Multistage flow guide filling structure of asymmetric scouring pit of offshore wind power pile foundation and construction method

Abstract

The invention relates to the field of offshore wind power engineering, and discloses a multistage flow guide filling structure of an asymmetric scouring pit of an offshore wind power pile foundation and a construction method, the structure comprises a fixed pile, a support pile, a foundation layer, a backfill layer and a V-shaped cover; the lower ends of the fixing piles penetrate through a seabed soft soil layer and are embedded into a seabed bearing layer, the top ends of the supporting piles are arranged in the soft soil layer, and the bottom ends are embedded into the seabed bearing layer. The V-shaped cover is of an annular structure defined by a plurality of surrounding plates, the surrounding plates are rotationally connected with the fixing piles through limiting rings, the surrounding plates with the V-shaped sections are composed of long plates and short plates, and ripraps and coarse sand are filled in preset spaces between the long plates and the fixing piles on the V-shaped cover to form a gravity anchoring structure to stabilize the V-shaped cover to resist water flow upward pulling force. And through holes allowing ripraps to penetrate through are formed in the short plates and the long plates. By arranging the V-shaped cover and filling riprap and coarse sand, the expansion speed of the scouring pit can be effectively reduced, the influence on the wind power pile foundation is reduced, and long-term stable operation of an offshore wind power project is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power engineering, and in particular to a multi-stage diversion filling structure and a construction method for an asymmetric scour pit of an offshore wind power pile foundation. Background Art

[0002] In offshore wind turbine projects, wind turbine pile foundations are often subjected to long-term scouring by seawater currents, forming asymmetric scour pits. These scour pits can seriously affect the stability of wind turbine pile foundations, reducing their bearing capacity and durability, and thus threatening the safe operation of offshore wind turbine projects. Traditional wind turbine pile foundation construction structures often struggle to effectively address the asymmetric development of scour pits, making it difficult to promptly and effectively fill and compensate for them. This makes maintenance difficult, leading to the continued expansion of scour pits and increasing the risk to pile foundations.

[0003] Therefore, it is necessary to propose a new solution to the above problems. Summary of the Invention

[0004] The present invention overcomes the deficiencies of the prior art and provides a multi-stage diversion filling structure and a construction method for an asymmetric scour pit of an offshore wind power pile foundation.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation, comprising fixed piles driven vertically into the seabed, support piles arranged in an annular array outside the fixed piles, a foundation layer placed on top of the support piles, a backfill layer placed on top of the foundation layer, and a V-shaped cover arranged on top of the backfill layer; the lower end of the fixed pile penetrates the soft soil layer of the seabed and is embedded in the seabed bearing layer; the top end of the support pile is placed in the soft soil layer, and the bottom end is embedded in the seabed bearing layer; the foundation layer and the backfill layer are both placed in the soft soil layer; the V-shaped cover is composed of several The enclosure forms an annular structure, and several of the enclosures are rotatably connected to the fixed piles through limiting rings fixedly connected to the fixed piles. The cross-section of the enclosure is V-shaped and consists of a long plate and a short plate fixedly connected to each other. The long plate is located on the inner side close to the fixed piles, and the short plate is placed on the outer side away from the fixed piles. The preset space on the V-shaped cover and between the long plate and the fixed piles is filled with riprap and coarse sand to form a gravity anchoring structure to stabilize the V-shaped cover to resist the upward pulling force of the water flow; through holes are provided on both the short plate and the long plate for the passage of riprap, and the dynamic filling of the subsequent new scouring pit is achieved through the through holes.

[0006] In a preferred embodiment of the present invention, the support piles are a multi-layer annular array structure, including inner ring piles, middle ring piles, and outer ring piles; the inner ring piles are concentrically arranged with the fixed piles, and the middle ring piles are located between the inner ring piles and the outer ring piles; the support piles of adjacent levels are staggered; the support piles are made of underwater self-compacting concrete.

[0007] In a preferred embodiment of the present invention, the base layer is a cement bonding layer, and the base layer is connected to the support piles through a grouting process to form a reinforcement system.

