A microbial grouting method for enclosing and reinforcing surrounding rock during construction of a diversion tunnel

Abstract

The present application relates to a kind of microbial grouting method for diversion tunnel construction period surrounding rock closure reinforcement, in particular to rock mass reinforcement technical field.The method of the present application comprises: according to the crack opening degree grading of surrounding rock, grouting scheme is determined;Bacillus pasteurii culture solution is prepared and cementing fluid is prepared;Drilling grouting hole and installing grouting pipe and stop plug;Using step injection process, first inject bacteria solution and stand adsorption, then inject cementing fluid to induce calcium carbonate precipitation, after circulation multiple times, maintenance solidification.The present application also discloses a kind of grouting device, including bacteria solution storage tank, cementing fluid storage tank, double liquid variable grouting pump, conveying pipeline, orifice mixer, grouting pipe, stop plug, pressure gauge, flowmeter and data logger.The present application can effectively block micro crack (0.3mm), so that the permeability coefficient of surrounding rock is reduced by more than 90%, cement consumption is reduced by 80%, and there is no adverse effect on water quality in later period, with the advantages of green, efficient and strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of rock mass reinforcement technology, and in particular to a microbial grouting method for sealing and reinforcing the surrounding rock during the construction of water diversion tunnels. Background Technology

[0002] Water diversion tunnels are key structures in the water conveyance system of water conservancy and hydropower projects, and their construction quality directly affects the safe operation and service life of the entire project. However, the following technical problems and deficiencies are commonly found during the construction of water diversion tunnels:

[0003] First, groundwater seepage affects construction progress and quality. Water diversion tunnels typically traverse areas with complex hydrogeological conditions, and groundwater seepage is a frequent problem during construction. Groundwater seeps into the tunnel from areas with well-developed rock fissures, resulting in a persistently damp environment at the tunnel face and walls. This not only affects the bonding effect between the shotcrete and the surrounding rock but also causes problems such as corrosion of construction machinery and equipment, moisture-induced failure of blasting materials, and a harsh working environment, severely restricting construction progress.

[0004] Secondly, traditional grouting materials have poor injectability in microfractured rock masses. For the widely developed microfractures (fracture width less than 0.3 mm) in the surrounding rock, traditional cement-based grouts are difficult to penetrate effectively due to their large particle size. Even with ultrafine cement, injectability is still limited by the fracture size, resulting in unsatisfactory grouting and sealing effects, and the problem of groundwater seepage cannot be fundamentally solved.

[0005] Third, traditional reinforcement methods have environmental disturbance and cost issues. Currently, the main methods for reinforcing the surrounding rock of tunnels are cement mortar grouting and chemical grouting. These methods have the following drawbacks: (1) Cement production has high carbon emissions, which does not meet the requirements of green construction; (2) Chemical grouts such as epoxy resin contain volatile organic compounds, which limit their application in sensitive ecological areas; (3) High-pressure jet grouting, deep mixing and other processes cause great in-situ disturbance to the surrounding rock, which can easily cause secondary cracks; (4) It is difficult for large grouting equipment to enter the site for construction in the narrow space of the tunnel.

[0006] Fourth, the concealed nature of rock fissures makes it difficult to guarantee the effectiveness of reinforcement. Micro-fissures in rock masses are often interconnected, forming complex seepage networks. Traditional grouting methods struggle to achieve uniform penetration and complete sealing, often resulting in surface sealing while internal seepage channels remain.

[0007] In recent years, microbially induced calcium carbonate precipitation (MICP) technology has shown promising application prospects in soil reinforcement. This technology utilizes urease produced by microbial metabolism to decompose urea, generating carbonate ions, which combine with calcium ions to form calcium carbonate crystals, cementing loose particles or filling fissures. Compared with traditional cement grouting, microbial grout has advantages such as small particle size, low viscosity, and good fluidity, providing a new approach for sealing micro-fractures in rock masses. Existing studies have shown that MIP technology can effectively seal rock joints and fissures, with an average reduction in permeability of up to 97% in treated specimens.

[0008] However, currently, MICP technology is mainly applied to sandy soil foundation reinforcement, slope stabilization, and concrete crack repair, with limited research on its application in the sealing and reinforcement of surrounding rock during the construction of water diversion tunnels. In particular, a mature microbial grouting process has not yet been developed to address the critical issue of groundwater seepage control during tunnel construction. Furthermore, the impact of microbial reinforcement on the quality of water flowing through the tunnels, a unique application scenario, lacks systematic research.

[0009] Based on this, a microbial grouting method suitable for the construction period of water diversion tunnels was developed. This method can effectively seal micro-fractures in the surrounding rock, control groundwater seepage, and ensure the safety of water quality during the later water diversion process, which has important engineering application value. Summary of the Invention

[0010] (1) Technical solution

[0011] This invention provides a microbial grouting method for sealing and reinforcing the surrounding rock during the construction of water diversion tunnels, comprising the following steps:

[0012] Step 1: Conduct a rock fissure characteristic survey of the section of the water diversion tunnel to be reinforced, and determine the grouting scheme based on the fissure opening.

