Wind turbine foundation and construction method thereof

Abstract

The present invention relates to a cross-shaped hybrid wind turbine foundation and a construction method thereof. The cross-shaped hybrid wind turbine foundation comprises a pile cap (1) is cast of reinforced concrete in the shape of a inverted drum, consisting of an outer cylinder (9), an inner cylinder (10), and radial walls (11) arranged radially on the outer surface of the inner cylinder (10) to connect the inner cylinder (10) with the outer cylinder (9), forming a integrated rigid slab. A slab (12) covers the top surface of the pile cap (1), creating enclosed chambers between the slab (12), the outer cylinder (9), the inner cylinder (10), and the radial walls (11), allowing for vacuum suction when placing the pile cap (1) on the seabed ground; a adapter tower (2) is connected to the top surface of the pile cap (1); an upper pile segment (3) is connected to the bottom surface of the pile cap (1), and a lower pile segment (4) is inserted inside the upper pile segment (3); a upper anchored wire ropes (6) connects the pile cap (1) to the upper end of the adapter tower (2), and a lower anchored wire ropes (5) connects the pile cap (1) to the upper pile segment (3).

Description

[0001] WIND TURBINE FOUNDATION AND CONSTRUCTION METHOD THEREOF

[0002] Technical Field

[0003] The present invention relates to the field of construction technology of wind turbine tower foundations, and more particularly, to a cross-shaped hybrid wind turbine foundation that is combined between a shallow foundation and a monopile foundation, the cross-shaped hybrid wind turbine foundations including a adapter tower, a pile cap and a pile, which can increase the bearing capacity, increase the bending stiffness, reduce the horizontal displacement and rotational displacement of the pile. In addition, the present invention also refers to the construction method of this cross-shaped hybrid wind turbine foundation.

[0004] Background Art

[0005] Currently, the wind turbines in operation typically have a capacity ranging from 6 MW to 12 MW, and will increase to 12 MW to 25 MW in the future. The wind turbine towers utilized in industrial wind power plants are mainly built in areas characterized by unstable soil conditions such as shorelines, floodplains, and sea areas in shallow water depths less than 50 meters. Such areas often exhibit weak soil geology. Therefore, the wind turbine foundation systems in these areas must adhere to specific criteria to ensure the bearing capacity and structural stability on unstable ground, thus ensuring the overall stability of the wind turbines.

[0006] The common types of wind turbine foundations commonly used for areas with the above properties can be categorized based on their structure and installation methods, which are described below.

[0007] The gravity foundation: the gravity foundations (also known as shallow foundations) have a large foundation base in direct contact with the ground and use the weight of the turbine and the tower along with the weight of the foundation base itself and the soil mass on the foundation to create gravity to keep the wind turbine stable. This gravity foundation structure is only suitable when the layers of soil under the foundation base have good bearing capacity. However, for areas with weak soil geological conditions with great depths, especially coastal wetlands, this gravity foundation structure cannot be applied.

[0008] The monopile foundation: the monopile foundation is usually applied to turbine foundations built on the sea sea in a water depth of 20 - 40 m. The monopile foundation is made of a steel pile with a large diameter of 5-9 m that is driven into the ground on the seabed from 30-100 m. The advantage of monopile foundation is a fast construction. However, monopile foundations have limitations in that the displacement of the pile head is large, the load is incurred due to the deformation of large structures, the price is very high and requires modem super-heavy mechanized construction methods and high- quality manpower, leading to large costs. The limitation of this monopile foundation is only applicable to wind turbines with capacity of less than 8-10 MW because of the limitations of transportation and installation equipment.

[0009] Summary of the Invention

[0010] Considering the aforementioned problems of current wind turbine foundation structures, the object of the present invention is to provide a crossshaped hybrid wind turbine foundation that is combined between a shallow foundation and a monopile foundation, forming a cross-shaped structure comprising a pile cap, a pile and anchored wire ropes. This cross-shaped hybrid wind turbine foundation aims to take advantage of the benefits while effectively mitigating the limitations associated with existing foundation structures.

[0011] Another object of the present invention is to provide a construction method of the cross-shaped hybrid wind turbine foundation capable of saving costs, well controlling quality and speeding up the construction schedule.

[0012] To achieve the above mentioned objects, one aspect of the present invention provides the cross-shaped hybrid wind turbine foundation includes: the pile cap (1), adapter tower (2) connected to the upper surface of the pile cap (1), the upper pile segment (3) connected to the lower surface of the pile cap (1), the upper anchored wire ropes (6) connects the pile cap (1) with the upper end of the adapter tower (2), and the lower anchored wire ropes (5) connects the pile cap (1) to the upper pile segment (3), wherein: the pile cap (1) is cast of reinforced concrete in the shape of a inverted drum, consisting of two hollow columns arranged concentrically and connected to each other through radial walls, the pile cap (1) includes: the outer cylinder (9) with a diameter of 20-50 m, a height of 3-8 m, and a thickness of 0.3-0.7 m; the inner cylinder (10) with a diameter of 4-15 m, a height of 3-8 m, and a thickness of 0.3-2.0 m; the radial walls (11) are arranged radially on the outer circumference surface of the inner cylinder (10) to connect the inner cylinder (10) with the outer cylinder (9), forming a integrated rigid slab; and the slab (12) covering the upper surface of the pile cap (1) so that enclosed chambers are formed between the slab (12), the outer cylinder (9), the inner cylinder (10), and the radial walls (11) to facilitate for perform vacuum suction when placing the pile cap (1) on the seabed; the adapter tower (2) has a diameter of 6-15 m and is made of reinforced concrete or steel. The upper end of the adapter tower (2) is equipped with an anchoring cable system to connect to the upper anchored wire ropes (6); and the upper pile segment (3) is a hollow tubular section arranged inside and fixed to the inner cylinder (10) of the pile cap (1).

