Date of Award

Summer 2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials and Infrastructure Systems

First Advisor

Jay Wang

Abstract

Pile setup or freeze is a phenomenon where the bearing capacity of a pile increases over time both during and after the dissipation of pore pressure and the stabilization of lateral earth pressure. Driven piles gain capacity after installation because of the dissipation of excess pore pressure and soil aging. Incorporating accurate setup prediction into the design of the piles can significantly reduce the cost of many projects by reducing the size or number of required piles. Various simple, empirical mathematical models have been developed to predict pile setup. However, these models are often unreliable, resulting in very conservative designs. Currently, an effective deterministic pile setup prediction model accounting for pore pressure dissipation and soil aging is not available.

This study establishes a mechanistically-determined prediction model for pile setup in clay due to aging. It incorporates the remolded friction angle increase with time along the pile wall after the dissipation of excess pore water pressure induced during installation and the Over-Consolidation Ratio (OCR) of the soil. Two coefficients used in the model are determined that appear to be directly related to the properties of the soil. An experimental process is developed using conventional shear strength testing equipment to verify the relationships presented in the model. This new experimental process can be utilized to simulate shear strength increase behavior between a pile and soil over time. The results from the testing program indicate an increase in the residual shear strength between clay and concrete as time passes. The results also show a greater increase in frictional behavior when the soil has been subjected to a larger stress history prior to shearing. Combining the developed prediction model and the laboratory procedure, a method to predict the frictional resistance of a pile incorporating the pile setup mechanism of soil aging is presented. The calculated time-dependent pile capacity can be applied in the commonly utilized 13-method to design the pile dimensions.

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