[0013] Step 2: Cultivate mineralizing microbial culture with high urease activity and prepare a cementing solution containing urea and soluble calcium salts;

[0014] Step 3: Drill grouting holes in the section to be reinforced and install grouting pipes and grout-stopping devices;

[0015] Step 4: Inject microbial inoculum and cementing fluid into the surrounding rock in stages to induce calcium carbonate to precipitate in the fissures and block the seepage channels;

[0016] Step 5: After curing and solidification, test the effect of improved permeability of the surrounding rock.

[0017] Preferably, in step one, geological logging is performed on the section of the water diversion tunnel to be reinforced, and borehole television or fracture scanners are used to determine the occurrence, density, aperture, and connectivity of the surrounding rock fractures, measure the groundwater seepage rate and water quality parameters, and determine the arrangement spacing, depth, and grouting pressure parameters of the grouting holes based on the fracture characteristics; for micro fractures with a width of less than 0.5 mm, pure microbial grouting is used; for macro fractures with a width of more than 0.5 mm, microbial-cement composite grouting is used.

[0018] Preferably, in step two, the mineralizing microorganism is Bacillus pasteurellii, and the strain is ATCC11859 or DSMZ33; the strain is inoculated into liquid culture medium and cultured with shaking at 30-35℃ and pH 7.5-8.5 until the OD600 value is 1.0-2.0.

[0019] Preferably, in step two, the molar concentrations of urea and soluble calcium salt in the cementing solution are equal, both being 0.4-0.8 mol / L, and the calcium salt concentration is 0.4-0.8 mol / L; the soluble calcium salt is selected from one or more of calcium chloride, calcium nitrate, and calcium acetate; an adsorbent is added to the bacterial solution, the adsorbent being selected from montmorillonite or bentonite, and the amount added is 2%-5% of the bacterial solution mass.

[0020] Preferably, in the microbial-cement composite grouting, the water-cement ratio of the cement grout is 0.5:1 to 1:1, and the volume ratio of the bacterial solution, the binder and the cement grout is 1:0.8:0.5 to 1:1:1.

[0021] Preferably, in step three, grouting holes are drilled in the section of the tunnel to be reinforced. The hole diameter is 40-60mm, and the hole depth is determined according to the range of the loosened zone of the surrounding rock, with a hole depth of 1.5-3.0m. The grouting holes are arranged in a quincunx pattern with a hole spacing of 0.8-1.5m. Grouting pipes are installed in the grouting holes, and grout stop plugs are set at the pipe openings. The bacterial solution and cementing solution are packaged in different containers and connected to the grouting hole mixer through independent delivery pipelines.

[0022] Preferably, step four employs segmented grouting or skip-hole grouting methods, and is carried out according to the following procedures:

[0023] (1) Pretreatment water injection: Inject clean water into the grouting hole to moisten the surface of the crack. The amount of water injected is determined according to the degree of crack development.

[0024] (2) Injection of microbial solution: Inject microbial solution into the surrounding rock at a grouting pressure of 0.1-0.5MPa, and calculate the injection volume at 30-50L per meter of hole depth;

[0025] (3) Static adsorption: Stop grouting for 8-12 hours to allow microorganisms to fully adsorb onto the surface of rock fissures;

[0026] (4) Injecting cementing solution: Inject cementing solution at a grouting pressure of 0.2-0.8 MPa, with the injection volume to bacterial solution volume ratio being 0.8:1 to 1:1;

[0027] (5) Circulating grouting: Depending on the seepage of the surrounding rock, repeat steps (2) to (4) 2-4 times until the grouting pressure is stable or grout returns from the borehole.

[0028] (6) Curing and solidification: After the grouting is completed, the hole is sealed and cured for 48-72 hours to allow calcium carbonate to fully precipitate.

[0029] Preferably, in step four, for sections with high groundwater flow velocity, an intermittent grouting method is adopted, and the settling time after each injection of bacterial solution is extended to 24 hours.

[0030] Preferably, in step five, after grouting and curing are completed, the reinforcement effect is tested using the following method:

[0031] (1) Drill core samples to observe the fracture filling condition;

[0032] (2) The change in the permeability coefficient of the surrounding rock is determined by water injection test, and the permeability coefficient is required to decrease by more than 90%;

[0033] (3) Acoustic wave testing to assess the degree of improvement in the integrity of the surrounding rock.

[0034] Preferably, a microbial grouting device for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel includes: a microbial inoculum storage tank, a cementing liquid storage tank, a dual-liquid variable grouting pump, an inoculum delivery pipe, a cementing liquid delivery pipe, a mixed liquid delivery pipe, an orifice mixer, an grouting pipe, a grout stop plug, a pressure gauge, a flow meter, and a data recorder; the outlet of the microbial inoculum storage tank is connected to the first inlet of the dual-liquid variable grouting pump via the inoculum delivery pipe; the outlet of the cementing liquid storage tank is connected to the second inlet of the dual-liquid variable grouting pump via the cementing liquid delivery pipe; the outlet of the dual-liquid variable grouting pump is connected to the second inlet of the dual-liquid variable grouting pump via the mixed liquid delivery pipe. The feed pipe is connected to the inlet end of the orifice mixer; the outlet end of the orifice mixer is connected to the top end of the grouting pipe; the grout stop plug is sleeved on the outside of the grouting pipe; the pressure gauge and the flow meter are installed on both the bacterial liquid delivery pipe and the cementing liquid delivery pipe; the data logger is electrically connected to the pressure gauge and the flow meter; both the bacterial liquid delivery pipe and the cementing liquid delivery pipe are equipped with valves and check valves; the end of the grouting pipe extends beyond the grout stop plug and the pipe wall has a grout outlet hole with a diameter of 3-5mm; the microbial liquid storage tank is equipped with a first stirrer and a temperature control device; the cementing liquid storage tank is equipped with a second stirrer.

