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DOT employees visually inspect the I-5 bridge.
Existing bridges do not meet current earthquake standards
The two existing I-5 bridges, built in 1917 and 1958, are supported by timber
pilings driven approximately 70 feet below the river bottom. Recent geotechnical
studies have shown that the sandy soil under the bridges will likely liquefy during a significant earthquake
and could cause severe damage to
the bridges and possibly collapse.
Replacement bridges will be built to withstand earthquakes
Supports for the replacement bridge would have been extended through the sandy river bed to solid ground or rock. This would have improved structural safety in an earthquake to avoid collapse.
The replacement bridge would have been designed so that it remains functional, with minor repairs after a seismic event that occurs once in 500 years. Additionally, the bridge would have been designed so that it would not have collapsed when subjected to an event that occurs once in 2,500 years. The intent of this design is to prevent loss of life.
Additional information on the geologic and soils assessment of the project
area can be found in the
Geology and Soils Technical Report from the Final Environmental Impact
Panel Assessment of Interstate Bridges Seismic Vulnerabilities