Bird nest type pile foundation scour prevention system and construction method thereof

Abstract

The present application relates to a kind of offshore pile foundation engineering.The purpose is to provide a kind of bird nest type pile foundation scour protection system and its construction method;The pile foundation scour protection system can promote suspended sediment re-deposition, weaken scour pit development, and can reduce seawater flow rate, reduce the scouring ability of water flow.The technical scheme is a kind of bird nest type pile foundation scour protection system, characterized in that: the bird nest type scour protection system adopts circular structure, to be suitable for the sea area of various flow field characteristics.The bottom of the system is the inner ring beam and outer ring beam arranged coaxially with pile foundation, the radial bottom beam is arranged between the inner ring beam and outer ring beam as connection with pile foundation as center, and the length of bottom beam is about 1.5-3 times of pile diameter (specifically, it can be determined according to the prediction calculation of scour pit length).

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of offshore pile foundation engineering, especially bird nest type pile foundation scour protection system and its construction method. BACKGROUND

[0002] In the offshore sea area of our country, loose sand and silt are common bottom composition types, which are easily eroded by natural water power of sea waves and tidal currents due to the weak cohesive force between sand particles. In this case, pile foundation is widely used in marine engineering due to its strong bearing capacity, strong adaptability, good stability and convenient construction.

[0003] However, after the construction of pile foundation, the movement of water particles caused by tidal current and wave will be significantly affected by the pile foundation. First, the water particles collide with the pile foundation and accelerate downward to form a downward flow, and the incoming flow converges at the front of the pile foundation to form a horseshoe vortex; secondly, a vortex (Kármán vortex street) is formed at the backflow of the pile foundation; thirdly, the flow lines on both sides of the pile foundation will shrink. This change in local flow pattern will increase the shear stress of the water flow on the seabed, forming scour, and developing scour holes around the pile foundation. The existence of scour holes will reduce the depth of pile foundation into the soil, reduce the bearing capacity of pile foundation, affect the stability of pile foundation, and threaten the safety life of marine engineering.

[0004] The anti-scour measures for marine pile foundation engineering include active protection and passive protection. Active protection is to change the characteristics of the local flow field to weaken the intensity of the flow field and reduce the carrying capacity of the flow. Passive protection is to lay protective equipment on the seabed around the pile foundation to improve the anti-scour ability of the seabed around the pile foundation. At present, passive protection is mainly used in marine engineering, including measures such as riprap, sand bag (bag), solidified soil, and chain row. However, in actual engineering application, even if the above passive protection measures are used, there are still problems such as inadequate protection and secondary scour, and local scour still occurs around the pile foundation. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the background art, and to provide a bird nest type pile foundation scour protection system and its construction method. The pile foundation scour protection system can promote the re-deposition of suspended sediment, weaken the development of scour holes, and reduce the flow velocity and scouring capacity of the water flow. The construction method can avoid underwater construction, bringing great convenience to the construction.

[0006] The technical scheme adopted by the present application is: a bird nest type pile foundation scour prevention system, characterized in that: the bird nest type scour prevention system adopts a circular structure in the outer contour, so as to be suitable for various sea areas with different 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 1.5-3 times of the pile diameter (which 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 be used for the bottom support of the bird nest type scour prevention system; different height columns are arranged on the bottom beam to create and support a parabolic top surface; geotextile is arranged at the bottom of the bottom beam to further protect the seabed around the pile foundation from the scour of tidal current. Columns are arranged under the transition top surface between the inner arc top surface and the outer arc top surface, and hoisting steel bars / pipes are arranged along the columns, and hoisting bottom plates are arranged at the bottom.

[0007] The top surface of the bird nest type scour prevention system is arranged as an arc-shaped parabolic surface, including an inner arc top surface and an outer arc top surface; when the incoming flow collides with the pile foundation to form a downflow scouring the seabed to cause the suspension of seabed sediment, the suspended sediment is blocked by the top surface when diffusing around in the inner cavity space of the top surface and the bottom surface of the system along with the water flow, and the columns in the inner cavity have a certain spoiler effect to reduce the flow rate, so that the suspended sediment is deposited again when the flow rate and the sediment carrying capacity of the water flow are reduced, thereby weakening the development of the scour pit and achieving the purpose of pile foundation scour prevention. Meanwhile, the outer arc top surface is arranged as a concave arc surface gradually rising from outside to inside, and the flow guiding effect of the arc surface can reduce the flow rate, weaken the flow field and reduce the scouring capacity of the water flow; the inner arc top surface is arranged as a concave arc surface gradually decreasing from outside to inside, and the negative terrain created by the inner arc top surface is beneficial to the deposition of the suspended sediment of 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 arc top surface and the outer arc top surface can simultaneously partially serve as a wave breaker to dissipate waves. The inner cavity space of the bird nest type scour prevention system has a fishing effect and serves as an artificial fish reef to some extent.

