Offshore single-pile foundation with ground improvement by compaction grouting

Abstract

The present invention relates to an offshore monopile foundation with a compacted grouting reinforced foundation in the field of pile foundations for ocean engineering. The technical solution is that a steel pipe pile is sunk into the seabed, and the seabed is a soft soil foundation. In the soft soil foundation, a reinforced foundation using the compacted grouting process is arranged around the steel pipe pile. The reinforced foundation includes a compacted grouting slurry bulb, a drainage channel and the soft soil therebetween; the reinforced foundation is a rotating body coaxial with the steel pipe pile. It has high horizontal bearing capacity, small horizontal displacement at the pile top, small pile body inclination angle, and large foundation stiffness, adapts to the characteristics of large horizontal loads of offshore wind turbines, meets the strict requirements of offshore wind turbines for the horizontal displacement of the foundation and the pile body inclination angle, and meets the requirements of the overall natural vibration frequency of "structure + foundation".

Description

Technical Field

[0001] The present invention relates to the field of pile foundations for ocean engineering, and particularly to an offshore monopile foundation with high horizontal bearing capacity in soft soil foundations. Background Art

[0002] Offshore wind power generation is a key development area in the new energy field, with a very broad market prospect. Wind turbine units have strict control standards for the horizontal displacement and uneven settlement of the foundation, and the natural vibration frequency of the "structure + foundation" needs to avoid the driving frequency of external loads. Currently, common foundation types for offshore wind turbine generators include monopiles, high-pile capitals, multi-legged frames, jacket structures, gravity-type, suction bucket-type, and floating platform structures, etc. In offshore wind power projects, monopile foundations are widely used because of their advantages such as small land occupation, simple structure, fast construction, and low cost. On the other hand, the disadvantage of monopile foundations compared with other foundation types is that they are less rigid and more flexible. The seabed surface layer in the offshore waters of China is mostly thick soft soil, which to a certain extent restricts the application of this type of foundation. In a complex marine environment, waves, ocean currents, etc. will exert huge horizontal loads on the wind turbine foundation. As the single-unit capacity of wind turbines becomes larger, the hub height becomes higher, the blades become longer, and the wind turbine loads become greater. Although steel pipe piles have relatively large flexural stiffness, the soil on the surface layer of the pile perimeter foundation can provide limited horizontal restraint. If a conventional monopile foundation is used, methods such as increasing the pile diameter, pile length, or wall thickness will result in the consumption of more materials, and the increase in the weight of the monopile also brings higher construction difficulty, leading to a rapid increase in the foundation cost and affecting the power generation efficiency of the wind farm. Therefore, researching and developing an offshore monopile foundation with high horizontal bearing capacity in soft soil foundations has practical engineering significance. Summary of the Invention

[0003] In view of the difficulties in the application of monopile foundations in soft soil foundation waters, the purpose of the present invention is to provide an offshore monopile foundation with ground consolidation by compaction grouting, which has high horizontal bearing capacity, small horizontal displacement at the pile top, small pile inclination, and large foundation stiffness, adapts to the characteristics of large horizontal loads of offshore wind turbines, meets the strict requirements of offshore wind turbines for the horizontal displacement and pile inclination of the foundation, and meets the requirements of the natural vibration frequency of the "structure + foundation" as a whole.

[0004] The basic technical solution is as follows: An offshore monopile foundation with ground consolidation by compaction grouting, in which a steel pipe pile is sunk into the seabed, the seabed is a soft soil foundation, and in the soft soil foundation, a ground consolidation using the compaction grouting process is arranged around the steel pipe pile. The ground consolidation includes compaction grouting slurry bulbs, drainage channels, and the soft soil therebetween; the ground consolidation is a rotating body coaxial with the steel pipe pile. The compaction grouting process can be implemented according to the "Technical Code for Ground Treatment in Shanghai" (DG TJ08 - 40 - 2010). The role of the drainage channel is to facilitate the drainage of water in the foundation and achieve a more dense arrangement of solid particles in the soil.

[0005] Based on the above technical features: on the upper surface of the soft soil foundation, a scour prevention structure around the steel pipe piles is provided.

[0006] Based on the above technical features: the scour prevention structure around the piles is a covering layer made of riprap or geotextile mattress or interlocking blocks or solidified soil.

[0007] Based on the above technical features: the compaction grouting bubbles and drainage channels are arranged at intervals along concentric circles with different radii of the steel pipe piles.

[0008] Based on the above technical features: the compaction grouting bubbles and drainage channels are arranged in an array.

[0009] Based on the above technical features: an accessory structure is installed outside the pile body of the steel pipe pile above the seabed. The accessory structure mainly includes but is not limited to a steel platform, a berthing structure, and a cable pipe. Reserved positions are provided on the steel pipe pile for connecting with the accessory structure.

