Multi-limb diagonal bracing reinforcing system for machine changing and capacity increasing of old single pile foundation and construction method

Abstract

The invention provides a multi-limb diagonal bracing reinforcing system for machine changing and capacity increasing of an old single pile foundation and a construction method. The reinforcing system comprises an outer sleeve arranged outside the original single pile foundation in a sleeving mode, a supporting structure and a foundation anchoring structure. Shear keys are arranged on the inner wall of the outer sleeve, the supporting structure comprises supporting seats arranged on the periphery of the outer sleeve and at least three inclined struts, the upper ends of the inclined struts are hinged to the corresponding supporting seats through first pin shafts, and the lower ends of the inclined struts are hinged to the corresponding suction anchors through second pin shafts. Reinforcing girders and a center cylinder which are distributed in a radial mode are arranged below the suction anchor top cover. According to the construction method, grouting locking is conducted between the outer sleeve and the original single-pile foundation, and the outer sleeve and the original single-pile foundation are hinged and matched with the double pin shafts, so that in-situ reinforcement is achieved. According to the invention, the unit load after machine changing and capacity increasing is synergistically shared through multiple components, the overall rigidity of the foundation is improved, the problem that the prior art depends on preset convex rings or underwater welding is solved, the construction alignment precision requirement is reduced, and the method is suitable for reinforcing and transforming the offshore wind turbine foundation.

Description

Technical Field

[0001] This invention relates to the field of offshore wind turbine foundation reinforcement, specifically to a multi-limb diagonal bracing reinforcement system and construction method for replacing and increasing the capacity of old monopile foundations. Background Technology

[0002] With the development of the offshore wind power industry, a batch of early-built offshore wind turbines have gradually entered the mid-to-late stages of service. Upgrading existing turbines to increase capacity has become an important way to enhance the power generation capacity of wind farms per unit area. The new generation of offshore wind turbines has a larger single-unit capacity, and the operating load of the units is significantly higher than that of earlier units. The original monopile foundations typically only meet the initial service requirements; if large-capacity units are directly replaced without effective treatment, the foundations may experience insufficient load-bearing margin and deteriorated dynamic response.

[0003] Existing reinforcement technologies, such as the post-installation reinforcement device for monopile foundations disclosed in CN112814021B, mainly rely on the connection of collars and diagonal braces. However, in practical applications, such solutions heavily depend on multiple protruding rings pre-welded to the pile body during the early stages of monopile manufacturing. For older monopile foundations that have been in service for many years, such protruding rings are not pre-installed on their surfaces, and the complex deep-water environment at sea makes underwater welding of protruding rings a complex, costly process that is prone to generating heat-affected zones, weakening the integrity of the original structure. Furthermore, simple collar connections, without a reliable non-welded locking interface, are insufficient to cope with the dramatic increase in overturning moments and cyclic loads after capacity expansion. Therefore, how to provide a reinforcement system and construction method that is applicable to older monopile foundations without pre-installed structures and possesses high reliability in force transmission and a high construction tolerance has become a pressing technical challenge in this field. Summary of the Invention

[0004] To address the issues of insufficient bearing capacity and difficulties in construction alignment faced by old offshore wind turbine monopile foundations during turbine replacement and capacity expansion, this invention proposes a multi-limb inclined bracing reinforcement system and construction method for old monopile foundations during turbine replacement and capacity expansion.

[0005] The present invention adopts the following technical solution: a multi-limb inclined brace reinforcement system for upgrading and expanding the capacity of old monopile foundations, comprising an outer sleeve, a support structure, and a foundation anchoring structure; the outer sleeve is used to fit around the outside of the original monopile foundation, and the inner wall of the outer sleeve is provided with shear keys; the support structure includes a support seat disposed on the outer periphery of the outer sleeve and fixedly connected thereto, and at least three inclined braces; the upper end of each inclined brace is respectively hinged to the corresponding support seat through a first pin; the foundation anchoring structure includes suction anchors corresponding to each inclined brace, and the lower end of each inclined brace is respectively hinged to the corresponding suction anchor through a second pin.