[0009] The bird nest type scour prevention system can adopt a reinforced concrete structure or a steel structure. In order to increase the rigidity and weight of the system, facilitate the overall hoisting and sinking construction and reduce the cost, the reinforced concrete structure is recommended. Before construction, the bird nest type scour prevention system can be integrally cast on land, transported to the sea by a transport ship and hoisted and sunk at one time. During construction, the post-pile construction method is adopted, the bird nest type scour prevention system is hoisted and sunk on the sea surface as a whole, a steel pipe pile is inserted into the central hole reserved in the bird nest type scour prevention system, and the bird nest type scour prevention system serves as a pile sinking guide frame to sink the steel pipe pile into position.

[0010] The present application has the following beneficial effects:

[0011] 1. The top surface of the bird nest type scour prevention system blocks the suspension and diffusion of the scouring sediment of the seabed, promotes the re-deposition of the suspended sediment and weakens the development of the scour pit.

[0012] 2. The guiding effect of the outer arc top surface can reduce the flow velocity, weaken the outward flow field intensity, and reduce the scouring capacity of the water flow. The negative topography created by the inner arc top surface is conducive to the deposition of suspended sediment in the water. When the sea area is shallow, the inner and outer arc top surfaces can also partially serve a wave-damping function similar to a breakwater.

[0013] 3. During construction, the bird's nest-shaped anti-scour system is first hoisted to the designated position on the seabed, and then the steel pipe piles of the pile foundation are inserted through the reserved central hole of the system. The system also serves as a guide frame for pile driving. At the same time, the internal space of the system has a fish-gathering effect and can also serve as a certain artificial reef.

[0014] 4. This system adopts land-based prefabrication and overall sea-based hoisting, making the entire anti-scour system visible and avoiding difficulties such as underwater construction and acceptance by divers, which greatly facilitates construction. Attached Figure Description

[0015] Fig. 1 This is a frontal view of an embodiment of the present invention.

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

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

[0018] Figure label:

[0019] 1. Pile foundation; 2-1. Inner arc top surface; 2-2. Outer arc top surface; 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 of steel bars / pipes; 8-2. Hoisting of bottom slab. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments.

[0021] Figs. 1-2The bird nest type scour protection system shown, the bottom support structure is composed of two concentric circle beams (inner circle beam 3-1 and outer circle beam 3-2) with pile foundation as the center and twelve bottom beams 4 arranged radially between the inner and outer circle beams and with pile foundation as the center; the two ends of the bottom beam are respectively connected to the inner and outer circle beams, and the bottom beam and the inner and outer circle beams are integrated as a whole, stabilizing the bottom structure of the system. Four vertical columns of different heights (including first column 5-1, second column 5-2, third column 5-3 and fourth column 5-4 arranged along the outer diameter direction) are vertically fixed on each bottom beam 4 for supporting 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 by a transition top surface; the top end of the first column 5-1 is connected to and supports the inner arc top surface 2-1, the top end of the second column 5-2 is connected to and supports the transition top surface, and the top ends of the third column 5-3 and the fourth column 5-4 are connected to and support 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 surface structure, and a top beam 6 is further provided above the column 5-2 for connecting and reinforcing the inner and outer arc top surfaces, and the top beam 6 is coaxially arranged with the pile foundation axis and connects and holds the transition top surface. The bottom of the bottom beam 4 is provided with a bottom sealing geotextile 7, which can further strengthen the scour protection of the surrounding seabed of the pile foundation. Corresponding to the second column 5-2 arranged below the top beam 6, a hoisting steel bar / tube (prior art) 8-1 is also arranged, and the bottom of the steel bar / tube is provided with a hoisting bottom plate 8-2; the bottom of the hoisting steel bar / tube 8-1 is welded with the hoisting bottom plate 8-2 as a whole, and during construction, it is poured into the column 5-2 to form a whole with the column.

