Seismic Performance of Bridge Foundations in Liquefiable Soils

AUTC project number: 309010

PI(s):

Zhaohui (Joey) Yang (UAA)

Funding:
  • US Department of Transportation (RITA)
  • Alaska Department of Transportation & Public Facilities
  • Start Date: Aug 1, 2009
  • End Date: Sep 12, 2012

Project Summary

What happens to a bridge foundation during an earthquake if it is built on a frozen crust of ground that rests on a layer of liquefiable soil (soil that changes from behaving as a solid to behaving as a liquid during an earthquake)? How large are the loads generated by the interaction of frozen crust and foundation during a winter earthquake, and how should a designer deal with them? How can engineers make bridges safe and strong enough to withstand such forces of nature? These questions are unique to arctic areas such as Alaska, but there are no seismic analysis guidelines to account for how frozen-ground crust affects bridge foundations at a liquefiable site. This project provides the first quantitative evaluation of loads imposed on bridge foundations by a frozen crust with liquefaction and lateral spreading. Study results will improve seismic design of highway bridge foundations in areas of arctic conditions and seismic activity. Better seismic performance of Alaska's bridges will increase transportation safety and reduce maintenance and reconstruction costs following a seismic event. In the first year of this two-year project, a sophisticated model capable of simulating soil liquefaction has been calibrated and validated with physical testing data. This validated model has been applied to simulate the response of a bridge pile foundation typical in Alaska, embedded in liquefiable soils with an unfrozen or a frozen crust. Preliminary results show that pile performance is very sensitive to crust conditions. The internal forces of the pile (for example, bending moment and shear force) change by about 50% when the crust freezes. These results demonstrate the great need to further this research. Numerical simulation seems insufficient in such determinations, researchers have proposed an experimental component to supplement this project.