GB2278871A - Foundation for an offshore platform - Google Patents
Foundation for an offshore platform Download PDFInfo
- Publication number
- GB2278871A GB2278871A GB9411682A GB9411682A GB2278871A GB 2278871 A GB2278871 A GB 2278871A GB 9411682 A GB9411682 A GB 9411682A GB 9411682 A GB9411682 A GB 9411682A GB 2278871 A GB2278871 A GB 2278871A
- Authority
- GB
- United Kingdom
- Prior art keywords
- pile
- sleeve
- foundation
- pin
- platform
- Prior art date
- Legal status (The legal status 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 status listed.)
- Granted
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
- E02B17/0008—Methods for grouting offshore structures; apparatus therefor
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Mechanical Engineering (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Foundations (AREA)
Abstract
Foundation for an offshore platform, comprising a tubular pile 15 pre-installed in the subsea strata with a bearing ring 16 resting on its upper end; a sleeve 14 of generally similar cross sectional shape to the pile and adapted to rest on the bearing ring in co-axial alignment with the pile, such sleeve being rigidly connected to the platform; and a pin 17 which can be lowered within the sleeve 14 and the pile 15 in a generally co-axial alignment therewith, to bear on an upper surface of the sleeve, so that compressive loads between the platform and the pile are carried in bearing in the sleeve, and grout introduced between the inner surface of the pile and the outer surface of the pin will carry tensile loads between the platform and the pile. <IMAGE>
Description
FOUNDATION AND METHOD OF INSTALLATION
The invention relates to a foundation for a platform, and in particular relates to a foundation and to a method for installing or reinstalling a substructure on that foundation to form an offshore platform.
Offshore platforms have conventionally incorporated a support portion or substructure (known within the offshore industry as a jacket) secured to the seabed by piles. These piles have been driven through pile sleeves attached to the jacket just above the seabed, and then grouted to those pile sleeves.
The connection securing the piles to the pile sleeves has conventionally been grouting within the annuli between the pile sleeves and the piles. The primary load transfer mechanism for both compressive and tensile loads has conventionally been in shear through the grouted annul us. Compressive loads result from the weight of the platform plus the download from resisting overturning moments, while tensile loads result from the upload from resisting overturning moments less the weight of the platform. Clearly the compressive loads carried in shear through the grouted annul us will exceed the tensile loads.
Heretofore jackets have been purpose built for particular applications at specific offshore locations. In general these jackets have been scheduled for removal at the ends of their lives because they would otherwise become hazards. Few attempts have been made to salvage large jackets for reuse.
In the past it has been common practice to set a jacket with pile sleeves attached thereto on to a seabed, and then to stab and drive foundation piles through the pile sleeves. However, use has recently been made of a pre-installed foundation concept.
One proposal for the salvage and reuse of a jacket has adopted the preinstalled foundation concept featured in US Patent No. 4,669,918. This concept involves the installation of foundation piling prior to jacket installation, using a pile placement template. The pile placement template is a planar frame incorporating pile guide sleeves which enable the positioning and driving of foundation piling in a prescribed pattern and to within very precise tolerances. Depending on the required base dimensions of the jacket, a pile placement template may wholly or fractionally define the base. A fractional pile placement template - to be relocated on existing installed piles and/or rotated on special locator piles - may capitalize on structural symmetry. Such templates can be recovered after the foundation piling has been installed, and can then be stored for reuse.However, a pile placement template may be left in place without obstructing subsequent jacket installation.
This concept has been promoted for the salvage and reuse of specially designed jackets which are intended to be detached from their piled foundations just above seabed level. It has been proposed that the specially designed jacket is then deballasted and moved elsewhere for reinstallation on top of another pre-installed foundation. The concept also allows the adaptation and reuse of existing conventional structures that can be wholly recovered. Comparatively minor modifications - basically the addition of extensions to the legs - allow reinstallation onto pre-installed foundation piling at another location.
The use of the pre-installed foundation concept for the salvage and reuse of purpose designed jackets is subject to a number of disadvantages.
The support method pre-supposes that the structure is wholly recovered and returned to the surface, to be refitted with new extensions. This may be applicable to small jackets, with the use of complex and potentially dangerous marine lifting operations, but it would currently be impractical for large jackets. Moreover, fairly tight dimensional tolerances must be maintained, and there is no provision for distortions of the jacket which may arise during the recovery of that jacket. These disadvantages impede the general acceptance of pre-installed foundation techniques for the removal and reuse of substructures.
