AUTC project number: 107017
This interdisciplinary project combined seismic data recorded at bridge sites with computer models to identify how highway bridges built on permanently and seasonally frozen ground behave during an earthquake. Two sites – one in Anchorage and one in Fairbanks – were selected for seismic site-response testing. In assessing seismic motion in frozen soil, the thickness of seasonally frozen soil, depth to permafrost and its thickness, and depth to bedrock were considered. Results show that the presence of frozen soil, particularly permafrost, significantly changes ground motion characteristics. The research team concluded that while it is generally safe to ignore the effects of seasonally frozen ground on site response, it is not always safe to classify permafrost soil sites using only the seismic motion of the upper 30 meters of frozen or unfrozen soil, or to use code-defined site coefficients for seismic design. Study results will contribute to new guidelines that help engineers design better highway bridges and embankments in Alaska, ideally identifying how to account for permafrost effects in a simpler manner.