A construction method of a multi-stage expanding diameter structure pile for offshore wind power pile foundation reinforcement

Abstract

The application discloses a construction method of a multi-stage expanding-diameter structure pile for offshore wind power pile foundation reinforcement, and the multi-stage expanding-diameter structure pile comprises a pile body, at least three expanding-diameter bodies arranged along an axial direction at one end of the pile body, the diameters of two adjacent expanding-diameter bodies are not equal, the diameter of each expanding-diameter body is dynamically adjusted according to geological stratification, and adjacent expanding-diameter bodies are connected through a variable-diameter section to form a continuous variable cross-section structure; the construction method comprises geological exploration, prefabrication of the structure pile, dragging and transportation and pile driving; the structure pile is a whole structure, does not need additional structures, the diameter of the expanding-diameter body is dynamically adjusted according to the geological stratification, and the lateral stability and the bearing capacity of the pile are increased.

Description

Technical Field

[0001] This invention relates to the field of pile foundation reinforcement technology, specifically to a construction method for multi-stage enlarged diameter structural piles used for offshore wind power pile foundation reinforcement. Background Technology

[0002] Traditional offshore wind turbine monopile foundations, when used in deep weathered rock layers or medium-depth bedrock seabeds, often suffer from insufficient bearing capacity due to the overlying soil layer, necessitating embedding into the underlying bedrock. However, this embedding process relies on large drilling rigs and auxiliary equipment, resulting in long offshore operation cycles and safety risks such as borehole collapse, leading to low construction efficiency and high costs. Furthermore, the application of shallow overlying bedrock seabeds further limits the lateral stability of the monopile. The soil around the pile is prone to localized scour pits under ocean currents, reducing its support for lateral loads. Studies show that increased scour depth leads to a significant decrease in the lateral stiffness and bearing capacity of the monopile. Moreover, as offshore wind power develops towards deeper waters and larger unit capacities (e.g., 10 MW and above), the turbine load increases significantly, demanding higher foundation stiffness and horizontal bearing capacity. Traditional monopiles require larger diameters or lengths to meet these demands, but excessively large diameters may exceed the limits of manufacturing and construction equipment, reducing economic efficiency. Therefore, adopting an effective reinforcement method and inventing a multi-stage diameter-expanding structural pile is of great significance for solving this problem.

[0003] Existing technologies primarily involve welding connecting blocks to the outside of the pile foundation and installing a cone-shaped ballast unit that is larger at the top and smaller at the bottom. The ballast unit consists of a load-bearing plate, a connecting plate, and an arc-shaped shell plate, with internal reinforcing plates. The surrounding soil is then compacted by hammering the ballast unit to reinforce the pile foundation. However, this reinforcement method requires welding the ballast unit after pile driving. Offshore welding operations are greatly affected by weather and may damage the pile's anti-corrosion coating. Stress concentration easily occurs at the contact surface between the connecting block and the ballast unit, potentially leading to weld cracking under long-term loads. Furthermore, the cone structure has limited compaction effectiveness in soft soil layers and is difficult to adapt to complex multi-layered geological conditions. Therefore, relying on additional structures leads to complex construction and increased costs; it also lacks dynamic adjustment capabilities for complex strata (such as alternating soft soil and bedrock). Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing single-pile foundation reinforcement schemes by providing a multi-stage enlarged diameter structural pile and its construction method that reduces costs, dynamically adjusts to complex geological formations, and is less affected by weather. It aims to overcome the reliance on external auxiliary structures in existing technologies and meet the practical needs of offshore wind power foundation reinforcement.

[0005] The first aspect of this invention is a multi-stage diameter-enlarged structural pile for reinforcing offshore wind power foundations, the technical solution of which is as follows:

[0006] A multi-stage enlarged diameter structure pile for offshore wind power pile foundation reinforcement includes a pile body and at least three stages of enlarged diameter bodies arranged axially along one end of the pile body. The diameters of adjacent stages of enlarged diameter bodies are not equal. The diameter of each stage of enlarged diameter body is dynamically adjusted according to geological stratification, and adjacent enlarged diameter bodies are transitioned through variable diameter sections to form a continuous variable cross-section structure.

[0007] The pile body, each stage of the diameter expansion body, and each diameter-changing section are set coaxially.

[0008] Furthermore, the pile body is a round steel pipe made of weathering steel; the expanded diameter body is a cylinder with a solid concrete structure, and its circumferential surface is provided with spiral ribs with a rib height of 50-200mm and a pitch of 1-3m; the variable diameter section is a frustum with a solid concrete structure and a cone angle range of 15°-45°.

