Method for retrofitting a wind power foundation based on a lattice tower

Abstract

The application relates to the technical field of wind power foundation engineering, and discloses a wind power foundation reconstruction method based on a truss tower, which comprises the following steps: investigating an existing foundation, prefabricating a bearing platform, a lattice tower, a conversion section, a ground beam and a pile foundation; sinking the pile foundation based on the existing foundation, symmetrically installing the bearing platform around the periphery of the pile foundation, and controlling the bottom surface to be at the same elevation; hoisting and assembling the lattice tower above the bearing platform, and installing the conversion section at the top end; installing the ground beam, connecting the ground beam with the side surface of the bearing platform and the side wall of the existing foundation; fixing the upper end of a prestressed anchor cable through the reserved channel of the conversion section, applying a pretightening force to the anchor cable, and locking the lower end of the anchor cable through the reserved perforation of the foundation ring. The existing foundation is used as a counterweight to resist the overturning moment, and the newly-built structure bears the newly-added load; the new and old foundations are jointly stressed through the ground beam and the anchor cable, the overall demolition of the original foundation is avoided, and the overall bearing capacity and the overturning stability of the foundation are effectively improved.

Description

Technical Field

[0001] This application relates to the field of wind power foundation engineering technology, specifically a method for upgrading and expanding existing wind power foundations based on truss towers. Background Technology

[0002] As early-built wind farms have been in operation for many years, aging turbines are facing low power generation efficiency. Upgrading and replacing the existing low-power turbines with high-power turbines has become an industry necessity. However, due to the significant increase in hub height and rotor weight of newly built high-power turbines, the vertical downward pressure load and horizontal overturning moment generated during operation far exceed the original design standards, causing existing wind turbine foundations to be unable to meet the overall load-bearing and anti-overturning requirements of the new turbines.

[0003] In conventional capacity expansion and renovation projects, to address the insufficient bearing capacity of the original foundation, the existing large-volume reinforced concrete foundation is typically demolished and rebuilt in situ. This method suffers from long construction periods and high renovation costs, and the solid waste generated by large-scale demolition operations burdens the surrounding ecological environment. To preserve the original foundation and save costs, some engineering solutions attempt to directly tie reinforcing bars to the outside of the existing foundation and encase it with poured concrete, thereby increasing the foundation's base area and self-weight. However, due to material limitations, there are differences in shrinkage and creep at the interface between the old and new concrete. This simple reinforcement method cannot guarantee the shear strength of the interface, and under the long-term alternating loads of the wind turbine, the interface is prone to cracking and peeling, failing to form a stable and reliable overall load-bearing structure. In addition, early wind turbine foundations generally used a hollow foundation ring connection structure, and after years of service, the concrete around the foundation ring often exhibits a certain degree of fatigue damage. If the traditional single-tube tower is still used after the capacity expansion and renovation, the huge concentrated load of the new unit will continue to be directly transmitted to the existing foundation ring area. This will exacerbate the stress concentration phenomenon of the original components, causing local failure or even structural damage in the core stress area. Due to the limitations of the existing renovation methods, there is a need for a foundation renovation scheme that can effectively distribute and transfer the new load and ensure long-term operational stability through structural system transformation without completely demolishing the original structure. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a method for upgrading and expanding wind power foundations based on truss towers. This method solves the problems of high cost and long cycle when the existing wind power foundations are completely demolished and rebuilt for the expansion of high-power units. Conventional in-situ reinforcement methods cannot guarantee the long-term stress coordination between the old and new foundation interfaces. Furthermore, the newly generated concentrated loads from the new high-power units are directly transmitted to the existing old foundation ring, which can easily lead to stress concentration and local structural damage.

[0005] This application provides a method for upgrading and expanding the capacity of wind power foundations based on truss towers, the method comprising the following steps:

[0006] The existing foundation was investigated, including the precast pile caps, lattice towers containing steel-concrete composite columns, reinforced concrete transfer sections, ground beams, and pile foundations. Using the existing foundation as a reference, the lines are laid out, the pile foundation is driven in, and the pile caps are installed in a centrally symmetrical arrangement around the periphery of the existing foundation. The bottom surface of the pier cap is controlled to be at the same elevation as the bottom surface of the existing foundation; The lattice tower, which is assembled in a spatial A-frame shape with eight legs, is hoisted and assembled above the pier, and the conversion section is installed at the top of the lattice tower. Install the ground beam and connect it to the side of the foundation and the side wall of the existing foundation. Pass the prestressed anchor cable through the reserved channel in the transition section and fix the upper end, and apply prestressing force to the prestressed anchor cable; The lower end of the prestressed anchor cable passes through the pre-drilled anchor cable hole at the upper end of the exposed foundation ring on the top of the existing foundation and is locked.

[0007] As a further improvement of this application, the existing foundation does not bear the vertical downward pressure load generated by the new unit, and the existing foundation participates in resisting the overturning moment as a counterweight module; The connection of the ground beam to the side of the foundation and the side wall of the existing foundation specifically includes: A compressible damping pad is laid between the sidewall of the existing foundation and the end contact surface of the ground beam, and a shear-resistant steel pin is installed in the area of ​​the damping pad to penetrate the interface between the old and new surfaces formed by the sidewall and the end contact surface for flexible shear connection.

[0008] As a further improvement to this application, the installation of the bearing platform, which is centrally symmetrically arranged around the periphery of the existing foundation, specifically includes: Four independent foundations are provided, such that the geometric center formed by the combination of the four foundations coincides with the central vertical axis of the existing foundation. After the ground beam is installed, the load conditions along the main axis of the 0-degree plane and along the main axis of the 45-degree plane are extracted. For the pile foundation, the ultimate bearing capacity of the single pile is verified in both compressive and tensile dimensions. By comparing the calculated value of the maximum axial compressive reaction force borne by the single pile with the design value of the single pile compressive bearing capacity, and the calculated value of the maximum axial tensile reaction force with the design value of the single pile tensile bearing capacity under the most unfavorable load combination, it is ensured that the peak stress of the independent pile foundation is limited to the range of the design value of the single pile compressive bearing capacity or the design value of the single pile tensile bearing capacity.

[0009] As a further improvement of this application, when assembling the lattice tower, the bottom ends of the four sets of assembled steel-concrete composite main columns are respectively anchored above the corresponding foundation, so that the top ends of the adjacent steel-concrete composite main columns are inclined to converge towards the central vertical axis of the existing foundation, and are connected to the transition section above by bolts. Diagonal and horizontal braces are installed within the spatial grid formed by the main steel-concrete composite column. The diagonal and horizontal braces are connected to the main steel-concrete composite column by factory prefabrication and on-site bolt splicing.

[0010] As a further improvement of this application, when processing the prefabricated transition section, the transition section is made into a reinforced concrete structure; an anchoring end plate is embedded inside the transition section, and the anchoring end plate is welded and fixed to the reinforcing steel inside the transition section; Meanwhile, a through steel pipe is pre-embedded inside the transition section as a channel for the prestressed anchor cable to pass through.

[0011] As a further improvement of this application, the portion of the base ring exposed above the existing foundation is cleaned and rusted, and multiple radial shear steel brackets are welded through the inner wall of the base ring at equal intervals. High-strength, non-shrink structural grout is poured into the entire cross-section of the internal cavity of the foundation ring, transforming the original hollow steel cylinder formed by the foundation ring into a solid composite section in which the steel shell and the internal grout work together to bear the force. An annular pressure-bearing steel pad is added to the outside of the top flange of the base ring. The annular pressure-bearing steel pad is fastened by high-strength bolts through the existing flange hole at the top of the base ring. Epoxy resin structural adhesive is injected between the annular pressure-bearing steel pad and the top flange of the base ring.

[0012] As a further improvement of this application, the prestressed anchor cable is a prestressed steel strand cable, and the upper end of the prestressed anchor cable is embedded in the working anchor inside the transition section for locking; The lower end of the prestressed anchor cable passes through the anchor cable through hole reserved at the upper end of the foundation ring at the top of the existing foundation and is embedded in the anchorable structure of the foundation ring for locking, thereby reinforcing the structure between the foundation ring and the transition section. The free section of the prestressed anchor cable is wrapped with a high-density polyethylene corrugated pipe, and the inside of the corrugated pipe is filled with anti-corrosion grease.

[0013] As a further improvement of this application, the through-holes of the prestressed anchor cables inside the foundation are arranged in a multi-ring concentric array, so that the outer ring anchor cable group is arranged close to the stress edge of the foundation, and the inner ring anchor cable group is evenly distributed in the core area within the projection plane of the existing foundation. Below the working anchor at the upper end of each ring of anchor cables, a continuous annular pressure-bearing steel plate is pre-embedded, and a spiral anti-crack steel mesh is densely arranged in the concrete body of the foundation below the annular pressure-bearing steel plate.

[0014] As a further improvement of this application, during the construction process of driving the pile foundation, a static pile driving process is used to drive precast high-strength concrete pipe piles as new peripheral pile foundations, and a precast integral rigid guide frame is used to limit the initial plane coordinates of the pipe piles. A smart pile cap integrating a dual-axis tilt sensor and a hydraulic pressure transmitter is installed on the top of the pipe pile. An adaptive spherical leveling pad is set inside the smart pile cap, and the dual-axis tilt sensor and the hydraulic pressure transmitter are integrated and encapsulated in the shockproof isolation cavity of the side wall of the smart pile cap.

