INSTALLATION OF STRUCTURES IN WATER.

BACKGROUND INFORMATION

This invention relates to methods of and means for installing structures in seabeds or the beds of other volumes of water.

In particular, this invention relates to sea beds (river beds or the beds other large volumes of moving water) (hereinafter referred to in this specification and claims as seabeds) of upstanding structures that generally (but not necessarily) project above the surface of the water..

Whilst the applications for such mounted structures can be, for example, the support of wind or water current driven turbines, or marine structures such as jetties or lights this invention relates to the construction and installation of such forms of structures regardless of their purpose.

A major practical difficulty arising with the installation of offshore seabed mounted structures is the time required for large installation vessels such as a heavy-lift crane-barge or a jack-up barge to be on site to complete any necessary foundation works. In practice, such vessels are necessary to position the required structure. However, the lengthy time requirements for installing such structures involves consequential lengthy installation times for the use of such vessels and this not only results in very high costs per installation but also reduces the numbers of installations a given vessel can complete in a given time.

OBJECTS OF THE INVENTION

It is an object of the invention to provide methods of and means for installing the structures in a seabed.

STATEMENTS OF THE INVENTION

Broadly according to a first aspect of the invention there is provided a method of installing an elongate upstanding structure in a seabed, including the step providing a hollow guide assembly capable of accommodating the structure to be installed in the seabed using the hollow guide assembly to position and set the structure at a required position and orientation into the seabed as to become self supporting.

A further aspect of the provides a method of installing an elongate structure in a seabed, including the steps of providing a hollow guide assembly capable of accommodating the structure to be installed in the seabed using the hollow guide assembly to position and set the structure in said seabed at said position and in an upstanding orientation, positioning the hollow guide assembly on the sea bed at the position it is required to install the structure in upstanding manner in the seabed , setting the orientation of the guide assembly at the orientation required for the structure when upstanding, downwardly displacing the structure relative to the guide assembly to cause the structure to become self supporting at said position and at said orientation.

In practice, the method includes the step of totally removing the guide assembly as to leave the structure totally free standing.

Alternatively the hollow guide can be partially removed so as to leave the structure partially supported by the assembly.

In practice, where the guide assembly is such that following the installation of the upstanding structure a portion of the guide assembly may project above the surface of the water this projecting portion of the guide assembly is removed thereby to leave a submerged portion thereof in situ so as subsequently to be able

to form the foundation or part of the foundation for the subsequent addition of further structure-

Conveniently the guide assembly is transported by means of a crane barge (or a jack-up barge with a crane) onto the seabed.

Preferably, the guide assembly has facilities for accommodating unevenness in the seabed.

Conveniently the upper regions and/or top of the guide assembly can be provided with a platform that is to be positionable above the water surface, the platform including facilities to support drilling, handling and grouting equipment needed to create the necessary socket in the seabed so as to permanently install the upstanding structure .

Conveniently the upstanding structure can be a pile (or a multiplicity of such piles) which can each act as a mounting spigot (or spigots) for a prefabricated structure to be installed later.

Moreover, the guide assembly serves as a temporary structure that is designed to act as a template for use in ensuring correct positioning and verticality of the upstanding structure (pile or piles) to be installed. After the pile or piles have been installed in drilled sockets, and if necessary grouted into place, a crane (or jack-up) barge returns and can lift the temporary guide assembly from its position leaving the pile or piles in place, and transports the guide assembly for reuse for further installations.

In practice, the same (or a different) heavy-lift crane barge can bring the final structure to be installed, for example a tidal current turbine, a wind turbine or some other such offshore device, and this can be craned so as to either fit over or into the seabed mounted upstanding structure/spigot. Once correctly positioned the aforementioned "final structure" can be grouted (or affixed in any other

appropriate manner such as welding or bolting) to the upstanding structure/spigot.

In this way the guide assembly itself can provide the facility and a template for positioning and drilling piles for permanently fixing some prefabricated device or structure in place. The major installation vessel can leave as soon as the upstanding structure is positioned correctly with required equipment mounted on it and no longer has to be attendance during subsequent drilling and grouting operations.

In most cases the necessary equipment may be prefabricated ashore so that the entire structure can be quickly lowered into the desired location and the delivery vessel may leave the site to continue with other such installations. Using a prefabricated structure not only reduces expensive and difficult offshore operations but also makes assembly both more likely to be accurate and to the best quality standards as well as safer from the point of view of exposure of personnel to offshore working conditions.

