Multi-stage expanding structure pile for offshore wind power pile foundation reinforcement and construction method of multi-stage expanding structure pile

Abstract

The invention discloses a multistage expanding structure pile for offshore wind power pile foundation reinforcement and a construction method thereof.The multistage expanding structure pile comprises a pile body and at least three stages of expanding bodies arranged at one end of the pile body in the axial direction, the diameters of the adjacent two stages of expanding bodies are not equal, and the diameter of each stage of expanding body is dynamically adjusted according to geological stratification; the adjacent expanding bodies are transited through reducing sections to form a continuous variable cross-section structure; the construction method comprises the steps of geological exploration, structural pile prefabrication, hauling and piling, the structural pile is of an integral structure, an additional structure is not needed, the diameter of the expanding body is dynamically adjusted according to geological layering, and the lateral stability and bearing capacity of the pile are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of pile foundation reinforcement, and specifically to a multi-stage expanded diameter structure pile and a construction method for offshore wind power pile foundation reinforcement. Background Art

[0002] Under the conditions of deep weathered rock stratum or medium buried bedrock seabed for traditional offshore wind power monopile foundations, the upper overlying soil cannot provide sufficient bearing capacity, and it is necessary to embed into the lower bedrock. However, rock-embedding construction relies on large drilling rigs and auxiliary equipment, with a long offshore operation cycle and safety risks such as hole collapse, resulting in low construction efficiency and high costs. In addition, the application difficulties of shallow overlying rock bedrock seabeds further limit the lateral stability of monopiles. The soil around the pile is prone to form local scour pits under the action of ocean currents, reducing the support of the soil around the pile to lateral loads. Research shows that an increase in scour depth will lead to a significant decrease in the lateral stiffness and bearing capacity of monopiles. And as offshore wind power develops towards deep waters and large single-unit capacities (such as above 10 MW), the unit load increases significantly, requiring higher foundation stiffness and horizontal bearing capacity. Traditional monopiles need to increase the pile diameter or length to meet the requirements, but an overly large pile diameter may exceed the limits of manufacturing and construction equipment and reduce economy. Therefore, adopting an effective reinforcement method and inventing a multi-stage expanded diameter structure pile are of great significance for solving this problem.

[0003] The existing technology mainly welds connection blocks on the outside of the pile foundation and installs a conical ballast unit with a large upper part and a small lower part. The ballast unit consists of a stress-bearing plate, a connecting plate, and an arc-shaped shell plate, with reinforcing plates arranged inside, and then compacts the surrounding soil by hammering the ballast unit to achieve the reinforcement of the pile foundation. However, for this reinforcement scheme, the ballast unit needs to be welded after the pile driving is completed. Offshore welding operations are greatly affected by weather and may damage the anti-corrosion coating of the pile body; stress concentration is likely to occur at the contact surface between the connection block and the ballast unit, and weld cracking may be caused under long-term loads; the compaction effect of the conical structure in soft soil layers is limited and it is difficult to adapt to multi-layer complex geological conditions. Therefore, relying on additional structures leads to complex construction and increased costs; there is a lack of dynamic adjustment ability for complex strata (such as alternating soft soil and bedrock). Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of existing single-pile foundation reinforcement schemes, and provide a multi-stage expanded diameter structure pile and a construction method thereof that can reduce costs, have dynamic adjustment ability for complex strata, and are less affected by weather. It aims to overcome the problem of relying on external additional structures in the existing technology and meet the actual needs of offshore wind power pile foundation reinforcement.

[0005] The first aspect of the present invention is a multi-stage expanded diameter structure pile for offshore wind power pile foundation reinforcement, and its technical solution is as follows: A multi - stage diameter - expanding structure pile for offshore wind power pile foundation reinforcement, comprising a pile body and at least three - stage diameter - expanding bodies arranged axially along one end of the pile body. The diameters of adjacent second - stage diameter - expanding bodies are not equal. The diameter of each stage of the diameter - expanding body is dynamically adjusted according to the geological stratification, and the adjacent diameter - expanding bodies are transitioned through a variable - diameter section to form a continuous variable - cross - section structure.

[0006] The pile body, each stage of the diameter - expanding body and each variable - diameter section are coaxially arranged.

[0007] Further, the pile body is a circular steel pipe made of weathering steel; the diameter - expanding body is a cylinder with a solid concrete structure, and spiral ribs are arranged on its circumferential surface, with a rib height of 50 - 200 mm and a pitch of 1 - 3 m; the variable - diameter section is a frustum of a cone with a solid concrete structure, and its cone angle range is 15° - 45°.

