E P Heerema. This paper was first published in GE’s January 1979 edition.
A simple laboratory test arrangement is described which simulates the action of a steel pile wall in the soil during driving, and which is suitable for determination of relationships between wall friction, horizontal stress at the pile/soil interface, and pile wall velocity, in sand and in clay. These tests were run in order to provide more realistic input parameters for pile driveability studies (e.g. wave equation analyses).
The results of the tests demonstrate that during pile driving in sand a simple Coulomb friction behaviour is exhibited: the friction force is linearly dependent on normal stress and independent of velocity. Conversely, in clays, it is found that wall friction is, in an unexpected manner, dependent on the stress condition at the clay/pile interface, on the undrained shear strength of the clay adjacent to the pile, and on the velocity at which the pile wall displaces.
Comment is given on the commonly held view that clay remoulding is the cause of the phenomenon that static friction during driving is lower than bearing friction after set-up.