Heerema Marine Contractors Develops Concepts for Silent Foundations
DNV GL awarded Heerema Marine Contractors Statements of Feasibility for two concepts designed to reduce the noise of offshore structure installation.
Heerema Marine Contractors has been awarded Statements of Feasibility by DNV GL for two offshore foundation concepts that it has been developing with the assistance of the University of Dundee. The two concepts, which the Dutch company has termed “silent foundations,” are aimed at installation without the loud hammering typical of installation of pile foundations for offshore structures. Such noise can harm marine life, and existing noise-mitigation systems often produce carbon dioxide. The systems under development, termed push-in piles and helical or screw piles, reflect an initiative by the Leiden-based company to support environmentally sustainable marine operations.
The Statements of Feasibility represent the first formal step toward qualification of the concepts for field use. They were granted after a process, conducted throughout 2020 using online formats, that included testing and modeling at the University of Dundee, technology qualification, and workshops held with DNV GL to review foundational concepts and stages of development.
While the offshore industry has been transformed by the need for operations mindful of sustainability, noise pollution remains an area with a significant development gap. Noisy offshore construction, dependent on heavy and powerful machinery, can present a profound threat to marine life, both causing direct hearing damage and disrupting communication and navigational signals, which in turn can disrupt migration. Many nations have implemented underwater noise-level restrictions, but the concepts of silent foundations represent an approach to noise abatement that exceeds existing standards.
The first of the two concepts, push-in pile design, replaces a traditional single open tubular pile with a cluster of four smaller-diameter open tubular piles. In a number of strokes, each of the piles in this cluster is statically pushed into the soil, with two or three piles of the cluster providing the uplift resistance required to push in a third pile, with a tool gripping on the uplift piles and pushing down onto the pile that is penetrating. By pushing in each of the piles sequentially while holding on to others, the whole cluster is implanted into the seabed.
The helical pile foundation, which has been used onshore in the past, suits foundations that require shallow penetration in the seabed. This concept replaces a traditional single open tubular pile offshore with one or more helical piles. The novelty of the concept developed by Heerema is the large pile size and the use of a very large rig that will make it possible to screw the pile down, plus the option to use a pile with different diameters along its length. The pile uses a helical blade at its tip that rotates during installation to allow the pile to penetrate the soil. This concept includes a moment arm that will connect to one of the company’s vessels to provide the required reaction force. Also, the pile design improves the cost and sustainability of operations at the end of life; when the process is reversed, foundations can be removed, allowing low-cost decommissioning and full recycling or reuse of piles.