[0013] According to the present invention, the wind turbine foundation further includes the lower pile segment (4) with a diameter smaller by 10-100 cm than the inner diameter of the upper pile segment (3), inserted inside the upper pile segment (3) and driven deep into the underlying soil.

[0014] According to the present invention, the upper pile segment (3) is a hollow tube with a diameter smaller by 10-100 cm than the inner diameter of the inner cylinder (10) of the pile cap (1). The upper end of the upper pile segment (3) is secured to the inner cylinder (10) by pouring high-strength grout into the overlapping joint (7), and the lower end of the upper pile segment is connected to the lower pile segment (4) at the joint (8) using high-strength grout.

[0015] According to the present invention, the upper pile segment (3) is a steel tube with a thickness of 3-15 cm, and the top of the upper pile segment (3) is formed a flange (14), the outer diameter of the flange (14) being smaller than the inner diameter of the inner cylinder (10).

[0016] According to the present invention, the lower end of the upper pile segment (3) is formed with a lower collar (15) opposite to the flange (14), where the inner diameter of the lower collar (15) is larger than the outer diameter of the lower pile segment (4).

[0017] According to the present invention, the wind turbine foundation further includes a cap (30) secured to the top of the upper pile segment (3) by welding so that the top of the upper pile segment (3) is sealed.

[0018] According to the present invention, the flange (14) and the lower collar (15) are formed with evenly spaced circular holes to connect the bolt system of the upper pile segment (3) with the inner cylinder (10) and the lower pile segment (4), respectively. According to the present invention, the lower pile segment (4) is a steel tube with the top end formed with a lower pile collar (16), such that the outer diameter of the lower pile collar (16) is larger than the inner diameter of the lower collar (15) of the upper pile segment (3).

[0019] According to the present invention, the lower pile collar (16) is formed with evenly spaced circular holes corresponding to the holes of the lower collar (15) to connect the bolt system of the upper pile segment (3) with the lower pile segment (4).

[0020] According to the present invention, the bottom end of the inner cylinder (10) of the pile cap is formed with a bottom flange (13), wherein the inner diameter of the bottom flange (13) is larger than the outer diameter of the upper pile segment (3) and smaller than the outer diameter of the flange (14).

[0021] According to the present invention, the bottom flange (13) is formed with evenly spaced circular holes corresponding to the holes of the flange (14) to connect the bolt system of the inner cylinder (10) of the pile cap with the upper pile segment (3).

[0022] According to the present invention, one end of the lower anchored wire ropes (5) is anchored to the radial walls (11) at the intersection with the outer cylinder (9), and the other end of the lower anchored wire ropes (5) is anchored to the wall of the upper pile segment (3), the lower anchored wire ropes (5) are arranged radially so that the lower anchored wire rope (5) forms an angle (a) of approximately 20-70° with the horizontal direction.

[0023] According to the present invention, one end of the upper anchored wire ropes (6) are connected to the lower anchored wire ropes (5) in a saddle form at the ends of the radial walls ( 11 ) of the pile cap, and the other end of the upper anchored wire ropes (6) are connected to the upper end of the adapter tower (2). According to the present invention, the number of cables in the lower anchored wire ropes (5) and the upper anchored wire ropes (6) is 3 to 12 cables arranged circularly around the central axis of the foundation, preferably, the number of cables in the lower anchored wire ropes (5) and the upper anchored wire ropes (6) is equal to the number of radial walls (11).

[0024] Another aspect of the present invention also provide a construction method for the hybrid cross-shaped wind turbine foundation according to the above aspect, in which this method includes the following steps: casting the precast concrete foundation with reinforced concrete, insert the upper pile segment (3) of the pile through the inner cylinder (10) of the pile cap (1), the upper pile segment (3) and the pile cap (1) are temporarily fixed together using the bolt system (17), install the upper anchored wire ropes (6), with the one ends are connected to the pile cap (1), and the other ends of the cables of the upper anchored wire ropes (6) are connected to the upper end of the adapter tower (2), install the lower anchored wire ropes (5), with one ends connected to the pile cap (1), and the other end sof the cables of the lower anchored wire ropes (5) are connected to the lower end of the upper pile segment (3), and then, the entire system is transported to the construction site; lowering the pile cap (1) to the ground by vacuuming the enclosed chambers between the slab (12), the outer cylinder (9), the inner cylinder (10), and the radial walls (11) of the pile cap (1) until the slab (12) comes into contact with the seabed; lowering the upper pile segment (3) along with the cables of the lower anchored wire ropes (5) fixed to the lower end of the upper pile segment (3) moves down to the design elevation by using the inner cylinder (10) of the foundation as a guide frame and tensioning the bolt system (17) to push the upper pile segment (3) downward; connecting the pile cap (1) and the upper pile segment (3) by pumping high-strength grout at the joint (7); and securing the other ends of the cables of the lower anchored wire ropes (5) to the radial walls (3) of the pile cap, and the cables of the lower anchored wire ropes (5) are tensioned.