[0008] In a preferred embodiment of the present invention, the backfill layer is composed of a layered compacted structure of fine sand and coarse sand, specifically comprising: a fine sand layer disposed near the base layer, with a particle size ranging from 0.075 to 2 mm, for improving cohesion and shear strength; a coarse sand layer disposed outside the fine sand layer, with a particle size ranging from 2 to 10 mm, for controlling permeability and reducing porosity;

[0009] In a preferred embodiment of the present invention, the diameter of the through holes ranges from 5 to 20 cm, and the distribution density of the through holes is adjusted according to the shape of the scour pit.

[0010] In a preferred embodiment of the present invention, the density of the riprap and coarse sand filled inside the V-shaped cover is greater than 1500 kg / m 3 .

[0011] In a preferred embodiment of the present invention, the limiting ring includes a ring body fixedly connected to the fixed pile, and a plurality of rotating rings fixedly connected to the outer ring surface of the ring body; a plurality of filling holes are opened near the outer edge of the ring body for filling the preset space between the fixed pile and the long plate with stones and fine sand.

[0012] In a preferred embodiment of the present invention, a geogrid is provided at the bottom of the backfill layer and fixed to the support piles by anchor nails to prevent the backfill layer from sliding laterally;

[0013] The top of the backfill layer is provided with an anti-scour net which is made of a composite of a polyethylene woven net and an underwater curing resin. The porosity of the anti-scour net is controlled at 30%-40%.

[0014] The present invention also provides a construction method for a multi-stage diversion filling structure of an asymmetric scour pit of an offshore wind power pile foundation, which specifically includes the following steps:

[0015] S1: Drive the fixed piles of the wind turbine foundation vertically into the seabed to the designed depth, ensuring that their lower ends penetrate the soft soil layer and embed into the seabed bearing layer;

[0016] S2: Use a hydraulic pile driver to install inner ring piles, middle ring piles and outer ring piles in sequence;

[0017] S3: The grouting pipe is lowered to the designed depth along with the support pile construction drill rod. The reverse circulation grouting process is used to inject cement slurry into the soft soil layer beside the support pile through the grouting pipe to form the base layer.

[0018] S4: Lay a fine sand layer on top of the base layer, compact it, and then lay a coarse sand layer to form a backfill layer;

[0019] S5: The coaming of the V-shaped cover is rotatably connected to the fixed pile via a limiting ring fixedly connected to the fixed pile, and a mixture of riprap and coarse sand is filled in the pre-set space between the long plate and the fixed pile on the V-shaped cover through the filling hole opened on the ring body of the limiting ring to form a gravity anchoring structure;

[0020] S6: Circularly distribute counterweights on the upper ends of the riprap and coarse sand in the V-shaped cover, wherein the counterweights are one or more of sandbags, concrete blocks, and natural stones.

[0021] In a preferred embodiment of the present invention, in step S1, the penetration depth of the fixed pile must satisfy that the pile end enters the seabed bearing layer ≥ 3 times the pile diameter, and the ratio of the soft soil layer thickness around the pile to the pile diameter is controlled within the range of 5:1-8:1;

[0022] In step S2, adjacent pile positions are staggered at a phase angle of 30°-45°; the spacing between the inner ring piles and the fixed piles is 1.2-1.5 times the pile diameter, and the radial spacing between the rings is 0.8-1 times the pile diameter; the slump of the underwater self-compacting concrete is controlled at 220±20mm, and the concrete is cured for at least 72 hours after pouring before proceeding to the next step;

[0023] In step S3, the grouting slurry water-cement mass ratio is 0.6:1-0.8:1, the grouting pressure is 0.3-0.5 MPa; the grouting pipe lifting rate is ≤0.5 m / min, the grouting volume per meter is ≥150 L, and the thickness of the formed continuous cemented body is ≥50 cm;

[0024] In step S4, the fine sand layer is laid in three steps, with a single layer thickness of 30-35 cm, and is compacted by underwater vibrating rammer to a compaction degree of ≥92%; the coarse sand layer is laid in two steps, with a single layer thickness of 40-45 cm. Before laying the fine sand layer, a bidirectional geogrid is laid at the bottom of the backfill layer and locked to the top of the support pile by stainless steel anchor nails;

[0025] In step S5, the riprap filling is made by mixing crushed stones with a particle size of 5-20 cm and coarse sand in a volume ratio of 4:1, with a filling density of ≥1500 kg / m 3 .

