The influence of offshore geohazards and soil conditions on infrastructure installation approaches

M. Brown

This presentation will consider the effect of offshore geohazards and soil variability (both natural and anthropogenically induced) on the form and installation methods used to deploy common forms of offshore infrastructure. In an offshore setting this could simply be unanticipated soil variability and its effect on pipeline and cable plough progress and the significant effect on time and cost for installation. Installation of cables and pipelines (product) by jetting creates its own difficult soil situations where the product has to have enough self-weight to avoid flotation for a period after installation when self-weight consolidation of the backfill occurs. Adding additional self-weight over large product distances results in significant fabrication and handling cost increases so installation contractors would always like to make the product as light as possible creating a balance between installation security and cost-effective installation. Getting the balance wrong could lead to significant increases in costs in terms or unanticipated rock dumping which has additional environmental and sustainability implications. Installation by ploughing may encounter other geohazards other than simple soil variability for example sloping seabeds, sand waves and buried vegetation as well as similar buoyancy issues during rapid pipeline burial or bachkfilling. This presentation will consider some of the above issues and outline research that has been undertaken to allow more informed decision making that can be used to reduce risks of offshore operations in zones of geohazards thus leading to more cost effective solutions and confidence in installing in areas that may normally be avoided.