WO1985004682A1 - Plate-forme a gravite pour une grande profondeur d'eau, son procede de fabrication et utilisation d'une telle plate-forme - Google Patents

Plate-forme a gravite pour une grande profondeur d'eau, son procede de fabrication et utilisation d'une telle plate-forme Download PDF

Info

Publication number
WO1985004682A1
WO1985004682A1 PCT/NO1985/000020 NO8500020W WO8504682A1 WO 1985004682 A1 WO1985004682 A1 WO 1985004682A1 NO 8500020 W NO8500020 W NO 8500020W WO 8504682 A1 WO8504682 A1 WO 8504682A1
Authority
WO
WIPO (PCT)
Prior art keywords
platform
caisson
framework
floating
framework structure
Prior art date
Application number
PCT/NO1985/000020
Other languages
English (en)
Inventor
Per Bull HAUGSÖEN
Original Assignee
Haugsoeen Per Bull
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Haugsoeen Per Bull filed Critical Haugsoeen Per Bull
Priority to BR8506602A priority Critical patent/BR8506602A/pt
Publication of WO1985004682A1 publication Critical patent/WO1985004682A1/fr

Links

Classifications

    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B17/02—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto
    • E02B17/027—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto steel structures
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B17/02—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto
    • E02B17/025—Reinforced concrete structures
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B2017/0039—Methods for placing the offshore structure
    • E02B2017/0043—Placing the offshore structure on a pre-installed foundation structure
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B2017/0056—Platforms with supporting legs
    • E02B2017/0069—Gravity structures
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B2017/0056—Platforms with supporting legs
    • E02B2017/0073—Details of sea bottom engaging footing
    • E02B2017/0086—Large footings connecting several legs or serving as a reservoir for the storage of oil or gas

