PhD Oral Exam - Fabrizio Di Camillo, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Piles are slender foundation elements that transfer structural loads through weak near-surface soils to stronger, deeper strata, resisting both vertical and uplift forces to provide stability against overturning and reduce settlement. Consequently, they are used where shallow foundations cannot provide adequate support. Despite the long history of pile foundation design, significant uncertainty persists due to wide discrepancies among existing methods, largely arising from simplifying assumptions used to model the complex pile–soil interaction, which, while necessary for analysis, reduce accuracy and limit confidence in any single predictive approach. This thesis presents an experimental investigation into the load-bearing behavior of driven piles in overconsolidated cohesionless soils. Laboratory experiments were conducted using instrumented model piles equipped with pressure transducers and load cells to quantify stress distribution and load response during installation and loading. A sand-placement procedure was developed and calibrated to ensure reproducible specimens with prescribed relative densities and stress profiles. A complementary series of tests was carried out using half-pile models to facilitate particle image velocimetry (PIV) observations within a transparent strongbox. The half-pile configuration exposed the pile–soil interface, enabling high-resolution tracking of soil particle movements under controlled plane-strain conditions. This setup provided detailed insight into localized deformation patterns and the evolution of soil–pile interaction during installation and loading, which cannot be directly captured in fully embedded pile tests. A theoretical model is proposed that incorporates the effect of overconsolidation on pile tip resistance and provides a rigorous evaluation of bearing capacity under axisymmetric conditions. The model is supported by data obtained from pile load tests and deformation measurements derived from PIV analysis, which were used to establish and validate the underlying assumptions of the predictive framework. An adjustment to the base angle of the assumed failure mechanism is introduced to reflect the influence of confining pressures on soil response, without invoking a change in the overall kinematic form of the mechanism. Within this framework, an equivalent bearing-capacity factor, N_q^*, is defined, accounting for the combined effects of soil friction angle and overconsolidation ratio on pile tip resistance.