[0008] Further, the multi - stage diameter - expanding structure pile is a three - stage diameter - expanding structure pile. The diameter - expanding bodies include a first diameter - expanding body, a second diameter - expanding body and a third diameter - expanding body, and the variable - diameter sections include a first variable - diameter section and a second variable - diameter section. The multi - stage diameter - expanding structure pile is an integral structure, and from top to bottom, it is successively the pile body, the first diameter - expanding body, the first variable - diameter section, the second diameter - expanding body, the second variable - diameter section and the third diameter - expanding body.

[0009] The second aspect of the present invention is a construction method of the multi - stage diameter - expanding structure pile for offshore wind power pile foundation reinforcement based on the first aspect, and its technical solution is as follows: The 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 pile is to be inserted, clarify the geological stratification of the seabed, determine the boundary depth of each soil layer, and require the error ≤ 0.5 m; S1 - 2: Mark the best installation position of the three - stage diameter - expanding structure pile, and pay attention to avoiding the soil - quality mutation layer; Step 2: S2 Prefabricate the structure pile S2 - 1: According to the geological stratification situation explored in step S1, determine the diameter of the diameter - expanding body and the diameter - expanding ratio; S2 - 2: Pre - fabricate the three - stage diameter - expanding structure pile on the shore, use C60 marine concrete, add 12% silica fume, pour, vibrate compactly, maintain and conduct quality inspection; Step 3: S3 Haul Haul the three - stage diameter - expanding structure pile qualified in S2 - 2 to the sea area where the pile is to be inserted; Step 4: S4 Driving the pile Use a pile - driving vessel to drive the three - stage diameter - expanding structure pile into the seabed.

[0010] The diameter expansion ratio in the above step S2-1 is the ratio of the diameter of the diameter-expanded body to the diameter of the pile body. The geological stratification of the seabed and the corresponding diameter expansion ratios are as follows: soft silt layer: the diameter expansion ratio is 1.5; sandy clay layer: the diameter expansion ratio is 2.0; dense sand layer: the diameter expansion ratio is 1.2; rock-based seabed: the diameter expansion ratio is 3.

[0011] The quality control in the above step S2-2 includes: 1. The roundness deviation of the diameter-expanded body ≤ 1%D, where D is the designed diameter; 2. The deviation of the center lines of adjacent diameter-expanded bodies ≤ 30 mm; 3. Use a rebound hammer to detect the concrete strength, and the required 28-day strength ≥ 58 MPa. Beneficial effects

[0012] 1. This structural pile does not require external additional structures, so problems such as stress concentration and possible weld cracking under long-term loads do not need to be considered. 2. This structural pile is an integral whole, so it does not need to be welded at sea, is less affected by weather, and will not damage the anti-corrosion coating of the pile body, which can effectively reduce costs. 3. The structural pile can be dynamically adjusted according to the geological stratification so that the diameters of each diameter-expanded body are different, so it can better adapt to multi-layer complex geological conditions. 4. The multi-stage structure of the pile increases the contact area with the soil, and spiral ribs are arranged on the surface of the diameter-expanded body to increase the friction coefficient with the soil, which can better combine with the soft soil layer, reduce the compressive stress of the soft soil, and thus increase the lateral stability and bearing capacity of the pile. Description of the drawings

[0013] Figure 1 It is an axonometric view of the multi-stage diameter-expanded structural pile of Embodiment 1; Figure 2 It is a front sectional view of the multi-stage diameter-expanded structural pile of Embodiment 1.

[0014] In the figure, 1 is the pile body; 2 is the first diameter-expanded body; 3 is the second diameter-expanded body; 4 is the third diameter-expanded body; 5 is the spiral rib, 6 is the first diameter-changing section; 7 is the second diameter-changing section. Specific implementation manners

[0015] To make the purposes, 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 drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] Embodiment 1: Please refer to Figure 1, The multi-stage expanded-diameter structure pile for offshore wind power pile foundation reinforcement is an integral structure, including a pile body 1 and at least three levels of expanded-diameter bodies arranged axially at one end of the pile body 1. The diameters of adjacent expanded-diameter bodies at the second level are not equal, and the diameter of each level of expanded-diameter body is dynamically adjusted according to the geological stratification. And the adjacent expanded-diameter bodies are transitioned through a stepped-diameter section to form a continuous variable cross-section structure, and spiral ribs are arranged on the surface of the expanded-diameter body to enhance the pile-soil friction.

[0017] In this embodiment, the cross-section of the pile body 1 is circular, and the expanded-diameter bodies are three levels, namely the first expanded-diameter body 2, the second expanded-diameter body 3, and the third expanded-diameter body 4; the diameters of each expanded-diameter body are dynamically adjusted according to the geological stratification so that the diameters of each expanded-diameter body are different, and the expanded-diameter bodies are transitioned through a stepped-diameter section to form a continuous variable cross-section structure. The stepped-diameter section is a frustum structure. The first stepped-diameter section 6 is between the first expanded-diameter body 2 and the second expanded-diameter body 3, and the second stepped-diameter section 7 is between the second expanded-diameter body 3 and the third expanded-diameter body 4.

