HYBRID ANCHOR

Abstract

A hybrid anchor (10) comprises a caisson comprising a lid (35) and a rigid skirt (37) wherein the skirt defines an open end of the caisson and the lid comprises a valve, the skirt of the caisson being configured to engage with a substrate upon which it is placed, thus defining a sealed interior space and, in use, the skirt (37) is induced to sink into the substrate by evacuating the contents of the interior space through the valve. A drilling template is fixed to the lid (35) of the caisson, the drilling template being configured to receive at least one pile (40) at a respective location relative to the caisson lid (35) such that the at least one pile (40) may be driven though the caisson lid and into the substrate at an angle from 90 degrees to the plane of the lid up to an angle avoiding intersection between the at least one pile and the skirt to fix the position of the hybrid anchor within the substrate.

Claims

1. A hybrid anchor comprising: a caisson comprising a lid and a rigid skirt wherein the skirt defines an open end of the caisson and the lid comprises a valve, the skirt of the caisson being configured to engage with a substrate upon which it is placed, thus defining a sealed interior space and, in use, the skirt is induced to sink into the substrate by evacuating the contents of the interior space through the valve; and a drilling template fixed to the lid of the caisson, the drilling template being configured to receive at least one pile at a respective location relative to the caisson lid such that the at least one pile may be driven though the caisson lid and into the substrate at an angle ranging from approximately perpendicular to the lid through to an angle avoiding intersection between the at least one pile and the skirt to fix the position of the hybrid anchor within the substrate, wherein the at least one pile comprises a micropile comprising at least one hollow cylindrical shell defining an axial channel and one or more apertures in said shell allowing grout injected through said channel to pass through said apertures and to bond said micropile in place within said substrate.

2. (canceled)

3. The hybrid anchor of claim 1 comprising a plurality of piles.

4. A subsea foundation system comprising a plurality of hybrid anchors in accordance with claim 1.

5. A method of installing the hybrid anchor of claim 1 comprising: positioning the drilling template in fixed relationship to the lid of the caisson; deploying the caisson to the substrate; evacuating the interior space of the caisson such that the caisson sinks into the substrate; locating at least one pile in the drilling template; and drilling the at least one pile through the caisson lid into the substrate.

6. The method of claim 5 further comprising: injecting grout through the at least one pile to bond said pile in place within said substrate.

7. The method of claim 5 further comprising: positioning another pile at a location within said drilling template spaced apart from a location of a previous pile; drilling the another pile into the substrate; and repeating the previous two steps until the desired number of piles have been located in said substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present application will now be described, by way of example, with reference to the accompanying drawing in which:

[0012] FIG. 1 illustrates an elevation view of a hybrid anchor in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0013] Referring now to FIG. 1, there is illustrated an elevation view of a hybrid anchor, generally indicated as (10) according to an embodiment of the present invention.

[0014] The hybrid anchor is shown in situ as it is partially submerged in a substrate 20 upon which it is sitting.

[0015] The hybrid anchor comprises a traditional suction caisson (also known as suction anchor or suction bucket) type anchor 30 which is described in the background section above, wherein the suction caisson is employed, in conjunction with a drilling template (not shown) which is fixed on the lid 35 of the caisson. The drilling template is located on the caisson prior to loading it onto the vessel for transport to the installation site. In an alternative embodiment, the drilling template and the caisson may be loaded onto the vessel separately and assembled on the vessel, platform or other suitable structure prior to deployment to the seabed. Initially, the drilling template holds a plurality of micropiles 40 (only 3 shown) in position on top of the lid 35 of the caisson. Once the caisson is located in place in the substrate 20, the piles are drilled through the caisson lid 35 and into the substrate 20. In the example, each pile 40 is drilled into the substrate at an angle of 90 degrees to the plane of the lid of the caisson. However, in variations of the embodiment, the piles 40 may be oriented at an angle up to the point where the piles would intersect with the caisson skirt 37, so avoiding interference between any pile 40 and the caisson skirt 37.

[0016] As detailed above in the background section, micropiles are small diameter (<300 mm) drilled and grouted friction piles. Each pile includes steel reinforcement elements which are bonded into the bearing soil or rock—usually with cement grout.

[0017] The hybrid anchor combines elements of both suction caisson and micropile installation in order to function as seabed anchor or foundation solution. Suctions caissons traditionally require large sizing in order to benefit from self-weight as an initial driving force for the caisson into the substrate. In combining the teachings of these two considerably different anchor technologies, it is possible to reduce the traditional size of the caisson elements to a significantly smaller size than that of traditional suction caissons for an equivalent load requirement.

[0018] The hybrid anchor additionally comprises a drilling template, which enables at least one micropile to be driven through the caisson element at one of number of predetermined positions once the caisson 30 has been deployed to its optimal anchored position within the substrate 20.

[0019] The hybrid anchor provides a solution which enhances both lateral stiffness of the anchor and ability to precisely position the anchor during installation according to project requirements.

[0020] In the illustrated example a single hybrid anchor 20 is shown, however, it will be appreciated that multiple hybrid anchors can deployed as a subsea foundation system in order to support a large structure.

[0021] In some cases, one hybrid anchor 20 can be located at the foot of each leg of the structure, directly connecting the structure to the substrate 20.

[0022] Advantages of the hybrid anchor 20 include: [0023] Reduced size, weight and cost of anchor/foundation solution compared with alternative technologies and traditional methods. [0024] Ability to install anchors in a wide range of soil conditions as hybrid anchor caissons 30 do not need to penetrate deep into the soil (thus avoiding certain obstructions), whereas micropiles 40 can be drilled through obstructions and into rock formations. [0025] Retain ability for levelling foundations and platforms by adjusting differential pressure on each caisson until the desired position is achieved. [0026] Combined structures are able to withstand substantial horizontal and vertical load resistance with minimal deflection. [0027] After positioning, any remaining internal space within the hybrid anchor bases can optionally be filled with grout to enhance bonding between the soil and structure. [0028] Less costly installation equipment—in subsea applications as each micropile of the hybrid anchor is remotely installed with a seabed drill, the need for an expensive deep water drilling rig on the sea surface is eliminated. [0029] As the hybrid anchor employs a suction functionality in order to position the caisson, hybrid anchors are classified as direct embedment anchors. This means the precise location and depth of the anchor is known and they may be deployed in areas where a clear area to drag an anchor to the desired location may not be possible.