Pile-raft foundations combine shallow and deep foundation elements into a single system where load is shared between the raft and the piles. Rather than relying solely on piles to carry the load, the raft can contribute significantly to stiffness and settlement control, enabling more efficient and economical designs.

Building on previous discussions of pile and pile-group behaviour, this Coffee Corner focuses on how these interaction mechanisms can be used in practice to optimise foundation performance. We will explore how load sharing develops between raft and piles, how soil conditions and stiffness influence the response, and how modelling assumptions affect predicted settlements and forces.

Using practical PLAXIS examples, we will demonstrate how to model pile-raft systems and how to interpret key results such as settlement, load distribution, and structural response. The session will focus on translating numerical results into actionable design insights, helping engineers move from conservative pile-only approaches towards more efficient combined foundation solutions.

Learning Points:

Understand load sharing in pile–raft foundations: Learn how loads are distributed between raft and piles, and how soil conditions, stiffness, and layout influence this behaviour. Model pile-raft systems effectively in PLAXIS: Discover practical approaches for modelling the combined soil-structure system, including raft, piles, and interfaces. Interpret results for design and optimisation: Learn how to evaluate settlement, load distribution, and structural response to identify opportunities for more efficient foundation design.