Definitions

  • Gravity platform for great water depth, method of manufacturing same, and use of such a platform
  • the invention relates to a gravity platform for a great water depth, wherein the platform in operational condition is intended to stand stably on the sea bed essentially by its own weight and in this position is intended to project above the water surface for support of a deck structure, the platform comprising a lower part in the form of a base and a caisson structure of concrete, and an upper part in the form of a framework structure carried by the caisson structure. Further, the invention relates to a method of manufacturing such a platform, and use of a gravity platform of the stated type.
  • Gravity platforms for shallow water very often are characterized by a concrete caisson consisting of a plurality of cells, and hollow columns projecting upwards from the caisson. Usually, the columns will partly be submerged during towing-out of the platform so that, during the towing-out phase, they contribute to stabilizing the platform. Both the concrete caisson and the columns will be able to be subjected to substantial wave forces. This principle is that which is mostly utilized on gravity platforms in the North Sea today. For the columns, also the circumstance applies that even if they are wave-loaded as a result of the volumes they possess, the same volumes to a substantial degree provide a positive contribution to supporting useful load during towing-out to the site of installation.
  • a typical gravitation platform for shallow water is "Condeep G3TM from Norwegian Contractors. This platform has substantial parts of the buoyancy volume at a high level. This shows that the requirement for reducing the wave forces in the upper part of the structure usually is not particularly great at shallow water, and that - from a total evaluation - it may be directly desirable to have a great volume at a high level, volume and water plane area giving a positive contribution to useful load on the deck during the towing-out.
  • Gravity platforms for a great water depth have so far not been installed.
  • a platform with the designation "T300” from Norwegian Contractors. This is a pure concrete platform for deep water and consists of a caisson base, oblique columns, a so called “riegel” and one or more columns carrying the platform deck.
  • a relatively large part of the structure projects above the water line during towing-out, and the structure is subjected to large wave forces in the operational condition.
  • Tecnomare (Tecnomare) .
  • the separate “flasks” provide for buoyancy and stability, and the steel framework has for its task to keep the flasks together.
  • any lower monolithic caisson structure - as in the present platform.
  • the principle of a caisson structure and a separate frame ⁇ work on the top thereof does not apply for the Tecnomare platform, either.
  • a gravity platform of the introductorily stated type which, according to the invention, is characterized in that the framework structure as well as the caisson structure has a height of at least 90 meters, and that the caisson structure is amonolithic structure of such a great height that the centre of gravity of the platform is located below its centre of buoyancy in a floating position during towing-out at a draft which is essentially equal to or less than the total height of the caisson structure, so that the platform is floating-stable without external means.
  • a method of manufacturing such a platform which method is characterized in that the framework structure and the caisson structure are built separately at respective sites, and that at least a part of the framework structure as an essentially finished unit in a floating position is brought into position to be connected to the caisson structure which is in a suitably submerged floating position for said interconnection.
  • An important aspect of the present invention also consists in the use of a gravity platform which in operational condition is intended to stand stably on the sea bed essentially by its own weight and in this position is intended to project above the water surface for support of a deck structure, the platform comprising a lower part in the form of a base and a caisson structure of concrete, and an upper part in the form of a framework structure carried by the caisson structure, at a water depth which is so great that the wave action in the depth region in which the caisson extends is unessential in relation to the wave action in the depth region in which the framework structure extends, the caisson still being so high that it contributes to the quite substantial portion of the floating stability of the platform during towing thereof without any external stabilizing means.
  • the platforms for shallow and deep water are to carry the same useful load on the deck during towing to the site of installation. Further, it is presupposed that it is decisive to minimize the horizontal forces on the platform. Therefore, the following calculation example is performed with the horizontal force as a criterion of whether a favourable platform is under consideration.
  • the first calculation example relates to a shallow water platform with a tower where the water depths is 150 m and the caisson height is chosen equal to 60 m.
  • the dimensioning wave height is 31 m with a period of 17 seconds.
  • the tower (105 m above the sea bed) is ca. 1.20 m/s .
  • Top ballast in the caisson is supposed to be located ca. 20
  • the mass coefficient of the tower is set equal to 2.0 and for the caisson equal to 1.5.
  • the efficiency factor E is by definition:
  • the ratio between the efficiency factors is ca. 1.0. This means that, for a platform wherein the horizontal force is of substantial importance for geotechnical stability, it is of little importance whether the caisson is made higher or whether the tower is expanded in the central area.
  • the second calculation example applies to a deep- water platform with a tower where the water depth is 300 m and the caisson height is chosen equal to 200 m, so that the central point of the tower is ca. 250 m above the sea bed.
  • Dimensioning wave height is 31 m with a period of 17 seconds. The wave acceleration at the top of the caisson
  • the efficiency factor is calculated as in the example of the shallow water platform.
