Integrated grouting device and offshore wind power single pile foundation anti-scouring construction method based on indigenous microorganism precuring seabed

Abstract

The invention relates to an integrated grouting device and an offshore wind power single pile foundation anti-scour construction method based on an indigenous microorganism precuring seabed, and the method comprises the following steps: prefabricating a special integrated grouting device according to the installation condition of an offshore wind power single pile foundation; an integrated grouting device is installed on the seabed of the to-be-constructed area through a hammering method and a negative pressure method; urease microorganisms are enriched and cultivated in in-situ seabed soil through an integrated grouting device, the microorganisms are induced to generate calcium carbonate gelatinization crystals so as to bond sandy soil particles, and the overall strength of a surface seabed is improved; and a single-pile foundation is installed on the microorganism solidification seabed. Before pile sinking construction, the surface seabed of the to-be-constructed area is intensified in advance through in-situ enrichment cultivation of indigenous urease microorganisms and induction of mineralization and crystallization of the microorganisms, scouring protection of the single pile foundation in the whole service cycle is achieved, and then the local scouring problem in the pile sinking process is solved.

Description

Technical Field

[0001] The present invention relates to an integrated grouting device and a construction method for preventing scour of a monopile foundation of an offshore wind turbine based on indigenous microorganism pre-cured seabed, belonging to the technical field of offshore wind power foundation construction and scour protection. Background Art

[0002] As a highly potential clean energy, offshore wind power exhibits many remarkable advantages. It has high power generation efficiency, does not occupy precious land resources, is suitable for large-scale development, and at the same time, the transportation of wind turbines is convenient and can be achieved by waterway. These characteristics have attracted much attention. China has rich offshore wind energy resources and great development potential.

[0003] However, offshore wind power is in a complex dynamic environment and needs to bear strong wind loads, seawater erosion and wave impacts simultaneously. This makes severe scour phenomena prone to occur around the foundation, thus threatening the stability and safety of offshore wind power. Therefore, in addition to increasing the pile length and embedded depth, measures such as dumping stones, laying sandbags and seabed reinforcement are often taken to conduct regular scour protection for the wind turbine foundation. Invention patents ZL202111516393.8 and ZL202211345930.1 describe the conventional installation process of monopile foundations. Generally, the installation construction of large-diameter monopile foundations of offshore wind turbines includes the following steps: using a special pile-hoisting ship to transport the precast monopile foundation to the construction site, hoisting and positioning the pile foundation, and then driving the pile foundation into the seabed through a pile hammer until the preset embedded depth requirement is reached. During the pile driving construction process, the presence of the pile foundation will disrupt the morphology of the surrounding flow field, thus triggering local scour phenomena and continuously developing during the construction process; if scour protection measures are taken during the pile driving construction stage, it can not only improve the stability and accuracy of the construction process, but also effectively inhibit the further development of scour, and at the same time reduce the cost brought by increasing the embedded depth of the pile foundation. For this reason, patent ZL 201410661498.6 proposes to pre-lay a gravel or concrete block protective layer at the installation position of the monopile foundation, and then install the pile foundation on the protective layer to alleviate the scour problem during the pile driving construction process. However, the dumped stones are mined from inland, and the transportation cost to the construction site is relatively high. Moreover, the stones are easily displaced and lost due to water flow impact, resulting in serious material loss and economic loss. In addition, the gravel protective layer will cause irreversible damage to the bottom of the pile foundation and weaken its bearing capacity, and the anti-corrosion layer of the foundation structure will also be damaged due to gravel friction, easily leading to structural rust, thus affecting the overall stability of the wind turbine unit.

[0004] With the continuous development of interdisciplinary research in microbiology, geochemistry, civil engineering, environmental engineering, etc., the Microbially Induced Carbonate Precipitation (MICP) technology has been gradually applied to fields such as soft soil foundation improvement and erosion prevention. This technology mainly transmits urease microbial cells and mineralization nutrients to loose sandy soil foundations at low pressure, and finally rapidly precipitates calcium carbonate gel crystals in the sand pores to bond sand particles, thereby improving the integrity and mechanical properties of the soil mass. The MICP grouting material is basically a water-based material with low viscosity and good fluidity, so it has advantages such as low energy consumption and simple construction; at the same time, compared with traditional chemical grouting reinforcement, the MICP technology has better biocompatibility and environmental friendliness. At present, MICP-solidified sand can significantly improve its anti-scour performance at a relatively low cementation strength, and this technology can still significantly improve the soil strength in the marine environment. For example, after the loose sand is treated with the MICP grouting solution once, its compressive strength can be increased to 400 - 800 kPa, which is sufficient to resist the water flow scouring of 4 - 6 m / s, and the reinforced sand body with this strength will not cause interference and damage to the pile foundation structure.