The invention provides a foundation for an offshore platform, comprising a tubular pile pre-installed in the subsea strata with a bearing ring resting on its upper end; a sleeve of generally similar cross sectional shape to the pile and adapted to rest on the bearing ring in co-axial alignment with the pile, such sleeve being rigidly connected to the platform; and a pin which can be lowered within the sleeve and the pile in a generally co-axial alignment therewith, to bear on an upper surface of the sleeve, so that compressive loads between the platform and the pile are carried in bearing in the sleeve, and grout introduced between the inner surface of the pile and the outer surface of the pin will carry tensile loads between the platform and the pile.
It is preferred that the bearing ring is separate from the upper end of the pre-installed pile, and is adapted to rest thereon.
It is further preferred that the configuration of the bearing ring at the upper end of the pre-installed pile can be modified to suit minor inaccuracies of angle and elevation.
The bearing ring at the upper end of the pre-installed pile may be formed with an upwardly directed conical guide to assist in the alignment of the sleeve with the pile when the sleeve is lowered onto the pile.
In one form of the invention the pin is mounted for limited rotational movement on a shaft extending from the pin to a cross head which bears on the upper surface of the sleeve.
In this form it is preferred that the pin is mounted on a universal coupling at the end of the shaft away from the cross head.
The grouted connection between pin and pile may be replaced by a swaged connection.
Advantageously the pin carries one or more grout supply lines and/or one or more packer inflation lines whereby the grout may be introduced into and/or confined within an annular space between the inner surface of the pile and the outer surface of the pin.
The invention includes a foundation as described above, and comprising a group of piles, sleeves and pins.
The invention also provides a method of securing an offshore platform to the seabed which comprises the steps of installing a tubular pile into the seabed with a bearing ring at its upper end; placing the platform over the pile such that a sleeve rigidly connected to the platform rests on the bearing ring in co-axial arrangement with that pile; lowering a pin through the sleeve into the pile in co-axial alignment therewith; and introducing grout into the annular space between the inner surface of the pile and the outer surface of the pin, whereby compression loads between the platform and the pile are carried in bearing in the sleeve, and tension loads are carried in the grout.
It is preferred that a separate bearing ring has its configuration modified as necessary to suit minor inaccuracies of angle and elevation, and is then placed on top of the tubular pile.
The invention includes an offshore platform having foundations formed as described above.
Two specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 is an illustration of a jacket set on a pre-installed foundation;
Figure 2 is a diagrammatic cross section taken through a vertical plane and showing a first embodiment of the attachment of a single foundation pile to the jacket; and
Figure 3 is a similar cross section of a second embodiment.
Figure 1 shows a jacket 10 with tubular steel legs 11 disposed over a pre-installed foundation spacer template 8. The jacket is secured to the seabed with tubular steel piles 15.
Figures 2 and 3 show diagrammatically how the jacket 10 is secured to the piles 15. It must be emphasised that these figures are illustrative only, and do not necessarily show practical wall thicknesses or clearances.
As shown in Figure 2, the foot of a leg 11 of the jacket 10 has an outstanding shear plate 12. A cylindrical sleeve 14 is connected to the shear plate 12 so that the axis of the sleeve 14 is vertical.
While the jacket is elsewhere (e.g. still under construction in a fabrication yard), a pre-installed foundation is set on the seabed at the intended site of the platform. The pre-installed foundation includes a pile 15 driven into the subsea strata through a guide cone 9 (shown in dashed lines) of the pre-installed foundation spacer template 8. At the upper end of the pile 15 there is provision for a separate bearing ring 16. When all the piles of the pre-installed foundation have been driven, the tops of those piles can be surveyed for level and angle, and individual bearing rings can be cut to suit these levels and angles to form a suitable base for the jacket.This obviates any mismatch which might be caused by uneven driving of the piles. (It will be understood that, as shown in figure 1, the jacket 10 has a number of sleeves 14 each of which rests on the bearing ring 16 of a corresponding pile 15. This description will refer only to the single pile 15 shown in Figure 2).
The separate bearing ring 16 is shaped to rest on the upper end of the pile 15, so that the sleeve 14 can be set on the pile 15 to transfer compressive loads in direct bearing from the jacket to the subsea strata.
At the time of installation, the jacket is positioned over the preinstalled foundation and lowered so that a lower peripheral rim of the sleeve 14 rests on the bearing ring 16.
To complete the foundation connection, a hold down pin 17 having a bearing cap 18 is lowered through the sleeve 14 and pile 15, and rests with its bearing cap 18 on an upper peripheral rim of the sleeve 14. Grout packers 21 and 22 are attached to the pin 17, for inflation through primary and secondary lines 23 and 24 in the bearing cap 18. Primary and secondary grout lines 25 and 26 are arranged to supply grout to inlets 27 and 27A respectively, and there is a grout monitor 28 to determine when the annul us between pile 15 and pin 17 is fully grouted. (Details of the grouting arrangements form no part of this invention.)
