An assembled splash zone protection sleeve for offshore wind steel monopile foundations and a method of installation

Abstract

This application relates to the technical field of water conservancy and hydropower engineering, and in particular to a prefabricated splash zone protection sleeve and installation method for offshore wind power steel monopile foundations. This protective sleeve includes a prefabricated composite shell, a grouting layer, and fasteners. The prefabricated composite shell, which surrounds the outside of the steel monopile, is a segmented prefabricated component, with a UHPC outer layer and an ECC inner layer arranged radially from the outside to the inside. The grouting layer, formed by curing high-performance grout, has a continuous annular structure and fills the annular cavity between the ECC inner layer and the steel monopile. Fasteners are used to achieve a mechanical connection between the prefabricated composite shell and the steel monopile. The prefabricated composite shell has fastening holes, grouting holes, and venting holes. The segments of the shell are spliced ​​together by fasteners to form a closed protective sleeve. This protective sleeve can achieve a synergistic effect of outer layer impermeability, wear resistance, and impact resistance, and inner layer crack control and coordinated deformation, reducing the frequency of high-risk offshore maintenance.

Description

Technical Field

[0001] This application relates to the technical field of water conservancy and hydropower engineering, and in particular to a prefabricated splash zone protection sleeve for offshore wind power steel monopile foundations and its installation method. Background Technology

[0002] Among various offshore wind turbine foundation structures, steel monopile foundations have long held a dominant market position due to their significant advantages, including mature manufacturing processes, high construction efficiency, and suitability for large-scale nearshore development. Currently, nearly 75% of offshore wind farms in operation worldwide use monopile foundations, making it the mainstream structural form for offshore wind turbine foundations. However, steel monopile foundations operate in harsh marine environments, especially in the splash zone, where they must withstand the combined effects of chloride corrosion, wet-dry cycles, wave erosion, and impact from floating debris. This significantly accelerates corrosion and structural deterioration in this area, severely impacting the service life and structural safety of the monopile foundation. Therefore, the development of durability protection technologies for offshore wind turbine steel monopile foundations, particularly in the splash zone, is of paramount engineering importance and urgent practical need.

[0003] Current anti-corrosion measures for steel monopile foundations in the engineering field mainly focus on anti-corrosion coatings, cathodic protection, cladding and isolation, and surface cleaning and maintenance. Their core objectives are to reduce the corrosion rate of steel or delay the failure of the protective layer. However, they generally have the limitation of not being able to simultaneously improve the bearing capacity and stiffness of the monopile structure, and are difficult to meet the long-term protection requirements in the harsh environment of the splash zone. Specifically, while existing heavy-duty anti-corrosion coatings can address aging and corrosion issues in marine environments, they are essentially still coating-based isolation protection. Under conditions of high-frequency impact and abrasion in the splash zone and localized coating damage, the protection still faces the risk of failure, and offshore repair operations are difficult and costly. Existing impressed current cathodic protection technology addresses the pain points of traditional cathodic protection systems—high maintenance and replacement difficulty, high cost, and high underwater operation risks—by improving cable arrangement. However, this method only reduces the corrosion rate of steel piles and cannot effectively improve the structural mechanical performance of monopile foundations. Existing maintenance and cleaning technologies weaken corrosion by regularly removing marine organisms, salt crystals, and slime, and employ low-salinity water flushing schemes with specific parameters to enhance cleaning effectiveness. However, these still fall under the category of routine maintenance and cleaning, offering limited repair for monopile surface damage caused by impact and abrasion in the splash zone, and cannot improve the long-term structural redundancy of monopile foundations. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a prefabricated splash zone protection sleeve and installation method for offshore wind power steel monopile foundations. This sleeve can achieve the synergistic effect of an outer layer that is impermeable, wear-resistant, and impact-resistant, and an inner layer that controls cracking and coordinates deformation. It also has the characteristics of rapid replacement and repair, thereby significantly extending the long-term service life of the monopile foundation, reducing the frequency of high-risk offshore maintenance, controlling the total life cycle cost, and providing technical support for the large-scale and sustainable development of the offshore wind power industry.

