JP2021195754A - Marine gravity-based foundation - Google Patents

Abstract

To provide a marine gravity-base foundation allowing resistance performance against omnidirectional horizontal force to be improved.SOLUTION: A marine gravity-based foundation 11 has a bottom part 12 located on a sea bottom 13, wherein a concave or convex cone surface 14 is formed on a lower surface of the bottom part 12, the cone surface 14 and the sea bottom are tightly adhered to each other. Resistance force R generated by friction between the sea bottom 13 and the bottom part 12 in accordance with horizontal force P is R=r×W in a case of a dead weight W of the marine gravity-based foundation 11, the horizontal force P acting on the bottom part 12, and a coefficient r sharing the horizontal force. As the coefficient r increases according to a gradient angle θ with inclination in a friction direction, the resistance force are able to be increased. The gradient angle θ of the cone surface 14 is 1 degree or more to 10 degree or less. Scouring-protection bodies 18 expanding downward are arranged around the bottom part 12.SELECTED DRAWING: Figure 2

Description

The present invention relates to an ocean gravity foundation.

As fixed foundations for offshore wind power generation facilities, there are pile foundations that are fixed to the seabed by pile driving, and gravity foundations that support structures by placing heavy foundation blocks on the seabed. It is used (see Patent Documents 1 and 2).
When the ground is strong, the gravity type foundation is often used because the pile type foundation etc. is complicated to construct at sea and the construction cost and construction period increase.

Japanese Unexamined Patent Publication No. 2002-206474 Japanese Unexamined Patent Publication No. 2006-322400

In the above-mentioned gravity foundation, the bottom of the foundation is placed on the seabed or crushed stone laid on the seabed to support superstructures such as towers and blades fixed to the foundation. This causes the weight of the superstructure and the foundation itself to act vertically downward from the foundation to the seabed.
In addition, horizontal force and overturning moment act from all directions of 360 degrees on the foundation due to wind load, wave force, tidal current force, seismic force, etc., which are also borne by the bottom of the foundation to the sea floor.
If the ground is good, the gravity foundation can resist the vertically downward load relatively easily. For the overturning moment, the resistance moment can be increased by increasing the bottom of the foundation. However, since it resists the horizontal force with a frictional force proportional to the weight of the foundation, it is necessary to make the foundation significantly heavier in order to increase the resistance. As the foundation becomes larger, external forces such as wave power and seismic force also increase, so that the foundation becomes larger, which causes a problem that the workability deteriorates and the construction cost increases.

An object of the present invention is to provide an ocean gravity foundation capable of enhancing resistance to horizontal forces from all directions.

The ocean gravity foundation of the present invention is an ocean gravity foundation whose bottom is placed on the seabed, and a concave or convex cone surface is formed on the lower surface of the bottom, and the cone surface and the seabed are in close contact with each other. It is characterized by being done.
In the present invention, the pyramid surface is a conical surface or a polygonal pyramid surface, and the polygonal pyramid surface includes a triangular pyramid surface, a quadrangular pyramid surface, or a pyramid surface having a number of faces equal to or more than that. The pyramidal surface of the present invention preferably has a flat pyramidal shape, that is, a shape having a sufficiently small height with respect to the bottom diameter and a gentle gradient angle as described later.
In the present invention as described above, the seabed in close contact with the concave pyramidal surface is convex, and the seabed in close contact with the convex pyramid surface is concave. When a horizontal force is applied to such a bottom from any direction, a drag force corresponding to the horizontal force is generated on the sea floor in contact with the bottom, and this drag force is the above-mentioned pyramid surface (conical or polygonal pyramid shape). Is increased by the gradient of.

In FIG. 1 (A), when the bottom 2 of the ocean gravity foundation 1 and the sea floor 3 are in contact with each other on the concave pyramidal surface 4, the own weight W of the ocean gravity foundation 1, the horizontal force P applied to the bottom 2, and the horizontal force are applied. As the coefficient r that shares the above, the drag force R generated by the friction between the seabed 3 and the bottom 2 according to the horizontal force P is R = r × W. This coefficient r is given by r = (sinθ + μcosθ) / (cosθ−μsinθ) as the gradient angle θ (inclination angle of the generatrix) of the pyramidal surface 4 and the original friction coefficient μ in the absence of a gradient. That is, the coefficient r increases according to the gradient angle θ as the friction direction is inclined, and therefore the drag force R can be increased.

