The Society for Underwater Technology invite you to the OSIGp May 2022 Evening Technical Meeting:

Recent advances in offshore geotechnics – select outputs from the OFFshore Hub at UWA

The evening will focus on the following three topics:

1. New approaches to integrated site characterisation

Speaker: Fraser Bransby (UWA)

Characterising the mechanical properties of the seabed is a key part of geotechnical design, from which all further advice stems. It is particularly challenging to provide design inputs away from geotechnically investigated locations, and given that it is impossible to investigate all locations (e.g. all along a pipeline or cable) and that subsea layouts often change after the SI programme, this assessment is required more often than not.  Currently, site characterisation often involves simple statistical analysis of geotechnical measurements melded with engineering judgement, and backed up by (generally) qualitative information obtained from geophysical surveys.  This presentation will discuss these challenges and present preliminary quantitative geophysical interpretation and statistical approaches that are being developed as part of the OFFshore Hub and the new TIDE Research Hub thanks to the use of site investigation data from the North West Shelf and the engagement of geophysical experts and data scientists.

2. Improved design of offshore conductors

Speaker: Mariajose Guevara (UWA, Fugro)

Offshore conductors are used to support the riser system that transports hydrocarbons from the reservoir to the floating vessel. Movement of the riser system translates to movement at the well head, resulting in stress cycles in the conductor. Upcoming international codes propose significant changes related to the fatigue design of conductors, specifically in terms of response from the soil to lateral movement – whereas recent testing by the OFFshore Hub suggests this guidance may over-estimate soil stiffness at the governing levels of motion.  In addition, current design methods do not account for changes in soil response over the life of the conductor, associated with progressive periods of cyclic softening and recovery.  A combination of numerical and physical model experiments has been undertaken to support new models for predicting fatigue performance of offshore conductors.

3. A framework to capture strength and stiffness changes due to remoulding and consolidation

Speaker: Conleth O’Loughlin (UWA)

This brief presentation will introduce a new analysis framework to capture the effects of maintained and cyclic loads and the subsequent reconsolidation processes on the geotechnical capacity, based on estimation of the changing soil strength. The framework was developed using critical state concepts in the effective stress domain, and by discretising the soil domain as a one-dimensional column of soil elements. This framework is designed as the simplest basis on which to capture spatially varying changes in strength due to maintained and cyclic loads, and the associated remoulding and reconsolidation processes – and it can be used to interpret cyclic penetrometer tests as well as foundation behaviour.

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Contact OSIGp directly by emailing: Michael Cocjin (m.cocjin@fugro.com)

Many thanks to our event sponsor:

ARC Offshore HUB UWA