[0009] Furthermore, the multi-stage diameter expansion structure pile is a three-stage diameter expansion structure pile, with an expansion body including a first expansion body, a second expansion body and a third expansion body, and a diameter changing section including a first diameter changing section and a second diameter changing section. The multi-stage diameter expansion structure pile is an integral structure, consisting of the pile body, the first expansion body, the first diameter changing section, the second expansion body, the second diameter changing section and the third expansion body from top to bottom.

[0010] The second aspect of this invention is a construction method for multi-stage enlarged diameter structural piles for offshore wind power foundation reinforcement, based on the first aspect, and its technical solution is as follows:

[0011] The steps are as follows:

[0012] Step 1: S1 Geological Exploration

[0013] S1-1: Use a CPT static cone penetrometer to conduct geological exploration on the seabed where the piles are to be driven, clarify the geological stratification of the seabed, and determine the depth of the boundary between each soil layer, with an error of ≤0.5m.

[0014] S1-2: Mark the optimal installation location for the third-stage expanded diameter structural piles, taking care to avoid soil abrupt change layers;

[0015] Step 2: S2 Precast Structural Piles

[0016] S2-1: Determine the diameter and enlargement ratio of the enlarged body based on the geological stratification explored in step S1;

[0017] S2-2: Pre-fabricate three-stage diameter expansion structural piles on shore, using C60 marine concrete mixed with 12% silica fume, and then pour, vibrate, compact, cure, and inspect the quality.

[0018] Step 3: S3 Transport

[0019] The qualified Class III enlarged diameter structural piles in S2-2 will be towed to the sea area where they will be driven.

[0020] Step 4: S4 Piling

[0021] A piling vessel was used to drive the three-stage expanded diameter structural piles into the seabed.

[0022] The enlargement ratio mentioned in step S2-1 above is the ratio of the diameter of the enlarged body to the diameter of the pile body. The geological stratification of the seabed and the corresponding enlargement ratios are as follows: soft silt layer: enlargement ratio is 1.5; sandy clay layer: enlargement ratio is 2.0; dense sand layer: enlargement ratio is 1.2; rock-bedded seabed: enlargement ratio is 3.

[0023] The quality control in step S2-2 above includes:

[0024] (1) The roundness deviation of the expanded body is ≤1%D, where D is the design diameter;

[0025] (2) The deviation of the centerline between adjacent expanded bodies is ≤30mm;

[0026] (3) The concrete strength is tested using a rebound hammer, and the 28-day strength is required to be ≥58MPa.

[0027] The beneficial effects of this invention are:

[0028] 1. This structural pile requires no external additional structures, thus eliminating concerns about stress concentration and potential weld cracking under long-term loads. 2. As a single unit, the structural pile eliminates the need for offshore welding, minimizing weather impact and preventing damage to the pile's anti-corrosion coating, effectively reducing costs. 3. The structural pile can dynamically adjust the diameter of each expansion section according to geological stratification, better adapting to complex multi-layered geological conditions. 4. The multi-stage structure of the pile increases the contact area with the soil, and the spiral ribs on the expansion section surface increase the friction coefficient with the soil, enabling better bonding with weak soil layers, reducing compressive stress in weak soil, and thereby increasing the pile's lateral stability and bearing capacity. Attached Figure Description

[0029] Figure 1 This is an isometric view of the multi-stage diameter-expanding pile structure in Example 1;

[0030] Figure 2 This is a front sectional view of the multi-stage diameter expansion structure pile of Example 1.

[0031] In the diagram, 1 represents the pile body; 2 represents the first diameter-expanding body; 3 represents the second diameter-expanding body; 4 represents the third diameter-expanding body; 5 represents the spiral rib; 6 represents the first diameter-changing section; and 7 represents the second diameter-changing section. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: Please refer to Figure 1 The multi-stage enlarged diameter structure pile used for offshore wind power pile foundation reinforcement is an integral structure, including pile body 1 and at least three stages of enlarged diameter bodies arranged axially along one end of pile body 1. The diameters of adjacent stages of enlarged diameter bodies are not equal, and the diameter of each stage of enlarged diameter body is dynamically adjusted according to geological stratification. Adjacent enlarged diameter bodies are transitioned through variable diameter sections to form a continuous variable cross-section structure, and spiral ribs are provided on the surface of the enlarged diameter bodies to enhance pile-soil friction.

[0034] In this embodiment, the cross-section of the pile body 1 is circular, and the expansion body is in three stages, namely the first expansion body 2, the second expansion body 3, and the third expansion body 4. The diameter of each expansion body is dynamically adjusted according to the geological stratification so that the diameter of each expansion body is different, and the expansion bodies are transitioned through the diameter-changing section to form a continuous variable cross-section structure. The diameter-changing section is a frustum structure. The first diameter-changing section 6 is between the first expansion body 2 and the second expansion body 3, and the second diameter-changing section 7 is between the second expansion body 3 and the third expansion body 4.