[0006] As can be seen, the shear keys on the inner wall of the outer sleeve are suitable for forming a reliable locking interface through grouting around the original monopile foundation, solving the reinforcement problem of old monopile foundations lacking pre-set convex rings and being unable to be welded. After the capacity increase, the load generated by the unit is transferred to the outer suction anchor foundation through the outer sleeve and multiple diagonal braces, forming a multi-path collaborative force system, which significantly improves the stress state of the original foundation. Setting at least three diagonal braces can form a stable spatial support frame, resisting overturning moments in all directions.

[0007] Furthermore, the upper and lower edges of the outer sleeve are respectively provided with outwardly flared horn-shaped structures.

[0008] It is evident that the flared structure mitigates the abrupt change in stiffness at the reinforced boundary, effectively preventing stress cutting of the original pile at both ends of the reinforced zone.

[0009] Furthermore, the middle part of the outer sleeve is a constant diameter section, and the shear key is a spiral shear key disposed on the inner wall of the constant diameter section.

[0010] It is evident that the spiral shear key within the equal-diameter section, combined with the high-strength grouting layer after construction, significantly improves the shear force transmission efficiency between the outer sleeve and the original pile.

[0011] Furthermore, the support base includes an upper horizontal reinforcing ring and a lower horizontal reinforcing ring arranged along the circumference of the outer sleeve, and multiple sets of ear plates fixedly connected between them. Furthermore, a preset stress avoidance distance is provided between the support base and the flared structure.

[0012] It is evident that the design of the double horizontal reinforcing rings provides a stable anchoring base for the ear plate, while the stress avoidance spacing prevents the superposition of local loads and edge effects.

[0013] Furthermore, a vertical reinforcing rib is welded between the upper horizontal reinforcing ring and the lower horizontal reinforcing ring. The multiple sets of ear plates, the upper horizontal reinforcing ring, the lower horizontal reinforcing ring, and the vertical reinforcing rib together with the outer wall of the outer sleeve constitute a spatial box-type load-bearing structure.

[0014] It is evident that the spatial box-type load-bearing structure greatly improves the local stiffness and compressive strength of the connection nodes.

[0015] Furthermore, each of the ear plates includes two parallel vertical plates.

[0016] It is evident that the parallel vertical plate design provides reliable limiting and stress space for the ear plates at the ends of the diagonal braces, thereby improving the reliability of the node connection.

[0017] Furthermore, the suction anchor is provided with a bearing plate at the top, and the bearing plate is provided with an ear plate structure. There are symmetrically arranged stiffening ribs between the ear plate structure and the bearing plate.

[0018] It is evident that the symmetrical stiffening ribs enhance the local stress strength of the top node of the suction anchor, ensuring the reliable diffusion of the diagonal brace thrust.

[0019] Furthermore, a radially distributed reinforcing beam and a central tube are provided below the bearing plate, with the central tube located at the geometric center below the bearing plate; the inner ends of the multiple reinforcing beams are welded to the central tube, and the outer ends are welded to the inner surface of the suction anchor sidewall.

[0020] It is evident that by using the central tube as the load convergence center and cooperating with the radially distributed reinforcing beams, the concentrated load at the top can be uniformly and efficiently transferred to the sidewalls of the suction anchor, thereby improving the overall stability of the foundation anchoring structure.

[0021] Furthermore, the number of diagonal braces is four, the number of suction anchors is four, and the four diagonal braces are circumferentially symmetrically distributed along the outer periphery of the outer sleeve.

[0022] It is evident that the symmetrical arrangement of the four diagonal braces can provide the monopile foundation with isotropic optimal overturning resistance, further balancing the complex alternating loads in the marine environment.

[0023] Finally, the present invention also provides a construction method for a multi-limb diagonal bracing reinforcement system. This includes the following steps: S1. Clean up the external attachments of the original single pile foundation, measure and determine the reinforcement area; S2. Lift the outer sleeve and place it outside the original single pile foundation, so that the outer sleeve and the original single pile foundation maintain an annular gap. S3. Grout is injected into the annular gap to form a high-strength grouting layer. The non-welded locking between the outer sleeve and the original single pile foundation is achieved through the interlocking of the high-strength grouting layer and the shear key. S4. Sink and insert suction anchors into the seabed surrounding the original monopile foundation; S5. The upper end of each diagonal brace is hinged to the corresponding support seat through the first pin, and the lower end is hinged to the corresponding suction anchor through the second pin.