[0026] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0027] (1) This application forms a three-dimensional protection system from deep foundation to surface filling by constructing a multi-level combination of "fixed piles-support piles-base layer-backfill layer-V-shaped cover". The fixed piles are embedded in the bearing layer to provide core anchoring, and the annular staggered layout of the support piles enhances the overall anti-overturning ability; the cement bonding process of the base layer solidifies the soft soil layer, while the fine / coarse sand layer of the backfill layer is compacted in layers to improve the shear resistance; the V-shaped cover realizes the dynamic migration of riprap through the through-hole design. It significantly reduces the asymmetry of the scour pit; compared with the traditional riprap method of the prior art, this structure forms a continuous and stable protective layer through multi-level collaboration, and this construction method is simple and easy to construct.

[0028] (2) This application can effectively reduce the expansion speed of the scour pit and reduce the impact on the wind turbine pile foundation by setting up a V-shaped cover and filling the V-shaped cover with riprap and coarse sand. Riprap and coarse sand are filled in the preset space between the long plate and the fixed pile on the V-shaped cover to form a gravity anchoring structure to stabilize the V-shaped cover to resist the upward pull of the water flow, and through holes for riprap to pass through are opened on both the short plate and the long plate, which can realize the dynamic filling of new scour pits in the future. Compared with traditional structures, it can significantly reduce the asymmetry of the scour pit, reduce the risk of pile foundation tilting, ensure the long-term stable operation of offshore wind power projects, and has good application prospects.

[0029] (3) The fixed piles of the present application cooperate with the supporting piles of the annular array, and the supporting piles of adjacent layers are staggered at phase angles. Such a structural layout enhances the overall bearing capacity and stability of the foundation, and provides a solid support base for the superstructure. When dealing with the problem of asymmetric scour pits in offshore wind power pile foundations, compared with the traditional single pile foundation structure, it can more evenly distribute the load and reduce the local stress concentration of the pile foundation caused by scour, further improving the stability and durability of the wind power pile foundation in complex marine environments, reducing the risk of pile foundation tilting or damage, and effectively ensuring the long-term reliable operation of offshore wind power projects.

[0030] (4) The backfill layer of this application adopts a structure of fine sand and coarse sand layered and compacted, with a bidirectional geogrid pre-laid at the bottom and an anti-scouring net set on the top. The fine sand layer is close to the base layer. Through layered laying and underwater vibration compaction, the cohesion and shear strength are improved; the coarse sand layer helps to control the permeability coefficient and reduce the porosity. The bidirectional geogrid is locked with the top of the support pile to effectively prevent the lateral slippage of the backfill layer; the anti-scouring net can prevent the backfill layer from being scour-damaged by seawater. Compared with the traditional backfill method, this structural design can significantly improve the stability and anti-scouring performance of the backfill layer, reduce the loss of backfill material, and further provide good support and protection for the wind power pile foundation, ensuring the safety and stability of offshore wind power projects in complex marine environments and extending the service life of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0032] Figure 1 It is a structural schematic diagram of a preferred embodiment of the present invention;

[0033] Figure 2 is a distribution diagram of support piles in a preferred embodiment of the present invention;

[0034] In the figure: 1. Fixed piles; 2. Support piles; 3. Base layer; 4. Backfill layer; 5. V-shaped cover. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0037] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0038] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0039] Example structure:

[0040] like Figure 1 and Figure 2 As shown, a multi-stage diversion and filling structure for asymmetric scour pits in offshore wind turbine pile foundations is used to address the problem of asymmetric scour pits in offshore wind turbine pile foundations. The structure includes fixed piles 1 driven vertically into the seabed, support piles 2 arranged in a circular array outside the fixed piles 1, a foundation layer 3 placed on top of the support piles 2, a backfill layer 4 placed on top of the foundation layer 3, and a V-shaped cover 5 provided on top of the backfill layer 4.

[0041] Preferably, the lower end of the fixed pile 1 penetrates the soft soil layer of the seabed and is embedded in the seabed bearing layer. The fixed pile 1 serves as the core supporting part of the entire structure and penetrates into the harder bearing layer to ensure the stability of the wind power equipment.

[0042] Preferably, a multi-layer annular array of support piles 2 is arranged around the outside of the fixed piles 1 according to a specific rule to form a foundation reinforcement structure, including inner ring piles, middle ring piles and outer ring piles. They are concentrically arranged with the fixed piles 1, and the adjacent layers are staggered at a phase angle of 30° to 45°. The support piles 2 are prepared using underwater self-compacting concrete, and rely on their own weight and self-compactness to self-compact in the underwater environment to form a stable support structure; specifically, the top of the support pile 2 is placed in the soft soil layer, and the bottom end is embedded in the bearing layer, cooperating with the fixed piles 1 to bear the load of the superstructure and transfer its force to the deep bearing layer.