[0035] (2) Beneficial effects

[0036] The present invention proposes a microbial grouting method for sealing and reinforcing the surrounding rock during the construction of water diversion tunnels. Compared with the prior art, the present invention has the following advantages:

[0037] 1. This invention utilizes microbial-induced calcium carbonate precipitation to seal micro-fractures in surrounding rock, effectively controlling groundwater seepage, reducing humidity within the tunnel, and improving the construction environment. The microbial slurry has low viscosity and good fluidity, enabling it to penetrate micro-fractures (fracture width <0.3mm) that traditional cement slurry cannot reach, thus cutting off seepage channels at their source. Construction practice shows that the hydraulic conductivity of fractured rock mass treated with MIP technology decreases in a "stepwise" manner, demonstrating a significant sealing effect. This solves problems such as poor adhesion of shotcrete, equipment corrosion, and moisture absorption of blasting materials caused by groundwater in water diversion tunnel construction, significantly improving construction efficiency and shortening the construction period.

[0038] 2. In traditional grouting methods, direct mixing and injection of bacterial solution and cementing solution can easily lead to rapid surface sealing of cracks while the internal structure remains loose. This invention employs a step-by-step injection process. First, bacterial solution is injected and allowed to stand for adsorption, allowing microorganisms to adhere evenly to the crack surface. Then, cementing solution is injected to induce calcium carbonate precipitation, achieving uniform reinforcement from the shallow to the deep part of the crack. Simultaneously, by adding adsorbents such as montmorillonite, the microorganisms are released slowly, prolonging the mineralization reaction time and improving the grouting depth and reinforcement uniformity. Research has found that during the microbial mineralization sealing process, the grout flows in a channel pattern within the crack. As precipitation continuously blocks the flow channels, permeability gradually decreases, ultimately achieving complete sealing.

[0039] 3. This invention utilizes the natural process of microbial mineralization for surrounding rock reinforcement, avoiding the use of petroleum-based chemical materials such as epoxy resins and thus preventing the release of volatile organic compounds. The *Pasteurella multocida* used in the MICP technology is a common, non-pathogenic bacterium found in nature; urea and calcium chloride are both low-toxicity substances; and the main reaction byproduct is ammonium salt, making it significantly more environmentally friendly than traditional chemical grouts. Compared to cement grouting, this invention can significantly reduce cement usage, lowering the substantial carbon emissions generated by cement production. For fracture-developed sections, the use of microbial-cement composite grouting can reduce cement usage by 30%-50% while ensuring reinforcement effectiveness, aligning with the development direction of green construction and low-carbon engineering.

[0040] 4. This invention addresses the diverse nature of rock fissures in water diversion tunnels by providing a tiered grouting scheme: for micro-fissures (<0.5mm), pure microbial grouting is used to fully utilize the grout's good fluidity; for macro-fissures (>0.5mm), a microbial-cement composite grouting method is used to balance sealing effectiveness and early strength; and for high-velocity groundwater sections, intermittent grouting is employed to ensure effective microbial adhesion. This tiered and categorized process design enables this invention to adapt to water diversion tunnel construction under different hydrogeological conditions, demonstrating broad applicability.

[0041] 5. In view of the requirements for the water diversion tunnel's later water supply function, this invention specifically considers the impact of microbial reinforcement on water quality and has the following protection mechanisms:

[0042] (1) After the mineralization reaction is completed, Bacillus pasteurellii will gradually form spores and enter a dormant state due to the depletion of its nutrient source (urea), and will no longer carry out active metabolic activities. The calcium carbonate precipitate formed is an inert mineral with stable chemical properties and will not release harmful substances into the water.

[0043] (2) The ammonium ions (NH4+) produced by the MICP reaction can be gradually converted into nitrates by naturally occurring nitrifying bacteria in the water after water is introduced into the tunnel, thus participating in the normal nitrogen cycle of the water. Studies have shown that complex microbial ecosystems exist in long-distance water diversion projects, possessing the ability to biogeochemically cycle elements such as carbon, nitrogen, and sulfur. The small amount of ammonium salts produced during short-term grouting can be naturally absorbed by the ecosystem during long-term water introduction.

[0044] (3) The calcium carbonate layer formed by MIP plugging in rock joints maintains good stability under acidic conditions. The test results show that the permeability coefficient of the MIP-plugged specimens decreased by more than 95% after acid erosion. The calcium carbonate dissolution mainly occurred in the edge area of ​​the specimens, while the internal plugging effect remained good. This means that even if the water quality fluctuates to some extent during the long-term operation of the water diversion tunnel, the microbial reinforcement layer can still maintain a stable plugging effect and will not cause secondary pollution due to dissolution and release.