[0005] Therefore, before the installation of the large-diameter monopile foundation of the offshore wind turbine, using the indigenous urease microorganism-induced carbonate precipitation technology to reinforce the seabed in the construction area not only is expected to inhibit the local scouring problem during the pile driving process, but also can avoid the adverse effects of rubble dumping on the pile foundation structure, which helps to improve the stability of the large-diameter monopile foundation of the offshore wind turbine and reduce the maintenance cost. However, the traditional MICP process is likely to cause biological invasion hazards when introducing exogenous microorganisms. Therefore, when expanding the application method of the MICP technology in the field of offshore wind power pile foundation scour protection, it is necessary to reasonably develop and utilize the indigenous urease microorganisms in the construction area for mineralization. Summary of the Invention

[0006] The present invention provides an integrated grouting device and a construction method for preventing scour of an offshore wind power monopile foundation based on pre-solidifying the seabed with indigenous microorganisms. Before the pile driving construction, the surface seabed in the proposed construction area is pre-strengthened by in-situ enrichment and cultivation of indigenous urease microorganisms and induction of microbial mineralization crystallization, thereby solving the local scouring problem during the pile driving process.

[0007] The technical solution adopted by the present invention to solve its technical problems is:

[0008] An integrated grouting device includes a caisson, which is cylindrical. Define the diameter of the caisson as D and the diameter of the monopile foundation of the offshore wind turbine as d, and set the diameter D of the caisson to be between 5d and 6d;

[0009] The interior of the caisson is a slurry diffusion chamber. A slurry inlet is opened at the center of the top of the caisson, and several syringe-shaped slurry outlets are evenly distributed at the bottom. The conical tips of the slurry outlets are perpendicular to the bottom of the caisson. The number of slurry outlets is set as n, and the grouting rate is defined as Q, then n = (250 × D / Q) 2 , a grouting cofferdam is set at the bottom of the caisson along the circumference of the cylinder;

[0010] A plurality of perforated guide baffles are also arranged in the slurry diffusion chamber. The perforated guide baffles are arranged in sequence from the top to the bottom of the caisson along the central axis of the caisson. The perforated guide baffles are conical in shape, and the thickness of the surface facing the top of the caisson gradually decreases from the center to the edge, and the inclination angle from the center to the edge is 5-10 degrees.

[0011] Furthermore, an ammonia nitrogen ion sensor is embedded in the cofferdam wall of the grouting cofferdam to monitor the urease microbial activity in the grouting cofferdam;

[0012] Furthermore, the slurry outlet includes a hollow cylinder and a conical tip, and the hollow cylinder is connected to the conical tip;

[0013] 3-8 rows of circular slurry outlet holes are evenly distributed on the circumference of the hollow cylinder, with 6-8 holes in each row;

[0014] Two layers of filter membranes are set on the inner side of the slurry outlet wall, namely a steel mesh close to the inner side of the outer wall and a geotextile close to the steel mesh;

[0015] Furthermore, a plurality of circular holes are opened on the perforated guide baffle, and the diameters of the circular holes gradually increase from the center to the edge of the perforated guide baffle;

[0016] The anti-scour construction method for offshore wind power monopile foundation based on pre-solidification of seabed by indigenous microorganisms specifically includes the following steps:

[0017] Step S1, collecting undisturbed seabed soil in the construction area and measuring its porosity, which is defined as e;

[0018] Step S2: towing the integrated grouting device according to claim 1 to a predetermined installation area of the offshore wind turbine monopile foundation by a construction vessel, and lowering the integrated grouting device to the seabed surface using a lifting frame on the construction vessel, ensuring that the integrated grouting device and the seabed are kept horizontal, and at the same time ensuring that the slurry inlet faces the sky and the slurry outlet faces the seabed;

[0019] Step S3: sink the integrated grouting device into the seabed by its own weight or hammering. After it is initially stabilized, one end of the slurry delivery pipe is connected to the slurry inlet through a flange, and the other end of the slurry delivery pipe is connected to a centrifugal pump installed in the water tower on the construction vessel;

[0020] Step S4: Start the centrifugal pump to pump out the seawater in the grouting cofferdam from the slurry inlet, creating a pressure difference inside and outside the integrated grouting device. At this time, the integrated grouting device continues to sink until the slurry outlet is completely buried in the seabed, while ensuring that the slurry diffusion chamber is located on the seabed surface. Then, turn off the centrifugal pump.

[0021] Step S5: Pump the seawater near the construction area through the seawater slurry pipeline and transport it to the water tower. Add a carbon source, a nitrogen source, and trace elements to the seawater to prepare an indigenous urease microbial activator.

[0022] Step S6: Start the centrifugal pump again to transport the indigenous urease microbial activator into the integrated grouting device through the slurry pipeline. The indigenous urease microbial activator is shunted and adjusted by several perforated flow guiding partitions, diffusing evenly around the integrated grouting device and flowing into the seabed soil through the slurry outlet.

[0023] Step S7: Inject the indigenous urease microbial activator into the seabed soil in the construction area once every 24 hours until the change rate of the ammonia nitrogen ion concentration in the grouting cofferdam reaches 3 - 10 mM / min, then stop the injection.

[0024] Step S8: Pump the seawater near the construction area through the seawater slurry pipeline and transport it to the water tower. Add urea and calcium chloride to the seawater and adjust the pH of the mixed solution to 4.0 with acetic acid to prepare a microbial mineralization nutrient solution.

[0025] Step S9: Start the centrifugal pump to transport the microbial mineralization nutrient solution into the integrated grouting device through the slurry pipeline and evenly inject it into the surface seabed soil in the construction area, so that gelled calcium carbonate precipitates continuously in the seabed soil.

[0026] Step S10: Inject the microbial mineralization nutrient solution into the seabed soil in the construction area once every 24 hours until the strength of the seabed soil meets the engineering requirements.