According to a further aspect of the present invention, there is provided for use with an upstanding structures/spigots to be installed in a seabed a guide assembly including jacket type structure including a single tubular vertical column with a number of seabed engaging footings, most commonly three or four arranged symmetrically around its base.

Preferably, these footings are ballasted so as to achieve a high enough weight that the entire structure can stand securely and non-moveable by waves, wind or currents, on the sea bed with the upper part of the structure tall enough to project above the water surface.

Conveniently the guide assembly carries above the water surface a strong deck or platform which carries rotary (or percussion) drilling equipment which will be used to drill a hole or holes in the seabed. It also carries a crane and/or other lifting and

positioning equipment to service the drilling system and to move personnel, equipment and consumables such as grout compound safely to and from servicing vessels. There is also a power source (or sources) to power the crane and the drilling equipment.

Although the preferred and most commonly applied embodiment of the guide assembly involves a structure with a single tubular vertical column the concepts of the invention can be applied to a guide assembly structure with a plurality of such vertical columns, each one of which can be used to install and position a foundation pile.

Moreover if a foundation pile is required to enter the seabed at some angle other than vertical, the same principles to be described can be applied by using a jacket type structure where one or more tubular columns are set at the required angle to the seabed instead of being vertical. However in most cases it is expected vertical orientation will be a requirement.

Although a tubular vertical column as so far described is a preferred embodiment for most purposes, the principles of this invention may also be applied by substituting a lattice-structure or other adequately strong form of support structure for the operational platform.

The jacket structure is designed so that it can be lowered to the seabed from a suitable vessel with a heavy lift crane. Once positioned on the bed involved it can be levelled to allow for the lack of flatness of the bed conditions; for example by employing different feet constructions designed to apply the appropriate load stress to the seabed would be used on a rocky or hardbed than on a soft or sandy one.

As has been mentioned since the jacket structure may be at risk of being moved by currents, waves or wind during the installation period for the upstanding structure, when necessary extra weight may be added to the temporary guide

assembly structure to maintain sufficient friction with the seabed during the installation process, and the extra weight may be removed together with the installation equipment after procedures are completed. It is also possible to deploy an anchor spread from the structure to provide stability.

The end result from applying this invention is one or more tubular piles embedded and when necessary grouted into the seabed and positioned at a precisely required spot at an inclination (usually but not necessarily verticaljdictated by the geometry of the temporary works template structure just described.

Essentially this guide assembly performs the functions of a jack-up barge for installing offshore piling, but without the need to use a jack-up barge.

Furthermore the proposals of the invention allows the guide assembly and the upstanding structure to be transported to installation site without the use of a heavy lift crane barge or jack-up barge, but using some form of attached buoyancy such as floodable tanks or flotation bags so that the assembly may be floated into position and sunk at the required sport in a controlled manner such that it can be correctly positioned and orientated. This procedure can then be reversed once the installation is complete by re-floating the guide assembly and towing it away.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how to carry the same into effect reference will now be made to the accompanying drawings in which :-

Figure 1 is a schematic elevation view of a guide assembly for use in the installation of an upstanding structure/spigot in a seabed;

Figure 2 is a cross sectional view of the guide assembly shown in Figure 1;

Figure 3 schematically illustrates the guide assembly after it has been used to lower the upstanding structure/spigot into contact the seabed;

Figure 4 schematically illustrates the use of a drill string following the positioning stage for the upstanding structure/spigot shown in Figure 3;

Figure 5 schematically illustrates a further stage in the mounting the upstanding structure/spigot namely the under-reaming of the upstanding structure/spigot;

Figure 6 schematically illustrates the installation stage at which the drilling and under reaming has been completed and grouting carried out if required;

Figure 7 schematically illustrates the use of a heavy-lift crane-barge for removing the guide assembly from the upstanding structure/spigot;

Figure 8 schematically illustrates the upstanding structure/spigot mounted to the sea bed whilst awaiting the arrival of equipment or other structures to be mounted there upon;

Figure 9 schematically illustrates the use of a heavy-lift crane-barge for mounting a pre-assembled tidal turbine assembly onto the upstanding structure/spigot of Figure 8; and

Figure 10 schematically illustrates the tidal turbine assembly positioned on the upstanding structure/spigot and grouted (if necessary) into place.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to Figures 1 and 2 in which Figure 1 shows a schematic view in vertical elevation of an embodiment of an assembly 1 including a monolithic tubular column/support 2 is carried on four footings 3 (of which only three are illustrated in the Figure 1) which are equiangularly disposed around the support 2 and are connected thereto by bracing members 4. A tubular pile or upstanding structure/spigot 5 which is to be installed into a socket in the seabed is supplied within the vertical column/support 2 and is shown in Figure 1 as a hidden component using broken lines.