[0025] According to the present invention, the construction method for the wind turbine foundations further includes the step of inserting the lower pile segment (4) into the cavity of the upper pile segment (3) and temporarily fixing the upper pile segment (3) and the lower pile segment (4) together using the bolt system (18) before performing the step of lowering the pile cap (1) onto the ground.

[0026] According to the present invention, the construction method for the wind turbine foundations further includes the step of lowering the lower pile segment (4) inside the upper pile segment (3) to the design depth, using the upper pile segment (3) as a guide frame and tensioning the bolt system (18) to push the lower pile segment down immediately after lowering the upper pile segment (3) to the design elevation.

[0027] According to the present invention, the construction method for the wind turbine foundations further includes the step of connecting the upper pile segment (3) and the lower pile segment (4) by pumping high-strength grout at the joint (8) before performing the step of connecting the pile cap (1) and the upper pile segment (3).

[0028] According to the present invention, the top of the upper pile segment (3) is fixed with the cap (30) by welding, ensuring that the top of the upper pile segment (3) is sealed, and then, the upper pile segment (3) is lowered to the design elevation is performed by vacuum suction to generate the vacuum pressure inside the upper pile segment (3). According to the present invention, the cables of the lower anchored wire ropes (5) are tensioned between the radial walls (11) of the foundation and the lower end of the upper pile segment (3), forming an inclination angle (a) of approximately 20-70° with respect to the horizontal plane, preferably forming an inclination angle of 35-60°, and most preferably forming an inclination angle of 50-60°.

[0029] Advantageous Effects

[0030] The cross-shaped hybrid wind turbine foundation of the present invention is a combination of shallow foundation and a pile foundation that allows the pile to bear vertical loads, in which the pile cap is subjected to horizontal loads and torsional moment. The pile cap together with the upper pile segment and the lower pile segment, in which the lower end of the upper pile segment connected to the outer circumference of the pile cap by the anchored wire ropes, will bear the load caused by the bending moment, increasing the bending resistance moment of the whole foundation system.

[0031] The cross-shaped hybrid wind turbine foundation of the present invention allows to maximize the bearing capacity of the ground even in weak soil layers above, with a reasonable foundation bearing diagram allowing to increase bearing capacity and reduce material usage.

[0032] By fixing the lower end of the upper pile segment with radial walls at the intersection with the outer cylinder by the anchored wire ropes of the crossshaped hybrid wind turbine foundation of the present invention, transfer the structure from the cantilever system of one free end and one fixed in the soil to a bar of one fixed end and an one spring end. Accordingly, when the pile includes the upper pile segment and lower pile segment, is fixed to the pile cap, with the same bending moment, it is allowed to reduce horizontal displacement and rotational displacement by 2 times in the absence of anchored wire ropes, while horizontal displacement and rotational displacement are reduced by 7-12 times in the presence of anchored wire ropes.

[0033] The cross-shaped hybrid wind turbine foundation of the present invention allows to reduce the material used and the size of the pile, they allow save about 20-30% the construction cost. And it also allow used design for the large size of wind turbine nowadays out of the limit of monopile foundation.

[0034] The radial walls, the upper pile segment with the tension steel wire ropes, allow to enhance the bending resistance rigidity of the foundation, as well as creating a fixed point that reduces the slenderness of the entire pile system includes the upper pile segment and lower pile segment.

[0035] The cross-shaped hybrid wind turbine foundation of the present invention is lowered into the soil by lowering the foundation components in sequence: first the pile cap, then the upper pile segment, and finally the lower pile segment. This method helps to divide the total energy to lower the entire foundation system into small sections, thus eliminating the need for specific large-capacity equipment and reduces construction costs. With the construction by pressure to split the pile sections, there is no additional fatigue load during the construction like driving a monopile, thereby prolonging the life of the foundation system.

[0036] The cross-shaped hybrid wind turbine foundation can be installed without producing loud noises that may affect organisms living in the built environment.

[0037] The cross-shaped hybrid wind turbine foundation allows to solve the problem of cleaning and restoring the original environmental site by utilizing pile cap as an anchor system to pull out the lower and upper pile segments, and the entire pile cap can then be returned to the original environment, this allows for the retrieval of used materials for recycling.

[0038] Description of Drawings

[0039] Fig. 1 is a partial cross-sectional perspective view of the cross-shaped hybrid wind turbine foundation according to the embodiment of the present invention;

[0040] Fig. 2 is a partial cross-sectional perspective view of the cross-shaped hybrid wind turbine foundation according to the another embodiment of the present invention;

[0041] Fig. 3 is a partial cross-sectional perspective view of the Cross-shaped hybrid wind turbine foundation according to the another embodiment of the present invention;

[0042] Fig. 4 is the top view of the turbine foundation in Fig. 1;

[0043] Fig. 5 is a cross-sectional view illustrating the method of connecting the components of the wind turbine foundation according to the present invention in preparation for installation and lowering the foundation;

[0044] Fig. 6 is a cross-sectional view showing the state of the wind turbine foundation according to the present invention after lowering the upper pile segment;

[0045] Fig. 7 is a cross-sectional view showing the state of the wind turbine foundation according to the present invention after the upper pile segment has been fully lowered; and

[0046] Fig. 8 is a drawing comparing the changes in horizontal displacement and rotational displacement of the structure when the boundary conditions are changed.

[0047] Detailed Description of the Invention Hereafter, the structure of the cross-shaped hybrid wind turbine foundation according to the present invention will be described in detail with reference to the accompanying drawings.