[0024] It is evident that this method, through in-situ grouting locking and pin hinge connection, achieves efficient in-situ reinforcement of old monopile foundations and reduces reliance on high-precision alignment equipment. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with their description, serve to explain the principles of the invention.

[0026] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention; Figure 2 This is a top view of the overall layout of an embodiment of the present invention; Figure 3 This is a schematic diagram of the outer sleeve structure in an embodiment of the present invention; Figure 4 This is a schematic diagram of the support base in an embodiment of the present invention; Figure 5 This is a schematic diagram of the upper connection node of the suction anchor in an embodiment of the present invention; Figure 6 This is a perspective view of the internal reinforcement structure of the suction anchor in an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached drawings: 1. Original single pile foundation; 2. Outer sleeve; 21. Shear key; 22. High-strength grouting layer; 23. Trumpet-shaped structure; 3. Diagonal brace; 31. Connecting ear plate; 32. First pin; 33. Second pin; 4. Support seat; 41. Upper horizontal reinforcing ring; 42. Lower horizontal reinforcing ring; 43. Vertical reinforcing rib; 44. Ear plate; 5. Suction anchor; 51. Bearing plate; 52. Reinforcing beam; 53. Central tube; 54. Stiffening rib; 55. Ear plate structure. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

[0029] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0030] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0031] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0032] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0033] Example 1: System Structure Description refer to Figures 1 to 6 This embodiment provides a multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations. The system provides external support reinforcement for existing monopile wind turbines, and its core structure consists of an outer sleeve 2, a support base 4, diagonal braces 3, and suction anchors 5.

[0034] refer to Figure 1 and Figure 3 The outer sleeve 2 is a thick-walled steel cylinder with a cylindrical main body, used to coaxially fit over the critical stress area above the mud surface outside the original single pile foundation 1. The geometry of the outer sleeve 2 consists of a central equal-diameter cylindrical section and flared structures 23 located at the upper and lower edges. The diameter of the flared structure 23 is smoothly flared outward, used to achieve a smooth transition of bending stiffness at both ends of the reinforced area, avoiding stress cutting of the original pile. On the inner wall of the outer sleeve 2, there is a pre-fabricated inwardly protruding shear key 21. In this embodiment, the shear key 21 is preferably a spiral shear key set on the inner wall of the equal-diameter section. The inner diameter of the outer sleeve 2 is larger than the outer diameter of the original single pile foundation 1, forming an annular gap between them during installation. The entire cross-section of this gap is suitable for filling with a dense high-strength grouting layer 22. After the high-strength grouting layer 22 is cured, it holds the original pile tightly through the material bonding force at the interface, and interlocks with the shear key 21 to establish a strong mechanical interlocking effect. Thus, without the need for any destructive underwater welding, the outer sleeve 2 and the original single pile foundation 1 are fully rigidly locked in the axial, radial and circumferential directions.

[0035] refer to Figure 1 and Figure 4 A support seat 4 for connecting diagonal braces is provided at the center of the outer periphery of the outer sleeve 2. To prevent the superposition of local loads and edge effects, sufficient longitudinal stress avoidance spacing is provided between the interface and the upper and lower flared structures 23. The specific construction of the support seat 4 is as follows: the upper horizontal reinforcing ring 41 and the lower horizontal reinforcing ring 42 are parallel and fully welded around the outer wall of the outer sleeve 2. Between the two reinforcing rings, corresponding to the orientation of each diagonal brace 3, multiple sets of ear plates 44 are fixedly connected, which act as force transmission bridges. Each set of ear plates 44 consists of two parallel thick vertical plates, with the plate surface extending perpendicular to the outer wall surface of the outer sleeve 2. In order to support these two vertical plates and improve the compressive buckling resistance of the entire annular area, multiple vertically placed reinforcing ribs 43 are welded evenly at intervals along the circumference in the blank area between the two reinforcing rings. Thus, the upper horizontal reinforcing ring 41, the lower horizontal reinforcing ring 42, the ear plates 44, the vertical reinforcing ribs 43, and the outer wall of the outer sleeve 2 together enclose and weld to form a multi-compartment spatial box-shaped load-bearing structure. This structure can effectively transform the huge and concentrated piercing load transmitted from the end of the diagonal brace into a distributed load that spreads to the entire circumference of the outer sleeve 2.

