PhD Oral Exam - Sergio Rosales Garzon, 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

The plane-strain (PS) critical-state (CS) friction angle is an important soil parameter in the design of several geotechnical projects. The static angle of repose, which is known to be the same as the PS-CS friction angle for normally consolidated cohesionless soil (NC), and the associated initial constant-volume friction angle were measured for three granular materials in the laboratory to validate the flow rule that accounts for dilatancy and accordingly the pore pressure coefficient A. To derive the flow rule, the law of conservation of energy and limit equilibrium technique were used to develop a bidimensional micromechanical model representing granular media in CS. The flow rule was then used to predict the at-rest coefficient K0-OC and theoretical porosity thresholds for the contractive, dilative, and collapsible behavior. The lateral stresses of silica sand under the standard and modified Proctor energies of compaction, and non-compacted, were measured in the laboratory for different Dr and OCR to validate the proposed K0-OC. As a by-product of the previous finding, a new methodology to determine OCR in compacted backfills was developed. For the active and passive states, the variational limit equilibrium method applied on NC dry granular media and the PS-CS friction angle were adopted to derive the nonlinear geometry of the slip-failure surface and the associated nonlinear coefficients Ka and Kp. The present micromechanical model was further used to develop a numerical approach to model the stress‒strain path and determine the minimum wall rotation required to develop PS-CS failure. Practical application, and design framework were prepared for various spreadsheets and illustrative examples.