[0015] As a further improvement of this application, the prestressed anchor cable is applied with a graded tensioning process, and the first stage of prestressing initial tensioning is carried out before the bottom section of the lattice tower is hoisted. The tensioning operation uses an intelligent hydraulic jack cluster equipped with a microcomputer communication bus. The intelligent hydraulic jack cluster integrates a flow proportional valve and a high-frequency displacement sensor, and is connected to the upper end of each channel of the prestressed anchor cable through parallel hydraulic manifolds and pressure equalizing rings. The intelligent hydraulic jack cluster is connected to a closed-loop synchronous control host, which dynamically adjusts the opening degree of the flow proportional valve in the oil inlet circuit of each jack based on the real-time feedback of the high-frequency displacement sensor.

[0016] The innovative principles and beneficial effects of this application are as follows: The modification method described in this application alters the force transmission path of the foundation structure by adding centrally symmetrically arranged pile caps and lattice-type towers around the existing foundation. The vertical downward pressure load generated by the new wind turbine and the overturning moment caused by wind load are mainly borne by the newly built pile caps and the surrounding pile foundations. The existing foundation withdraws from the vertical load-bearing system and instead acts as a counterweight module to resist the overturning moment of the system. A ground beam connects the pile caps and the existing foundation, integrating the old and new parts into a cohesive whole. Prestressed anchor cables run through the top transition section and the bottom foundation ring, providing overall pre-tension and improving the lateral stiffness of the modified foundation system.

[0017] A compressible damping pad and shear-resistant steel pins are installed between the ground beam and the existing foundation sidewall to form a flexible shear-resistant connection node. This connection method can accommodate uneven settlement displacement caused by differences in materials or load-bearing history between the new and old foundations, reduce stress concentration at the interface, and ensure the overall structural continuity.

[0018] The lattice-type tower adopts a spatial truss system with steel-concrete composite main columns converging towards the center. This structural form can provide the moment of inertia of the cross section, improving the tower's wind and earthquake resistance. The transfer section is made of reinforced concrete and has pre-embedded anchor end plates and steel pipe channels inside, providing space for the tensioning of prestressed anchor cables and force transmission supports.

[0019] For the existing foundation ring on top of the foundation, radial shear-resistant steel brackets were welded in and high-strength, non-shrinkage structural grout was poured into the cavity, transforming the original thin-walled hollow steel cylinder into a solid composite section where the steel shell and internal grout share the load. This structural modification improves the local bearing capacity and shear resistance of the foundation ring, meeting the requirements of the larger concentrated load transmitted by the expanded wind turbine.

[0020] The prestressed anchor cable ducts are arranged in a multi-ring concentric array within the pile cap. Combined with pre-embedded annular bearing steel plates and crack-resistant steel mesh, the local high-pressure stress generated by anchoring is evenly diffused into the concrete structure, preventing the pile cap from cracking under tension. In static pile driving, an intelligent pile cap is introduced. A dual-axis tilt sensor and a hydraulic pressure transmitter monitor the pile driving posture and penetration resistance in real time. An adaptive spherical leveling pad automatically compensates for end-face contact errors, reducing the breakage rate of the pipe pile under eccentric pressure. The closed-loop synchronous control host dynamically adjusts the flow proportional valve based on displacement sensor feedback to achieve synchronous and uniform tensioning of the jack cluster, ensuring the uniformity of prestress application.

[0021] This application provides a method for upgrading and expanding the capacity of wind turbine foundations based on truss towers. It offers the following advantages: 1. This application retains the existing wind turbine foundation and adds a centrally symmetrical pile cap and a newly constructed pile foundation around it. The existing foundation acts as a counterweight module to resist the overturning moment, ensuring that the increased vertical downward load from the new turbine is primarily borne by the outer pile cap and pile foundation. This structural arrangement avoids the complete demolition of the original deep foundation pit concrete structure, reducing the initial workload and renovation costs. Simultaneously, by using ground beams to connect the side of the new pile cap to the sidewall of the existing foundation, spatial force coordination between the old and new foundations is achieved, effectively increasing the overall load-bearing capacity of the foundation within the original turbine location to accommodate the expanded turbine.

[0022] 2. This application employs a prestressed anchor cable system that penetrates the transition section, extends from the existing foundation downwards into stable rock strata, and applies graded pre-tensioning forces to directly anchor the upper lattice tower, lower foundation, and underground soil and rock mass into a single unit. The vertical tension provided by the anchor cables can actively balance the enormous overturning moment generated by the large-capacity turbine unit under extreme operating conditions, reducing the risk of foundation detachment. This feature structurally restricts the tilting displacement of the foundation and tower, improving the overturning stability and dynamic stiffness of the wind turbine system under complex wind loads.

[0023] 3. This application modifies the existing foundation ring by creating a solid composite section. Radial shear steel brackets are welded to its inner wall, and high-strength, non-shrinkage structural grout is poured across the entire internal cavity, transforming the original hollow steel cylinder into a solid node where steel and concrete work together to bear loads. In conjunction with the addition of an annular bearing steel pad on the outside of the top flange and the injection of epoxy resin structural adhesive, the bearing area and local section stiffness are increased when loads are transferred downwards. This alleviates the stress concentration problem of the old foundation ring when bearing alternating loads from larger tonnage units and extends the service life of critical load-bearing nodes. Attached Figure Description

[0024] Figure 1 This is a top view of the overall shape of the old and new bases of this application; Figure 2 This is a sectional view showing the connection method between the old and new foundations in this application; Figure 3 This is a side view of the connection method between the old and new basic structures in this application; Figure 4 This is a structural diagram of the basic scheme of this application; Figure 5 This is a diagram showing the arrangement of prestressed anchor cables in this application; Figure 6 An anchor cable perforation diagram is provided for the foundation ring plate of this application; Figure 7 This is the overall elevation view of this application; Figure 8 This is a flowchart of the wind power foundation reuse and capacity expansion method proposed in this application.

[0025] in: 10. Existing foundation; 20. Pier cap; 30. Ground beam; 40. Foundation ring; 50. Lattice tower; 60. Transfer section; 70. Prestressed anchor cable. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0027] See attached document Figure 1 To be continued Figure 7 , Figure 7 This is an overall elevation view according to one embodiment of this application. Figure 8This is a flowchart of a wind power foundation reuse and capacity expansion method according to an embodiment of this application. This application provides a wind power foundation reuse and capacity expansion method based on a truss tower. The wind power foundation renovation structure involved in this method mainly includes: an existing foundation 10, a pile cap 20, a ground beam 30, a foundation ring 40, a lattice tower 50, a transfer section 60, and prestressed anchor cables 70.

[0028] The existing foundation 10 is located at the bottom layer and is the original foundation structure of the wind turbine. The pile cap 20 is arranged symmetrically around the perimeter of the existing foundation 10, and the newly built pile foundation is connected to the bottom of the pile cap 20.

[0029] The ground beam 30 is horizontally positioned between the foundation cap 20 and the side wall of the existing foundation 10. The foundation ring 40 is positioned on top of the existing foundation 10.

[0030] The base of the lattice tower 50 is supported above the foundation 20 and extends upwards. The transition section 60 is connected to the top of the lattice tower 50. Prestressed anchor cables 70 are arranged vertically and pass through the transition section 60 at the top and the foundation ring 40 at the bottom.

[0031] Under the above structural configuration, the existing foundation 10 does not serve as a load-bearing structure directly bearing the downward load of the upper unit, but rather as a counterweight module to resist overturning of the overall structure. The vertical load of the new unit is borne by the pile cap 20 and the pile foundation below it. The overturning moment generated under extreme working conditions is transferred to the existing foundation 10 by the prestressed anchor cables 70, so that the pile cap 20 and the existing foundation 10 form a cooperative force-bearing system.

[0032] See attached document Figure 8 , Figure 8 This is a flowchart of a wind power foundation reuse and capacity expansion method according to an embodiment of this application. Based on the above structural composition, the wind power foundation reuse and capacity expansion method provided by this application includes the following steps: S100. Conduct survey and prefabrication work. Survey the existing foundation 10 of the target site to confirm its appearance, structural condition, and concrete strength. Complete the prefabrication of the foundation 20, the columns of the lattice tower 50, the transfer section 60, the ground beam 30, and the pile foundation in the factory, and transport the prefabricated components to the construction site.

[0033] S200. Perform pile driving and pile cap 20 construction work. Using the existing foundation 10 as a reference, lay out the lines to determine the installation position of the pile cap 20. Drive the precast pile foundation and install four symmetrically arranged pile caps 20. Control the bottom surface of the pile cap 20 to be at the same elevation as the bottom surface of the existing foundation 10, and ensure that the geometric center of the four pile caps 20 coincides with the center of the existing foundation 10.