[0035] All the expansion bodies have the same shape, and their dimensions can be determined according to the geological stratification of the seabed. In this embodiment, the first expansion body 2, the second expansion body 3, and the third expansion body 4 are all cylindrical structures, but their dimensions are different.

[0036] Pile body 1, each enlarged diameter body and each variable diameter section are set coaxially.

[0037] The ratio of the diameter of pile body 1 to the diameter of the enlarged body, i.e., the enlargement ratio, ranges from 1.2 to 3. Please refer to [link / reference]. Figure 1 In this embodiment, the outer diameter of the pile body 1 is 3.5m, the diameter of the first expansion body 2 is 5.25m, and the expansion ratio of the first expansion body 2 is 1.5; the diameter of the second expansion body 3 is 7m, and the expansion ratio of the second expansion body 3 is 2.0; the diameter of the third expansion body 4 is 4.2m, and the expansion ratio of the third expansion body 4 is 1.2.

[0038] The diameter-changing section between the expanding bodies is a frustum of a cone, with a cone angle ranging from 15° to 45°. Please refer to [link / reference needed]. Figure 2 In this embodiment, 2α is the cone angle of the first variable diameter section 6, and 2β is the cone angle of the second variable diameter section 7. Both 2α and 2β are 25°.

[0039] The surface of the expanded body is provided with spiral ribs 5, with a rib height of 50-200mm and a pitch of 1-3m. Please refer to [link / reference]. Figure 1 In this embodiment, spiral ribs 5 are welded to the circumferential surfaces of the cylinders of the first expansion body 2, the second expansion body 3 and the third expansion body 4. The rib height is 100mm and the pitch is 1.5m.

[0040] In this embodiment, in order to improve the pull-out force and strength of the multi-stage expanded diameter structure pile used for offshore wind power pile foundation reinforcement, the pile body 1 is made of round steel pipe with a wall thickness of 50mm, made of Q355NC weathering steel, and 40m in length; the first expanded diameter body 2, the second expanded diameter body 3, the third expanded diameter body 4, the first variable diameter section 6 and the second variable diameter section 7 are made of solid concrete structure.

[0041] Before prefabrication, the size and ratio of the enlarged diameter structure pile of this invention should be determined based on the geological stratification of the seabed. Therefore, geological exploration should be conducted on the seabed where the piles are to be inserted to clarify the geological stratification. The size and ratio of the enlarged diameter structure pile are then determined based on the stratification. For example: soft silt layer: enlargement ratio 1.5; sandy clay layer: enlargement ratio 2.0; dense sand layer: enlargement ratio 1.2; rocky seabed: enlargement ratio 3.

[0042] In this embodiment, the first enlarged body 2 is 4m high and located 10-14m below the seabed (silt layer), the second enlarged body 3 is 6m high and located 20-26m (sandy clay layer), and the third enlarged body 4 is 3m high and embedded in a 30-33m dense sand layer.

[0043] This structural pile requires no external additional structures, thus eliminating concerns about stress concentration and potential weld cracking under long-term loads. Because the pile is a single unit, it eliminates the need for offshore welding, minimizing weather impact and preserving the anti-corrosion coating, effectively reducing costs. Furthermore, the pile's multi-stage structure dynamically adjusts the diameter of each enlarged section according to geological stratification, allowing for better adaptation to complex, multi-layered geological conditions. The multi-stage structure also increases the contact area with the soil, and the spiral ribs on the enlarged sections enhance the friction coefficient, resulting in better bonding with soft soil layers, reducing compressive stress in these layers, and ultimately increasing the pile's lateral stability and bearing capacity.

[0044] The implementation results are shown in Table 1:

[0045] Table 1 Comparison of Implementation Results

[0046] index Traditional single-stage diameter expansion pile Grade III Enlarged Diameter Piles Grade 5 expanded diameter piles Horizontal bearing capacity 12MN 18MN (↑40%) 22MN (↑70%) Settlement 58mm 32mm (↓45%) 25mm (↓58%) Construction period 22 days 28 days 35 days Material costs ¥5.6 million ¥4.2 million (↓25%) ¥5.8 million (↑8%)

[0047] Example 2: This example uses the construction method of multi-stage enlarged diameter structure pile insertion for offshore wind power pile foundation reinforcement as described in Example 1. The steps are as follows:

[0048] Step 1: S1 Geological Exploration

[0049] S1-1: Use a CPT static cone penetrometer to conduct geological exploration on the seabed where the piles are to be driven, clarify the geological stratification of the seabed, and determine the depth of the boundary between each soil layer, with an error of ≤0.5m.

