Offshore large-diameter thin-wall steel pipe pile foundation and preparation method

Abstract

The invention provides an offshore large-diameter thin-wall steel pipe pile foundation and a preparation method thereof.The preparation method comprises the steps that 1, a to-be-designed single pile foundation is divided into three sections, namely the first section of single pile sub-foundation, the second section of single pile sub-foundation and the third section of single pile sub-foundation, and the first section is a mud entering section; the second section is a mud entering section under an in-place working condition; the third section is the section above the mud surface under the in-place working condition; 2, setting an initial radius-thickness ratio range of each section of single pile sub-foundation; 3, selecting the initial diameter-thickness ratio of each section of the single-pile sub-foundation according to the set initial diameter-thickness ratio range, and setting the structure of each section of the sub-foundation to obtain an initial single-pile foundation; 4, whether the initial single-pile foundation meets the corresponding technological requirements or not is judged through the bearing capacity, the deformation amount, the self-weight mud entering depth, the buckling stress and the total fatigue damage value in sequence, if not, the third step is executed, and if yes, the final single-pile foundation is obtained; the defect that the weight reduction space of a single-pile foundation is limited is effectively overcome.

Description

Technical Field

[0001] The present invention belongs to the field of wind power foundations, and in particular relates to an offshore large-diameter thin-walled steel pipe pile foundation and a preparation method thereof. Background Art

[0002] With the introduction of the national clean energy policy, wind power has achieved rapid development. As an important component of wind power generation, the cost of wind power foundation accounts for about one-third of the cost of offshore wind power construction. Reducing the cost of offshore wind power foundation is of great significance to reducing the cost of offshore wind power development. The large-diameter single pile foundation of offshore wind power is the most common foundation form in the field of offshore wind power. Its weight is about 1,000 tons to 2,500 tons. Refined design can reduce the cost of the structure. In order to ensure the local stability of the large-diameter single pile foundation during construction and in-situ working conditions, the diameter-to-thickness ratio of conventional large-diameter single pile foundations is limited to D / t≤120, which leads to limited weight reduction space for conventional single pile foundations. Summary of the invention

[0003] The purpose of the present invention is to propose an offshore large-diameter thin-walled steel pipe pile foundation and a preparation method, which solves the defect that the conventional large-diameter single pile foundation has limited weight reduction space due to the limitation of the diameter-to-thickness ratio, thereby making its manufacturing cost too high.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: The present invention provides a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation, comprising the following steps: Step 1, dividing the single pile foundation to be designed into three sections, namely the first section single pile foundation, the second section single pile foundation and the third section single pile foundation, wherein the first section is the mud entry section; the second section is the mud entry section under the in-situ working condition; and the third section is the section above the mud surface under the in-situ working condition; Each single pile sub-foundation is composed of multiple sub-segment foundations; Step 2, setting the initial diameter-to-thickness ratio range of each section of the single pile foundation; Step 3, selecting the initial diameter-thickness ratio of each sub-segment foundation according to the set initial diameter-thickness ratio range, and setting the structure of each sub-segment foundation to obtain an initial single pile foundation; Step 4, use the bearing capacity, deformation, self-weight penetration depth, buckling stress and total fatigue damage value in turn to determine whether the initial single pile foundation meets the corresponding process requirements. If not, return to step 3. If yes, the final single pile foundation is obtained.

[0005] Preferably, in step 2, the initial diameter-to-thickness ratio range of each section of the single pile foundation is set by: The diameter-to-thickness ratio of the first section single pile foundation is less than or equal to 200; the diameter-to-thickness ratio of the second section single pile foundation is less than or equal to 180; the diameter-to-thickness ratio of the third section single pile foundation is less than or equal to 120.

[0006] Preferably, in step 3, The basic structure of each sub-segment is as follows: Each sub-segment foundation is a straight or conical structure, and the inner diameter of the lower end of the previous sub-segment foundation is equal to the outer diameter of the upper end of the next sub-segment foundation.

