Perhaps one of the most challenging features of an integrated design approach, is the heavily multidisciplinary nature of the design work we undertake. There are many examples of how an optimised design can be achieved and the benefits of taking an integrated approach to design. In this blog post, I shall use pipeline protection system as a vehicle to highlight some of the interesting opportunities we can exploit.
Pipeline Protection Systems
Surface laid pipelines have traditionally been protected using crushed rock (rock dump), concrete mattresses or other forms of mechanical protection. This provides a form of restraint on the pipeline, with the corresponding forces generating global stability (buckling) problems and considerable loads at the tie-in structures. This has led to more sophisticated protection methods, e.g. covers in Glass Reinforced Plastic (GRP), steel or concrete, See Figure 1.
One of the major challenges for all geotechnical engineers when considering foundations on layered soil, is that “design codes” don’t provide closed form solutions for calculating the bearing capacity. The design methods specified in such codes are typically for drained or undrained conditions including linearly increasing strength gradient if one is lucky. It is normally left to the designer to satisfy him/herself that the chosen design method and assumed failure mechanism are suitable for the foundation geometry, soil conditions and loading under consideration.
There are some approaches available for considering load distribution on layered soil i.e. onto an underlying layer, and these are sometimes used for checking for critical failure mechanisms and evaluating the bearing capacity of foundations of mobile drilling units (Figure 1).
Figure 1: Alternative Failure Mechanisms for A Foundation on Layered Soil
When installing a jack-up rig footing (spud can) the loading is quite clearly dominated by vertical loading and the SNAME guidelines on site specific assessment for jack-up mobile drilling units (MODUs) provide a useful commentary when considering installation on layered soils. Some would argue though that the method outlined in this document it is still some way from being a robust approach. Continue reading “Design of Foundations on Layered Soil”