[0018] The shapes of each expanded-diameter body are the same, and the sizes can be the same or different according to the seabed geological stratification. In this embodiment, the shapes of the first expanded-diameter body 2, the second expanded-diameter body 3, and the third expanded-diameter body 4 are all cylindrical structures, and the sizes are different.

[0019] The pile body 1, each expanded-diameter body, and each stepped-diameter section are coaxially arranged.

[0020] The ratio of the diameter of the pile body 1 to the diameter of the expanded-diameter body, that is, the expanded-diameter ratio ranges from 1.2 to 3. Please refer to Figure 1 , In this embodiment, the outer diameter of the pile body 1 is 3.5 m, the diameter of the first expanded-diameter body 2 is 5.25 m, and the expanded-diameter ratio of the first expanded-diameter body 2 is 1.5; the diameter of the second expanded-diameter body 3 is 7 m, and the expanded-diameter ratio of the second expanded-diameter body 3 is 2.0; the diameter of the third expanded-diameter body 4 is 4.2 m, and the expanded-diameter ratio of the third expanded-diameter body 4 is 1.2.

[0021] The stepped-diameter section between the expanded-diameter bodies is a frustum, and its cone angle ranges from 15° to 45°. Please refer to Figure 2 , In this embodiment, 2α is the cone angle of the first stepped-diameter section 6, 2β is the cone angle of the second stepped-diameter section 7, and the angles taken by 2α and 2β are both 25°.

[0022] Spiral ribs 5 are arranged on the surface of the expanded-diameter body, with a rib height of 50 - 200 mm and a pitch of 1 - 3 m. Please refer to Figure 1 , In this embodiment, spiral ribs 5 are welded on the circumferential surfaces of the cylinders of the first expanded-diameter body 2, the second expanded-diameter body 3, and the third expanded-diameter body 4, with a rib height of 100 mm and a pitch of 1.5 m.

[0023] In this embodiment, to improve the uplift resistance and strength of the multi-stage expanded-diameter structure pile for offshore wind power pile foundation reinforcement, the pile body 1 is made of circular steel pipe with a wall thickness of 50 mm, made of Q355NC weathering steel, and has a length of 40 m; the first expanded-diameter body 2, the second expanded-diameter body 3, the third expanded-diameter body 4, the first diameter-changing section 6, and the second diameter-changing section 7 adopt concrete solid structures.

[0024] For the multi-stage expanded-diameter structure pile of the present invention, before precasting, the dimensions and expansion ratios of the expanded-diameter bodies should be determined according to the geological stratification of the seabed where the pile is to be inserted. Therefore, geological exploration is carried out on the seabed where the pile is to be inserted in advance to clarify the geological stratification of the seabed, and then the dimensions and expansion ratios of the expanded-diameter bodies are determined according to the stratification situation. Soft silt layer: the expansion ratio is 1.5; sandy clay layer: the expansion ratio is 2.0; dense sand layer: the expansion ratio is 1.2; rock-based seabed: the expansion ratio is 3.

[0025] In this embodiment, the first expanded-diameter body 2 has a height of 4 m and is located 10 - 14 m (silt layer) below the seabed surface, the second expanded-diameter body 3 has a height of 6 m and is located at 20 - 26 m (sandy clay layer), and the third expanded-diameter body 4 has a height of 3 m and is embedded in the 30 - 33 m dense sand layer.

[0026] This structure pile does not require external additional structures, so problems such as stress concentration and possible weld cracking under long-term loads do not need to be considered. Since this pile is an integral body, it does not need to be welded at sea, is less affected by the weather, and will not damage the anti-corrosion coating of the pile body, which can effectively reduce costs. Because the structure pile can be dynamically adjusted according to the geological stratification to make the diameters of each expanded-diameter body different, it can better adapt to multi-layer complex geological conditions. Also, due to the multi-stage structure of the pile increasing the contact area with the soil, and spiral ribs are arranged on the surface of the expanded-diameter body to increase the friction coefficient with the soil, it can better combine with the soft soil layer, reduce the compressive stress of the soft soil, and thus increase the lateral stability and bearing capacity of the pile.

[0027] The implementation effects are compared as shown in Table 1.