[0007] Preferably, in step 4, the bearing capacity, deformation, self-weighted immersion depth, buckling stress and total fatigue damage value are used in turn to judge whether the initial single pile foundation meets the corresponding process requirements. If not, return to step 3. If satisfied, the final single pile foundation is obtained. The specific method is: S41, obtaining the bearing capacity and deformation of each sub-segment foundation, and judging whether the bearing capacity and deformation of each sub-segment foundation meet the requirements. If so, the intermediate single pile foundation is obtained and the process proceeds to S42, otherwise, the process proceeds to step 3; S42, obtaining the self-weighted depth of the middle single pile foundation into the mud, wherein, if the self-weighted depth of the middle single pile foundation into the mud is less than the length of the first section of the single pile sub-foundation, returning to step 1 to re-segment the single pile foundation to be designed, and reducing the length of the first section of the single pile sub-foundation; otherwise, proceeding to S43; S43, the middle single pile foundation is put into the mud by its own weight; S44, obtaining the first buckling stress of the intermediate single pile foundation after entering the mud, and judging whether the first buckling stress exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, proceeding to step S45; S45, hammering the middle single pile foundation after entering the mud once, and calculating the buckling stress of the middle single pile foundation under the hammering force; S46, judging whether the corresponding buckling stress during the hammering process exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, returning to S47; S47, repeating steps S45 and S46 until the middle single pile foundation is hammered to a specified depth; S48, calculate the fatigue damage caused by wind turbine load and wave current load to the intermediate single pile foundation after hammering to a specified depth, and calculate the fatigue damage of the pile body during the hammering process; S49, calculating the total fatigue damage value corresponding to the intermediate single pile foundation, and determining whether the total fatigue damage value exceeds the limit, wherein if it exceeds the limit, returning to step 3; otherwise, obtaining the final single pile foundation.

[0008] Preferably, in S41, the bearing capacity and deformation of each sub-segment foundation are obtained by: The structural form of each selected sub-segment foundation is analyzed in situ to obtain the bearing capacity and deformation of each sub-segment foundation.

[0009] Preferably, in S42, the self-weight penetration depth of the middle single pile foundation is obtained, and the specific method is: The weight of the single pile foundation to be designed is combined with the soil layer parameters at the machine position to calculate the depth of the middle single pile foundation's self-weight penetration into the mud.

[0010] Preferably, in S44, the buckling stress corresponding to each hammering of the intermediate single pile foundation after entering the mud and the fatigue damage suffered by the pile body are obtained, and the specific method is: The first buckling stress of the intermediate single pile foundation after entering the mud is obtained by: Based on the shape of the intermediate single pile foundation after entering the mud, a perfect solid finite element model considering the single pile foundation and soil is established; The obtained perfect solid finite element model is used to perform modal analysis on the intermediate single pile foundation to obtain the first-order mode, and the obtained first-order mode is applied to the perfect solid finite element model in equal proportion as a geometric defect to obtain a solid finite element model with geometric defects, wherein the maximum value of the geometric defect is determined according to the manufacturing capacity of the steel structure manufacturing unit; The wave load is applied to the solid finite element model with geometric defects to carry out buckling analysis, and the first buckling stress corresponding to the intermediate single pile foundation is obtained.

[0011] Preferably, In S45, the middle single pile foundation is hammered once after entering the mud, and the buckling stress of the middle single pile foundation under the hammer force is calculated. The specific method is: Based on the shape of the intermediate single pile foundation after entering the mud, a perfect solid finite element model considering the single pile foundation and soil is established; The maximum axial force on the middle single pile foundation during hammering is obtained based on the pile driving analysis method based on the wave equation. The obtained perfect solid finite element model is used to perform modal analysis on the intermediate single pile foundation to obtain the first-order mode, and the obtained first-order mode is applied to the perfect solid finite element model in equal proportion as a geometric defect to obtain a solid finite element model with geometric defects, wherein the maximum value of the geometric defect is determined according to the manufacturing capacity of the steel structure manufacturing unit; The wave load and the obtained maximum axial force are applied to the solid finite element model with geometric defects for buckling analysis, and the buckling stress of the middle single pile foundation under the hammer force is obtained.

[0012] An offshore large-diameter thin-walled steel pipe pile foundation is prepared by using the method.

[0013] Preferably, each section of the single pile sub-foundation is formed by axially splicing a plurality of sub-segment foundations; and the height of each sub-segment foundation is 1m-3m.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation. First, the single pile foundation to be designed is divided into three sections; each section can take a different diameter-to-thickness ratio, thereby breaking through the limitation of the diameter-to-thickness ratio of 120 and achieving the purpose of reducing the weight of the structure; then, the bearing capacity, deformation, self-weight penetration depth into the mud, buckling stress and total fatigue damage value are used in turn to judge whether the initial single pile foundation meets the corresponding process requirements, thereby ensuring the stable progress of the pile sinking process.