[0043] Preferably, the base layer 3 is composed of a cement bonding layer and is connected to the support pile 2 through a grouting process to form a reinforcement system. When preparing the base layer, the grouting pipe is sunk to the designed depth along with the construction drill rod of the support pile 2. Then, a reverse circulation grouting process is used to pour cement slurry with a water-cement ratio between 0.6:1 and 0.8:1 into the soft soil layer beside the support pile 2 at a pressure of 0.3MPa to 0.5MPa. The grouting pipe is raised at a rate not exceeding 0.5m / min to ensure that the grouting volume per meter is not less than 150L, ​​thereby forming a continuous cementing body with a thickness of not less than 50cm, thereby enhancing the bearing capacity and stability of the foundation.

[0044] Preferably, the backfill layer 4 is located above the base layer 3 and adopts a structure of layered compaction of fine sand and coarse sand; the fine sand layer is close to the base layer 3, with a particle size range of 0.075-2mm, and is laid three times with a thickness of 30-35cm each time, and compacted to a compaction degree of not less than 92% by underwater vibration rammer, so as to improve cohesion and shear strength; the coarse sand layer is located outside the fine sand layer, with a particle size of 2-10mm, and is laid twice with a thickness of 40-45cm each time. Its larger particle size helps to control the permeability coefficient and reduce the porosity; a bidirectional geogrid is pre-laid at the bottom of the backfill layer 4 and locked with the top of the support pile 2 using stainless steel anchor nails to prevent the backfill layer 4 from lateral slippage; an anti-scouring net is set on the top of the backfill layer 4, which is composed of a composite of polyethylene woven mesh and underwater curing resin, and the porosity is controlled at 30%-40% to prevent seawater from scouring and damaging the backfill layer 4.

[0045] Preferably, a V-shaped cover 5 is located on the upper part of the backfill layer 4 and is rotatably connected to the fixed pile 1 through a limiting ring fixedly connected to the fixed pile 1. The V-shaped cover 5 is an annular structure composed of multiple panels. The cross-section of the panel is V-shaped and is formed in one piece by a long plate and a short plate. The long plate is close to the fixed pile 1, and the short plate is toward the outside of the fixed pile 1. Furthermore, the limiting ring is composed of a ring body fixedly connected to the fixed pile 1 and a plurality of rotating rings welded to the outer annular surface of the ring body. Filling holes are opened near the outer edge of the ring body. Riprap and coarse sand are filled into the preset space inside the V-shaped cover 5 and between the long plate and the fixed pile 1 through these filling holes. The riprap used has a particle size of 5-20 cm and is mixed with coarse sand at a volume ratio of 4:1, with a filling density of 1500 kg / m 3 The above structure constructs a gravity anchoring structure to resist the upward pull of water flow. At the same time, through holes with a diameter of 5-20 cm are opened on the short plate and the long plate, and the distribution density is adjusted according to the shape of the scour pit. After the through holes are set, the riprap and coarse sand in the space between the V-shaped cover 5, the V-shaped cover 5 and the fixed pile 1, and the space outside the V-shaped cover 5 can form a flow. Due to the presence of the short plate of the V-shaped cover 5, subsequent water flow will form a horseshoe-shaped vortex at the contact surface between the short plate and the backfill layer 4, carrying away the filling sand in the backfill layer 4 and forming a new scour pit. Due to the presence of the through holes in the V-shaped cover 5, the filling riprap and coarse sand placed between the V-shaped cover 5 and the fixed pile 1 gradually deviate into the newly formed scour pit outside the short plate and fill it, thereby reducing the expansion speed of the scour pit and reducing the impact of the formation of the scour pit on the wind turbine pile foundation. This dynamic scour pit compensation mechanism ensures that the entire structure can stably protect the wind turbine pile foundation in the long term and resist water scour in complex marine environments.

