at which point a precipitation reaction begins to reinforce the soil.
[0040] Furthermore, the transmission components can pressurize the bacterial solution and the cementing solution separately. For shallow to medium-level soil solidification, the injection pressure of the cementing solution should be slightly greater than that of the bacterial solution, with a pressure ratio of 1:1 to 1.2 being preferable. For deep soil solidification, the injection pressure of the cementing solution should be less than that of the bacterial solution, with a pressure ratio of 1:0.3 to 1:0.7 being preferable. For microbial solidification, the reference distances for shallow soil layers are 1–1.5 m from the grouting point, for medium layers 1.5–3 m, and for deep layers 3 m and above.
[0041] Specifically, the bacteria used can be: 1) *Pasteurella multocida*, with a *Pasteurella multocida* culture in the incubator; 2) Denitrifying bacteria, with denitrifying bacteria and dilute nitric acid solution in the incubator, and the incubator appropriately filled with nitrogen gas. Unlike *Pasteurella multocida*, denitrifying bacteria are suitable for anaerobic environments. However, the soil in tunnels generally has low oxygen content, so the application effect of denitrifying bacteria here is the same as that of *Pasteurella multocida*; 3) Sulfate-reducing bacteria, with sulfate-reducing bacteria and a soluble sulfate solution, such as sodium sulfate, in the incubator. Sulfate-reducing bacteria are also only suitable for anaerobic environments.
[0042] Furthermore, *Bacillus pasteurellii* is low in cost, widely applicable, and highly effective. The preferred bacterial solution is *Bacillus pasteurellii*, whose cell wall surface carries a large number of negatively charged functional groups, enabling it to effectively adsorb calcium from cementing fluids and soil. 2+ The main metal cations are urease, which is produced by Bacillus pasteurellium during its metabolism. Urease hydrolyzes urea in the cementing solution to generate carbonate ions. The carbonate ions and metal cations combine to form precipitates, which effectively cement and solidify the soil, thereby reinforcing the soil at the tunnel starting shaft entrance.
[0043] In one embodiment, such as Figure 1 As shown, the storage component consists of a detachable, temperature-displaying, and temperature-adjustable constant temperature chamber A1 and a constant temperature chamber B2. The constant temperature chamber A1 contains Bacillus pasteurellium culture, and the constant temperature chamber B2 contains a gelling liquid. The temperature of the Bacillus pasteurellium culture and the gelling liquid is controlled by adjusting the temperature of the constant temperature chamber A1 and the constant temperature chamber B2.
[0044] The multi-connector miniature high-pressure pump 3 has two independent channels. The inlet of the first channel is connected to the constant temperature chamber A1 via a conduit, and the inlet of the second channel is connected to the constant temperature chamber B2 via a conduit. The conduit is a plastic flexible tube with a circular cross-section. The multi-connector miniature high-pressure pump 3 is equipped with a water shortage protection device 4, a booster pump 5, a pressure sensor 6, and a check valve 7. The water shortage protection device 4 is located at the inlet of the multi-connector miniature high-pressure pump 3 and can shut down the multi-connector miniature high-pressure pump 3 when there is a lack of liquid at the inlet. The booster pump 5 provides pressurization to the multi-connector miniature high-pressure pump 3. The pressure sensor 6 displays the pressure of the liquid output from the outlet of the multi-connector miniature high-pressure pump 3. The check valve 7 is located at the outlet of the multi-connector miniature high-pressure pump 3 to prevent backflow of the liquid output from the outlet of the multi-connector miniature high-pressure pump.