[0048] One aspect of the present invention provides the cross-shaped hybrid wind turbine foundation.

[0049] As shown in Figs. 1 and 4, the cross-shaped hybrid wind turbine foundation according to the first embodiment of the present invention is a combination of a shallow foundation and a monopile foundation with a crossshape, including a pile cap 1 connected to a adapter tower 2, a pile including an upper pile segment 3 and a lower pile segment 4, and a lower anchored wire ropes 5 and an upper anchored wire ropes 6, these components are connected at joints 7 and 8, thereby take advantage of the benefits while effectively mitigating the limitations associated with existing foundation structures.

[0050] Refer to Figs. 1 and 4, the pile cap 1 is cast of reinforced concrete in the shape of an inverted drum with a closed top, consisting of two hollow columns arranged concentrically and connected to each other through radial walls, forming an integrated rigid slab. The pile cap 1 includes the outer cylinder 9 and the inner cylinder 10, which are connected by radially arranged radial walls 11, and the slab 12 on the upper surfaces of the outer cylinder 9, inner cylinder 10, and the radial walls 11 to cover the top surface of the pile cap 1.

[0051] As shown in Fig. 1, the outer cylinder 9 can be made of concrete or steel, with a diameter ranging from 20 - 50 m and a height from 3 - 8 m. The slab 12 is formed perpendicular to the outer cylinder 9, extending from the inner perimeter at the top of the outer cylinder 9 toward the inner cylinder 10 to completely cover the top surface of the pile cap 1, ensuring that the pile cap 1 has the shape of a inverted drum and creates enclosed chambers to facilitate lowering the pile cap 1 below the seabed through the perform of vacuum suction. However, the present invention is not limited to the slab 12 being formed perpendicular to the outer cylinder 9, the slab 12 may be inclined relative to the outer cylinder 9 so that the top surface of the pile cap 1 has a conical shape.

[0052] As shown in Figs. 1 and 4, the inner cylinder 10 made in reinforced concrete or steel, with a diameter of 4 - 15 m, at the bottom of the inner cylinder 10 is a bottom flange 13 to connect the pile and the pile cap. The outer and inner cylinders are connected by radial walls 11, which can vary in number from 3 to 12 walls. All system is covered by a slab 12. The structure forms the close compartment when we put the pile cap on the seabed.

[0053] As shown in Fig. 1 and Fig. 4, the inner cylinder 10 can be made of concrete or steel, with a diameter ranging from 4 - 15 m. The bottom of the inner cylinder 10 is equipped with a bottom flange 13 protruding inward from the inner cylinder 10. The bottom flange 13 serves as a support point to guide and secure the upper pile segment 3. On the surface of the a bottom flange 13, evenly spaced circular holes are created to guide and connect the bolts of the inner cylinder 10 of the pile cap 1 with the upper pile segment 3.

[0054] The radial walls 11 are arranged radially on the outer periphery surface of the inner cylinder 10 to connect with the outer cylinder 9 and the bottom of the slab 12. The radial walls have the function of connecting and reinforcing the pile cap 1. According to the embodiment of the present invention, depending on the diameter size of the outer cylinder 9 of the pile cap 1, the number of radial walls 11 arranged radially at equal intervals on the outer periphery surface of the inner cylinder 10 will vary from 3 to 12. At the outer ends of the radial walls 11 adjacent to the outer cylinder 9, anchorage systems are arranged to connect with the lower and upper anchored wire ropes 5 and 6.

[0055] The adapter tower 2 made of steel or concrete, is connected to the top of the inner cylinder 10, The adapter tower 2 is a transitional part that allows easy connection to the tower of the wind turbine. According to another embodiment of the present invention as shown in Fig. 2, the adapter tower 2 can be made integral with the inner cylinder of the pile cap 1 , which allows increasing the rigidity of each connection between the pile cap and the tower of the wind turbine.

[0056] As shown on Figs. 1, 2 and 5, the pile consists of the upper pile segment 3 and the lower pile segment 4. The upper pile segment 3 has the form of a hollow cylinder with a diameter of 10-100 cm smaller than the inner diameter of the inner cylinder 10 of the pile cap, so that the upper pile segment 3 inserted through the bottom flange 13 of the inner cylinder 10. The flange 14 is extended outward from the outer surface at the upper end of the upper pile segment 3, and the evenly spaced circular holes are provided on the surface of the flange 14 corresponding to the holes of the bottom flange 13 so that the bolt systems 17 can pass through the corresponding holes to lower the upper pile segment 3 and secure it to the inner cylinder 10. The lower collar 15 is extended inward from the inner surface at the lower end of the upper pile segment 3 so that the extension directions of the flange 14 and the lower collar 15 are opposite. The lower collar 15 is provided with evenly spaced circular holes to connect the bolt system of the upper pile segment 3 with the lower pile segment 4. The lower pile segment 4 is in the shape of a hollow cylinder with a diameter 10-50 cm smaller than the upper pile segment 3 so that the lower pile segment 4 inserted through the lower collar 15 of the upper pile segment 3. The lower pile collar 16 is extended outward from the outer surface at the upper end of the lower pile segment 4, and the evenly spaced circular holes are provided on on the surface of the lower pile collar 16 corresponding to the holes of the lower collar 15 of the upper pile segment 3 so that the bolt systems 18 inserted through the corresponding holes to lower the lower pile segment 4 and fix it to the upper pile segment 3. The lower end of the lower pile segment 4 is chamfered to facilitate construction easily. According to the present invention, the inside of the lower pile segment can be equipped with a stopper plate to prevent water from entering the inside of the lower pile segment 4, but the present invention is not limited here.