[0027] Step S11: After the microbial reinforcement is completed, pull out the integrated grouting device from the seabed through the lifting frame on the construction ship and recycle it.

[0028] Step S12: Sink the monopile foundation of the offshore wind turbine into the seabed solidified by microorganisms by means of static pressure or hammering to complete the construction.

[0029] Furthermore, in the slurry diffusion chamber, 2 - 4 layers of perforated flow guiding partitions are arranged according to the slurry volume, grouting rate, and reinforcement range.

[0030] A number of round holes are opened on the perforated flow guiding plate, and the aperture of the round holes is 0.4 - 1 m.

[0031] Among them, the slurry volume is the grouting volume. Define the grouting volume as V, and the expected solidification depth of the seabed as h. Then V = 0.375×π×D 2 ×h×e; the grouting volume V is 1.5 times the sand pore volume within the range of the seabed to be reinforced;

[0032] The relationship between the grouting rate Q, the grouting volume, and the grouting time is: Q = V / t, where t is the grouting time and t ≤ 1.5, with the unit being hours.

[0033] Through the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The anti-scour construction method for the monopile foundation of offshore wind turbines based on indigenous microorganism pre-solidified seabed provided by the present invention is different from the traditional construction method of "driving piles first and then protecting". This method adopts the construction sequence of "strengthening and protecting the seabed first and then driving piles", which can effectively avoid the formation and development of local scour pits during the pile foundation installation process, and is expected to achieve scour protection for the monopile foundation throughout its service life, thereby ensuring the long-term stability of the wind turbine support structure;

[0035] 2. The anti-scour construction method for the monopile foundation of offshore wind turbines based on indigenous microorganism pre-solidified seabed provided by the present invention uses the seawater around the construction area to prepare microbial nutrient slurry and in-situ enrich and cultivate indigenous urease microorganisms, which not only saves the long-distance transportation cost of fresh water associated with the preparation of fresh water-based grouting liquid in the past, but also avoids the threat of biological invasion caused by the introduction of exogenous microorganisms into the construction area, further enhancing the ecological environment friendliness of the process;

[0036] 3. The anti-scour construction method for the monopile foundation of offshore wind turbines based on indigenous microorganism pre-solidified seabed provided by the present invention strengthens the seabed through the microbial mineralization reinforcement process, and can significantly improve the anti-scour performance of the construction area in a short time; compared with the traditional riprap protection layer, the solidified seabed soil by this method will not cause structural damage or anti-corrosion layer wear to the monopile foundation, and at the same time can effectively save the construction cost caused by the long-distance transportation of riprap;

[0037] 4. The integrated grouting device provided by the present invention has a reasonable structural design, can effectively improve the grouting efficiency, ensure the uniform diffusion of the slurry, prevent the loss of the slurry and the backflow of sand, has strong adaptability, and is convenient for construction. Description of the Drawings

[0038] The present invention will be further described below with reference to the drawings and embodiments.

[0039] Figure 1 is the overall structural schematic diagram after the traditional installation construction of the monopile foundation in the prior art;

[0040] Figure 2It is the front view of the preferred embodiment provided by the present invention regarding the integrated grouting device;

[0041] Figure 3 It is the bottom view of the preferred embodiment provided by the present invention regarding the integrated grouting device;

[0042] Figure 4 It is the cross-sectional view of the preferred embodiment provided by the present invention regarding the integrated grouting device;

[0043] Figure 5 It is the schematic diagram of the microbial grouting construction using the preferred integrated grouting device of the present invention;

[0044] Figure 6 It is the cross-sectional view of the microbial grouting construction using the preferred integrated grouting device of the present invention;

[0045] Figure 7 It is the schematic diagram of the microbial solidified seabed structure formed after the construction of the present invention;

[0046] Figure 8 It is the schematic diagram of the single-pile foundation structure based on the microbial reinforcement of the seabed pretreatment finally formed by the present invention.

[0047] In the figure: 1 is the single-pile foundation of the offshore wind turbine, 2 is the local scouring pit around the single-pile foundation, 3 is the slurry inlet, 4 is the slurry diffusion chamber, 5 is the grouting cofferdam, 6 is the slurry outlet, 7 is the slurry outlet hole, 8 is the ammonia nitrogen ion sensor, 9 is the perforated flow guiding partition, 10 is the slurry conveying pipe, 11 is the construction ship, 12 is the water tower, 13 is the seawater slurry conveying pipe, 14 is the microbial solidified seabed layer. Detailed implementation manners

[0048] Now, the present invention will be further described in detail with reference to the accompanying drawings. In the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as "left side", "right side", "upper part", "lower part", etc. is the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second", etc. do not represent the importance of the components, so they cannot be understood as limitations to the present invention. The specific dimensions adopted in this embodiment are only for illustrative purposes of the technical solution and do not limit the protection scope of the present invention.

