[0001] The invention relates to a foundation structure to be built offshore. More closely
defined, the object of the invention is a shell structure of a foundation structure
to be built, operating together with the soil inside it.
[0002] Solutions are previously known, in which the offshore foundation structure is made
by pile-driving the framework structure submerged in water to the bottom. Such solutions
have been shown, for example, in the
patent specifications US 3 832 857,
US 3 638 436 and
US 5 127 767. The use of one large pile anchored or submerged to the bottom is known as a different
alternative. Such a solution has been disclosed, for example, in the
patent specification US 3 677 113 and the
patent application WO 00/28153. It can be used both on a soft or hard bottom. On the rock bottom, a hollow is formed
to the rock, to which the large steel pile is soldered. A third alternative is to
transport to the site or to manufacture on site a massive foundation structure (of
steel and/or concrete), onto which a construction, for example a wind power station,
to be joined to the foundation structure and extending either partly below the water
surface or being totally above the water surface, is installed. Such constructions
that are disclosed, for example, in the patent specifications U 3 793 840 and
US 5 613 808 can be either fixed or movable. Also this alternative is suitable both for a soft
and hard bottom. When a different bottom is concerned, the installation only requires
slightly different manufacturing procedures for the installation.
[0003] In
US 3 117 423 is presented a mould structure, which is used for construction of bridge support
or such. The mold is a thin structure, which is disassembled and used again in the
next construction site. It is used as a construction time support to the actual structure.
Due to the different use of the structure it has no ring footing or any reinforcements
(bracings) in the shell structure.
[0004] In
US 5 316 413 is disclosed an offshore double cone structure comprising the features of the preamble
part of claim 1.
[0005] The problem with the previously used solutions has been the heavy special equipment
needed in the transport of the foundation structures, which is available to a very
limited extent. In addition, the use of special equipment is very expensive, especially
when preparing the foundation structures in offshore circumstances, in which the weather
windows suitable for working are short. In the Northern conditions, the season that
is best suitable for working, only lasts the summer months. In all bottom conditions
that come to question, the foundation piles are rather massive. The time needed for
the driving of the piles is long in relation to the weather window that can be predicted,
even in ideal conditions. In difficult bottom circumstances, the length of the drive
time increases and becomes very difficult to predict. The required bottom work, such
as for example, the loosening of moraine by exploding that has to be performed now
and then may considerably increase the time. The fast and even hard changes in weather
may interrupt the foundation project, and even force to demobilise and remobilise
expensive equipment. If several foundation structures are to be installed to the same
area, for example when building a wind park, it is extremely difficult to work out
a fixed schedule, and advantages of serial production are lost.
[0006] When rock bottom is concerned, the preparing of the rock hollow for the caisson pile
is very expensive and time-consuming. It involves risks related with rock conditions
and the same schedule and weather risks that have been mentioned above. When the rock
bottom is covered by a thick soil layer, the use of any kind of pile solution is generally
out of the question.
[0007] Concrete caissons are also used as offshore foundation structures. There is a limited
number of dockyards used for their building, and their use in connection of other
productional activities is expensive and difficult. Also the reservoir to be separately
built for the manufacture of caissons is in practice often an expensive and time-consuming
solution. Weather and schedule risks are involved in the transport of caissons by
floating or by heavy equipment and in the ballasting. The use of the caisson is made
more difficult, because it cannot be installed to a very uneven bottom. In addition,
the caisson solution in its entirety is expensive.
[0008] The object of the present invention is to avoid the drawbacks mentioned above that
are related to expensive foundation solutions, the use of special equipment, and the
predictability of schedules. When preparing several foundation structures to the same
offshore area, for example, when a wind park is concerned, one has to strive for well
programmed serial work, in which the time required by expensive marine work operations
is short and the schedule risk related with them can be controlled. The equipment
to be used should be moderately-priced standard equipment. Work requiring expensive
special equipment, such as the installation of shaft and mill, has to be performed
as serial work so that one single work stage offshore would preferably last less than
24 hours, in which case the weather risk can be controlled. In this way, the entire
wind park could be installed and implemented during one summer.
[0009] For achieving this, a thin shell structure, preferably of steel, is prepared, which
is filled with soil after embedding, for example, with natural non-cohesive soil,
crushed stone or mixed blasted stone. A conical structure located in the water line
and a structural braced ring footing form a part of the shell structure. The conical
structure improves the suitability of the foundation structure for demanding conditions,
but in stable ice conditions and on marginal ice areas or iceless areas the shell
structure can be a straight cylinder.