[0057] The lower anchored wire ropes 5 is evenly arranged around the upper pile segment 3 to connect the lower end of the upper pile segment 3 with the anchor head systems at the outer ends of the radial walls 11 of the pile cap 1, the lower anchored wire ropes 5 forms an inclination angle a with the vertical direction in range of 20 - 70°, preferably an inclination angle a in the range of 50 - 60°. According to the embodiment of the present invention, the number of the lower anchored wire ropes 5 distributed will be equal to the number of radial walls or a divisor of the radial walls so that the cables of the lower anchored wire ropes 5 are arranged radially around the upper pile segment 3.

[0058] In the present invention, in the case of the height of the adapter tower 2 is more than approximately 15 - 20 m, it is necessary to limit lateral displacement and rotation at the top of the adapter tower, the upper anchored wire ropes 6 include a plurality of cables is provided, wherein one end of the cables is arranged radially at regular intervals around the circumference at the upper end of the adapter tower 2 and the other end is connected to the anchor head systems at the outer end of the radial wall 11 of the pile cap 1 at the locations connected to the cables of the lower steel wire ropes 5.

[0059] The pile cap 1, the upper pile segment 3, and the lower pile segment 4 are located, connected and fixed together through bolt systems 17 and concrete mortar at joint 7 between the bottom flange 13 of the inner cylinder 10 and the flange 14 of the upper pile segment 3, and through bolt systems 18 and concrete mortar at joint 8 between the lower collar 15 of the upper pile segment 3 and the lower pile collar 16 of the lower pile segment 4.

[0060] As shown in drawings, the cross-shaped hybrid wind turbine foundation according to the present invention is formed to optimize a structure with variable rigidity according to the bending moment diagram. The pile cap 1 is embedded in the ground under the seabed to allow maximum utilization of strength and stiffness of the top soil layer to reduce horizontal displacement by using the horizontal reaction of the soil on the wall of the outer cylinder 9, in addition this reaction also significantly contributing to reducing rotational displacement of the pile section. The radial walls 3, in addition to creating stiffness of the pile cap 1 and forming the close compartment, are also responsible for increasing the torsional resistance of the entire foundation system by using the horizontal pressure of the soil on the surface of the radial walls 11, thereby reducing the entire torsional load acting on the pile body itself as well as the connections beneath the pile cap 1.

[0061] The combination of the upper and lower steel wire ropes system 5 and 6, together with the pile cap 1 and upper and lower pile segments 3 and 4 forms rigid frames that pass through the central axis of the foundation system, significantly increasing the bending stiffness of the foundation system at locations and large bending moments, reducing internal forces in the pile system. Furthermore, the cable system is anchored to the upper pile segment of the piles, creating a stable point that minimizes the slenderness of the entire pile system, allowing to reduce the size and material requirements of the foundation.

[0062] By fixing the lower end of the upper pile segment 3 with the anchor head systems of the radial walls 11 through the cables of the lower steel wire ropes 5 and large diameter of the pile cap 1 of the cross-shaped hybrid wind turbine foundation according to the present invention, it is transferred the structure of the monopile foundation from the cantilever with one free end and one fixed end in the soil to a fixed end and an elastic spring end. As show in the Fig. 8, by using the simulation software program to simulate the compatibility of the soil with the same condition under the application of a bending moment Mo, monopile foundations (one fixed end in soil) with the free end (upper end) will produce an horizontal displacement 5o and rotation displacement of angle (po, when the pile is fixed to the pile cap by steel wire r es (one fixed end in the soil and one lastic spring end), the upper end w produce an horizontal displacement — and rotation displacement of angle — as shown in the right k k drawing, in the absence of anchored wire ropes linking piles and pedestal, the index k = 2, this means that horizontal displacement and rotational displacement are reduced by 2 times, in the case of using steel wire ropes fixing the lower end of the upper pile segment 3 with radial wall 11 of the pile cap 1, index k = 7-12, this means that horizontal displacement and rotation displacement decrease by 7-12 times.

[0063] The pile cap 1 according to the present invention is structured with a reasonable shape that allows good mobilisation of the bearing capacity of the weak ground above, creating a large resistance that reduce horizontal displacement and rotational displacement at the top of the pile, thereby making the redistribution of bending moment in the pile by taking advantage of the symmetry of the pile, and to create a large torsional resistance. That allows saving about 20-30% of materials.

[0064] The cross-shaped hybrid wind turbine foundation according to the present invention allow for the creation of fixed points in the pile body (the upper pile segment 3) through the use of the lower anchored wire ropes 5, on one hand, this increases resistance to bending, on the other hand, it reduces the buckling length of the pile by 2-4 times, which enables a reduction in the size and material requirements for the piles, resulting in cost savings and reduced construction equipment needs. Minimising the buckling length of the pile also mitigates the risk of generating additional internal forces during the construction process that could potentially damage the piles during installation..

[0065] The cross-shaped hybrid wind turbine foundation according to the present invention create a reasonable structure foundation model in terms of bearing, creating a transparent and effective calculation scheme, making good use of the strengths of the material in terms of bearing capacity, as well as the corrosion resistance of aggressive environments, reinforced concrete pile cap with good corrosion resistance is arranged in the zone of strong erosion, steel piles are arranged in the zone of weaker erosion.