[0049] As described in the background art, due to the environment in which the single-pile foundation of the offshore wind turbine is located, it needs to withstand strong winds and the interference of seawater, such as Figure 1In the installation construction of the traditional offshore wind power monopile foundation shown in the figure, local scouring pits 2 are likely to occur around the monopile foundation during the pile driving process, which increases the difficulty and cost of construction design and later maintenance. Therefore, the treatment methods of the existing technology include, in addition to increasing the pile length and the embedded depth, dumping rubble, laying sandbags, and seabed reinforcement, etc. In particular, the measure of laying a rubble anti-scouring layer in the construction area before the installation of the monopile foundation is the most common. However, the rubble layer will cause irreversible structural damage to the pile foundation structure and wear of the anti-corrosion layer, and the long-distance transportation of rubble will also cause a non-negligible construction cost.

[0050] Based on this, the present application provides a construction method for preventing scouring of an offshore wind power monopile foundation based on indigenous microorganisms pre-curing the seabed. Before the monopile foundation is sunk into the seabed, the indigenous urease microorganisms in the construction area are used to strengthen the seabed, which can not only prevent the development of local scouring during the pile driving process in a green and sustainable manner, but also avoid irreversible damage to the pile foundation structure caused by the soil strengthening anti-scouring layer. Here, one of the innovation points of the present application can be known. Using specific nutrient elements to directionally stimulate the activity of naturally occurring urease microorganisms in the soil of the construction area can ensure the adaptability of the microorganisms to the local environment, avoid the ecological risk of introducing alien species, and has ecological adaptability. Secondly, only by collecting the seawater near the construction area to prepare the microbial stimulating liquid and the microbial mineralization nutrient solution, it is beneficial to shorten the microbial culture cycle and save the cost of long-distance transportation of fresh water, achieving the purpose of low-cost and high-efficiency cultivation. If the MICP grouting liquid is to be evenly diffused into the pores between the soil particles on the seabed surface, a grouting device is needed, which can evenly inject the slurry into the seabed soil and at the same time realize the enrichment of indigenous microorganisms and the microbial-induced soil solidification. Therefore, the present application provides an integrated grouting device. The so-called integration means "indigenous microorganism enrichment and reinforcement", and its overall structure is as Figure 2 shown, including a caisson, which is cylindrical. Considering that the maximum possible scouring range of the local scouring pit of the offshore wind turbine monopile foundation is 6 times the diameter of the monopile, the diameter of the caisson is defined as D, and the diameter of the offshore wind turbine monopile foundation 1 is d. It is set that the diameter D of the caisson is between 5d and 6d. Inside the caisson is a hollow disc-shaped slurry diffusion chamber 4, and a slurry inlet 3 is opened at the center of the top of the caisson. Figure 3 As shown, a number of syringe-shaped slurry outlets 6 are evenly arranged at the bottom, and the conical tip of the slurry outlet is vertically oriented towards the bottom of the caisson; regarding the structure of the slurry outlet, Figure 3 - Figure 4It can be clearly seen that the slurry outlet includes a hollow cylinder and a conical tip, and the hollow cylinder is connected to the conical tip. The conical tip can effectively break through the soil layer. To ensure the uniform diffusion of the slurry along the height direction of the soil, the height of the slurry outlet is set as the planned grouting depth. 3-8 rows of circular slurry outlet holes 7 are evenly distributed on the circumference of the hollow cylinder, with 6-8 holes in each row. Of course, the diameter, number of rows and number of each row of the slurry outlet can be flexibly adjusted according to the specific grouting range. At the same time, two layers of filter membranes are also arranged on the inner side of the side wall of the slurry outlet, namely the wire mesh closely attached to the inner side of the outer wall and the geotextile closely attached to the wire mesh, to prevent sand particles from flowing back into the slurry outlet.

[0051] Regarding the set number of slurry outlets, the quantity is determined by the caisson diameter and the grouting rate. Specifically, the number of slurry outlets is set as n, and the grouting rate is defined as Q, then n=(250×D / Q) 2 ; After determining the number, arrange them outward with the center of the caisson bottom as the center. The grouting rate Q is related to the grouting volume and the grouting time. Specifically, Q = V / t, where t is the grouting time, and the grouting time is generally controlled within 1.5 hours to avoid the influence of long-term microbial mineralization reaction on the grouting uniformity.

[0052] Along the circumference of the cylinder at the bottom of the caisson, a grouting cofferdam 5 is arranged to limit the grouting range and guide the uniform diffusion of the slurry within the construction area. Further, the diameter and the thickness of the cofferdam wall of the grouting cofferdam are consistent with the slurry diffusion chamber. The lowermost end of the grouting cofferdam is designed as a wedge-shaped tip, which helps the cofferdam sink smoothly into the seabed; the height of the cofferdam is 1.5-2 times the planned grouting depth to prevent the grouting liquid from flowing out from the bottom of the cofferdam.

[0053] Figure 4 As shown, several perforated flow guiding partitions 9 are also arranged in the slurry diffusion chamber to guide the slurry injected into the chamber to uniformly diffuse along the radial direction of the disc. Several perforated flow guiding partitions are arranged in sequence from the top to the bottom of the caisson along the central axis of the caisson; the perforated flow guiding partitions are conical, and the thickness of the surface facing the top of the caisson gradually decreases from the center to the edge, which helps the slurry to diffuse around; and the inclination angle from the center to the edge is 5-10°, which can not only avoid uneven diffusion caused by excessive inclination, but also effectively reduce the overall height of the slurry diffusion chamber. Several round holes are opened on the perforated flow guiding partitions. The aperture of the round holes in the central area is smaller, and the aperture in the edge area is larger, to compensate for the uneven flow distribution caused by distance or pressure differences, and further ensure that the slurry can uniformly flow into the seabed from the slurry outlet at the bottom of the slurry diffusion chamber. According to the slurry volume, grouting rate and reinforcement range, 2-4 layers of perforated flow guiding partitions can be arranged in the slurry diffusion chamber, and the aperture of the round holes is 0.4-1m. Here, the slurry volume is the grouting volume. Define the grouting volume as V, and the expected solidification depth of the seabed as h, then V = 0.375×π×D 2×h×e; the grouting volume V is 1.5 times the pore volume of the sand within the seabed to be reinforced.