[0010] Such a thin shell structure can be lifted and transported to the installation location
by using conventional equipment, in which case the costs are considerably reduced.
The assembling of the thin steel shell requires no extensive investments, but it can
be done on quayside or in a workshop near the installation area. Compared with a rock
hollow to be done, for example, by exploding, the bottom work required by the foundation
structure can be performed fast, at low cost and with moderate tolerance.
[0011] The above-mentioned advantages are achieved with the solution of the invention, which
is characterised in what is disclosed in the enclosed patent claims.
[0012] The invention is next described in more detail, referring to the enclosed drawings,
in which
Figure 1 is a cross-section of a foundation structure manufactured of a thin-walled,
rotationally symmetrical shell structure,
Figure 2 is a cross-section of a foundation manufactured of a thin-walled, rotationally
symmetrical shell structure, in which the conical structure has been inverted, and
Figure 3 presents an example for installing a foundation structure onto rock bottom;
this example is not covered by claim 1.
[0013] Figure 1 shows an advantageous embodiment of the offshore foundation structure of
the invention. The foundation structure advantageously consists of the rotationally
symmetrical shell structure 1 of steel and of the braced ring footing 2 in the plane
of foundation, attached to the shell structure. The shell structure 1 can also be
of some other form besides rotationally symmetrical. For example, it can be a polygon.
The shell structure 1 contains the conical area 3, with which the dynamic ice loads
directed to the structure are reduced, and above all, the intensity of ice induced
vibrations is reduced by an order of magnitude. The intensity of vibrations is extremely
significant especially if the foundation structure is used as the foundation for a
wind power station. Their reduction improves the operation and durability of the wind
power station. The conical area 3 is located substantially on the level of the water
surface 4. The conical area 3 improves the suitability of the foundation structure
to demanding conditions, but in stable ice conditions and on marginal ice areas or
iceless areas, the shell structure 1 can be a straight cylinder. The conical structure
3 is braced with horizontal and/or vertical bracings attached to the surface of the
thin shell structure 1 so that a connection plate 6, closing the shell structure partly
or entirely from above, can be more firmly connected to the shell structure. A braced
steel plate or a reinforced concrete plate can be used as the connection plate 6.
With the help of the connection plate 6, a structure above the water surface 4, such
as a wind power station, a fixed navigation mark, a lighthouse, or some other structure,
is attached to the foundation structure. The shell-structured 1 foundation can further
be used, for example, for quays, dolphins, oil loading structures, oil drilling structures,
or as ice-resistant bridge piers. In this case, the form of the shell structure 1
can also differ from the rotationally symmetrical form. The diameter of the shell
structure 1 is preferably 4 - 40 m and the thickness preferably 6 - 40 mm. In the
water line, also a steel plate with a stronger thickness can be used for reinforcing
the structure.
[0014] The structural braced ring footing 2 according to Figure 1 on the plane of foundation
ensures the cooperation of the shell structure 1 and the fill 7, consisting of soil,
in relation to dynamic loadings. Without the ring footing 2 there is the risk that
the foundation structure will gradually tilt by the action of the dynamic loadings.
In the structure, the ring footing 2 works as an anchorage in relation to dynamic
forces. The ring footing 2 can be provided with a uniform or segmented skirt/skirts
21, penetrating into the soil. The skirt/skirts 21 improve the stability of the foundation
structure. Before embedding the shell structure 1 to the installation location, the
installation location is levelled with the soil layer 8, when required. Thus, as good
a base as possible is produced for the foundation structure to be made. At the final
stage of the installation of the foundation structure, soil material 9 is brought
outside the shell structure 1 for covering the ring footing 2 for the external part
of the shell structure 1 for protecting the structure from erosion and for improving
stability.
[0015] The conical structure 3 can also be inverted, as in Figure 2, which facilitates the
control of wave loads. By manufacturing the connection plate 6 to have a bigger diameter
than the overlying structure to be installed to it, the free area remaining for the
connection plate can advantageously be used as an entrance/working plane.
[0016] When required, the building of the foundation structure of the invention begins by
preparing the bottom 10 of the installation area. This step can comprise, for example,
the transport of soil to the site by barge. The filling of shell by soil is performed
by using standard equipment (for example, a combination of barge and bucket loader),
and it is thus relatively fast and inexpensive. In some cases, the bottom 10 can be
ready for shell placement without any additional measures. The thin steel shell 1
can be simultaneously assembled in the vicinity of the water area in a workshop and
on quay from prefabricated segments without expensive special preparations.
