Pile Foundations: An Introduction

About this course.

A pile foundation is a deep foundation made up of slender structural elements — piles — that transfer the loads from a structure down through weak, compressible or unsuitable near-surface soil into deeper, stronger and more reliable ground or rock. You use piles instead of shallow footings whenever the soil near the surface cannot safely and economically carry the loads without unacceptable settlement: typically where near-surface soils are weak, soft or highly variable; where loads are very high or concentrated; where soils are expansive or reactive; or where the structure must reach down to a firmer stratum. Shallow footings, by contrast, spread load into the soil just below the surface and work well only when that soil is competent.

The distinction between shallow and deep foundations is fundamentally about where the load ends up. A pad or strip footing bears on soil close to the surface and relies on that soil having enough strength and stiffness to carry the pressure without excessive or uneven settlement. When the near-surface ground is inadequate, we either have to improve it, spread the load over a very large raft, or bypass it by taking the load deeper — and taking it deeper is what piles do.