[0034] S300. Perform the hoisting and prestressing of the upper support structure. Hoist and assemble the lattice tower 50, which is arranged in a spatial A-frame shape with eight legs, above the pier cap 20. Connect and install the transition section 60 at the top of the lattice tower 50. Pass the prestressed anchor cables 70 through the reserved channels in the transition section 60 and fix the upper end. Use tensioning equipment to apply prestress to the prestressed anchor cables 70, so that the columns of the lattice tower 50 are under compression, eliminating the tensile stress in the columns.

[0035] S400. Install the ground beam 30. Connect the ground beam 30 to the side of the pile cap 20 and the side wall of the existing foundation 10 to form a cohesive load-bearing structure. After construction, perform compressive and tensile strength calculations on the pile foundations in the 0-degree and 45-degree planes along the main axis.

[0036] S500, Perform the locking operation of the prestressed anchor cable 70. The lower end of the prestressed anchor cable 70 passes through the anchor cable through hole reserved at the upper end of the foundation ring 40, and is connected and locked to the foundation ring 40.

[0037] See attached document Figure 1 To be continued Figure 3 , Figure 1 This is a top view of the overall shape of the old and new bases according to an embodiment of this application. Figure 2 This is a cross-sectional view of the new and old basic connection method according to an embodiment of this application. Figure 3 This is a side view of the connection method between the old and new foundations according to an embodiment of this application. In this embodiment, the existing foundation 10 is the original circular reinforced concrete foundation of the wind farm. During the wind turbine capacity expansion and renovation process, due to the increase in the tower height and rotor diameter of the new unit, the overall structure faces greater downward pressure load and overturning moment.

[0038] To meet load-bearing requirements and achieve the goal of reusing existing infrastructure, this embodiment restructures the function of the existing foundation 10. As a preferred approach, the existing foundation 10 no longer participates in bearing the vertical downward load generated by the new generating unit; this downward load is borne by the newly constructed pile cap 20 and the pile foundation beneath it. The existing foundation 10 serves as a counterweight module in the overall renovated structural system, utilizing its own gravitational potential energy to resist the overturning moment generated by wind loads.

[0039] Under extreme wind conditions, the wind turbine system is subjected to enormous horizontal thrust, which generates a tendency to overturn at the foundation bottom, leading to structural instability. By incorporating the existing foundation 10 into the overall anti-overturning force system, a restoring moment to resist this overturning tendency can be directly provided. Based on this, the design achieves force distribution and state verification through the following steps: S101. Obtain the structural parameters of the existing foundation 10 and determine its effective self-weight. Obtain the geometric dimensions and material density of the existing foundation 10 through on-site survey, and calculate its effective self-weight accordingly. In the stress analysis, the existing foundation 10 is treated as a homogeneous rigid body, and its line of action is positioned on the geometric central axis of the foundation.

[0040] S102. Construct an overall anti-overturning collaborative calculation model that includes the self-weight parameters of the existing foundation 10. In this model, the overall anti-overturning moment of the system is provided by the self-weight of the existing foundation 10, the self-weight of the newly constructed superstructure, and the self-weight of the newly constructed substructure. The formula for calculating the overall anti-overturning moment is as follows: ; in, Indicates the overall anti-overturning moment; This indicates the effective self-weight of the existing foundation 10; This indicates the total weight of the newly constructed superstructure, which includes the nacelle, blades, tower, lattice tower 50, and transfer section 60. This indicates the total weight of the newly constructed foundation 20 and ground beam 30; It represents the equivalent force arm distance from the centroidal axis of rotation of the overall structure to the line of action of the system's gravity.

[0041] The physical meaning of this formula is that it uses the lever principle to directly convert the gravity parameters of each structural component in space into a static torque that keeps the structure stable and prevents it from collapsing, thereby quantifying the contribution of gravitational potential energy to the overall stability of the system at the theoretical level.

[0042] S103. Verify the overall overturning safety factor. Based on the obtained wind load boundary conditions and the overall overturning resistance moment calculated from the model, calculate the overturning safety factor of the modified structural system. The formula for determining the overturning safety factor is as follows: ; in, Indicates the system's overturning safety factor; This represents the overall overturning moment caused by wind load acting on the foundation base under extreme conditions. The threshold value of 1.0 in the above formula represents the physical boundary at which the structure is in a critical overturning state. In engineering applications, the system's overturning safety factor... The value range is set to be greater than or equal to the safety margin specified in the corresponding design specifications, but its judgment bottom line must be strictly greater than or equal to 1.0, which serves as one of the multi-dimensional judgment criteria for evaluating the effectiveness of the existing foundation 10 counterweight.

[0043] For the determination and calculation of the overall overturning moment of wind load acting on the foundation bottom surface under extreme conditions, those skilled in the art can calculate it based on the wind resource data of the target location and the aerodynamic parameters of the new unit. The specific calculation logic and parameter acquisition method are well-known technologies in this field and will not be elaborated here.

[0044] Based on the aforementioned multi-dimensional mechanical judgment logic and parameter coordination settings, the existing foundation 10 is transformed from a load-bearing component that originally bore vertical pressure into an active counterweight component that provides restoring moment in the new structural system. This design cuts off the path of vertical load transmission from the new unit to the existing foundation 10, allowing the heavy-tonnage downward load to be directly transferred to the deep pile foundation via the pile cap 20, thus avoiding the settlement difference and stress concentration problems caused by the mismatch in vertical stiffness between the old and new structures.

[0045] See attached document Figure 1 Appendix Figure 2 and appendix Figure 4 , Figure 1 This is a top view of the overall shape of the old and new bases according to an embodiment of this application. Figure 2 This is a cross-sectional view of the new and old basic connection method according to an embodiment of this application. Figure 4 This is a structural diagram of a basic scheme according to an embodiment of this application. In this embodiment, the newly constructed load-bearing core of the wind power foundation renovation structure is the pile cap 20 and the newly constructed pile foundation connected below it.

[0046] To ensure the safe transfer of loads from a large-capacity wind turbine without demolishing the existing foundation 10, this embodiment features a specific design for the spatial layout and internal structure of the newly constructed pile foundation and pile caps 20. As a preferred approach, four independent concrete pile caps 20 are constructed, arranged symmetrically around the perimeter of the existing foundation 10. In terms of spatial geometric constraints, the bottom elevation of the pile caps 20 is set to be at the same elevation as the bottom surface of the existing foundation 10. Based on this shared elevation principle, the geometric centroid of the four pile caps 20 is strictly coincident with the central vertical axis of the existing foundation 10.

[0047] The general technical principle of the above spatial layout lies in the fact that, since the stiffness of the soil stratum usually varies non-linearly with depth, by controlling the design at the same elevation, it can be ensured that the new pile foundation and the existing foundation 10 are in the same bearing layer environment, thereby avoiding destructive redistribution of internal forces caused by the difference in foundation settlement under the long-term dynamic action of alternating wind loads. The centroid coincidence design ensures that the point of application of the resultant force of the vertical static load transmitted by the superstructure coincides with the centroid of the pile group. This arrangement eliminates the initial additional bending moment caused by eccentric compression in terms of physical mechanism, providing a clear static benchmark for subsequent stress analysis.

[0048] The bearing capacity distribution and state verification of this newly constructed pile group structure are performed through the following steps: S201. Construct a local coordinate system for the pile group and obtain the pile foundation coordinate parameters. Establish a local coordinate system with the geometric centroid formed by the combination of four pile caps as the origin, and collect the geometric coordinates of the newly built pile foundation.

[0049] S202. Perform pile group stress distribution calculation. Based on the theory of eccentric compression, the total vertical load and bidirectional overturning moment acting on the pile group foundation are decoupled and transformed into uniform axial force in the foundation plane and additional axial force around the bidirectional vertical axis, thereby obtaining the actual vertical reaction force borne by each independent pile foundation.

[0050] S203. Multi-dimensional determination of the ultimate bearing capacity of a single pile is performed along the characteristic principal axis direction. The 45-degree diagonal principal axis direction, where the bending stiffness of the pile group is weakest, is extracted as the core verification condition. The output results are determined based on a dual-dimensional logic of compressive and tensile strength. By comparing the calculated value of the maximum axial compressive reaction force borne by a single pile with the design value of the single pile compressive bearing capacity under the most unfavorable load combination, and the calculated value of the maximum axial tensile reaction force with the design value of the single pile tensile bearing capacity, it is ensured that the peak stress of the independent pile foundation is strictly limited within the design threshold range, preventing crushing or pull-out instability. The specific calculation of the above-mentioned bearing capacity design value is a well-known technique in this field and will not be elaborated here.

[0051] Based on the above multi-dimensional parameter design and mechanical state verification, the pile cap 20 and the pile foundation below it not only effectively replace the vertical bearing function of the existing foundation 10, but also provide a reliable base with high bending stiffness and no initial stress eccentric load for the upper lattice tower 50.

[0052] See attached document Figure 1 and attached Figure 2 , Figure 1 This is a top view of the overall shape of the old and new bases according to an embodiment of this application. Figure 2 This is a cross-sectional view of the connection method between the new and old foundations according to an embodiment of this application. In this embodiment, the independent foundation 20 and the existing foundation 10 located in the central area are connected laterally by a ground beam 30. The ground beam 30 is a reinforced concrete structure cast in situ, with its two ends connected to the side of the newly built foundation 20 and the outer wall of the existing foundation 10, respectively, thereby physically coupling the scattered foundation components and the central counterweight entity into a complete planar distributed topology network.

