Challenges of offshore geotechnical engineering

Design practice in offshore geotechnical engineering grew out of onshore practice, but the two application areas have tended to diverge over the last 30 years, driven partly by the scale of the foundation elements used offshore, and partly by fundamental differences in construction (or installation) techniques. Groups of many moderate-sized piles are replaced by a few very large diameter piles; excavation of shallow soft sediments is replaced by the use of deep skirts, transferring the effective foundation depth to the level of the skirt tips, or by forcing footings to penetrate several diameters into the seabed; underwater installation has allowed the use of 'suction' (or under-pressure) to aid installation of skirted foundations and caissons. Emphasis in design is focused more on capacity, paying particular attention to the effects of cyclic loading but generally with less concern on deformations compared with onshore design. These differences have led to the development of separate design codes for offshore structures, which are in most cases more prescriptive than onshore codes but are also more sophisticated in key areas. The paper describes design principles for foundation and anchoring systems ranging from shallow footings to piles and caissons, highlighting differences between onshore and offshore practice and also the link (or gap) between research and practice.</p

The design of Subsea foundations subject to general cyclic loading using a massively scalable web based application

Subsea developments require the design of large numbers of shallow skirted foundations to support structures such as manifolds, pipeline and umbilical terminations and in-line tees. Safe and economic design relies on the accurate assessment of foundation capacity against thousands of load-combinations. Performing these design calculations is a significant computational task. The objective of this paper is to demonstrate how new developments in cloud computing can be utilized to optimize foundation design.Engineering design is no longer limited by computing power thanks to the introduction of low-cost on-demand cloud computing platforms. This paper describes a massively scalable cloud based application for rapidly assessing the vertical-horizontal-moment-torsional capacity of shallow skirted foundations against thousands of cyclic load case combinations that arise from numerous environmental and service conditions. The detrimental effect of cyclic loading and the beneficial effect of consolidation on soil strength are incorporated within a single workflow.It is shown that cloud technologies can radically improve traditional engineering design procedures, allowing engineers to focus on the innovative and creative aspects of their work, while the tasks of preparing, executing and documenting calculations become near instantaneous and more easily assessed for quality assurance. More critically, the technology allows rapid and rigorous optimization of the foundation dimensions to achieve the most cost-effective solution that satisfies all load cases. The scalability of the application allows multiple users to run large numbers of calculations simultaneously across a virtually unlimited number of computer nodes. The system can be accessed through a standard web browser and can run simulations on any internet-connected device. Results are saved in the cloud and can be accessed anywhere and shared among colleagues, enhancing collaboration and quality assurance. The approach results in demonstrably superior design outcomes, achieved more quickly.This paper presents what is believed to be the world's first web based application for shallow foundation design that exploits the availability of low cost on-demand cloud computing services. The paper will explain some of the challenges in implementing such a system and provide examples. We believe this type of technology represents the future for geotechnical design work, providing better design in a more efficient manner.<br/

PIPELINE STABILISATION USING PRE-TRENCHING AND SAND BACKFILL

ABSTRACT Stabilizing large diameter natural gas pipelines on the seabed against extreme hydrodynamic loading conditions has proven to be challenging in the northwest of Australia. Tropical storms, which affect the area annually between November and April, can generate wave heights exceeding 30 m and onbottom steady-state currents of 2 m/s or more. Consequently, in shallow water depths, typically less than 40 -60 m, subsea pipelines can experience very high hydrodynamic loads, potentially causing significant lateral movement. If the seabed is rugged, or at locations where the pipeline approaches a point of fixity, this can lead to the pipeline suffering mechanical damage, which is undesirable