  • the illustrated examples show that when a platform is to have a certain stabilizing capacity during towing to the site of installation, and at the same time is to have minimalized horizontal forces subsequent to installation, this is optimalized in different manners for a shallow water platform and a deep water platform.
  • the effect of an adjustment of the caisson or an adjustment of the tower volume is rather equal.
  • the above-mentioned ratio is 0.5 or 2.0 is of little interest.
  • this ratio has changed quite substantially. And this applies even if no limitation exists in the towing draft of the platform (towing draft limitation) .
  • the caisson is a volume structure which to a dominating degree is influenced by forces of inertia from the water particles.
  • forces resulting from water particle velocity will be dominating.
  • the maximum values of these loads are quite out of phase in relation to each other. Totally seen, this gives a favourable load situation for the platform, even if the greatest force comes in an intermediate phase with some contribution from each type of load.
  • An advantageous embodiment of the platform according to the invention is characterized in that, in connection with the framework, there is provided at least one hollow, air-filled column extending at least between the top of the framework structure and the top of the caisson structure and providing at least temporary dry access to the lower part of the platform, and which is arranged for exercise of operational control during different phases, such as assembly, towing, installation and operation of the platform.
  • the hollow column may be arranged in several different _ D manners. It may be a se ⁇ arate column which is outside of the framework structure and which is braced thereagainst, or it may be disposed and braced inside of the panels of the framework structure.
  • the hollow column may also be a part of the framework structure and it may be a hollow leg,
  • the platform structure according to the invention may • also comprise combination solutions wherein the above- mentioned advantages are achieved in combination with a tower structure projecting upwards from the caisson structure. 5
  • the tower structure In addition to the tower structure there will be columns having the support of the cantilevered tower structure.
  • the tower structure may be reduced to the smallest possible size as the necessary support for carrying deck structures and the like to a substantial degree will take place by 0 means of the columns.
  • Risers- and the like may be placed outside of the tower structure.
  • the platform includes such a tower which is cantilevered from the caisson structure and supports surrounding columns, the tower will also form an access shaft to the lower part of
  • a dry compartment in the lowermost part of the caisson, where the compartment constitutes an extension of the dry access shaft.
  • the compartment is used to pull in tubes from the outside of
  • casings which outermost consist of conductors curving out from the vertical already before reaching down to the sea bed. This may be done in several manners.
  • the tubes may extend through a corbeled structure, but they may also extend completely on the outside.
  • the method has advantages as compared to known methods.
  • the circum ⁇ stance that the tubes do not pass through air-filled buoyancy chambers means that no boring-out of concrete plugs is to be carried out, such as for the installed Condeep platforms. Further, this is advantageous as compared to known solutions, in that the tubes may be curved out to a substantial degree above the sea bed.
  • the combination of framework and caisson structure means that the curving-out of the tubes may be substantial already at the top of the caisson structure. This is also an improvement as compared to known platform alternatives for deep water wherein the tower geometry poses limitations. For some petroleum reservoirs it is of great importance to establish the tube-curving-out as high up ' as possible. Conductor, pipes carried obliquely outwards from a structure and. into the ground may be subjected to adverse compulsory deformations in settling of the platform. As a special measure here it may be desirable to have an outer guide tube for the conductor pipes allowing the conductor pipes a certain flexibility at a level directly above and possibly just below sea bed level. This will be able to reduce stresses due to settling deformations.
  • the caisson structure normally will be built up by a number of upstanding cells, and the conductor pipes may then pass through the top domes and the bottom domes of the cells. They may here extend in guide tubes creating a seal between external water and the interior of the cells. They may also be guided through the cells after installation in the field in that concrete plugs are bored out in the domes.
  • a S a special measure when the platform is installed in connection with pre-drilled wells, the lowermost part of the conductor pipes may be curved. This will cause a continued curving after the conductor pipes have been carried down into the loose masses, and the total stresses in critical zones will be reduced.
  • Fig. 1 shows a side view of a first embodiment of a platform according to the invention
  • Fig. 2 shows an enlarged section along the line II-II in Fig. 1;
  • Fig. 3 shows a section along the line III-III in Fig.l
  • Fig. 4 shows a side view of a second embodiment of a platform according to the invention
  • Fig. 5 shows a section along the line V-V in Fig. 4;
  • Fig. 6 shows a side view of a third embodiment of a platform according to the invention.
  • Fig. 7 shows a side view of a fourth embodiment of a platform according to the invention wherein the caisson h s only one cell;
  • Fig. 8 shows a cross-section of the caisson along the line VIII-VI I in Fig. 7;
  • Fig. 9 shows a side view of a fifth embodiment of a platform according to the- invention
  • Fig. 10 shows a section along the line 10-10 in Fig.9;
  • Fig. 11 shows a longitudinal partial section of an embodiment wherein a portion of the base of the platform is raised for the formation of a space for pre-drilled wells;
  • Fig. 12 shows a section through a cell configuration
  • Fig. 13 shows an embodiment of an interconnection between a caisson structure and a framework structure
  • Figs. 14-16 show three different phases of a first embodiment of the method according to the invention for manufacturing the platform according to the invention;