[0015] In summary, the present invention effectively solves the defect of limited weight reduction space of the single pile foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the form of a single pile foundation under deadweight; Figure 2 It is the form of a single pile foundation in place; Figure 3 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0017] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0018] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0019] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0020] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0021] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0022] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0023] Example 1 The present embodiment provides a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation, comprising the following steps: Step 1, dividing the single pile foundation to be designed into three sections, namely the first section single pile foundation, the second section single pile foundation and the third section single pile foundation, wherein the first section is the mud entry section; the second section is the mud entry section under the in-situ working condition; and the third section is the section above the mud surface under the in-situ working condition; Each single pile sub-foundation is composed of multiple sub-segment foundations; Step 2, setting the initial diameter-to-thickness ratio range of each section of the single pile foundation; Step 3, selecting the initial diameter-thickness ratio of each sub-segment foundation according to the set initial diameter-thickness ratio range, and setting the structure of each sub-segment foundation to obtain an initial single pile foundation; Step 4, use the bearing capacity, deformation, self-weight penetration depth, buckling stress and total fatigue damage value in turn to determine whether the initial single pile foundation meets the corresponding process requirements. If not, return to step 3. If yes, the final single pile foundation is obtained.

[0024] Example 2 like Figures 1 to 3As shown, the present embodiment provides a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation, comprising the following steps: Step 1, divide the single pile foundation to be designed into three sections, namely the first section single pile sub-foundation, the second section single pile foundation and the third section single pile foundation, wherein the first section is the mud entry section; the second section is the mud entry section under the in-situ working condition; the third section is the section above the mud surface under the in-situ working condition; each section of the single pile sub-foundation is composed of multiple sub-segment foundations.

[0025] Step 2, setting the initial diameter-to-thickness ratio range of each section of the single pile foundation, wherein the diameter-to-thickness ratio of the first section of the single pile foundation is less than or equal to 200; the diameter-to-thickness ratio of the second section of the single pile foundation is less than or equal to 180; and the diameter-to-thickness ratio of the third section of the single pile foundation is less than or equal to 120.

[0026] Step 3, selecting the initial diameter-to-thickness ratio of each sub-segment foundation according to the set initial diameter-to-thickness ratio range, and setting the structure of each sub-segment foundation to obtain an initial single pile foundation, wherein each sub-segment foundation is a straight or conical structure, and the inner diameter of the lower end of the previous sub-segment foundation is equal to the outer diameter of the upper end of the next sub-segment foundation; Step 4, perform in-situ working condition analysis according to the structural form of each selected sub-segment foundation, obtain the bearing capacity and deformation of each sub-segment foundation, and judge whether the bearing capacity and deformation of each sub-segment foundation meet the requirements. If they meet the requirements, obtain the intermediate single pile foundation and proceed to step 5, otherwise proceed to step 3; Step 5, calculate the weight of the single pile foundation to be designed, and calculate the self-weight penetration depth L by combining the obtained weight with the soil layer parameters of the machine position, wherein, if the self-weight penetration depth L is less than the length of the first section of the single pile foundation, return to step 1 to re-segment the single pile foundation to be designed, and reduce the length of the first section of the single pile foundation according to the self-weight penetration depth L; otherwise, proceed to step 6; Step 6, the middle single pile foundation is buried in the mud by its own weight; Step 7, obtaining the first buckling stress of the intermediate single pile foundation after entering the mud, and judging whether the first buckling stress exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, proceeding to step 8; Step 8, hammering the middle single pile foundation after entering the mud once, and obtaining the buckling stress of the middle single pile foundation under the hammering force; Step 9, determining whether the buckling stress corresponding to the hammering process exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, proceeding to step 10; Step 10, repeating steps 8 to 9 until the middle single pile foundation is hammered to a specified depth; Step 11, calculating the fatigue damage caused by the wind turbine load and the wave and current load to the intermediate single pile foundation after being hammered to a specified depth, and calculating the fatigue damage suffered by the pile body during the hammering process; Step 12, calculate the total fatigue damage value corresponding to the intermediate single pile foundation, and determine whether the total fatigue damage value exceeds the limit, wherein if it exceeds the limit, return to step 3; otherwise, obtain the final single pile foundation.