[0036] refer to Figure 1 , Figure 2 and Figure 5To create stable resistance in three-dimensional space, the system is equipped with at least three diagonal braces 3 and at least three corresponding suction anchors 5 (distributed at 120 degrees). In this embodiment, to obtain the best isotropic overturning resistance and to meet the construction conditions of conventional machine positions, it is preferable to use four large-diameter high-strength steel pipes to manufacture the diagonal braces 3 (i.e., steel diagonal braces). The four diagonal braces 3 are radially distributed symmetrically at a preset angle in the four quadrants of the outer sleeve 2. The upper and lower ends of the diagonal braces 3 are provided with connecting lugs 31 by means of diameter reduction or direct welding. In this embodiment, the connecting lugs 31 are preferably single-piece steel plate structures. The connecting lugs 31 at the upper end of the diagonal brace 3 are inserted into the gap formed by the two lugs 44 of the support base 4, and are hinged by a first pin 32 that passes horizontally through the three-layer plate hole; similarly, the connecting lugs 31 at the lower end of the diagonal brace 3 are inserted between the lug structures 55 at the top of the suction anchors 5, and are hinged by a second pin 33. The double-pin hinge design at both ends makes the diagonal brace 3 a two-force member with a clearly defined load (mainly bearing axial tension and compression), and releases the bending moment constraint at the ends. This not only avoids fatigue cracking that is prone to occur in rigid nodes, but also gives the system a great assembly tolerance. It should be understood that the single-ear and double-ear fit is only a preferred combination in this embodiment, and their assembly positions can also be interchanged, or a multi-ear plate plug-in fit can be used, all of which are within the protection scope of this invention.

[0037] refer to Figure 5 and Figure 6 The suction anchor 5 is a negative pressure sinking foundation with an inverted cylindrical shape as its main body. The top of each suction anchor 5 is closed by a single thick bearing plate 51. At the center of the upper surface of the bearing plate 51, the aforementioned ear plate structure 55 for connecting with the diagonal brace is vertically welded (in this embodiment, it is preferably a double ear plate structure composed of two parallel steel plates). To ensure a smooth force path and avoid lateral shear torque, the plane of the ear plate structure 55 is strictly parallel to the projection direction of the axis of the corresponding diagonal brace 3 onto the bearing plate 51 (i.e., precisely matching the inclined insertion position of the diagonal brace). To prevent the ear plate structure 55 from tearing or overturning under the huge load of the diagonal brace, multiple symmetrically arranged stiffening ribs 54 are vertically welded between the outer facade of the ear plate and the upper surface of the bearing plate 51. In this embodiment, the stiffening ribs 54 are preferably rectangular steel plates. Figure 6From the perspective, it can be seen that in order to bear the huge vertical load of the downward thrusting of the diagonal brace 3, a force transmission frame is set directly below the bearing plate 51 inside the suction anchor 5. This frame includes a central cylinder 53 located at the geometric center of the suction anchor. With the central cylinder 53 as the converging hub, multiple vertically placed reinforcing beams 52 (preferably rectangular cross-section beams in this embodiment) are arranged radially and evenly. The top edges of these reinforcing beams 52 are welded to the lower surface of the bearing plate 51, the inner ends are welded to the outer wall of the central cylinder 53, and the outer ends are welded to the inner surface of the cylindrical sidewall of the suction anchor 5. Through this three-dimensional support network similar to the hub and spokes of a wheel, the concentrated thrust load received at the center of the bearing plate 51 will be instantly and evenly distributed and diffused through the central cylinder 53 and the radial reinforcing beams 52 to the extensive sidewall perimeter of the suction anchor 5 and the surrounding seabed soil.

