U.S. patent application number 12/681398 was filed with the patent office on 2010-11-25 for underwater foundation.
This patent application is currently assigned to AQUAMARINE POWER LIMITED. Invention is credited to Allan Robert Thomson.
Application Number | 20100296875 12/681398 |
Document ID | / |
Family ID | 38739189 |
Filed Date | 2010-11-25 |
United States Patent
Application |
20100296875 |
Kind Code |
A1 |
Thomson; Allan Robert |
November 25, 2010 |
UNDERWATER FOUNDATION
Abstract
A method of installing an underwater foundation, suitable for
use in supporting or anchoring wave or tidal energy capture devices
is provided. The method comprises providing a foundation unit (1)
equipped with a submersible drilling rig (16); placing the
foundation unit (1) on the bed (50) of a body of water at a
selected location; activating the submersible drilling rig (16) to
drill a plurality of pile holes (56) in the bed of the body of
water; and securing the foundation unit (1) to the bed of the body
of water by means of piles (54) or tendons, inserted in pile holes
(56) and secured to the foundation unit (1). A foundation unit (1)
and a submersible drilling rig (16) for use in the method are also
provided.
Inventors: |
Thomson; Allan Robert;
(Inverness, GB) |
Correspondence
Address: |
SNELL & WILMER L.L.P. (Main)
400 EAST VAN BUREN, ONE ARIZONA CENTER
PHOENIX
AZ
85004-2202
US
|
Assignee: |
AQUAMARINE POWER LIMITED
Glasgow
GB
|
Family ID: |
38739189 |
Appl. No.: |
12/681398 |
Filed: |
October 3, 2008 |
PCT Filed: |
October 3, 2008 |
PCT NO: |
PCT/GB2008/003360 |
371 Date: |
May 26, 2010 |
Current U.S.
Class: |
405/224 ;
405/232 |
Current CPC
Class: |
E02B 17/025 20130101;
E02B 2017/0082 20130101; Y02E 10/20 20130101; Y02E 10/30 20130101;
E02B 9/08 20130101 |
Class at
Publication: |
405/224 ;
405/232 |
International
Class: |
E02D 27/52 20060101
E02D027/52; E02D 13/00 20060101 E02D013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2007 |
GB |
0719484.8 |
Claims
1. A method of installing an underwater foundation, suitable for
use in supporting or anchoring wave or tidal energy capture
devices, the method comprising: providing a foundation unit
equipped with a submersible drilling rig that includes a drill head
driver; a drill string magazine, and a transfer device for
transferring drill string sections to the drill head drive; placing
said foundation unit on the bed of a body of water at a selected
location; activating said submersible drilling rig to drill a
plurality of pile holes in said bed of the body of water; and
securing said foundation unit to the bed of the body of water by
means of piles inserted in said pile holes, and secured to said
foundation unit; wherein the drill string sections used when
drilling the pile holes, are used to form the piles and the piles
are subsequently tensioned.
2. A method according to claim 1 wherein the foundation unit has
air or gas filled chambers which are filled with water, or a denser
filling material than water, when the unit is placed on the bed of
the water body.
3. A method according to claim 1 further comprising the steps of
aligning the foundation unit to a selected attitude.
4. A method according to claim 3 wherein the foundation unit is
aligned by providing the unit with at least three remotely
controlled or automatic jacking devices and operating the jacking
devices to align the foundation unit on the bed of a body of
water.
5. A method according to claim 3 wherein control of alignment makes
use of at least one levelling device, which provides feedback on
the attitude of the foundation unit to an operator or to an
automatic system.
6. A method according to claim 1 further comprising the step of
interposing a layer of a grouting compound between the base of the
foundation unit and the surface of the bed.
7. A method according to claim 1 wherein the drilling rig is
remotely activated or remotely controlled or automatic in
operation.
8. A method according to claim 1 wherein the pile holes are drilled
to a depth of up to 15 m and have a diameter of 100-150 mm.
9. A method according to claim 1 wherein the foundation unit is
from 10 to 20 m.sup.2 in area and between 50 and 100 pile holes are
drilled.