[0027] Example 3 On the basis of Example 2, this example provides a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation. In step 7, the first buckling stress of the intermediate single pile foundation after entering the mud is obtained. The specific method is: S71, based on the shape of the intermediate single pile foundation after entering the mud, a perfect solid finite element model considering the single pile foundation and soil is established; S72, using the perfect solid finite element model obtained in S71 to perform modal analysis on the intermediate single pile foundation to obtain a first-order mode, applying the obtained first-order mode in equal proportion as a geometric defect to the perfect solid finite element model obtained in S71 to obtain a solid finite element model with geometric defects, wherein the value of the maximum value δ of the geometric defect is determined according to the manufacturing capacity of the steel structure manufacturing unit; S73, applying wave loads to the solid finite element model with geometric defects to perform buckling analysis and obtain the first buckling stress of the intermediate single pile foundation after entering the mud.

[0028] Example 4 On the basis of Example 2, this embodiment provides a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation. In step 8, the buckling stress corresponding to the intermediate single pile foundation after hammering is obtained. The specific method is: S81, based on the shape of the intermediate single pile foundation after entering the mud, a perfect solid finite element model considering the single pile foundation and soil is established; S82, based on the wave equation pile driving analysis method, analyzes the maximum axial force on the middle pile foundation during each hammering. S83, using the perfect solid finite element model obtained in S81 to perform modal analysis on the intermediate single pile foundation to obtain a first-order mode, applying the obtained first-order mode in equal proportion as a geometric defect to the perfect solid finite element model obtained in S81 to obtain a solid finite element model with geometric defects, wherein the value of the maximum value δ of the geometric defect is determined according to the manufacturing capacity of the steel structure manufacturing unit; S84, applying the wave load and the maximum axial force obtained in S82 to the solid finite element model with geometric defects to perform buckling analysis and obtain the buckling stress of the middle single pile foundation under the hammer force.

[0029] Example 5 On the basis of Example 2, this example provides a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation. In step 11, the fatigue damage to the pile body during the hammering process is calculated. The specific method is: The fatigue damage of the pile body during the hammering process of the intermediate single pile foundation is obtained using the rainflow counting method.

[0030] Example 6 This embodiment provides an offshore large-diameter thin-walled steel pipe pile foundation, which is prepared by a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation.

[0031] Among them, a method for preparing an offshore large-diameter thin-walled steel pipe pile foundation comprises the following steps: Step 1, dividing the single pile foundation to be designed into three sections, namely the first section single pile foundation, the second section single pile foundation and the third section single pile foundation, wherein the first section is the mud entry section; the second section is the mud entry section under the in-situ working condition; and the third section is the section above the mud surface under the in-situ working condition; Each single pile sub-foundation is composed of multiple sub-segment foundations; Step 2, setting the initial diameter-to-thickness ratio range of each section of the single pile foundation, wherein the diameter-to-thickness ratio of the first section of the single pile foundation is less than or equal to 200; the diameter-to-thickness ratio of the second section of the single pile foundation is less than or equal to 180; and the diameter-to-thickness ratio of the third section of the single pile foundation is less than or equal to 120; Step 3, selecting the initial diameter-to-thickness ratio of each sub-segment foundation according to the set initial diameter-to-thickness ratio range, and setting the structure of each sub-segment foundation to obtain an initial single pile foundation, wherein each sub-segment foundation is a straight or conical structure, and the inner diameter of the lower end of the previous sub-segment foundation is equal to the outer diameter of the upper end of the next sub-segment foundation; Step 4, perform in-situ working condition analysis according to the structural form of each selected sub-segment foundation, obtain the bearing capacity and deformation of each sub-segment foundation, and judge whether the bearing capacity and deformation of each sub-segment foundation meet the requirements. If they meet the requirements, obtain the intermediate single pile foundation and proceed to step 5, otherwise proceed to step 3; Step 5, calculate the weight of the single pile foundation to be designed, and calculate the self-weight penetration depth L by combining the obtained weight with the soil layer parameters of the machine position, wherein, if the self-weight penetration depth L is less than the length of the first section of the single pile foundation, return to step 1 to re-segment the single pile foundation to be designed, and reduce the length of the first section of the single pile foundation according to the self-weight penetration depth L; otherwise, proceed to step 6; Step 6, the middle single pile foundation is buried in the mud by its own weight; Step 7, based on the shape of the intermediate single pile foundation after entering the mud, a perfect solid finite element model considering the single pile foundation and soil is established; Step 8, using the perfect solid finite element model obtained in step 7 to perform modal analysis on the intermediate single pile foundation, obtain the first-order mode, and apply the obtained first-order mode in equal proportion as a geometric defect to the perfect solid finite element model obtained in step 7 to obtain a solid finite element model with geometric defects, wherein the value of the maximum value of the geometric defect δ is determined according to the manufacturing capacity of the steel structure manufacturing unit Step 9, applying wave load to the solid finite element model with geometric defects to perform buckling analysis, and obtain the first buckling stress corresponding to the middle single pile foundation; Step 10, determining whether the first buckling stress exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, proceeding to step 11; Step 11, hammering the middle single pile foundation after entering the mud once, and establishing a perfect solid finite element model considering the single pile foundation and soil based on the shape of the middle single pile foundation after entering the mud; Step 12, based on the wave equation pile driving analysis method, analyzing the maximum axial force received by the middle single pile foundation each time when the middle single pile foundation is hammered; Step 13, using the perfect solid finite element model obtained in step 11 to perform modal analysis on the intermediate single pile foundation to obtain a first-order mode, and applying the obtained first-order mode in equal proportion as a geometric defect to the perfect solid finite element model obtained in step 11 to obtain a solid finite element model with geometric defects, wherein the value of the maximum value δ of the geometric defect is determined according to the manufacturing capacity of the steel structure manufacturing unit; Step 14, applying the wave load and the maximum axial force obtained in step 12 to the solid finite element model with geometric defects to perform buckling analysis, and obtain the buckling stress of the middle single pile foundation under the hammer force; Step 15, determining whether the buckling stress corresponding to the hammering process exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, proceeding to step 16; Step 16, repeating steps 11 to 15 until the middle single pile foundation is hammered to a specified depth; Step 17, calculating the fatigue damage caused by the wind turbine load and the wave and current load to the intermediate single pile foundation after being hammered to a specified depth, and calculating the fatigue damage suffered by the pile body during the hammering process; Step 18, calculate the total fatigue damage value corresponding to the intermediate single pile foundation, and determine whether the total fatigue damage value exceeds the limit, wherein if it exceeds the limit, return to step 3; otherwise, obtain the final single pile foundation.

