Use of an energy-based liquefaction approach to predicting deformation in silts due to pile driving
Due to the lack of understanding of the cyclic degradation of Rhode Island silts there exists no practical method, numerical model, or otherwise to assist a practicing engineer to determine potential actual hazards to existing structures during pile installation activities. Therefore, the ultimate objective of this research is to predict the onset of significant ground movement during pile driving in silts and to provide practicing engineers with a hazard assessment model that can be utilized to identify the radial extent of significant soil degradation (e.g. the onset of significant induced strains) prior to the onset of construction activities. To meet the research objective, a review of the literature was performed to determine the applicability of various liquefaction-based analyses to both non-plastic fines (i.e. silts) and for predicting the resulting behavior from pile-induced vibrations. Additionally, a review of the current State-of-Practice was conducted to identify how the hazard of pile-induced vibrations are assessed. It was concluded that energy-based approaches are the most adaptive for this research moreover, the current State-of-Practice does not consider the hazards associated with soil degradation with depth (at best only considers surface vibrations). Secondly, a laboratory-testing program was developed and implemented to determine the response of non-plastic silts in terms of normalized energy capacity. A reconstitution methodology was developed whereby laboratory specimens could be reconstituted to mimic in-situ behavior at any density state through a newly developed normalized density state thus, negating the need for in-situ samples. Lastly, a total stress hazard prediction model was developed based on determining the spatial Factor of Safety, defined as the ratio of normalized energy capacity to normalized energy demand, against the onset of significant movement. The model was then validated against a well-documented case history, wherein the predicted radial hazard extent was in good agreement with the observed deformations. A parametric study was performed to identify model sensitivities. It was concluded that the radial extent of the hazard is most influenced by the effectives stress profile, pile hammer, and pile properties (ultimate capacity, composition, etc.). Therefore, the use of the hazard model, presented herein, would provide practicing engineers with the ability to mitigate potential hazards to adjacent structures during the construction design phase.
Oliver-Denzil Somerville Taylor,
"Use of an energy-based liquefaction approach to predicting deformation in silts due to pile driving"
Dissertations and Master's Theses (Campus Access).