Bird nest type pile foundation anti-scouring system and construction method thereof

Abstract

The invention relates to offshore pile foundation engineering. The invention aims to provide the bird nest type pile foundation anti-scouring system and the construction method thereof. The pile foundation anti-scour system can promote redeposition of suspended sediment, weaken development of scour pits, reduce the flow velocity of seawater and reduce the water flow scour capacity. According to the technical scheme, the bird nest type pile foundation anti-scouring system is characterized in that the outer contour of the bird nest type anti-scouring system is of a circular structure so that the bird nest type pile foundation anti-scouring system can be suitable for sea areas with various flow field characteristics. An inner ring beam and an outer ring beam which are coaxially arranged with a pile foundation are arranged at the bottom of the system, a radial bottom beam with the pile foundation as the center is arranged between the inner ring beam and the outer ring beam for connection, and the length of the bottom beam is about 1.5-3 times of the pile diameter (specifically, the length of a scouring pit can be predicted and calculated).

Description

Technical Field

[0001] The invention relates to an offshore pile foundation project, in particular to a bird's nest type pile foundation anti-scouring system and a construction method thereof. Background Art

[0002] In my country's offshore waters, loose sand and silt are common types of bottom components. Such sand and silt are easily scour and eroded by waves and tidal natural hydrodynamics due to the weak bonding between the sand particles. In this case, pile foundations are widely used in marine engineering due to their strong bearing capacity, strong adaptability, good stability and convenient construction.

[0003] However, after the pile foundation is constructed, the movement of water particles caused by tides and waves will be significantly affected by the pile foundation. First, the water particles collide with the pile foundation and accelerate downflow along the pile foundation to produce a downwelling flow, which merges with the incoming flow from the seabed surface to form a horseshoe vortex in front of the pile foundation; secondly, an eddy current (Karman vortex street) will be formed at the backflow of the pile foundation; thirdly, the streamlines on both sides of the pile foundation will shrink. This change in local flow state will increase the shear stress of the water flow on the bottom bed, form scour, and develop scour pits on the seabed around the pile foundation. The existence of scour pits will reduce the depth of the pile foundation into the ground, reduce the bearing capacity of the pile foundation, affect the stability of the pile foundation, and threaten the safe life of the marine engineering.

[0004] There are two types of anti-scour measures for marine pile foundation projects: active protection and passive protection. Active protection is to weaken the flow field strength by changing the local flow field characteristics and reduce the sand-carrying capacity of the flow. Passive protection is to lay protective equipment on the seabed surface around the pile foundation to improve the anti-scour capacity of the seabed surface around the pile foundation. At present, passive protection is mostly used in marine projects, mainly anti-scour measures such as riprap, sand blankets (bags), solidified soil, interlocking rows, etc. However, in actual engineering applications, even if the above-mentioned passive protection measures are adopted, most of them have problems such as inadequate protection and secondary scour, and local scour will still occur around the pile foundation. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a bird's nest type pile foundation anti-scour system and a construction method thereof; the pile foundation anti-scour system can promote the re-deposition of suspended sediment, weaken the development of scour pits, and can reduce the flow rate of seawater and reduce the scouring capacity of water flow; the construction method can avoid underwater construction, which brings great convenience to the construction.

[0006] The technical solution adopted by the present invention is: a bird's nest type pile foundation anti-scour system, characterized in that: the outer contour of the bird's nest type anti-scour system adopts a circular structure to be suitable for sea areas with various flow field characteristics. The bottom of the system is an inner ring beam and an outer ring beam coaxially arranged with the pile foundation, and a radial bottom beam centered on the pile foundation is arranged between the inner ring beam and the outer ring beam as a connection, and the length of the bottom beam is about 1.5 to 3 times the pile diameter (specifically, it can be determined according to the predicted calculation of the scour pit length). The inner ring beam, the outer ring beam, and the bottom beam are combined to support the bottom of the bird's nest type anti-scour system; columns of different heights are arranged on the bottom beam to create and support the parabolic top surface; a geotextile bottom cover is arranged at the bottom of the bottom beam to further protect the seabed around the pile foundation from being scoured by the tide. A column is arranged under the transition top surface between the inner and outer arc top surfaces, and hoisting steel bars / pipes are arranged along the column, and a hoisting bottom plate is arranged at the bottom. The bottom of the hoisting steel bars / pipes is welded to the hoisting bottom plate as a whole.

