Case Studies

Subsea Foundation Preparation of a U.S Offshore Wind Project

How Deep C removed soil plugs and cleaned 12 large steel piles prior to installation

YEAR
2024-2025

LOCATION
East Coast of the U.S.

PROJECT OBJECTIVE
Soil plug removal and internal pile cleaning

SEABED CONDITION
Stiff clay and sand, harder and more variable than predicted

CHALLENGES
Variable soil conditions
Tight installation schedule
Uncertain offshore conditions

EQUIPMENT
Soil Plug Removal Tool
Pile Cleaning Tool

Project Overview

During 2024–2025, Deep C supported the preparation of three subsea foundations for an offshore wind development located off the U.S. East Coast.

Each platform foundation consists of four large steel piles, giving a total of twelve piles requiring soil plug removal and internal cleaning ahead of grouting and installation. The work was executed across three offshore campaigns, each lasting approximately four to five days.

Accurate and uniform cleaning was required to prepare the internal steel surfaces prior to grouting and installation. Project planning and environmental conditions introduced uncertainty, while maintaining the installation schedule remained an operational priority.

The Deep C Solution

Deep C deployed its Soil Plug Removal Tool (SPRT), a topside-controlled system combining high-pressure jetting, suction and 360° internal wall cleaning. The tool was launched from a landing frame positioned on each pile and operated from the vessel through an umbilical system, while ROV monitoring provided visual support during deployment and operation.

During operation, the SPRT disintegrated and removed the soil plug while simultaneously cleaning the internal wall as the tool descended toward the target depth. A rotating nozzle system ensured full circumferential coverage while maintaining controlled soil removal, allowing soil disintegration, extraction and wall cleaning to be performed within the same operation.

To complement the internal preparation work, a dedicated external cleaning tool was mobilised to remove seabed-level fouling on the outside of the piles. Because installation occurred several weeks after the first operation, Deep C later returned offshore with its Pile Cleaning Tool (PCT) to perform a pre-installation re-clean, ensuring the surfaces met the required cleanliness standard ahead of grouting.

Throughout the work, ROV visuals provided situational awareness and supported safe positioning of the equipment during subsea operations.

Key Data Points

Technical & Dimensional		Operational & Performance
Number of piles:	12 piles across 3 foundations	Scope:	Soil plug removal, internal pile cleaning, external cleaning and pre-installation re-clean
Pile dimensions:	Outer diameter 2473 mm, wall thickness 50-90 mm, average pile length 74 m (max 82 m)	Operational execution:	3 offshore campaigns; approx. 4-5 days per foundation (4 piles), totalling ~15 days of SPRT operations
Water depth:	Approx. 30 m	Safety performance:	Zero incidents
Target soil removal depth:	300 mm below jacket leg (+/- 100 mm tolerance)	Operation performance:	No downtime impacting the installation schedule
Soil conditions:	Stiff clay and sand, harder and more variable than predicted
Volume of soil plugs removed:	Approx. 500 m³
Cleaning standard:	Clean steel internal surfaces in accordance with ISO 8501-4:2006

Results

Deep C delivered consistent and precise pile preparation, achieving fully cleaned internal steel surfaces and reliable soil plug removal on all twelve piles. The work was executed across three offshore campaigns and was completed with zero incidents and without downtime affecting the installation schedule.

Despite variable soil conditions and off-spec water quality, the cleaning ensured predictable conditions for grouting. The pre-installation re-clean restored the required surface quality ahead of final assembly.

By combining field-proven tools, topside-controlled operations and responsive offshore execution, Deep C enabled safe and effective preparation of the foundations prior to installation, contributing to overall project reliability. The client expressed satisfaction with the execution and outcome of the operations.