Post installation sediment evolution in dynamic seabed conditions: impact on offshore wind cable installation, protection and performance

Project Description:

This PhD scholarship is offered by the EPSRC CDT in Offshore Wind Energy Sustainability and Resilience; a partnership between the Universities of Durham, Hull, Loughborough and Sheffield. The project is sponsored by industry partner, The Turbidites Research Group. The successful applicant will undertake six-month of training with the rest of the CDT cohort at the University of Hull before continuing their PhD research at Durham University.

The installation of infrastructure for offshore wind, such as power transmission cables, requires operations on the seabed that disturb shallow sediments.  This can take several forms, from seabed ploughing using clearance, through cable, pipeline and backfilling ploughs depending on the site specific conditions and the presence of problematic units (such as boulders), to jet trenching to fluidise sediments, to chain cutting in harder materials.  Once the cable is installed, hopefully at the bottom of the cut trench, sediments will backfill the trench naturally (for example after the use of a cable plough or jet trenching) or be mechanically placed via a backfill plough. Understanding the state of the sediments post operation, and the evolution of the sediments’ state over time, is critical to understand the behaviour of the installed cables in terms of both their mechanical and thermal response.  However, it is not possible to use conventional site investigation techniques (such as Cone Penetration Tests, CPTs) to understand the state of the disturbed sediments due to the presence of the installed infrastructure.  This project is focused on understanding the evolution of the sediments under dynamic seabed conditions post cable/pipeline installation and developing predictive models under diverse sediment conditions (i.e. sands and clays).        

This project has the potential to impact on a number of areas, such as: 

• Lightweight cabling: issues exist with the installation of lightweight cabling for offshore renewables installations, e.g., inter-array lines in certain seabed conditions. Cabling made using low specific gravity materials, such as aluminium, is often difficult to bend into place in a trench in which the seabed sediments are effectively fluidised due to the trenching operation [1]. The initial stability following installation is then affected by sediment settlement above and around the cable, and by vibrations transmitted along the cable. It is currently difficult to predict sediment (and cable) behaviour and new tools are needed to understand the behaviour of the cable during installation, the position of the cable immediately after installation, and any potential movement over time.  It is not possible to develop these tools without understanding the sediment behaviour.   
• Anchor-cable interaction: EPSRC-funded research at Durham University and the University of Dundee has shown that the behaviour of drag anchors (such as penetration depth and general kinematics) is sensitive to the state of the sediment when interacting with ploughed regions of the seabed; anchors can increase in penetration depth and roll depending on the interaction angle between the anchor and the backfilled trench.  It has been suggested by others that this is a short-term effect and over time sediments quickly return to their original state (reference).  However, the physical mechanism for the re-dedensification of the sediments is not clear and models describing this evolution (or lack thereof) are required.  This project would not directly model the interaction with anchors, but rather provide a model to explain the evolution of the sediments over time and therefore inform anchor-trench interaction. 
• Cable thermal performance: the thermal performance of cables is sensitive to the state of the sediments surrounding the cable. For example, higher permeability sediments, such as sands, can help to dissipate excessive heat via convective heat transfer [2,3]. Conversely, low permeability sediments, such as clays can effectively insulate cables. This again requires accurate models to explain post installation sediment evolution, and could be combined with lab-scale physical modelling at the University of Hull.   

Training and development

You will benefit from a taught programme, giving you a broad understanding of the breadth and depth of current and emerging offshore wind sector needs. This begins with an intensive six-month programme at the University of Hull for the new student intake, drawing on the expertise and facilities of all four academic partners. It is supplemented by Continuing Professional Development (CPD), which is embedded throughout your 4-year research scholarship.

The successful candidate will join a large and vibrant research network as part of the inter-disciplinary Turbidites Research Group (TRG). The TRG has a number of on-going research projects related to deep-marine clastic sedimentology via field studies, physical and numerical modelling, and subsurface studies. As such, the candidate will benefit from interaction with over fifty collaborative academics across the globe, gain access to our marine science research databases, exposure to and interaction with our national and international sponsors, and have the opportunity to present their work at our twice annual research group meetings.  

Entry requirements

If you have received a First-class Honours degree, or a 2:1 Honours degree and a Masters, or a Distinction at Masters level with any undergraduate degree (or the international equivalents) in engineering, computer science or physics, and can demonstrate experience of coding, we would like to hear from you.

If your first language is not English, or you require Tier 4 student visa to study, you will be required to provide evidence of your English language proficiency level that meets the requirements of the Aura CDT’s academic partners. This course requires academic IELTS 7.0 overall, with no less than 6.0 in each skill.

If you have any queries about this research project, please address them to Prof Will Coombs.

You may also address queries about the CDT to auracdt@hull.ac.uk.

Watch our short video to hear from Aura CDT students, academics and industry partners:

Funding

The CDT is funded by the EPSRC, allowing us to provide scholarships that cover fees plus a stipend set at the UKRI nationally agreed rates. These are currently circa £19,795 per annum at 2025/26 rates and will increase in line with the EPSRC guidelines for the subsequent years (subject to progress).

Eligibility

Research Council funding for postgraduate research has residence requirements. CDT scholarships are available to Home (UK) Students. To be considered a Home student, and therefore eligible for a full award, a student must have no restrictions on how long they can stay in the UK and have been ordinarily resident in the UK for at least 3 years prior to the start of the scholarship (with some further constraint regarding residence for education). For full eligibility information, please refer to the EPSRC website.

We also allocate a number of scholarships for International Students per cohort.

References:

[1] Atangana Njock, Pierre Guy, Qian Zheng, Ning Zhang, and Ye-Shuang Xu. (2020), Perspective Review on Subsea Jet Trenching Technology and Modeling Journal of Marine Science and Engineering 8, no. 6: 460.

[2] Zeng Cao, Xu Liang, Yu Deng, Chizhong Wang, Lizhong Wang, Ronghua Zhu, Jiangning Zeng, (2021) Influence of multi-layered sediment characteristics on the thermal performance of buried submarine high-voltage cables, Ocean Engineering, Volume 242,110030.

[3] Hughes, T., Henstock, Timothy J., Pilgrim, J.A., Dix, J.K., Gernon, T.M. and Thompson, C.E.L. (2015), Effect of Sediment Properties on the Thermal Performance of Submarine HV Cables. IEEE Transactions on Power Delivery, 30 (6), 2443-2450.