[0053] To simplify the internal stress system at the junction of the old and new foundations and prevent irreversible secondary damage to the aging concrete, this embodiment features a specially designed connection mechanism for the ground beam 30. As a preferred approach, the interface between the ground beam 30 and the existing foundation 10 abandons the traditionally used large-scale deep-hole rebar anchoring and other rigid consolidation methods. Instead, it employs a semi-hinged or flexible shear-resistant connection structure that releases rotational freedom. Specifically, this flexible shear-resistant connection structure involves pre-laying a compressible damping pad of a predetermined thickness between the sidewall of the existing foundation 10 and the end contact surface of the ground beam 30. This isolates the direct rigid interlocking of the concrete. Within this damping pad area, only shear-resistant steel pins penetrating the interface between the old and new foundations are configured to specifically transmit vertical shear forces.

[0054] The general technical principle behind the above structural design is that, under the long-term action of wind turbine gravity and alternating loads, the newly built deep pile foundation and the shallowly buried existing foundation 10 will inevitably have a difference in settlement rate in terms of physical and mechanical properties. If the interface between the new and old foundations is connected with absolute rigidity, this differential settlement will induce highly destructive additional parasitic bending moments within the ground beam 30 and on the sidewalls of the existing foundation 10. Based on this, by artificially weakening the bending stiffness of the interface at the structural level, and retaining only the transmission channels for vertical shear force and horizontal axial force, the ground beam 30 can act as a force transmission link to lift the existing foundation 10 and participate in anti-overturning when encountering extreme overturning and uplift conditions, while allowing the two to produce small independent displacements under normal downlift conditions, thereby physically isolating the spread of destructive internal forces.

[0055] The stress state verification of the above-mentioned flexible shear connection structure is performed through the following steps: S301. Obtain the interface geometric parameters and settlement boundary conditions of the ground beam 30. Collect the effective contact area between the ground beam 30 and the sidewall of the existing foundation 10, and obtain the predicted limit value of the vertical relative settlement between the new foundation 20 and the existing foundation 10 based on the geological survey data.

[0056] S302. Construct a moment release evaluation calculation model for the interface. To quantify the mitigation effect of the non-rigid connection structure on the additional bending moment, a moment release coefficient is introduced for state characterization. The calculation formula for the moment release coefficient of the interface is as follows: ; in, This represents the moment release coefficient at the interface. This represents the actual constraint bending moment at the interface, induced by the predicted limit value of vertical relative settlement, under the actual flexible shear connection structure. This represents the theoretical peak bending moment caused by the same amount of settlement, assuming the interface is absolutely rigidly consolidated.

[0057] The technical purpose of this formula is to quantify the degree of flexibility and buffering in structural construction using mathematical ratios. Engineering design requires consideration of the moment release coefficient at the interface. The value range is set to be greater than or equal to 0.8. The basis for setting this threshold is to ensure that most of the bending moment failure energy can be absorbed or released by the deformation of the compressible damping pad itself, thereby avoiding the occurrence of tensile cracking of the concrete at the end of the ground beam 30.

[0058] S303. Multi-dimensional determination of interface shear capacity under collaborative working conditions. While releasing the bending moment, the ground beam 30 must possess sufficient shear force transfer capacity to utilize the existing gravity counterweight of the foundation 10. To avoid a one-sided determination based on a single extreme value, a multi-dimensional state verification is performed here, combining the linkage effect of vertical shear compression and tension counterweight. The formula for determining the interface shear capacity is as follows: ; in, This indicates the extreme value of the vertical shear force calculation at the interface that the ground beam 30 needs to transfer to the existing foundation 10 under extreme overturning conditions; This represents the design value of the shear strength of the old concrete material on the outer side wall of the existing foundation 10. This indicates the effective contact area between the ground beam 30 and the sidewall of the existing foundation 10; This represents the structural safety importance coefficient of the joint.

[0059] The physical meaning of this formula lies in establishing the limit state equation to verify that the interface, when transmitting tensile counterweight loads, will not experience shear slip failure along the cross-section due to excessive local shear stress in the old concrete body. The structural safety importance coefficient of the interface in the formula... The safety level of the renovation project was set to a constant value greater than 1.0.

[0060] For obtaining the vertical relative settlement prediction limit value between the newly built foundation 20 and the existing foundation 10, those skilled in the art can derive the settlement integral by combining the layered summation method with the soil compression modulus. The specific settlement consolidation theory and derivation process are well-known technologies in this field and will not be elaborated here.

[0061] Based on the judgment logic established on the dual dimensions of mechanical release and shear constraint, a reliable flexible collaborative boundary is constructed between the ground beam 30 and the existing foundation 10, which cuts off the transmission failure path of secondary stress while ensuring the effective linkage of the counterweight system.

[0062] See attached document Figure 5 and attached Figure 6 , Figure 5 This is a prestressed anchor cable arrangement diagram according to an embodiment of this application. Figure 6This is a diagram showing the pre-reserved anchor cable perforation on the foundation ring plate according to one embodiment of this application. In this embodiment, the lattice tower 50 constitutes the core spatial force transmission hub connecting the lower independent bearing platform 20 and the upper transition section 60. Due to the significant increase in the hub height of newly built large-capacity wind turbine units, the overall flexibility of the tower body increases accordingly. Traditional single-tube tower structures are prone to lateral resonance and excessive deflection when facing extreme working conditions.

[0063] To effectively control the dynamic response deformation of the overall foundation system while increasing the unit height, this embodiment refines the internal spatial topology and node connection mechanism of the lattice tower 50. As a preferred approach, the lattice tower 50 employs a steel pipe truss system with eight legs arranged in a spatial herringbone pattern. Specifically, this structure consists of four sets of inverted V-shaped main columns, each anchored at its base to four centrally symmetrically distributed abutments 20 via pre-embedded high-strength anchors. The tops of adjacent main columns converge towards the central axis and are connected to the upper transition section 60 via flanges using high-strength bolts. Within the spatial grid formed by the main columns, seamless steel pipe diagonal and transverse braces are discretely arranged along the vertical height. To ensure the effective transmission of complex internal forces between the grids, the ends of the diagonal and transverse braces are connected to the outer wall of the main columns via fully penetrated welded node plates, forming a semi-rigid node structure that avoids localized pipe wall tearing. This creates a geometrically invariant load-bearing skeleton in physical space, capable of resisting localized instability.

[0064] The general technical principle of the aforementioned spatial lattice structure design lies in the fact that, based on the static equilibrium characteristics of the truss nodes, the overall overturning moment transmitted from the transition section 60 is transformed into pure axial tension and axial compression within the four corner main columns through the principle of spatial force decomposition. This force mechanism cuts off the transmission path of bending moment directly generating bending stress within a single slender member. By utilizing the lateral widening of the structural geometry, the moment arm resisting overturning of the system is significantly increased, thereby achieving lateral stiffness far exceeding that of a single-tube tower with the same amount of steel.

[0065] The force analysis and multi-dimensional state determination of this system are performed through the following steps: S401. Obtain the spatial geometric input parameters and material mechanical properties of the lattice tower 50, including the inclination angle, length, and cross-sectional area of ​​the main column.

[0066] S402. Perform analytical calculations to decompose the internal forces of the spatial truss. Based on the principle of spatial force distribution, the total vertical downward load and overall overturning moment acting on the top of the transition section 60 are converted into pure axial tensile and axial compressive forces within each main column.

[0067] S403. A multi-dimensional determination of the limit state of the members is performed by combining strength and global instability mechanisms. The strength reserve is established by verifying whether the maximum axial working stress of the main column section is less than the design value of the tensile and compressive strength of the steel. Simultaneously, the Euler buckling critical force formula, considering the calculated length factor and the moment of inertia of the section, is introduced to ensure that, after introducing a structural overall stability safety factor greater than or equal to 1.2, the maximum axial internal force borne by the members still satisfies the anti-instability boundary conditions. The related spatial buckling mode extraction and calculated length determination are well-known techniques in this field and will not be elaborated upon here.

[0068] Based on the design judgments established on the decoupling of spatial topology and multi-dimensional mechanics, the lattice tower 50 achieves a balance between large-span force transmission and lightweight control, providing a physical support structure with a smooth transition in stiffness between the upper heavy-duty wind turbine and the lower distributed pier group.

[0069] See attached document Figure 5 and attached Figure 7 , Figure 5 This is a prestressed anchor cable arrangement diagram according to an embodiment of this application. Figure 7 This is an overall elevation view according to one embodiment of this application. In this embodiment, the transition section 60, as a core structural component connecting the upper single circular tower and the lower discrete lattice tower 50, plays a crucial role in the transformation of spatial load forms and the redistribution of internal forces. Due to the significant difference in stiffness characteristics between the upper continuous shell and the lower point support, the structural junction is prone to becoming a weak point of stress concentration.

