Effect of Density on Skin Friction Response of Piles Embedded in Sand by Simple Shear Interface Tests

This study focuses on a particular phenomenon related to the reduction in sand-pile skin friction with initial relative density increment from medium to dense. Frictional behaviour of sand-pile interface is simulated using a simple shear-type device capable of inducing constant normal stiffness condition. Sand-pile interface sliding and soil deformation components are distinguished quantitatively. The effects of initial relative density of sand, initial normal load, and constant normal stiffness are examined on the magnitude of the pile skin friction and shear displacement at failure. Results indicate that the magnitude of the mobilized shear stress at failure significantly relies on the shear stress state concerning the inflexion point on volume change graph, which is equivalent to the position of peak stress ratio. Good correlations exist between results of this study and field data of several heavily instrumented piles embedded in dense to very dense sands. The presented procedure is a useful framework for establishing more accurate skin friction calculation methodologies and t-z curve developments of axially loaded piles.