10. A method according to claim 1 wherein forming of each pile is
completed by injection of a suitable grouting compound into each
pile hole, filling spaces between the drill string and the walls of
the hole and optionally filling the drill string sections.
11. A method according to claim 1 wherein the piles are secured to
the foundation unit by means of nut runners screwed down a portion
of the pile projecting from the top surface of the foundation unit
until they contact the foundation unit and tighten against it.
12. A foundation unit, for an underwater foundation suitable for
use in supporting or anchoring a wave or tidal energy capture
device to the bed of a body of water, said unit comprising a
submersible drilling rig for drilling a plurality of pile holes in
the bed of a body of water, said drilling rig comprising; a drill
head driver; a drill string magazine, and a transfer device for
transferring drill string sections to the drill head drive from the
drill string magazine, wherein drill string sections are used to
form piles and the piles are provided with securing and tensioning
devices for securing and tensioning them to the foundation
unit.
13. A foundation unit according to claim 12 wherein the submersible
drilling rig is equipped for securing said foundation unit to the
bed of the body of water by means of piles inserted in said pile
holes and secured to said foundation unit.
14. A foundation unit according to claim 12 wherein the submersible
drilling rig is a remotely controllable, or automatic, submersible
drilling rig.
15. A foundation unit according to claim 12 wherein said
submersible drilling rig comprises: a drill head driver, mounted on
at least one extendible mounting arm, said mounting arm turning
about a pivot, in use on a said foundation unit, in use of the
drilling rig.
16. A foundation unit according to claim 12 further comprising air
or gas filled chambers, which are filled with water, or a denser
filling material than water, when the unit is placed on the bed of
the water body.
17. A foundation unit according to claim 12 further comprising at
least three remotely controlled or automatic lacking devices.
18. A foundation unit according to claim 12 further comprising
deformable grout retention skirts provided around its periphery, or
deformable grout retention tubes provided underneath the base of
the unit.
19. A foundation unit according to claim 12 further comprising a
stub or anchor points for attachment of a wave or tidal energy
capture device.
20. A foundation unit according to claim 12 further comprising a
quick connecting system for attachment of a wave or tidal energy
capture device.
21. A remotely controllable or automatic submersible drilling rig,
said drilling rig comprising: a drill head drive, mounted on at
least one extendible mounting arm, said mounting arm turning about
a pivot, in use on a said foundation unit; a drill string magazine,
and a transfer device for transferring drill string units to the
drill head drive, in use of the drilling rig.
22. A foundation for use in supporting or anchoring a wave or tidal
energy capture device comprising: a foundation unit connected by a
plurality of piles to the bed of a body of water; wherein the piles
are secured and tensioned to the foundation unit by securing and
tensioning devices.
Description
[0001] The present invention relates to a method for installing
underwater foundations particularly suited for supporting wave or
tidal energy capture devices.
[0002] Underwater foundations (or anchors) are placed on the bed of
a body of water to secure and provide support for a wide range of
structures. These include wave or tidal energy capture devices and
offshore wind energy capture devices. When used to support or
anchor such structures foundations have to have sufficient strength
and be sufficiently well secured to the bed of the body of water to
resist the large turning, sliding, tension, compression and uplift
movements and interaction of the structure with the high energy
environment caused by tidal or wave movements. The devices may be
tall, projecting a considerable height above the water bed and have
substantial mass. Severe weather or sea state conditions increase
the forces experienced on a foundation or anchor even more, leading
to uprooting or dragging of foundations.
[0003] Using a large substantial mass as a foundation (a `gravity
anchor`) has been found to provide insufficient resistance to the
forces involved or to be prohibitively costly. The conventional
approach is to use piling to secure a structure to the bed of the
body of water. A typical foundation for a wave or tidal energy
capture device may require single or multiple piles up to 4-5 m
diameter driven up to 20 m or more into the bed of the water body.
Whilst such arrangements may be effective they are expensive and
difficult to install. The large excavation or piling operation
required is carried out by using a `jack-up`drilling rig or ship
which sails or is towed into position. The rig or ship then lowers
legs down to the water bed to provide a stable platform on or above
the water. Alternatively a ship may use a dynamic positioning
system to maintain its position above a selected location.