[0028] Table 1 Comparison of implementation effects 。

[0029] Example 2: This example is about the construction method of inserting the multi-stage expanded-diameter structure pile for offshore wind power pile foundation reinforcement in Example 1, and the 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 pile is to be inserted, clarify the geological stratification of the seabed, and determine the boundary depth of each soil layer, with the requirement that the error ≤ 0.5 m; S1-2: Mark the best installation position of the expanded-diameter body, and pay attention to avoiding the soil mutation layer; Step 2: S2 Precast structure pile S2-1: Determine the size and expansion ratio of the expanded body according to the layering situation in S1; S2-2: Pre-cast the three-stage expanded pile on the shore with C60 marine concrete mixed with 12% silica fume, pour, vibrate compactly, maintain and conduct quality inspection; Step 3: S3 Transportation Transport the expanded pile qualified in S2-2 to the sea area where the pile is to be inserted; Step 4: S4 Piling Drive the expanded pile into the seabed with a piling barge.

[0030] The expansion ratio in the above S2-1 step is the ratio of the diameter of the expanded body to the diameter of the pile body (1). The geological layering 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-based seabed: expansion ratio is 3.

[0031] The quality control in the above S2-2 step includes: 1. The roundness deviation of the expanded body ≤ 1%D, where D is the design diameter; 2. The center line deviation between adjacent expanded bodies ≤ 30 mm 3. Use a rebound hammer to detect the concrete strength, and the required 28-day strength ≥ 58 MPa.

[0032] Inspired by the ideal embodiments of the present invention described above, 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. A multi-stage diameter-expanded structural pile for offshore wind power pile foundation reinforcement, characterized in that It includes a pile body (1), and at least three levels of diameter-expanded bodies arranged axially at one end of the pile body (1). The diameters of adjacent secondary diameter-expanded bodies are not equal. The diameter of each level of diameter-expanded body is dynamically adjusted according to the geological stratification, and the adjacent diameter-expanded bodies are transitioned through a reduced-diameter section to form a continuous variable cross-section structure; The pile body (1), each level of diameter-expanded body, and each reduced-diameter section are coaxially arranged.

2. The multi-stage expanded diameter structural pile for offshore wind power pile foundation reinforcement according to claim 1, characterized in that, The pile body (1) is a circular steel pipe made of weathering steel; the diameter-expanded body is a cylinder with a solid concrete structure, and spiral ribs (5) are arranged on its circumferential surface, with a rib height of 50 - 200 mm and a pitch of 1 - 3 m; the reduced-diameter section is a frustum of a cone with a solid concrete structure, and its cone angle ranges from 15° to 45°.

3. The multi-stage expanded diameter structural pile for offshore wind power pile foundation reinforcement according to claim 2, characterized in that, The multi-level diameter-expanded structure pile is a three-level diameter-expanded structure pile. The diameter-expanded bodies include a first diameter-expanded body (2), a second diameter-expanded body (3), and a third diameter-expanded body (4). The reduced-diameter sections include a first reduced-diameter section (6) and a second reduced-diameter section (7). The multi-level diameter-expanded structure pile is an integral structure, and from top to bottom, it is successively the pile body (1), the first diameter-expanded body (2), the first reduced-diameter section (6), the second diameter-expanded body (3), the second reduced-diameter section (7), and the third diameter-expanded body (4).

4. The construction method of the multi-stage expanded diameter structure pile for offshore wind power pile foundation reinforcement according to claim 3, characterized in that, The 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 pile is to be inserted, clarify the geological stratification of the seabed, determine the boundary depth of each soil layer, and the requirement for the error is ≤ 0.5 m; S1-2: Mark the best installation position of the three-level diameter-expanded structure pile, and pay attention to avoiding the soil mutation layer; Step 2: S2 Prefabricate the structural pile S2-1: According to the geological stratification situation explored in Step S1, determine the diameter and diameter expansion ratio of the diameter-expanded body; S2-2: Prefabricate the three-level diameter-expanded structure pile on the shore in advance, use C60 marine concrete, add 12% silica fume, pour, vibrate compactly, maintain, and conduct quality inspection; Step 3: S3 Haulage Haul the qualified three-level diameter-expanded structure pile in S2-2 to the sea area where the pile is to be inserted; Step 4: S4 Pile driving Use a pile driving vessel to drive the three-level diameter-expanded structure pile into the seabed.

5. The construction method according to claim 4, characterized in that, The diameter expansion ratio in Step S2-1 is the ratio of the diameter of the diameter-expanded body to the diameter of the pile body (1). The geological stratification of the seabed and the corresponding diameter expansion ratios are as follows: soft silt layer: the diameter expansion ratio is 1.5; sandy clay layer: the diameter expansion ratio is 2.0; dense sand layer: the diameter expansion ratio is 1.2; bedrock seabed: the diameter expansion ratio is 3.

6. The construction method according to claim 4, characterized in that, The quality control in Step S2-2 includes:

1. The roundness deviation of the diameter-expanded body ≤ 1%D, where D is the design diameter; 2. The center line deviation between adjacent diameter-expanded bodies ≤ 30 mm 3. Use a rebound hammer to detect the concrete strength, and the requirement is that the 28-day strength ≥ 58 MPa.

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