  • Fig. 17 shows a second embodiment of the method according to the invention;
  • Figs. 18-21 show different phases of a third embodiment of the method according to the invention
  • Figs. 22-24 show different phases of a fourth embodiment of the method according to the invention
  • Figs. 25-27 show different phases of a fifth embodiment of the method according to the invention.
  • Figs. 28-30 show different phases of a sixth o embodiment of the method according to the invention.
  • Figs. 31-32 show different phases of a seventh embodiment of the method according to the invention.
  • the gravity platform shown in Fig.l consists of a lov/er 0 part in the form of a caisson structure 1, and an upper part in the form of a framework structure 2.
  • the platform is placed on a sea bed 3, and the framework structure projects above the water surface 4 and supports a deck structure 5.
  • the caisson structure 1 is composed of a plurality of cells cast together to a monolithic structure.
  • the cells constitute a number of cell groups of which an outer, low cell group 6 and an inwardly located, somewhat higher cell group 7 form a o base structure resting on the sea bed 3.
  • a skirt 8 constituted by circular cell walls in concrete or steel, depends from the base and penetrates the sea bed.
  • the base or foundation may have a relatively large area, for
  • parts of the base may have low 5 height, e.g. less than 30 m.
  • Parts of the base are extended upwards in the form of a central cell group constituting the upper part of the caisson and consisting of vertical cells 9.
  • the cells 9 are of round cross-section and are 0 cylindrically shaped, but they may also have another cross- sectional shape, for example polygonal, as shown in Fig. 12.
  • the height of the cell group 9 is substantially greater than the width.
  • the number of cells and their mutual arrangement may vary.
  • the cell diameter may vary when there are several 5 cells.
  • the cells of the cell groups 6 and 7 of the base structure are closed at the top by curved shell structures 10, and also the high, central cells 9 are closed by corresponding shell or plate structures (domes) 11.
  • the framework structure 2 of the platform consists of four columns 12 carried by the corner cells of the cell group 9, and a number of schematically shown, horizontal struts 13 and oblique struts 14.
  • the horizontal struts 13 extend between the columns 12 as shown in Fig. 3.
  • the columns 12 carry the deck structure 5, and at least one of the columns may be a hollow, air-filled column providing dry access to at least the uppermost part of the caisson 1.
  • the column contains a shaft 15 (Fig. 3) in which there may be arranged stairs and/or a hoisting means (not shown) for controlling personnel for execution of operational control, at least during the towing and installation phases of the platform.
  • the columns 12 are shown to be vertical, but they may also be slightly sloping towards each other towards the top.
  • Fig. 4 there is shown a second embodiment of the platform according to the invention.
  • the caisson structure 1 is of the same design as in Fig. 1, but the framework structure 16 is different and here consists of a plurality of vertical columns or posts 17 between which there extend a plurality of horizontal struts 18 and oblique struts 19.
  • the framework surrounds a hollow column 20 corresponding to the hollow column 12 in Fig. 1.
  • the column 20 does not necessarily constitute a part of the actual framework structure, such as is the case in the embodiment in Fig. 1.
  • the hollow column 20 may suitably be dimensioned to withstand the ambient loads on the site of installation only when it is connected to and supported by the framework, but to have sufficient strength to withstand the ambient loads when it stands unbraced in sheltered waters.
  • the hollow column 20 is here shown centric inside of the panels of the framework structure. This is only an example.
  • the hollow column may be placed at any place inside of the panels, it may be placed outside of the panels or it may be a part of the framework structure.
  • the embodiment in Fig. 4 is schematically shown to include a number of casings or conductor pipes extending outside of the caisson and having an oblique course in the area of penetration into the sea bed.
  • a first type of tube 5 21 goes straightly down and a possible deviation from a vertical line is made beneath the sea bed.
  • Another type of tube 22 gets a deviation before the sea bed, but is inside of the caisson.
  • a third type of tube 23 gets a deviation high up and is carried at the outside of the caisson, and
  • All or some of the tubes may be surrounded by a jacket forming a larger, closed volume, and the wave forces will even be able to reduce the mass forces totally. Simultaneously, this volume may be able to form a safety volume and cause the interconnection with the deck in
  • the framework 16 and the caisson 1 may be built separate fr ⁇ rt each other
  • the framework is then floated in place above the caisson when this is in a suitably submerged
  • the framework may then be built with a side opening for introduction of the column 20, as suggested at 25 in Fig. 5. In this case it may be topical to post-assemble a limited number of struts 26 and 27, e.g. as shown in Fig . 5.
  • the framework structure 16 is carried out in the same manner as in Fig. 4, but the caisson 28 is different from the embodiment in Figs. 1 and 4.
  • the caisson comprises several oblique, upwards converging cells 29 carried upwards from a base 30 without the cells having any mutual connection between the upper side of the base and the uppermost portion of the caisson where the cells 29 are cast together.
  • a skirt 31 depends from the base in order to penetrate the sea bed on the site of installation.
  • casings 32 extending at the outside of the caisson, and also at the outside of the framework structure.
  • Figs. 7 and 8 there is shown a platform embodiment wherein the caisson is formed by only one cell 33 having a circular cross-section.
  • a fifth embodiment of the platform according to the invention consisting of a caisson 34 and a framework structure 35.
  • a strong column 36 is ° cantilevered frc the caisson structure.
  • To this column 36 there is braced a lighter structure of columns 37. It is the strong column 36 which braces the total structure above the caisson 34.