[0004] Piling, drilling or other excavation techniques are then
carried out to provide the desired strong anchorage into the rock
of the water bed onto which the rest of the structure is secured.
Jack up rigs or vessels using dynamic positioning systems are very
expensive to operate and can only be positioned and used in
favourable weather conditions when wave height and sea swell and
tidal current are relatively low. Therefore foundation installation
costs can be prohibitive and subject to long delays.
[0005] Another difficulty encountered when installing foundations
is the risk to divers, who are often required to carry out delicate
engineering operations when foundations are installed or when the
energy capture device is installed on or anchored to the
foundation. Diver operations can only be carried out in favourable
weather conditions.
[0006] Furthermore in the case of tidal energy capture devices the
tidal flows in the areas best suited for energy capture may be so
great that diver operations are simply not feasible, or only so at
the brief moment of slack water.
[0007] It is an object of the present invention to provide methods
for installing underwater foundations or anchors that avoids or at
least reduces some of the abovementioned problems.
[0008] It is a further object of the present invention to provide
foundation units or anchors that are economic in manufacture and
installation and have sufficient strength for supporting or
anchoring energy capture units.
[0009] The present invention provides a method of installing an
underwater foundation, suitable for use in supporting or anchoring
wave or tidal energy capture devices, comprising the steps of:
providing a foundation unit equipped with a submersible drilling
rig; placing said foundation unit on the bed of a body of water at
a selected location; activating said submersible drilling rig to
drill a plurality of pile holes in said bed of the body of water;
and securing said foundation unit to the bed of the body of water
by means of piles or tendons inserted in said, pile holes and
secured to said foundation unit.
[0010] The foundation units, which are installed using the method
of the invention, constitute a second aspect of the invention. They
are preferably towed into position before lowering to the bed of
the water body. Towing can be achieved by attaching buoyancy to the
foundation unit so that it floats. Preferably the foundation units
employed in the method are themselves buoyant. Preferably the
buoyant foundation units have air or gas filled chambers which are
filled with water, or a denser filling material than water when the
unit is being placed on the bed of the water body.
[0011] Using buoyant foundation units avoids the expense and
complexity of attaching external buoyancy and then (on
installation) removing it. Preferably the air or gas filled
chambers of a buoyant foundation unit are filled with a filler,
such as a grout or a cement, for example, that is denser than water
to provide a bond or key to resist lateral motion. The increased
mass provided by the grout or cement increases the stability of the
foundation unit. Grout or other fluid agents are readily supplied
via suitable hoses from the vessel installing the foundation unit.
Alternatively the foundation unit may be temporarily or permanently
fitted with a grout tank which supplies the grout during
installation of the foundation unit. The grout tank may
conveniently be a flexible tank. The flexible tank is collapsible
and expands as grout is loaded into it.
[0012] Preferably the method also comprises the steps of aligning
the foundation unit to a selected attitude. For most installations,
where an energy capture device is supported by the unit, the
foundation unit must be located on the bed of the water body at an
appropriate attitude so that an energy capture device that is
attached thereto is itself correctly aligned to allow efficient
energy extraction from the waves and/or tide. For example, a
turbine powered by tidal flow may be mounted on a vertical mast
with the blades in a vertical plane. Aligning (or "levelling") the
foundation unit which supports the mast is essential to ensure the
correct orientation of the turbine blades to the tidal flow.
[0013] The foundation unit can be aligned on an uneven bed by
providing the unit with at least three remotely controlled or
automatic jacking devices. When the foundation unit is placed on
the bed the jacking devices are operated to align or "level" the
foundation unit.
[0014] Advantageously control of the operation can be achieved by
providing at least one levelling device, which provides feedback on
the attitude of the foundation unit to an operator or to an
automatic system. The levelling device may be, a spirit level
viewed by a camera transmitting pictures to a remote (above water)
operator of the jacks or it may be an electronic or optoelectronic
"spirit level" of the types well known in the art.
[0015] After the alignment operation has been carried out the
jacking devices are locked into place. This may be achieved by
mechanical locking devices. Preferably, where the jacking devices
are hydraulically operated they are locked into place by using a
fluid such as a grout in the hydraulic cylinder which will set
after the levelling operation is complete. This locks each of the
jacking device legs at the selected extension.