[0010] Applying the offshore monopile foundation with compaction grouting for foundation reinforcement can make the monopile foundation applicable to a wider sea area and larger wind turbine models. From the basic level of wind turbine foundation selection, it can avoid using foundation types with higher costs such as high-piled capitals, multi-legged scaffolds, and jacket platforms, thereby effectively reducing the engineering cost of offshore wind turbine foundations, shortening the construction period, and improving the power generation efficiency of the wind farm.

[0011] The offshore monopile foundation with compaction grouting for foundation reinforcement of the present invention, compared with ordinary offshore monopile foundations, has effectively improved horizontal bearing capacity, effectively reduced the horizontal lateral displacement at the pile top, effectively reduced the rotation angle at the mud surface of the single pile, improved the overall natural vibration frequency of the "structure + foundation", and at the same time has the benefit of saving the steel consumption of the single pile foundation.

[0012] As described above, the offshore monopile foundation with high horizontal bearing performance in the soft soil foundation of the present invention has the following beneficial effects: the offshore monopile foundation with high horizontal bearing performance in the soft soil foundation is economical, safe, and reliable, applicable to a wider sea area and larger wind turbine models, and has been greatly reduced in terms of engineering cost; moreover, the construction process is simple, only requiring a small range of compaction grouting construction to be added, which is convenient and effective to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic structural diagram of the offshore monopile foundation with compaction grouting for foundation reinforcement of the present invention.

[0014] Figure 2 It is a plan view of the first embodiment of the offshore monopile foundation with compaction grouting for foundation reinforcement of the present invention.

[0015] Figure 3 It is a plan view of the second embodiment of the offshore monopile foundation with compaction grouting for foundation reinforcement of the present invention.

[0016] Figure 4 This is the plan view of the third implementation mode of the single pile foundation on the sea with ground consolidation by compaction grouting for the present invention.

[0017] Label description

[0018] Soft soil foundation 1; Steel pipe pile 2; Compaction grouting slurry bulb 3; Consolidated foundation 4; Anti-scouring structure around the pile 5; Drainage channel 6; Auxiliary structure 7; Mud surface 8. Specific implementation mode

[0019] The following further details the specific implementation mode of the present invention with reference to the accompanying drawings. These implementation modes are only used to illustrate the present invention and are not intended to limit the present invention.

[0020] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0021] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, indirectly connected through an intermediate medium, or the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0022] In addition, in the description of the present invention, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0023] Such as Figure 1As shown in the figure, the steel pipe pile 2 is sunk into the seabed, which is a soft soil foundation 1. Inside the soft soil foundation 1, a reinforced foundation 4 using the compaction grouting process is arranged around the steel pipe pile 2. The reinforced foundation 4 includes compaction grouting slurry bubbles 3, drainage channels 6, and the soft soil in between. The reinforced foundation 4 is arranged as a rotating body coaxial with the steel pipe pile 2. The top elevation of the reinforced foundation 4 is located below the mud surface 8 of the soft soil foundation, and the bottom elevation of the reinforced foundation is determined in combination with the engineering requirements and construction equipment conditions. The size of the reinforced foundation can be determined according to the actual situation of each project, comprehensively considering the bearing capacity requirements of the steel pipe pile, deformation control, and project cost. On the upper surface of the soft soil foundation, a layer of anti-erosion structure 5 around the steel pipe pile 2 is arranged. The anti-erosion structure around the pile can adopt different schemes, such as a covering layer paved with riprap, geotextile mattress, interlocking blocks, solidified soil, etc. Its function is to prevent the soil around the pile from being washed away by the water flow. The geotextile mattress includes geotextiles and fillers, etc.; the interlocking blocks include reinforced concrete, etc. The planar shape of the anti-erosion structure 5 around the pile is not limited, and the outer edge can be designed as a circle, polygon, or irregular shape, and its size can be determined according to the actual situation of each project. An accessory structure 7 is installed outside the pile body of the steel pipe pile above the seabed. The accessory structure 7 mainly includes but is not limited to a steel platform, a mooring structure, and a cable pipe. Reserved positions are provided on the steel pipe pile for connecting with the accessory structure 7.

[0024] In the present invention, the steel pipe pile 2 is used to support the wind turbine tower and transfer the load of the upper structure. The main function of the reinforced foundation 4 using the compaction grouting process is to provide horizontal restraint for the steel pipe pile 2 and diffuse and transfer the horizontal load to the soft soil foundation 1. The anti-erosion structure 5 around the pile is used to protect the soft soil foundation 1 and the reinforced foundation 4, and prevent the horizontal restraint from not being provided due to the erosion of the soil around the steel pipe pile 2.