[0066] As shown in Fig.3, the cross-shaped hybrid wind turbine foundation according to another embodiment of the present invention is applied to the wind turbine foundation built in an area with good ground, the depth of the pile system is not too large. The structure of the wind turbine foundation according to this embodiment is basically similar to the cross-shaped hybrid wind turbine foundation described above, the difference is that the cross-shaped hybrid wind turbine foundation according to this embodiment only uses the upper pile segment 3, and the cap 30 is sealed to the top of the upper pile segment 3. The cap 30 is fixed to the top of the upper pile segment 3 by welding so that the top of the upper pile segment 3 is sealed, so that the upper pile segment 3 can be lowered to the design depth by the vacuum method. Specifically, by sealing the top of the upper pile segment 3 with the cap 30 by welding, the method of completely sucking out the air in the cavity of the upper pile segment 3 is implemented to create a vacuum pressure in the cavity of the upper pile segment 3 to create a compressive force to bring the upper pile segment 3 to the design elevation. According to the embodiment of the present invention, the cap 30 is welded to the top of the upper pile segment 3 so that the holes on the flange 14 of the upper pile segment 3 are not covered by the cap 30.

[0067] The other aspect of the present invention provide the construction method of the cross-shaped hybrid wind turbine foundation described above as shown in Figs. 5 to 7, the construction method including:

[0068] Firstly, manufacture and arrange the components that make up the crossshaped hybrid wind turbine foundation and transport the entire system to the construction site, placing it at the seabed as shown in Fig. 5. Specifically, casting the pile cap 1 with reinforced concrete, inserting the upper pile segment 3 through the inner cylinder 10 of the pile cap 1, inserting the lower pile segment 4 into the internal of the upper pile segment 3, the lower pile segment 4, the upper pile segment 3 and pile cap 1 are temporarily fixed together through the bolt system 17, 18, installing the upper steel wire ropes 6 with one end connected to the pile cap 1 and the other end of the cables of the upper lower steel wire ropes 6 connected to the upper end of the adapter tower 2, then transporting the entire system to the construction site. In which, the pile cap 1, the upper pile segment 3 and the lower pile segment 4 are arranged at the same bottom level, the upper pile segment 3 and the pile cap 1 are connected together by a bolt system 17 connecting the bottom flange 13 and the flange 14 of the upper pile segment 3; the upper pile segment 3 and the lower pile segment 4 are connected together through a bolt system 18 connecting the lower collar 15 of the upper pile segment 3 and the lower pile collar 16 of the lower pile segment 4.

[0069] Next, lowering the pile cap 1 into the ground by vacuuming in the closed chambers of the pile cap 1 or by vibrating the entire foundation system gradually moving the entire system into the ground from position 19 when the process begins to position 20 when the foundation system is fully embedded. According to the embodiment, use the vacuum method to suck the air inside the closed chambers of the pile cap 1, creating negative pressure on the upper surface of the pile cap 1, thereby creating downward compressive forces and bringing the entire pile cap 1 deep into the ground until slab 12 comes into contact with the seabed.

[0070] Subsequently, utilize the embedded pile cap 1 as a support point, and the guiding system proceeds to tighten the bolt system 17 to lower both the upper pile segment 3 and the lower pile segment 4 along with the lower anchored wire ropes 5, securing them to the lower end of the upper pile segment 3, moving them to the design position as shown in Fig. 6.

[0071] Then, step of tightening the bolt system 18 to lower the lower pile segment 4 inside the upper pile segment 3 to the designed depth by using the upper pile segment 3 as a guiding system; securing the other ends of the lower anchored wire ropes 5 at positions on the radial walls 11 of the pile cap 1, and proceed to tension the lower anchored wire ropes 5.

[0072] Pumping the high-strength grout into the joints 7, 8 to link the components of the foundation together.

[0073] The construction method according to the present invention is relatively simple, suitable for existing equipment and many different construction methods can be selected. In addition, the simple structure of the foundation helps the construction to be carried out quickly, allowing to shorten the construction progress and reduce construction costs.

[0074] The construction method according to the present invention allows to make the most of the foundation components as construction measures such as the platform to lower the piles or the temporary anchor system to press the upper pile segment 3 and the lower pile segment 4, thereby reducing the cost and construction time of the auxiliary systems serving the construction. Therefore, the present invention allows to shorten the construction time at the construction site as well as minimize the effects of weather, tides and the marine environment, overcoming the difficulties when having to construct at sea, on the water surface, etc.

[0075] The construction method according to the present invention allows to divide the total energy to lower the entire foundation system into small sections, thus eliminating the need for large-scale machinery. Additionally, construction methods involving vacuum suction and bolt tensioning produce minimal noise, reducing disturbances to marine life.

[0076] Another aspect of the present invention also provide a construction method of a cross-shaped hybrid wind turbine foundation as shown in Fig. 3, the method includes the following steps: the step of welding the cap 30 to the top of the upper pile segment 3 to seal the top of the pile section 3 ; the step of casting the pile cap with reinforced concrete, inserting the upper pile segment 3 through the inner cylinder 10 of the pile cap 1, the upper pile segment 3 and the pile cap 1 are temporarily fixed together through the bolt system 17, installing the upper anchored wire ropes 6 with one end connected to the pile cap 1, and the other end of the cables of the upper anchored wire ropes 6 is connected to the upper end of the adapter tower 2 then transporting the whole system to the construction site; step of lowerring the upper pile segment 3 together with the cables of the lower anchored wire ropes 5 fixed to the lower end of the upper pile segment 3 to move down to the design elevation by using the inner cylinder 10 of the pile cap 1 and the bolt system 17 as a guide system and press the upper pile segment 3 down by using the vacuum method to suck the air inside the cavity of the upper pile segment 3; step of connecting the pile cap 1 and the upper pile segment 3 by pumping high-strength mortar at the joint 7; and step of fixing the other ends of the cables of the lower anchored wire ropes 5 to the positions on the radial walls 11 of the pile cap 1 , and proceed to tension the cables of the lower anchored wire ropes 5.