[0016] The foundation units are placed on the bed of the water
body. Advantageously, to provide resistance to dragging caused by
tidal and wave forces, a layer of a suitable grouting compound is
interposed between the base of the foundation unit and the surface
of the bed. This layer provides the benefit of filling in any
unevenness between the bed and the foundation unit so that the unit
is evenly supported across its entire base area. In addition the
grout, when set, provides a degree of adhesion to the bed,
resisting lateral movement i.e. dragging of the foundation. A
further benefit is that the grout adds to the mass of the
foundation unit, thereby increasing its effectiveness.
[0017] Advantageously the foundation unit is provided with
deformable grout retention skirts around its periphery or
deformable grout retention tubes underneath the base. The skirts or
tubes may be made of any suitable material that will deform
(crumple) when the foundation unit is lowered into position. The
skirts or tubes then provide a barrier, located between the bed and
the underside of the foundation unit. The barrier defines a volume
underneath the foundation, into which grout can be pumped to
displace water and form the layer between the bed and the
foundation unit as described above.
[0018] The deformable skirts or tubes may, for example be made of
thin steel sheeting or a suitable textile material of sufficient
strength to retain grout until it sets. Where grout retention
skirts or tubes are used the foundation unit is lowered onto the
bed with the levelling jacks at least partially extended. As the
aligning or levelling operation is carried out the skirts or tubes
conform to the bed surface, providing a barrier to retain grout
pumped under the foundation unit following the levelling
operation.
[0019] The foundation unit is provided with a drilling rig.
Preferably the drilling rig is remotely activated, for example in
response to a signal from an operator on the vessel that is
carrying out the installation.
[0020] Advantageously the drilling rig is remotely controlled or
automatic. This avoids the need for any diver intervention when
starting the drilling operations. Once the foundation unit is
located in position and any alignment operations are completed then
piling operations using the drilling rig are commenced.
[0021] Preferably the drilling rig comprises a magazine of drill
string lengths. Preferably the drilling rig includes a conveyance
mechanism for transfer of drill string lengths from the magazine to
the drill drive. Preferably the drilling rig operation is automatic
or semi-automatic with a sequence of pile holes being drilled
according to a pre-programmed sequence. Automatic or semi-automatic
operation has the benefit of reducing or removing the requirement
for constant operator supervision during the installation of a
foundation unit. The drilling rig operates in a generally
conventional manner with drill string sections being connected
sequentially as required to the drill string to drive the drill bit
as the hole being drilled deepens.
[0022] Advantageously the drill is mounted so as to move about a
pivot point on the foundation unit on an extendible mounting arm or
arms. This arrangement allows a hole to be drilled at almost any
location on the foundation unit, into the bed of the body of water
underneath. Advantageously the drill is mounted for movement about
a central point of the foundation unit. A typical foundation unit
may include a "stub" or short upwardly directed projection
(typically a tube section) to which the energy capture device will
be connected in due course. Typically this is located on the centre
of the foundation unit. Conveniently the extendible mounting arms
of the drilling rig rotate about this stub. Conveniently the drill
string magazine comprises an array of drill string sections
arranged around the outside of the stub.
[0023] It will be understood that the pile holes may be drilled
through the foundation unit, any associated grout and then into the
bed. Advantageously the foundation unit may be provided with guide
holes through which the drill string passes freely before entering
the bed.
[0024] Advantageously the drill string magazine is located at or
near the pivot point about which the drill moves. Drill string
sections can then be conveyed outwards to the location of the drill
by a suitable conveyor or transport device and connected to the end
of the in use drill string, in the conventional manner.
[0025] The pile holes and the piles or tendons subsequently placed
in them can be smaller in diameter and/or depth in comparison with
typical piles employed for securing foundations for wave or tidal
energy capture devices. This provides the advantage that making
each pile hole in the bed of the water body and fitting of a pile
or tendon is easier to achieve. Nevertheless by providing a
suitable number of smaller ("mini") piles or tendons, which share
the loads experienced by the foundation unit, a secure foundation
or anchor for tidal or wave energy capture devices, or other
structures secured to the bed of a body of water, can be
realised.