r = (sinθ + μcosθ) / (cosθ−μsinθ) is derived as follows.
As the slope orthogonal component Wcosθ of the own weight W and the slope orthogonal component Psinθ of the horizontal force P, the slope orthogonal load Wb = Wcosθ + Psinθ, and the frictional force along the slope is μ · Wb = μ (Wcosθ + Psinθ).
On the other hand, the slope parallel component Wsinθ of the own weight W, the slope parallel component Pcosθ of the horizontal force P, and the slope parallel load Pb = Wsinθ−Pcosθ.
In order for the ocean gravity foundation 1 not to move even with a horizontal force P, a slope parallel load Pb <friction force (μ · Wb) is required, in other words, a safety factor SF = μ · Wb / Pb and SF> 1 is required. be.

In FIG. 1B, the same applies when the bottom 2 of the ocean gravity foundation 1 and the sea bottom 3 are in contact with each other on the convex conical surface 4A, and the coefficient r is determined according to the gradient angle θ due to the inclination of the friction direction. It can be increased and thus the drag R can be increased.

Since the bottom and the seabed are in contact with each other on the pyramidal surface, the effect of increasing the drag force by the contact surface having such a gradient can be obtained in the same manner regardless of the direction in which the horizontal force acts at 360 degrees.
The pyramid surface may have a conical shape or a polygonal pyramid shape with sharp vertices, or may have a cone shape such as a truncated cone or a polygonal cone with flat apex. Further, although there may be a flat portion around the pyramidal surface of the bottom, it is desirable to increase the area ratio of the pyramidal surface to the bottom as much as possible in order to effectively utilize the bottom.

In the ocean gravity foundation of the present invention, the gradient angle of the pyramidal surface is preferably 1 degree or more and 10 degrees or less.
As described above, in the present invention, by increasing the slope angle of the pyramidal surface, the frictional force between the bottom and the seabed in close contact with the bottom can be increased, and the drag against the horizontal force can be increased. However, if the gradient angle exceeds 10 degrees, the seafloor may self-destruct before the ocean gravity foundation slides out. On the other hand, in the present invention, by setting the gradient angle to 10 degrees or less, it is possible to obtain the effect of enhancing stable resistance performance while ensuring the above-mentioned drag force.

In the ocean gravity foundation of the present invention, it is preferable that the bottom thereof is provided with a plurality of pyramidal surfaces.
In such an invention, a sufficient drag force can be generated at a plurality of points against a horizontal force in a specific direction. Further, by arranging a plurality of pyramidal surfaces on the bottom, the area ratio of the pyramidal surface to the bottom can be increased.
It is preferable that the plurality of pyramidal surfaces are arranged point-symmetrically with respect to the bottom so as to be able to cope with horizontal forces in all directions. Further, a plurality of cone surfaces having different diameter dimensions (diameter of the bottom surface for a conical surface and diameter of an circumscribed circle or an inscribed circle of the bottom surface for a polygonal cone surface) may be combined.

In the ocean gravity foundation of the present invention, it is preferable that a frustum-shaped scouring preventive body extending downward is provided around the bottom.
In the present invention as described above, it is possible to prevent scouring due to the tidal current along the seabed.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an ocean gravity type foundation capable of enhancing resistance performance against horizontal force from all directions.

The schematic diagram which shows the principle of this invention. The side view which shows the ocean gravity type foundation of 1st Embodiment of this invention. The side view which shows the installation state of the 1st Embodiment. The side view which shows the 2nd Embodiment of this invention. The bottom view which shows the 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
In FIG. 2, the offshore wind power generation device 10 includes an ocean gravity foundation 11 that supports the wind power generation facility 19 offshore.
The ocean gravity foundation 11 is composed of a heavy concrete structure or a steel frame structure, and the bottom portion 12 is placed on the seabed 13 and fixed by its own weight.

A concave pyramidal surface 14 is formed on the lower surface of the bottom portion 12.
A convex portion 15 having the same shape as the concave pyramidal surface 14 is formed on the seabed 13, and the convex portion 15 fits into the pyramid surface 14 so that the pyramid surface 14 and the seabed 13 are in close contact with each other.