[0005] The above-mentioned objective of this application is achieved through the following technical solution: A prefabricated splash zone protection sleeve for offshore wind turbine steel monopile foundations includes a prefabricated composite shell, a grouting layer, and fasteners. The prefabricated composite shell, positioned around the outside of the steel monopile, is a segmented prefabricated component with a UHPC outer layer and an ECC inner layer arranged radially from the outside to the inside. The grouting layer, formed by curing a high-performance grouting material, has a continuous annular structure and fills the annular cavity between the ECC inner layer and the steel monopile. The fasteners provide a mechanical connection between the prefabricated composite shell and the steel monopile. The prefabricated composite shell has fastening holes, grouting holes, and venting holes. The segments of the shell are joined together by the fasteners to form a closed protective sleeve.

[0006] As a preferred embodiment of the present invention, the lower end of the assembled composite shell is provided with a bottom grout sealing structure. This sealing structure is a water-swellable sealing component, which is arranged in the circumferential sealing area between the bottom edge of the shell and the steel monopile, and is set in the circumferential groove to prevent displacement during grouting.

[0007] As a preferred embodiment of the present invention, the number of segments n of the segmented precast component is 2-6 segments, and the number of segments is selected according to the outer diameter D of the steel monopile: when D≤4m, 2 segments are used; when 4m<D≤6m, 3 segments are used; when D>6m, 4-6 segments are used.

[0008] As a preferred embodiment of the present invention, the circumferential joints of adjacent shell lobes are staggered, and a sealing structure is provided at the joint. The sealing structure is selected from one or more of elastic sealing strips, sealant, or tongue-and-groove overlapping structures, and is used to achieve leakage prevention during the grouting process and waterproof sealing during service.

[0009] As a preferred embodiment of the present invention, the grouting layer and the steel monopile are bonded together by means of interface bonding enhancement measures, specifically: the outer surface of the steel monopile is roughened by sandblasting or mechanical grinding to make the surface profile height reach 50-150μm; the interface humidity is controlled before grouting to keep the interface in a surface dry or slightly wet state in order to suppress the attenuation of bonding performance caused by the interface water film.

[0010] As a preferred embodiment of the present invention, the fastener is a through pin, which passes through the assembled composite shell and forms a limiting connection with the steel monopile to improve the anti-detachment performance between the protective sleeve and the monopile.

[0011] As a preferred embodiment of the present invention, the thickness of the UHPC outer layer is 30-60mm, the thickness of the ECC inner layer is 15-30mm, and the thickness of the grouting layer is 20-60mm.

[0012] As a preferred embodiment of the present invention, the inner side of the prefabricated composite shell is provided with a plurality of positioning pads. The positioning pads are used to temporarily support the prefabricated composite shell during installation and maintain the design thickness of the annular cavity between the ECC inner layer and the steel monopile.

[0013] A method for installing a prefabricated protective sleeve, characterized by comprising the following steps: S1. Single pile surface treatment: Rust removal and roughening treatment of the outer surface of the splash zone of the steel single pile, and wetting treatment of the interface after cleaning. S2. Shell positioning: The segmented assembled composite shell is hoisted to the design elevation in sections, the design thickness of the annular cavity is maintained with the help of positioning pads, and the sealing treatment of each shell segment joint is completed. S3. Fastening connection: Fasteners are installed through the fastening holes on the assembled composite shell to close each shell segment, and the composite connection assembly is installed to form a mechanical limit. S4. Grouting and molding: High-performance grout is injected into the annular cavity from the grouting hole in a bottom-up manner, while air in the cavity is discharged through the vent hole. After the vent hole continuously discharges grout, the vent hole is sealed. S5. Curing and Sealing: Thoroughly seal the grouting holes and vent holes, and cure them to the design strength using either moist curing or sealed curing methods before putting them into service.

[0014] As a preferred embodiment of the present invention, during the grouting process, the grouting pressure is controlled at 0.05-0.30 MPa to effectively prevent grout leakage at the joint.

[0015] In summary, the beneficial technical effects of this application are as follows: 1. Triple Protection Composite System: This invention constructs a composite protection structure of "UHPC outer layer - ECC inner layer - grouting layer". The UHPC outer layer forms a highly dense impermeable barrier with wear resistance and impact resistance, effectively resisting erosion and chloride salt corrosion in the splash zone; the ECC inner layer has high ductility and crack control capabilities, inhibiting through cracks caused by UHPC shrinkage or external loads, and acts as a coordinating layer to alleviate deformation inconsistencies between the protective sleeve and the grouting layer; the grouting layer continuously fills the annular cavity, enabling stress buffering and transfer, thereby upgrading the protection system from a single isolation barrier to a composite protection system with material-structure synergy.

