Design Challenges and Solutions for the I-205 Abernethy Bridge Retrofit and Widening Project-Video

Video Transcription

Video Summary

The presentation outlines the geotechnical design for the Abernethy Bridge retrofit and widening in Oregon, a key lifeline route exposed to potential magnitude-9 Cascadia earthquakes. Built in 1971, the 2,700-foot bridge crosses the Willamette River and has foundations that require seismic upgrades.<br /><br />A detailed subsurface investigation identified deep, soft silt, liquefiable sands, gravel, and variable bedrock. Laboratory testing and site-response analyses were used to estimate earthquake-induced ground deformation and provide inputs to a nonlinear three-dimensional structural model. Analyses showed substantial, variable movements along the bridge, with both deformation patterns and magnitudes affecting foundation demands.<br /><br />The final design combines targeted jet-grout ground improvement with structural measures, including larger drilled shafts and isolation bearings. Solutions were tailored to individual piers to address site constraints, constructability, and cost. Existing foundations were retained and strengthened where feasible. The bridge is currently under construction.

Keywords

Abernethy Bridge

geotechnical design

seismic retrofit

Cascadia earthquake

jet-grout ground improvement

drilled shafts