[0026] The drill string sections may be solid or they may be
hollow, to allow passage of drill cuttings. Typically 5 m sections
of drill string of 100-150 mm diameter are used. Each pile hole may
be drilled to a depth of about 15 m (i.e. three drill string
sections are employed).
[0027] A typical foundation unit may be of the order of 10 to 20
metres square in area and 50-100 pile holes may be drilled for the
piles. It will be appreciated however that the depth of drilling
and the number of pile holes drilled will vary depending on the
local water conditions and water bed geology, when considered in
the light of the structure to be supported.
[0028] It will also be understood that the pile holes may be
drilled vertically into the bed or may be drilled at an angle from
the vertical to suit the piling structure required to support the
energy capture device or other structure fitted to the foundation
unit.
[0029] The foundation unit is secured to the bed of the body of
water by means of piles or tendons inserted in the pile holes.
Separate piles may be provided for this purpose and can be inserted
by use of the drilling rig or by a separate pile driver. Preferably
the drill string sections, used when drilling the pile holes, are
used to form the piles. The drill string, including the drill bit,
used to form a pile hole is left in situ with a fresh drill bit and
drill string being used for each subsequent hole. Forming of each
pile is then completed by injection of a suitable grouting compound
into the hole, filling spaces between the drill string and the
walls of the hole and optionally filling the drill string sections
(if hollow).
[0030] If piles are used they are secured to the foundation unit.
This may be by means of a grout or by fastenings such as bolts or
clamps. Advantageously the piles are provided with nut runners or
other suitable securing and tensioning devices. The nut runners are
screwed down a portion of the pile projecting from the top surface
of the foundation unit until they contact the foundation unit and
tighten against it. This secures the pile to the foundation unit.
The method then includes the additional step of activating the nut
runners to secure and tension the piles to the foundation unit.
This provides a particularly secure fixing of the foundation unit
to the bed.
[0031] Alternatively tendons rather than piles may be used to
secure the foundation. Tendons are cables, typically of steel
provided with an anti-corrosion coating of a polymer, such as an
epoxy polymer. A sacrificial anode may also be fitted to the cable
to reduce corrosion. The tendons are installed in the pile holes,
fixed in position and then secured to the foundation unit, under
tension, to provide secure fixing.
[0032] After securing the foundation unit to the bed of this body
of water the energy capture device or other underwater structure is
then secured to the foundation unit. This can be achieved in a
number of ways. Where a stub is supplied on the foundation unit, as
described above, the structure or device may have a docking portion
that fits into or onto the stub and can be secured thereto by means
of grout, welding, bolts etc. Alternatively proprietory quick
connecting systems such as Ballgrab.RTM. or Kwik-lok.RTM. may be
employed as appropriate for the strength of join required.
[0033] Alternatively where a floating or buoyant structure is to be
anchored to the foundation unit it may be secured by means of
suitable cables attached to anchor points provided on the unit.
[0034] According to a third aspect the present invention provides a
foundation for use in supporting or anchoring a wave or tidal
energy capture device comprising:
a foundation unit connected by a plurality of piles to the bed of a
body of water.
[0035] According to a fourth aspect the present invention provides
a remotely controllable or automatic submersible drilling rig for
use with a foundation unit, said drilling rig comprising:
a drill head drive, mounted on at least one extendible mounting
arm, said mounting arm turning about a pivot, in use on a said
foundation unit; a drill string magazine, and a transfer device for
transferring drill string units to the drill head drive, in use of
the drilling rig.
[0036] Further preferred features and advantages of the present
invention will appear from the following detailed description given
by way of example of some preferred embodiments illustrated with
reference to the accompanying drawings in which:
[0037] FIG. 1 shows in schematic perspective view a foundation unit
ready for installation according to the method of the
invention;
[0038] FIG. 2a shows the foundation unit of FIG. 1 in schematic
plan view;
[0039] FIG. 2b shows the unit of FIG. 1 in schematic cross
section;
[0040] FIG. 2c shows a detail from FIG. 2b showing operation of a
jacking device;
[0041] FIG. 2d shows the device of FIG. 1 in elevation;
[0042] FIG. 3 shows shows in a cross section detail the foundation
unit of FIG. 1 installed on a water bed;
[0043] FIG. 4a shows in schematic perspective view another
foundation unit ready for installation according to the method of
the invention; and
[0044] FIG. 4b shows the foundation unit of FIG. 4a in schematic
plan view.