  • the arrangement of the columns 37 of the framework with associated braces or struts 38, 39 appears ° from the cross-section in Fig. 10.
  • Fig. 9 there is shown an access shaft 40 extending downwards through the caisson 34, so that dry access is established all the way from the deck 41 via the hollow column 36 and down to the sea bed 42.
  • the 5 access shaft 40 passes into a chamber 43 which may be used for different technical devices which are necessary to establish the platform, 1.7
  • the platform in Fig. 9 is shown to be fixed to the sea bed by means of piles 45. Such piling may be necessary, e.g. to reduce settlings.
  • the lowermost part of the framework structure may be made of strong columns with braces.
  • the columns may be cast in concrete or made in steel.
  • the uppermost part of the framework structure may be a lighter structure in steel which is mounted on top of the former.
  • the lowermost part may also be conical columns without braces.
  • the upper framework structure may consist of four supporting legs connected to oblique plates arranged such that each of them intersects a pair of other oblique plates. This enables extra many connections which transfer horizontal force, so that the lifetime of the platform increases.
  • the outer legs as well as the braces are stepped downwards.
  • inner legs are constructed which are pulled into the outer ones.
  • the inner and outer legs are adapted in relation to each other so that there is a little distance therebetween. Connection is obtained by injection of mortar (grouting) .
  • Fig. 11 shows a sixth embodiment of the platform according to the invention and illustrates a special arrangement of the lower concrete structure.
  • the base here consists of a pair of concentric rings of totally eighteen domes 46 at bottom level.
  • a central compartment 47 is provided to give room for pre-drilled wells 48. If such a compartment is not to be provided, the central opening will be covered by an additional dome 46.
  • At least twelve outermost domes and the central dome (when this is present) are supported by skirts 49 penetrating the sea bed. All domes or a selection thereof may be covered with flat discs. These discs may be prestressed in a simple manner so that tensile stresses resulting in cracks are avoided.
  • the seven inner domes are covered by cells 50 up to another level of domes 51.
  • Inclined planes 52 extend from the periphery of the twelve outermost cells up to the latter dome level.
  • the seven inner cells continue further upwards from this dome level in the form of* cells 53 forming the caisson structure 54 of the platform.
  • the cells 53 are terminated•with domes 55.
  • the stated solution renders an inner floating volume to these surfaces during the first floating phases. Totally, the solution provides a relatively light base which to a great extent can be finished in dock with limited towing draft out to the deep water location for further construction.
  • the walls in the cells of the caisson may have a decreasing thickness upwards from a certain level. This is favourable for i.a. the floating stability and is made possible as a result of the fact that the hydrostatic pressure, which is dimensioning, decreases. In slip forming this will require a special slip form system with variable bents which are previously not known on structures having several connected cells.
  • Said compartment 47 which is arranged to give room for pre-drilled wells rising above the sea bed, is in principle formed by raising the bottom of the base structure in a suitable region.
  • the pre-drilled wells are drilled from a drillingrig before the platform is installed. Thereafter the well tubes will be extended to deck level.
  • an access shaft in the form of a hollow cylinder 56 extending downwards through the framework structure 57 as well as the caisson 54.
  • a special solution for a part of the mechanical systems is conceivable in that these are finished in a container which is subsequently transported in position so that it can be lifted up to a dome and then be placed there. This container may then form an extension of the inner, hollow cylinder.
  • a container 58 is shown in Fig. 11.
  • the container 58 with mechanical systems is connected to a riser tunnel 59 which may consist of a large steel tube or concrete tube and is pulled into the base structure.
  • the cells 53 above the base structure may consist of circular cells which are tangent to each other. As shown in Fig. 12, the cells may alternatively consist of elements
  • connection between the upper framework structure and the lower concrete structure may for example be obtained _ as shown in Fig. 13, in that the framework structure is terminated by a flat bottom plate 62 going beyond the cylinder shape of the legs 63.
  • the plates 62 are placed on concrete columns 64 cast around the cylinder walls on the concrete structure 65.
  • Connection between the two structures is S obtained by prestressing, e.g. prestressed cables 66. Braces transferring horizontal forces down into the concrete structure must be fixed by a similar method.
  • the frame ⁇ work structure 70 with cantilevered auxiliary structure 71 is finished in upright position on a separate place. It is 5 thereafter brought onto floating bodies 72 as shown in Fig. 15 and is towed in over the ballasted caisson 73 as shown in Fig. 16 and is interconnected (mated) therewith in that the caisson is deballasted. Thereafter the framework structure may be securely fixed to the caisson.
  • the platform embodiment shown in Fig. 17 there is established a divided column for use in the interconnection of the framework structure and the caisson.
  • the platform embodiment corresponds to the embodiment in Fig. 6. It appears from Fig. 17 that the hollow column 20 in Fig.
  • the construction phase is divided into an upper column part 20a arranged in the upper portion of the framework structure 16, and a lower column part 20b projecting upwards from the caisson 28.
  • the hollow, air-filled column does not need to be divided in the shown manner.
  • the hollow column 20b is built on the caisson 28, this is submerged as shown in Fig. 17 so that only a small part of the column rises above the water surface 4.
  • the separately built framework structure 16 with the column part 20a is floated in vertical position with submerged lower end to the position of the caisson and is mated therewith, the operation being controlled by means of controlling personnel in the hollow column.