[0054] An ammonia nitrogen ion sensor 8 is embedded in the cofferdam wall of the grouting cofferdam for monitoring the urease microbial activity within the grouting cofferdam. Preferably, the ammonia nitrogen ion sensor is an ammonia nitrogen ion selective electrode, which contains an ion selective membrane inside and can specifically interact with ammonia nitrogen ions, converting the change in ammonia nitrogen ion concentration into an electrical potential signal; the ammonia nitrogen ion sensor is embedded in the inner surface of the side wall of the grouting cofferdam, and multiple sensors are evenly arranged along the circumference and depth of the side wall for real-time detection of the change in ammonia nitrogen ion concentration within the grouting area.

[0055] Next is the construction method for preventing scour of the monopile foundation of an offshore wind turbine based on indigenous microorganism pre-solidification of the seabed provided by this application, which specifically includes the following steps:

[0056] Step S1, collect the undisturbed seabed soil within the construction area and measure its porosity, defined as e.

[0057] Step S2, tow the integrated grouting device to the predetermined installation area of the monopile foundation of the offshore wind turbine by the construction ship 11, and use the lifting frame on the construction ship to lower the integrated grouting device to the seabed surface, ensuring that the integrated grouting device is kept horizontal with the seabed, and at the same time ensuring that the slurry inlet faces the sky and the slurry outlet faces the seabed.

[0058] Step S3, rely on the self-weight of the integrated grouting device or the hammering method to sink it into the seabed. During the sinking process, the edge of the grouting cofferdam at the bottom of the device cuts the soil to form a sealed chamber inside the grouting cofferdam. When the integrated grouting device is difficult to continue sinking, connect one end of the slurry delivery pipe 10 to the slurry inlet through a flange, and the other end of the slurry delivery pipe is connected to the centrifugal pump installed in the water tower 12 on the construction ship.

[0059] Step S4, start the centrifugal pump to pump out the seawater within the grouting cofferdam from the slurry inlet, creating a pressure difference inside and outside the integrated grouting device. At this time, the integrated grouting device continues to sink until the slurry outlet is completely buried in the seabed, and at the same time ensure that the slurry diffusion chamber is located on the seabed surface, then turn off the centrifugal pump.

[0060] Step S5, pump the seawater near the construction area through the seawater slurry delivery pipe 13 to the water tower, and add carbon source, nitrogen source and trace elements to the seawater to prepare the indigenous urease microorganism stimulating solution. Preparing the stimulating solution based on the seawater near the construction area, the real seawater provides the ionic environment required for the growth and reproduction of marine indigenous urease microorganisms, and the specific combination of nutrient elements can match the growth requirements of indigenous urease microorganisms, temporarily increasing the total amount and urease activity of urease microorganisms within the construction area, which is conducive to achieving efficient microbial solidification of sand and soil; in addition, relying on indigenous microorganisms rather than chemical curing agents is conducive to reducing secondary pollution to the marine environment.

[0061] Step S6, start the centrifugal pump again, and transport the indigenous urease microorganism stimulating liquid to the integrated grouting device through the slurry pipe. The indigenous urease microorganism stimulating liquid is diverted and adjusted by several perforated guide baffles, and evenly diffuses around the integrated grouting device and flows into the seabed soil through the slurry outlet, and finally flows into the interior of the seabed soil to achieve uniform grouting.

[0062] In step S7, a solution stimulating indigenous urease-producing microorganisms is injected into the seabed soil of the construction area every 24 hours to promote the accumulation of urease-producing microorganisms, simulate the natural metabolic cycle of microorganisms, and avoid overstimulation that could lead to community imbalance. An ammonia nitrogen ion sensor embedded in the grouting cofferdam wall monitors the activity of urease-producing microorganisms within the cofferdam. After a specific injection of the stimulating solution, when the rate of change of ammonia nitrogen ion concentration within the grouting cofferdam reaches 3-10 mM / min, the injection is stopped to prevent overnutrition that could cause microbial death or algae blooms.

[0063] Step S8: Extract seawater near the construction area and transport it to the water tower through the seawater slurry pipe. Add urea and calcium chloride to the seawater, and adjust the pH of the mixed solution to 4.0 with acetic acid. This acidic liquid environment is to inhibit the urease microbial mineralization reaction rate during the injection of microbial mineralization nutrient solution, so as to avoid the violent mineralization reaction during the grouting process and produce excessive mineralization crystals near the slurry outlet, thereby promoting the uniform diffusion of the slurry within the target soil range. At this point, urea acts as a carbonate ion precursor, and calcium chloride provides Ca 2 +, acetic acid adjusts the pH to 4.0 to provide a stable grouting solution. The three synergistically promote the precipitation of calcium carbonate and prepare a microbial mineralization nutrient salt solution.