Grout is then introduced into the annul us between the pile 15 and the pin 17 to transfer tensile loads from the jacket to the foundation.Prior to installation a weld bead may be applied to the inside of the pile 15 and to the outside of the pin 17 over the length W, so to enhance the load carrying capacity of the pile/grout/pin combination. (No grout is shown in the figures.)
Thus connection of the pile 15 to the jacket for vertical downthrust is through bearing on the ring 16 rather than in shear through a grouted annul us. Uplift is carried in tension through the pin 17 which is connected to the inside of the pile 15 through shear via the grouted annul us.
Consequently, the length of the annul us is less than on a conventional jacket because it carries only tensile load, which will be less than the compressive load in a conventional jacket. There is also a saving in the pile sleeve of a conventional jacket, as this function is now carried out by the inside of the tubular pile itself.
The pile length is reduced because it does not have to stand above the seabed, thereby saving typically 11 metres per pile. The length of the pin compensates for this in part, but as stated previously it is required to be of a shorter length than the sleeve.
Figure 3 shows a foundation arrangement generally similar to that shown in Figure 2, with an outstanding shear plate 112, sleeve 114 and pile 115.
In this case the hold down pin 17 is replaced by an internal sleeve 117 supported on a universal coupling 131 connected by a solid bar 132 to a cross head beam 133. (The cross head beam 133 replaces the bearing cap 18 in Figure 2.) The universal coupling 131 may be unnecessary if the bar 132 is sufficiently flexible to allow the sleeve 117 to make small angular deflections within the pile 115. The cross head beam has tensioning means such as hydraulic tensioning or a nut 134 on a threaded extension to the bar 132.
Shown also in Figure 3 (but equally applicable to the embodiment of
Figure 2) is a coned top to the separate bearing ring 116 (or 16 in
Figure 2) to guide the sleeve 114 onto the pre-installed pile 115. The bearing ring 116 can be cut to suit pile elevation and angle, if the piling of the pre-installed foundation template is uneven.
In the event that the jacket 10 is to be re-used at another offshore site, the jacket can be released from its foundations by cutting the bar 132 or removing the nut 134. The cross head 133 can be recovered, and the sleeve 114, shear plate 112 and jacket can be raised off the seabed for relocation. The pile 115, bearing ring 116, internal sleeve 117, coupling 131 and bar 132 remain on the seabed. The jacket can subsequently be reused on another pre-installed foundation at another site.
There may be occasions where a pre-installed foundation could lead to major cost savings. One example would be in the case of a jacket to be set over a pre-installed drilling template in a soft soils area. The preinstalled foundation would enable savings to be made on mudmats, because the jacket would not require mudmats for initial on-bottom stability. In addition, the need for a docking pile within the pre-installed drilling template would be avoided as the pre-installed foundation for the jacket could be used. Finally there would be weight savings on the jacket by the reduced lengths of pile sleeves, and possibly reduced numbers, due to the use of one of the foundation piles under each leg. As well as saving fabrication costs, these weight savings might make the difference between a jacket being launched and lifted.
Claims (15)
1. Foundation for an offshore platform, comprising a tubular pile pre
installed in the subsea strata with a bearing ring resting on its upper
end; a sleeve of generally similar cross sectional shape to the pile and
adapted to rest on the bearing ring in co-axial alignment with the pile,
such sleeve being rigidly connected to the platform; and a pin which can
be lowered within the sleeve and the pile in a generally co-axial
alignment therewith, to bear on an upper surface of the sleeve, so that
compressive loads between the platform and the pile are carried in
bearing in the sleeve, and grout introduced between the inner surface
of the pile and the outer surface of the pin will carry tensile loads
between the platform and the pile.
2. Foundation as claimed in Claim 1 in which the bearing ring is separate
from the upper end of the pre-installed pile, and is adapted to rest
thereon.
3. Foundation as claimed in Claim 2 in which the configuration of the
bearing ring at the upper end of the pre-installed pile can be modified
to suit minor inaccuracies of angle and elevation.
4. Foundation as claimed in any one of the preceeding claims in which the
bearing ring at the upper end of the pre-installed pile is formed with
an upwardly directed conical guide to assist in the alignment of the
sleeve with the pile when the sleeve is lowered onto the pile.
5. Foundation as claimed in any one of the preceeding claims in which the
pin is mounted for limited rotational movement on a shaft extending from
the pin to a cross head which bears on the upper surface of the sleeve.