[0070] As a preferred embodiment, the transition section 60 is a reinforced concrete structure. An anchoring end plate is embedded inside the transition section 60, and the anchoring end plate is welded and fixed to the reinforcing steel bars inside the transition section 60. Simultaneously, a through steel pipe is pre-embedded inside the transition section 60 as a channel for the prestressed anchor cable 70 to pass through. Through this construction, the transition section 60 achieves a smooth load transition from a thin-shell continuum to a discrete lattice structure without causing local structural damage.

[0071] The force analysis and multi-dimensional state determination for this region are performed through the following steps: S501. Obtain the geometric parameters of the internal stiffening components of the transition section 60 and the extreme concentrated shear force transmitted upward from the lower main column node.

[0072] S502. Perform analytical calculation of shear force diffusion in the local area above the node. Based on the assumption of uniform shear stress distribution, the highly concentrated nodal shear force is forcibly dispersed to multiple radial stiffeners using the structural geometry to obtain the calculated local average shear stress value.

[0073] S503. Multi-dimensional yield state determination of local shell elements is performed by combining bidirectional normal stress and shear stress. An equivalent stress theory based on stress tensor combination is introduced, comprehensively considering the radial normal stress, circumferential normal stress, and nodal shear stress in the local area of ​​the shell wall to obtain a comprehensive equivalent stress calculation value. It is verified whether this equivalent stress, after introducing material resistance partial factors, is strictly less than the standard value of the yield strength of steel, thereby preventing local plastic yielding of the material. The relevant finite element stress extraction rules are well-known techniques in this field and will not be elaborated here.

[0074] Based on the design established by the internal stiffening system and the multi-directional stress decoupling judgment, the transition section 60 achieves a smooth load transition from the thin shell continuum to the discrete lattice structure without causing local structural damage, providing a stable and reliable transition force transmission structure for the entire upper support system.

[0075] In this embodiment, the foundation ring 40 pre-embedded inside the existing foundation 10 is the main force transmission component of the old wind turbine. Since the foundation ring 40 is deeply embedded inside the concrete of the existing foundation 10, complete removal would face extremely high renovation costs and would seriously damage the integrity of the original structure.

[0076] To fully utilize the residual bearing capacity of the existing foundation ring 40 and adapt to the load requirements of newly built large-capacity units, this embodiment adopts a modification mechanism of in-situ reuse and local reinforcement for the foundation ring 40. As a preferred method, the reinforcement modification of the foundation ring 40 is specifically manifested in the following ways: the exposed part of the foundation ring 40 on the top surface of the existing foundation 10 is cleaned and rusted, and multiple radial shear steel brackets are welded through it at equal intervals in the circumferential direction. After completing the above steel structure welding, high-strength non-shrinkage structural grout is poured into the entire cross-section of the internal cavity of the foundation ring 40, transforming the original thin-walled hollow steel cylinder into a solid composite section in which the steel shell and the internal grout work together to bear the load. At the same time, an annular pressure-bearing steel pad is added to the outside of the top flange of the foundation ring 40. To avoid stress concentration caused by deformation of the old flange surface, the annular pressure-bearing steel pad is fastened by high-strength bolts penetrating the existing flange holes. Epoxy resin structural adhesive is injected between the steel pad and the top flange of the foundation ring 40 for leveling and filling, for direct connection with the upper transition section or lattice tower.

[0077] The general technical principle of the aforementioned reinforcement and renovation mechanism lies in the fact that newly built units will generate an overall overturning moment far exceeding the original design standard during operation. If the old foundation ring 40 is used directly, its weak cylinder wall is prone to local buckling instability deformation on the pressure side. To address this mechanical hazard, the overall compressive stiffness of this section is significantly improved by incorporating radial shear steel brackets and high-strength non-shrinkage structural grouting material, utilizing the excellent compressive properties of the grouting material. Based on this, the implantation of radial shear steel brackets not only provides compressive support but also enhances the mechanical interlocking force between the steel shell and the internal core solidified body at the interface, effectively preventing interlayer relative slippage between two materials with different elastic moduli under alternating loads, thereby establishing a common working boundary for the composite materials in terms of physical stress state.

[0078] The determination of the shear and compressive strength of the modified part is carried out through the following steps: S601. Obtain the pre-embedded depth and outer diameter parameters of the foundation ring 40, as well as the mechanical properties of the newly poured high-strength non-shrinkage structural grout.

[0079] S602. Perform analytical calculation of the pull-out bearing capacity of the foundation ring interface. The extreme vertical pull-out force transmitted to the foundation ring 40 under extreme conditions is converted into the actual pull-out shear stress on the ring interface based on the contact area. Engineering evaluation standards require that this calculated shear stress value must be strictly less than the design value of the interfacial bond strength of the existing foundation 10 old concrete to avoid the risk of debonding and slippage.

[0080] S603. The ultimate compressive strength state is determined by considering the characteristics of the solid composite section. The theory of load-bearing capacity distribution in composite structures is introduced, comprehensively considering the synergistic compressive strength contribution of the solid steel section of the foundation ring and the internal grouting section. After deducting the load-bearing capacity reduction caused by Poisson's ratio differences and introducing a safety factor for the compressive strength of the composite section, it is verified whether the overall compressive bearing capacity of the composite section is greater than the extreme vertical downward pressure. The relevant interfacial bond strength calculation process is a well-known technique in this field and will not be elaborated here.

[0081] Based on the judgment logic established by the dual verification of internal solidification and stress analysis, the foundation ring 40 reinforces the local stiffness deficiency of the original cylinder wall, effectively extending its service life without the need for large-scale demolition, and providing a uniformly stressed bottom support platform for the upper conversion components.

[0082] In this embodiment, the prestressed anchor cable 70 constitutes the main pull-out resistance system that actively applies compressive stress and connects the newly built independent foundation 20, the existing foundation 10, and the deep foundation soil layer. Due to the significant increase in the overturning moment of the newly built large-capacity wind turbine, the self-weight of the foundation components alone is no longer sufficient to balance the extreme uplift load, and the bottom surface of the foundation is very prone to detachment failure.

[0083] As a preferred method, the prestressed anchor cable 70 is a prestressed steel strand. Both ends of the anchor cable are embedded in the transition section 60 and the anchorable structure of the foundation ring 40, respectively. The lower end of the prestressed anchor cable 70 passes through and is locked into pre-reserved anchor cable perforations evenly distributed circumferentially at the upper end of the foundation ring 40. This reinforces the structure between the transition section and the foundation ring, optimizes the stress distribution within the structure, and acts on the existing foundation 10 through the foundation ring 40, using the existing foundation 10 as a counterweight to improve the overall overturning resistance of the structure. To address the corrosion risk during long service life, the free section of the prestressed anchor cable 70 is wrapped with a high-density polyethylene corrugated pipe, and the inside of the pipe is filled with anti-corrosion grease.

[0084] The determination of the internal force distribution and ground anchorage state of this system is performed through the following steps: S701. Obtain the inclination angle, effective anchorage length, borehole diameter, and elastic modulus of the prestressed anchor cable 70, as well as other geological and material parameters.

[0085] S702. Perform analytical calculation of active prestressing stress at the interface. The initial tension of multiple prestressed anchor cables arranged at different angles is synthesized by rigid body mechanics along the normal direction of the interface to calculate the average normal prestressing stress in the contact area, thereby quantifying the contribution of prestressing to the improvement of the interface's shear slip resistance.

[0086] S703. A multi-dimensional determination of the end anchorage limit state is performed by combining rock mass friction theory and steel deformation coordination mechanism. On the one hand, it verifies whether the maximum tensile force of a single anchor cable is less than the ultimate lateral resistance provided by the deep rock strata, ensuring that overall pull-out does not occur. On the other hand, the theoretical elastic elongation of the anchor cable is calculated based on the maximum tensile force to verify the structural displacement coordination during the tension control stage, preventing premature stress relaxation loss. The relevant methods for extracting standard values ​​of lateral resistance are well-known techniques in this field and will not be elaborated here.

[0087] Based on the design mechanism established by the above-mentioned multi-directional spatial routing and interface stress control dual verification, the prestressed anchor cable 70 makes up for the lack of self-weight resistance to overturning of old foundations and establishes an effective prestress transfer path between structural layers of different materials.

[0088] In this embodiment, the newly built large-capacity wind turbine will generate significant eccentric overturning loads during operation. When this load is transmitted downwards to the foundation, it can easily induce tensile stress inside the concrete structure on the windward side and at the interface between the foundation and the ground. Due to the low tensile strength of the concrete material and the soil interface, the occurrence of tensile stress often leads to the initiation of structural cracking or base separation.

[0089] To proactively eliminate the aforementioned tensile stress hazards, this embodiment incorporates an intervention design for the coordinated stress state of the prestressed anchor cable system and the foundation structure. As a preferred approach, the prestressed anchor cable ducts within the newly constructed independent foundation 20 are arranged in a multi-ring concentric array. The outer ring of anchor cables is positioned close to the stress-bearing edge of the independent foundation 20 to provide the maximum lever arm to resist extreme bending moments; the inner ring of anchor cables is evenly distributed within the core area of ​​the existing foundation 10's projection plane to compensate for insufficient overall vertical axial pressure. Below the working anchor at the top of each ring of anchor cables, a continuous annular bearing steel plate is pre-embedded. To address the potential for localized high prestress concentration that could crush the surface concrete, a dense spiral anti-crack steel mesh is arranged within the concrete structure beneath the annular bearing steel plate to smoothly disperse the highly concentrated point-like prestress onto the broad concrete bearing surface below.