[0017] When the bottom 10 is suitable for installation, the steel shell 1 is transported
to site using standard transport equipment, such as a transport barge. No special
equipment is needed, because the structure is notably light, compared with the solutions
previously used. The steel shell 1 can be lifted from the transport equipment using
standard crane equipment, and it is sunk to the bottom 10.
[0018] The filling of the steel shell 1 is carried out by using soil 7. It is also preferable
to roll soil and blocks along the conical surface to the bottom of the steel structure
onto the footing 2 so that, for this part, the soil 9 works as a protection from erosion
and increases the total stability of the structure. The soil 7 installed inside the
steel shell 1 is arching as in a silo, and the entity formed by the shell and the
soil operates with certain preconditions almost like a solid block, both in relation
to tilting and sliding. In addition, the soil 7 supports the thin-walled steel shell
1, thus preventing the loss of stability of the shell under stress, the shell being
extremely thin-walled in relation to its diameter. Further, the soil 7 supports the
steel shell 1 also in relation to local ice loads and wave impacts. The internal filling
7 also efficiently suppresses the vibrations of the structure. Because of the arching
effect of the internal filling 7 of the steel shell 1 it is I possible to use normal
piles 12 provided with pile caps 11 for supporting the structure, when building on
a soft bottom 10, as is later shown in Figure 4. There is no need for an underwater
bedplate in this case, either.
[0019] Figure 3 illustrates an installation to be made on uneven rock bottom 16. In the
installation to be made on rock bottom 16, a ring footing 17 of concrete and an internal
anchoring of the structure are preferably used; the foundation structure can be attached
to the rock with the said anchoring without an expensive rock hollow, which is difficult
to realise. The shell structure 1 is attached to the rock 16 through the bed casting
19 and the concrete footing 17 levelling the bottom, using groutable rock anchors
18. The stability of the shell structure 1 is at the installation stage ensured by
installation bolts 20 to be attached to the concrete footing 17.
[0020] Filling the thin shell structure 1 internally with soil 7 offers the structure the
mass required by its total stability, prevents the loss of stability of the thin-walled
shell under stress, supports the thin-walled shell against local loads, and acts as
a dampener in relation to structural vibrations.
[0021] It is obvious for one skilled in the art that the various embodiments of the invention
are not restricted to the examples presented above, but they can vary within the scope
of the enclosed claims.
1. Offshore foundation structure for structures above the water surface (4), such as
for a wind power station, a fixed navigation mark, a lighthouse, quays, dophins, oil
loading structures, oil drilling structures or ice-resistant bridge piers, the offshore
foundation structure comprising a shell structure (1) and a braced connection plate
(6) connected to the shell structure (1) for attaching the structure above the water
surface to the foundation structure, wherein the shell structure (1) of the foundation
structure is thin in relation to the diameter of the structure and comprises a ring
footing (2) attached to the shell structure (1) at the foundation level to be in use
placed against the bottom of the water area, acting as the anchorage in relation to
dynamic forces, and longitudinal and/or transverse bracings (5) are connected to the shell structure (1), characterised in that the shell structure (1) is filled with soil (7).
2. Foundation structure according to claim 1, characterised in that at least part of the shell structure (1) is shaped conical in relation to the vertical
axis, and that the conical surface (3) is located at the height of the water surface
(4).
3. Foundation structure according to claim 2, characterised in that the foundation structure is attached to the bottom (15, 16) of the water area with
piles (12) or rock anchors (18).
4. Foundation structure according to claim 3, characterised in that the shell structure (1) of the foundation structure consists of two or several parts
(13, 14).
5. Foundation structure according to claim 4, characterised in that the foundation structure has the ring footing (17) of concrete, levelling the bottom,
and that it is internally anchored to the bottom (16) of the water area with rock
anchors (18).
6. Foundation structure according to claim 4, characterised in that the braced ring footing (2) in the plane of foundation is covered with soil (9) for
the external part of the shell structure (1).
7. Foundation structure according to claim 5 or 6, characterised in that the diameter of the shell structure (1) is 4 - 40 m and the thickness 6 - 40 mm.
