Multiscale modelling of shelly carbonate sands for foundation design of offshore structures (MuMShell)

Carbonate soils cover over 40% of the world's seabed, where offshore structures, pipelines, artificial islands and other marine structures are founded. For the most part, carbonate soils are of biogenic origin comprising skeleton bodies and shells of small organisms, the shelly carbonate sands. These soils are a complex and poorly understood material as evidenced by a number of accidents reported during platform installation in the 80s. As a consequence, shelly sands have been placed into a niche classification of "problematic soils" in most design guides. While failures are now relatively rare, conservative methods and high factors of safety are commonly used. Understanding the behaviour of shelly carbonate sand is critical for the design of foundations for offshore structures. In particular, understanding the physical phenomena taking place at the microscale has the potential to spur the development of robust computational methods to be integrated into novel or existing design approaches.

Image-based geomechanics is a fascinating research field that has the potential to transform the way soils are investigated and modeled. The ability to follow deformation at the microscale has helped to answer fundamental questions about the soil behaviour observed at the macro-scale. The proposed research uses 4D synchrotron x-ray imaging and post analysis to investigate the kinematics and the strain maps of a shelly carbonate sand under compression. The outcomes will contribute scientific understanding on the multiscale behaviour of shelly carbonate sands. This will form the basis to develop fabric-informed constitutive models to better predict the soil response, thus improving design practices for foundations of offshore structures. The ambition of this project is to contribute towards safer, less conservative and more sustainable ground structures and reduce the financial risks associated with unforeseen ground response during construction of offshore foundations. This multiscale methodology and image algorithms here developed, will be valuable to the broad granular media community to simulate mechanical processes in additive manufacturing, mining, food and pharmaceutical industries.

This research project has been designed to have an impact beyond the academic environment. It is anticipated that the short and mid-term beneficiaries of this research project will be:

Marine and offshore engineering industry, including:
- Design engineers of offshore foundations will have access to advanced multiscale computational tools for shelly carbonate sands to incorporate in their design approaches. This will improve design practices, thus contributing to enhance business revenue and the innovative capacity of the UK offshore industry, noting that UK engineers are engaged with foundation design around the world.
- Contractors of offshore structures will benefit from better design practices for shelly sands, which will avoid additional cost associated with over-designed foundations.
- Companies working on site investigation technology will benefit from further investment in R&D on soils with complex mechanical behaviour, stimulated by this research
- Consultancy companies in the UK and abroad will benefit from hiring graduate students with a better knowledge of soils of biogenic origin as a result of the teaching material and textbooks complemented with the outcomes from this project

Granular media and materials processing industry, which will benefit from:
- A better simulation of processes such as compaction and grain damage/fracture of granular products following further R&D actions motivated by the multiscale methodology and algorithms available from this research project
- A new generation of scientists engaged with multiscale approaches for innovative industry-oriented research, which will contribute with advanced processing and handling solutions for granular materials with a clear advantage to the UK and rapid emergent economies.

Longer term socio-economic impact of this research project is also anticipated and it is envisaged that this might include:
- Safer, cost effective and more sustainable construction practices for offshore engineering with a direct impact on i) the UK economy and ii) on the quality of life of communities living in regions rich in shelly carbonate deposits.
- The lower cost of products, such as food and medication, resulting from the optimisation of the processing and handling of granular materials from the perspective of time and energy saving.
- An increased number of graduate engineers, encouraged to study STEM subject areas by high-tech and exciting research as this project, which will contribute with practical solutions to the 21st century challenges of sustainability, housing and an ageing population.