In Figure 2 which is a vertical cross-sectional view of Figure 1, the tubular pile or structure/spigot 5 can be seen more clearly inside the monolithic tubular support 2. Means (not shown) are provided to hold the upstanding tubular pile/structure/spigot 5 in place within the tubular support so as to prevent it from

⁵ falling through the tubular support 2. Such holding means may be as simple as temporarily welding the upstanding tubular pile/structure/spigot 5 to temporary support members (not shown) that may be flame-cut away to release the pile or structure/spigot 5 at the appropriate time i.e., when in contact with the seabed, or alternatively inflatable rubber internal grippers, or jacks (screw or hydraulic)

10 may be used as clamps.

Each footing 3 stands on an adjustable foot 6 which for the embodiment shown is capable of being moved through some small distance vertically as well as being attached in a pivotable manner. The foot includes forcefully extendable devices such as hydraulic rams 6A, but which, in practice, could be screw jacks, inflation

15 bags or any other means capable of providing sufficient force to lift or lower the associated foot 6 to a desired level and to be able to adjust the vertical position and angle of the foot with respect to the tubular pile or column/support 2 so as to allow adjustments to be made that will keep the main structure levelled despite unevenness (within predefined limits) of the seabed. The adjustment mechanisms

^ 0 will be described in more detail later and may not necessarily be exactly in the form shown by way of example providing it can compensate adequately for unevenness of the seabed.

It should be noted that the guide assembly/jacket 1 can be used in conjunction with .other forms of structure to the monolithic tubular one as shown. For 5 example an open lattice framework or a multiplicity of vertical structural columns as previously mentioned may have advantages in certain situations or for special purposes.

Figure 1 also shows a superstructure platform 7 located above the water level WL, which platform can generally can carry a crane or other form of lifting and positioning equipment 8.

A subsidiary structure 9 supports a conventional drilling rig 10 with a rotary drill 11 or a percussive drill (not illustrated). There may also need to be additional weights (not illustrated) which can be added after the rig 10 is positioned to ensure the frictional contact with the seabed during installation remains sufficient to prevent any movement under the influence of currents, waves and/or wind.

Referring now to Figure 2 this shows as has been mentioned a vertical cross- section of the installation of Figure 1 thereby to illustrate more clearly how the upstanding structure/spigot 5 can be installed within the column/support 2 It is possible, for example, where the weight of the structure 2 is prohibitive with the pile/structure/spigot 5 installed in relation to crane lifting capabilities, to place the structure 2 first from a heavy-lift barge (not shown) and then to install the pile /structure/spigot 5 once the structure i2 is standing and levelled. To do this the drilling platform 9 and drilling equipment 10/11 would also be fitted in place only after the upstanding pile/structure/spigot 5 is inside the column/support 2 and is ready to be drilled into position.

Referring now to Figure 3 this Figure illustrates how, after the guide assembly 1 has been effectively positioned and levelled, the internally located upstanding pile/structure/spigot 5 is lowered to rest on the seabed through the assembly structure 2. This can be done using a winch or the onboard crane (not shown). In some situations it may also be possible simply to release the pile/structure/spigot 5 and let it fall to the seabed.

Figure 4 illustrates how in the case of rotary drilling a drill string 12 that has been assembled in a conventional manner and the drill cutting head 11 has been positioned for drilling through the tubular upstanding pile/structure/spigot 5. Alternatively, percussive or hammer drive drilling can be carried out through the

upstanding pile/structure/spigot 5. This is a procedure can be carried out from jack-up barges where a conductor tube is held in place and drilling takes place through the conductor tube. In this case the upstanding pile/structure/spigot 5 doubles as the conductor tube.

Figure 5 shows how the drilling can be done by under-reaming the upstanding pile/structure/spigot 5 so it falls under its weight (or it can be restrained by a winch provided upon the platform 7 thereby stopping waste material falling into the hole/socket produced by the drilling operation.. Local water i.e., sea water can be used to flush the drillings detritus from the hole/socket. Such drilling detritus can be discharged into the sea or stored in a barge moored alongside for eventual disposal elsewhere.

Figure 6 shows how, after the drilling operation has been completed, the drill train/string 12 can be dismantled and removed. Alternatively in situations in which the removal of the drill train/string is difficult it can be left in place and only dismantled from the top of the upstanding pile/structure/spigot 5. In most cases the upstanding pile/ structure/spigot 5 will be grouted in place in the sea bed by connecting grout hoses to, for example, grout pipes (not shown) that were designed into the upstanding pile/structure/spigot 5 to distribute cementitious grout into the annular space surrounding the pile/structure/spigot 5. Arrangements for carrying out such grouting will follow known and understood procedures and are therefore neither illustrated or discussed.