[0046] The exemplary structure of the present application is centered on a fixed pile 1 vertically embedded in the seabed bearing layer, the lower end of which penetrates the soft soil layer and is anchored in the hard bedrock, providing rigid support for the upper structure; the inner ring, middle ring and outer ring support piles 2 surrounding the outside of the fixed pile 1 are cast with underwater self-compacting concrete, and are arranged at a staggered phase angle of 30° to 45° to form a mesh reinforcement system, which effectively transfers the load to the deep bearing layer by virtue of the bonding effect between the self-compacting material and the soft soil layer; the cement bond formed by the reverse circulation grouting process of the base layer 3 not only enhances the overall shear strength of the foundation, but also blocks the erosion path of the deep soil by the water flow through the infiltration control of the coarse sand layer; the V-shaped cover 5 on the top of the backfill layer 4 is rotatably connected to the fixed pile 1 through a limit ring, and its V-shaped cross-section enclosure structure has a through hole on the short plate side, and a mixture of riprap and coarse sand is injected into the filling hole to construct a gravity anchoring system to resist the uplift force of the water flow. When seawater scours the contact surface between the short plate and the backfill layer 4 to form a horseshoe-shaped vortex, carrying away the filling sand to form a new scour pit, the through holes of the V-shaped cover 5 guide the filling material to deviate toward the new scour pit, and compensate for the scour loss through the inertia of the coarse particles of the riprap and the fluidity of the coarse sand, while the high cohesion of the fine sand layer ensures the stability of the unscoured area, ultimately forming a triple protection effect of dynamic filling, local compensation, and overall reinforcement.

[0047] The structure of the present application realizes the synergistic effect of full-level protection from deep foundation to surface layer through the rigid support of fixed piles 1, load transfer and anti-scour dispersion of supporting piles 2, bonding enhancement of foundation layer 3, layered anti-seepage of backfill layer 4 and dynamic compensation mechanism of V-shaped cover 5, effectively suppresses the expansion rate of scour pits, and significantly extends the service life of wind turbine pile foundations in strong flow rate environments; through the combination of fixed piles 1, annular array of supporting piles 2, foundation layer 3, backfill layer 4 and V-shaped cover 5, the entire multi-stage diversion filling structure can effectively deal with the problem of asymmetric scour pits of offshore wind turbine pile foundations, improve the stability and durability of wind turbine pile foundations, and ensure the safe operation of offshore wind power projects.

[0048] Exemplary methods:

[0049] The construction method of a multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation comprises the following steps:

[0050] S1: Drive the fixed pile 1 of the wind turbine pile foundation vertically into the seabed to the designed depth, ensuring that its lower end penetrates the soft soil layer and embeds into the seabed bearing layer;

[0051] S2: Use a hydraulic pile driver to install inner ring piles, middle ring piles and outer ring piles in sequence;

[0052] S3: The grouting pipe is lowered to the designed depth along with the construction drill rod of the support pile 2. The cement slurry is poured into the soft soil layer beside the support pile 2 through the grouting pipe using the reverse circulation grouting process to form the base layer 3;

[0053] S4: Lay a fine sand layer on top of the base layer 3, and after compaction, lay a coarse sand layer to form a backfill layer 4;

[0054] S5: The enclosure of the V-shaped cover 5 is rotatably connected to the fixed pile 1 through a limiting ring fixedly connected to the fixed pile 1, and a mixture of riprap and coarse sand is filled in the pre-set space between the long plate and the fixed pile 1 on the V-shaped cover 5 through the filling hole opened on the ring body of the limiting ring to form a gravity anchoring structure;

[0055] S6: Circularly distribute counterweights on the upper ends of the riprap and coarse sand in the V-shaped cover 5. The counterweights can be one or more of sandbags, concrete blocks, and natural stones.

[0056] Preferably, in step S1, the penetration depth of the fixed pile 1 must satisfy that the pile end enters the seabed bearing layer ≥ 3 times the pile diameter, and the ratio of the soft soil layer thickness around the pile to the pile diameter is controlled within the range of 5:1-8:1;

[0057] Preferably, in step S2, adjacent pile positions are staggered at a phase angle of 30°-45°; the spacing between the inner ring piles and the fixed piles 1 is 1.2-1.5 times the pile diameter, and the radial spacing between the rings is 0.8-1 times the pile diameter; the slump of the underwater self-compacting concrete is controlled at 220±20mm, and the concrete is cured for at least 72 hours after pouring before proceeding to the next step;