[0077] In addition, the cross-shaped hybrid wind turbine foundation according to the present invention also allows cleaning and returning the site to its original state when dismantling when no longer in use. Specifically, the steps to recover the unused cross-shaped hybrid wind turbine foundation are as follows:

[0078] First, connect the lower pile collar 16 of the lower pile segment 4 with the lower colla 15 of the upper pile segment 3 with a cable system, and proceed to tension the cables to pull up the lower pile segment 4;

[0079] Next, connect the cable system between the flange 14 of the upper pile segment 3 with the upper surface of the adapter tower 2 to tension the cables and pull up the upper pile segment 3.

[0080] Then, proceed to demolish and recover the pile cap and return the site to its original state.

[0081] The cross-shaped hybrid wind turbine foundation and the construction method according to the present invention solve the current major problem that most existing foundation solutions fail to address: the restoration of the environment once wind power plants cease operation. The present invention enables the complete retrieval of constructed materials, mitigating environmental impact and promoting the recycling of used materials and components. As a result, it reduces project investment costs and provides robust environmental protection.

[0082] While the present invention is disclosed through the preferred embodiments described above, it is not intended to limit the present invention. Various modifications and variations in the embodiments described above that fall within the scope of the present invention can be made by those skilled in the art without departing from the technical principle and scope of the present invention. Therefore, the true scope of rights of the present invention should be defined by the appended claims.

Claims

AMENDED CLAIMS received by the International Bureau on 06 June 2025 (06.06.2025)CLAIM1. A cross-shaped hybrid wind turbine foundation comprising a pile cap (1), adapter tower (2) connected to the upper surface of the pile cap (1), the upper pile segment (3) connected to the lower surface of the pile cap (1), the upper anchored wire ropes (6) connects the pile cap (1) with the upper end of the adapter tower (2), and the lower anchored wire ropes (5) connects the pile cap (1) to the upper pile segment (3), wherein: the pile cap (1) is cast of reinforced concrete in the shape of a inverted drum, consisting of two hollow columns arranged concentrically and connected to each other through radial walls, the pile cap (1) includes: the outer cylinder (9) with a diameter of 20-50 m, a height of 3-8 m; the inner cylinder (10) with a diameter of 4-15 m, a height of 3-8 m; the radial walls (11) are arranged radially on the outer circumference surface of the inner cylinder (10) to connect the inner cylinder (10) with the outer cylinder (9), forming a integrated rigid slab; and the slab (12) covering the upper surface of the pile cap (1) so that enclosed chambers are formed between the slab (12), the outer cylinder (9), the inner cylinder (10), and the radial walls (11) to facilitate for perform vacuum suction when placing the pile cap (1) on the seabed; the adapter tower (2) has a diameter of 6-15 m and is made of reinforced concrete or steel, the upper end of the adapter tower (2) is equipped with an anchoring cable system to connect to the upper anchored wire ropes (6); the upper pile segment (3) is a hollow tubular section arranged inside and fixed to the inner cylinder (10) of the pile cap (1); and the lower pile segment (4) with a diameter smaller by 10-100 cm than theinner diameter of the upper pile segment (3), inserted inside the upper pile segment (3) and driven deep into the underlying soil; wherein the upper pile segment (3) is a hollow tube with a diameter smaller by 10-100 cm than the inner diameter of the inner cylinder (10) of the pile cap (1), the upper end of the upper pile segment (3) is secured to the inner cylinder (10) by pouring high-strength grout into the overlapping joint (7), and the lower end of the upper pile segment is connected to the lower pile segment (4) at the joint (8) using high-strength grout; wherein the upper pile segment (3) is a steel tube with a thickness of 3-15 cm, and the top of the upper pile segment (3) is formed a flange (14), the outer diameter of the flange (14) being smaller than the inner diameter of the inner cylinder (10); wherein the lower end of the upper pile segment (3) is formed with an lower collar (15) opposite to the flange (14), where the inner diameter of the lower collar (15) is larger than the outer diameter of the lower pile segment (4); and wherein the flange (14) and the lower collar (15) are formed with evenly spaced circular holes to connect the bolt system of the upper pile segment (3) with the inner cylinder (10) and the lower pile segment (4), respectively.

2. The wind turbine foundation of claim 1, wherein the wind turbine foundation further includes a cap (30) secured to the top of the upper pile segment (3) by welding so that the top of the upper pile segment (3) is sealed.

3. The wind turbine foundation of claim 1, wherein the lower pile segment (4) is a steel tube with the top end formed with a lower pile collar (16), such that the outer diameter of the lower pile collar (16) is larger than the inner diameter of the lower collar (15) of the upper pile segment (3).

4. The wind turbine foundation of claim 3, wherein the lower pile collar (16) is formed with evenly spaced circular holes corresponding to the holes of the lower collar (15) to connect the bolt system of the upper pile segment (3) with the lower pile segment (4).