[0045] The injection component is a combined grouting device, consisting of a rotatable grouting head 8 and a grouting conduit 9; the grouting conduit 9 is as follows: Figure 2 and Figure 3As shown, it consists of two semi-cylindrical rigid tubes of the same length and 2cm in diameter. The two semi-cylindrical rigid tubes are joined together to form a cylinder with two independent cavities. The outlet of the first channel of the multi-connected micro high-pressure pump 3 is connected to one of the cavities through a conduit, and the outlet of the second channel is connected to the other cavity through a conduit. The grouting conduit 9 is 4m long, and each of the two semi-cylindrical rigid tubes has a small hole with a diameter of 3mm at the top of the arc every 0.1m along the longitudinal direction. The rotatable grouting head 8 is installed on the top of the grouting conduit and can be rotated automatically or manually. At the same time, it evenly sprays the Bacillus pasteurellium liquid and cementing liquid onto the soil at the tunnel starting shaft entrance, so as to achieve the effect of uniform reinforcement or local reinforcement of the soil at the tunnel starting shaft entrance.
[0046] In one embodiment, the method of reinforcing the soil at the tunnel starting shaft entrance by injecting microbial grout using the above-described device is as follows: Figure 4 As shown, the specific steps are as follows:
[0047] Step 1: Use an ultrasonic detector to detect cracks in the soil within the reinforcement area of the shield tunnel launch shaft. The reinforcement area of the shield tunnel launch shaft is 5m longitudinally along the shield tunnel axis, 6m outside the tunnel centerline, 3m above the outer top of the shield tunnel structure, and 3m below the outer bottom of the structure. All soil between the left and right tunnels is reinforced. Calculate the required volume of reinforced soil to estimate the required mass of bacterial solution, liquid culture medium, and cementing solution. For 1 cubic meter of sandy soil without cracks or cavities, the required grouting volume (microbial grout) is 150L to 200L. If the soil within the reinforcement area is more cohesive than sandy soil and has fewer cracks and cavities, the grouting volume should be reduced accordingly. If the soil within the reinforcement area is sandy soil or has many cracks and cavities, the grouting volume should be increased accordingly.
[0048] Step 2: The prepared Bacillus pasteurellosis bacterial suspension and liquid culture medium (if the bacterial suspension has been left on site for a long time, add appropriate liquid culture medium to maintain bacterial metabolism) are loaded into the detachable constant temperature box A1 at a volume ratio of 1:1. The binding liquid is loaded into the detachable constant temperature box B2. The constant temperature boxes A1 and B2 can display and maintain the set temperature inside the boxes. The storage components are then transported to the construction site.
[0049] Step 3: Drill grouting holes with a depth of more than 3m and a diameter of 4-5cm within the soil reinforcement area of the shield tunneling starting shaft. Insert the grouting pipe 9 of the combined grouting device into the soil. The rotatable grouting head 8 is embedded in the grouting hole. Under the action of the rotatable grouting head 8, the grouting pipe 9 can rotate along its own longitudinal axis.
[0050] Step 4: Using a multi-connected micro high-pressure pump, the Pasteurella multocida solution in constant temperature chamber A1 and the cementing solution in constant temperature chamber B2 are pumped into the two independent cavities of the grouting conduit 9 of the combined grouting machine, respectively.
[0051] The rotatable grouting head 8 rotates, thereby pulling the grouting pipe 9, which is connected to the soil, to rotate. The Pasteurella multocida liquid and the cementing liquid are injected into the soil through the grouting pipe at a high pressure by a number of small holes evenly set at the top of the arc, and mixed to form a microbial slurry, which reinforces the soil at the entrance of the starting well.
[0052] Specifically, the preparation methods for the *Bacillus pasteurellii* bacterial suspension and gelling solution are as follows: First, add 20g of yeast powder and 10g of ammonium chloride solid to each liter of pure water, adjust the pH to 8.5, and prepare a liquid culture medium; then, inoculate the original *Bacillus pasteurellii* bacterial suspension into the liquid culture medium under sterile conditions, with a volume ratio of original bacterial suspension to liquid culture medium of 1:100. After inoculation, place it on a shaker for expansion culture to obtain the *Bacillus pasteurellii* bacterial suspension; the concentration of the gelling solution is 1.0–1.2 mol / L, and it is prepared by mixing equal volumes and concentrations of calcium chloride solution and urea solution.