[0058] Preferably, in step S3, the water-cement mass ratio of the grouting slurry is 0.6:1-0.8:1, the grouting pressure is 0.3-0.5 MPa; the grouting pipe lifting rate is ≤0.5 m / min, the grouting volume per meter is ≥150 L, and the thickness of the formed continuous cemented body is ≥50 cm;

[0059] Preferably, in step S4, the fine sand layer is laid in three times, with a single layer thickness of 30-35 cm, and is compacted by underwater vibrating rammer to a compaction degree of ≥92%; the coarse sand layer is laid in two times, with a single layer thickness of 40-45 cm, and before laying the fine sand layer, a bidirectional geogrid is laid at the bottom of the backfill layer 4 and locked to the top of the support pile 2 by stainless steel anchor nails;

[0060] Preferably, in step S5, the riprap filling is made by mixing crushed stones with a particle size of 5-20 cm and coarse sand in a volume ratio of 4:1, with a filling density of ≥1500 kg / m 3 .

[0061] Example 1:

[0062] In the construction of a certain offshore wind farm, the above-mentioned multi-stage diversion filling structure and construction method were adopted. The specific parameters and steps are as follows:

[0063] S1. Fixed pile 1 uses a 2-meter diameter steel pipe pile, which is driven vertically into the seabed to the designed depth, ensuring that the pile tip enters the seabed bearing layer for 6 meters (3 times the pile diameter). At the same time, the thickness of the soft soil layer around the pile is controlled to 10 meters;

[0064] S2. Use a hydraulic pile driver to sequentially install the inner, middle, and outer ring piles. Support piles 2 are made of underwater self-compacting concrete, with a slump strictly controlled at 240 mm. Adjacent piles are staggered at a 35° phase angle to enhance the overall stability of the structure. The distance between the inner ring piles and fixed piles 1 is 2.8 meters (1.4 times the pile diameter), and the radial spacing between the rings is 1.6 meters (0.8 times the pile diameter). After pouring, support piles 2 are cured for 72 hours to ensure that the concrete reaches the designed strength before proceeding to the next construction step.

[0065] S3. Construction of the foundation layer 3 is carried out. The grouting pipe is lowered to the designed depth along with the drill rod for the support pile 2. A reverse circulation grouting process is used to inject cement slurry with a water-cement ratio of 0.7:1 into the soft soil layer beside the support pile 2 through the grouting pipe. The grouting pressure is controlled at 0.4 MPa, and the grouting pipe is raised at a rate of 0.4 m / min. The grouting volume per meter is strictly controlled to 180 L, forming a continuous cemented body with a thickness of 60 cm to enhance the bearing capacity and stability of the foundation layer 3.

[0066] S4. Construct the backfill layer 4. First, lay a fine sand layer on the upper part of the base layer 3. The fine sand layer has a particle size range of 0.075-2 mm and is laid in three layers, each layer is 30 cm thick and compacted with an underwater vibratory tamper until the compaction reaches 95%. Then, lay a coarse sand layer with a particle size range of 2-10 mm and also lay it in two layers, each layer is 40 cm thick. Before laying the fine sand layer, lay a bidirectional geogrid at the bottom of the backfill layer 4 and lock it to the top of the support pile 2 with stainless steel anchor nails to prevent the backfill layer 4 from sliding sideways.

[0067] S5. Install the V-shaped cover 5. Rotate the V-shaped cover 5, which consists of the enclosure panels, to the fixed pile 1 through a limiting ring. The limiting ring consists of a ring body fixedly connected to the fixed pile 1 and multiple rotating rings welded to the outer ring surface of the ring body. Filling holes are provided near the outer edge of the ring body. Through these filling holes, a mixture of riprap and coarse sand is filled into the pre-set space inside the V-shaped cover 5 and between the long plate and the fixed pile 1. The riprap particle size is 10-15 cm, and it is mixed with the coarse sand in a volume ratio of 4:1, with a filling density of 2000±50 kg / m 3 , forming a gravity anchoring structure to effectively resist the uplift force of water flow; at the same time, through holes with a diameter of 10cm are opened on the short and long boards to facilitate dynamic filling when new scour pits are formed, ensuring the long-term stability of the entire structure;

[0068] S6. Place weighted sandbags with a mass of 30-50 kg / bag in a circular pattern on the upper ends of the riprap and coarse sand in the V-shaped cover 5 to strengthen gravity anchoring.