5. The wind turbine foundation of claim 1, wherein the bottom end of the inner cylinder (10) of the pile cap is formed with a bottom flange (13), wherein the inner diameter of the bottom flange (13) is larger than the outer diameter of the upper pile segment (3) and smaller than the outer diameter of the flange (14).

6. The wind turbine foundation of claim 5, wherein the bottom flange (13) is formed with evenly spaced circular holes corresponding to the holes of the flange (14) to connect the bolt system of the inner cylinder (10) of the pile cap with the upper pile segment (3).

7. The wind turbine foundation of claim 1, wherein the one end of the lower anchored wire ropes (5) is anchored to the radial walls (11) at the intersection with the outer cylinder (9), and the other end of the lower anchored wire ropes (5) is anchored to the wall of the upper pile segment (3), the lower anchored wire ropes (5) are arranged radially so that the lower anchored wire rope (5) forms an angle (a) of approximately 20-70° with the horizontal direction.

8. The wind turbine foundation of claim 7, wherein the one end of the upper anchored wire ropes (6) are connected to the lower anchored wire ropes (5) in a saddle form at the ends of the radial walls (11) of the pile cap, and the other end of the upper anchored wire ropes (6) are connected to the upper end of the adapter tower (2).

9. The wind turbine foundation of claim 8, wherein the number of cables in the lower anchored wire ropes (5) and the upper anchored wire ropes (6) is 3 to 12 cables arranged circularly around the central axis of the foundation, preferably,the number of cables in the lower anchored wire ropes (5) and the upper anchored wire ropes (6) is equal to the number of radial walls (11).

10. The construction method for the hybrid cross-shaped wind turbine foundation of any of claims 1 to 9, wherein the construction method includes the following steps: casting the precast concrete foundation with reinforced concrete, insert the upper pile segment (3) of the pile through the inner cylinder (10) of the pile cap (1), the upper pile segment (3) and the pile cap (1) are temporarily fixed together using the bolt system (17), install the upper anchored wire ropes (6), with the one ends are connected to the pile cap (1), and the other ends of the cables of the upper anchored wire ropes (6) are connected to the upper end of the adapter tower (2), install the lower anchored wire ropes (5), with one ends connected to the pile cap (1), and the other end of the cables of the lower anchored wire ropes (5) are connected to the lower end of the upper pile segment (3), and then, the entire system is transported to the construction site; lowering the pile cap (1) to the ground by vacuuming the enclosed chambers between the slab (12), the outer cylinder (9), the inner cylinder (10), and the radial walls (11) of the pile cap (1) until the slab (12) comes into contact with the seabed; lowering the upper pile segment (3) along with the cables of the lower anchored wire ropes (5) fixed to the lower end of the upper pile segment (3) moves down to the design elevation by using the inner cylinder (10) of the foundation as a guide frame and tensioning the bolt system (17) to push the upper pile segment (3) downward; connecting the pile cap (1) and the upper pile segment (3) by pumping high-strength grout at the joint (7); andsecuring the other ends of the cables of the lower anchored wire ropes (5) to the radial walls (3) of the pile cap, and the cables of the lower anchored wire ropes (5) are tensioned.

11. The method of claim 10, wherein the method further includes the step of inserting the lower pile segment (4) into the cavity of the upper pile segment(3) and temporarily fixing the upper pile segment (3) and the lower pile segment(4) together using the bolt system (18) before performing the step of lowering the pile cap (1) onto the ground.

12. The method of claim 11, wherein the method further includes the step of lowering the lower pile segment (4) inside the upper pile segment (3) to the design depth, using the upper pile segment (3) as a guide frame and tensioning the bolt system (18) to push the lower pile segment down immediately after lowering the upper pile segment (3) to the design elevation.

13. The method of claim 12, wherein the method further includes the step of connecting the upper pile segment (3) and the lower pile segment (4) by pumping high-strength grout at the joint (8) before performing the step of connecting the pile cap (1) and the upper pile segment (3).

14. The method of claim 10, wherein the top of the upper pile segment (3) is fixed with the cap (30) by welding, ensuring that the top of the upper pile segment (3) is sealed, and then, the upper pile segment (3) is lowered to the design elevation is performed by vacuum suction to generate the vacuum pressure inside the upper pile segment (3).

15. The method of claim 10, wherein the cables of the lower anchored wire ropes (5) are tensioned between the radial walls (11) of the foundation and the lower end of the upper pile segment (3), forming an inclination angle (a) of approximately 20-70° with respect to the horizontal plane, preferably formingan inclination angle of 35-60°, and most preferably forming an inclination angle of 50-60°.STATEMENT UNDER ARTICLE 19(1)Dear The Office,Regarding the above patent application, we, on behalf of the Applicants, respectfully submit an amendment to the claims of the above PCT application as follows:AMENDMENTClaim 1 is amended by combining all technical features of original claims 2 to 5 and 7;Original claims 2 to 5 are cancelled;Claim 6 is unchanged;Original claim 7 is cancelled;Claims 8-20 are unchanged;SCOPE OF INVENTIONThe basis of the amendment of claim 1 can be found in the original claims 2 to 5 and 7 as filed.By the above arguments, it is obvious that the above-mentioned amendments do not extend the scope of the disclosure as originally filed, therefore, it complies with the requirements of PCT Article 19(2).CONCLUSIONWHEREFORE, NOW, based on the foregoing arguments, the above PCT application, after amending, has met the requirement of allowance.

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