“I-5 Bridge ‘tough topic’ in transportation plan” (Aug. 6). The Columbian) states: “The I-5 Bridge is actually two bridges, one of which is 60 years old, the other being 101. Neither one is seismically stable, as their pilings rest on riverbed sediment, not bedrock.”
This statement is questionable. The 101-year-old bridge has never been said to be settling or tipping. In fact, when the bridge was modified to have a hump, the existing columns and pier supports were utilized and there’s been no indication of problems using the existing supports or it would have been well reported. The columns and piers are not pilings.
The contractor who constructed the bridge knew the river bottom sediment couldn’t keep the bridge in total true operating condition, therefore they drove hundreds of pilings in the river bottom for the columns and piers to rest on. Workers know to drive wood pilings to the desired depth before stopping short. If attempting to drive pilings a few more feet the next day, they would not move. Therefore, the 101-year-old columns and piers are stable.
There’s probably no bedrock near the bridge. If bedrock must be utilized, the bridge should be constructed near the rock quarry east of Vancouver.