[0038] After the unit is upgraded and its capacity increased, when the large-capacity unit is subjected to extreme wind, waves, and currents, the resulting enormous horizontal shear force and overturning moment first act on the original monopile foundation 1. This load is then transferred to the outer sleeve 2 through the high-strength grouting layer 22 and captured by the support seat 4. Subsequently, the load is converted into axial tensile and thrust forces from multiple diagonal braces 3, extending to the seabed along the inclination angle of the braces. The suction anchor 5 on the compression side uses its internal radial skeleton to steadily absorb the thrust; the suction anchor 5 on the tension side uses the negative pressure of the soil inside its cylinder and the friction of the side walls to provide pull-out resistance. The single-point bending of the original monopile is successfully transformed into the push-pull resistance of the outer large-span frame, greatly improving the overall structural stiffness and bearing capacity.

[0039] Example 2: Construction Method Description This embodiment provides a construction method for in-situ modification using the multi-limb diagonal bracing reinforcement system described in Embodiment 1. The specific steps are as follows: S1. Preliminary preparation and cleaning: Dispatch divers or underwater robots (ROVs) to clean marine organisms and conduct flaw detection on the outer wall of the reinforced section above the mud surface of the existing monopile foundation 1. Confirm the actual pile diameter and inclination through measuring equipment, and customize the processing dimensions of each component accordingly.

[0040] S2. Lowering and Positioning of the Outer Jacket: Using a marine crane vessel, the prefabricated outer jacket 2 is lifted as a whole and vertically fitted over the wind turbine tower (or after the old turbine head is removed) onto the outside of the original monopile foundation 1. After being lowered to the design elevation, it is fixed using temporary limiting fixtures to ensure that a relatively uniform annular gap is maintained between the outer jacket 2 and the original monopile foundation 1.

[0041] S3. Underwater grouting and locking: From the bottom of the annular gap upwards, a special high-strength, non-shrink marine grout is continuously pumped into the grouting pipeline. The process is stopped after the grout displaces the seawater and fills the entire equal-diameter section. After static curing, the high-strength grout layer 22 tightly interlocks with the shear keys 21 on the inner wall, forming a high-strength, non-welded friction-mechanical composite locking interface.

[0042] S4. Suction Anchor Negative Pressure Penetration: At a predetermined position around the monopile, the suction anchor 5 is hoisted into the water and brought into contact with the seabed. The penetration installation of the suction anchor 5 does not require the heavy hammering of a traditional pile driver, but is achieved by utilizing the principle of "pressure difference", specifically including: (1) sinking by its own weight: the suction anchor 5 is hoisted to the seabed, and its own weight causes the bottom of the cylinder to cut into the seabed soil, thereby achieving the initial sealing of the closed space inside the cylinder; (2) pumping to form negative pressure: the pump set connected to the top bearing plate 51 is started to pump the seawater in the closed space inside the cylinder; (3) pressing force: as the seawater inside the cylinder is pumped out, the pressure inside the cylinder gradually decreases, and the hydrostatic pressure of the seawater outside the cylinder and the negative pressure inside the cylinder form a huge pressure difference, which is used to press the suction anchor 5 smoothly into the stratum at the predetermined depth. After penetrating to the design elevation, ensure that the top ear plate structure 55 is roughly aligned with the center direction of the outer sleeve.

[0043] S5. Flexible Diagonal Bracing Assembly: Lifting Diagonal Bracing 3. First, slide the connecting lug 31 at the upper end of the diagonal bracing into the gap of the lug 44 of the outer sleeve box-type interface, and drive in the first pin 32 laterally to complete the upper hinge connection; then, using the free rotation angle of the diagonal bracing around the upper pin, lower it to accurately guide the connecting lug 31 at the lower end into the lug structure 55 at the top of the suction anchor, and drive in the second pin 33. The double hinge system automatically absorbs the spatial position error accumulated by the sinking of the suction anchor and the deflection of the single pile, completing stress-free assembly, and the reinforcement system can be put into use.