The pyramidal surface 14 is a conical surface, and its gradient angle (inclination angle of the generatrix) is 1 degree or more and 10 degrees or less. The pyramid surface 14 may be a polygonal pyramid surface.
A scouring preventive body 18 is provided around the bottom portion 12.
The scouring preventive body 18 is a member made of a frustum-shaped (conical cone-shaped or pyramidal-shaped) steel plate that extends downward from the middle of the peripheral surface of the bottom portion 12, and the outer lower edge is connected to the seabed 13. It is installed in.

In FIG. 3, when the ocean gravity foundation 11 is installed on the seabed 13, a convex portion 15 is formed on the seabed 13 in a rough shape. Then, by covering the bottom portion 12 from above the convex portion 15, the convex portion 15 is introduced into the inside of the pyramidal surface 14 and is brought into close contact with each other.
After installing the ocean gravity foundation 11 on the seabed 13, the offshore wind power generation device 10 is constructed by installing the wind power generation equipment 19 on the seabed 13 and installing the scour prevention body 18 around the bottom 12. Can be done.

In the present embodiment, as shown in FIG. 3, when a horizontal force P is applied to the bottom 12 of the ocean gravity foundation 11 from an arbitrary direction, a drag force R corresponding to the horizontal force P is generated on the sea bottom 13. At this time, the drag force R is increased by the pyramidal surface-like gradient of the pyramidal surface 14 and the convex portion 15.

When the concave pyramidal surface 14 of the bottom 12 and the convex portion 15 of the sea bottom 13 come into contact with each other, the weight W of the ocean gravity foundation 11, the horizontal force P applied to the bottom 12, and the coefficient r that shares the horizontal force are horizontal. The drag force R generated by the friction between the sea bottom 13 and the bottom 12 according to the force P is R = r × W. This coefficient r is given by r = (sinθ + μcosθ) / (cosθ−μsinθ) as the gradient angle θ (inclination angle of the generatrix) of the cone surface 14 and the friction coefficient μ in the absence of a gradient. That is, the coefficient r increases according to the gradient angle θ as the friction direction is inclined, and therefore the drag force R can be increased.
As a result, according to the present embodiment, in the ocean gravity type foundation 11, the resistance performance against the horizontal force P from all directions can be enhanced.

In the present embodiment, since the gradient angle θ of the pyramidal surface 14 is set to an arbitrary angle of 1 degree or more and 10 degrees or less, it is possible to obtain the effect of enhancing stable resistance performance while ensuring the drag force R.
That is, by increasing the gradient angle θ of the pyramidal surface 14, the frictional force between the pyramidal surface 14 of the bottom portion 12 and the convex portion 15 of the seabed 13 in close contact with the pyramidal surface 14 is increased, and the drag force R against the horizontal force P is increased. Can be done. However, if the gradient angle exceeds 10 degrees, the seafloor 13 may self-destruct before the ocean gravity foundation 11 slides out. On the other hand, by setting the gradient angle to 10 degrees or less, it is possible to obtain the effect of enhancing stable resistance performance while ensuring the drag force R.

In the present embodiment, since the frustum-shaped scouring preventive body 18 that extends downward is provided around the bottom portion 12, scouring due to the tidal current along the seabed 13 can be prevented. As a result, the uneven shape of the seabed 13 is not washed away, so that the resistance performance can be maintained or enhanced.

[Second Embodiment]
In the first embodiment described above, in the ocean gravity type foundation 11 of the offshore wind power generation device 10, a concave pyramidal surface 14 is formed on the lower surface of the bottom portion 12, and the convex portion 15 formed on the seabed 13 is brought into close contact with the pyramidal surface 14. Was there.
As shown in FIG. 4, in the present embodiment, in the ocean gravity type foundation 11A of the offshore wind power generation device 10A, a convex cone surface 14A is formed on the lower surface of the bottom portion 12, and the recess 15A formed on the seabed 13 is formed on the cone surface. It is in close contact with 14A.
The other configurations of the offshore wind power generation device 10A are the same as those of the above-mentioned offshore wind power generation device 10, and overlapping description will be omitted.

Also in this embodiment as described above, when the convex cone surface 14A and the concave portion 15A come into contact with each other, the drag force R is R = r × W due to the friction between the seabed 13 and the bottom 12A according to the horizontal force P. As in the first embodiment, this coefficient r has a gradient angle θ (inclination angle of the generatrix) of the cone surface 14A and an original friction coefficient μ in the absence of a gradient, and r = (sinθ + μcosθ) / (cosθ−μsinθ). ). That is, the coefficient r increases according to the gradient angle θ as the friction direction is inclined, and therefore the drag force R can be increased.
As a result, the resistance performance against the horizontal force P from all directions can be enhanced in the ocean gravity type foundation 11A also by this embodiment.