[0064] Step S9: Start the centrifugal pump to transport the microbial mineralized nutrient solution through the slurry pipe to the integrated grouting device, and evenly inject it into the surface seabed soil in the construction area. During the maintenance period, gelled calcium carbonate precipitation will continue to form between the surface sand particles in the seabed of the construction area, thereby improving the integrity and anti-scour properties of the soil.

[0065] It should be explained here that the reason for the formation of gelled calcium carbonate precipitation is that a type of bacteria that can secrete urease protein molecules through metabolism is the urease microorganisms mentioned above. Under the induction of specific mineralized nutrients, these bacteria catalyze the hydrolysis of urea to produce carbonate ions (CO3 2- ), CO3 2- Ca in the environment 2 + combines to form calcium carbonate (CaCO3) with a cementing effect in the pores of the sand, thereby bonding the sand particles and enhancing the integrity and strength of the soil.

[0066] Step S10: Inject the microbial mineralized nutrient solution into the seabed soil in the construction area once every 24 hours until the seabed soil strength meets the engineering requirements.

[0067] Step S11: After the microbial reinforcement is completed, pull out the integrated grouting device from the seabed by the lifting frame on the construction ship and recycle it.

[0068] Step S12: Sink the monopile foundation of the offshore wind turbine into the seabed solidified by microorganisms by means of static pressure or hammering to complete the construction. During this process, the strengthened seabed soil can effectively resist water flow erosion and avoid the occurrence of local scour pits during the pile sinking process.

[0069] Example:

[0070] Next, this application provides a specific case. Taking the pile sinking and installation of the monopile foundation of an offshore wind turbine with a diameter of d = 5m as an implementation case, it is planned to carry out microbial reinforcement on the soil within a depth of 5m from the surface of the seabed in the construction area. The provided construction method includes:

[0071] First step: Design the cable route and burial depth, and lay the cable into the seabed in the planned construction area in advance; collect the near-undisturbed seabed soil in the construction area and measure its porosity e = 0.4.

[0072] Second step: Precast a cylindrical caisson-type indigenous microorganism enrichment and reinforcement integrated grouting device as shown in Figure 2 . The main part of the device is a hollow disc-shaped slurry diffusion chamber 4, and set D = 30m, and the height is 0.2 times the diameter of the slurry diffusion chamber. Two layers of perforated diversion partitions 9 are horizontally arranged in the slurry diffusion chamber. The perforated diversion partitions are higher in the center and lower at the edges, and the inclination angle from the center to the edge is set to 5°; on each layer of perforated diversion partition, a circle of round holes is evenly arranged every 4m around the center of the partition, with a total of four circles, and each circle has eight round holes. The diameters of the round holes from the central area to the edge area are 0.4m, 0.6m, 0.8m, and 1.0m respectively. The layout of the holes with a small center and a large edge is to compensate for the uneven flow distribution caused by distance or pressure differences.

[0073] At the center of the top surface of the slurry diffusion chamber 4, there is a slurry inlet 3, and several syringe-shaped slurry outlets 6 are evenly arranged on the bottom surface. The height of the slurry outlet is equal to the planned grouting depth, that is, 5m; six rows of circular slurry outlet holes are evenly arranged along the axial direction on the side wall of the slurry outlet, and six slurry outlet holes are arranged in each row. Two layers of filter membranes are arranged on the inner side of the side wall of the slurry outlet, namely the wire mesh closely attached to the inner side of the outer wall and the geotextile closely attached to the wire mesh, to prevent sand and soil particles from flowing back into the slurry outlet; the slurry outlets are evenly distributed on the bottom surface of the slurry diffusion chamber and are arranged radially outward with the center of the bottom surface as the center.

[0074] Calculate the required volume of grouting based on the expected curing depth, the porosity of seabed sand, and the diameter of the integrated grouting device, i.e., V = 0.375×π×30 2 ×5×0.4 = 2120m 3 ; To control the grouting time within 1.5 hours, design the grouting rate to be 1500m 3 / h; Furthermore, the required number of slurry outlets 6 can be calculated, i.e., n = (250×D / Q) 2 = 25; Therefore, the layout plan of the slurry outlets is to set one slurry outlet 6 at the center, and then arrange a circle of slurry outlets 6 every six meters along the radius, with a total of two circles, eight in the inner circle and sixteen in the outer circle, as shown in Figure 3 .

[0075] A hollow grouting cofferdam 5 is also provided at the bottom, which is a hollow cylinder structure, and its diameter and the thickness of the grouting cofferdam wall are the same as those of the slurry diffusion chamber; the lowest end of the grouting cofferdam wall is designed as a wedge tip to help the cofferdam sink smoothly into the seabed; the height of the cofferdam is 1.5 times the depth of the planned grouting, i.e., 7.5m, to prevent the grouting liquid from flowing out from the bottom of the cofferdam, as shown in Figure 2 and Figure 3 .