[0007] The top surface of the bird's nest type anti-scour system is set as an arc-shaped parabola, including the inner arc top surface and the outer arc top surface; when the incoming flow collides with the pile foundation to form a downflow that scours the seabed and causes the suspension of seabed sediment, the suspended sediment is blocked by the top surface when it diffuses to the surrounding with the water flow in the inner cavity space of the top and bottom surfaces of the system. At the same time, the columns in the inner cavity have a certain flow disturbance effect to reduce the flow velocity. When the flow velocity decreases and the sand-carrying capacity of the water flow decreases, the suspended sediment is deposited again, thereby weakening the development of the scour pit and achieving the purpose of pile foundation anti-scour. At the same time, the outer arc top surface is set as an inner concave arc surface that gradually rises from the outside to the inside. The diversion effect of the arc surface can reduce the flow velocity, weaken the flow field, and reduce the scouring capacity of the water flow; the inner arc top surface is set as an inner concave arc surface that gradually decreases from the outside to the inside. The negative terrain created by the inner arc top surface is conducive to the deposition of suspended sediment in the water body.

[0008] In addition, when the water depth of the sea area where the pile foundation is located is relatively shallow, the inner and outer arc top surfaces can also partially take into account the wave-breaking function similar to that of a breakwater. The inner cavity space of the bird's nest type anti-scour system has a fish-collecting effect and takes into account a certain artificial fishing reef function.

[0009] The bird's nest type anti-scour system can be made of reinforced concrete or steel. In order to increase its own rigidity and weight, facilitate the overall hoisting construction and reduce costs, it is recommended to use reinforced concrete structure. Before construction, the bird's nest type anti-scour system can be cast in one piece on land, transported to the sea by a transport ship, and hoisted and sunk as a whole. During construction, the post-pile construction method is adopted. First, the bird's nest type anti-scour system is hoisted and placed on the sea surface as a whole, and then the steel pipe pile is inserted from the reserved center hole. The bird's nest type anti-scour system also serves as a pile sinking guide frame to sink the steel pipe pile into place.

[0010] The beneficial effects of the present invention are:

[0011] 1. The top surface of the bird's nest anti-scour system blocks the suspended diffusion of scoured sediment on the seabed, promotes the re-deposition of suspended sediment, and weakens the development of scour pits.

[0012] 2. The diversion effect of the outer arc top surface can reduce the flow velocity, weaken the strength of the outer flow field, and reduce the scouring capacity of the water flow. The negative terrain created by the inner arc top surface is conducive to the deposition of suspended sediment in the water body. When the water depth is shallow, the inner and outer arc top surfaces can also partially take into account the wave dissipation function similar to that of a breakwater.

[0013] 3. During construction, the bird's nest type anti-scour system is first hoisted to the designated position on the seabed, and then the pile foundation steel pipe pile is inserted through the central hole reserved in the system. The system also serves as a pile sinking guide frame. At the same time, the inner cavity space of the system has a fish gathering effect and can take into account a certain artificial fishing reef function.

[0014] 4. This system is prefabricated on land and hoisted as a whole in the sea, so that the entire anti-scour system can be visualized, avoiding underwater construction by divers and difficulties in acceptance, which greatly facilitates the construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic elevation view of an embodiment of the present invention.

[0016] Figure 2 2 is a schematic top view of an embodiment of the present invention.

[0017] Figure 3 It is an enlarged structural schematic diagram of the hoisting steel bars / pipes according to an embodiment of the present invention.