[0045] (4) Pasteurella multocida is a common soil microorganism, not a pathogenic microorganism, and harmless to humans and animals. Its spore morphology is highly resistant to stress and can survive for a long time without nutrients, but without metabolic activity. It will not multiply in large quantities after water is introduced and affect water quality. Existing studies have applied MIP technology to the repair of concrete cracks in drinking water projects, verifying its biosafety. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the microbial grouting device of the present invention.

[0047] Figure 2 This is a schematic diagram of the microbial reinforcement of tunnel fissures according to the present invention.

[0048] The attached figures are labeled as follows: 1-Microbial inoculum storage tank; 2-Cementing liquid storage tank; 3-Dual-liquid variable grouting pump; 31-First inlet; 32-Second inlet; 33-Outlet; 4-Inoculum delivery pipe; 5-Cementing liquid delivery pipe; 6-Mixed liquid delivery pipe; 7-Orifice mixer; 71-Inlet end; 72-Outlet end; 8-Grouting pipe; 81-Grouting outlet; 9-Stop plug; 10-Pressure gauge; 11-Flow meter; 12-Data logger; 13-Valve; 14-Check valve; 15-First agitator; 16-Temperature control device; 17-Second agitator. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to specific embodiments. However, it should be understood that the embodiments of this invention are for illustrative purposes only and are not intended to limit the scope of the invention.

[0050] First, the specific structure and preferred implementation of the microbial grouting device provided by the present invention will be described in detail.

[0051] The microbial grouting device provided by this invention, such as Figure 1 As shown, the system includes: a microbial inoculum storage tank 1, a cementing liquid storage tank 2, a dual-liquid variable displacement grouting pump 3, an inoculum delivery pipe 4, a cementing liquid delivery pipe 5, a mixed liquid delivery pipe 6, an orifice mixer 7, a grouting pipe 8, a grout stop plug 9, a pressure gauge 10, a flow meter 11, and a data logger 12. The connection relationships of the components have been described in the invention description section; the specific structure and preferred parameters of each component are described in detail below.

[0052] (1) Microbial inoculum storage tank 1

[0053] It is used to store mature Bacillus pasteurellium culture solution, ensuring the activity and uniformity of the solution during the grouting process. Its specific characteristics are as follows:

[0054] ① Tank Structure: The tank adopts a double-layer stainless steel structure, with an inner liner made of food-grade 304 stainless steel and an outer heat-insulating layer. The tank volume is determined based on the amount of grout injected per batch, preferably 50–500L. The top of the tank is equipped with a bacterial solution filling port, an exhaust valve, a pressure balancing port, and a cleaning spray system.

[0055] ② Agitation device: A side-entry or top-entry low-speed agitator (i.e., the first agitator 15) is installed inside the tank, with a stirring speed of 20-60 rpm. The blades are anchor-type or propeller-type to ensure that the microbial cells in the bacterial solution are evenly suspended and prevent sedimentation. The agitator motor is explosion-proof and suitable for the humid environment of the tunnel.

[0056] ③ Temperature control device 16: Since the optimal growth temperature for Bacillus pasteurellii is 30-35℃, the temperature of the bacterial solution needs to be kept stable during the grouting process. The temperature control device includes: an electric heating belt or jacketed heater with adjustable power; a compressor refrigeration unit (for high-temperature seasons or long-term storage); a PT100 temperature sensor to monitor the temperature inside the tank in real time; and an automatic temperature control module with a control accuracy of ±1℃.

[0057] ④ pH monitoring and adjustment interface (optional): An online pH meter 18 is installed on the side wall of the tank, which can display the pH value of the bacterial solution in real time. If the pH deviates from the range of 7.5 to 8.5, it can be finely adjusted by adding dilute alkali or acid through the liquid addition port.

[0058] ⑤ Level gauge 17: Uses a magnetic or ultrasonic level gauge to display the remaining amount of bacterial liquid in the tank in real time, and is linked with the control system to realize low level alarm.

[0059] (2) Cementing liquid storage tank 2

[0060] This solution is used for preparing and storing a gelling solution composed of urea and soluble calcium salts, where precipitation and crystallization must be avoided, and microbial contamination must be prevented. Its design is as follows:

[0061] ① Tank structure: Made of 304 stainless steel or corrosion-resistant plastic (such as HDPE), with a volume matching the bacterial solution tank. Since the cementing solution does not contain living microorganisms, it has lower temperature requirements and does not require complex temperature control, but direct sunlight should be avoided to prevent urea decomposition.

[0062] ② Stirring device: Equipped with a low-speed stirrer (i.e., the second stirrer 17), with a rotation speed of 30-80 rpm, and the impeller adopts a folding turbine type to ensure uniform concentration and prevent crystallization due to temperature changes. If calcium chloride is used, because its solubility varies greatly with temperature, stirring can prevent local supersaturation and precipitation.

[0063] ③ Anti-crystallization measures: Install a 100-mesh filter screen at the liquid outlet to intercept any possible tiny crystals; the outside of the pipeline can be wrapped with a heat tracing cable for gentle heating (≤40℃) in low-temperature seasons.

