Recent papers from UWA/COFS have presented cutting edge developments in subsea foundation design which can allow significant optimisation of foundation sizes.  This has direct practical benefits that have been seen in practise.  As such, these papers have been of great use to the offshore industry and they are well summarised in this paper. Starting from the codified approaches of developing VHM interaction envelopes, how these have been improved upon to generate refined VHMT envelopes, how further gains can be made by accounting for consolidation from sustained vertical and lateral loading and then moving onto their work on sliding foundations.  A similar publication was also made at OTC (OTC-27703​)

​One of the critical aspects in subsea shallow foundation is the ability to assess them differently to fixed offshore installations which is typically the focal point of design codes). The figures below demonstrate the difference in typical ​loading regime and how this may impact the respective soil strength over time from foundation design perspective.

In the final section of the paper a worked example of presented showing that for a particular PLET it may be possible to reduce the foundation size by 75% using the design methods provided, in the end moving from a fixed foundation with a structural sliding mechanism to accommodate pipeline expansion to a foundation which is designed to slide upon the seabed.

The following observations are made:

• ​The foundation size of the PLET may be governed by many things other than the foundation capacity, such as the length of piping/piping arrangement, magnitude of pipeline expansion, spool/jumper limitations, connector type, vessel limitations etc....
• The loading regime for a sliding PLET would be quite different than that of a PLET with a fixed foundation and sliding mechanism.  As such, it would be extremely unusual to have a PLET with a fixed foundation to be designed to resist a lateral load of 320 kN, the PLET would be designed such that it never comes to the end of the sliding rails and therefore the lateral load (assuming negligible environmental loads) all comes from friction on the rails from the weight of the structure (say 10% to 20% of its weight) which would therefore have to be >3200 kN in this example.  It is usually vertical load and overturning moments which governs PLET design.
• It is not uncommon for PLET foundation sizing to be governed by short term loading (often they require significant equipment weight to facilitate hydrotest, spool tie-in or even the change of valve seal which could happen at anytime during its life) which would generally preclude the advantages of consolidation from being adopted.​
  

As such, the paper summarises some excellent research which allows industry to optimise the way that shallow foundations can be designed.  However, the worked example that is provided does not best reflect how it can be used to optimise PLET foundation design. 

 
The downturn of the global oil and gas market has challenged every professional within the industry to look at the way they work and look to where costs can be reduced or removed. 
 
Design engineers could be forgiven for thinking that their calling would be optimise their analyses as far as possible therefore saving steel and fabrication costs with the knock on effect of improving installability / offshore construction costs.
 
Is this the future?
 
The few oil & gas projects, however, which have been sanctioned over the past few years have been driven forward at a relentless pace putting what would have previously been seen as ‘fast track’ to shame.  The obvious way to accommodate this change has been to squeeze the engineering schedule whilst accelerating fabrication.  The results is commencement of fabrication (and upon occasion, completion of fabrication) before the design has been completed.  Rather than optimise, engineers are forced to design with margin attempting to allow for uncertain input data and potential for unforeseen (but inevitable) changes.  Within this framework there is limited opportunity for optimisation.
 
Stand-alone/single company FEED studies and interfacing with 3rd parties are two of the main obstacles to this type of engineering/scheduling.  To this end we have seen a number of mergers or alliances of large companies with historically different specialisms (technipfmc, Subsea7 and OSS, KG7).  These link-ups should facilitate the flow of critical design data which in theory, should assist earlier commencement of detailed design.  How this fits in with the traditional project delivery approach remains to be fully realised.  However the way that offshore oil & gas projects are delivered has changed and will continue to change significantly over the coming years.
 
Over the past few years however, it has been common for operators to engage site investigation contractors at an extremely early PRE-FEED phase on complex developments.  It would not be uncommon for years of investigation and geohazard assessment to ensue in an effort to understand the project ground risk prior to final investment decisions.
 
With the changes we have seen to the how end users of the geotechnical, geophysical and geohazard data will execute projects.  Will or how will the role of SI contractors be impacted by the changing nature of the offshore oil & gas industry?  Can this be accommodated as the industry moves into ever more challenging field development?

The Society for Underwater Technology (SUT) held the 8th Offshore Site Investigation & Geotechnics (OSIG) conference in September at the Royal Geographical Society (RGS) in London.

