Design of Foundations on Layered Soil

The Challenge of Foundations on Layered Soils

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

Traditional Failure Mechanisms for Foundations On Layered Soil Under Vertical Load

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”