[0064] ④ Concentration monitoring: An optional conductivity meter can be installed to indirectly reflect the concentration of urea and calcium salts through the conductivity of the solution. An alarm will be issued when the concentration deviates from the set value by ±5%.

[0065] (3) The dual-liquid variable displacement grouting pump 3 adopts a dual-liquid variable displacement plunger pump to realize independent delivery, proportion adjustment and pressure control of bacterial solution and cementing solution. Specific features are as follows:

[0066] ① Pump body: Each liquid cylinder can independently adjust the stroke or frequency to achieve different flow ratios of bacterial solution and cementing solution (volume ratio adjustable from 0.5:1 to 2:1), suitable for grouting pressures of 0.5 to 5 MPa, with stable flow and small pulsation.

[0067] ② Flow regulation: The pump is equipped with a variable frequency speed control motor or pneumatic regulation mechanism, with a flow regulation range of 0~100L / min and a control accuracy of ±2%. The target flow rates of bacterial liquid and cementing liquid can be set separately and automatically corrected through closed-loop feedback.

[0068] ③ Pressure control: A pressure sensor is installed at the pump outlet. When the grouting pressure exceeds the preset upper limit (e.g., 1.0 MPa), the pump speed is automatically reduced or the return valve is opened to prevent fracturing of the surrounding rock. A safety valve is provided to release pressure to the return tank in case of overpressure.

[0069] ④ Anti-backflow device: A one-way valve 14 is installed on each pump outlet pipeline to prevent grout from flowing back or mixing during grouting intervals.

[0070] (4) Delivery pipeline

[0071] It includes a bacterial liquid delivery pipe 4, a cementing liquid delivery pipe 5, and a mixed liquid delivery pipe 6, which are responsible for delivering the bacterial liquid and cementing liquid from the storage tank to the grouting hole and mixing them at the hole opening.

[0072] ① Pipeline material: Corrosion-resistant and pressure-resistant polyurethane or nylon braided hoses are used, with an inner diameter of 10-25mm and a working pressure ≥1.5 times the maximum grouting pressure. Pipeline color differentiation: the bacterial solution pipe is blue, and the cementing solution pipe is yellow for easy identification.

[0073] ② Pipeline length: determined according to the tunnel cross-section width and grouting hole location. A single pipeline is generally 10 to 30 meters long and can be extended in sections using quick connectors.

[0074] ③ Orifice Mixer 7: Installed at the end of the grouting pipe (closely to the outside of the grout stop plug), the interior is a static mixing element or a small Y-shaped tee, made of 316L stainless steel, and can be disassembled for cleaning. The bacterial solution and cementing solution are initially mixed here and immediately enter the surrounding rock fissures to avoid premature reaction and blockage of the pipeline.

[0075] ④ Grout stopper 9 and grouting pipe 8: The grout stopper has an expansion rubber structure and its diameter matches the borehole. The grouting pipe is made of PVC or metal perforated pipe, with the end extending 50-100mm beyond the grout stopper. The pipe wall has grout outlet holes 81 with a diameter of 3-5mm to facilitate the diffusion of grout into the surrounding rock.

[0076] (5) Grouting parameter monitoring system

[0077] It includes a pressure gauge 10, a flow meter 11, and a data logger 12, which collect and record key parameters in the grouting process in real time, providing a basis for process control and effect evaluation.

[0078] ① Pressure gauge 10: Install one pressure gauge at the outlet of the dual-liquid pump, one before the orifice mixer, and one outside the grout stop plug. The pump outlet pressure reflects the grouting power; the orifice pressure is used to calculate the grouting pressure; the pressure outside the grout stop plug can determine whether there is grout seepage. The pressure gauge range is 0~1.6MPa, with an accuracy of 0.5 class. Vibration-resistant pressure gauges or digital pressure transmitters can be selected.

[0079] ② Flowmeter 11: Install either an electromagnetic flowmeter or a mass flowmeter on the delivery pipelines of the bacterial solution and the cementing solution, respectively. The electromagnetic flowmeter is suitable for bacterial solutions and cementing solutions (both containing electrolytes) with good conductivity, with an accuracy of ±1%; the mass flowmeter can directly measure the mass flow rate and is not affected by temperature or density. The flowmeter outputs a 4-20mA signal to the data logger.

[0080] ③ Data Logger 12: Adopts an industrial-grade touchscreen data logger with the following functions: Multi-channel input: Can input signals such as pressure, flow rate, temperature, pH, and conductivity; Real-time display: Displays the changes of each parameter over time in digital and curve form; Data storage: Built-in SD card or solid-state drive, storage frequency 1-10Hz, can save complete grouting process data; Alarm output: When the pressure exceeds the limit, the flow rate deviation is too large, or the liquid level is too low, it will issue an audible and visual alarm and automatically record the time of the fault; Report generation: Can export grouting logs and parameter curves for quality traceability.

[0081] ④ In-hole imaging-assisted monitoring (optional): A miniature endoscope camera is placed in individual pilot holes to observe the diffusion of slurry and the morphology of calcium carbonate precipitation in the fracture in real time, serving as a visual reference for parameter adjustment.