  • the framework structure is suitably provided with extra buoyancy tanks 74 for keeping the structure floating and for controlling the lowering of the framework to a suitable depth in relation to the top of the caisson.
  • the caisson is deballasted for raising of the entire framework structure to a position above the water surface, whereafter the framework structure is secured to the caisson and the hollow column in free air, and also the upper and lower column parts are interconnected in a tight manner.
  • Figs. 18-21 show different phases of a third embodiment of the method for establishing the framework structure on the caisson.
  • the framework structure 75 is built horizontally in a known manner. Thereafter it is set afloat and ballasted until it is vertical.
  • Hoisting means 76 are attached on floating bodies 77 or barges to the framework structure 75, and this is either raised up above the water or raised to a small draft.
  • the framework structure 75 is brought in above the down-ballasted caisson 78 and interconnection is effected. If the framework structure is not quite free of the water surface, the caisson must have parts which project upwards and which do not inter ⁇ fere with the framework structure. This is suggested in Fig. 21 wherein an extra safety volume 79 is built above the upper domes of the caisson.
  • the framework structure and the caisson will be equipped with special means for achieving a safe securing of these platform parts to each other. These means may be of various types, e.g. such as described in connection with Fig. 13.
  • Said extra safety volume 79 on the caisson 78 may be established in different manners, e.g. by casting a cofferdam. If this cofferdam interferes with the framework, one defers introducing some of the lowermost rods in the framework until after assembly. The assembly itself takes place in that the framework is floated over the concrete structure. If convenient, the framework is kept stationary and the concrete structure is moved. The concrete structure is controlled via the safety volume or a separate control column.
  • thewhole caisson may be lowered .under water before interconnection with the framework.
  • the caisson may be stabilized by use of temporary buoyancy bodies, or by use of crane equipment. For safety reasons it may be conceivable that the caisson is deballasted on a place where there will be a small bottom clearance.
  • a temporary articulation means 80 as a connection between the concrete structure 81 and the framework structure 82 which in turn is lying in floating condition on a barge 83.
  • the concrete part is submerged under water, and the framework on the barge then rises progressively because of the buoyancy.
  • Final assembly is carried out after the structure is deballasted so that the articulation comes into free air.
  • the structure is secured against getting lost in that it is taken care that the sea bed is at a suitable level. It will be clear that this method may also be used in connection with a concrete caisson including a column projecting therefrom as shown in Figs. 6 and 17.
  • Fig. 25-27 show an embodiment wherein the caisson con ⁇ struction 84, i.e. the concrete part, is caused to assume a floating position deviating maximum 90 from vertical position of the caisson, so that the concrete part 84 and the framework part 85 in corresponding floating position can be coupled together before the entire structure is again erected by ballasting.
  • Fig. 28-30 shows an embodiment wherein the caisson structure 86 is ballasted to an oblique floating position and is brought into position adjacent to the lower end of the framework structure 87 floating in a horizontal (or suitably inclined) position on a floating means 88.
  • the caisson and framework are thereafter interconnected by means of an articulation means 89 at the lower, adjacent end portions, whereafter the two parts 86, 87 by means of suitable ballast and possibly also buoyancy means are caused to assume the corresponding oblique position shown in Fig.29, so that provisional or partial interconnection can be effected.
  • the whole structure is ballasted so that it is brought to upright position, whereafter final interconnection is effected.
  • the framework part may be brought to an oblique floating position, corresponding to that of the concrete part by means of suitable floating or buoyancy bodies, before the two parts are moved together and interconnected provisionally to each other and the entire structure thereafter is ballasted to an upright position. Said articulation between the concrete part and the framework part may then be omitted.
  • Fig. 31-32 illustrate an embodiment wherein the framework structure is built in an upright position in two or more parts 90,91 and transported by barges 92 for inter- connection with the caisson structure 93 which is in a suitably submerged floating position.
  • Final interconnection of the different parts can be effected in free air, either by welding or by injection of mortar (grouting) .
  • the caisson may be provided with temporary auxiliary bodies mounted thereon and projecting upwards from the upper end of the caisson. These bodies are then utilized in ballasting-down of the caisson, so that this in a safe manner can be lowered down a suitable distance beneath the water surface. It is thereby achieved that the framework structure in a simple and safe manner can be brought in over the caisson structure, the framework being possibly partly submerged in a stable position on suitable floating means.
  • one or more columns may be cast in concrete by slip forming in embodiments corresponding to the embodiment in Fig. 1, the columns being cast directly on the caisson structure.
  • the columns are mutually braced by means of braces in steel or concrete. It may be suitable to ballast the platform to a greater draft when the bracing is mounted.
  • the framework structure may also be built in that e.g. four panels are transported separately on barges and coupled to the concrete part by means of a hinge. The concrete part is gradually submerged, and the panels, which are connected to the barges, are pivoted to an upright position.
  • the framework may then consist of eight supporting columns which are connected in pairs.
  • the barges may be replaced by containers which are subsequently used as an integrated part of the deck structure of the platform.