1. Offshore-Gründungsstruktur für Strukturen oberhalb der Wasseroberfläche (4), wie beispielsweise
für eine Windkraftanlage, ein feststehendes Navigationszeichen, einen Leuchtturm,
Kais, Dalben, Ölverladestrukturen, Ölbohrungsstrukturen oder eisfeste Brückenpfeiler,
wobei die Offshore-Gründungsstruktur eine Ummantelungsstruktur (1) und eine versteifte
Verbindungsplatte (6) umfasst, die mit der Ummantelungsstruktur (1) verbunden ist,
um die Struktur oberhalb der Wasseroberfläche an der Gründungsstruktur anzubringen,
wobei die Ummantelungsstruktur (1) der Gründungsstruktur im Verhältnis zum Durchmesser
der Struktur dünn ist und ein Ringfundament (2) umfasst, das an der Ummantelungsstruktur
(1) auf Höhe der Gründung angebracht ist, um während der Verwendung auf dem Grund
des Gewässers angeordnet zu sein, und das als Verankerung im Verhältnis zu dynamischen
Kräften dient, wobei Längs- und/oder Querversteifungen (5) mit der Ummantelungsstruktur
(1) verbunden sind, dadurch gekennzeichnet, dass die Ummantelungsstruktur (1) mit Erde (7) gefüllt ist.
2. Gründungsstruktur nach Anspruch 1, dadurch gekennzeichnet, dass mindestens ein Teil der Ummantelungsstruktur (1) im Verhältnis zur vertikalen Achse
konisch geformt ist und dass die konische Oberfläche (3) auf Höhe der Wasseroberfläche
(4) angeordnet ist.
3. Gründungsstruktur nach Anspruch 2, dadurch gekennzeichnet, dass die Gründungsstruktur mit Pfählen (12) oder Felsverankerungen (18) am Grund (15,
16) des Gewässers angebracht ist.
4. Gründungsstruktur nach Anspruch 3, dadurch gekennzeichnet, dass die Ummantelungsstruktur (1) der Gründungsstruktur aus zwei oder mehr Teilen (13,
14) besteht.
5. Gründungsstruktur nach Anspruch 4, dadurch gekennzeichnet, dass das Ringfundament (17) der Gründungsstruktur aus Beton besteht, der den Grund ebnet,
und dass es innerlich mit Felsverankerungen (18) im Grund (16) des Gewässers verankert
ist.
6. Gründungsstruktur nach Anspruch 4, dadurch gekennzeichnet, dass das versteifte Ringfundament (2) auf der Gründungsebene mit Erde (9) für den äußeren
Teil der Ummantelungsstruktur (1) bedeckt ist.
7. Gründungsstruktur nach Anspruch 5 oder 6, dadurch gekennzeichnet, dass der Durchmesser der Ummantelungsstruktur (1) 4 bis 40 m und die Dicke 6 bis 40 mm
beträgt.
1. Structure de fondation offshore pour structure située au-dessus de la surface de l'eau
(4) telle que station éolienne, marque de navigation fixe, phare, quai, dauphins,
structure de chargement de pétrole, structure de forage de pétrole ou piles de ponts
résistants aux glaces, la structure de fondation offshore comprenant une structure
de coque (1) et une plaque de connexion arrimée (6) connectée à la structure de coque
(1) pour fixer la structure située au-dessus de la surface de l'eau à la structure
de fondation, la structure de coque (1) de la structure de fondation étant mince par
rapport au diamètre de la structure et comprenant un pied annulaire (2) fixé à la
structure de coque (1) au niveau de la fondation et destiné à être utilisé positionné
contre le fond de la zone située dans l'eau en agissant comme ancrage par rapport
aux forces dynamiques et que des arrimages longitudinaux et/ou transversaux (5) sont
connectés à la structure de coque (1), caractérisée en ce que la structure de coque (1) est remplie de terre (7).
2. Structure de fondation selon la revendication 1, caractérisée en ce qu'au moins une partie de la structure de coque (1) a une forme conique par rapport à
l'axe vertical et que la surface conique (3) est située au niveau de la surface de
l'eau (4).
3. Structure de fondation selon la revendication 2, caractérisée en ce que la structure de fondation est fixée au fond (15, 16) de la zone située dans l'eau
par des piles (12) ou des ancres de roche (18).
4. Structure de fondation selon la revendication 3, caractérisée en ce que la structure de coque (1) de la structure de fondation est composée de deux ou plusieurs
pièces (13, 14).
5. Structure de fondation selon la revendication 4, caractérisée en ce que la structure de fondation comporte le pied annulaire (17) en béton qui nivelle le
fond et qui est ancré par l'intérieur au fond (16) de la zone située sous l'eau par
des ancres de roche (18).
6. Structure de fondation selon la revendication 4, caractérisée en ce que le pied annulaire arrimé (2) dans le plan de la fondation est recouvert de terre
(9) pour la partie externe de la structure de coque (1).
7. Structure de fondation selon la revendication 5 ou 6, caractérisée en ce que le diamètre de la structure de coque (1) est de 4 à 40 m et l'épaisseur de 6 à 40
mm.