Simulating pile set-up in a DEM centrifuge chamber

Abstract

Pile set-up, defined as the pile shaft capacity increase with time, is a well-established behavioural feature of displacement piles installed in sand. To date, the mechanisms underlying set-up are poorly understood and, as a consequence, is difficult to reliably incorporate this phenomena into design. Micromechanical investigations have recently shown that pile set-up may be directly related to the time dependent breakage of sand around the pile. Following the idea that fracture propagation has an inherent timescale, a fracture based quartz sand discrete element method (DEM) model, previously validated on creep/stress relaxation experimental results, was implemented into a DEM centrifuge chamber to simulate pile set-up. The particle refinement method was implemented to ensure a manageable number of elements. The model pile was either jacked or driven to the target depth. One month creep period under load was applied to age the system. Pull-out pile tests were simulated for the fresh pile and aged pile conditions. The results show a mobilized shaft capacity increase of over 20% for jacked piles and over 50% for driven piles, within the range reported from field pile tests.