[0018] Reference numerals:

[0019] 1. Pile foundation; 2-1. Top surface of inner arc; 2-2. Top surface of outer arc; 3-1. Inner ring beam; 3-2. Outer ring beam; 4. Bottom beam; 5-1. First column; 5-2. Second column; 5-3. Third column; 5-4. Fourth column; 6. Top beam; 7. Geotextile; 8-1. Hoisting steel bars / pipes; 8-2. Hoisting bottom plate. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments.

[0021] Figure 1 to Figure 2The bird's nest type anti-scour system shown in the figure has a bottom support structure composed of two concentric ring beams (inner ring beam 3-1 and outer ring beam 3-2) with the pile foundation as the center of the circle and twelve bottom beams 4 radially arranged between the inner and outer ring beams and with the pile foundation as the center of the circle; the inner and outer ring beams are connected at both ends of the bottom beam, and the bottom beam and the inner and outer ring beams are consolidated into one, stabilizing the bottom structure of the system. Four columns of different heights (including the first column 5-1, the second column 5-2, the third column 5-3 and the fourth column 5-4 arranged in sequence along the outer diameter direction) are vertically fixed on each bottom beam 4 to support the inner arc top surface 2-1 and the outer arc top surface 2-2; wherein: the outer diameter edge of the inner arc top surface and the inner diameter edge of the outer arc top surface are connected through the transition top surface; the top end of the first column 5-1 is connected and supports the inner arc top surface 2-1, the top end of the second column 5-2 is connected and supports the transition top surface, and the third column 5-3 is connected to the top end of the fourth column 5-4 and supports the outer arc top surface. The inner arc top surface 2-1 and the outer arc top surface 2-2 both adopt a concave parabolic structure. A top beam 6 is also arranged above the column 5-2 to connect and reinforce the inner and outer arc top surfaces. The top beam 6 is coaxially arranged with the axis of the pile foundation and connects and supports the transition top surface. A bottom geotextile 7 is arranged at the bottom of the bottom beam 4 to further strengthen the anti-scouring of the seabed around the pile foundation. Corresponding to the second column 5-2 arranged at the lower side of the top beam 6, a lifting steel bar / tube (existing technology) 8-1 is also arranged, and a lifting bottom plate 8-2 is configured at the bottom of the steel bar / tube; the bottom of the lifting steel bar / tube 8-1 is welded to the lifting bottom plate 8-2 as a whole, and during construction, it is cast in the column 5-2 to form a whole with the column.

[0022] The guiding effect of the arc parabola of the outer arc top surface 2-2 can weaken the peripheral flow field; the radial dimension of the inner arc top surface (radial dimension of the horizontal plane projection) is smaller than the radial dimension of the horizontal plane projection of the outer arc top surface. As recommended, the ratio of the radial dimension of the horizontal plane projection of the inner arc top surface to the radial dimension of the horizontal plane projection of the outer arc top surface is 1:2.

[0023] The negative terrain created by the inner arc top surface 2-1 is conducive to the deposition of suspended sediment in the water body; the suspended sediment driven by the seabed scouring is blocked by the top surface when it diffuses in the inner cavity of the system and is not easily carried away by the water flow. The flow disturbance effect of the column can promote the reduction of flow velocity and the re-deposition of suspended sediment, thereby weakening the development of scour pits. When the water depth in the sea area is shallow, the inner and outer arc top surfaces can take into account the wave-breaking function similar to that of a breakwater. The space below the inner and outer arc top surfaces of the system has a fish-gathering function and takes into account a certain artificial fishing reef function.

[0024] The bird's nest type anti-scour system can adopt a reinforced concrete structure or a steel structure; in order to increase its own rigidity and weight, facilitate the overall hoisting construction and reduce costs, it is recommended to adopt a reinforced concrete structure. Before construction, the bird's nest type anti-scour system can be cast in one piece on land, transported to the sea by a transport ship, and hoisted and sunk as a whole at one time. During construction, the post-pile construction mode is adopted, that is, the bird's nest type anti-scour system is first hoisted to the sea surface, and then the steel pipe pile of the pile foundation 1 is inserted from its reserved center hole. The anti-scour system also serves as a pile sinking guide frame to sink the steel pipe pile into place.