[0045] FIG. 1 shows a foundation unit 1 which has a base portion 2.
The base portion 2 is a concrete slab 4 of the order of 10 m
square. The base portion 2 is buoyant by the provision of cavities
6 (see FIG. 2) which are air filled. Access holes 8 are provided
into the cavities 6 but are kept sealed until the foundation unit 1
is lowered underwater.
[0046] The concrete slab 4 has a deformable skirt 10, of thin sheet
steel, placed around its lower edge 12. A stub 14, a cylindrical
projection from the centre top 15 of the slab 4, has a remotely
controllable drilling rig, generally indicated by the reference
numeral 16 fitted to it.
[0047] The drilling rig 16 includes a magazine 18, of drill string
sections 20 disposed around the outside of the stub 14. The
drilling rig 16 includes a frame 22 which rotates around the stub
14. The frame 22 has a pair of extendible arm sections 24,26 each
of which has a drill vertical drive 28 and drill clamps 30 of
generally conventional design mounted to a vertical support 31. The
extendible arms 24,26 also include a feed conveyor mechanism 32 for
delivering drill sections 20 from the magazine 18 to the vertical
support 31. Towing eyes 34 are supplied on the slab 4 to allow the
foundation unit to be towed along on the water surface. The towing
eyes 34 can also be used as anchor attachment points for securing a
floating or buoyant energy capture device (not shown) in use of the
foundation unit.
[0048] Further features and details of the foundation unit can be
seen from the plan and cross sectional views of FIG. 2.
[0049] The plan view of FIG. 2a shows the location of three jacking
devices 36 which are used for levelling the foundation unit 1 (see
also the cross section of FIG. 2b taken along the line BB shown on
FIG. 2a). One of the jacking devices 36 is shown in more detail in
the partial cross section view in FIG. 2c (magnification of the
circled portion C of FIG. 2b). The jacking device consists of a
piston 38 in a cylinder 40. The piston 38 can be moved
hydraulically by the injection of a grout compound 42 through the
grout passage 44 in the slab 4 of the foundation unit 1. A seal 46
prevents grout 42 passing out of the cylinder 40. An electronic
levelling device 47 (FIG. 2a) is fitted on top of the stub 14 for
use in conjunction with the jacking devices 36.
[0050] FIG. 2a also shows, in dashed lines, the positions of
cavities 6 (see also FIG. 2d) each of which has an access hole 8,
in the top of the slab 4. Also shown in FIG. 2a are guide holes 48
which are sized to allow free passage of drill bits and associated
drill string sections 20 through the slab 4. Only one row of guide
holes is shown on the drawing, for clarity. An array of 50-100
guide holes 48 disposed more or less evenly across the slab 4 will
normally be used. The number of guide holes provided and the actual
number of piles used to secure a foundation unit to the bed of a
body of water can be varied as required, including outside this
typical range. The number of piles is chosen to be adequate to
support the anticipated load and depending on the geology of the
location.
[0051] FIG. 3 shows in cross section a portion of a foundation unit
1 installed on a water bed 50. The foundation unit 1 is supported
by jacking devices 36 (not shown, see FIG. 2d) and by a layer 52 of
grout 42 interposed under the slab 4 and retained by the deformable
skirt 10. A pile 54 comprising drill string sections 20 passes
through a guide hole 48 into a pile hole 56. The pile 54 is secured
in place by grout 42. The pile 54 is further secured to the
foundation unit by means of a nut runner 58, a nut turned onto a
threaded section 60 of the pile 54 to tighten against the top of
the slab 4. As an alternative to the pile 54 a tendon (not shown)
can be placed in the pile hole 56 and secured and tensioned to the
slab 4 in a similar fashion.
[0052] FIG. 4a shows a foundation unit 1 of generally similar form
to that of FIG. 1, with like parts numbered the same. The
foundation unit of FIG. 4a includes, as additional structural
support for the stub 14, a tripod support structure 62, comprising
three legs 64 extending from the stub 14 to the top of the slab 4.