[0090] The general technical principle of the above design lies in applying vertical active prestress using multiple concentric rings of prestressed anchor cables, which shifts the overall stress state of the foundation section towards the compression zone. Based on the principle of stress superposition in elasticity, when the amplitude of the artificially applied uniform compressive stress is greater than or equal to the amplitude of the maximum tensile stress at the edge caused by the overturning moment, the net stress on the section will always remain compressive stress, thus achieving effective tensile stress relief at the interface between the concrete structure and the substrate at the constitutive mechanical level.

[0091] The analytical and multi-dimensional determination of the stress state of the base section is performed through the following steps: S801. Obtain the effective contact area and bending section modulus of the foundation bottom surface, and extract the overall overturning moment and vertical dead load standard value at the same time node.

[0092] S802. Perform analytical calculations of the extreme normal stress at the base edge. Using the theory of eccentric compression, the structural self-weight, the total vertical preload applied by the prestressed anchor cables, and the overall overturning moment are transformed into equivalent normal stress calculations at the base edges on the windward and leeward sides.

[0093] S803. A multi-dimensional determination of the structural internal force state is performed by combining tensile and compressive boundary conditions. A tensile margin control coefficient is introduced, requiring that the stress state on the windward side fully enter the compression zone or retain only a small allowable tensile stress (i.e., satisfying the tensile margin control boundary); simultaneously, the peak value of the equivalent compressive stress on the leeward side is forcibly limited to not exceeding the design value of the compressive strength of the concrete at the bottom of the foundation. Through bidirectional closed-loop control of tension and compression, the initiation of fatigue cracks is prevented. The relevant non-destructive field strength estimation methods are well-known in the field and will not be elaborated here.

[0094] Based on the aforementioned control mechanism established on load time alignment and tensile-compressive dual boundary constraints, the foundation structure can maintain an overall compressive working state under complex alternating wind loads, which physically blocks the initiation and propagation path of fatigue cracks, ensuring the long-term structural stability of the new and old foundation combination system.

[0095] In this embodiment, the main engineering obstacle to the in-situ renovation of old wind power foundations is that the existing foundation 10 has a densely packed, hidden old steel mesh inside, and after years of settlement and material degradation, its actual physical outline often has a large geometric deviation from the initial design drawings.

[0096] To avoid cutting the main reinforcing bars of the existing foundation 10 during subsequent drilling, rebar installation, or anchoring operations, and to ensure precise connection between the newly constructed independent foundation cap and the original structure, this embodiment incorporates a site survey and high-precision prefabrication process before actual construction. As a preferred method, the site survey is implemented as follows: a 3D laser scanner is used to acquire high-density point cloud data of the exposed surface of the existing foundation 10; simultaneously, a ground-penetrating radar array is used to perform a gridded scan on the top surface of the foundation, extracting the actual 3D spatial coordinates of the top layer and vertically distributed reinforcing bars. To meet the high-precision prefabrication requirements and ensure the accuracy of the prestressed duct installation on-site, scattered duct reinforcement binding is not performed on-site. Instead, based on the interference-free spatial coordinates obtained from the survey, an integral rigid guide frame, including positioning steel plates and directional sleeves, is prefabricated in the factory. Due to the unevenness and construction errors on the surface of the existing foundation 10, based on the previous point cloud reverse engineering, a three-dimensional positioning reference surface that matches the local feature contour of the exposed surface of the existing foundation 10 is prefabricated at the bottom of the overall rigid guide frame, and is equipped with adjustable screw legs for elevation leveling, so as to achieve rigid alignment between the measurement coordinate system and the physical coordinate system during on-site assembly.

[0097] The general technical principle of the aforementioned surveying and prefabrication mechanism lies in transforming unknown underground hidden works into a visualized three-dimensional spatial mapping model through non-destructive testing. Within this unified absolute spatial coordinate system, the planned anchor cable borehole trajectory vector and the detected rebar axis vector are subjected to analytical geometric spatial interference verification. This allows for the identification and elimination of collision interference points before physical construction, thereby guiding the customized production parameters of the rigid guide frame.

[0098] The determination of the safe distance between the drilling trajectory and the concealed rebar is performed through the following steps: S901. Obtain the existing steel reinforcement axis vector and reference point coordinates obtained from the ground penetrating radar, as well as the planned borehole trajectory direction vector and starting point coordinates.

[0099] S902. Perform analytical calculation of the minimum spatial distance between the borehole trajectory and the concealed rebar. Using spatial analytical geometry methods, the collision avoidance problem is transformed into solving for the minimum common perpendicular distance between two skew lines (the borehole trajectory and the rebar axis).

[0100] S903. A multi-dimensional determination of high-precision prefabrication parameters is performed by combining spatial clearance distance and equipment construction deviation. It is mandatory that the calculated minimum spatial distance must be greater than the sum of the physical radius of the borehole, the physical radius of the reinforcing steel, and the drill bit skew error that accumulates linearly with the borehole depth. Only after meeting the above clearance verification can the coordinate data be locked for guide frame prefabrication. The related point cloud denoising and registration process is a well-known technology in this field and will not be elaborated here.

[0101] Based on the aforementioned prefabrication mechanism, which is based on dual verification of non-destructive testing and spatial interferometry, the irreversible weakening of the bearing capacity of old structures caused by blind on-site drilling is avoided, and a highly reliable physical and geometric benchmark is established for subsequent deep hole operations and the establishment of prestressed systems.

[0102] In this embodiment, the expansion of old wind turbine foundations typically requires the addition of micropiles or precast piles around the existing foundation cap to expand the load-bearing boundary of the foundation. However, driving piles in the limited space adjacent to the existing foundation can easily cause microcracks to appear in the existing concrete structure due to soil squeezing or high-frequency vibration.

[0103] To proactively control the disturbance to the surrounding soil during pile driving and ensure the geometric positioning accuracy of the pile group, this embodiment features a targeted design for the pile driving positioning and control mechanism. As a preferred method, the newly constructed peripheral pile foundation employs static pile driving to drive precast high-strength concrete pipe piles. A ring-shaped steel track plate is pre-laid around the existing foundation 10 as the walking and working platform for the pile driver. A flange positioning collar extends outward from the aforementioned precast integral rigid guide frame, physically limiting the initial plane coordinates of the pipe pile. Simultaneously, an intelligent pile driving cap integrating a dual-axis tilt sensor and a hydraulic pressure transmitter is installed on the top of the pipe pile for real-time acquisition of position and mechanical feedback data during the pile driving process. To address the potential for sensor failure due to the large vertical load during static driving, the intelligent pile driving cap is equipped with an adaptive spherical leveling pad, and the dual-axis tilt sensor and hydraulic pressure transmitter are integrated and encapsulated within a shock-resistant isolation cavity on the side wall of the pile driving cap to isolate the vertical principal stress transmission path.

[0104] The general technical principle of the above construction mechanism lies in the static driving method, which uniformly presses the pile into the foundation, using the continuous static pressure applied by the hydraulic system to overcome the side friction and end resistance of the soil on the pile. Throughout the entire pile driving cycle, the sensor array acquires the dynamic changes in soil resistance in real time. Based on the soil consolidation and strength recovery theory in soil mechanics, and combined with the final pressing force, the ultimate bearing capacity of a single pile after the soil rests can be deduced, thereby achieving quantitative control of the foundation's compressive stiffness during the construction phase.

[0105] The multi-dimensional determination of single pile bearing capacity prediction and attitude deviation is performed through the following steps: S1001. Obtain the real-time hydraulic gauge pressure of the pile driver, the depth of the pipe pile into the soil, the horizontal displacement deviation of the pile top, and extract the soil strength time recovery coefficient.

[0106] S1002. Perform analytical calculations on the vertical ultimate bearing capacity and attitude deviation rate of a single pile. Calculate the short-term construction resistance using the mechanical transmission efficiency of the hydraulic system and the cylinder pressure, and predict the ultimate bearing capacity after the consolidation rest period based on a time-effect empirical model; simultaneously, calculate the current pile verticality deviation rate using the three-dimensional coordinate space deviation geometric formula.

[0107] S1003. A multi-dimensional determination of the pile driving termination state is made by combining structural bearing capacity requirements with allowable deviations in the specifications. This involves comprehensively verifying whether the predicted vertical ultimate bearing capacity of a single pile exceeds the design axial force extreme value, whether the penetration depth meets the bearing stratum requirements, and whether the pile verticality deviation rate is less than the maximum allowable threshold in the specifications (e.g., 1%). Pile driving can only be terminated if all three criteria are met. The relevant static load test verification process is well-known in this field and will not be elaborated here.

