What is the fundamental difference in how a friction pile transfers load to the soil compared to an end-bearing pile?

The fundamental difference lies in the primary mechanism by which each pile type transfers the structural load it carries to the surrounding or underlying soil. A friction pile transfers its load predominantly through skin friction (also known as shaft friction), while an end-bearing pile transfers its load primarily through end bearing (also known as toe bearing).

In a friction pile, the structural load is resisted by the frictional forces developed along the entire surface area of the pile shaft that is in contact with the surrounding soil. As the pile attempts to settle under load, the interface between the pile's side and the soil creates resistance. This resistance, or skin friction, arises from the adhesion and interlocking of soil particles with the pile surface. The load is distributed and resisted over a significant length of the pile. Friction piles are most effective in cohesive soils, such as clays, which possess sufficient shear strength to generate substantial frictional resistance along the pile shaft.

In contrast, an end-bearing pile transfers its load by seating its tip directly onto a strong, incompressible stratum, such as rock, very dense sand, or gravel, located at a greater depth. The structural load is transmitted down the pile shaft to its base, where the resistance is developed primarily by the bearing capacity of this firm stratum. The pile acts like a column, pushing against this solid layer. While some incidental skin friction may develop along the shaft of an end-bearing pile, its contribution to the overall load transfer is considered secondary and often negligible compared to the bearing resistance at the tip. End-bearing piles are chosen when a firm bearing stratum is accessible within a practical driving or drilling depth.