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Revetment (AREA)
  • Road Signs Or Road Markings (AREA)

Abstract

Plate-forme à gravité pour une grande profondeur d'eau, où la plate-forme en condition de fonctionnement est conçue pour reposer de manière stable sur le fond de la mer (3) essentiellement en raison de son propre poids et pour saillir dans cette position au-dessus de la surface de l'eau (4) afin de servir de support à la structure de pont (5). La plate-forme comporte une partie inférieure ayant la forme d'une base (6, 7) et une structure de caisson (1) en béton ainsi qu'une partie supérieure ayant la forme d'une structure de bâti (2). Afin de tenir compte des circonstances et des conditions naturelles d'une manière optimale, entre autres, les limites existantes en ce qui concerne la pression de halage disponible à partir de la zone côtière abritée jusqu'au site d'installation, la structure de bâti (2) et la structure de caisson ont une hauteur d'au moins 100 mètres, alors que la structure de caisson monolithe (1) à une grande hauteur par rapport à la structure de bâti (2) telle que le centre de gravité de la plate-forme se trouve essentiellement en dessous de son centre de flottabilité en position de flottage pendant le halage à une profondeur essentiellement égale ou supérieure à la hauteur de la structure de caisson (1). Ainsi, la plate-forme est stable en flottage à la profondeur en question sans nécessiter de mécanismes extérieurs.
PCT/NO1985/000020 1984-04-06 1985-04-02 Plate-forme a gravite pour une grande profondeur d'eau, son procede de fabrication et utilisation d'une telle plate-forme WO1985004682A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
BR8506602A BR8506602A (pt) 1984-04-06 1985-04-02 Plataforma de gravidade para grande profundidade de agua,processo de fabricacao da mesma,e emprego de uma plataforma deste tipo

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO841368A NO841368L (no) 1984-04-06 1984-04-06 Hybrid gravitasjonsplattform for stort vanndyp
NO841368 1984-04-06

Publications (1)

Publication Number Publication Date
WO1985004682A1 true WO1985004682A1 (fr) 1985-10-24

Family

ID=19887588

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/NO1985/000020 WO1985004682A1 (fr) 1984-04-06 1985-04-02 Plate-forme a gravite pour une grande profondeur d'eau, son procede de fabrication et utilisation d'une telle plate-forme

Country Status (5)

Country Link
EP (1) EP0178311A1 (fr)
AU (1) AU4210285A (fr)
BR (1) BR8506602A (fr)
NO (1) NO841368L (fr)
WO (1) WO1985004682A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2182084B (en) * 1985-10-23 1989-04-19 Norwegian Contractors Offshore platform structure of reinforced concrete and a method of building the structure
FR2726302A1 (fr) * 1994-10-26 1996-05-03 Doris Engineering Procede de construction et d'installation d'une structure de plate-forme marine gravitaire et structure de plate-forme concue pour la mise en oeuvre de ce procede
NL2003012C2 (en) * 2009-06-12 2010-12-15 D E M E N V Hybrid offshore large pile - gravity foundation for constructions, and installation method therefor.