[0108] Based on the aforementioned pile driving mechanism, which is constrained by both real-time force feedback and geometric posture monitoring, it ensures that each precast pipe pile is accurately positioned at the design coordinates and provides reliable end and lateral support, thus constructing a stable bearing base for the subsequent pouring of the foundation concrete and the tensioning and anchoring of the prestressed system.

[0109] In this embodiment, after the new foundation cap is poured and reaches a specific threshold of design strength, the project enters the tower erection stage. As the large-capacity wind turbine tower is hoisted section by section, the vertical dead load on the foundation structure gradually increases. To provide the necessary shear friction resistance and overall stiffness to the interface between the old and new foundations in the early stages of tower assembly, the prestressed anchor cables penetrating the foundation need to be initially tensioned. However, if the full design prestress is applied directly under no-load conditions without the pressure of the upper equipment, the large active prestress will cause the concrete foundation to undergo reverse upward arching deformation, leading to tensile cracking on the top surface.

[0110] To address the issue of asynchronous evolution between prestress and structural dead load, this embodiment employs a staged tensioning process. As a preferred method, the first stage of prestressing is performed before the tower base section is hoisted. To ensure the uniformity of the tensioning process and prevent localized stress concentration caused by the anchor group effect, an intelligent hydraulic jack cluster equipped with a microcomputer communication bus is used for on-site operations. To further disclose the lower-level characteristic support of this cluster system, the intelligent hydraulic jack cluster integrates a flow proportional valve and a high-frequency displacement sensor, and is connected to the tensioning end of each channel via parallel hydraulic manifolds and equalizing rings. Considering the differences in friction between long-distance pipelines and various channels, simple hydraulic parallel connection cannot guarantee absolute displacement synchronization. The intelligent hydraulic jack cluster is also equipped with a closed-loop synchronous control host. Based on the real-time feedback of high-frequency displacement sensors, the host dynamically adjusts the opening of the flow proportional valve in the oil inlet circuit of each jack, controlling the tension displacement difference of the anchor group within the millimeter tolerance range. Thus, at the hardware level, symmetrical and synchronous pulling of the annular anchor group is achieved, transforming the dispersed point load into a stable planar uniform compressive stress on the foundation section.

[0111] The general technical principle of the aforementioned initial tensioning mechanism lies in using the load balance theory in structural mechanics as a counterweight reaction force based on the self-weight of the foundation already applied in the early stages, thereby defining a safe preload application range. During the tensioning process, it is necessary to compare the theoretical elongation with the actual elongation to implement a dual-control verification that prioritizes stress control and supplements it with elongation verification. This verifies the matching between the duct friction loss and the elastic modulus of the anchor cable at the physical constitutive level, ensuring that the anchor cable body can enter the linear elastic working state as designed.

[0112] The multi-dimensional determination of anchor cable tension and elongation is performed through the following steps: S1101. Obtain the cross-sectional area, physical length, and elastic modulus of the prestressed anchor cable, and simultaneously extract the spatial curve equation and friction coefficient of the duct.

[0113] S1102. Perform analytical calculation of the theoretical elongation during the initial tensioning stage. Based on the theory of mechanical friction, deduct the prestress friction loss caused by duct deflection and local deviations, calculate the effective average tension actually borne by the anchor cable body, and derive its theoretical elastic elongation according to Hooke's law.

[0114] S1103. A multi-dimensional assessment of the initial tensioning execution quality is conducted by combining displacement tolerance and the preset tension force ratio. A dual-control verification system is implemented, prioritizing stress control and supplementing it with elongation verification: the actual tension force must reach the set ratio range of the total design tension force (typically 0.3 to 0.5); and the deviation between the actual elongation and the theoretical elongation must be within the maximum allowable deviation limit (e.g., 6%) specified in the standard to prevent hidden failures. The calibration and regression testing of related instruments are well-known techniques in this field and will not be elaborated upon here.

[0115] Based on the aforementioned initial tensioning coordination mechanism established on the dual constraints of precise stress control and deformation tracking feedback, the anchor cable system smoothly passed the initial risk period of prestress introduction, providing a structural safety foundation for the subsequent panoramic hoisting of the tower and ultimate full-load tensioning.

[0116] In this embodiment, with the completion of the hoisting of the upper wind turbine units, the foundation structure faces extreme eccentric loads. In order to integrate the newly built static pressure pipe pile group with the existing old foundation, it is necessary to carry out the cast-in-place construction of radial ground beams and to systematically verify the overturning and pull-out resistance of the overall composite foundation.

[0117] To ensure that the interface between the new and old concrete does not undergo shear delamination under complex alternating loads, this embodiment features a targeted design for the cast-in-place connection structure of the ground beam. As a preferred method, the specific implementation of the cast-in-place ground beam structure is as follows: The area where the outer wall of the existing foundation 10 contacts the ground beam is deeply roughened using high-pressure water jets to expose fresh coarse aggregate, and then coated with an epoxy resin-based structural interface agent. Micro-expansion compensating shrinkage concrete is selected as the cast-in-place material, and distributed fiber optic temperature sensors are pre-embedded inside the ground beam. Considering that large-volume ground beams are prone to shrinkage tensile stress during the hydration heat cooling stage, intelligent temperature-controlled circulating water pipes are simultaneously laid in the core and boundary areas of the ground beam before pouring. By utilizing the volume expansion effect of the micro-expansion compensating shrinkage concrete during the curing process, combined with a real-time temperature control system—that is, when the local temperature drop rate fed back by the distributed fiber optic temperature sensor exceeds a set threshold (e.g., 2℃ / d), the temperature-regulating pump station is automatically triggered to adjust the circulating water flow rate and the continuous rigid channel for transmission.

[0118] After the aforementioned cast-in-place molding, the overall foundation enters a state of coordinated stress. The general technical principle of coordinated pull-out resistance verification lies in converting the enormous overturning moment generated by the wind turbine under extreme conditions into a local pull-out force at the bottom edge of the foundation, based on the rigid foundation assumption and deformation coordination equation. By quantifying the pull-out resistance provided by the existing foundation's self-weight, prestressed anchor cables, and the pull-out friction resistance of the new piles, a resistance balance equation under the limit state is established within a three-dimensional mechanical system. This equation determines whether the modified overall structure has the mechanical margin to resist overturning failure.

[0119] The multi-dimensional verification of pull-out bearing capacity and overall overturning tolerance is performed through the following steps: S1201. Perform timestamp alignment and extract the extreme overturning moment, total self-weight, and radial coordinates of each pull-out member relative to the centroid under the same working conditions.

[0120] S1202. Perform analytical calculations on the local maximum uplift force and the ultimate limit of the combined resistance. After deducting the contribution of self-weight to overturning resistance, distribute the remaining load moment according to the stiffness ratio and calculate the maximum local uplift force borne by the outermost tension node of the foundation; at the same time, combine the reduced pile side pull-out friction and the prestressed anchor cable tension to quantify the comprehensive ultimate limit of the combined resistance of the single node.

[0121] S1203. A multi-dimensional assessment of system safety is conducted by combining resistance partial factors and local stress tolerances. It requires that the actual comprehensive pull-out force provided by each node, after introducing a safety factor, is still greater than the local maximum pull-out force; and the ultimate overturning recovery moment of the overall foundation, after multiplying by the bearing capacity utilization factor, must be greater than the extreme input overturning moment, achieving dual constraints of microscopic strength and macroscopic stability. The relevant envelope analysis process is a well-known technique in this field and will not be elaborated upon here.

[0122] Based on the above-mentioned cast-in-place ground beam mechanism, which is based on the dual guarantee of interface modification treatment and multi-dimensional spatial stiffness verification, the outer pull-out members and the internal anchoring system realize the closed-loop synergy of mechanical boundaries, providing a stable and reliable bearing foundation for wind turbines to resist severe typhoon conditions throughout their entire life cycle.

[0123] In this embodiment, with the installation and placement of all upper equipment of the wind turbine and the concrete strength of the ground beam reaching the final design value, the foundation system enters the final process before formal grid connection and service, namely, the final locking of the prestressed anchor cables under the design tension and the overall commissioning of the foundation. To ensure that the temporary internal forces established in the previous stage of initial tensioning smoothly transition to the permanent service state, it is necessary to compensate for the prestress attenuation caused by physical factors such as anchor deformation and material creep.

[0124] To establish a long-lasting and non-degrading prestressed stress field within the foundation, this embodiment features a targeted design for the anchor cable final locking structure and integrated control mechanism. As a preferred method, the specific physical structure of the anchor cable final locking is as follows: a double-acting hydraulic jack is used for full-load pulling. After reaching the target over-tension control force and stabilizing the pressure, the permanent working clamp is forcibly pushed into the tool anchor hole by an independent pressure piston inside the jack to complete the mechanical locking. Considering that steel strands exposed to long-term environments are highly susceptible to stress corrosion cracking, after final locking, the system installs polymer sealing covers at both ends of the prestressed duct and uses vacuum-assisted grouting equipment to inject micro-expansion cement-based grout into the duct, thereby expelling residual air and effectively blocking the intrusion of oxygen and free moisture at a physical level, converting the unbonded state into a bonded, synergistic stress-bearing state.

