Heerema researches silent offshore foundations
The increasing focus on sustainability has led to underwater noise restrictions for offshore construction. Heerema is now involved in a research project seeking to develop alternative pile foundations that can be installed without producing significant underwater noise.
The project is being carried out by Heerema Marine Contractors, Heerema Fabrication Group and the University of Dundee’s School of Science and Engineering. According to Heerema noise pollution, especially within offshore construction, is an area that still requires significant improvements.
There are concerns that noise pollution can cause direct hearing damage in animals (temporary or permanent) alongside disruption to their communication and navigation signals, which in turn can affect migratory patterns. With difficulties gathering data, the long-term impact is unknown.
During the installation of wind turbines, wind farm substations, converter platforms, and traditional oil and gas facilities, pile-driving operations generate considerable noise. Globally, several countries are challenging noise pollution by introducing underwater noise restrictions. In an effort to go beyond compliance, Heerema now seeks to create “silent foundations”, that can be installed without producing significant noise.
Two foundation concepts are under development, and these are push-in piles and large helical or screw piles. The push-in pile design replaces a traditional single open tubular pile with a cluster of four smaller diameter open tubular piles. This design can eliminate noise pollution as it requires no pile-driving or hammering – instead, after some strokes, each of the piles is pushed into the soil with two or three providing the uplift resistance required to push in the fourth. This concept might sound complicated, but it uses a similar principle to onshore installations of sheet pile walls.
The helical pile foundation suits foundations that require shallow penetration in the seabed. The pile has a helical blade at its tip rotated during installation to allow the pile to penetrate the soil. This concept includes a moment arm that will connect to one of Heerema’s vessels to provide the required reaction force. Also, this pile is prepared for the future as by reversing the process, we can use it for removing foundations allowing low-cost decommissioning and full recycling or re-use of piles.
Testing and modelling
The University of Dundee’s School of Science and Engineering is carrying out a 6-month testing and modelling program. The researchers involved have considerable experience developing helical piles in previous research projects in collaboration with Durham University and the University of Southampton. This program includes physically testing the piles using 3D-printed steel models in a geo-centrifuge, a device that simulates realistic soil stresses and installation conditions to match full-scale behaviour using small models (1 to 100th scale).
In the centrifuge, the installation requirements (forces and torques) and the installed capacity of the piles and pile clusters can be tested and measured directly. These tests complement the University of Dundee’s ongoing research using discrete element method (DEM) modelling for varying soil conditions and pile designs. By using this method, a complete evaluation of the installation process and in-place performance can be analysed using a range of variables.
Their process replaces the millions of soil particles the pile would contact with on the seabed with larger balls with the same behaviour as sand particles. Using this approach of combining physical and numerical modelling helps with rapid development in a controlled environment where many impacts on pile behaviour can be assessed. The testing program will reduce development costs when moving to full-scale tooling development and helps to de-risk future use of these low noise and sustainable foundation concepts.