The OSIG is held every 5 years and is dedicated to offshore geotechnical engineering, site investigations, geohazards and geosciences.  It stands alongside the ISFOG (International Symposium on Frontiers in Offshore Geotechnics) as a highlight in the conference calendar.

This edition of the conference title was entitled “Smarter Solutions for Future Offshore Developments” with the following challenge in the call for papers:
 
“The challenges currently faced by the offshore oil & gas industry call for innovative approaches to improve efficiency and rigour in practice, while the offshore renewable energy industry has identified and addressed, through major research programmes, key technical issues that must be solved to support its growing strength. High profile international incidents have also occurred across all sectors in recent years that pose significant data acquisition, engineering and operational challenges.”

With this in mind it is interesting to note that this is first time that delegates from the renewables sector outnumbered those from oil & gas at the OSIG conference.

In addition to the 4th McClelland Lecture being delivered at the conference the following keynote papers were presented:

• Steve Thomas – Fugro Geoscience Technical Authority:​ A Phased And Integrated Data Interpretation Approach to Site Characterisation
• Justin Dix – Southampton University​: Substrate Controls on the Life-Time Performance of Marine HV Cables
• Byron Byrne – University of Oxford: PISA: New Design Methods for Offshore Wind Turbine Monopiles 
• Philippe Jeanjean – Geotechnical Technical Authority, BP​: A Framework for Monotonic p-y Curves in Clays
• Professor Barry Lehane – University of Western Australia​: Characteristics of Unified Databases for Driven Piles

The published proceedings (comprising 1323 pages) are split into 2 volumes and 12 sections including:

•  Vol 1;International Society for Soil Mechanics and Geotechnical Engineering - 4th McClelland lecture and keynote addresses (8), Geohazards & Geophysics (10), Geotechnical Site Investigation & Design (16), Advanced Soil Characterisation (10), Suction Installed Foundations (11)

• Vol 2; Pile Design and Installation (16), Subsea Shallow Foundations (14), Pipelines (11), Mooring Systems (13), Wind Turbine Foundations (14), Geotechnical Design Studies (13) and Case Studies (8).

 
Parallel presentation sessions were introduced in order to fit in a huge number of presentations and presentations times were kept short (5 min in the parallel sessions, which was described as a speed dating equivalent for geotechnical engineers).
 
A knovel approach to Q&A was available in plenary sessions where delegates could use a social media forum to submit questions during the presentations.  This has benefits and draw backs (with some delegates choosing to make anonymous questions or using fake names which takes away from the collaborative spirit of the event).  However, it probably encouraged more questions which is a positive if not making more work for session chairs.
 
​A few of the conference papers (in addition to the keynotes above) which best answer the challenge made in the call for papers, in my opinion are summarised below:

• D Rushton, L Jones, T Nott, M Rattley: Geospatial Analysis for Offshore Geotechnical Design

• S Frankenmolen, C Erbrich, R Fearon: Successful Installation of Large Suction Caissons and Driven Piles in Carbonate Soils

• S Abyaneh, A Maconochie, J Oliphant: The Undrained Capacity of Shallow Two-Foundation Systems Acting in Consort Under Three-Dimensional Loading

• R Wallerand, M Cafi , D Kay, P Dimmock, M Randolph: Hybrid Subsea Foundations – From Research to Project Application

• S Gourvenec, S Stanier, D White, N Morgan, M Banimahd, J Chen: Whole-Life Assessment of Subsea Shallow Foundation Capacity
• Low, M Ramm, MF Bransby, DJ White, ZJ Westgate: Effect of Through-Life Changes in Soil Strength and Axial Pipe-Seabed Resistance for HPHT Pipeline Design
• K Sassi, MY-H Kuo, H Versteele, DN Cathie, S Zehzouh: Insights into the Mechanisms of Anchor Chain Trench Formation​
• D Abadias, L Zdravkovic, D Taborda, D Potts: The Implications of Advanced Monopile Design Methodologies in Offshore Wind Turbines

• S Holm, R Klinkvort, N Boylan, W-E Semm, K Price, C Clausen: Back Analyses of Monopile Installation in North Sea Sands

The latter paper is one of the most informative pile driving papers that I've had the pleasure to read providing a good summary of traditional SRD prediction models, an NGI model and a comparison against back analysed field data.

Over the course of the 3 days there were some excellent presentations and there are of course many other fantastic papers.  A great event and we look forward to the next one in 5 years time.