Openings (not illustrated) may be provided in the tubular column/support 2 of the assembly 1 at strategic points to permit grout hoses to be attached and detached from the top of the upstanding pile/structure/spigot 5 for this purpose. In some cases it may be advantageous to use a lattice structure rather than a monolithic tubular column as shown in the figures since this would more readily permit access to the upstanding structure/spigot/pile for attaching and removing said grout hoses.

Figure 7 shows how the entire assembly 1 can be lifted vertically off the upstanding pile/structure/spigot once the latter is securely grouted into position, by reversing the procedure used in initially lowering the assembly to the seabed from a heavy lift crane barge.

In some cases the entire assembly 1 can be lifted bodily in one piece, but if the lift capacity of the crane is inadequate for such purpose the assembly 1 may be partially dismantled and removed in several separate operations.

Figure 8 illustrates the desired end-result of the procedural stages above discussed namely, the vertical positioning of an upstanding pile/structure/spigot 5 at a desired location in a seabed, such that the thus installed pile/structure/spigot 5 is ready to receive and mount a prefabricated device 13 can be lowered bodily onto it as is shown in Figure 9

Figure 9 which illustrates ,by way of example,the installation of a tidal turbine particularly of the kind developed by the Applicants.

it will be understood that the method of installing in a seabed SB the upstanding piles/structures/spigots involved may be used for what ever purpose required, for example, such piles/structures/spigots could similarly be used to support a wind turbine, or any other form of desired 'off shore' structure.

Figure 10 illustrates how the prefabricated device 13 may be grouted over, or into the upstanding structure/spigot or pile. It may require screw jacks or other means to centre and align it vertically over or inside the spigot or pile and it may also be aligned by having a tapered fit. Such features are not illustrated but will follow already proven methods and procedures. In some cases it may not need to be grouted but other forms of attachment may be preferred including bolting, welding or simply an accurate fit into a tapered fitting or fittings such that it can stand under its own weight with no risk of lateral movement.

From the forgoing it will be noted that a jacketed type of assembly structure capable of being lowered into the seabed (or into a river or lake or other expanse of water), which is designed to accommodate one or more upstanding structures/spigots/piles and to be temporarily self standing by being heavy enough to withstand currents, waves and wind induced forces while being held in position by friction with the seabed. As mentioned the aforementioned structure has a platform above sea level with facilities to drill by any appropriate means (e.g. rotary or hammer drilling) a socket (or in some cases several sockets) into the seabed and to deposit the aforementioned internally accommodated upstanding structure/spigot/pile or a plurality of same into this socket(s). A further alternative is to use the conventional technique of pile driving from the platform in cases where ground conditions are suitable. The structure also has footings which are adjustable so as to level the structure prior to drilling the socket despite the likely unevenness of the seabed, within adequate but predefined limits

Thus the proposals of the invention provide a jacket type of assembly structure for the purpose of installing piles or spigots into the seabed and which can be rapidly deployed from either a heavy-lift crane barge, from a jack-up barge, or by being floated into place using attached floatation arrangements such that it can be sunk into the correct position in a controlled manner and subsequently re-floated and towed away after the pile (or piles) installation procedure is completed.

A further aspect provides a jacket type of structure for the purpose of installing piles or spigots into the seabed, where extra weights or ballast material can be added if necessary to generate sufficient friction to prevent movement and which may be removed after the piling operation has been completed. In some cases extra weight may be provided by having water tanks attached to the assembly structure above the water surface which may be filled with water during the installation as a means to add weight, and then emptied when the installation works are completed.

In general there is provided a self-standing temporary structure which can be used to carry a drilling platform mounted above water level and cranes and other handling equipment so as to permit piles or spigots to be installed in sockets drilled into the seabed and which can be removed in its entirety after the aforementioned upstanding structures/spigots/piles are successfully installed.

The above discussed structure can be provided with footings that can be adjusted for height and alignment to permit the structure to be levelled before drilling and spigot/pile installation operations take place, the force for so doing being provided by hydraulic rams, screw jacks or any other such appropriate mechanisms 5 capable of lifting or lowering the footings to a desired level.

Furthermore, the use of piles or spigots where said piles have drillings or internal pipes to permit grout to be pumped via hoses from the surface so as to emerge in such a way that the grout will fill the concentric voids between the piles and the surrounding seabed.