[Third Embodiment]
In the first embodiment and the second embodiment described above, one concave or convex pyramidal surface 14, 14A is formed on the lower surface of the bottom portions 12, 12A. However, a plurality of such pyramidal surfaces 14, 14A may be formed.
In FIG. 5, in the present embodiment, in the ocean gravity type foundation 11B of the offshore wind power generation device 10B, four pyramidal surfaces 14B and five pyramidal surfaces 14C are formed on the lower surface of the bottom portion 12B. The pyramid surfaces 14B and 14C of the present embodiment shown in FIG. 5 are conical surfaces, but may be polygonal pyramid surfaces.

Each of the four pyramidal surfaces 14B has a larger diameter than the pyramidal surface 14C. The five pyramidal surfaces 14C are each disposed between the pyramidal surfaces 14B, one of which is located in the center of the lower surface of the bottom 12B.
In the present embodiment, by making the sizes of the plurality of pyramidal surfaces 14B and 14C different in size, the large and small pyramidal surfaces 14B and 14C can be arranged on the lower surface of the bottom portion 12B as closely as possible, and therefore on the lower surface of the bottom portion 12B. The area ratio of the pyramidal surfaces 14B and 14C can be increased.

[Modification example]
The present invention is not limited to the above-described embodiment, and modifications to the extent that the object of the present invention can be achieved are included in the present invention.
In the third embodiment, the pyramidal surfaces 14B and 14C may all have the same diameter dimension, or may have three or more types of diameter dimensions. Further, the pyramidal surfaces 14B and 14C may be all concave or all convex, or may be partially convex and the other concave.

In the first embodiment and the second embodiment, the pyramidal surfaces 14, 14A may be formed on the entire surface of the bottoms 12, 12A, but the pyramidal surfaces 14, 14A are formed to have a slightly smaller diameter, and the periphery of the pyramidal surfaces 14, 14A is formed. The lower surface of the bottoms 12 and 12A may be left on the bottom. As the pyramid surfaces 14, 14A, either a conical surface or a polygonal pyramid surface may be used, and the polygonal pyramid surface may be a triangular pyramid surface, a quadrangular pyramid surface, or a larger number of surfaces, and these are different. You may use a mixture of different types of pyramid surfaces.
In each of the above-described embodiments, the bottom portions 12, 12A, and 12B are not limited to a columnar shape, and may have a prismatic or other shape, and the shape of the lower surface thereof may be not limited to a circle or a rectangle, but may be another shape.
In each of the above embodiments, the ocean gravity foundations 11, 11A, 11B are not limited to the foundations of the offshore wind power generation devices 10, 10A, 10B, and may support equipment different from the wind power generation equipment 19 at sea. good.
In the above embodiment, a frustum-shaped scour prevention body 18 that extends downward is provided around the bottom portion 12, but this may be omitted.

The present invention can be used for ocean gravity foundations.

10, 10A, 10B ... Offshore wind power generator, 11, 11A, 11B ... Ocean gravity foundation, 12, 12A, 12B ... Bottom, 13 ... Sea bottom, 14, 14A, 14B, 14C ... Pyramid surface, 15 ... Convex, 15A ... recess, 18 ... scour prevention body, 19 ... wind power generation equipment, θ ... gradient angle.

Claims (4)

It is an ocean gravity foundation whose bottom is placed on the seabed.
An ocean gravity foundation characterized in that a concave or convex pyramidal surface is formed on the lower surface of the bottom portion, and the pyramidal surface and the seabed are in close contact with each other. In the ocean gravity foundation according to claim 1,
An ocean gravity foundation characterized in that the gradient angle of the pyramidal surface is 1 degree or more and 10 degrees or less. In the ocean gravity foundation according to claim 1 or 2.
An ocean gravity foundation characterized in that a plurality of pyramidal surfaces are provided on the bottom. In the ocean gravity foundation according to any one of claims 1 to 3.
An ocean gravity foundation characterized by a frustum-shaped scour prevention body that extends downward around the bottom.

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