[0076] In the third step, tow the integrated grouting device to the predetermined installation area of the single-pile foundation by the construction ship 11, and use the lifting frame of the construction ship 11 to slowly lower the integrated grouting device to the seabed surface, ensuring that the device is horizontal with the seabed, and at the same time ensuring that the slurry inlet 3 faces upward and the slurry outlet 6 faces downward. First, rely on the self-weight of the device or the hammering method to make it partially sink into the seabed; during the sinking process, the edge of the grouting cofferdam 5 at the bottom of the device cuts the soil to form a sealed chamber inside the grouting cofferdam 5.

[0077] In the fourth step, when the integrated grouting device is difficult to continue sinking, connect one end of the slurry delivery pipe 10 to the slurry inlet 3 of the device through a flange, and the other end to a centrifugal pump, while the centrifugal pump is installed in a water tower 12 on the construction ship for preparing the grouting liquid; use the centrifugal pump to pump out the seawater inside the grouting cofferdam 5 from the slurry inlet 3 to form an internal and external pressure difference, so that the device continues to sink until the slurry outlet 6 is completely buried in the seabed, and the slurry diffusion chamber 4 of the grouting device remains above the seabed surface, as shown in Figure 5 .

[0078] In the fifth step, according to the calculated required volume of grouting, adjust the amount of seawater in the water tower using the seawater delivery pipe 13, and then add the nutrients required for enriching and culturing urease microorganisms to real seawater to prepare the indigenous urease microorganism stimulating solution; the main components of the stimulating solution can be set as 20g / L yeast extract, 15g / L ammonium chloride, 6g / L urea, and 0.1mmol / L nickel chloride.

[0079] Step 6: Use a centrifugal pump to transport the indigenous urease microbial activator to the integrated grouting device. After the activator enters the slurry diffusion chamber 4, it is shunted and adjusted by two layers of perforated flow guiding partitions 9 in the chamber, and evenly diffuses around the device and enters the slurry outlet 6, and finally flows into the seabed soil to achieve uniform grouting. See Figure 6 .

[0080] Step 7: Inject the indigenous urease microbial activator into the seabed soil in the proposed construction area once every 24 hours to promote the enrichment of urease microorganisms; monitor the urease microbial activity in the cofferdam through the ammonia nitrogen ion sensor 8 embedded in the cofferdam wall 5. The ammonia nitrogen ion sensor 8 is embedded in the inner surface of the cofferdam side wall, and three layers of ammonia nitrogen ion sensors 8 are evenly arranged, with eight in each layer, and the ammonia nitrogen concentration at a depth of up to 5 m can be measured to detect the microbial urease activity in the grouting area in real time.

[0081] When the change rate of the ammonia nitrogen ion concentration in the cofferdam reaches 3 - 10 mM / min after a certain injection of the activator, the urease microbial activity in the grouting cofferdam 5 has met the requirements of subsequent microbial mineralization reactions, and further injection of the indigenous urease microbial activator is stopped.

[0082] Step 8: Draw seawater near the construction area into the water tower 12 through the seawater slurry pipeline 13, add urea and calcium chloride to the real seawater, and adjust the pH of the mixed solution to about 4.0 with acetic acid to prepare the microbial mineralization nutrient solution; the concentrations of urea and calcium chloride are 1 mol / L; reducing the pH of the mixed solution is to inhibit the urease microbial mineralization reaction rate during the injection of the microbial mineralization nutrient solution to avoid excessive mineralization crystallization near the slurry outlet during the intense mineralization reaction and affect the grouting uniformity.

[0083] Step 9: Use a centrifugal pump to evenly inject the microbial mineralization nutrient solution in the water tower 12 into the surface seabed soil in the construction area through the integrated grouting device; during the curing period, gel-like calcium carbonate precipitates will continuously form between the sand particles on the seabed surface in the construction area, thereby improving the integrity and erosion resistance of the soil mass; taking 24 hours as a curing cycle, repeat injecting the microbial mineralization nutrient solution until the seabed soil strength reaches the engineering requirements. See Figure 7 .

[0084] Step 10: After the microbial reinforcement is completed, use the lifting frame on the construction ship 11 to pull out the hollow disc-shaped seabed grouting device from the seabed and recycle the device, and finally form the microbial solidified seabed layer 14 as shown in Figure 7 .

[0085] In the eleventh step, the monopile foundation 1 of the offshore wind turbine is sunk into the microbial solidified seabed layer 14 by means of static pressure or hammering. During this process, the strengthened seabed soil can effectively resist water flow erosion and avoid the occurrence of local scour pits during the pile sinking process, as shown in Figure 8 .

[0086] Those skilled in the art of the present technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those of ordinary skill in the art to which this application belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with their meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless defined as herein.

[0087] The meaning of "and / or" as described in this application refers to the situation where each exists alone or both exist simultaneously.

[0088] The meaning of "connection" as described in this application can be a direct connection between components or an indirect connection between components through other components.

[0089] Inspired by the above-described ideal embodiments of the present invention, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. An integrated grouting device, characterized in that: It includes a caisson, which is cylindrical. Define the diameter of the caisson as D and the diameter of the monopile foundation of the offshore wind turbine as d, and set the diameter D of the caisson to be between 5d and 6d; The interior of the caisson is a slurry diffusion chamber. A slurry inlet is provided at the center of the top of the caisson, and a number of syringe-shaped slurry outlets are evenly arranged at the bottom thereof. The conical tip of the slurry outlet is vertically directed towards the bottom of the caisson. Let the number of slurry outlets be n and the grouting rate be Q, then n=(250×D / Q). 2 , a grouting cofferdam is arranged along the circumference of the cylinder at the bottom of the caisson; A number of perforated guiding partitions are also arranged in the slurry diffusion chamber. The number of perforated guiding partitions is arranged sequentially from the top to the bottom of the caisson along the central axis of the caisson; the perforated guiding partition is conical, and the thickness of the surface facing the top of the caisson gradually decreases from the center to the edge, and the inclination angle from the center to the edge is 5-10°.