[0016] 2. Enhanced interfacial debonding resistance: This invention significantly reduces the risk of interfacial water seepage and debonding by roughening the surface of the steel pile and combining it with interfacial bonding enhancement measures. At the same time, mechanical connections such as through pins are introduced on the basis of bonding to form a composite connection mechanism. Even if the interfacial performance fluctuates or there are micro-defects in some areas, it can still maintain anti-slip and anti-peeling capabilities, and improve the durability and safety of the splash zone under repeated loading and extreme sea conditions.

[0017] 3. Reduced difficulty and cost of construction and operation and maintenance: The present invention adopts a segmented prefabricated shell with fastening holes, grouting holes and venting / holes, which facilitates rapid placement, positioning and grouting during the offshore window period, reducing on-site work and construction difficulty; when the sheath is damaged in a local area, it can be disassembled and replaced in sections, avoiding complete removal or large-scale secondary painting, shortening downtime and reducing offshore maintenance risks and costs.

[0018] 4. Balancing protection and improved mechanical performance: Unlike coatings and electrochemical protection measures that only provide corrosion protection, this invention forms a continuous grouting layer between the protective sleeve and the steel pile, making the high-performance UHPC-ECC shell-grouting-steel pile a composite system that can work together, thereby improving the local stiffness and bearing capacity of a single pile.

[0019] 5. Controllable sealing and construction quality, and high long-term reliability: This invention can achieve joint sealing through staggered joints or tongue-and-groove overlaps and other joint structures, combined with sealing strips or sealants, reducing the risk of leakage caused by joint penetration; the setting of grouting holes and venting holes ensures sufficient venting of the cavity and easy determination of grout filling degree, improves grouting density and overall continuity, reduces early defects and improves long-term service reliability and durability stability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the protective sleeve of the present invention.

[0021] Figure 2 This is a top view of the overall structure of the protective sleeve of the present invention.

[0022] Figure 3 This is a schematic diagram of the tongue-and-groove joint and sealing structure of a prefabricated segmented shell.

[0023] Figure 4 This is a schematic diagram of the structure of a through-pin composite connection assembly.

[0024] The reference numerals in the attached diagrams are as follows: 1. Prefabricated composite shell; 2. Grouting layer; 3. Fastener; 4. Steel monopile; 5. Sealing structure; 6. Positioning pad; 7. UHPC outer layer; 8. ECC inner layer; 9. Fastening hole; 10. Grouting hole; 11. Vent hole; 12. Bottom grout sealing structure; 13. Sealing adhesive; 14. Sealing strip. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the accompanying drawings.

[0026] like Figure 1 As shown, this application relates to a prefabricated splash zone protection sleeve for offshore wind power steel monopile foundations, as illustrated in the attached figure. Figure 1 -Appendix Figure 4 As shown, it includes a prefabricated composite shell 1, a grouting layer 2, and fasteners 3, which, after assembly, surround the outside of the splash zone of the steel monopile 4 to form a protective structure.

[0027] The prefabricated composite shell 1 is a segmented prefabricated component. In this embodiment, the outer diameter of the steel monopile is D=6.0m, and a three-segment shell is preferred. The prefabricated composite shell 1 includes a UHPC outer layer 7 and an ECC inner layer 8 in the radial direction from the outside to the inside. The thickness of the UHPC outer layer 7 is 40mm, the thickness of the ECC inner layer 8 is 20mm, and a 40mm thick annular cavity is reserved between the inner side of the shell and the steel monopile 5 to form the grouting layer 2.