[0082] (6) Device working process

[0083] Taking a typical step-by-step grouting process as an example, the workflow of this grouting device is as follows:

[0084] ①Preparation stage: Pump the cultured bacterial solution into bacterial solution storage tank 1, turn on the first stirrer 15 and temperature control device 16; prepare the cementing solution and inject it into cementing solution storage tank 2, turn on the second stirrer 17. Check the pipeline connections and confirm the valve status.

[0085] ② Parameter setting: Input the target grouting pressure (e.g., 0.3MPa), bacterial solution and cementing solution flow rate (e.g., 30L / min), grouting time, number of cycles, etc. into the control system of the data logger 12.

[0086] ③ Injection of bacterial solution: Start the bacterial solution side of the dual-liquid variable grouting pump 3, open valve 13 on the bacterial solution delivery pipe 4, and the bacterial solution enters the surrounding rock fissures through the bacterial solution delivery pipe 4, the dual-liquid variable grouting pump 3, the mixed solution delivery pipe 6, the orifice mixer 7, and the grouting pipe 8. The flow meter 11 and pressure gauge 10 provide real-time feedback, and the PLC automatically adjusts the pump speed to maintain constant pressure. The pump automatically stops after the set volume is injected.

[0087] ④ Settling: The system enters the waiting timer phase, displaying the remaining settling time (e.g., 10 hours). During this period, the stirrer runs at a low speed, and the temperature control continues to operate.

[0088] ⑤ Injecting cementing fluid: After the settling period, start the cementing fluid side of the dual-liquid variable grouting pump 3, open valve 13 on the cementing fluid delivery pipe 5, and inject cementing fluid in the same manner.

[0089] ⑥ Loop: Automatically repeat steps ③ to ⑤ according to the set number of times.

[0090] ⑦ Completion and Cleaning: After grouting is completed, the system automatically switches to the clean water pipeline to backwash the pump body, pipelines, and mixer to prevent residual grout from solidifying and clogging. The flushing wastewater is discharged into a designated collection tank.

[0091] ⑧ Data output: After the operation is completed, the data logger 12 generates a grouting report, which can be exported to a USB flash drive or uploaded to the cloud platform.

[0092] The following specific embodiments further illustrate the microbial grouting method of the present invention and its effects.

[0093] Example 1: Microbial grouting reinforcement of surrounding rock in the water-rich section of a water diversion tunnel

[0094] A water diversion tunnel project traverses a granite area. During construction at chainage 2+350 to 2+450, well-developed rock fissures were discovered, resulting in significant groundwater seepage. The tunnel face was severely damp, and the shotcrete was not bonding well with the surrounding rock, seriously impacting construction progress. On-site investigation revealed that the surrounding rock in this section is primarily slightly weathered granite, with three sets of joints. The fissure density is 3-5 fissures / m, with fissure widths mainly ranging from 0.1-0.4 mm, locally reaching 1.0 mm. Groundwater flow is observed in a drip to linear pattern.

[0095] The reinforcement treatment using the method of this invention includes the following specific implementation steps:

[0096] 1. Grouting scheme design: Based on the characteristics of the cracks, pure microbial grouting is used for sections with crack width <0.5mm, and microbial-cement composite grouting is used for sections with local crack width >0.5mm. The grouting holes are arranged in a quincunx pattern with a spacing of 1.2m × 1.2m, and the hole depth is 2.5m.

[0097] 2. Microbial culture: *Bacillus pasteurellii* strain ATCC11859 was selected and inoculated into a culture medium (15 g / L tryptone, 5 g / L soybean peptone, 5 g / L sodium chloride). The culture was incubated at 30°C and pH 7.5 with shaking for 24 hours until the OD600 value reached 1.5. The bacterial concentration was approximately 5 × 10⁻⁶. 7 cells / mL.

[0098] 3. Preparation of cementitious grout: Prepare a mixed solution containing 0.5 mol / L urea and 0.5 mol / L calcium chloride, and stir well before use. For the microbial-cement composite grouting section, prepare a 425 ordinary Portland cement grout with a water-cement ratio of 0.6:1.

[0099] 4. Grouting Device Installation: Assemble the grouting device according to the following connection relationship: The outlet of the microbial liquid storage tank 1 is connected to the first inlet 31 of the dual-liquid variable grouting pump 3 through the liquid delivery pipe 4; the outlet of the cementing liquid storage tank 2 is connected to the second inlet 32 ​​of the dual-liquid variable grouting pump 3 through the cementing liquid delivery pipe 5; the outlet 33 of the dual-liquid variable grouting pump 3 is connected to the inlet end 71 of the orifice mixer 7 through the mixed liquid delivery pipe 6; the outlet end 72 of the orifice mixer 7 is connected to the top of the grouting pipe 8; a stop plug 9 is fitted on the grouting pipe 8; a pressure gauge 10, a flow meter 11, a valve 13, and a check valve 14 are installed on the liquid delivery pipe 4 and the cementing liquid delivery pipe 5 respectively; the data recorder 12 is electrically connected to each pressure gauge 10 and flow meter 11.