[0053] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A device for reinforcing the soil at the entrance of a tunnel starting shaft by injecting microbial slurry, characterized in that, It includes storage components, transmission components, and injection components, wherein: The storage component includes two constant temperature chambers, which are used to hold bacterial solution and gelling solution respectively; the transmission component includes a multi-connected micro high-pressure pump, which has two independent liquid channels. The injection component includes a grouting conduit and a rotating grouting head. The grouting conduit comprises two hollow semi-cylindrical tubes, the longitudinal surfaces of which are joined together to form a cylinder with two independent longitudinal cavities. The tops of the two independent longitudinal cavities are connected to two constant temperature chambers through different liquid channels. Multiple spray holes are evenly opened longitudinally on the arc surface of the hollow semi-cylindrical tubes. The rotating grouting head is used to drive the grouting conduit to rotate. The nozzles on the two hollow semi-cylindrical tubes are arranged in a longitudinally staggered manner; On the hollow semi-cylindrical tube, the distance between two adjacent nozzles is 0.05m to 0.2m, and the nozzle diameter is 2mm to 4mm.
2. The device for reinforcing the soil at the tunnel starting shaft entrance by injecting microbial grout as described in claim 1, characterized in that, A valve is installed on the hollow semi-cylindrical tube, which is used to control the opening and closing of the nozzle.
3. The device for reinforcing the soil at the tunnel starting shaft entrance by injecting microbial grout as described in claim 1, characterized in that, The transmission component also includes a water shortage protection device and a check valve. The water shortage protection device is located at the inlet of the multi-connected micro high-pressure pump, and the check valve is located at the outlet of the multi-connected micro high-pressure pump.
4. The device for reinforcing the soil at the tunnel starting shaft entrance by injecting microbial grout as described in any one of claims 1-3, characterized in that, The transmission component also includes a high-pressure pump and a pressure sensor. The high-pressure pump is used to provide pressurization for the multi-connected micro high-pressure pump, and the pressure sensor is used to test the pressure of the liquid at the outlet of the multi-connected micro high-pressure pump.
5. A method for reinforcing the soil at the entrance of a tunnel starting shaft using microbial grout based on the device described in claim 1, characterized in that, Includes the following steps: Detect the cracks in the soil at the tunnel's starting shaft entrance, and prepare appropriate amounts of bacterial solution and cementing solution, which are then placed in two constant temperature chambers respectively. Drill grouting holes within the reinforcement area of the soil at the tunnel starting shaft entrance, insert grouting guide pipes into the grouting holes, and rotate the grouting guide pipes. The bacterial solution and cementing solution in the two constant temperature chambers are pressurized and pumped into two hollow semi-cylindrical pipes through a multi-connected micro high-pressure pump. The bacterial solution and cementing solution are injected into the soil through the nozzles on the hollow semi-cylindrical pipes and mixed in the soil to form a microbial slurry, thereby reinforcing the soil at the tunnel starting shaft entrance.
6. The method for reinforcing the soil at the tunnel launch shaft entrance by injecting microbial grout as described in claim 5, characterized in that, When preparing the cementitious solution, the pH value of the cementitious solution is lowered separately so that the bacterial solution will not immediately begin to precipitate after mixing with the cementitious solution in the soil. Instead, after penetrating deep into the soil, the pH value will continuously rise to neutral as the bacterial solution hydrolyzes the urea in the cementitious solution, thus initiating the precipitation reaction and reinforcing the soil.
7. The method for reinforcing the soil at the tunnel launch shaft entrance by injecting microbial grout as described in claim 5, characterized in that, The bacterial solution is a Bacillus pasteurellii bacterial solution.
8. The method for reinforcing the soil at the entrance of a tunnel starting shaft by injecting microbial grout as described in any one of claims 5-7, characterized in that, The reinforcement range of the soil at the tunnel starting shaft entrance is all the soil within 5m longitudinally along the tunnel axis, 6m outside the tunnel centerline, 3m above the tunnel top, and 3m below the tunnel bottom.