[0028] The prefabricated composite shell 1 has prefabricated fastening holes 9, grouting holes 10, and venting holes 11. The fastening holes 9 are distributed circumferentially along the shell and are used to install fasteners 3 to achieve the closure of adjacent shell segments. The fasteners 3 pass through the prefabricated composite shell 1 and form a limiting connection with the steel monopile 4. Reliable anchoring of the pin and monopile is achieved through welded anchor seats and sleeve structures, providing mechanical limiting and anti-detachment redundancy. The grouting holes 10 are preferably located at the lower part of the shell. The venting holes 11 are preferably located at the upper part of the shell, facilitating grouting and venting and serving as a criterion for completion of filling. The circumferential joints of adjacent shell segments are staggered, and the joint positions of adjacent shell segments are staggered in the circumferential direction to avoid leakage or the formation of weakened zones due to through-joints, thereby improving the overall impact resistance, impermeability, and durability. To achieve leak prevention during grouting and waterproof sealing during service, a tongue-and-groove joint structure is used at the joints, and an elastic sealing strip 14 is installed at the tongue-and-groove contact area. Sealant 13 is also applied to the outside of the joint to form a double seal. Several positioning pads 6 are arranged circumferentially on the inner side of the prefabricated composite shell 1. The positioning pads 6 are used for temporary support during installation and to maintain the thickness of the annular cavity, so as to make the shell coaxially positioned and prevent uneven grouting caused by cavity thickness deviation. A bottom grout sealing structure 12 is provided at the bottom of the prefabricated composite shell 1 to improve the reliability of leak prevention during grouting and waterproofing during service.

[0029] To improve the interfacial bonding and anti-debonding ability between the grouting layer 2 and the steel monopile 4, the following interfacial bonding enhancement measures are adopted: the outer surface of the splash zone of the steel monopile 4 is derusted and roughened by mechanical grinding to make its surface contour height 50-150μm; the interface humidity is controlled before grouting to keep the interface in a slightly moist state and suppress the bonding attenuation caused by the interface water film.

[0030] The proportions of the three materials are as follows: The outer layer of UHPC uses a high-density, ultra-high-performance cement-based material, which significantly improves the outer layer's impermeability, wear resistance, and impact resistance, and enhances its resistance to chloride salt corrosion. By weight, its composition is as follows: P·II 52.5 cement: 1.0, silica fume: 0.25, quartz powder: 0.30, quartz sand (0.1-1.2mm): 1.10, water: 0.20, steel fiber: 2.0% by volume, polycarboxylate superplasticizer: 0.03.

[0031] The inner layer of the ECC uses a high-ductility fiber-reinforced cementitious composite material, which has good strain hardening and multi-crack cracking capabilities. It can suppress crack width development under wave impact, temperature and humidity cycling, and deformation coordination requirements, thereby improving the overall toughness and crack resistance of the shell. The composition by weight is as follows: cement: 1.00, fly ash (Grade II): 1.5, river sand (≤0.6mm): 0.80, water: 0.75, PVA fiber: 2.0% by volume, polycarboxylate superplasticizer: 0.01.

[0032] The grouting material is a high-strength, micro-expansion or non-shrinkage high-performance grouting material with good fluidity and strength development capability. It can ensure complete filling of the annular cavity and form a continuous and dense annular layer after curing, thereby improving the overall load-bearing stability of the sheath. The proportions by weight are as follows: cement: 1.00, slag powder: 0.40, silica fume: 0.05, quartz sand: 1.20, water: 0.28, water-reducing agent: 0.01, expansion agent: 0.05.

[0033] This application also relates to an installation method for a prefabricated protective sleeve, comprising the following steps: First, the outer surface of the splash zone of the steel monopile 4 is derusted and roughened, and the surface contour height is made to 50-150μm by mechanical grinding; after cleaning, the interface is wetted and controlled to be in a slightly damp state. Then, the segmented prefabricated composite shell 1 is hoisted to the design elevation in sections and surrounded on the outside of the steel monopile 4; the thickness of the annular cavity between the shell and the monopile is maintained by the positioning pads 6, and the coaxiality and joint gap are adjusted; a sealing structure 5 is installed at the joint of the shell segments to complete the waterproof sealing of the joint. Then, fasteners 3 are installed through the fastening holes 9 to splice the shell segments into a closed protective sleeve, so that a reliable mechanical limiting connection is formed between the shell and the monopile. High-performance grout is then injected into the annular cavity through grouting hole 10, while venting occurs through vent hole 11. Grouting is performed from bottom to top, with the grouting pressure controlled between 0.05 and 0.30 MPa to prevent joint leakage and ensure dense filling. Grouting is stopped once grout continuously flows from the vent hole. Finally, grouting hole 10 and vent hole 11 are sealed. The outer surface of the shell and the vent holes are then moistened or sealed for curing. The grouting layer 2 is put into service after reaching its design strength.