[0100] 5. Grouting implementation:

[0101] (1) Drilling: Grouting holes were drilled using a pneumatic rock drill with a diameter of 42 mm and a depth of 2.5 m;

[0102] (2) Install grouting pipe: Insert a 25mm diameter PVC grouting pipe into the hole and install a grout stop plug at the pipe opening;

[0103] (3) Pretreatment: Inject 50L of clean water into the hole to moisten the surface of the crack;

[0104] (4) Injecting bacterial solution: Inject bacterial solution at a pressure of 0.3 MPa, with an injection volume of 100 L per well;

[0105] (5) Static adsorption: Stop grouting for 10 hours;

[0106] (6) Injecting cementitious liquid: Inject cementitious liquid at a pressure of 0.5 MPa, with an injection volume of 100 L per hole;

[0107] (7) Circulating grouting: Repeat the above bacterial solution + cementing solution injection twice;

[0108] (8) Curing: Seal the opening and cure for 72 hours.

[0109] For the composite grouting section, during the second cycle, the binder and cement grout are mixed at a volume ratio of 1:0.8 and then injected.

[0110] 6. Effect detection:

[0111] Water injection test: The permeability coefficient of the surrounding rock before treatment was 5.6 × 10⁻⁶. -4 cm / s, reduced to 2.3 × 10 cm / s after treatment. -5cm / s, a decrease of 95.9%;

[0112] Core sampling observation: White calcium carbonate filling material was visible in the rock core fractures, and the filling was dense;

[0113] Construction results: After treatment, water seepage in the surrounding rock section basically stopped, the tunnel wall dried, and the shotcrete construction proceeded normally.

[0114] Example 2: Simulation Experiment of the Impact of Microbial Grouting on Subsequent Water Quality

[0115] To verify the safety of the method of this invention for the water quality during the later stages of water diversion tunnel operation, an indoor simulation experiment was designed:

[0116] 1. Experimental Design: Granite specimens with artificial fissures (300mm×300mm×300mm, fissure width 0.3mm) were prepared and sealed using the MICP method. After treatment, the specimens were installed in a water circulation system, using tap water as the medium to simulate the water flow conditions of a water diversion tunnel, with the flow velocity controlled at 0.1m / s.

[0117] 2. Water quality monitoring: Water samples were collected on days 1, 3, 7, 14, 28, and 56 after water supply was initiated, and pH and ammonia nitrogen (NH4+) were measured. + -N), nitrate nitrogen (NO3) - -N), nitrite nitrogen (NO2) - The system monitors indicators such as total nitrogen (TN) and total organic carbon (TOC), and also monitors the number of live bacteria in the water.

[0118] 3. Results Analysis:

[0119] During the initial water supply period (days 1-3): a small amount of ammonia nitrogen was detected in the water sample (peak value 0.8 mg / L), the pH increased slightly (from 7.2 to 7.8), and the viable bacteria count was 10. 2 -10 3 CFU / mL;

[0120] Mid-stage water supply (days 7-14): Ammonia nitrogen concentration gradually decreased to below 0.2 mg / L, nitrate nitrogen slightly increased, and viable bacteria count decreased to below 10 CFU / mL;

[0121] During the later stages of water supply (days 28-56): all water quality indicators returned to background levels (ammonia nitrogen <0.1 mg / L, nitrate nitrogen <2.0 mg / L), with no statistically significant difference compared to the untreated control group, and the number of viable bacteria was below the detection limit.

[0122] 4. Conclusion: After MIP grouting, a small amount of ammonia nitrogen will be released in the short term, but it will return to normal levels within two weeks under the natural nitrification of the water body; the microorganisms exist in spore form and will not multiply in large quantities in the water body. Simulation experiments confirm that the method of this invention has no significant adverse effects on the water quality during the later stages of water flow.

[0123] Example 3: Comparative Test with Traditional Cement Grouting

[0124] A comparative test was conducted in a test section of a water diversion tunnel. Traditional cement grouting (control group) and the method of this invention (test group) were used for reinforcement treatment, and the reinforcement effects were compared.

[0125]

[0126] The comparative results show that the method of the present invention is superior to traditional cement grouting in terms of injectability, sealing effect, construction efficiency, and environmental friendliness.

[0127] The embodiments described above are merely preferred embodiments of the present invention, and are described in a relatively specific and detailed manner. However, the present invention is not limited to these embodiments. It should be noted that for those skilled in the art, any modifications made without departing from the spirit of the present invention fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A microbial grouting method for sealing and reinforcing surrounding rock during the construction of water diversion tunnels, characterized in that, Includes the following steps: Step 1: Conduct a rock fissure characteristic survey of the section of the water diversion tunnel to be reinforced, and determine the grouting scheme based on the fissure opening. Step 2: Cultivate mineralizing microbial culture with high urease activity and prepare a cementing solution containing urea and soluble calcium salts; Step 3: Drill grouting holes in the section to be reinforced and install grouting pipes and grout-stopping devices; Step 4: Inject microbial inoculum and cementing fluid into the surrounding rock in stages to induce calcium carbonate to precipitate in the fissures and block the seepage channels; Step 5: After curing and solidification, test the effect of improved permeability of the surrounding rock.

2. The microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel according to claim 1, characterized in that, In step one, geological logging is performed on the section of the water diversion tunnel to be reinforced. The occurrence, density, aperture, and connectivity of the surrounding rock fissures are determined using borehole television or fissure scanners. The groundwater seepage rate and water quality parameters are measured. Based on the fissure characteristics, the spacing, depth, and grouting pressure parameters of the grouting holes are determined. For micro-fissures with a width of less than 0.5 mm, pure microbial grouting is used. For macro-fissures with a width of more than 0.5 mm, microbial-cement composite grouting is used.

