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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 will extend through the sandy river bed
to solid ground or rock. This improves structural safety in an earthquake
to avoid collapse.
The replacement bridge will be designed so that it remains functional, with
minor repairs after a seismic event that occurs once in 500 years. Additionally,
the bridge will be designed so that it will not collapse 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