6. Foundation as claimed in Claim 5 in which the pin is mounted on a
universal coupling at the end of the shaft away from the cross head.
7. Foundation as claimed in any one of the preceeding claims in which the
grouted connection between pin and pile is replaced by a swaged
connection.
8. Foundation as claimed in any one of the preceding Claims 1 to 6 in which
the pin carries one or more grout supply lines and/or one or more packer
inflation lines whereby the grout may be introduced into and/or confined
within an annular space between the inner surface of the pile and the
outer surface of the pin.
9. Foundation as claimed in any one of the preceding claims, comprising a
group of piles, sleeves and pins as claimed in Claim 1.
10. A method of securing an offshore platform to the seabed which comprises
the steps of installing a tubular pile into the seabed with a bearing
ring at its upper end; placing the platform over the pile such that a
sleeve rigidly connected to the platform rests on the bearing ring in
co-axial arrangement with that pile; lowering a pin through the sleeve
into the pile in co-axial alignment therewith; and introducing grout
into the annular space between the inner surface of the pile and the
outer surface of the pin, whereby compression loads between the platform
and the pile are carried in bearing in the sleeve, and tension loads are
carried in the grout.
11. A method as claimed in Claim 10 in which a separate bearing ring has its
configuration modified as necessary to suit minor inaccuracies of angle
and elevation, and is then placed on top of the tubular pile.
12. An offshore platform having foundations formed in accordance with any
one of the preceding claims.
13. Foundation substantially as hereinbefore described with reference to and
as shown in Figure 2 or Figure 3 of the accompanying drawings.
14. A method substantially as hereinbefore described with reference to
Figure 2 or Figure 3 of the accompanying drawings.
15. An offshore platform having the foundations of Claim 13 or when
installed in accordance with the method of Claim 14.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB939312059A GB9312059D0 (en) | 1993-06-11 | 1993-06-11 | Foundation and method of installation |
Publications (3)
Publication Number | Publication Date |
---|---|
GB9411682D0 GB9411682D0 (en) | 1994-08-03 |
GB2278871A true GB2278871A (en) | 1994-12-14 |
GB2278871B GB2278871B (en) | 1997-03-05 |
Family
ID=10736998
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB939312059A Pending GB9312059D0 (en) | 1993-06-11 | 1993-06-11 | Foundation and method of installation |
GB9411682A Expired - Fee Related GB2278871B (en) | 1993-06-11 | 1994-06-10 | Foundation and method of installation |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB939312059A Pending GB9312059D0 (en) | 1993-06-11 | 1993-06-11 | Foundation and method of installation |
Country Status (2)
Country | Link |
---|---|
AU (1) | AU680244B2 (en) |
GB (2) | GB9312059D0 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2011147479A1 (en) * | 2010-05-25 | 2011-12-01 | Siemens Aktiengesellschaft | A foundation for a wind turbine installation |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN105155569B (en) * | 2015-08-03 | 2017-05-31 | 浙江华蕴海洋工程技术服务有限公司 | The constructing device and construction method of piling offshore wind turbine foundation after a kind of |
CN107882058B (en) * | 2017-10-26 | 2019-11-08 | 河海大学 | A kind of the suction barrel base and its delamination pour slurry compacted soil layer method of protection against erosion |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1596926A (en) * | 1977-01-13 | 1981-09-03 | Raymond Int Builders | Anchoring of structures |
GB1601622A (en) * | 1977-03-01 | 1981-11-04 | Shields C N | Submerged pile grouting |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4669918A (en) * | 1986-02-04 | 1987-06-02 | Riles William G | Offshore platform construction including preinstallation of pilings |
-
1993
- 1993-06-11 GB GB939312059A patent/GB9312059D0/en active Pending
-
1994
- 1994-06-08 AU AU64630/94A patent/AU680244B2/en not_active Ceased
- 1994-06-10 GB GB9411682A patent/GB2278871B/en not_active Expired - Fee Related
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1596926A (en) * | 1977-01-13 | 1981-09-03 | Raymond Int Builders | Anchoring of structures |
GB1601622A (en) * | 1977-03-01 | 1981-11-04 | Shields C N | Submerged pile grouting |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2011147479A1 (en) * | 2010-05-25 | 2011-12-01 | Siemens Aktiengesellschaft | A foundation for a wind turbine installation |
Also Published As
Publication number | Publication date |
---|---|
GB9312059D0 (en) | 1993-07-28 |
AU680244B2 (en) | 1997-07-24 |
GB9411682D0 (en) | 1994-08-03 |
GB2278871B (en) | 1997-03-05 |
AU6463094A (en) | 1994-12-15 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20000610 |