[0025] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention; therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A bird's nest type pile foundation anti-scour system, characterized by: The system comprises an inner ring beam (3-1) and an outer ring beam (3-2) laid on the seabed and arranged coaxially with the pile foundation (1), a plurality of bottom beams (4) radially arranged between the inner ring beam and the outer ring beam and fixedly connected to the inner ring beam and the outer ring beam at both ends, an inner arc top surface (2-1) and an outer arc top surface (2-2) arranged coaxially with the pile foundation and connected to each other from the inside to the outside, and a plurality of vertically arranged columns with the bottom ends connected to the bottom beams and the top ends connected to the inner arc top surface or the outer arc top surface to reduce the tidal current velocity; The inner arc top surface and the outer arc top surface are both parabolic surfaces that are concave with the axis of the pile foundation as the symmetry axis, so as to prevent the suspended sediment caused by scouring the seabed from spreading to the surroundings; The transition top surface connecting the inner arc top surface to the outer arc top surface is fixed on a top beam (6), and the top beam is arranged coaxially with the pile foundation and is fixed on the bottom beam through a second vertically arranged column (5-2); The edge on one side where the inner arc top surface and the outer arc top surface connect to the transition top surface is the highest point, the edge on the other side of the inner arc top surface away from the transition top surface is the second highest point, and the edge on the other side of the outer arc top surface away from the transition top surface is the lowest point.

2. The bird's nest type pile foundation anti-scour system according to claim 1, characterized in that: The other side edge of the inner arc top surface away from the transition top surface is consolidated with the top end of the first column; the other side edge of the outer arc top surface away from the transition top surface is consolidated with the outer ring beam.

3. The bird's nest type pile foundation anti-scour system according to claim 2, characterized in that: The second column is provided with a hoisting steel bar / tube (8-1) formed as one piece by casting, and a hoisting bottom plate (8-2) connected to the bottom beam steel bar is welded to the bottom end of the hoisting steel bar / tube.

4. The bird's nest type pile foundation anti-scour system according to claim 3, characterized in that: The plurality of columns include a first column (5-1), a second column (5-2), a third column (5-3) and a fourth column (5-4) which are sequentially arranged along the outer diameter direction.

5. The bird's nest type pile foundation anti-scour system according to claim 4, characterized in that: The radial dimension of the inner arc top surface is smaller than the radial dimension of the outer arc top surface.

6. The bird's nest type pile foundation anti-scour system according to claim 5, characterized in that: The bottom of the bottom beam is provided with a geotextile (7) for bottom sealing to resist the scouring of the sea tide around the pile foundation.

7. The bird's nest type pile foundation anti-scour system according to claim 6, characterized in that: The length of the bottom beam is 1.5 to 3 times the diameter of the pile foundation.

8. The bird's nest type pile foundation anti-scour system according to claim 7, characterized in that: The inner ring beam, the outer ring beam, the inner arc top surface, the outer arc top surface and a plurality of columns are all reinforced concrete structures or steel structures.

9. The construction method of the bird's nest type anti-scour system according to claim 8 is carried out according to the following steps: (1) Before the pile foundation construction, the bird's nest type anti-scour system can be cast in one piece on land, transported to the sea by a transport ship, and hoisted and sunk as a whole at one time; (2) During pile foundation construction, the post-pile driving construction method is adopted. First, the bird's nest type anti-scour system is hoisted and lowered to the sea surface as a whole; then the steel pipe piles of the pile foundation are inserted into the central hole of the inner ring beam reserved for piling; the bird's nest type anti-scour system also serves as a pile sinking guide frame to sink the steel pipe piles into place.

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