[0044] In summary, the multi-limb bracing reinforcement system and construction method for upgrading and expanding the capacity of aging monopile foundations provided by this invention effectively distributes the large load after the upgrade and expansion of the turbines without damaging the original aging piles. This is achieved through the coordinated work of the grout-locked outer sleeve interface, the multi-node pin hinge path, and the radial skeleton inside the suction anchor. The system and method not only solve the technical bottlenecks of underwater welding and poor construction tolerance for aging monopile foundations, but also avoid the high costs and environmental impacts of overall demolition and reconstruction, providing a highly reliable engineering solution for the efficient life extension and efficiency improvement of offshore wind power assets.

[0045] While specific embodiments of the invention have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of the invention. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims

1. A multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations, characterized in that, This includes the outer sleeve, support structure, and foundation anchoring structure; The outer sleeve is used to be fitted onto the outside of the original single pile foundation, and the inner wall of the outer sleeve is provided with shear keys; The support structure includes a support base disposed on and fixedly connected to the outer periphery of the outer sleeve, and at least three diagonal braces; the upper end of each diagonal brace is respectively hinged to the corresponding support base through a first pin. The basic anchoring structure includes suction anchors corresponding to the diagonal braces one by one, and the lower end of each diagonal brace is hinged to the corresponding suction anchor through a second pin.

2. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 1, characterized in that: The upper and lower edges of the outer sleeve are respectively provided with outwardly flared horn-shaped structures.

3. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 1, characterized in that: The middle section of the outer sleeve is a constant diameter section, and the shear key is a spiral shear key disposed on the inner wall of the constant diameter section.

4. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 2, characterized in that: The support base includes an upper horizontal reinforcing ring and a lower horizontal reinforcing ring arranged along the circumference of the outer sleeve, as well as multiple sets of ear plates fixedly connected between the upper horizontal reinforcing ring and the lower horizontal reinforcing ring; a preset stress avoidance distance is left between the support base and the flared structure.

5. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 4, characterized in that: A vertical reinforcing rib plate is welded between the upper horizontal reinforcing ring and the lower horizontal reinforcing ring. The multiple sets of ear plates, the upper horizontal reinforcing ring, the lower horizontal reinforcing ring, and the vertical reinforcing rib plate together with the outer wall of the outer sleeve constitute a space box-type load-bearing structure.

6. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 5, characterized in that: Each set of ear plates includes two parallel vertical plates, which are arranged perpendicular to the outer wall surface of the outer sleeve.

7. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 1, characterized in that: The suction anchor is provided with a bearing plate at the top, and the bearing plate is provided with a lug structure for connecting with the lower end of the diagonal brace. There are symmetrically arranged stiffening ribs between the lug structure and the bearing plate.

8. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 7, characterized in that: The bearing plate is provided with radially distributed reinforcing beams and a central tube, the central tube being located at the geometric center below the bearing plate; the inner ends of the multiple reinforcing beams are respectively welded to the outer wall of the central tube, and the outer ends are respectively welded to the inner side wall of the suction anchor.

9. The multi-limb diagonal bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations according to claim 1, characterized in that: The number of diagonal braces is four, and the number of suction anchors is four. The four diagonal braces are circumferentially symmetrically distributed along the outer periphery of the outer sleeve.

10. A construction method for a multi-limb inclined bracing reinforcement system for upgrading and expanding the capacity of old monopile foundations as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Clean the external wall attachments of the original single pile foundation, measure and determine the reinforcement area; S2. Lift the outer sleeve and place it over the outside of the original single pile foundation, so that an annular gap is maintained between the outer sleeve and the original single pile foundation; S3. Grout is injected into the annular gap to form a high-strength grouting layer. The high-strength grouting layer and the shear key are interlocked to achieve non-welding locking between the outer sleeve and the original single pile foundation. S4. The suction anchor is sunk and inserted into the seabed surrounding the original monopile foundation. S5. The upper end of each of the diagonal braces is hinged to the corresponding support seat through the first pin, and the lower end is hinged to the corresponding suction anchor through the second pin.

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