[0125] The general technical principle of the aforementioned final locking and joint commissioning lies in quantifying the reduction of internal forces caused by the retraction of the tensioning end clamps and the long-term relaxation of the steel, based on the theory of long-term prestress loss. Based on this, a moderate over-tension force is applied during final locking for physical compensation. After locking, a dynamic test load is applied using the yaw mechanism of the wind turbine nacelle. By comparing the relationship between the unbalanced torque and the change in the foundation's micro-tilt angle, the macroscopic rotational stiffness of the modified composite foundation is verified, thereby confirming at the system level whether the old and new structures have achieved physical rigid consolidation. To support the accurate acquisition of the aforementioned joint commissioning data, the foundation's micro-tilt angle is not based on theoretical deduction, but is synchronously collected by a high-precision dual-axis tilt sensor array pre-deployed on the orthogonal axis of the top surface of the foundation ring flange, thus ensuring the physical authenticity of the test feedback.

[0126] The multi-dimensional analysis of the over-tension compensation force and the overall rotational stiffness of the foundation is performed through the following steps: S1301. Extract the measured shrinkage of the anchorage and the relaxation rate of the steel on site, and perform timestamp alignment.

[0127] S1302. Perform analytical calculations on the final locking compensation force and effective prestress. Quantitatively superimpose the transient prestress loss caused by the mechanical deformation and retraction of the anchorage, and the long-term relaxation loss of the steel strand based on age fitting. Add this loss to the total design tension of a single strand to determine the over-tensioning compensation control force required for the final locking.

[0128] S1303. A multi-dimensional assessment of the overall foundation integration is conducted by combining stiffness limits and dynamic test feedback. A real transient unbalance test torque is applied using the nacelle yaw, and this torque is divided by the rotational tilt angle of the foundation top surface, synchronously acquired by dual-axis tilt sensors, to obtain the measured anti-overturning rotational stiffness. This measured stiffness is then verified to ensure it meets the minimum design stiffness limit after introducing a dynamic safety factor, thus confirming the effectiveness of the rigid consolidation between the old and new structures. The relevant grouting process is well-known in the field and will not be elaborated upon here.

[0129] Based on the aforementioned final locking and commissioning mechanism, which is established under the dual constraints of full loss compensation and actual macroscopic stiffness measurement, the entire wind power foundation renovation project has achieved a physical reconstruction from dispersed components to a rigid whole, providing a reliable load-bearing structure for the long-term stable operation of wind turbine units in harsh environments.

Claims

1. A method for upgrading and expanding wind power foundations based on truss towers, characterized in that, The modification method includes the following steps: The existing foundation (10) was investigated, including the precast pile cap (20), the lattice tower (50) containing the steel pipe concrete column, the reinforced concrete transfer section (60), the ground beam (30) and the pile foundation; Using the existing foundation (10) as a reference, the pile foundation is driven in and the pile cap (20) is installed in a centrally symmetrical arrangement around the periphery of the existing foundation (10). Control the bottom surface of the foundation (20) to be at the same elevation as the bottom surface of the existing foundation (10); The lattice tower (50), which is assembled in a spatial A-frame eight-leg arrangement, is hoisted and assembled above the pier (20), and the conversion section (60) is installed at the top of the lattice tower (50). Install the ground beam (30) and connect the ground beam (30) to the side of the foundation (20) and the side wall of the existing foundation (10); Pass the prestressed anchor cable (70) through the reserved channel in the transition section (60) and fix the upper end, and apply a pre-tightening force to the prestressed anchor cable (70); The lower end of the prestressed anchor cable (70) passes through the anchor cable perforation reserved at the upper end of the exposed foundation ring (40) on the top of the existing foundation (10) and is locked.

2. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, The existing foundation (10) does not bear the vertical downward pressure load generated by the new unit, and the existing foundation (10) participates in resisting the overturning moment as a counterweight module; The connection between the ground beam (30) and the side of the foundation (20) and the side wall of the existing foundation (10) specifically includes: A compressible damping pad is laid between the sidewall of the existing foundation (10) and the end contact surface of the ground beam (30), and a shear-resistant steel pin is provided in the damping pad area to penetrate the interface between the old and new surfaces formed by the sidewall and the end contact surface for flexible shear connection.

3. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, The installation of the foundation (20) arranged symmetrically around the periphery of the existing foundation (10) specifically includes: Four independent foundations (20) are set up so that the geometric center of the combination of the four foundations (20) coincides with the central vertical axis of the existing foundation (10); After the ground beam (30) is installed, the load conditions along the main axis of the 0-degree plane and along the main axis of the 45-degree plane are extracted. For the pile foundation, the dual-dimensional state verification of the ultimate bearing capacity of the single pile is performed in terms of compressive and tensile strength. By comparing the calculated value of the maximum axial compressive reaction force borne by the single pile with the design value of the single pile compressive bearing capacity under the most unfavorable load combination, and the calculated value of the maximum axial tensile reaction force with the design value of the single pile tensile bearing capacity, it is ensured that the peak force of the independent pile foundation is limited to the range of the design value of the single pile compressive bearing capacity or the design value of the single pile tensile bearing capacity.

4. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, When assembling the lattice tower (50), the bottom ends of the four assembled steel-concrete main columns are anchored above the corresponding foundation (20), so that the top ends of the adjacent steel-concrete main columns are inclined to converge towards the central vertical axis of the existing foundation (10), and are connected to the upper transition section (60) by bolts. Diagonal and horizontal braces are installed within the spatial grid formed by the main steel-concrete composite column. The diagonal and horizontal braces are connected to the main steel-concrete composite column by factory prefabrication and on-site bolt splicing.

5. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, When processing the prefabricated transition section (60), the transition section (60) is made into a reinforced concrete structure; an anchor end plate is embedded inside the transition section (60), and the anchor end plate is welded and fixed to the steel bars inside the transition section (60); Meanwhile, a through steel pipe is pre-embedded inside the transition section (60) as a channel for the prestressed anchor cable (70) to pass through.

6. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, Rust removal and cleaning are performed on the part of the base ring (40) exposed on the top surface of the existing foundation (10), and multiple radial shear steel brackets are welded through the inner wall of the base ring (40) at equal intervals. High-strength, non-shrinkage structural grout is poured into the entire cross-section of the internal cavity of the foundation ring (40), so that the original hollow steel cylinder formed by the foundation ring (40) is transformed into a solid composite section in which the steel shell and the internal grout work together to bear the force. An annular pressure-bearing steel pad is added to the outside of the top flange of the base ring (40). The annular pressure-bearing steel pad is fastened by high-strength bolts through the existing flange hole at the top of the base ring (40). Epoxy resin structural adhesive is injected between the annular pressure-bearing steel pad and the top flange of the base ring (40).

7. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, The prestressed anchor cable (70) is a prestressed steel strand, and the upper end of the prestressed anchor cable (70) is embedded in the working anchor inside the transition section (60) for locking; The lower end of the prestressed anchor cable (70) passes through the anchor cable hole reserved at the upper end of the foundation ring (40) on the top of the existing foundation (10) and is locked in the anchorable structure of the foundation ring (40) to reinforce the structure between the foundation ring (40) and the transition section (60). A high-density polyethylene corrugated pipe is wrapped around the free section of the prestressed anchor cable (70), and the inside of the corrugated pipe is filled with anti-corrosion grease.

8. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, The passageways of the prestressed anchor cables (70) inside the foundation (20) are arranged in a multi-ring concentric array, so that the outer ring anchor cable group is arranged close to the stress edge of the foundation (20), and the inner ring anchor cable group is evenly distributed in the core area within the projection plane of the existing foundation (10). Below the working anchor at the upper end of each ring of anchor cables, a continuous annular pressure-bearing steel plate is pre-embedded, and a spiral anti-crack steel mesh is densely arranged in the concrete body of the foundation (20) below the annular pressure-bearing steel plate.

9. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, During the construction process of the pile foundation, a static pile driving process is used to drive precast high-strength concrete pipe piles as new peripheral pile foundations, and a precast integral rigid guide frame is used to limit the initial plane coordinates of the pipe piles. A smart pile cap integrating a dual-axis tilt sensor and a hydraulic pressure transmitter is installed on the top of the pipe pile. An adaptive spherical leveling pad is set inside the smart pile cap, and the dual-axis tilt sensor and the hydraulic pressure transmitter are integrated and encapsulated in the shockproof isolation cavity of the side wall of the smart pile cap.

10. The method for upgrading and expanding wind power foundations based on truss towers as described in claim 1, characterized in that, The prestressed anchor cable (70) is prestressed by a graded tensioning process, and the first stage of prestressing is carried out before the bottom section of the lattice tower (50) is hoisted. The tensioning operation uses an intelligent hydraulic jack cluster equipped with a microcomputer communication bus. The intelligent hydraulic jack cluster integrates a flow proportional valve and a high-frequency displacement sensor, and is connected to the upper end of each channel of the prestressed anchor cable (70) through parallel hydraulic manifolds and equalizing rings. The intelligent hydraulic jack cluster is connected to a closed-loop synchronous control host, which dynamically adjusts the opening degree of the flow proportional valve in the oil inlet circuit of each jack based on the real-time feedback of the high-frequency displacement sensor.

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