[0025] Figure 2 The figure shows a plan view of the first embodiment of the offshore monopile foundation with a compaction grouting reinforced foundation of the present invention. The compaction grouting slurry bubbles 3 and the drainage channels 6 are arranged at intervals along concentric circles with different radii of the steel pipe pile 2.

[0026] Figure 3 and Figure 4 are plan views of the other two embodiments of the offshore monopile foundation with a compaction grouting reinforced foundation of the present invention. The compaction grouting slurry bubbles 3 and the drainage channels 6 are arranged in an array. As Figure 3 shown, the compaction grouting slurry bubbles 3 and the drainage channels 6 are arranged in a square array. As Figure 4 shown, the compaction grouting slurry bubbles 3 and the drainage channels 6 are arranged in an equilateral triangle array.

[0027] Example of the construction method of the monopile foundation for offshore wind turbines in the present invention: First, drainage channels 6 are arranged in a concentric circle, an equilateral triangle, or a square according to the design drawings. The drainage channels 6 can be realized by inserting plastic drainage boards, setting sand drains in bags, or ordinary sand drains, which belong to the conventional techniques of the compaction grouting process. Then, the pile driving construction of the steel pipe piles 2 is completed. Drilling is carried out according to the design drawings, and cement slurry is injected at the set elevation to form the compaction grouting slurry bulb 3. Thus, the foundation 4 is reinforced by the compaction grouting process. The anti-scour structure 5 is made, and finally, the accessory structure 7 is installed. In the present invention, the horizontal load of the wind turbine is transmitted through the steel pipe piles 2 to the foundation 4 reinforced by the compaction grouting process and then to the surrounding soft soil foundation 1, and the force transmission path is simple and direct.

[0028] In summary, the present invention uses the compaction grouting method to improve the strength and stiffness of the soil around the pile, and enhance the horizontal bearing capacity of the soft soil foundation, which is economical, safe, and reliable. The present invention has high horizontal bearing capacity, small horizontal displacement at the pile top, small inclination angle of the pile body, and large foundation stiffness, which is suitable for the characteristics of large horizontal loads of offshore wind turbines, meets the strict requirements of offshore wind turbines for the horizontal displacement of the foundation and the inclination angle of the pile body, and meets the requirements of the overall natural vibration frequency of the "structure + foundation". The monopile foundation for offshore wind turbines with high horizontal bearing capacity in the soft soil foundation breaks through the constraints of the soft soil foundation on the monopile foundation, is applicable to a wider sea area, and is applicable to wind turbines with larger single-unit capacity, higher hub height, longer blades, and larger horizontal loads. From the basic level of the selection of the wind turbine foundation, it is possible to avoid using foundation types with higher costs such as high-pile caps, multi-legged frames, and jacket platforms, thereby effectively reducing the engineering cost of the offshore wind turbine foundation, shortening the construction period, and improving the economic benefits of the offshore wind farm. Moreover, the construction process is simple, only requiring a small-scale compaction grouting construction to be added, which is convenient and effective to implement. Therefore, the present invention effectively overcomes the difficulties in the application of the existing monopile foundation in the soft soil foundation, and thus has high industrial utilization value.

[0029] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. An offshore single-pile foundation with a ground-improved compaction grouting, where a steel pipe pile (2) is sunk into the seabed which is a soft soil foundation (1), characterized in that: Within the soft soil foundation, a reinforced foundation (4) using the compaction grouting process is arranged around the steel pipe pile (2). The reinforced foundation (4) includes compaction grouting slurry bulbs (3), drainage channels (6), and the soft soil therebetween. The reinforced foundation (4) is a rotating body coaxial with the steel pipe pile (2); cement slurry is injected into the boreholes in the soft soil foundation to form the compaction grouting slurry bulbs (3); the compaction grouting bulbs (3) and the drainage channels (6) are arranged at intervals along concentric circles with different radii of the steel pipe pile (2), or the compaction grouting bulbs (3) and the drainage channels (6) are arranged in an array.

2. The offshore single-pile foundation with a ground improved by compaction grouting according to claim 1, characterized in that: On the upper surface of the soft soil foundation (1), a scour prevention structure (5) around the steel pipe pile (2) is arranged.

3. The offshore single-pile foundation with ground consolidation by compaction grouting according to claim 2, characterized in that: The scour prevention structure (5) around the pile is a covering layer paved with riprap, geotextile mattress, interlocking blocks, or solidified soil.

4. A single pile foundation in the sea with a ground foundation reinforced by compaction grouting according to any one of claims 1 to 3, characterized in that: An accessory structure (7) is installed outside the pile body of the steel pipe pile (2) above the seabed.

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