[0069] Two months after construction, the above construction area was surveyed using the following methods:

[0070] High-resolution sonar (accuracy ±5cm) was used to conduct three-dimensional topographic mapping within a 50m radius around the pile foundation, focusing on monitoring the shape and depth changes of scour pits;

[0071] The density distribution of the filling material inside and outside the V-shaped cover 5 is measured by a radioactive density meter to verify the dynamic migration path of the riprap;

[0072] Install inclination sensors (accuracy 0.01°) and strain gauges on the top of fixed pile 1 and support pile 2 to record structural displacement and stress changes;

[0073] The flow status of riprap at the through hole and the integrity of the anti-scour net were directly photographed by underwater robot (ROV).

[0074] The conclusions obtained through the above detection method are as follows:

[0075] The above detection method found that a local scour pit with a maximum depth of 0.6m was formed on the upstream side (mainstream direction) of the pile foundation (the original design allowable value was ≤1.5m), while the scour depth on the downstream side was only 0.2m, significantly reducing the asymmetry (traditional structures usually have a difference of more than 1.5m).

[0076] Three new scour pits (depth 0.3-0.4m) appeared on the outside of the short plate of the V-shaped cover 5, but riprap and coarse sand accumulations flowing out of the through holes were visible at the bottom of the pits, and the pit expansion rate was ≤5cm / month;

[0077] The gamma ray test showed that the density of the riprap inside the V-shaped cover 5 increased from the initial 2000±50kg / m 3 Reduced to 1850±50kg / m 3 The density of riprap in the new scouring pit outside the short plate is 1600kg / m 3 , confirming that the riprap migrated to the scour area through the through-hole;

[0078] ROV images show that coarse sand continues to flow out of the through hole, forming a natural filter layer to prevent the loss of fine sand. The fine sand loss rate of backfill layer 4 is less than 3%.

[0079] Through the above embodiments, the problem of asymmetric scour pits in the wind turbine pile foundation of the offshore wind farm is effectively solved, the stability and durability of the pile foundation are significantly improved, and a strong guarantee is provided for the safe operation of the offshore wind power project.

[0080] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation, characterized in that: It comprises fixed piles (1) driven vertically into the seabed, support piles (2) arranged in an annular array outside the fixed piles (1), a base layer (3) placed on top of the support piles (2), a backfill layer (4) placed on top of the base layer (3), and a V-shaped cover (5) arranged on top of the backfill layer (4); The lower end of the fixed pile (1) penetrates the soft soil layer of the seabed and is embedded in the bearing layer of the seabed; The top end of the support pile (2) is placed in the soft soil layer, and the bottom end is embedded in the seabed bearing layer; The base layer (3) and the backfill layer (4) are both placed in a soft soil layer; The V-shaped cover (5) is formed of a ring structure formed by a plurality of panels, and the plurality of panels are rotatably connected to the fixed pile (1) through a limit ring fixedly connected to the fixed pile (1). The panel cross section is V-shaped and consists of a long plate and a short plate fixedly connected to each other. The long plate is located on the inner side close to the fixed pile (1), and the short plate is located on the outer side away from the fixed pile (1). The preset space between the long plate and the fixed pile (1) on the V-shaped cover (5) is filled with riprap and coarse sand, so as to form a gravity anchoring structure to stabilize the V-shaped cover (5) and resist the upward pull of the water flow. The short plate and the long plate are both provided with through holes for riprap to pass through, and the dynamic filling of subsequent new scouring pits can be achieved through the through holes.

2. The multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 1, characterized in that: The support piles (2) are a multi-layered annular array structure, including inner ring piles, middle ring piles, and outer ring piles; The inner ring pile and the fixed pile (1) are arranged concentrically, and the middle ring pile is located between the inner ring pile and the outer ring pile; The support piles (2) at adjacent levels are staggered; The support piles (2) are prepared using underwater self-compacting concrete.

3. The multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 1 is characterized by: The base layer (3) is a cement bonding layer, and the base layer (3) is connected to the support piles (2) through a grouting process to form a reinforcement system.

4. The multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 1, characterized in that: The backfill layer (4) is composed of a layered compacted structure of fine sand and coarse sand, specifically comprising: a fine sand layer arranged close to the base layer (3), with a particle size ranging from 0.075 to 2 mm, for improving cohesion and shear strength; and a coarse sand layer arranged outside the fine sand layer, with a particle size ranging from 2 to 10 mm, for controlling permeability and reducing porosity.