[0032] Example 5 On the basis of Example 4, this example provides an offshore large-diameter thin-walled steel pipe pile foundation, wherein each section of a single pile sub-foundation is formed by axially splicing a plurality of sub-segment foundations; and the height of each sub-segment foundation is 1m-3m.

[0033] Each sub-segment foundation is made of rolled steel plates.

[0034] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for preparing an offshore large-diameter thin-walled steel pipe pile foundation, characterized in that: The following steps are involved: Step 1, dividing the single pile foundation to be designed into three sections, namely the first section single pile foundation, the second section single pile foundation and the third section single pile foundation, wherein the first section is the mud entry section; the second section is the mud entry section under the in-situ working condition; and the third section is the section above the mud surface under the in-situ working condition; Each single pile sub-foundation is composed of multiple sub-segment foundations; Step 2, setting the initial diameter-to-thickness ratio range of each section of the single pile foundation; Step 3, selecting the initial diameter-thickness ratio of each sub-segment foundation according to the set initial diameter-thickness ratio range, and setting the structure of each sub-segment foundation to obtain an initial single pile foundation; Step 4, use the bearing capacity, deformation, self-weight penetration depth, buckling stress and total fatigue damage value in turn to determine whether the initial single pile foundation meets the corresponding process requirements. If not, return to step 3. If yes, the final single pile foundation is obtained.

2. The method for preparing an offshore large-diameter thin-walled steel pipe pile foundation according to claim 1, characterized in that: In step 2, the initial diameter-to-thickness ratio range of each single pile foundation is set. The specific method is: The diameter-to-thickness ratio of the first section single pile foundation is less than or equal to 200; the diameter-to-thickness ratio of the second section single pile foundation is less than or equal to 180; the diameter-to-thickness ratio of the third section single pile foundation is less than or equal to 120.

3. The method for preparing an offshore large-diameter thin-walled steel pipe pile foundation according to claim 1, characterized in that: In step 3, the structure of each sub-segment basis is as follows: Each sub-segment foundation is a straight or conical structure, and the inner diameter of the lower end of the previous sub-segment foundation is equal to the outer diameter of the upper end of the next sub-segment foundation.