[0022] The flow guiding effect of the arc-shaped parabolic surface of the outer arc top surface 2-2 can weaken the peripheral flow field; the radial dimension (horizontal plane projection radial dimension) of the inner arc top surface is smaller than the radial dimension of the outer arc top surface, and as a recommendation, the ratio of the horizontal plane projection radial dimension of the inner arc top surface to the horizontal plane projection radial dimension 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 seabed scouring is difficult to be carried away by the water flow when it spreads in the inner cavity of the system due to the obstruction of the top surface, and 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 of the sea area is relatively shallow, the inner and outer arc top surfaces can also have the wave dissipation function similar to that of a breakwater. The space below the inner and outer arc top surfaces of the system has a fishing function, and also has a certain artificial fish reef function.

[0024] The bird nest type scour prevention system can adopt a reinforced concrete structure or a steel structure; in order to increase its own rigidity, weight, facilitate integral hoisting construction and reduce cost, the reinforced concrete structure is recommended. Before construction, the bird nest type scour prevention system can be integrally poured on land, transported to the sea by a transport ship and hoisted and sunk in one time. During construction, a post-piling construction mode is adopted, that is, the bird nest type scour prevention system is hoisted and sunk on the sea surface, and then the steel pipe pile of the pile foundation 1 is penetrated into the center hole reserved in the bird nest type scour prevention system, the bird nest type scour prevention system functions as a pile sinking guide frame and sinks the steel pipe pile into position.

[0025] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application; therefore, equivalent changes made on the basis of the structure, shape and principle of the present application should be covered within the protection scope of the present application.

Claims

1. A bird's nest-type pile foundation scour prevention system, characterized in that: The system includes an inner ring beam (3-1) and an outer ring beam (3-2) laid on the seabed and coaxially arranged with the pile foundation (1), several bottom beams (4) arranged radially between the inner ring beam and the outer ring beam and fixed at both ends to the inner ring beam and the outer ring beam, 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 several vertical columns that are connected at the bottom end to the bottom beam and at the top end to the inner arc top surface or the outer arc top surface to reduce the tidal current velocity; Both the inner and outer arc top surfaces are symmetrical pile foundation axes and concave parabolic surfaces to prevent suspended sediment caused by seabed erosion from spreading to the surrounding area. The transition surface connecting the inner arc top surface to the outer arc top surface is fixed on the top beam (6). The top beam is coaxial with the pile foundation and is fixed on the bottom beam by the vertically arranged second column (5-2). The highest point is the edge on one side of the transition surface connecting the inner arc top surface and the outer arc top surface; the second highest point is the edge on the other side of the inner arc top surface away from the transition surface; and the lowest point is the edge on the other side of the outer arc top surface away from the transition surface. The edge of the inner arc top surface that is away from the transition top surface is fixed to the top of the first column; the edge of the outer arc top surface that is away from the transition top surface is fixed to the outer ring beam. The second column is equipped with a hoisting steel bar / pipe (8-1) formed by casting, and the bottom end of the hoisting steel bar / pipe is welded with a hoisting base plate (8-2) that connects to the bottom beam steel bar. 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) arranged sequentially along the outer diameter direction.

2. The bird's nest-type pile foundation scour prevention system according to claim 1, characterized in that: The radial dimension of the inner arc top surface is smaller than the radial dimension of the outer arc top surface.

3. The bird's nest-type pile foundation scour prevention system according to claim 2, characterized in that: The bottom of each bottom beam is provided with geotextile (7) for sealing the bottom, in order to resist the erosion of the sea tide around the pile foundation.

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

5. The bird's nest-type pile foundation scour prevention system according to claim 4, characterized in that: The inner ring beam, outer ring beam, inner arc top surface, outer arc top surface, and several columns are all reinforced concrete or steel structures.

6. The construction method of the bird's nest-type pile foundation scour prevention system according to claim 1 shall be carried out according to the following steps: (1) Before the pile foundation construction, the bird nest-shaped pile foundation anti-scour system can be cast in one piece on land and transported to the sea by transport ship for overall hoisting and sinking in one go; (2) During the construction of the pile foundation, the post-pile driving method is adopted. First, the bird's nest-shaped pile foundation anti-scour system is hoisted to the sea surface as a whole; then, the steel pipe piles of the pile foundation are driven through the reserved center hole of the inner ring beam. The bird's nest-shaped pile foundation anti-scour system also serves as a pile driving guide frame to drive the steel pipe piles into place.

Images