3. The microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel according to claim 1, characterized in that, In step two, the mineralizing microorganism is Bacillus pasteurellii, strain ATCC11859 or DSMZ33; the strain is inoculated into liquid culture medium and cultured with shaking at 30-35℃ and pH 7.5-8.5 until the OD600 value is 1.0-2.

0.

4. The microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel according to claim 1, characterized in that, In step two, the molar concentrations of urea and soluble calcium salt in the cementing solution are equal, both being 0.4-0.8 mol / L, and the calcium salt concentration is 0.4-0.8 mol / L; the soluble calcium salt is selected from one or more of calcium chloride, calcium nitrate, and calcium acetate; an adsorbent is added to the bacterial solution, the adsorbent being selected from montmorillonite or bentonite, and the amount added is 2%-5% of the bacterial solution mass.

5. A microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel, as described in claim 2, is characterized in that... In the microbial-cement composite grouting, the water-cement ratio of the cement grout is 0.5:1 to 1:1, and the volume ratio of the bacterial solution, the binder, and the cement grout is 1:0.8:0.5 to 1:1:

1.

6. The microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel according to claim 1, characterized in that, In step three, grouting holes are drilled in the section of the tunnel to be reinforced. The hole diameter is 40-60mm, and the hole depth is determined according to the range of the loosened zone of the surrounding rock, with a hole depth of 1.5-3.0m. The grouting holes are arranged in a quincunx pattern with a hole spacing of 0.8-1.5m. Grouting pipes are installed in the grouting holes, and grout stop plugs are set at the pipe openings. The bacterial solution and cementing solution are packaged in different containers and connected to the grouting hole mixer through independent delivery pipelines.

7. A microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel, as described in claim 1, is characterized in that... Step four, which employs segmented grouting or skip-hole grouting, is carried out according to the following procedures: (1) Pretreatment water injection: Inject clean water into the grouting hole to moisten the surface of the crack. The amount of water injected is determined according to the degree of crack development. (2) Injection of microbial solution: Inject microbial solution into the surrounding rock at a grouting pressure of 0.1-0.5MPa, and calculate the injection volume at 30-50L per meter of hole depth; (3) Static adsorption: Stop grouting for 8-12 hours to allow microorganisms to fully adsorb onto the surface of rock fissures; (4) Injecting cementing solution: Inject cementing solution at a grouting pressure of 0.2-0.8 MPa, with the injection volume to bacterial solution volume ratio being 0.8:1 to 1:1; (5) Circulating grouting: Depending on the seepage of the surrounding rock, repeat steps (2) to (4) 2-4 times until the grouting pressure is stable or grout returns from the borehole. (6) Curing and solidification: After the grouting is completed, the hole is sealed and cured for 48-72 hours to allow calcium carbonate to fully precipitate.

8. A microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel, as described in claim 1, is characterized in that... In step four, for sections with high groundwater flow velocity, intermittent grouting is used, and the settling time after each injection of bacterial solution is extended to 24 hours.

9. A microbial grouting method for sealing and reinforcing surrounding rock during the construction of a water diversion tunnel, as described in claim 1, is characterized in that... In step five, after grouting and curing are completed, the reinforcement effect is tested using the following methods: (1) Drill core samples to observe the fracture filling condition; (2) The change in the permeability coefficient of the surrounding rock is determined by water injection test, and the permeability coefficient is required to decrease by more than 90%; (3) Acoustic wave testing to assess the degree of improvement in the integrity of the surrounding rock.

10. A microbial grouting device employing the method described in any one of claims 1-9, characterized in that, include: The system includes a microbial inoculum storage tank, a cementing liquid storage tank, a two-liquid variable displacement grouting pump, an inoculum delivery pipe, a cementing liquid delivery pipe, a mixed liquid delivery pipe, an orifice mixer, an injection pipe, a stop plug, a pressure gauge, a flow meter, and a data logger. The outlet of the microbial inoculum storage tank is connected to the first inlet of the two-liquid variable displacement grouting pump via the inoculum delivery pipe. The outlet of the cementing liquid storage tank is connected to the second inlet of the two-liquid variable displacement grouting pump via the cementing liquid delivery pipe. The outlet of the two-liquid variable displacement grouting pump is connected to the inlet of the orifice mixer via the mixed liquid delivery pipe. The outlet end of the orifice mixer is connected to the top of the grouting pipe; the grout stopper is sleeved on the outside of the grouting pipe; the pressure gauge and the flow meter are installed on both the bacterial liquid delivery pipe and the cementing liquid delivery pipe; the data recorder is electrically connected to the pressure gauge and the flow meter; both the bacterial liquid delivery pipe and the cementing liquid delivery pipe are equipped with valves and check valves; the end of the grouting pipe extends beyond the grout stopper and the pipe wall has a grout outlet hole with a diameter of 3-5mm; the microbial liquid storage tank is equipped with a first stirrer and a temperature control device; the cementing liquid storage tank is equipped with a second stirrer.

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