4. The method for preparing an offshore large-diameter thin-walled steel pipe pile foundation according to claim 1, characterized in that: In step 4, the bearing capacity, deformation, self-weight penetration depth, buckling stress and total fatigue damage value are used in turn to judge whether the initial single pile foundation meets the corresponding process requirements. If not, return to step 3. If yes, the final single pile foundation is obtained. The specific method is: S41, obtaining the bearing capacity and deformation of each sub-segment foundation, and judging whether the bearing capacity and deformation of each sub-segment foundation meet the requirements. If so, the intermediate single pile foundation is obtained and the process proceeds to S42, otherwise, the process proceeds to step 3; S42, obtaining the self-weighted depth of the middle single pile foundation into the mud, wherein, if the self-weighted depth of the middle single pile foundation into the mud is less than the length of the first section of the single pile sub-foundation, returning to step 1 to re-segment the single pile foundation to be designed, and reducing the length of the first section of the single pile sub-foundation; otherwise, proceeding to S43; S43, the middle single pile foundation is put into the mud by its own weight; S44, obtaining the first buckling stress of the intermediate single pile foundation after entering the mud, and judging whether the first buckling stress exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, proceeding to step S45; S45, hammering the middle single pile foundation after entering the mud once, and calculating the buckling stress of the middle single pile foundation under the hammering force; S46, judging whether the corresponding buckling stress during the hammering process exceeds the allowable stress value, wherein if it exceeds, proceeding to step 3; otherwise, returning to S47; S47, repeating steps S45 and S46 until the middle single pile foundation is hammered to a specified depth; S48, calculate the fatigue damage caused by wind turbine load and wave current load to the intermediate single pile foundation after hammering to a specified depth, and calculate the fatigue damage of the pile body during the hammering process; S49, calculating the total fatigue damage value corresponding to the intermediate single pile foundation, and determining whether the total fatigue damage value exceeds the limit, wherein if it exceeds the limit, returning to step 3; otherwise, obtaining the final single pile foundation.

5. The method for preparing an offshore large-diameter thin-walled steel pipe pile foundation according to claim 4, characterized in that: In S41, the bearing capacity and deformation of each sub-segment foundation are obtained. The specific method is: The structural form of each selected sub-segment foundation is analyzed in situ to obtain the bearing capacity and deformation of each sub-segment foundation.

6. The method for preparing an offshore large-diameter thin-walled steel pipe pile foundation according to claim 4, characterized in that: In S42, the self-weight penetration depth of the middle single pile foundation is obtained. The specific method is: The weight of the single pile foundation to be designed is combined with the soil layer parameters at the machine position to calculate the depth of the middle single pile foundation's self-weight penetration into the mud.

7. The method for preparing an offshore large-diameter thin-walled steel pipe pile foundation according to claim 4, characterized in that: In S44, the first buckling stress of the intermediate single pile foundation after entering the mud is obtained. The specific method is: Based on the shape of the intermediate single pile foundation after entering the mud, a perfect solid finite element model considering the single pile foundation and soil is established; The obtained perfect solid finite element model is used to perform modal analysis on the intermediate single pile foundation to obtain the first-order mode, and the obtained first-order mode is applied to the perfect solid finite element model in equal proportion as a geometric defect to obtain a solid finite element model with geometric defects, wherein the maximum value of the geometric defect is determined according to the manufacturing capacity of the steel structure manufacturing unit; The wave load is applied to the solid finite element model with geometric defects to perform buckling analysis, and the buckling stress corresponding to the intermediate single pile foundation after entering the mud is obtained.

8. The method for preparing an offshore large-diameter thin-walled steel pipe pile foundation according to claim 4, characterized in that: In S45, the middle single pile foundation is hammered once after entering the mud, and the buckling stress of the middle single pile foundation under the hammer force is calculated. The specific method is: Based on the shape of the intermediate single pile foundation after entering the mud, a perfect solid finite element model considering the single pile foundation and soil is established; The maximum axial force on the middle single pile foundation during hammering is obtained based on the pile driving analysis method based on the wave equation. The obtained perfect solid finite element model is used to perform modal analysis on the intermediate single pile foundation to obtain the first-order mode, and the obtained first-order mode is applied to the perfect solid finite element model in equal proportion as a geometric defect to obtain a solid finite element model with geometric defects, wherein the maximum value of the geometric defect is determined according to the manufacturing capacity of the steel structure manufacturing unit; The wave load and the obtained maximum axial force are applied to the solid finite element model with geometric defects for buckling analysis, and the buckling stress of the middle single pile foundation under the hammer force is obtained.

9. An offshore large-diameter thin-walled steel pipe pile foundation, characterized in that: Prepared by the method according to any one of claims 1 to 8.

10. The offshore large-diameter thin-walled steel pipe pile foundation according to claim 9, characterized in that: Each single pile sub-foundation is composed of multiple sub-segment foundations spliced ​​together along the axial direction; the height of each sub-segment foundation is 1m-3m.

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