The tripod legs 64, in this example are spaced at 120.degree.
angles around stub 14 (see FIG. 4b). The tripod structure 62
provides additional structural stability and strength for the
drilling rig 16 and for a wave, tidal or wind energy capture device
(not shown) when fitted to the stub 14 following removal of the
drilling rig 16. Alternative support structures, for example a
four-legged arrangement may be employed (tetrapod).
[0053] The foundation unit 1 of FIG. 4a also features an integral
grout tank 66 located on the stub 14 inside the magazine 18 of the
drilling rig 16. Also shown on the unit 1 of this figure is an
umbilical connection 68 to the surface and a convenient additional
towing eye/anchor point 70 on top of the grout tank 66. The tank 66
supplies grout as required for the various operations described
below in deploying the foundation 1. The grout tank 66 may be empty
when the foundation 1 is being towed to a location and then filled
with grout to assist in sinking the foundation to the bed of the
water body. The grout tank 66 may be detachable so that it can be
removed from the foundation unit 1 at the same time as the drilling
rig 16.
[0054] The operation of the method of the invention using the
foundation unit 1 of the Figures will now be described.
[0055] The location for the foundation unit on the bed of the body
of water is first prepared by `cleaning` i.e. removal of loose
material such as small rocks and/or levelling of the surface. The
buoyant foundation unit 1 is towed into position above the selected
location and the buoyancy removed by flooding the cavities 6 with
water or filling them with grout 42. If the foundation includes the
integral grout tank 66 as shown in FIG. 4a then the grout tank may
be filled at the same time or just prior to flooding the cavities
6. When the foundation unit 1 reaches the surface of the water bed
the deformable skirt 10 conforms to any irregularities in the water
bed surface 50 (see FIG. 3) and the pistons 38 of the jacking
devices 36 rest on the water bed surface 50. The pistons 38 are
then activated by injection of grout into the cylinders 40 to level
the foundation unit 1 in accordance with the output signals from
the electronic levelling device 47.
[0056] Once the unit 1 has been levelled the space between the unit
1 and the water bed surface, bounded by the skirt 10, is filled
with a grout layer 52. After the grout 42 has set the drilling
operation is started. Pile holes 56 are drilled in the water bed
via the guide holes 48 in the slab 4 of the foundation unit 1. As
each hole 56 lengthens drill string sections 20 are added from the
magazine 18 as required.
[0057] Once the pile hole 56 is the desired depth the drill string
is disconnected from the drilling rig 16, which is then removed by
means of rotation about the stub 14, and movement of the extendible
arm section 24 or 26 to a new location above a new guide hole 48.
This process is repeated to provide a pile 54, of drill string
sections 20, in each pile hole 56.
[0058] The piles 54 are then secured into their respective pile
holes 56 by means of grout injections. Conveniently the drilling
rig 16 may carry a grouting umbilical which communicates with a
grout supply on the water surface (not shown) for supply of grout
as required. Alternatively grout may be supplied from the integral
grout tank 66 shown in FIG. 4a, for some or all grouting
operations. Each pile (of drill string sections) can then be
grouted into place while still connected to the drilling rig 16.
The grout injected is also used to fill the space between the guide
hole 48 and the drill string 20 sections, securing the piles 54 to
the foundation unit 1. Nut runners 58 are then used to further
secure the piles, by screwing down on the projecting pile ends onto
the top of the slab 4. The drilling rig 16 may be fitted with
appropriate tools for carrying out this operation.
[0059] After the foundation unit 1 is fully secured to the water
bed 50 the drilling rig 16 (including grout tank 66, if fitted) is
removed to the surface for reuse and a wave, tidal or wind energy
capture device (not shown) can be attached to the stub 14. All of
the operations of the drilling rig 16 (for example grouting,
drilling and fixing nut runners), and of any other ancillary
equipment fitted to the foundation 1, may be remotely controlled
from the water surface, by means of signals supplied via an
umbilical 68 such as that shown in FIG. 4a. The umbilical 68 or
other umbilicals where fitted may also be used to supply services
such as electricity, compressed air, drilling mud or grout as may
be required for foundation fixing operations.
* * * * *