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3911687A (en) * 1972-05-02 1975-10-14 Olav Mo Foundation method for caissons
US4045968A (en) * 1974-12-24 1977-09-06 Kajima Corporation Offshore platform and method for its installation
US4126011A (en) * 1976-05-20 1978-11-21 Compagnie Generale Pour Les Developpements Operationnels Des Richesses Sous-Marines "C.G. Doris" Method of fabrication of offshore structures and offshore structures made according to the method

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3911687A (en) * 1972-05-02 1975-10-14 Olav Mo Foundation method for caissons
US4045968A (en) * 1974-12-24 1977-09-06 Kajima Corporation Offshore platform and method for its installation
US4126011A (en) * 1976-05-20 1978-11-21 Compagnie Generale Pour Les Developpements Operationnels Des Richesses Sous-Marines "C.G. Doris" Method of fabrication of offshore structures and offshore structures made according to the method

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2182084B (en) * 1985-10-23 1989-04-19 Norwegian Contractors Offshore platform structure of reinforced concrete and a method of building the structure
FR2726302A1 (fr) * 1994-10-26 1996-05-03 Doris Engineering Procede de construction et d'installation d'une structure de plate-forme marine gravitaire et structure de plate-forme concue pour la mise en oeuvre de ce procede
NL2003012C2 (en) * 2009-06-12 2010-12-15 D E M E N V Hybrid offshore large pile - gravity foundation for constructions, and installation method therefor.
EP2261425A1 (fr) * 2009-06-12 2010-12-15 D.E.M.E. Nv Fondation offshore gravitaire hybride à pieu large pour constructions, et sa méthode d'installation

Also Published As

Publication number Publication date
BR8506602A (pt) 1986-04-15
EP0178311A1 (fr) 1986-04-23
AU4210285A (en) 1985-11-01
NO841368L (no) 1985-10-07

Similar Documents

Publication Publication Date Title
CA2728430C (fr) Structure de support destinee a etre utilisee dans l'industrie des parcs eoliens maritimes
EP1777348B1 (fr) Dispositif et procédé pour installer construction offshore
CN110382781B (zh) 用于在海洋环境中利用重力铺设建筑物、设备和风力涡轮机的基础的海事结构
US8820254B2 (en) Catamaran ship used for assembling, transporting and installing a marine wind turbine on the seafloor
US20120093589A1 (en) Foundation support system for an offshore wind energy convertor, corresponding to an offshore wind power generating facility
CA2980959C (fr) Fondation ballastee destinee a l'installation d'eoliennes en haute mer
CN103255752B (zh) 支撑海上风机、海洋建筑物的浮力支撑固定平台
JPS5857571B2 (ja) 構造体を海底に固定する継手
US4711601A (en) Method of installing offshore constructions
CA1228990A (fr) Plate-forme de forage en mer
US4448570A (en) Method of constructing a concrete off-shore structure more than 200 m high stabilized on the sea bed by its own weight
WO1985004682A1 (fr) Plate-forme a gravite pour une grande profondeur d'eau, son procede de fabrication et utilisation d'une telle plate-forme
CN111636465B (zh) 一种一体式深水基础及其施工方法
KR20230162941A (ko) 해상 풍력 터빈용 기초
US20220162825A1 (en) Method for the installation of an offshore maritime structure and offshore maritime structure
AU689950B2 (en) Method for constructing and installing an offshore gravity plaftorm structure and platform structure designed for the implementation of this method
NO142535B (no) Fralandskonstruksjon for store dybder.
GB1590177A (en) Marine structure
EP2189576A1 (fr) Système de fondation pour structures marine en eaux profondes
JP2024064177A (ja) スパー型浮体を備えた洋上風力発電設備の浮体建造方法
CA1052108A (fr) Tour de beton
CA1288960C (fr) Methode d'implantation de structures en haute mer
JP2953818B2 (ja) 大水深用構造物の建造方法
AU2021202442A1 (en) Gravity-Based Structure For Off-Shore Structures
GB2034789A (en) Offshore structure

Legal Events

Date Code Title Description
AK Designated states

Designated state(s): AU BR GB JP SE US

AL Designated countries for regional patents

Designated state(s): AT BE CH DE FR GB IT LU NL SE

WWE Wipo information: entry into national phase

Ref document number: 1985901612

Country of ref document: EP

WWP Wipo information: published in national office

Ref document number: 1985901612

Country of ref document: EP

WWW Wipo information: withdrawn in national office

Ref document number: 1985901612

Country of ref document: EP