The development of new technologies is enabling offshore oil and gas exploration and development in increasingly deep waters. The mooring of floating production ships and platforms at these depths requires sophisticated cables, anchors and subsea foundation systems.
This research stream works to create robust models for near-seabed behavior, where infrastructure such as pipelines, risers, and sliding foundations need to accommodate mobility within weak seabed sediments. Offshore engineering in deeper water requires increasingly subtle solutions that LRF funding is making possible.
Mudmat foundations Subsea structures have historically been supported by shallow mudmat foundations, but in deeper water, loads applied to mudmats have increased. Installation vessels are not equipped with the lifting capability or technology to handle conventional foundations at the scale necessary to support infrastructure in these depths.
COFS' researcher Dr Xiaowei Feng, together with colleagues Prof Susan Gourvenec and Prof Mark Randolph, and industry partner Regis Wallerand from Subsea 7, are working towards an improved design methodology for safer and more efficient mudmat foundations. The research focuses on rectangular mudmats with a length to breadth aspect ratio of 2 and embedment ratios from 0 to 0.2 times the foundation breadth. The results are interpreted through the failure envelope method, encapsulated in a design methodology and presented in a spread-sheet based design tool. Designs are subjected to advanced numerical modeling and a series of centrifuge tests assessing 6 degrees-of-freedom loading.
This research has shown that the loading capacity of mudmat foundations is enhanced through pile and mat interaction. The addition of corner pin piles can reduce the size of subsea mudmats by up to 20%, or allow a mudmat of specified size to withstand larger loads. This design methodology is being extended to incorporate a new ‘hybrid subsea foundation’ with mudmat loading augmented through corner pinned piles.