[0050] S1-2: Mark the optimal installation location for the expansion body, taking care to avoid soil abrupt changes;

[0051] Step 2: S2 Precast Structural Piles

[0052] S2-1: Determine the size and expansion ratio of the expanded body based on the layering in S1;

[0053] S2-2: The third-stage expansion piles are pre-cast on shore using C60 marine concrete with 12% silica fume, then compacted, cured, and inspected for quality.

[0054] Step 3: S3 Transport

[0055] The expanded diameter piles that passed inspection in S2-2 will be towed to the sea area where they will be driven.

[0056] Step 4: S4 Piling

[0057] Piling vessels are used to drive enlarged-diameter piles into the seabed.

[0058] The expansion ratio mentioned in step S2-1 above is the ratio of the diameter of the expanded body to the diameter of the pile body (1). The geological stratification of the seabed and the corresponding expansion ratios are as follows: soft silt layer: expansion ratio is 1.5; sandy clay layer: expansion ratio is 2.0; dense sand layer: expansion ratio is 1.2; rock-bedded seabed: expansion ratio is 3.

[0059] The quality control in step S2-2 above includes:

[0060] (1) The roundness deviation of the expanded body is ≤1%D, where D is the design diameter;

[0061] (2) The deviation of the centerline of adjacent expanded bodies is ≤30mm

[0062] (3) The concrete strength is tested using a rebound hammer, and the 28-day strength is required to be ≥58MPa.

[0063] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A construction method for multi-stage enlarged diameter structural piles used for offshore wind power foundation reinforcement, characterized in that, The multi-stage diameter-expanding structure pile includes a pile body (1), an expansion body, and a variable diameter section. The expansion body and the variable diameter section are coaxially arranged at the lower part of the pile body (1). The expansion body and the variable diameter section are alternately connected, and the diameters of adjacent expansion bodies at each stage are not equal. Along the axial direction of the pile body, there is at least one expansion body whose diameter is larger than the diameter of the expansion body above it. The diameter of each expansion body is dynamically adjusted according to the geological stratification. The pile body (1) is a round steel pipe made of weathering steel. The expansion body is a cylinder with a solid concrete structure. Spiral ribs (5) are provided on its circumferential surface, with a rib height of 50-200 mm. m, pitch is 1-3m; the variable diameter section is a frustum, solid concrete structure, its cone angle range is 15°-45°; the multi-stage expansion structure pile is a three-stage expansion structure pile, the expansion body includes the first expansion body (2), the second expansion body (3) and the third expansion body (4), the variable diameter section includes the first variable diameter section (6) and the second variable diameter section (7), the multi-stage expansion structure pile is an integral structure, from top to bottom are pile body (1), first expansion body (2), first variable diameter section (6), second expansion body (3), second variable diameter section (7) and third expansion body (4); The construction method and steps are as follows: Step 1: S1 Geological Exploration; S1-1: Use a CPT static cone penetrometer to conduct geological exploration on the seabed where the piles are to be driven, clarify the geological stratification of the seabed, and determine the depth of the boundary between each soil layer, with an error of ≤0.5m. S1-2: Mark the optimal installation location for the third-stage expanded diameter structural piles, taking care to avoid soil abrupt change layers; Step 2: S2 precast structural piles; S2-1: Determine the diameter and enlargement ratio of the enlarged body based on the geological stratification explored in step S1; S2-2: Pre-fabricate three-stage diameter expansion structural piles on shore, using C60 marine concrete mixed with 12% silica fume, and then pour, vibrate, compact, cure, and inspect the quality. Step 3: S3 Transport; The qualified Class III enlarged diameter structural piles in S2-2 will be towed to the sea area where they will be driven. Step 4: S4 Piling; A piling vessel was used to drive the three-stage expanded diameter structural piles into the seabed.

2. The construction method according to claim 1, characterized in that, The enlargement ratio mentioned in step S2-1 is the ratio of the diameter of the enlarged body to the diameter of the pile body (1). The geological stratification of the seabed and the corresponding enlargement ratios are as follows: soft silt layer: enlargement ratio is 1.5; sandy clay layer: enlargement ratio is 2.0; dense sand layer: enlargement ratio is 1.2; rock-bedded seabed: enlargement ratio is 3.

3. The construction method according to claim 1, characterized in that, Quality control in step S2-2 includes: (1) The roundness deviation of the expanded body is ≤1%D, where D is the design diameter; (2) The deviation of the centerline between adjacent expanded diameter bodies is ≤30mm; (3) The concrete strength was tested using a rebound hammer, and the 28-day strength was required to be ≥58MPa.

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