2. The integrated grouting device according to claim 1, characterized in that: An ammonia nitrogen ion sensor is embedded in the cofferdam wall of the grouting cofferdam to monitor the urease microbial activity in the grouting cofferdam.

3. The integrated grouting device according to claim 1, wherein: The slurry outlet includes a hollow cylinder and a conical tip, and the hollow cylinder is connected to the conical tip; 3-8 rows of circular slurry outlet holes are evenly arranged on the circumference of the hollow cylinder, and 6-8 holes are arranged in each row; Two layers of filter membranes are arranged on the inner side of the side wall of the slurry outlet, which are a wire mesh closely attached to the inner side of the outer wall and a geotextile closely attached to the wire mesh.

4. The integrated grouting device according to claim 1, characterized in that: A number of circular holes are opened on the perforated guiding partition, and the diameter of the circular holes gradually increases from the center to the edge of the perforated guiding plate.

5. The anti-erosion construction method for the monopile foundation of offshore wind turbines based on pre-solidified seabed with indigenous microorganisms is characterized in that: Specifically, it includes the following steps: Step S1, collect the undisturbed seabed soil in the construction area and measure its porosity, defined as e; Step S2, tow the integrated grouting device described in claim 1 to the predetermined installation area of the monopile foundation of the offshore wind turbine by a construction ship. Use the lifting frame on the construction ship to lower the integrated grouting device to the seabed surface, ensure that the integrated grouting device is kept horizontal with the seabed, and at the same time ensure that the slurry inlet is facing the sky and the slurry outlet is facing the seabed; Step S3, rely on the self-weight of the integrated grouting device or the hammering method to sink it into the seabed. After preliminary stabilization, connect one end of the slurry delivery pipe to the slurry inlet through a flange, and the other end of the slurry delivery pipe is connected to the centrifugal pump installed in the water tower of the construction ship; Step S4, start the centrifugal pump, pump the seawater in the grouting cofferdam out of the slurry inlet, form a pressure difference inside and outside the integrated grouting device. At this time, the integrated grouting device continues to sink until the slurry outlet is completely buried in the seabed, and at the same time ensure that the slurry diffusion chamber is on the seabed surface, and then turn off the centrifugal pump; Step S5, pump the seawater near the construction area through the seawater slurry delivery pipe to the water tower, add a carbon source, a nitrogen source and trace elements to the seawater to prepare an indigenous urease microbial stimulating solution; Step S6, start the centrifugal pump again, and transport the indigenous urease microbial stimulating solution to the integrated grouting device through the slurry delivery pipe. The indigenous urease microbial stimulating solution is shunted and adjusted by a number of perforated guiding partitions, diffuses evenly around the integrated grouting device and flows into the seabed soil through the slurry outlet; Step S7, inject the indigenous urease microbial stimulating solution into the seabed soil in the construction area once every 24 hours until the change rate of the ammonia nitrogen ion concentration in the grouting cofferdam reaches 3-10 mM / min, and then stop injection; Step S8, pump the seawater near the construction area through the seawater slurry delivery pipe to the water tower, add urea and calcium chloride to the seawater, and adjust the pH of the mixed solution to 4.0 with acetic acid to prepare a microbial mineralization nutrient solution; Step S9: Start the centrifugal pump, and convey the microbial mineralized nutrient solution to the integrated grouting device through the slurry pipeline, and uniformly inject it into the surface seabed soil in the construction area, so that gelled calcium carbonate precipitation continuously forms in the seabed soil; Step S10: Inject the microbial mineralized nutrient solution into the seabed soil in the construction area every 24 hours until the strength of the seabed soil meets the engineering requirements; Step S11: After the microbial reinforcement is completed, pull out the integrated grouting device from the seabed by the lifting frame on the construction ship and recycle it; Step S12: Sink the monopile foundation of the offshore wind turbine into the seabed solidified by microorganisms by means of static pressure or hammering to complete the construction.

6. The construction method for preventing scour of the monopile foundation of an offshore wind turbine based on pre-solidifying the seabed with indigenous microorganisms according to claim 5, characterized in that: In the slurry diffusion chamber, arrange 2 - 4 layers of perforated flow guide partitions according to the slurry volume, grouting rate and reinforcement range; A number of round holes are opened on the perforated flow guide plate, and the aperture of the round holes is 0.4 - 1 m; Among them, the slurry volume is the grouting volume. Define the grouting volume as V, and the expected solidification depth of the seabed as h, then V = 0.375×π×D 2 ×h×e; the grouting volume V is 1.5 times the pore volume of the sand within the seabed to be reinforced; The relationship between the grouting rate Q, the grouting volume and the grouting time is: Q = V / t, where t is the grouting time and t ≤ 1.5, and the unit is hour.

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