In marine driven steel piles with reinforced concrete infill, the formation of soil plugs is a dynamic process influenced by several factors. Initially, the open-ended piles are driven through the soil, displacing it as they penetrate deeper.
As the pile driving continues, shaft friction gradually develops between the inner walls of the pile and the soil trapped inside. This friction is due to the interaction between the pile material and the soil particles, creating resistance against further downward movement.
The continuous hammering action of the driving process exerts forces on the soil within the pile. These forces, combined with the increasing internal friction, eventually exceed the bearing capacity of the soil at the pile’s base.
When this critical point is reached, the soil plug, which is a column of compacted soil within the lower portion of the pile, is forced downwards. This phenomenon is known as “plug driving” and is facilitated by the inertial forces of the internal soil mass, coupled with the friction along the pile walls.
This mechanism of soil plug formation is well-documented in M. J. Tomlinson’s 1977 research, highlighting the interplay of forces and soil behavior in marine pile driving.