Drilled anchor piles from a marine drill

Floating offshore wind, and an increasing share of fixed foundations, need anchor and foundation piles installed precisely on seabeds that range from soft sediment to hard rock, in water too deep for a jack-up to stand and where driven piling is impractical or noisy. Buying or chartering a dedicated heavy-lift piling vessel for that is slow and expensive. Our solution turns a geotechnical marine drilling vessel, the kind already working site investigation campaigns, into a drilled-pile and anchor installer, with a defined set of minor conversions and a grout spread. The same vessel that takes the soil samples can install the foundations they inform.

What problem it solves

Drilled-and-grouted anchor piles are the right answer where holding capacity, high line angles and difficult ground rule out gravity, suction or driven options, but the conventional route to installing them ties the work to scarce, costly heavy installation vessels. By adapting a geotechnical drill that already has the rotary, hoisting, handling and station-keeping it needs, the capability is unlocked for a fraction of the capital and mobilisation and brings the precision and ground-versatility of drilled foundations to floating-wind moorings and jacket/anchor foundations.

The conversion – minor, defined

We have a documented method, engineered since 2019, for converting a floating geotechnical drilling vessel into a large-diameter drilling and pile-installation system, independently validated in 2023 under an Offshore Wind Growth Partnership framework. Working from a dynamically-positioned vessel means anchor piles can be installed in water depths where a jack-up cannot stand and where hammer-driven piling is impractical.

The vessel’s geotechnical drill is up-rated and fitted out for large-diameter pile work, not rebuilt. The defined conversion items are:

• Large-diameter BHA – bottom-hole assembly sized for the pile, with under-reaming where the pile must pass the drill bit.
• Large-diameter pile / BHA / pipe handling system – deck handling with a travelling roll-over frame, carriage and power swivel to make up and trip the heavy string.
• Up-rated drill doors and a reverse-circulation-enabled power swivel.
• Seabed frame – large-diameter frame to react loads, guide and clamp the pile.
• Grouting-enabled bit guide – the grout spread and a bit guide that grouts the pile in place.
• Spoil-removal arrangement – reverse-circulation / airlift spoil handling, discharged subsea, overboard or fully to deck as the job requires. See airlifting / spoil removal.

Two installation methods, matched to the ground

• Cased open-hole installation – hard ground (typically >80–100 MPa) – sacrificial casing is set to the seabed behind the cutters to protect the hole from overburden; a rock socket is drilled through it; the drill string is recovered and the pile installed and grouted. Lower-risk in hard ground, and the open hole can be left cased on the seabed and returned to – so a closing weather window doesn’t cost the hole.
• Follow-on installation – soft ground (sands, gravels, clays) – the pile is pinned to the BHA behind the cutters and installed as the hole is drilled; at depth the pile is clamped in the seabed frame, unpinned and the string recovered, then grouted. A single-pass drill-and-install operation that lowers risk in unstable ground.

In both methods the pile is clamped by the seabed frame and grouted in place through the bit guide, vertical or raked. Indicative envelope from the concept design: piles to ~36 in (≈900 mm) class from a vessel working in deep water, confirmed to the project at enquiry.

Why install anchor piles this way

• Capital-efficient – converts a vessel and drill that already exist, rather than mobilising a dedicated piling spread.
• Water depth beyond jack-ups and hammers – works from a dynamically-positioned floating vessel.
• Hard and soft ground – one system, two methods, covering rock through to soft sediment.
• High-capacity drilled-and-grouted anchors – suited to the high, angled mooring loads of floating offshore wind and to jacket and anchor foundations.
• Single-party accountability – the drill up-rate, handling, spoil removal, grouting and controls are engineered and integrated as one system.

It is the productised, available expression of our subsea pile installation method, focused on anchor and foundation piles and it sits on the same drilled-foundation track as our forward-looking deep-set drilled anchor programme.