Design Approach for Piles Subject to Ice Jacking

Abstract

The uplifting of marina piles clue to a process known as ice jacking (cyclic incremental pullout of the pile by an ice sheet) is a widespread phenomena in many large bodies of water in northern regions. An effort has been made to use existing field performance data as a basis for a rational design process by evaluating pile uplift damage at 33 Great Lakes marina sites in light of local ice sheet and pile capacity estimates. An ice uplift index is proposed to characterize the uplift potential of an ice sheet. It is based on the “first crack” elastic analysis using an evaluation of the mean freeze index to estimate ice thickness and a geometry factor which accounts for the effect of shared load by neighboring piles. While this index does not yield the actual uplift force acting on a pile, it does offer an easily reproducible method for separating relatively severe ice conditions from milder ones. Available geotechnical information was used to estimate the pullout resistance of the piles in terms of six different indices based on different static pile capacity analysis methods. The uplift damage for each of the field cases has been classified using two indicators: (1) the percentage of uplifted piles; and (2) the magnitude of damage or annual movement. The various pile pullout resistance indices are plotted against the ice uplift index in an attempt to establish relationships which delineate between various levels of ice uplift damage. It is shown that several of these indices adequately differentiate between minimal, limited, and severe damage levels. Finally, a method of analysis is presented for minimizing the uplift damage in marina piles based on these empirical observations.