5. The multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 1 is characterized by: The diameter of the through holes ranges from 5 to 20 cm, and the distribution density of the through holes is adjusted according to the shape of the scour pit.

6. The multi-stage diversion filling structure and construction method for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 1, characterized in that: The density of the riprap and coarse sand filled inside the V-shaped cover (5) is greater than 1500kg / m 3 .

7. The multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 1, characterized in that: The limiting ring comprises a ring body fixedly connected to the fixed pile (1), and a plurality of rotating rings fixedly connected to the outer ring surface of the ring body; a plurality of filling holes are opened near the outer edge of the ring body for filling the preset space between the fixed pile (1) and the long board with riprap and fine sand.

8. The multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 1, characterized in that: A geogrid is provided at the bottom of the backfill layer (4) and fixed to the support piles (2) via anchor nails to prevent the backfill layer (4) from sliding sideways; The top of the backfill layer (4) is provided with an anti-scour net, which is made of a composite of a polyethylene woven net and an underwater curing resin. The porosity of the anti-scour net is controlled at 30%-40%.

9. A multi-stage diversion and filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to any one of claims 1 to 8, characterized in that: The construction method of the multi-stage diversion filling structure for the asymmetric scour pit of the offshore wind power pile foundation comprises the following steps: S1: driving the fixed piles (1) of the wind turbine pile foundation vertically into the seabed to the designed depth, ensuring that the lower ends thereof penetrate the soft soil layer and embed into the seabed bearing layer; S2: Use a hydraulic pile driver to install inner ring piles, middle ring piles and outer ring piles in sequence; S3: sinking the grouting pipe together with the construction drill rod of the support pile (2) to the designed depth, and using the reverse circulation grouting process to pour cement slurry into the soft soil layer beside the support pile (2) through the grouting pipe to form the base layer (3); S4: Laying a fine sand layer on the upper part of the base layer (3), and after compaction, laying a coarse sand layer to form a backfill layer (4); S5: The enclosure of the V-shaped cover (5) is rotatably connected to the fixed pile (1) through a limiting ring fixedly connected to the fixed pile (1), and a mixture of riprap and coarse sand is filled in the pre-set space between the long plate and the fixed pile (1) on the V-shaped cover (5) through a filling hole opened on the ring body of the limiting ring to form a gravity anchoring structure; S6: arranging counterweights in a circular manner on the upper ends of the riprap and coarse sand in the V-shaped cover (5), wherein the counterweights are one or more of sandbags, concrete blocks, and natural stones.

10. The construction method of a multi-stage diversion filling structure for an asymmetric scour pit of an offshore wind turbine pile foundation according to claim 9, characterized in that: In step S1, the penetration depth of the fixed pile (1) must satisfy that the pile end enters the seabed bearing layer ≥ 3 times the pile diameter, and the ratio of the soft soil layer thickness around the pile to the pile diameter is controlled within the range of 5:1-8:1; In step S2, adjacent pile positions are staggered at a phase angle of 30°-45°; the spacing between the inner ring piles and the fixed piles (1) is 1.2-1.5 times the pile diameter, and the radial spacing between the rings is 0.8-1 times the pile diameter; the slump of the underwater self-compacting concrete is controlled at 220±20mm, and the next process can be carried out after curing for at least 72 hours after pouring; In step S3, the grouting slurry water-cement mass ratio is 0.6:1-0.8:1, the grouting pressure is 0.3-0.5 MPa; the grouting pipe lifting rate is ≤0.5 m / min, the grouting volume per meter is ≥150 L, and the thickness of the formed continuous cemented body is ≥50 cm; In step S4, the fine sand layer is laid in three times, with a single layer thickness of 30-35 cm, and is compacted by underwater vibration rammer to a compaction degree of ≥92%; the coarse sand layer is laid in two times, with a single layer thickness of 40-45 cm, and before laying the fine sand layer, a bidirectional geogrid is laid at the bottom of the backfill layer (4) and locked with the top of the support pile (2) by stainless steel anchor nails; In step S5, the riprap filling is made by mixing crushed stones with a particle size of 5-20 cm and coarse sand in a volume ratio of 4:1, with a filling density of ≥1500 kg / m 3 .

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