[0034] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A prefabricated splash zone protection sleeve for offshore wind steel monopile foundations, characterized in that, The assembly includes a prefabricated composite shell (1), a grouting layer (2), and fasteners (3). The prefabricated composite shell (1) surrounds the outside of the steel monopile (4) and is a segmented prefabricated component. The UHPC outer layer (7) and ECC inner layer (8) are arranged radially from the outside to the inside. The grouting layer (2) is formed by curing high-performance grouting material and has a continuous ring structure. It fills the annular cavity between the ECC inner layer (8) and the steel monopile (4). The fasteners (3) are used to realize the mechanical connection between the prefabricated composite shell (1) and the steel monopile (4). The prefabricated composite shell (1) is provided with fastening holes (9), grouting holes (10) and venting holes (11). Each segment of the shell is spliced ​​together by the fasteners (3) to form a closed protective sleeve.

2. An offshore wind power steel monopile foundation assembly splash zone protection sleeve according to claim 1, characterized in that, The lower end of the prefabricated composite shell (1) is provided with a bottom grout sealing structure (12), which is arranged in the circumferential sealing area between the bottom edge of the shell and the steel single pile (4), and is set in the circumferential groove to prevent displacement during grouting.

3. An offshore wind farm steel monopile foundation assembly splash zone protection sleeve according to claim 1, characterised in that, The number of lobes n of the segmented precast component is 2-6 lobes, and the number of lobes is selected according to the outer diameter D of the steel monopile (4): when D≤4m, 2 lobes are used; when 4m<D≤6m, 3 lobes are used; when D>6m, 4-6 lobes are used.

4. An offshore wind farm steel monopile foundation assembly splash zone protection sleeve according to claim 3, characterised in that, The circumferential joints of adjacent shell lobes are staggered, and a sealing structure (5) is provided at the joint. The sealing structure (5) is selected from one or more of the elastic sealing strip (14), sealant (13) or tongue and groove overlap structure, and is used to achieve leakage prevention during grouting process and waterproof sealing during service.

5. An offshore wind farm steel monopile foundation assembly splash zone protection sleeve according to claim 2, characterised in that, The grouting layer (2) and the steel monopile (4) adopt interface bonding enhancement measures. The outer surface of the steel monopile (4) is roughened by sandblasting or mechanical grinding so that the surface profile height reaches 50-150μm. Before grouting, the interface humidity is controlled so that the interface is in a surface dry or slightly wet state to suppress the attenuation of bonding performance caused by the interface water film.

6. The prefabricated splash zone protective sleeve for offshore wind power steel monopile foundations according to claim 1, characterized in that, The fastener (3) is a through pin, which passes through the assembled composite shell (1) and forms a limiting connection with the steel monopile (4).

7. The prefabricated splash zone protective sleeve for offshore wind power steel monopile foundations according to claim 5, characterized in that, The thickness of the UHPC outer layer (7) is 30-60mm, the thickness of the ECC inner layer (8) is 15-30mm, and the thickness of the grouting layer (2) is 20-60mm.

8. The prefabricated splash zone protective sleeve for offshore wind power steel monopile foundations according to claim 1, characterized in that, The prefabricated composite shell (1) is provided with several positioning pads (6) on its inner side. The positioning pads (6) are used to temporarily support the prefabricated composite shell (1) during installation and maintain the design thickness of the annular cavity between the ECC inner layer (8) and the steel monopile (4).

9. A method for installing the assembled protective sleeve as described in claims 1-8, characterized in that, Includes the following steps: S1. Single pile surface treatment: Rust removal and roughening treatment of the outer surface of the splash zone of the steel single pile, and wetting treatment of the interface after cleaning. S2, Shell positioning: The segmented assembled composite shell is hoisted to the design elevation in sections, and the design thickness of the annular cavity is maintained by the positioning pads (6), and the sealing treatment of each shell segment joint is completed. S3, Fastening connection: Fasteners (3) are installed through the fastening holes (9) on the assembled composite shell (1) to close each shell segment, and the composite connection assembly is installed to form a mechanical limit; S4. Grouting and molding: High-performance grout is injected into the annular cavity from the grouting hole (10) in a bottom-up manner, while air in the cavity is discharged through the vent hole (11) until grout is continuously discharged from the vent hole (11), and then the vent hole (11) is sealed. S5. Curing and sealing: The grouting hole (10) and the vent hole (11) are completely sealed. After curing to the design strength by using wet curing or sealed curing methods, they are put into service.

10. The installation method according to claim 9, characterized in that, During the grouting process, the grouting pressure is controlled at 0.05-0.30 MPa to effectively prevent grout leakage at the joints.

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